Shape-Memory Behavior of Thermally Stimulated
形状记忆聚合物记忆过程热力学性能分析
形状记忆聚合物记忆过程热力学性能分析黄天麟;孙慧玉【摘要】Assuming shape memory polymers to be isotropic, with consideration of temperature-dependent creep residual strain,a three-dimensional thermo-mechanical constitutive equation of shape memory polymers( SMPs) is derived from one-dimensional con-stitutive relationship based on viscoelastic theory. A user material subroutine program of the CAE software ABAQUS is compiled to simulate the memory process. Strain/temperature rates impact on the thermo-mechanical and shape memory properties of SMPs is analyzed and it shows a good agreement with the experimental data.%考虑蠕变残余应变的温度相关性，假设形状记忆聚合物为各向同性材料，将一维热力学本构方程扩展到三维。
基于该增量形式的本构，在有限元软件ABAQUS中开发了适用于模拟形状记忆聚合物形状记忆过程的材料接口子程序，对形状记忆聚合物记忆过程进行有限元模拟。
分析了加载速率和变温速率对形状记忆聚合物的热力学性能和记忆性能的影响，数值模拟的结果与实验吻合良好。
【期刊名称】《机械制造与自动化》【年(卷),期】2015(000)004【总页数】4页(P91-94)【关键词】形状记忆聚合物;三维本构;率相关;有限元方法【作者】黄天麟;孙慧玉【作者单位】南京航空航天大学，江苏南京210016;南京航空航天大学，江苏南京210016【正文语种】中文【中图分类】TB381形状记忆聚合物(SMPs)具有变形量大、易赋形、不锈蚀、质轻价廉、响应温度便于调整等优点，受到了广泛关注[1-3]。
具有自修复功能的形状记忆聚合物的制备及性能表征
具有自修复功能的形状记忆聚合物的制备及性能表征一、本文概述随着材料科学的快速发展，形状记忆聚合物（Shape Memory Polymers, SMPs）作为一种新型智能材料，因其独特的形状记忆效应和可编程性在航空航天、生物医学、智能机器人等领域展现出广阔的应用前景。
然而，形状记忆聚合物在实际使用过程中常常因外界环境的恶劣和内部损伤的积累而导致性能下降，这极大地限制了其在实际应用中的长期稳定性和可靠性。
因此，开发具有自修复功能的形状记忆聚合物，对于延长材料的使用寿命、提高其在实际应用中的可靠性具有重要意义。
本文旨在介绍具有自修复功能的形状记忆聚合物的制备方法，并对其性能进行表征。
我们将概述形状记忆聚合物的基本原理和自修复材料的研究进展，为后续的制备和性能表征提供理论基础。
接着，我们将详细介绍几种具有自修复功能的形状记忆聚合物的制备方法，包括自修复机制的构建、材料的合成与加工等。
在此基础上，我们将对所制备的材料进行性能表征，包括形状记忆性能、自修复效率、机械性能等方面的测试与分析。
我们将讨论所制备材料的应用前景及未来发展方向，以期为形状记忆聚合物在实际应用中的推广提供有益的参考。
二、形状记忆聚合物的基本原理形状记忆聚合物（Shape Memory Polymers, SMPs）是一类具有独特“记忆”功能的智能材料，能够在外部刺激下，如热、光、电、磁等，恢复其原始形状。
这种特性源于SMPs内部的交联网络结构和可逆的物理或化学转变。
SMPs的基本原理主要基于两个过程：形状的固定和形状的回复。
在形状的固定过程中，SMPs通过交联网络的形成，将临时形状固定下来。
这个交联网络可以通过物理交联（如链缠结、结晶等）或化学交联（如共价键、离子键等）来实现。
一旦交联网络形成，SMPs就可以在不受外界影响的情况下保持临时形状。
在形状的回复过程中，当SMPs受到适当的外部刺激时，交联网络会发生可逆的物理或化学转变，从而释放出固定的临时形状，使SMPs回复到其原始形状。
Development of new device for measuring thermal stresses
Development of new device for measuring thermal stressesJang-Ho Jay Kim a ,Sang-Eun Jeon b ,Jin-Keun Kim b,*aDepartment of Civil and Environmental Engineering and Construction Technology Laboratory,Sejong University,98Kunja-dong,Kwangjin-gu,Seoul 143-747,South KoreabDepartment of Civil and Environmental Engineering,Korea Advanced Institute of Science and Technology,373-1Kuseong-dong,Yuseong-gu,Taejon 305-701,South KoreaReceived 18July 2001;accepted 30April 2002AbstractIn recent years,numerous analytical and experimental researches have been performed on the prediction of thermal stresses in mass concrete structures.However,due to the difficulty of the problem,limitations still exist for both analytical and experimental methods of measuring thermal stresses in mass concrete.In this research,a new experimental device measuring thermal stresses directly in a laboratory setting is developed.The equipment is located in a temperature chamber that follows the temperature history,which has been previously obtained from temperature distribution analyses.Thermal forces are measured continuously by two load cells in the device.The results show that the thermal stresses estimated by the newly developed device agree well with general stress variations in actual structures.D 2002Published by Elsevier Science Ltd.Keywords:Thermal stress;Modulus of elasticity;Coefficient of thermal expansion;Developed device;Degree of constraint1.IntroductionWhen constructing structures using mass concrete or high-strength concrete,specific thermal stress produced in a structure due to the hydration heat of cement could pose a serious problem to the integrity of structures.Specific thermal stress damages a structure and degrades the struc-tural serviceability,water tightness,and durability.There-fore,estimating the existing thermal stresses and the thermal cracks in concrete structures becomes vital.Specific thermal stresses are calculated by finite element method (FEM),which is the most commonly used analytical method,and are measured by experimental methods using a special equipment or gauge in actual and simulated structures or a thermal stress measuring device in controlled laboratory setting equipment.With respect to the analytical methods,a fundamental limitation is derived from the difficulty of predicting concrete properties,such as modulus of elasticity,coefficient of thermal expansion,and others.The problems with experimentally obtained results are their economic inefficiency and uncertainty related to field conditions.Therefore,developing a laboratory or controlled experi-mental device that can accurately measure thermal stresses of concrete with various mixing proportion and multiple loading conditions is urgently needed.In Japan and Europe,experimental laboratory equipment were invented and researches have been actively pursued since early 1980s.Tazawa and Iida [1]investigated hydra-tion heat-induced thermal stresses in concrete and their mechanism using thermal crack experimental apparatus.Aokage et al.[2]also experimentally measured effective modulus of elasticity of mass concrete with a similar apparatus.In Germany,the Technical University of Munich (TUM)developed an experimental tool called ‘‘cracking frame’’and estimated thermal stresses and cracking pattern of early age concrete [3–5].TUM also invented the Tem-perature Stress Testing Machine (TSTM),a modified ver-sion of the cracking frame [6,7].In this study,a laboratory test device measuring thermal stress was developed.The developed device can easily control the experimental variables,such as coefficient of thermal expansion of concrete and other cement-based materials.It is also designed to quantitatively measure the change of thermal stresses in various environmental con-ditions using a temperature and humidity chamber.0008-8846/02/$–see front matter D 2002Published by Elsevier Science Ltd.PII:S 0008-8846(02)00842-6*Corresponding author.Tel.:+82-42-869-3614;fax:+82-42-869-3610.E-mail address :kimjinkeun@cais.kaist.ac.kr (J.-K.Kim).Cement and Concrete Research 32(2002)1645–16512.Development of thermal stress measuring device2.1.BackgroundFig.1shows the basic concepts in developing a thermal stress measuring device.It is important to note that the thermal expansion coefficient of the frame material is different from that of concrete.When concrete and frame material are applied with same strains under the prescribed temperature history(Fig.1(a)),the variation of resultant stresses is dependent on thermal expansion coefficient of the frame material.More specifically,when a frame material with lower thermal expansion coefficient than that of concrete is used,this setup produces thermal stresses at interior of structures subjected to internal restraint or whole section of structures subjected to external restraint in actual structures(Fig.1(b)).However,if a frame material with higher thermal expansion is used,this setup produces thermal stresses at the surface of structures subjected to internal restraint in actual structures(Fig.1(c)).Based on the above concept and‘‘cracking frame’’design,the thermal stress measuring device is developed. This system can effectively measure thermal stresses within concrete specimens in a laboratory,offsetting uncertain properties of concrete.Fig.2shows the overall design of the system and the detailed descriptions of the device.The shape and dimensions of the device is similar to that of the‘‘cracking frame’’invented in Germany.The experi-mental procedures follow the procedures used for the thermal crack apparatus developed in Japan.However,the developed device is less expensive to manufacture and enhances the weaknesses that existed in the previously developed apparatuses.Temperature control of‘‘cracking frame’’was based on a semiadiabatic condition using wood and polystyrene,and thermal crack apparatus used thin copper or polyethylene plate to prevent drying shrinkage. However,the developed device is tested in a temperature and humidity chamber where the applied temperature is defined by a user and the humidity of over85%is main-tained to minimize drying.2.2.Experimental methodTwo load cells are used for measuring restrained forces in a frame.Thermocouples or temperature gauge are set at a chamber,frame,and concrete specimens to ascertain the applied temperature.To reduce plastic and drying shrink-ages from occurring in concrete specimens at early ages, humidity is kept at over85%.Effect of hydration heat on the applied temperature is ignored since the depth of specimens is no more than80mm(Fig.2)and thermal transfer is active at open surfaces of a concrete specimen.The left and right side surfaces of the specimen indicated as a dotted line in Fig.2is covered with thin steel plates before placing concrete.The plates are removed6h later.Also,friction between specimen and thin bottom plate supporting a frame is minimized by painting grease and oil on the thin steel plate.The application of lubrication during the test is controlled based on preliminary examinations.To predict thermal stresses in structures using the developed device,a temperature analysis is first performed, followed by experiments at a temperature and humidity chamber preprogrammed based on analysis results.To eliminate the unknown and external factors of experiments,the developed frame and specimen materials such as aggregates and water are kept at a constant temperature by storing them in the same temperature and humidity chamber before casting of specimens.Even though painstaking effort has been undertaken to control the temperature of the specimens and the frame,temper-Fig.1.Concepts of the development of thermal stress measuring device.(a)Prescribed temperature history.(b)Frame material with lower thermal expansion coefficient than that of concrete.(c)Frame material with higher thermal expansion than that of concrete.J.-H.J.Kim et al./Cement and Concrete Research32(2002)1645–16511646ature changes can occur due to the transportation and other procedures before and during the experiment.Therefore,the chamber is fixed at a required initial temperature for 6h after placing the frame and concrete specimen before the test.Then,the chamber is programmed to follow the re-quired temperature history.2.3.Measurement of thermal stressesFor the prediction of thermal stresses,uncertainties in material properties of early age concrete such as elastic modulus and coefficient of thermal expansion can be ignored using the developed device.More specifically,concrete specimens are placed in a frame attached with various metal plates of different thermal expansion coefficient.This frame setup under a known temperature history allows prediction of thermal stresses in concrete structures with a fully restrained condition.Under a fully restrained condition,thermal stress of concrete is expressed as (Eq.(1))f c ;res ¼F c ;res A cð1Þwhere,f c,res and F c,res are thermal stress and force of con-crete at fully restrained condition,respectively;and A c is thecross-sectional area of the concrete specimen in the frame.However,an application of the fully restrained condition is not feasible in this device.Therefore,the evaluated stress is modified and expressed as (Eq.(2))f c ¼F c A cð2Þwhere f c and F c are the evaluated stress and force from a concrete specimen,respectively.In the same manner,the evaluated stress of the frame is expressed as f s ¼F s A sð3Þwhere f s and F s are the evaluated stress and force of the frame,respectively,and A s is the cross-sectional area of the frame.A force equilibrium condition of the frame and the concrete specimen can be expressed as f s A s ¼A c f c :ð4ÞInserting Eq.(3)into Eq.(4)and solving for f c ,the thermal stress of concrete is expressed as f c ¼F sA c ¼F 0s ÀF comp A cð5Þwhere F s 0is the measured force from load cells and F comp refers to the compensation forces of load pensa-tion force is induced by temperature compensation of load cells,which can be obtained from preliminary tests.Under the same temperature and humidity conditions to that of the main test,the preliminary tests were performed prior to casting concrete to estimate the temperature compensation force of the developed system with load cells.Once the values for F s and A c at a specific time are experimentally obtained,thermal stress of an early age concrete can be calculated using Eq.(5).It is important to note that the thermal stress of early age concrete can be calculated even though its elastic modulus and thermal expansion coefficient areuncertain.Fig.2.Shape and dimensions of the developed device.J.-H.J.Kim et al./Cement and Concrete Research 32(2002)1645–165116472.4.Degree of constraint in the deviceTo reproduce variable restrained conditions like that of the TSTM,metal plates with a different coefficient of thermal expansion from that of concrete are set between two crossheads of the device.Fig.2shows the core of the developed device with metal plates between two crossheads.Theoretically,if the coefficient of thermal expansion or conductivity of the metal plates is zero,then fully or 100%restrained condition can be reproduced.However,a material with zero coefficient of thermal expansion does not exist.Therefore,materials with various coefficients of thermal expansion are used to effectively reproduce internal and external restrained conditions as described previously.Metal plates with various cross-sectional areas as well as coefficient of thermal expansions can vary the degree of constraint.This variation of the degree of constraint can be obtained from the following mathematical procedures.In this developed device,the constraint force of concrete specimen is actually obtained from constraint metals and load cells.From the same axial displacement condition (d l +d m =d c ),the following equation is obtained.l l a l D T þF s E l A l þl m a m D T þF sE m A m¼l c a c D T ÀF sE c A cð6Þwhere,l ,a ,and E are length,coefficient of thermal expansion,and elastic modulus,correspondingly.Subscripts l,m,and c represent load cell,constraint metal,and concrete,correspondingly.From Eq.(6),the constraint force F s is expressed as F s ¼l c a c Àl l a l Àl m a ml l =ðE l A l Þþl m =ðE m A m Þþl c =ðE c A c ÞD T :ð7ÞSince l c =l m +l l ,Eq.(7)can be modified as F s ¼ða c Àa l Þl l þða c Àa m Þl mE l A l þE c A cl l þE m A m þE c A cl m D T :ð8ÞIf E c and A c are constants in Eq.(8),the constraint forceincreases with the difference of coefficient of thermal expan-sion between concrete and frame materials (i.e.,load cells and constraint metals)denoted as (a c Àa l )or (a c Àa m ),and axial stiffness of frame denoted as (E l A l )/l l or (E m A m )/l m .Therefore,the degree of constraint in the developed device can be varied by using frames with various coefficients of thermal expansion and cross-sectional areas.Additionally,by directly measuring the displacement of a concrete specimen in the developed device,d c ,with linear displacement transducers,uncertain material properties of early age concrete such as modulus of elasticity and coefficient of thermal expansion can be evaluated from Eq.