复合材料复习题库.doc

复合材料复习题库

9? The transverse tensile strength of an aligned continuous fibre composite

(A)is obtained when testing normal to(垂直于)the fibre axis,

(B)is obtained when testing parallel to (平行于) the fibre axis,

(C)is the lowest tensile stength,

(D)is the highest tensile strength,

(E)depends mainly on the properties of the matrix and of the fibre- matrix interface,

(G) dep ends mainly on the properties of the fibres.

Each of the sentences in questions 11 to 14 consists of an assertion followed by a reason. Answer: (A)if both assertion and reason are true statements and the reason is a correct explanation of the assertion，

(B)if both assertion and reason are true statements but the reason is not a true explanation of the assertion,

(C)if the assertion is true but the reason is a false statement,

(D)if the assertion is false but the reason is a true statement,

(E)if both the assertion and reason are false statements.

The coefficient of thermal expansion of an MMC with a ceramic reinforcement is less than that of the matrix because the coefficient of thermal expansion of a ceramic is usually less than that of a metal.

12.Gen erally rein forcing a metal degrades both ductility and tough ness because there is an in crease in Youngs modulus ?

13.Unfortun ately reinf orceme nt of a metal markedly reduces the fatigue resista nee because cracks are readily formed within the reinforcement.

14.The specific stren gth and modulus of a silic on carbide particle(碳化硅米立子)rein forced aluminium alloy are superior to those of the matrix because silicon carbide is more dense than the com mon aluminium alloys.

9.A,C,E: 11. A; 12. B; 13. E; 14. B;

9.Reinforcing alumina with SiC whiskers ABE enhan ces the thermal shock resista nee, lowers the

coefficient of thermal expansion, decreases the thermal conductivity, in creases the den sity improves the toughness..

lO.The room temperature tensile stress-strain curves in Figure 4.35 are for LAS-SiC fibre composites. The break-down of linearity in the curves at the point marked M is due to C

(A)plastic deformation associated with dislocation motion,

(B)fracture of the fibres,

(C)matrix microcracking,

(D)viscous flow of a glassy phase,

(E)fibre pull-out.

A)B)OD )日

9

11. Chemical vapour depositi on of a carb on matrix BE

is also commonly known as gas carb on ization, is also commonly known as chemical vapour infiltration, produces a brittle composite with a glassy matrix, is independent of deposition pressure, is dependent on deposition temperature. ABE; 10. C; 11. BE Indicate whether statements 1 to 7 are true or false ? 1? Polyester (聚酉旨)tmd epoxy (T 不氧) are examples of thermosets

(A) true

(B) false

2. Phenolie resins known as resoles or one~stage resins require the addition of a curing agont

prior to fabrication ?

(A) true

(B)

false

Figure 4.35

6. 3. Polycarbonate (聚碳酸酯)is an accepted gen eric term for syn thetic polyamides (聚酰胺)

(A) true

(B) false

4? Hand lay-up (手糊成型)requires little capital equipment but is labour intensive

(A) true

(B) false

5. Figure 5. 24 is a diagram of matchecHdie moulding (对模成型)

(A) true

(B) false

It has been estimated tha t over t hree-quar ters of all mat rices of PMCs are thermosets and of these the majority is polyester.

(A) true

(B) false 7. Although many benefits accrue from reinforcing PEEK (聚瞇瞇铜), unfortunately the creep properties are signific&ntly degraded with the result that PEEK matrix composites cannot be used at temperatures in excess of 40 °

C.

Reactive components at

high pressure

Moulded comp onerd

Closed die

Figure 5.24

? .

^7

\—/

10A

B c

D E

n

z(\

- \)/ \)/ \)z \)/ A B c D E ? /(\ zl\ /<\ /(X /(X 2 ■ 亠

(A) true

(B) false

For each of the st ateme nts of questions 8 to 14, one or more of the comp I etions given are correct. Mark the correct completions.

8. Thermosett.ing polymers

(A)

are also known as thermoplastic polymers, (B)

are also known as rubbers, (C)

readily cross-link during curing, (D)

cannot be cured, (E) cannot be reheated and reshaped

9. Thermoplastics

(A)

are cross-linked polymers, (B)

are linear polymers, (C)

may have branchod chains, (D)

readily flow at elevated temperatures, (E)

cannot be reheated and shaped Polyetheretherketone (聚瞇瞇铜) is also known as PEEK, is a type of nylon, is a thermoplastic, is a semi-crystalline polymer, has a high glass-transition temperature of 143 °C 11 Spray-up

(A) is faster than hand lay-up,

(B) invoIves spraying a non-viscous resin at a preform,

(C) invoIves spraying chopped fibres and resin on to a mould,

(D) composites have to be rolled to give a smooth surface finish,

(E) composites have to be rolled to remove entrapped air,

(F) composites have to be vacuum degassed to remove entrapped air

Pultrusion is a slow labour intensive production method, is particularly suited to the production of large, complex, planar shapes, is used for the production of rods of uniform cross-section, involves pushing fibres into a closed mould containing resin, involves pulling resin impregnated fibres through a heated die.

13. The mechanical properties of glass-reinforced epoxies are affected by moisture

because

(A) the epoxy nurtrix becomes more brittle,

(B) the water acts as a plasticizer

? \

7 \)/ \7

\7 \)/

\1

(C) the glass transition temperature is reduced,

(D) the epoxy transforms to a weaker polyester,

(E) the glass fibres can be degraded.

Fatigue crack growth rate in PEEK matrix composites is slower than in monolithie PEEK for the same test conditions, is faster than in monolithie PEEK for the same test conditions, obeys the law of mixtures, obeys the Paris-Erdogan equation, is proportional to the stress intensity factor range raised to a power, is proportional to the square root of the creep modulus.