(6).Table 1tabulates various materials used for a verification of the developed device and their thermal expansion coef-ficients and elastic moduli.3.Experimental results 3.1.Concrete test results3.1.1.Mix proportionThe detailed mix proportion of concrete is shown in Table 2.3.1.2.Mechanical characteristic of concreteIn this study,experiments for two representative cases are performed.One is the interior of concrete structures sub-jected to internal restraint or the whole section subjected to external restraints.The other is the surface of concrete structures subject to internal restraint.For these cases,concrete cylinder specimens with f 100Â200mm are cured at different temperature histories shown in Fig.3(a)and Fig.4(a).Table 3shows test results for compressive and tensile strengths and elastic moduli of concrete.The experi-ment is performed for 4days in a temperature and humidity chamber.Cylinder specimens are cured under the same temperature and humidity conditions as those from the experiments with the developed device.As shown in Table 3,the concrete compressive and tensile strengths and elastic moduli for interior location are relatively higher than those located at the surface.This is due to the difference in the concrete maturity even when the specimen is cast from the same batch.3.2.Test results in the developed system3.2.1.Plate material (aluminum)with higher thermal expansion coefficient than concreteTo verify the validity of the developed device,tests using aluminum plate,which has a higher coefficient ofTable 1Materials used in the experiments and their properties Material Thermal expansioncoefficient (Â10À6/°C)Modulus of elasticity (Â104MPa)Concrete 10 2.94Steel1120.6Aluminum 247.18Invar4.52.83Table 2Mix proportion of concreteUnit content (kg/m 3)W/C S/A Water Cement Fineaggregate Coarse aggregate Admixture 0.50.421813607079891.81J.-H.J.Kim et al./Cement and Concrete Research 32(2002)1645–16511648thermal expansion than that of concrete,is performed.Fig.3(a)shows the measured temperatures of the concrete,aluminum plate,and chamber.In Fig.3(a),it is importantto note that the measured temperatures of the concrete specimen,the frame,and the temperature chamber are similar to the temperatures calculated from theanalysisFig. 3.Test results in aluminum frame (W/C =0.5,tension is pos-itive).(a)Temperature history.(b)Restrained load of frame.(c)Stress ofconcrete.Fig.4.Test results in invar frame (W/C =0.5,tension is positive).(a)Temperature history.(b)Restrained load of frame.(c)Stress of concrete.J.-H.J.Kim et al./Cement and Concrete Research 32(2002)1645–16511649(within1%of error).Therefore,the assumption of ignoring hydration heat of cement in concrete specimen is validated.Fig.3(b)shows the variation of restrained load of the frame with time.In Fig.3(b),it is important to note that the compressive loads are measured in the initial stage followed by the measurement of tensile loads during the descending part of the temperature curve.Using the restrained loads in Fig.3(b),restrained thermal stresses acting on the concrete specimen are computed by Eq.(4)as shown in Fig.3(c).Fig.3(c)is similar to the variation of thermal stresses appearing in the surface of mass concrete structures[8].Generally,thermal stresses initially are tensile and decrease gradually after the peak values at surfaces of structures.This is due to the fact that differential volume change based on temperature distribution is restrained by continuity of cross-section, which is called‘‘internal restraint.’’Therefore,it is safe to assume that the developed system can reproduce thermal stresses at surfaces of a structure subjected to internalrestrained condition.3.2.2.Plate material(invar)with lower thermal expansion coefficient than concreteFig.4shows the results from the experiment using invar plates.Fig.4(a)shows a similar tendency as the test results obtained using aluminum plate.Fig.4(c),however,indi-cates that the developed device can reproduce thermal stresses at the interior of structures subjected to internal restraint or the whole section of structures subjected to ex-ternal restraint.To verify Eq.(8),an equation representing numerical constraint forces,the computed stresses using Eq.(8)are compared to the experimentally obtained stresses of concrete using aluminum plates(Fig.5).In this calcula-tion,temperature history in Fig.3(a)and measured elastic modulus of concrete in Section3.1.2were used. Furthermore,the following data are used in the calcula-tion:coefficient of thermal expansion of12.0Â10À6/°C for concrete and load cell and24.0Â10À6/°C for aluminum plates,length of9.6and24.0cm for load cell and aluminum plates,respectively,and elastic moduli of20.6and7.18MPa for load cell and alumi-num plates,respectively.In Fig.5,the difference between calculated and experimental results is due to the inaccurate input data,such as properties of load cell and concrete as well as inelastic deformation due to creep of concrete.4.ConclusionsFrom the results obtained using the developed thermal stress measuring device,the following conclusions can be drawn.1.This device shows the possibility of measuringthermal stress variations of any position in concretestructures using different thermal expansion coef-ficient plates even though properties of concreteare uncertain.2.The application of various degrees of constraint canbe achieved by using constraint frame material withdifferent thermal expansion coefficient and cross-sectional area than those of concrete.3.A commercialized chamber,which is able to controltemperature and humidity,can be used with thisdeveloped device.AcknowledgmentsThis research was supported by the National Research Laboratory program of Year2000(2000-N-NL-01-C-033)from the Ministry of Science and Technology of Korea for the development of cracking Control Technique of Concrete Structure.This support is deeply appreciated.The financial support to the first author by a fund of the National Research Laboratory program of Year2000(2000-N-NL-01-C-162)is also gratefully appreciated.Table3Mechanical properties of concreteAge Compressivestrength(MPa)Splitting tensilestrength(MPa)Modulus of elasticity(Â104MPa)(days)Surface Interior Surface Interior Surface Interior 118.425.4 2.59 3.04 1.96 2.65 223.433.9 2.95 3.60 2.25 2.74 326.034.3 3.25 3.69 2.55parison between experimental and calculated results.J.-H.J.Kim et al./Cement and Concrete Research32(2002)1645–1651 1650References[1]E.Tazawa,K.Iida,Mechanism of thermal stress generation due tohydration heat of concrete,Trans.Jpn.Concr.Inst.5(1983)119–126.[2]H.Aokage,Y.Ito,N.Watanabe,Experimental study on effective mod-ulus of elasticity in massive concrete,Trans.Jpn.Concr.Inst.8(1986) 119–124.[3]RILEM TC119-TCE,Avoidance of Thermal Cracking in Concrete atEarly Ages,1997.[4]R.Breitenbucher,Investigation of thermal cracking with the cracking-frame,Mater.Struct.23(1990)172–177.[5]R.Springenschmid,R.Breitenbucher,M.Mangold,Development ofthe cracking frame and the temperature-stress testing machine,Proceed-ings of the International RILEM Symposium:Thermal Cracking in Concrete at Early Ages,E&FN Spon,1994,pp.137–144.[6]G.Thielen,W.Hintzen,Investigation of concrete behaviour underrestraint with a temperature-stress test machine,Proceedings of the International RILEM Symposium:Thermal Cracking in Concrete at Early Ages,E&FN Spon,1994,pp.145–152.[7]K.Schoppel,M.Plannerer,R.Springenschmid,Determination of re-straint stresses and of material properties during hydration of concrete with the temperature–stress testing machine,Proceedings of the Inter-national RILEM Symposium:Thermal Cracking in Concrete at Early Ages,E&FN Spon,1994,pp.153–160.[8]Korea Electric Power Research Institute,Reduction of Hydration Heatin Concrete Structures,1998(in Korean).J.-H.J.Kim et al./Cement and Concrete Research32(2002)1645–16511651。
光敏形状记忆聚合物
光敏形状记忆聚合物秦瑞丰朱光明*杜宗罡周海峰(西北工业大学化工系西安 710072)摘要综述了光敏形状记忆聚合物的研究进展。
主要关注了结构和形状记忆效应之间的关系。
光敏形状记忆聚合物的形状记忆效应主要与聚合物的链结构、生色团的种类、生色团的含量、生色团的位置及聚合物体系所处的相态等因素有关。
分别介绍了生色团位于聚合物侧链的光敏形状记忆聚合物、生色团位于主链的光敏形状记忆聚合物以及含生色团的有机小分子和聚合物经共混制得的光敏形状记忆聚合物体系。
另外还介绍了一种新的光敏形状记忆聚合物体系，液晶弹性体。
关键词形状记忆聚合物生色团光敏性形状记忆聚合物光异构化反应液晶弹性体Photosensitive Shape Memory PolymerQin Ruifeng, Zhu Guangming, Du Zonggang, Zhou Haifeng Deptpartment of Chemical Engineering, Northwestern Polytechnical University Xi’an 710072)Abstract The advances in photosensitive polymer and its shape memory effects are reviewed. The photoisomerization reaction of the photosensitive polymer and some factors that influence the shape memory effects, such as: the type of the Chromophore Group(CG),the chain structure of the polymer, the content of the CG, the position of the CG and the phase state of the polymer, are introduced. A novel photosensitive shape memory polymer, Liquid-Crystalline Elastomer is also introduced.Key words Shape memory polymer, Photoisomerization reaction, Chromophore group, Photosensitive shape memory polymer, Liquid-crystalline elastomer形状记忆聚合物[1](shape memory polymer)是一类新型功能高分子材料，是指能够感知环境变化的刺激，并响应这种变化，对其力学参数(如形状、位置、应变等)进行调整，从而回复到预先设定状态的高分子材料。
Constutive Model for SMA
σ
σ
AS S
AS f
AS σS
εL
σ fAS
σ SA S
Cm
Cs σ SA S σ SA f To
σ SA f
Input
AS SA AS, − σS σ fAS σ SA σ σ S f s
AS, − σs
ε L To
Cm
Cs
Formulation : Mechanical Shape Memory Alloy
& TWIN = f g & ( σ eq ) ε T ε eq
g
3 σ′ {σ eq }{ σ eq − σ Twin eff } 2 σ eq
n
G-function values (a,n and σ o ) should be selected to fit Exp. Curve Under Mf (Under Mf , Phase Transformation Strain = Twin Strain)
Shape Memory Alloy (SMA) : Nickel-Titanium alloys to show shape memory effect that severely deformed specimens, with residual strains up to 15%, regained their original shape after a loading cycle at a certain temperature.
(Contribution to Trip Strain : Starting with Vf = 0.0)
σ eq g ( σ eq ) = 1 − exp a σg o
超声矿物的溶解热力学模型
超声矿物的溶解热力学模型英文回答：Thermodynamic Modeling of Mineral Dissolution in Ultrasonic Environments.Ultrasonic waves, characterized by frequencies above the audible range (typically >20 kHz), possess unique properties that can influence the dissolution behavior of minerals. The application of ultrasonic irradiation to mineral dissolution processes has been shown to enhance dissolution rates and alter reaction pathways.The thermodynamic modeling of mineral dissolution under ultrasonic conditions requires consideration of the complex interplay between ultrasonic effects and the intrinsic properties of the mineral and solution. Several factors contribute to the enhanced dissolution observed in ultrasonic environments:Acoustic cavitation: Ultrasonic waves generate cavitation bubbles, which violently collapse, creating localized high-temperature and high-pressure zones. These extreme conditions facilitate mineral surface erosion and disrupt the diffusion boundary layer, enhancing mass transfer.Surface activation: Ultrasonic irradiation promotes mineral surface activation, increasing the number of active sites available for dissolution. This occurs through mechanical erosion, breaking down surface bonds and exposing fresh mineral surfaces.Hydrodynamic effects: Ultrasonic waves createturbulent flow patterns, which increase the fluid velocity and shear stress on mineral surfaces. This enhanced hydrodynamic environment promotes particle erosion and prevents the formation of stagnant zones.Temperature and pressure effects: Cavitation-induced localized heating and pressure changes can influence mineral dissolution kinetics. The elevated temperaturesincrease the dissolution rate of many minerals, while the pressure changes can affect the solubility and speciation of dissolved ions.To develop a comprehensive thermodynamic model for mineral dissolution under ultrasonic conditions, researchers must account for these factors and their combined effects. The model should incorporate the following elements:Thermodynamic database: A comprehensive thermodynamic database containing the necessary thermodynamic parameters for the mineral, solution species, and potential reaction products.Acoustic cavitation model: A model that simulates the generation and collapse of cavitation bubbles, estimating the localized temperature and pressure conditions.Surface activation model: A model that describes the surface activation process under ultrasonic irradiation, predicting the increase in active dissolution sites.Hydrodynamic model: A model that calculates the fluid velocity and shear stress on mineral surfaces, considering the ultrasonic-induced turbulence.Coupling of models: The integration of theseindividual models to simulate the coupled effects of ultrasound on mineral dissolution kinetics.By combining these elements, researchers can develop a robust thermodynamic model that accurately predicts the dissolution behavior of minerals in ultrasonic environments. Such a model would have significant applications in fields such as mineral processing, environmental remediation, and materials science.中文回答：超声条件下矿物溶解的热力学模型。
Meng-A review of shape memory polymer composites and blends
ReviewA review of shape memory polymer composites and blendsQinghao Meng,Jinlian Hu *Shape Memory Textiles Centre,The Hong Kong Polytechnic University,Kowloon,Hong Konga r t i c l e i n f o Article history:Received 25March 2009Received in revised form 17August 2009Accepted 18August 2009Keywords:A.Polymer-matrix composites (PMCs)B.Shape memory propertya b s t r a c tShape memory polymers (SMPs)are a kind of very important smart polymers.In order to improve the properties or obtain new functions of SMPs,SMP composites and blends are prepared.We thoroughly examine the research in SMP composites and blends achieved by numerous research groups around the world.The preparation of SMPs composites and blends is mainly for five aims:(1)to improve shape recovery stress and mechanical properties;(2)to decrease shape recovery induction time by increasing thermal conductivity;(3)to create new polymer/polymer blends with shape-memory effect (SME);(4)to tune switch temperature,mechanical properties,and biomedical properties of SMPs;(5)to fabricate shape memory materials sensitive to electricity,magnetic,light and moisture.The trend of SMP compos-ite development is discussed.SMP composites and blends exhibit novel properties that are different from the conventional SMPs and thus can be utilized in various applications.Ó2009Elsevier Ltd.All rights reserved.1.IntroductionShape memory polymers (SMPs)can rapidly change their shapes from a temporary shape to their original (or permanent)shapes under appropriate stimulus such as temperature,light,electric field,magnetic field,pH,specific ions or enzyme.Among stimulus sensitive SMPs,thermal sensitive SMP is a typical one,which has been widely studied and used in industry.Fig.1shows the molecular mechanism of thermal sensitive shape-memory effect (SME).Thermal sensitive SMPs usually have a physical cross-linking structure,crystalline/amorphous hard phase,or chemical cross-linking structure and a low temperature transition of crystalline,amorphous or liquid–crystal phase as a switch.They are processed or thermally set to have an original shape.Generally,in the permanent shape,internal stress is zero or very low.If the SMP is subject to deformation,large internal stress can be stored in the cross-linking structure by cooling the polymer below its switch transition temperature.By heating the polymer above the switch transition temperature,the SMP recovers its permanent shape as a result of releasing internal stress stored in the cross-linking structure.Over shape memory metallic alloys (SMAs)and shape memory ceramics,SMPs have the advantages of light weight,low cost,good processability,high shape deformability,high shape recoverability and tailor-able switch temperature [1–10].SMPs have found broad applications in smart textiles and apparels [11,12],intelligent medical devices [13–15],heat shrinkable packages for electronics[16],sensor and actuators [17,18],high performance water–vapor permeability materials [19,20],self-deployable structures in space-craft [11,21–25],and micro-systems [26]in the formats of solution,emulsion [25,27,28],film [29,30],foam [31–34]or bulk [35].Sev-eral excellent papers reviewing the synthesis,properties and appli-cations of SMPs have been published [25,35–41].This paper focuses on SMP composites and blends.2.SMP composites 2.1.Reinforcement of SMPsThough outstanding in some aspects compared with SMAs,SMPs have obvious shortcomings –low mechanical strength and shape recovery stress.The typical mechanical strength of a NiTi SMA is 700–1100MPa (annealed)or 1300–2000MPa (not an-nealed),and that of a Cu-based SMA is about 800MPa [42–48],while that of a SMP is in the range of above 5MPa and below 100MPa,which is related to the types of the SMP and the compo-sition of the SMP [39,49–51].The recovery stress of a SMA can reach as high as 800megapascal [42,52].While the recovery stress of a SMP is usually from a few tenths of a megapascal to a few tens of megapascals [8,39,53–59].One of the immediate methods to reinforce pristine SMPs is by using high modulus inorganic or or-ganic fillers.2.1.1.Microfiber or fabric/SMPChopped and continuous,especially continuous,microfibers and fabrics are superior to micro and nano-sized particles to im-prove the mechanical strength of SMPs.Due to the high elastic1359-835X/$-see front matter Ó2009Elsevier Ltd.All rights reserved.doi:10.1016/positesa.2009.08.011*Corresponding author.Address:Institute of Textiles and Clothing,The Hong Kong Polytechnic University,Hung Kom,Kowloon,Hong Kong.E-mail address:tchujl@.hk (J.Hu).Composites:Part A 40(2009)1661–1672Contents lists available at ScienceDirectComposites:Part Ajournal homepage:w w w.e l s e v i e r.c o m /l oc a t e /c o m p o s i t e samodulus offibers or fabrics,good SME cannot be observed in the fiber direction of the composite.SME is usually determined by bending the composite in thefiber transverse direction but not by tensile testing in thefiber direction.Literature[60]gives the protocol of bending SME tests.SMPs reinforced by microfiber/fabric are mainly for two appli-cations:spacecraft self-deployable devices and vibration control devices.Fiber/fabric reinforced SMPs for self-deployable space structures applications are also called Elastic Memory Composites (EMCs)[61–64].EMCs can be compacted on earth,stored in a com-pacted shape,and then self-deploy in space.Fiber/fabric reinforced SMPs are also used for vibration control.As vibration control mate-rials,SMP composites have the advantages of high energy absorp-tion efficiency,low density and high shape deformability.The studies of the reinforcement effect of choppedfiberglass, unidirectional Kevlarfiber and wovenfiberglass on thermoplastic shape memory polyurethane(SMPU)indicate thatfibers/fabrics can significantly increase the strength and stiffness of SMPs [51,65,66].Results on epoxy laminates reinforced by carbonfiber, glassfiber and Kevlarfiber also demonstrate that the microfibers or fabrics are effective in increasing the stiffness of epoxy SMP res-ins[67,68].The bending strain of the thermoset styrene-based SMP resin reinforced by fabric(plain weave)is mainly because of micro-buckling.The studies on the carbonfiber fabrics reinforced SMPU laminates show that the sequence and position of SMPUfilms and carbonfiber fabrics in laminates have significant influence on the shape memory properties[60].The failure mechanisms and deployment accuracy of EMCs are studied by Campbell,Tupper and Lake et al.[69–71].Lan et al.[72]prepared a self-deployable hinge using a thermoset styrene-based SMP reinforced with carbon fiber plain-weave fabrics.Fig.2shows the fabricated hinge,which consists of two curved circular SMP composite shells.The voltage applied on the embedded resistor heater in each laminate activates the deployment process.As vibration control materials,SMP composites can absorb vibration energy efficiently by shape deformation at around its glass transition temperature(T g).Yang et al.[73]prepared a sand-wich-structure composite sheet of SMPU with an epoxy beam as a vibration control material.The composite laminate showed as much as4times higher impact strength than epoxy beam alone.2.1.2.Carbon nanotube(CNT)or carbon nanofiber(CNF)/SMPDue to the exceptional mechanical strength with high elastic modulus and high aspect ratios,CNTs and CNFs are also effective in improving the mechanical strength and shape recovery stress of SMPs[74–84].Another advantage of CNTs/CNFs asfillers of SMPs is the potential electrical and infrared-light-active SME of the prepared SMP composites.Efforts to improve the CNT/CNF dis-persion in polymer matrix include the use of micro-scale twin-screw extruder,surfactants,oxidation or chemical functionaliza-tion of CNT/CNF surface and in situ polymerization[77,85–89].Gunes et al.[90]fabricated CNF/SMPU composites by melt mix-ing after the chain extension of a T m type SMPU(a melting transi-tion temperature as the switch temperature).CNFs with a diameter of60–200nm and length of30–100mm were used.The CNFs diminished the shape memory function of SMPUs which was as-cribed to the interference of CNFs on the crystallization of the soft segment.To improve the dispersion of CNFs in polyurethane ma-trix,in an earlier study,Jimenez and Jana[84]prepared CNF/SMPU composites by in situ polymerization in a chaotic mixer by chaotic two-dimensional mixing.The CNFs used were surface oxidized. Polyurethanesfilled with surface oxidized CNF showed better dis-persion,crystallinity,tensile properties,and higher shape recovery force than their counterparts with untreated CNFs.Koerner et al.[58]fabricated CNF/SMPU composites by solution mixing in a polar solvent,and slow evaporation of the solvent.The CNFs had an aver-age diameter of100nm and length above10l m.Anisotropic dis-tributed CNFs were obtained,which increased the rubber modulus by a factor of2–5.Shapefixity was improved due to the enhanced strain-induced crystallization.In comparison with pure SMPs, shape memory composites with a uniform dispersion of1–5vol.%CNFs produced up to50%more recovery stress.Similarly, Ni et al.[91]prepared CNF/SMPU composites by a solution mixing process with ultrasonic distribution.The CNFs have a diameter of about150nm and length10–20l m.The recovery stress of the composites at3.3wt.%CNF loading increased almost twice from pure SMPUs.Mondal and Hu[89]prepared functionalizedmulti-Fig.2.Self-deployment of a SMP hinge made of a thermoset styrene-based SMP reinforced with carbonfiber plain-weavefabrics.Fig.1.The molecular mechanism of thermal sensitive SME.1662Q.Meng,J.Hu/Composites:Part A40(2009)1661–1672walled carbon nanotube(MWNT)/SMPU composites by solution blending.The MWNTs having a diameter about15nm and length about50mm were functionalized in aniline at high temperature. It was found that the hard segment together with MWNTs helped to recover deformed shape.We[92]also prepared MWNTs/SMPU composites by in situ polymerization after the chemical function-alization of MWNTs.It was also found that CNTs have the function of improving shape recovery stress of SMPUs.In addition to the SMPU system,CTNs have been used to reinforce shape memory polyvinyl alcohol(PVA).Miaudet et al.[57]prepared CNT/polyvi-nyl alcohol(PVA)shape memoryfibers by a special coagulation spinning technique.Surfactant stabilized CNTs were injected in the co-flowing stream of the coagulating PVA solution.The maxi-mal stress generated by the compositefibers is from one to two or-ders of magnitude greater than that produced by conventional SMPs.The recovery stress is close to that of SMAs.In conclusion,all studies suggest that CNTs/CNFs are effective in improving the stiffness and recovery stress of SMPs.There is a maximum content of CNT/CNFs,above which the CNTs/CNFs dete-riorate the properties of the Ts and CNFs with different sizes may have different influences on the crystallinity of the soft segments of SMPUs[93].The results of the influences of nano-scale fillers on the shape-memory effect of different SMPs are not consis-tent.The inconsistent results may be due to the complexity of pre-paring composite materials.The properties of thefinal composite products are significantly affected by many factors such as process-ing techniques,filler distribution,interface,filler size,aspect ratio and matrix nature.2.1.3.Nanoclay/SMPOrganic-exfoliated nanoclay is a good material in some circum-stances to prepare functional composites with advanced anic-exfoliated nanoclay is also a good candidate for improving shape recovery tress and mechanical properties of SMPs.Kim et al.[94]intercalated macroazoinitiator(MAI),which has a hydrophilic poly(ethylene–glycol)(PEG)segment,as shown in Fig.3,into the gallery of Na-MMT(sodium montmorillonite). The Na-MMT intercalated with MAI was used to prepare poly(ethyl methacrylate)nanocomposites by in situ radical polymerization. The Na-MMT/PEG block linked to poly(ethyl methacrylate)plays its role as a hard phase contributing to shape memory properties and also as a moiety to enhance mechanical properties.Cao and Jana[95,96]synthesized organoclay/SMPU composites in a Brab-ender Plasticorder.The molar ratio of isocyanine–NCO and alco-holic–OH groups was maintained at1:1with–CH2CH2OH groups of the quaternary ammonium ions in organoclay contribut-ing a part of the total–OH functionality.The tethered reactive clay on polyurethane chains offers a new network,which adds addi-tional constraints to chain motion of SMPU especially of the hard segments.The nanocomposite at1wt.%organoclay offered about 20%higher recovery stress compared with pure SMPU.2.1.4.Nano SiC/SMPsSiC as afiller material can improve the elastic modulus of SMPs. However,it deteriorates the SME of SMPs even at a very low load-ing.Cho and lee[97]used a sol–gel process to incorporate silica from tetraethoxysilane(TEOS)into the SMPU matrix.The maxi-mum breaking stress and modulus were obtained at TEOS10 wt.%content.Liu et al.[98]reinforced thermoset shape memory epoxy with SiC particles.The SiC nano powder was added to the hardener during the synthesis process.The nano SiC increased the elastic modulus of the shape memory resin.Gall et al.[26]pre-pared nano SiC/epoxy,specially for Micro-Electro-Mechanical Sys-tems(MEMs)applications where structure size scales are in the range of a few hundred microns to several millimeters.The recov-ery force increased by about50%with a SiC content of20wt.%. However,the shape recovery ratio and recovery speed decreased. Gunes et al.[90,99]also observed negative effect of SiC on the SME of SMPUs,which they ascribed to the dramatically decreased soft segment crystallinity by the SiC.2.1.5.Carbon black(CB)/SMPPolymer compositesfilled with conducting CB have broad appli-cations in thefield of electric and electronics industry as polymer conductors,semi-conductors and the media for heat transferring. Compared to CNTs and CNFs,CBs are not so effective in improving the mechanical strength and shape recovery stress of SMPs.Fur-thermore,CBs deteriorate the shape recovery of SMPs severely.Li et al.[100]prepared CB/polyurethane composites hoping that the composites possess SME accompanying good electrical conductiv-ity.The composites were made by solution mixing and solution precipitation.The CBs decreased the shape recovery ratio and shape recovery speed of SMPU,especially at a high content,which was ascribed to the decreased crystallinity of the SMPUs by the CBs.Gunes et al.[90]prepared CB/SMPU composites by melt mix-ing and also found that the soft segment crystallinity decreased due to the constraining effect of CBs on the mobility of soft seg-ment during crystallization.2.1.6.Other inorganicfiller/SMPPoly(D,L-lactide)is a good shape memory biomaterial having good biodegradability and biocompatibility.Zheng et al.[101] reinforced poly(D,L-lactide)(PDLLA)with hydroxylapatite((Ca10-(PO4)6(OH)2)for hard tissue engineering.The composite showed good biodegradation,biocompatibility and shape memory proper-ties.PDLLA/hydroxylapatite composites at a suitable fraction ratio of between2.0:1and2.5:1had much higher shape recovery ratios and recover speed than pure PDLLA.Celite is a product from earth which is primarily composed of silica and alumina.It has surface hydroxyl groups,which can be coupled with SMPU chains.Park et al.[102]fabricated celite/SMPU composites with celite as a crosslinker,which was added in the middle of the polyurethane polymerization.The celite improved the shape memory and mechanical properties of SMPUs.The best mechanical properties and good SME were obtained at0.2wt.% celite content.anicfiller/SMPsSilsesquioxanes have a general formula(RSiO1.5)n,where R is an organic group or hydrogen.The silsesquioxanes with a cage struc-ture are called polyhedral oligomeric silsesquioxanes(POSS).POSS molecule with covalently bonded reactive functionalities can be suitable for polymerization or grafting POSS monomers to other polymer chains[103–112].Jeon et al.[113]studied the shape memory properties of norbornyl-POSS copolymers having either cyclohexyl corner groups(CyPOSS)or cyclopentyl corner groups (CpPOSS).It was found that the POSS macromers aggregated to form cylindrical domains,the size of which influences the shape memory properties.A preferred direction of POSS–POSS correlation appeared and was oriented along the draw axis,while orientation of polynorbornene chains along the draw axis was hindered(rela-tive to pure polynorbornene).The POSS composites showed two stages of strain recovery,a fast strain-recovery process related to the polynorbornene relaxation in the norbornyl matrix,and a sec-ond slow strain-recovery process which was assumed to berelated Fig.3.The structure of macroazoinitiator.Q.Meng,J.Hu/Composites:Part A40(2009)1661–16721663to the POSS rich domains.The POSS comonomers slightly decreased the recovery ratios,while increasing thermal stability significantly[113–116].Cellulose is the second organicfiller used to reinforce SMPs.Cel-lulose,which constitutes the main material in a wide variety of plant life,is one of the most abundant substances in nature.It has polar groups which can interact with polyurethane.Auad et al.[117]reinforced SMPU using nanocellulose crystals by sus-pension casting.A small amount of well-dispersed nanocellulose markedly improved the stiffness of SMP,while no obvious shape memory properties decreased.Generally,most of thefillers can significantly improve the stiff-ness of SMPs.Microfibers and fabrics are superior to micro or nano-sized particles to improve the mechanical strength of SMPs. Micro scale particles are not as effective as nanoparticles in improving the mechanical properties and shape recovery stress of SMPs.Furthermore,a small amount of microparticles can dam-age the shape recovery properties of SMPs.Nanoparticles can more effectively improve the shape recovery stress of SMPs.However,a high loading of nanoparticles i.e.above3wt.%decreases the shape recovery ratio[39,94].Simple physicalfilling of SMPs by various fillers does not give satisfied effect on improving the shape mem-ory properties and mechanical properties of SMPs simultaneously. Fillers which can have chemical bonding with SMP chains may be more efficient in improving the shape memory performance of SMPs.2.2.Thermal conductivity of SMP compositesBeing of organic nature,SMPs are thermal insulators with a thermal conductivity usually below0.30W/m K[118].Rapid heat-ing to release and rapid cooling tofix a deformed SMP is a chal-lenge to SMPs.Fillers such as alumina,fused silica,SiC,boron nitride(BN)and glassfiber,with heat transfer properties,can in-crease the thermal conductivity of SMPs.Liu and Mather [119,120]introduced BNfillers into crosslinked polycyclooctene (PCO).BN increased the PCO thermal conductivity significantly. The shape recovery induction time of PCO was significantly re-duced.Razzaq and Frormann[118]used aluminum nitride(AIN) asfillers to increase the thermal conductivity of SMPUs.An addi-tion of40wt.%AIN particles increased the thermal conductivity about50%at room temperature.2.3.Thermal expansion of SMP compositesDuring the shape recovery process,SMPs are subject to heat. Like other polymers,SMPs have a high coefficient of thermal expansion.This study is essential if an exact shape is needed after shape recovery.During the shape recovery process,because of heating,thermal expansion contradicts shape recovery shrinkage. Fillers,especially high aspect ratiofillers,decrease the thermal expansion of SMPs[121–124].Thermal expansion coefficient be-low and above the melting region of pure SMPUs is a constant, which is called the coefficient of linear thermal expansion(CLTE). At the melting range,this is a non-linear change of coefficient of thermal expansion due to crystal melting.The influences of organoclay,CNF,SiC,and CB on the thermal expansion of SMPUs have been studied.The shape memory composites with nano-sized fillers have a more moderating CLTE than that of micro-sizedfillers filled SMPs.High aspect ratiofillers,such as organoclay and CNF, are more effective in decreasing the CLTE than sphericalfillers. Gunes et al.[125]found that Kerner model[126]yields good agreement with spherical nano and microfillers,and Halpin model [127,128]is suitable for both organoclay and CNTfilled SMP composites.3.Polymer/polymer blends with SMEIn SMP area,polymer/polymer blending has two targets:(1)to tune or improve the properties of available SMPs such as switch temperature,mechanical properties and shape memory proper-ties;(2)to create new shape memory materials with one polymer forming thefixing phase and the second polymer as the reversible phase.3.1.Blending SMP/polymer to tune or improve the properties of available SMPsBy blending a SMP with its miscible polymer,the switch tem-perature and mechanical properties of the SMP can be tuned.Jeong et al.[129]prepared thermoplastic SMPU/phenoxy resin blends with tunable switch temperature between the T g s of soft segment of the SMPU and phenoxy resin.The soft segment of SMPU and the phenoxy resin are miscible at any composition in the blends.In a second report,Jeong and Song[130]blended thermoplastic SMPU with poly(vinyl chloride)to vary the switch temperature and im-prove the mechanical strength of SMPU.The poly(vinylchloride) is also miscible with the soft segment of the SMPU.The switch temperature of the blends could vary smoothly with different com-ponent compositions.Polylactide,a biodegradable SMP,has the disadvantages of high brittleness and low toughness.Zhang et al. [131]toughed polylactide using a polyamide elastomer from poly-amide-12and polytetramethyleneoxide.The polyamide elastomer is also biodegradable.The mechanical properties of the polylactide were markedly improved.3.2.Blending crystalline polymer/amorphous polymer to create new SMPsBlending crystalline and amorphous polymers is a facile strat-egy to create new SMPs[132].These blending SMPs are of great industrial interest compared to covalently crosslinked SMPs be-cause they can be immediately available by blending two poly-mers.The crystalline polymer acts as the cross-linking structure and the amorphous polymer provides the switch.The crystalline polymers which have been applied include poly(vinylidenefluo-ride),polylactide,poly(hydroxybutyrate),poly(ethylene–glycol), polyethylene,poly(ethylene-co-vinyl acetate),poly(vinyl chloride), poly(vinylidene chloride)and copolymers of poly(vinylidene chlo-ride)and poly(vinyl chloride).The amorphous polymers include poly(vinyl acetate),poly(methyl acrylate),poly(ethyl acrylate), atactic poly(methyl methacrylate),isotactic poly(methyl methac-rylate),syndiotactic poly(methyl methacrylate)and other poly(alk-yl methacrylate)s.Mather and his group members[133,134]have made a number of contributions in this area.The properties of the SMP blends can be changed smoothly because the pair of poly-mers is miscible.3.3.Blending crystalline polymer/crystalline polymer to create new SMPsBy using a crystalline polymer as thefixing phase and the sec-ond crystalline polymer as the reversible phase,SMP blends are also created.Behl et al.[135]reported binary biodegradable poly-mer blends from two crystalline polymers poly(p-dioxanone) (PPDO)and poly(caprolactone)with poly(alkylene adipate)media-tor as a compatibilizer.The crystalline PPDO provides the hard segment to determine the permanent shape and the poly(caprolac-tone)provides the soft segment to determine the switch tempera-ture.The mechanical properties of the blends are facially adjustable.Li et al.[136]prepared high-density polyethylene1664Q.Meng,J.Hu/Composites:Part A40(2009)1661–1672(HDPE)/poly(ethylene terephthalate)(PET)blends with ethylene-butyl acrylate-glycidyl methacrylate terpolymer(EBAGMA)as a reactive compatibilizer.The ethylene component of the EBAGMA is similar to HDPE,and the polarity of the butyl acrylate-glycidyl methacrylate component of EBAGMA is similar to one part of PET.The PET is used as thefixing phase,and the HDPE as the reversible patibilizers not only increase the compatibil-ity,but also increase the shape memory properties of the blends.3.4.Blending elastomer/crystalline or amorphous polymer to create new SMPsBlending an elastomer with a polymer having a low tempera-ture thermal transition can generate polymer blends with SME. Weiss et al.[137]designed a type of SMPs by blending an elasto-meric ionomer with low molar mass fatty acids and their salts. Nanophase separation of the ionomer is used to develop a cross-linking network,and fatty acids(salts)are used to produce a melt-ing temperature as the switch.The switch temperature is easily varied by choosing fatty acids with different melting points.Zhang et al.[138]blended a pair immiscible polymers,styrene–butadi-ene–styrene tri-block copolymer(SBS)/poly(caprolactone),to cre-ate new SMPs with tunable properties.The SBS phase provides thefixing phase and poly(caprolactone)provides the reversible phase for the SMP blends.The interrelation among the shape mem-ory properties,poly(caprolactone)loading and phase morphology of the blends is established.3.5.Blending and radiation crosslinking to create novel SMPsThrough blending and post-crosslinking,SMPs with interpene-trating polymer network(IPN)structures can be prepared.Zhang et al.[139]introduced poly(ethylene–glycol)dimethacrylate(PEG-DMA)to poly(lactide-co-glycolide)(PLGA)/isophorone diisocya-nate(IPDI)systems and formed IPNs with good shape memory and hydrophilic properties for biomedical applications.First,a hydrophilic network was formed by irradiation crosslinking of dimethacrylate groups in PEGDMA.Second,a polyurethane net-work was generated by the reaction of hydroxyl telechelic PLGA and IPDI.The crosslinking densities of polyurethane networks can be controlled by varying the arm lengths of oligomers PLGA. The hydrophilicity and mechanical properties of IPNs are conve-niently tuned by variation of compositions.The switch tempera-ture of the IPNs could be adjusted at around body temperature for potential clinical applications.Zhu et al.[140]improved the radiation efficiency of polycaprolactone by blending it with poly-methylvinylsiloxane(PMVS)before radiation crosslinking for bio-medical applications.The SME of poly(caprolactone)is usually very weak due to its low efficiency of radiation crosslinking and radiation-induced scission of molecular chains[141].The PMVS, shown in Fig.4,is a highflexible material with a breaking elonga-tion ratio as high as1500%.Like poly(caprolactone),PMVS is bio-compatible and nontoxic.The double bond of PMVS is sensitive to irradiation crosslink reaction.PMVS decreased the gelation dose and ratio of degradation to crosslinking.The radiation crosslinking efficiency was significantly increased.The crosslinked poly(capro-lactone)/PMVS blends exhibited better SMEs such as narrow switch temperature,high heat sensitivity and high recovery speed in comparison with pure poly(caprolactone).4.SMP composites and blends with special functions4.1.SMP composites with electromagnetic interference shieldingMany researchers have studied the novel properties of CNT reinforced SMPs and explored their potential application.Zhang et al.[142]investigated the electromagnetic interference shielding effectiveness(EMISE)of multi-wall-carbon-nanofibers(VGCFs) reinforced SMPUs.The evaluation of EMISE was carried out in three different frequency bands,8–26.5GHz(K band),33–50GHz(Q band)and50–75GHz(V band).The EMISE of VGCFs/SMPU nano-composite strongly depends on VGCFs content and the specimen thickness.VGCF/SMPU nanocomposites are excellent shielding materials for electromagnetic interference[143].4.2.SMP composites with UV-protectionThe CNTs reinforced SMPs can have good UV protection proper-ties arising from the UV-absorption property of CNTs[144–146]. We[147]treated cotton fabrics with hydrophilic SMPU solution which contained MWNT hoping to fabricate fabrics with not only smart water–vapor permeability but also good UV-protection. The hydrophilic polyurethanes was synthesized by using poly(tet-ramethylene oxide)glycol and PEG as the soft segment.Scoured and bleached fabrics were coated by a roller machine.The coated fabrics showed excellent protection against UV radiation.4.3.SMP composites with smart water–vapor permeability(WVP)Mass transport through the breathable dense polyurethane membranes strongly depends on microstructure of polyurethane. Jeong,Chen,and Mondal have studied the WVP of polyurethane membrane.Jeong et al.[148,149]modified the polyurethane struc-ture by employing hydrophilic segments such as dimethylpropion-ic acid(DMPA)and diol terminated poly(ethylene oxide)to enhance the sensitivity of the thermoresponsive WVP.Chen et al. [150]improved the WVP by increasing hydrophilic segment molecular weight and decreasing density of the chemical cross bonding.We[19,147,151–153]also found that the mass transfer properties were not only influenced by amorphous region,but also by the interaction between the polymer chains.The study on the influence of MWNTs on the WVP of SMPU showed that MWNTs at a high content increase WVP of the membrane.This is because in one aspect,MWNTs constrain the forming of ordered soft seg-ment phase structure;in another aspect,the straight MWNTs with large aspect ratios offer a relatively straight‘‘free”pathway for water molecule diffusion on the surface of MWNTs or inside MWNTs to pass through[92].4.4.SMP/thermoexpanded graphite(TEG)with significant volume changesBeloshenko et al.[154–158]in a series of reports described that in some polymer composite systems with a weak interphase inter-action,the shape the composite significantly changes.This phe-nomenon is associated with the relaxation of micro-stresses at interfaces which results in material loosening.The microstructure of an epoxy polymer(EP)-thermoexpanded graphite(TEG)com-posite at different shape memory stages are shown in Fig.5 [155].In the initial state,in Fig.5a,the composite has a two-phase structure with the clear phase separation.The dark phasecorre-Fig.4.The structure of PMVS.Q.Meng,J.Hu/Composites:Part A40(2009)1661–16721665。
5 Thermomechanical constitutive model of shape mempry polymer
es Sec;
2
where r; e and T denote stress, strain and temperature, respectively. The dot denotes time derivative. E; l; k and a represent modulus of elasticity, viscosity, retardation time and coecient of thermal expansion. E; l; and k depend on temperature. In the case of a standard linear elastic model, es a 0 in Eq. (1). In the creep recovery process, r 0 and therefore Eq. (1) becomes e_ e=k 0. Based on this equation, strain is recovered with lapse of time and ®nally is recovered perfectly. S in Eq. (2) is a proportional coecient. As expressed by Eq. (2), a certain ratio S of creep strain ec appears as irrecoverable strain es. At high temperature Th above the glass transition temperature Tg, large ec appears under low stress and ec is recovered after unloading. Therefore S is small at Th. On the contrary, at low temperature Tl below Tg, ec appears under high stress and large amount of ec remains after unloading. Therefore S is large at Tl.
18 MeV质子辐照对TiNi形状记忆合金R相变的影响
第15卷 第1期强激光与粒子束Vol.15,No.1 2003年1月HIGH POWER LASER AND PAR TICL E B EAMS Jan.,2003 文章编号:100124322(2003)012009720418Me V质子辐照对Ti Ni形状记忆合金R相变的影响Ξ王治国, 祖小涛, 封向东, 刘丽娟, 林理彬(四川大学物理系教育部辐射物理及技术重点实验室,四川成都610064) 摘 要: 研究了用HZ2B串列加速器的18MeV质子辐照对TiNi形状记忆合金R相变的影响,辐照在奥氏体母相状态下进行。
示差扫描量热法(DSC)表明,辐照后R相变开始温度T s R和逆马氏体相变结束温度T f A随辐照注量的增加而降低。
当注量为1.53×1014/cm2时,T s R和T f A分别下降6K和13K,辐照未引起R相变结束温度T f R和逆马氏体相变开始温度T s A的变化。
表明辐照后母相(奥氏体相)稳定。
透射电镜(TEM)分析表明辐照后没有引起合金可观察的微观组织变化。
辐照对R相变开始温度T s R和逆马氏体相变结束温度Af的影响可能是由于质子辐照后产生了孤立的缺陷团,形成了局部应力场,引起晶格有序度的下降所造成的。
关键词: TiNi形状记忆合金;质子辐照;R相变;示差扫描量热法;TEM 中图分类号:TG139.6 文献标识码:A TiNi形状记忆合金是目前应用最为广泛,也最成功的一种智能材料,集传感功能与驱动功能于一体,在核反应堆和太空等核辐射环境下用作传感与驱动元件已引起了关注[1,2]。
TiNi合金中R相变具有热滞后小,响应速度快的特点,在实际应用中得到了广泛的应用[3]。
在以前的研究中利用R相变得到了具有双向记忆效应的弹簧,伸缩率可达25%[4]。
由于核辐射会对形状记忆合金相变特性产生影响,因而研究其改变规律及机理对形状记忆合金在辐射环境下应用的可靠性和可行性是十分必要的。
金的等离子共振等综述
a b s t r a c t
This review describes the fundamental aspects of laser–gold nanoparticle (Au NP) interaction that leads to nanoscale energy deposition to the surroundings through light amplification and heat generation. Besides the importance of the primary process in physics and chemistry, application of the light–NP interaction has attracted significant interest from various areas ranging from analytical chemistry to material chemistry and biomedicine. Here we consider both mechanistic and application aspects. Our attention is focused on pulsed-laser-induced fast processes that revealed the heating–cooling dynamics of electrons, lattice (particle), and particle’s environment. On the application side, we focus on material fabrication and processing that beat diffraction-limited resolution. Together, we will shed a light on the essence of research activities carried out in the past 10 years. In addition to an abundance of latest information obtained from currently available literature, this review includes figures obtained by our own calculations to provide readers with a better understanding of the basics of the optical properties and energy and heat-transfer processes of Au NPs, which are not familiar to photochemists. © 2012 Elsevier B.V. All rights reserved.
Shape memory alloy thermal exposure monitor
专利名称：Shape memory alloy thermal exposuremonitor发明人：Jeffrey W. Akers,James Michael Zerkus申请号：US09301418申请日：19990428公开号：US06425343B1公开日：20020730专利内容由知识产权出版社提供专利附图：摘要：A thermal exposure monitor has a thermally-conductive housing adapted to be placed in close proximity to a product to be monitored and at least one thermally-responsive shape memory alloy member in the housing that has a first shape attemperatures below a critical temperature and a second shape at temperatures above the critical temperature and a transformation temperature range encompassing a prescribed detrimental temperature related to the product being monitored. An indicator associated with the thermally-responsive member is moved from an initial position as the thermally-responsive member changes from the first shape to the second shape so as to be visually observed through a window on the housing to visually indicate whether the product being monitored has been exposed to temperatures above the prescribed detrimental temperature for a period of time that would be detrimental to the product.申请人：AKERS JEFFREY W.,ZERKUS JAMES MICHAEL代理人：Kenneth A. Roddy更多信息请下载全文后查看。
Smoothed Molecular Dynamics For Thermally Embedded Systems
(1.2)
where Dp and D = Dq are the di erential operators with respect to p 2 R3N and q 2 R3N , the momenta and space coordinates of the N atoms of the considered molecular system. We assume that the potential V is given, and that it is a \good classical model" for the system. Then, if adequate initial conditions (q; p)(0) = (q0; p0 ) (1.3) are given, a solution of (1.2) describes the motion of the molecular system without interaction with any other system. Thus, we only have to care for an e cient, accurate, and stable numerical solution of (1.2). This is the idealized situation. There are several serious problems. Three of them will be explained in the following. They make up the starting point for the considerations in this paper.
Christof Schutte Konrad{Zuse{Zentrum Berlin Heilbronner Str. 10, D-10711 Berlin, Germany
热变形维卡软化点试验仪技术文章英语
热变形维卡软化点试验仪技术文章英语Vicat Softening Temperature Tester: A Comprehensive Technical Article.Introduction.The Vicat softening temperature test is a widely used technique for determining the softening point of thermoplastic materials. Developed by French chemist Louis Vicat in the early 19th century, this test evaluates the temperature at which a material undergoes a transition from a solid to a semi-liquid state. The Vicat softening temperature provides valuable insights into the material's thermal properties and behavior under load.Principle of the Test.The Vicat softening temperature test is performed using a specialized testing apparatus known as a Vicat softening temperature tester. The tester consists of a cylindricalheating bath, a needle-shaped indenter, and a weight-loading system. The test specimen, typically in the form of a cylindrical or prismatic shape, is placed in the bath and heated at a controlled rate.As the temperature rises, the specimen softens and begins to deform under the load applied by the indenter. The softening temperature is recorded as the temperature at which the indenter penetrates a specific distance (usually 1 mm) into the specimen. This point represents the transition from the solid to the semi-liquid state.Factors Affecting the Vicat Softening Temperature.Several factors can influence the Vicat softening temperature of a material, including:Material composition: Different polymers and additives have varying softening points. Materials with a higher molecular weight or higher crystallinity tend to have a higher Vicat softening temperature.Heating rate: The rate at which the test is performed can affect the softening point. A slower heating rate allows the material more time to deform, resulting in a lower softening temperature.Load: The weight applied to the indenter influences the penetration depth and, consequently, the softening temperature. A heavier load will result in a lower softening temperature.Specimen geometry: The shape and dimensions of the specimen can affect heat transfer and deformation, potentially altering the softening temperature.Applications of the Vicat Softening Temperature Test.The Vicat softening temperature test finds widespread application in various industries and fields:Polymer characterization: Evaluating the thermal stability, flow behavior, and processability of thermoplastic materials.Quality control: Monitoring product consistency and detecting variations in material properties.Research and development: Investigating the effects of different additives, processing conditions, and material formulations on thermal properties.Engineering design: Selecting materials for specific applications based on their softening temperature and other relevant properties.Performance evaluation: Assessing the performance of materials in elevated temperature environments.Advantages of the Vicat Softening Temperature Test.The Vicat softening temperature test offers several advantages over other methods of measuring softening point:Simple and straightforward: It is a relatively simple and straightforward test to perform, requiring minimaltechnical expertise.Versatile: It can be used to test a wide range of thermoplastic materials, including polymers, composites, and rubber.Reproducible: When performed under standardized conditions, the test provides reproducible and reliable results.Affordable: Vicat softening temperature testers are relatively affordable compared to other thermal analysis instruments.Limitations of the Vicat Softening Temperature Test.Despite its advantages, the Vicat softening temperature test has some limitations:Arbitrary: The softening temperature is an arbitrary value that depends on the specific test conditions, such as heating rate and load.Temperature range: The test is limited to materials that soften within the temperature range of the heating bath.Sample size: The test requires a relatively large sample size compared to other thermal analysis techniques.Conclusion.The Vicat softening temperature test is a valuable tool for characterizing the thermal properties of thermoplastic materials. It provides insights into their behavior under load at elevated temperatures and has applications in various industries and research fields. While it has some limitations, it remains a widely used and accepted method for measuring the softening point of thermoplastic materials.。
heat-stimuli shape memory effect -回复
heat-stimuli shape memory effect -回复标题：探索热刺激形状记忆效应的奥秘一、引言热刺激形状记忆效应，是一种独特的材料特性，它使得某些特定的材料在经历一定的热处理后，能够恢复到其原始形状。
这种现象在许多领域中都有广泛的应用，包括航空航天、医疗器械、汽车制造、电子设备等。
本文将深入探讨热刺激形状记忆效应的原理、影响因素以及其在实际应用中的价值。
二、热刺激形状记忆效应的原理热刺激形状记忆效应主要发生在形状记忆合金（Shape Memory Alloys, SMA）中，这类合金具有两种不同的晶体结构：低温下的马氏体结构和高温下的奥氏体结构。
当形状记忆合金在低温下受到外力变形并转变为马氏体结构时，一旦加热到一定温度，它会恢复到原来的奥氏体结构，并伴随着形状的恢复，这就是我们所说的热刺激形状记忆效应。
这个过程可以分为以下几个步骤：1. 马氏体相变：在低温下，合金受到外力作用发生塑性变形，由稳定的奥氏体结构转变为不稳定的马氏体结构。
2. 记忆存储：在马氏体状态下，合金“记住”了变形后的形状。
3. 形状恢复：当合金加热到一定温度时，马氏体结构重新转变为稳定的奥氏体结构，同时释放出储存的能量，使合金恢复到原始的形状。
三、影响热刺激形状记忆效应的因素热刺激形状记忆效应的性能受多种因素影响，主要包括以下几点：1. 材料类型：不同的形状记忆合金具有不同的形状记忆性能，如镍钛合金、铜基合金、铁基合金等。
2. 温度：形状记忆效应的激活温度与合金的相变温度有关，不同的合金具有不同的相变温度范围。
3. 应变量：形状记忆合金的记忆能力和恢复能力与其在马氏体状态下的应变量有关，过大或过小的应变量都可能影响其形状记忆效果。
4. 热处理条件：合金的热处理条件，如加热速率、冷却速率、保温时间等，也会影响其形状记忆性能。
四、热刺激形状记忆效应的应用热刺激形状记忆效应因其独特的性质，在许多领域中都有广泛的应用。
temperature operation range of shape memory
temperature operation range of shape memoryThe temperature operation range of shape memory alloys (SMA) is an important factor to consider when designing and utilizing these unique materials in various applications. SMA materials possess the ability to undergo large deformation when heated and then return to their original shape upon cooling, thus exhibiting shape memory effect. This thermal response enables SMA materials to be used in a wide range of applications, such as aerospace, biomedical, automotive, and robotics. Understanding the temperature operation range is crucial to ensure the effective and safe utilization of SMA materials. In this article, we will explore the temperature operation range of shape memory alloys in detail.Shape memory alloys, such as nickel-titanium (NiTi) and copper-aluminum-nickel (CuAlNi), demonstrate a characteristic phase transformation behavior, which is responsible for their unique mechanical properties. The transformation between different crystal structures, namely austenite and martensite, is accompanied by a reversible change in shape. The temperature at which the phase transformation occurs is known as the transformation temperature. The temperature ranges relevant to SMA applications are the transformation temperature range, ranging from the austenite start temperature to the austenite finish temperature, and the hysteresis range, which represents the temperature difference between the start and finish temperatures.The transformation temperature range is a crucial parameter as it determines the temperature range within which the shape memory effect can be observed. For example, in NiTi SMA, the transformation temperature range typically lies between -20 to 100degrees Celsius. Below the austenite start temperature, typically referred to as Ms, the material is in martensitic phase and exhibits superelasticity or pseudoelasticity. This means that the SMA material can undergo large deformation without permanent deformation upon mechanical loading. As the temperature is increased above Ms, the material undergoes a martensite-to-austenite transformation and recovers its original shape. This temperature is known as austenite finish temperature, Af.It is important to note that the transformation temperature range varies depending on the composition, treatment, and processing of the SMA material. The specific transformation temperature range can be tailored by adjusting the alloy composition and heat treatment processes. For instance, the addition of different elements, such as iron, cobalt, or palladium, can shift the transformation temperature range to higher or lower temperatures. Moreover, the transformation temperature range can also be influenced by the strain and thermal history of the SMA material. The hysteresis range is another important parameter to consider in SMA applications. The hysteresis represents the temperature difference between the start and finish temperatures of the transformation. This temperature difference is due to the energy dissipation during the transformation process. In SMA materials, the hysteresis range is typically several degrees Celsius, which means that the shape memory effect can be observed within a narrow temperature band. For example, the hysteresis range of NiTi SMA is around 10-20 degrees Celsius, depending on the alloy composition.The temperature operation range of SMA materials also depends on the intended application and environmental conditions. For instance, in aerospace applications, where SMA materials are used for actuation and control systems, the temperature operation range must encompass the expected operational temperatures of the aircraft. This range typically spans from -55 to 125 degrees Celsius, covering the possible temperature variations experienced during flight. In biomedical applications, SMA materials are used in various implants and devices, such as stents and orthopedic implants. In these applications, the temperature operation range must be compatible with the human body temperature, typically ranging from 35 to 40 degrees Celsius.To ensure the effective utilization and reliability of SMA materials, it is necessary to consider the thermal stability and fatigue resistance within the temperature operation range. SMA materials may undergo thermal degradation or fatigue failure when exposed to high-temperature conditions or subjected to cyclic loading. Thermal stability can be improved by alloying and heat treatment processes to enhance the resistance to phase transformation or oxidation at elevated temperatures. Fatigue resistance can be enhanced by optimizing the alloy composition and processing to increase the material's resistance to cyclic loading-induced deformation and failure.In conclusion, the temperature operation range of shape memory alloys plays a critical role in determining the range within which the shape memory effect can be observed and utilized. Various factors, including alloy composition, treatment, and processing, influence the transformation temperature range and hysteresis ofSMA materials. Understanding and optimizing the temperature operation range is crucial for designing and utilizing SMA materials effectively in different applications. Further research and development efforts are needed to explore new alloy compositions and processing techniques to expand the temperature operation range and improve the performance of SMA materials.。
heat-stimuli shape memory effect -回复
heat-stimuli shape memory effect -回复题目：热刺激形状记忆效应引言:热刺激形状记忆效应是一种材料特性，当材料受到热刺激时，能够恢复其最初的形状。
这种特性在材料科学和工程领域中得到广泛应用。
本文将逐步解释热刺激形状记忆效应的原理和应用。
第一部分：热刺激形状记忆效应的原理热刺激形状记忆效应基于材料的“记忆性”，即材料具有记忆其最初形状的能力。
这种记忆通过材料中的“形状记忆聚合物”实现，是特殊的聚合物，具有与普通聚合物不同的结构。
1. 形状记忆聚合物的结构形状记忆聚合物由交联聚合物链构成，具有三个重要的结构组分：聚合物链、交联结构和侧链。
这些组分共同作用，使得形状记忆聚合物在热刺激下发生形状变化。
2. 相变特性形状记忆聚合物具有两个相互转变的状态：诱导态（高温相）和存储态（低温相）。
在高温下，形状记忆聚合物处于诱导态，此时聚合物链呈现出无序排列，使得材料呈现出可塑性。
当温度下降到特定临界温度以下，聚合物链开始重新排列并形成交联结构，材料逐渐恢复存储态的形状。
3. 形状记忆聚合物的“记忆”形状记忆聚合物通过交联结构和侧链之间的相互作用，将存储态的形状记忆下来。
一旦材料受到热刺激，温度升高到诱导态，聚合物链会解开以放松能量，此时可以对材料进行可塑形状调整。
然而，一旦温度下降到特定临界温度以下，聚合物链重新排列并形成交联结构，材料将迅速恢复存储态的原始形状。
第二部分：热刺激形状记忆效应的应用热刺激形状记忆效应在多个领域中得到了应用，包括医疗器械、航天航空和纺织品等。
1. 医疗器械热刺激形状记忆效应可以用于制造生物活性的支架和植入物，这些材料能够适应患者体内的温度变化，并恢复到合适的形状，提供良好的支撑和修复功能。
2. 航天航空在航天航空领域，热刺激形状记忆效应被用于制造自动展开式太阳能阵列、形状可调整的变压器和自动调谐的天线等设备。
这些材料能够在受到热刺激后，根据具体应用的需求，自动调整形状和尺寸。
热致形状记忆高分子研究
热致形状记忆高分子研究近年来，热致形状记忆高分子（Thermally-Induced Shape Memory Polymer, TISMP）作为一种新型高分子材料，受到在材料学和工程学领域的广泛关注。
TISMP具有优异的力学性能，具有许多有利的应用特性，如耐高温、耐腐蚀、耐冲击、低失重以及可调节的形状记忆性能等，可应用于众多的产品和服务领域，如航空航天、汽车、轨道交通运输系统、机械产品等，将有力推动社会发展和经济增长。
TISMP是一种新型的高分子材料，其结构特征决定了它的特性和功能。
TISMP的形状记忆效果是由一种叫做热致形状记忆效应（Thermally-Induced Shape Memory Effect, TI-SMEE）的独特物理和化学性质作用产生的。
在TI-SMEE下，TISMP通过改变温度来激活形状记忆效应，即在回火温度以上形状记忆效应会发挥出最大值，当温度回落时，TISMP会自动回原形，这一过程可重复发生。
此外，TISMP 还具有一定的稳定性，可在常温下长期保持它的形状和性能。
在力学性能方面，TISMP具有良好的可靠性，耐久性和稳定性能。
它的拉伸强度、断裂伸长率和疲劳强度均大于典型的加工塑料，耐热性好，温度下降后不会发生分解反应，可以在室温下维持较长时间。
此外，能够有效承受低温和高温环境仍能表现出理想的性能，耐冲击性也非常好，具有较高的机械强度。
此外，TISMP不仅具有良好的性能特征，它的制造工艺也十分简单。
它可以通过一系列普通的热成型技术，如注射成型、挤出成型、热塑性成型、热变形等来制备。
由于TISMP的制造成本低，生产效率高，产品成本低，使它在工业前景广阔。
然而，TISMP仍面临着一些缺点。
首先，在形状记忆效应表现方面，其受到外界环境因素的影响，如温度、湿度、力学应力等因素，而影响形状记忆效应的性能。
其次，TISMP的回火温度较低，导致其性能的最大改善也较小，同时TISMP的结晶度较低，在形状再制和再次使用时可能会出现变形现象。
形状记忆合金薄板系统全局激变现象分析
形状记忆合金薄板系统全局激变现象分析岳晓乐; 向以琳; 张莹【期刊名称】《《物理学报》》【年(卷),期】2019(068)018【总页数】9页(P20-28)【关键词】形状记忆合金; 全局动力学; 激变; 分形域边界【作者】岳晓乐; 向以琳; 张莹【作者单位】西北工业大学应用数学系西安 710072【正文语种】中文1 引言形状记忆合金(shape memory alloy,SMA)表现出的独特力学性能来源于马氏体相变及其逆变化,相变的驱动力可以由温度变化和机械载荷提供,温度诱发的相变引起形状记忆效应,外加应力诱导的相变产生超弹性.利用这两个性质,SMA被制成各种参数可控的智能元件,在机翼结构的变形、精密机械系统的高速驱动及机器人仿生等方面得到广泛应用[1−5].目前关于SMA元件的力学性能研究主要集中在温度和载荷变化下SMA梁、振子及支架系统的平衡点稳定性、分岔行为及混沌现象等非线性动力学特征方面[6−10],对于SMA薄板系统的全局动力学研究较少,相较于局部分析,全局分析能够揭示更多的动力学信息[11],有利于从力学理论角度突破SMA 薄板系统在机械驱动和振动控制等领域的局限性.激变[12,13]作为混沌系统中较为常见的全局分岔现象,主要刻画了混沌吸引子和混沌鞍的不连续变化.常见的激变包括边界激变、内部激变和合并激变.边界激变是指混沌吸引子与吸引域边界上的不稳定周期轨道碰撞,导致吸引子的突然消失.内部激变是混沌吸引子与其所在吸引域内的不稳定周期轨道发生碰撞引起的.合并激变是指两个及以上的吸引子同时与吸引域边界上的不稳定周期轨道发生碰撞,合并形成新的吸引子.尽管通过分岔图可以观测到激变现象,但具体类型并不清楚,需进一步绘制全局图进行判断.近年来,不少系统的激变现象均有所研究,例如分数阶和单边碰撞系统[14−17].当系统中存在多个吸引子时,吸引域边界可以是光滑的,也可以呈现出“你中有我,我中有你”的分形结构.如果吸引子的个数为三个及以上,且边界上任一点的任意小领域,覆盖三个及以上吸引域,则称此域边界具有Wada特性.随着系统参数变化,域边界结构会突然发生改变,称为域边界突变,包括光滑-Wada域边界突变、分形-Wada域边界突变和Wada-Wada域边界突变等.域边界突变作为混沌动力学的一个研究重点,对于确定系统的整体结构具有重要的物理意义,在非光滑系统和准周期强迫系统[18,19]中都有所研究,但分形性使得动力系统的力学行为很难预测,随着胞映射技术的发展,域边界突变和激变现象的研究得到了突破.其中经典的广义胞映射、图胞映射、插值胞映射等方法均可获得系统的全局信息[20−22],但在刻画域边界时有一定的局限性.复合胞坐标系方法通过对连续相空间的多级分割构造一个复合胞空间,基于点映射的原理,不仅可以获取动力系统的吸引子、吸引域和鞍等信息,还能细化任意小区域,在全局图中优化对域边界的刻画.本文以SMA薄板动力系统为研究对象,温度和外部激励的振幅为分岔参数,在全局分岔图的基础上,通过复合胞坐标系方法进一步分析系统在演变过程中出现的激变类型和域边界突变现象,并通过对指定区域的细化,展示域边界的分形特征.研究结果在工程领域中对控制系统的动态响应有重要意义.2 SMA薄板动力系统在SMA薄板中,相对于奥氏体,马氏体更具延展性,当外加应力低于马氏体的屈服强度时,SMA薄板可表现出超弹性.马氏体的转变与温度相关,低温相称为马氏体,高温相称为奥氏体,降温时SMA薄板发生马氏体相变,呈现形状记忆效应.定义TM为马氏体相变临界温度,该温度之下,马氏体稳定; TA为奥氏体相变临界温度,该温度之上,奥氏体稳定,a,b,c均为材料常数,满足:根据Falk [23]的研究,SMA薄板的本构模型可以由一个五次多项式表示,该模型给出了应变(e)-应力(s)的关系:Savi等[10,24]给出了很多关于SMA弹簧振子的数学模型,文献[25]在此基础上演变出SMA薄板横向振动的非线性动力学模型.本文考虑密度r,厚度h,长宽分别为l1,l2的SMA薄板,在环境黏性阻尼e下,受到横向简谐激振力F0=FsinWt作用,如图1所示.图1 SMA薄板的横向振动Fig.1.Transverse vibration of SMA thin plate.薄板的横向位移为w (x,y,t),单位长度上的内力矩分别为Ux(x,y,t),Uy(x,y,t),Uxy(x,y,t),其横向振动方程为[25]薄板面内的3个应力分别为sx,sy,txy,内力矩为[25]在满足四周简支边界条件下取位移模式[25]:通过Galerkin原理和应变-应力本构关系,并对系统参数量纲归一化,得到SMA薄板的横向振动非线性动力学方程[25]:方程(6)可化为以下形式的一阶微分方程组:其中a,x,b,g均为正常数; q,g分别是无量纲化的温度和简谐激振力振幅.参数选取同文献[24]所示,x=0.2,a=1,b=1300,g=470000,W=1.接下来基于复合胞坐标系方法,分析温度q和激励振幅g两个参数变化时,SMA薄板系统的全局动力学特性变化过程.3 振幅对全局特性的影响当温度q=0.7,此时SMA薄板位于马氏体临界温度下,含有两个稳定的马氏体相.选取不同的初值点(–0.0553,–0.09),(–0.031,0.045),(0.083,–0.032),(0.047,0.059)构造Poincare映射,保留稳态映射点,得到对应的多值分岔图,如图2所示.随着幅值g 值的变化,系统呈现明显的多吸引子共存特征,并伴随有丰富的激变和域边界突变等现象.图2 系统(7)随振幅g变化的多值分岔图Fig.2.Multivalued bifurcation diagram of the system (7)with the variation of amplitude g.图3 系统(7)的全局图 (a) g=0.0471; (b) g=0.0472Fig.3.Global diagram of the system (7): (a) g=0.0471; (b) g=0.0472.在区域D={(x,y)|–0.1 ≤ x ≤ 0.1,–0.12 ≤ y ≤0.12}上,均匀划分1000×1200个胞,利用复合胞坐标系方法获取系统的吸引子、吸引域和边界鞍等全局信息,阐述g在0.0460到0.0727的范围内激变现象出现的机理.为更直观理解全局图,对以下图形做以下说明: 用△表示吸引子A,不同颜色代表不同的吸引子; 吸引域用B表示,不同吸引域颜色不同; S表示边界鞍; IS表示吸引域内部鞍; 下标表示吸引子、吸引域和内部鞍的个数,例如A1,A2表示系统两个吸引子共存,B1,B2为其对应的吸引域. 3.1 边界激变当g从0.0471增大到0.0472时,发生两次逆的边界激变,如图3所示.A5和A6表示周期为2的吸引子,A5与嵌在吸引域B1,B5边界的鞍S碰撞,A6和嵌入吸引域B2,B6边界的鞍S碰撞,使得A5,A6和部分边界鞍S突然消失,成为内部周期鞍IS1,IS2,同时吸引域B5,B6消失,吸引域B1,B2变大.当g从0.0482变化到0.0483时,系统再次发生两次边界激变,两个周期1吸引子A1和A2与边界上的鞍S发生碰撞,变为吸引域B5,B6的内部鞍IS5,IS6,同时吸引域B1和B2消失,如图4所示.图4 系统(7)的全局图 (a) g=0.0482; (b) g=0.0483Fig.4.Global diagram of the system (7): (a) g=0.0482; (b) g=0.0483.图5 系统(7)的全局图 (a) g=0.0491; (b) g=0.0492Fig.5.Global diagram of the system (7): (a) g=0.0491; (b) g=0.0492.图6 系统(7)的全局图 (a) g=0.0490; (b) g=0.0491Fig.6.Global diagram of the system (7): (a) g=0.0490; (b) g=0.0491.图7 系统(7)的全局图 (a) g=0.0596; (b) g=0.0597; (c) g=0.0726; (d)g=0.0727Fig.7.Global diagram of the system (7): (a) g=0.0596; (b)g=0.0597; (c) g=0.0726; (d) g=0.0727.当g从0.0491增大到0.0492时,混沌吸引子A2与吸引域边界上的混沌鞍S发生碰撞,发生边界激变,变成新的更大的边界混沌鞍,吸引域B2随之消失,状态空间中为四个周期吸引子和混沌边界鞍共存,如图5所示.3.2 合并激变当g从0.0490变化到0.0491时,混沌吸引子A2和A4不断接近吸引域边界上的混沌鞍S,发生合并激变,成为新的混沌吸引子A2,与此同时吸引域B2,B4合并为新的吸引域B2,如图6所示.当g从0.0596变化到0.0597时,混沌吸引子A1,A2与边界上的混沌鞍S碰撞,发生合并激变,变为新的混沌吸引子A1,如图7(a)和图7(b)所示.当g从0.0726增大到0.0727时,发生逆合并激变,混沌吸引子A1消失,出现两个新的周期1吸引子A1,A2及混沌边界鞍S,如图7(c)和图7(d)所示.图8 系统(7)的全局图 (a) g=0.0460; (b) g=0.0461Fig.8.Global diagram of the system (7): (a) g=0.0460; (b) g=0.0461.图9 系统(7)的全局图 (a) g=0.0478; (b) g=0.0479; (c),(d) 分别对应于(a),(b)图的区域细化Fig.9.Global diagram of the system (7): (a) g=0.0478; (b) g=0.0479;(c),(d) the region refinement of panels (a) and (b).图10 系统(7)的全局图 (a) g=0.0533; (b) g=0.0534Fig.10.Global diagram of the system (7): (a) g=0.0533; (b) g=0.0534.3.3 域边界突变当g=0.0460时,系统存在三个周期1吸引子A1,A2,A3和嵌在吸引域B1,B2,B3边界上的混沌鞍S,此时的域边界呈现出Wada特性.当g增大到0.0461时,系统新出现一个周期3吸引子A4,此时的域边界由4个吸引域构成,仍具有Wada特性,系统发生Wada-Wada域边界突变,如图8所示.当g从0.0478增大到0.0479时,吸引子的个数从6个变为7个,为判断吸引子变化过程,对区域v={(x,y)|–0.075 ≤ x ≤ –0.055,0.068 ≤ y ≤0.092}进行细化.可以发现,原周期3吸引子A4消失,并在其附近出现两个新的周期3吸引子A4和A7,如图9(c)和图9(d).原吸引域B4分裂为新吸引域B4和B7,且参数变化前后域边界均呈现Wada特性,域边界结构更加复杂,系统再次发生Wada-Wada域边界突变.当g=0.0533时,状态空间中有4个周期1吸引子共存,此时域边界仍具有Wada特性.当g增大到0.0534时,周期吸引子A3和A4消失,状态空间中仅剩2个周期1吸引子A1,A2,此时域边界的Wada特性消失,只呈现分形特性,系统发生Wada-分形域边界突变,如图10所示.4 温度对全局特性的影响温度作为SMA薄板的一个可控参数,利用温度改变SMA薄板的力学特性在工程领域中有重要运用.取g为0.06,分析温度q变化对系统的影响,选取不同的初值点(–0.0553,–0.09),(–0.031,0.045),(0.083,–0.032),(0.047,0.059)构造Poincare映射,得到对应的分岔图,如图11所示.可以发现,随温度q的变化,系统中吸引子个数、类型及大小会发生改变,并出现激变现象.为从全局角度分析温度变化对系统激变的影响,本节基于复合胞坐标系方法,将区域D={(x,y)| –0.1 ≤ x ≤ 0.1,–0.12 ≤y ≤ 0.12},均匀划分为1000×1200个胞,获得系统的吸引子、吸引域、鞍和域边界等全局特性.图11 系统(7)随温度q变化的多值分岔图Fig.11.Multivalued bifurcation diagram of the system (7)with the variation of temperature q.4.1 边界激变当q=0.8379时,状态空间中两个周期1吸引子A1和A2共存,S为嵌入在分形域边界上的混沌鞍,IS1,IS2是吸引域B1,B2内部的混沌鞍.当q增大为0.8380时,系统出现两个新的吸引子A3和A4,内部鞍IS1,IS2消失,系统发生两次逆边界激变,如图12所示.4.2 合并激变当q从0.4088变化到0.4089时,周期2吸引子A1和A2同时与域边界上的混沌鞍S发生碰撞,合并为一个新的混沌吸引子A1,吸引域B1和B2合并成为新吸引域B1,系统发生合并激变,如图13(a)和图13(b)所示.当q从0.7182增大到0.7183时,混沌吸引子A1消失,出现两个新的混沌吸引子A1和A2,以及嵌在域边界上的混沌鞍S,系统发生逆的合并激变,如图13(c)和图13(d)所示.图12 系统(7)的全局图 (a) q=0.8379; (b) q=0.8380Fig.12.Global diagram ofthe system (7): (a) q=0.8379; (b) q=0.08380.图13 系统(7)的全局图 (a) q=0.4088; (b) q=0.4089; (c) q=0.7182; (d)q=0.7183Fig.13.Global diagram of the system (7): (a) q=0.4088; (b)q=0.4089; (c) q=0.7182; (d) q=0.7183.图14 系统(7)的全局图 (a) q=0.0950; (b) q=0.0951Fig.14.Global diagram of the system (7): (a) q=0.0950; (b) q=0.0951.4.3 域边界突变当g=0.0950时,状态空间中两个周期2吸引子A1,A2,和两个周期1吸引子A3,A4共存,吸引域边界呈现Wada特性.当g增大为0.0951时,两个周期1吸引子A3和A4消失,吸引域边界变为由B1和B2构成的分形边界,系统发生Wada-分形域边界突变,如图14所示.5 结论考虑实际工程中温度和应力对于SMA的力学特性的影响,本文选取SMA薄板为研究对象,以温度q和激振力振幅g作为分岔参数,采用复合胞坐标系方法分析其全局分岔特性,探究在参数的连续变化下,系统激变现象及域边界突变的演化过程.在一定的参数变化范围内,系统呈现丰富的激变现象,如周期或混沌吸引子与域边界上的周期鞍或混沌鞍发生碰撞的边界激变,周期吸引子或混沌吸引子同时与边界上的混沌鞍发生碰撞的合并激变等.当多吸引子共存时,域边界会呈现分形结构,并随着参数的变化,发生Wada-Wada,Wada-分形和分形-Wada等域边界突变现象.本文的研究结果对于通过控制温度和激励强度等参数,调控SMA薄板系统的动态响应,优化机械设备的变形及振动控制等问题上提供有效的分析手段.参考文献【相关文献】[1]Yuan B,Zhu M,Chung C 2018 Materials 11 1716[2]Hartl D J,Lagoudas D C 2007 Proc.Inst.Mech.Eng.Part G: J.Aerosp.Eng.221 535[3]Lee J,Jin M,Ahn K K 2013 Mechatronics 23 310[4]Jani J M,Leary M,Subic A,Gibson M A 2014 Mater.Des.56 1078[5]Song G,Ma N,Li H N 2006 Eng.Struct.28 1266[6]Bernardini D,Rega G 2011 Int.J.Bifurcation Chaos 21 2769[7]Paula A S,Savi M A,Lagoudas D C 2012 J.Braz.Soc.Mech.Sci.Eng.34 401[8]Sado D,Pietrzakowski M 2010 Int.J.Non-Linear Mech.45 859[9]Hashemi S M T,Khadem S E 2006 Int.J.Mech.Sci.48 44[10]Savi M A 2015 Int.J.Non-Linear Mech.70 2[11]Han Q,Xu W,Yue X 2014 Int.J.Bifurcation Chaos 24 1450051[12]Grebogi C,Ott E,Yorke J A 1982 Phys.Rev.Lett.48 1507[13]Grebogi C,Ott E,Yorke J A 1983 Physica D 7 181[14]Chian A C L,Borotto F A,Rempel E L,Rogers C 2005 Chaos Solitons Fractals 24 869[15]Yue X,Xu W,Zhang Y 2012 Nonlinear Dyn.69 437[16]Liu L,Xu W,Yue X L,Han Q 2013 Acta Phys.Sin.62 200501 （in Chinese） [刘莉,徐伟,岳晓乐,韩群 2013 物理学报62 200501][17]Liu X J,Hong L,Jiang J 2016 Acta Phys.Sin.65 180502 （in Chinese） [刘晓君,洪灵,江俊2016 物理学报 65 180502][18]Yue X,Xu W,Wang L 2013 Commun.Nonlinear Sci.Numer.Simul.18 3567[19]Zhang Y 2013 Phys.Lett.A 377 1269[20]Hsu C S 1992 Int.J.Bifurcation Chaos 2 727[21]Hsu C S 1995 Int.J.Bifurcation Chaos 5 1085[22]Tongue B H 1987 Physica D 28 401[23]Falk F 1980 Acta Metall.Sin.28 1773[24]Machado L G,Savi M A,Pacheco P M C L 2004 Shock Vib.11 67[25]Huang Z H,Liu P,Du C C,Li Y H 2009 Chin.Quarterly Mech.30 71 （in Chinese） [黄志华,刘平,杜长城,李映辉 2009力学季刊 30 71]。
NiTiHf高温形状记忆合金研究进展
综述NiTi Hf高温形状记忆合金研究进展孟祥龙 王 中 赵连城( 哈尔滨工业大学材料科学与工程学院 哈尔滨 150001 )伊胜宁( 江苏钢绳集团公司 江阴 214433 )文 摘 介绍了Ni T i H f高温形状记忆合金的研究状况,重点评述了Ni T i H f合金的设计以及Hf的添加和热处理对合金的相变、力学行为和形状记忆效应的影响,并对它们所对应的微观机制作了一定的分析。
关键词 NiTiHf高温合金,形状记忆合金,合金设计,相变,力学行为,形状记忆效应Development of Ni Ti Hf High Temperature Shape Memory AlloysMeng Xianglong Wang Zhong Zhao Liancheng( School of Materials Science and Eng i neering,Harbin Insti tute of Technology Harbin 150001 )Yi Shengning( Jiangsu Steel Wire Rope Bloc Crop. Jiangyin 214433 )Abstract The research on Ni T i H f high te mperature shape me mory alloys is revie wed with emphasis on the design of NiTiHf alloys,and the effect of Hf addition and heat treatment on the alloys transformation,mechanical behavior and shape memory effect.Its micro mechanism is also briefly analyzed in this paper.Key words NiTiHf high te mperature alloys,Shape memory alloys,Design of the alloys,Transformation,Mechan ical behavior,Shape memory effect1 引言形状记忆合金是现代智能材料的主要代表之一,具有丰富的马氏体相变现象、奇特的形状记忆效应和良好的超弹性性能。
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Shape-Memory Behavior of Thermally Stimulated Polyurethane for Medical ApplicationsG.Baer,1T.S.Wilson,2D.L.Matthews,2D.J.Maitland21Department of Biomedical Engineering,University of California Davis,Davis,California956162Division of Medical Physics and Biophysics,Lawrence Livermore National Laboratory,Livermore,California94551Received24February2006;accepted27September2006DOI10.1002/app.25567Published online in Wiley InterScience().ABSTRACT:Shape memory polymers(SMPs)have been of great interest because of their ability to be thermally actu-ated to recover a predetermined shape.Medical applica-tions in clot extracting devices and stents are especially promising.We investigated the thermomechanical proper-ties of a series of Mitsubishi SMPs for potential application as medical devices.Glass transition temperatures and mod-uli were measured by differential scanning calorimetry and dynamic mechanical analysis.Tensile tests were performed with20and100%maximum strains,at37and808C,which are respectively,body temperature and actuation tempera-ture.Glass transitions are in a favorable range for use in the body(35–758C),with high glassy and rubbery shear moduli in the range of800and2MPa respectively.Constrained stress–strain recovery cycles showed very low hysteresis af-ter three cycles,which is important to know for precondi-tioning of the material to ensure identical properties during applications.Isothermal free recovery tests showed shape recoveries above94%for MP5510thermoset SMP cured at different temperatures.One material exhibited a shapefix-ity of99%and a shape recovery of85%at808C over one thermomechanical cycle.These polyurethanes appear par-ticularly well suited for medical applications in deployment devices such as stents or clot extractors.Ó2006Wiley Period-icals,Inc.J Appl Polym Sci103:3882–3892,2007Key words:polyurethanes;mechanical properties;thermal properties;glass transitionINTRODUCTIONShape memory polymers(SMPs)represent a very in-teresting class of polymers,because of their ability to recover a predetermined shape upon controlled heat activation.1They are increasingly being investigated for use as smart materials in a variety of applications ranging from textiles to ergonomic utensils.2In the medicalfield,new SMPs with adjustable moduli,high recovery ratios,sharp and adjustable transition temper-atures,and biocompatible drug-eluting surfaces have enabled their use in a variety of new applications.Spe-cifically,SMPs are currently being researched for appli-cations in aneurysms embolization,3as clot extraction devices,4–6and for vascular stents.7,8Because of their different mechanical properties above and below the glass transition temperature,the properties of heat activated SMPs can be optimized to offer both theflex-ibility,the resistance in compression,and the high shape recovery needed for proper insertion,position-ing,deployment,and functionality of these devices. They can be deployed by a variety of heat sources: light illumination,9,10electric current,11or simple hot saline solution.In addition,their surface can readily be modified for biocompatibility and drug elution.12,13 Thermomechanical behavior and shape memory properties have been reported for SMP materials made from polyurethanes,1,2,14–17ethylene-vinyl ace-tate copolymers,18oligo(e-caprolactones),19poly(ethyl-ene glycol),and poly(ethylene terephthalates).20The shape memory effect of thermal SMPs resides in the structure of the polymer,which is often described as being a two phase structure comprised of a hard,or fixing phase,and a soft,or reversible phase.The hard phase consists of a dispersed glassy phase,crystallin-ity,or/and chemical crosslinking.The soft phase can be either amorphous or semicrystalline.Varying the amount of hard and soft phase results in significant differences in shape memory behavior,as shown by Lin and Chen’s early studies with polyurethanes.21,22 Thermomechanical properties in thinfilms of Mitsu-bishi Heavy Industry polyurethane materials have previously been investigated.2,23,24Their shape mem-ory behavior was also studied when replacing and varying the amount of hard segment content.25These studies have shown that such materials have potential for biomedical applications,since they exhibit highCorrespondence to:T.S.Wilson(wilson97@). Contract grant sponsor:U.S.Department of Energy by Lawrence Livermore National Laboratory(LLNL);contract grant number:W-7405-ENG-48.Contract grant sponsor:National Institutes of Health/ National Institute of Biomedical Imaging and Bioengineer-ing;contract grant number:R01EB000462.Contract grant sponsor:LLNL Directed Research and Development;contract grant number:04-ERD-093. Contract grant sponsor:National Science Foundation Center for Biophotonics(CBST).Journal of Applied Polymer Science,Vol.103,3882–3892(2007)strain recovery,high glass/rubber modulus ratios, and their glass transition temperatures are in a favor-able range for use in the human body.Additionally, the good biocompatibility of polyurethanes is well known(e.g.,catheters26and heart valves27)and has been studied for these SMPs.In vitro and in vivo stud-ies by Metcalfe et al.of the same Mitsubishi polyur-ethane materials used as foams for endovascular inter-ventions have recently shown the material to be non-cytotoxic and poorly thrombogenic.3In vitro studies from our group(in the process of publication)show that the material used here has minimal effect on trig-gering an inflammatory response,thrombogenesis, and activation of platelets and neutrophils,reducing the risk of rejection of the implanted device.Such SMPs would appear useful for interventional medical devices,such as stents.Other requirements of a SMP stent reside in its ther-momechanical properties.The material needs to have a high shape recovery ratio when deployed at high temperature so that a small device can be inserted and navigated through the vasculature and deployed into a large device thatfits the target artery.In addition, when in place at body temperature,a high modulus is desired for resistance in tension and compression. Finally,thermomechanical properties need to be stable over time.These general requirements would apply to any SMP interventional medical device.However,results comparing the thermomechanical properties of different Mitsubishi materials of various glass transition temperatures available have not been reported.This knowledge would be extremely helpful as a base for choosing a particular material with opti-mal properties for a specific medical application. Additionally,it is well known that two phase systems such as segmented polyurethanes have structures that are affected by process history including shear,stress, and solvents if solution cast1;however,to our knowl-edge,the effect of cure profile on the behavior of SMPs has not been reported.It is of interest tofind out to what extend varying the curing temperature might confer different properties and shape memory behav-ior to SMPs.In this study,we have examined a variety of Mitsu-bishi polyurethanes within the scope of researching materials for stent applications.Several thermoplastic and thermoset polyurethanes with glass transition tem-peratures ranging from35to758C were investigated. In addition,we studied the effect of curing tempera-ture on thermal transitions and thermomechanical properties of one of the thermosets,by having a two step curing protocol and varying the temperature of thefirst step.Thermal transitions were characterized by differential scanning calorimetry(DSC),dynamic mechanical properties were analyzed by dynamic me-chanical analysis(DMTA),and cyclic tensile and recov-ery properties were examined using an MTS tensile tester.MTS experiments were performed at two tem-peratures relevant to a medical device functionality: 378C(body temperature)and808C(actuation tempera-ture).Previous studies reported by our group4have shown that temperatures of T g6208C are well into the glassy and the rubbery plateau respectively.Elonga-tion to failure,stress recovery cycles,and free recovery cycles were studied at maximum strains of20and 100%,which are reasonable ranges of deformation expected in medical device actuation.EXPERIMENTALMaterialsSMPsThe SMPs used in this study were obtained from DiAPLEX Company(a subsidiary of Mitsubishi Heavy Industries,Tokyo,Japan)either as two part thermoset resins or thermoplastic resin in pellet form.Thefirst two digits following the two letters represent the tem-perature,in degree centigrade,of thefirst glass transi-tion,indicated by the manufacturer.While the compo-sitions are proprietary,it is known that the material is a segmented polyurethane,which has a microphase separated morphology.28The primary shape is formed at a temperature above the highest glass(T gh)or crys-talline(T m)transition and the polymer is either cooled (thermoplastics)or crosslinked(thermosets)tofix the shape.The secondary shape is obtained by heating the material above the glass transition temperature of the soft phase(T gs)or the soft phase crystalline melt-ing temperature(T ms),applying a strain to the mate-rial,and cooling it down below the same soft phase temperature tofix the shape.The deformation is stored elastically as macromolecular chain orientation within the soft phase,while hard phase segments are relatively imperturbed by this stress.Thus,there is an entropic potential for shape recovery.By heating the material above T gs or T ms,soft phase segments spring back to their lower entropic state,resulting in recovery of the primary shape.Thermoset sample preparationGenerally,the thermoset SMPs MP3510,MP4510,and MP5510were processed according to the sample preparation guide provided by DiAPLEX.29Briefly,A and B components were vacuum dried at708C and1 Torr for1h,then mixed at the appropriate weight ra-tio,and degassed under vacuum(1Torr)for60s.The mixture was placed into a syringe and immediately used to inject specific molds.Aluminum molds were fabricated to cast samples according to ASTM stand-ards.DMTA samples were molded into4.65mm di-ameter,5-cm-long cylinders;tensile test samples were molded into1-mm-thick dogbones for failure analysisSMPs FOR MEDICAL APPLICATIONS3883Journal of Applied Polymer Science DOI10.1002/app(ASTM standard D638type V),and1mm thick,1cmwide bars(ASTM standard D882)for other tensiletests.Once the molds were injected,MP5510sampleswere cured in an oven under nitrogen for1h(curestep1)at one of the following temperatures:258C(T g À308C),458C(T gÀ108C),558C(T g)or658C(T gþ108C)followed by4h(cure step2)at808C.MP3510and MP4510samples were cured in one step for4h at808C.Samples were then cooled at room temperatureand stored in sealed containers before testing.DSCsamples were cut from molded strips.It should be notedthat the‘‘thermoset’’grade resins are actually comprisedof difunctional monomers and when fully cured at rec-ommended conditions were found to be soluble in ap-propriate solvents and melt processible.For example, heating these thermosets above the hard phase T g would allow for re-training of the primary shape.Thermoplastic SMP sample preparationTest specimens were prepared from the as received thermoplastic SMP MM5510,MM4520,MM5520, MM6520,and MM7520pellets for DSC and DMTA testing as follows.The pellets werefirst vacuum dried(40mTorr,508C)for120h.They were then compression molded into plaques with dimensions 3.2mmÂ100mmÂ100mm using a Carver hot press(2008C,15,000pounds,10min).The pressed plaques were quickly cooled by placement on an alu-minum block,demolded,stored in plastic bags,and cut into1cm strips for testing.Experimental proceduresThermal and mechanical characterization of SMPs were done using the following methods.Differential scanning calorimetryDSC measurements were made using a Perkin–Elmer Diamond DSC equipped with an Intracooler2,over a temperature range ofÀ20to2008C using a heating rate of208C/min,with561mg samples,consistent with ASTM D3418.Two heating/cooling cycles were used and the T g’s from both heating cycles are reported as the average of two repeats.Dynamic mechanical analysisDMTA measurements were made with an ARES LS2 under dynamic oscillatory mode at a frequency of 1Hz and initial strain of0.01%.Testing was done under dry air,from25to1208C at a linear ramp rate of18C/min,consistent with ASTM D4065.For testing thermosets,test specimens were used having a cylin-drical geometry of 4.65mm diameter and5cm long,while torsion rectangles of3.2mmÂ12mm Â50mm were used for testing thermoplastics.The shear storage modulus G0,shear loss modulus G00, and the ratio of loss to storage modulus(tan d)were plotted as a function of temperature;T g was deter-mined from the tan d peak,and the glassy and rub-bery moduli were read from the G0curve.In the case of the thermoplastics,first heating,first cooling,and second heating cycles were performed to capture the effect of thermal history(two repeats).TensileStress–strain measurements were performed on an MTS Synergie1000tensile tester with a load cell of 5kN,equipped with a custom forced air heating and a cooling system and a constant temperature chamber to which was attached a thermocouple.Tests were performed at37and808C after heating the sample at a rate of108C/min,and maintaining the sample at the desired temperature for5min before performing the experiment.Uniaxial elongation to failure tests were conducted at an engineering strain rate of 0.5minÀ1,as specified in ASTM D882.Initial modu-lus,peak load,peak stress,and strain at break were recorded for various thermosets with three repeats each.Constrained stress recoveryConstrained stress recovery cycles at high temperature were conducted on the MTS Synergue1000at a con-stant strain rate of5minÀ1with maximum strains of 20and100%and at constant temperatures of808C, according to the same heating protocol mentioned ear-lier.The machine was programmed to perform cycles of elongation to the maximum desired strain and return back to zero strain.Percentage recovery strain was calculated for each cycle.Five cycles were per-formed on various thermosets with three repeats.Isothermal free recoveryFree isothermal recovery tests at high temperature were performed on the MTS Synergie1000as in con-strained recovery cycles,except that after elongation to a maximum strain,unloading was done by pro-gramming the machine to return to a very low stress value close to0.The sample was allowed to freely recover its strain for15min before the next cycle.Per-centage strain recovery was then calculated.Various thermosets were tested with three repeats each.Thermomechanical cyclingThermomechanical cycling tests were conducted on the MTS Synergie1000at a constant strain rate of3884BAER ET AL. Journal of Applied Polymer Science DOI10.1002/app5min À1with maximum strains of 20and 100%with elongation at a constant temperature of 808C and sub-sequent cooling and recovery at 378C,as described by Kim et al.14Heating was performed according to the protocol mentioned earlier.The specimen was then elongated to the desired strain,held,and rapidly cooled down to 258C using nitrogen gas.After hold-ing the sample at this temperature for 5min,the stress was set to a low value close to 0,and the sam-ple was then allowed to freely recover to its recovery strain by rapid heating at 808C.Percentage shape fix-ity and Percentage shape recovery were calculated.One cycle was performed with one of the thermoset materials,with three repeats.RESULTS AND DISCUSSIONDifferential scanning calorimetryThe glass transition of the soft phase (T g )was calcu-lated from first and second heating curves generatedby DSC using the half-height technique as described by Wunderlich 30and as shown in Figure 1.Results for the thermoset and the thermoplastic series are shown in Table I.Also shown are results for the MP5510ther-moset series (manufacturer reported T g of 558C)pre-pared at different precuring temperatures.In general,the glass transition temperatures measured by DSC were lower than the ones indicated by the manufac-turer,by up to 108C.Since we have no specific infor-mation on the characterization method used by the manufacturer,we can only speculate on the source of this difference.The glass transition is a dynamic prop-erty and therefore varies with the cooling and heating rates of the samples.In addition,DSC and DMTA measurements often give different results;e.g.,the T g measured by DSC is often much lower than that deter-mined by the tan d peak,31which is discussed later.There was also a significant difference between the glass transition temperature obtained during the first and second heat,indicative of the importance of previ-ous process history on phase separation and quench-ing of the amorphous soft phase.Surprisingly,cure step 1temperature did not affect the glass transition temperature significantly.Dynamic mechanical analysisResults of the DMTA testing are shown in Figures 2through 3.Glass transitions were determined based on tan d peak and are reported in Table I.Figure 2(a)shows the shear storage modulus G 0and tan d for the different T g grade thermoset SMPs prepared accord-ing to manufacturer’s recommendations with one step curing.Figure 2(b)shows G 0and tan d for ther-moplastic SMP MM-5510during first heating,first cooling,and second heating.The effect of thermal his-tory is captured here.There is a shift in the curves between first heating and first cooling.The first cool-ing and the second heating display identical curves.Between the first heating and first cooling,there is aTABLE ISummary of DSC and DMTA Results on DiAPLEX1(Mitsubishi)SMPs and Comparison with Manufacturer’s ValuesSMP type Cure step 1conditions Cure step 2conditions Manufacturer’s soft phase T g (8C)T g by DSCfirst heat (8C)T g by DSC second heat (8C)T g by tan d (8C)Glassy plateau modulus (Pa)Rubbery plateau modulus (Pa)MP3510–4h 808C 3531.325.246.1 5.2E 8 1.6E 6MP4510–4h 808C 4542.535.954.17.0E 8 1.7E 6MP5510–4h 808C 5552.451.165.28.1E 8 1.9E 6MM5510–10min 2008C 5551.452.054.98.1E 8 1.6E 6MM4520–10min 2008C 4535.947.245.9 6.6E 8 1.3E 6MM5520–10min 2008C 5545.953.557.37.7E 8 1.4E 6MM6520–10min 2008C 6564.764.966.68.9E 8 2.1E 6MM7520–10min 2008C 7574.274.474.67.7E 8 1.8E 6MP55101h 258C 4h 808C 5544.352.455.97.9E 8 1.5E 7MP55101h 458C 4h 808C 5543.351.061.38.3E 8 5.9E 6MP55101h 558C 4h 808C 5541.755.265.47.6E 8 2.5E 6MP55101h 658C4h 808C5544.552.666.37.7E 82.1E6Figure 1General DSC behavior of thermoplastic and ther-moset polyurethane SMPs.Shown are first heating,first cooling,and second heating curves.SMPs FOR MEDICAL APPLICATIONS 3885Journal of Applied Polymer Science DOI 10.1002/appshift to lower T g .There is also a decrease in tan d peak height,indicating an increase in the hard phase content.In addition,the storage modulus in the glassy phase increases by a factor of 8between the first heating and the first cooling.These results can be understood as a rearrangement in the phase-separated structure of the polymer as a result of thermal history during testing.Initially,during preparation,the test specimens were quickly cooled from the melt and the segregation of soft phase segments and hard phase segments into separate phases did not have time to reach equilibrium.The result would be a structure made up of soft phase containing a relatively high hard-segment content.The results from the first heat-ing cycle are indicative of this structure up to the point at which the polymer had enough mobility to regain an equilibrium phase structure.On cooling and subse-quent reheating,the polymer has had time to reach this equilibrated structure in which a higher degree of phase separation has occurred,with the result that the soft phase now has a lower hard segment content(hence lower T g )and there is a larger amount of hard phase (hence higher modulus).It is likely that more cycling would show identical curves.Cure temperature effects can also be seen in the thermoset grade SMPs as seen in Figure 3,which shows G 0obtained with the MP5510thermoset mate-rials cured in two steps.Glass transitions were deter-mined based on tan d peak.The glassy and rubbery moduli can also be read;they are two elastic moduli of importance,which are approximately equal to the shear storage modulus G 0in the lower temperature higher stiffness ‘‘glassy’’plateau and in the higher temperature lower stiffness ‘‘rubber’’plateau,respec-tively.For SMPs,the rubbery and the glassy moduli are generally taken as the elastic moduli at T g 6258C,respectively.Results are shown in Table I.Overall,glass transition temperatures obtained by tan dpeakFigure 2Elastic modulus and tan d of SMPs.(a)Thermo-sets cured using suggested temperature profile and (b)first heating,first cooling,and second heating cycles for the MM5510thermoplastics.Figure 3Dynamic storage modulus (G 0)in the first heat for MP5510SMP cured at various cure step 1temperatures.Figure 4Glassy (G 0at T g þ258C),rubbery (G 0at T g À258C)modulus,and Elastic ratio (G 0at T g À258C/G 0at T g þ258C)versus cure step 1temperature for the thermoset polymers MP5510.3886BAER ET AL.Journal of Applied Polymer Science DOI 10.1002/appwere higher than the ones obtained by DSC.This isvery common;T g in DSC is taken at one half of the increase in heat capacity,while T g taken at the tan dpeak occurs after the shear loss modulus G00haspeaked,thus further into the glass transition and at ahigher temperature.30For the thermoplastic series,T gmeasured by tan d was close to the manufacturer’sT g.For the thermoset series cured in two steps,the T gmeasured by tan d varied between61.3and66.38C.The glassy shear modulus was roughly constant across all materials,in the order of800MPa.The rub-bery shear modulus seemed to be slightly more ele-vated in the thermoset materials when compared tothe thermoplastic materials,and overall varied be-tween1.3and15MPa,generally increasing with in-creasing T g.However,for the MP5510thermosetscured in a two-step process,while the glassy modulusremained essentially unchanged,the rubbery modulus significantly decreased with increasing precuring tem-perature,reaching a plateau for materials cured above558C during cure step1,as seen in Figures3and4.The elastic ratio,defined as the ratio of the glassyto rubbery modulus(G0(T gÀ258C)/G0(T gþ258C)), increased with increasing temperature during curestep1of the thermoset series,as shown in Table IIand Figure4.It has been reported that a high glassy modulus correlates with high shapefixity during si-multaneous cooling and unloading,and elasticityratios above100allow for greater resistance to defor-mation and better shape recovery.13According tothesefindings,material with cure step1at258Cshould exhibit less shape recovery than the others,since the elastic ratio is53while other elastic ratiosare above100.The increase in the elastic ratio,due to a decrease inthe rubbery modulus,could be explained by an in-crease in phase separation of the material,as the tem-perature is increased during cure step 1.14Visualobservations of the turbidity of the samples cured atthe different temperatures appear to support this idea.It was observed that in general,the degree of turbidityin the samples increased with initial(step1)cure tem-perature.Samples cured at25and458C in cure step1 showed little turbidity and were almost transparent, while the ones cured at55and658C in cure step1,and the ones cured at808C in one single step,showed in-creasing degrees of turbidity.Higher turbidity seemed to correlate with lower rubbery modulus.Turbidity or cloudiness occurs in multiphase systems because of the differences in the refractive indices between phases, in turn relating to different compositions,the presence of additives or dispersedfillers,or crystallinity.Here we believe increases in turbidity are related to the degree of phase separation and/or changes in size of the dispersed phase.MTS mechanical testingUniaxial tensile test to failure—MTS(37and808C) Figure5shows the stress–strain behavior during uni-axial tensile testing to failure at37and808C.At a given temperature test,the materials exhibited very similar curves,with quite different strains at break.The maxi-mum strain at break was100%at378C and270%at 808C.The material exhibited necking at378C,but not at808C.This is presumably due to cross section con-traction with realignment of the polymer chains along the extension direction.14Table III shows failure test re-sults at37and808C.The strain at break at378C was highest for the material precured at258C and de-creased with increasing precuring temperature,sug-gesting a lower degree of phase separation as curingTABLE IIGlass Transition Temperatures,Modulus,and Elastic Ratio for the MP5510Thermoset Series Cured at Various Temperatures in One or Two StepsCure step1 temperature (1h)(8C)Cure step2conditions(4h)(8C)T g from tan dpeak(8C)G0atT gþ25PaG0atT gÀ25PaElasticratio258055.9 1.5Eþ077.9Eþ0853458061.37.2Eþ068.7Eþ08121558065.4 2.7Eþ067.6Eþ08304658066.3 2.6Eþ068.2Eþ08327–8065.2 1.9Eþ068.5Eþ08426Figure5MP5510thermoset series tensile testing to failure. SMPs FOR MEDICAL APPLICATIONS3887Journal of Applied Polymer Science DOI10.1002/apptemperature increases.14Strain at break at 808C was highest in the material precured at 558C.Peak pres-tresses were similar across materials at a given test tem-perature,around 50MPa at 378C,and 19MPa at 808C.Isothermal constrained stress recovery cyclesCyclic behavior at 808C and 20%maximum strain.All isothermal constrained stress recovery cycles showed a hysteresis,which decreased with increasing cycle number.Figure 6shows the stress–strain cyclic behav-ior for the material precured at 258C.As seen in this figure,the greatest change in behavior is observed between the first and the second cycle.This is presum-ably due to entanglement decoupling of molecular chains,with relaxation of dangling chains and pulling out of hard segments from the hard phase.Cyclic properties become similar after the third cycle.This is important to know in terms of manufacturing and pre-conditioning the material to create a device with uni-form cyclic properties.In addition,as the number of cycles increases,the initial slope of the loading curve does not significantly change,which implies that the structure is unchanging.These results are similar to the ones reported by Tobushi et al.2This stress–strain behavior was observed in all the precured conditionsstudied.Figure 7(a,b)shows the first and the fifth cycle for materials precured at 25,45,55,and 658C.The material precured at 258C clearly exhibits higher stresses at 20%strain when compared to the other materials,which exhibit identical behavior.The mate-rial precured at 258C also had the largest initial slope,suggesting it has higher resistance to deformation among these materials.This suggests the existence of a transition precuring temperature between 25and 458C below which more phase separation occurs during preparation of the material.Cyclic behavior at 808C and 100%maximum strain.Figure 8shows the stress–strain cyclic behavior for the materialTABLE IIITensile Testing Results for the MP5510Thermoset SeriesSpecimenPeak load (N)Peak stress (MPa)Strain at break (%)Initial modulus (MPa)Cure step 1temperature (8C)Testtemperature (8C)2537142614661956519436164537149614861886819626355537158615161716820276186537153614961516319666162580686422622636123562458051641662245632661558060641962271682361658053641762241682761Figure 6Constrained isothermal stress recovery cycles at 808C for the material cured for 1h at 558C followed by 4h at 808C.Maximum strain20%.Figure 7MP5510thermoset series:constrained isothermal strain recovery at 808C,(a)cycle 1and (b)cycle 5.3888BAER ET AL.Journal of Applied Polymer Science DOI 10.1002/app。