Each of the sentences in questions 15 to 20 consists of an assertion followed by a reason. Answer:

(A) if both assertion and reason are true statements and the reason is a

correct explanation of the assertion,

(B) if both assertion and reason are true statements but the reason is not

a true explanation of the assertion,

(C) if the assert ion is true but the reason is a false statement,

(D) if the assertion is false but the reason is a true staternent,

(E) if both the assertion and reason are false statements

15. Thermosets are usually stiffer than thermoplastics because of the strong covale nt. bonding of the cross-links in the thermosets ?

16.

Many thermoplastics are partially crystal line because thermoplastics cross-link to form a rigid network 17.

Acrylonitrile-butadiene-styrene (ABS) is a terpolymer(三元共聚物) because it is a multi-phase moterial.

18. The moulds used in resin transFer moulding may be complex, large and made from relatively inexpensive materials such as glass reinforced plastics because only low pressures are employed in the process.

19? Vacuum forming requires matched-dies because, as in vacuum-assisted resin injection, extremely high pressures are involved ?

20. The longitudinal stiffness of continuous fibre reinforced epoxy is about 100 GPa irrespective of whether the reinforceme nt is glass, carb on or aramid because the glass-fibre reinforceci epoxy has the highest density.

Self-assessment

1. A;

2. B;

3. B,

4. A;

5. B;

6. A;

7. B;

8. C, E;

9. B, C, D; 10. A,

C, D, E; 11. A,C,D,E; 12. C, E; 13. B, C, E; 14. A,D, E; 15. A; 16. C;

17. B; 1& A; 19. E; 20. D;

1 ?为什么玻璃纤维的拉伸强度比同成分的块状玻璃高? 微裂纹假说：玻璃纤维高温成型时减少了玻璃溶液的不均匀性，使微裂纹产生的机会减少。此外，玻璃纤维断面较小，随断面积的减少，微裂纹存在的几率也减少，从而使纤维强度提高。玻璃纤维由于表面微裂纹尺寸与数量减少，从而减少了应力集屮，使纤维具有较高的强度。

分子取向假说：在玻璃纤维成型过程屮，由于拉丝机的牵引力作用，使玻璃纤维分子产生定向排列，从而提高了玻璃纤维的强度。

2?影响玻璃纤维强度的因索有哪些？如何影响？解释原因？

1、纤维直径和长度对拉伸强度的影响

一般情况，玻璃纤维的直径愈细，抗拉强度越高，但在不同的拉丝温度下拉制的同一直径的纤维强度，也可能有区别。玻璃纤维的拉伸强度和长度有

关，随着纤维长度的增加，拉伸强度显著下降直径和长度对玻璃纤维拉伸强度的影响，可以用微裂纹假说来解释。因为随着纤维直径和长度的减小，纤维屮微裂纹会相应减少，从而提高了纤维强度。

2、化学组成对强度的影响

一般是含碱量越高、强度越低。无碱纤维比有碱纤维的拉仲强度高20%研究证明，高强和无碱纤维，由于成型温度高，硬化速度快，结构链能大等原因，因此具有很高的抗拉强度。含K2O和PbO成分多的玻璃纤维强度较低。

3、玻璃液质量对玻璃纤维强度的影响

A）结晶杂质的影响：当玻璃成分波动或漏板温度波动或降低时，可能导致纤维屮结晶的出现。实践证明，有结晶的纤维比无结晶的纤维强度要低。

B）玻璃液屮的小气泡也会降低纤维的强度。曾试验用含小气泡的玻璃液拉直径为5.7um,的玻璃纤维其强度比用纯净玻璃液拉制的纤维强度降低

20% o

4、成型条件对玻璃纤维的影响

实践证明，用漏板拉制的玻璃纤维强度高于用玻璃棒法拉制的纤维。在玻璃棒法屮，用煤气加热生产的纤维乂比用电热丝加热生产的纤维强度为高。如用漏板法拉制10um,玻璃纤维的强度为1700MPa,而用棒法拉制相同直径的玻璃纤维强度仅为HOOMPao这是因为玻璃棒只加热到软化，粘度仍然很大，拉丝时纤维受到很大的应力；此外玻璃棒法是在较低温度下拉丝成型，其冷却速度要比漏板法为低。用各种不同成型方法生产的玻璃纤维的强度各不相同。用漏板法拉制的纤维强度最高，气流吹拉长棉次之，玻璃棒法再次之。

然后是蒸汽立吹短棉，强度最低是蒸汽喷吹矿棉。在采用漏板拉丝的方法屮，采用较高的成型温度，较小的漏孔直径，可以提高纤维强度。

5、表面处理对强度的影响在连续拉丝时，必须在单根纤维或纤维束上

敷以浸润剂，它在纤维表面上形成一层保护膜，防止在纺织加工过程屮，纤维间发生相互摩擦，而损伤纤维降低强度。玻璃布经热处理除去浸润剂后，强度下降很多，但在用屮间粘结剂处理后，强度一般都可回升，这是因为屮间粘结剂涂层一方而对纤维起到保护作用，另一方而对纤维表而缺陷有所弥补。

6、存放时间对强度的影响

玻璃纤维存放一段吋间后其强度会降低，这种现象称为纤维的老化。主要是空气屮的水分对纤维侵蚀的结果。此，化学稳定性高的纤维强度降低小，如同样存放233年的有碱纤维强度降低33%,而无碱纤维降低很少。

7、施加负荷吋间对强度的影响

玻璃纤维强度随着施加负荷吋间的增长而降低。半环境温度较高吋，尤其明显。可能是吸附在微裂纹屮的水分，在外力作用下，使微裂纹扩展速度加快的缘故。

3?复合材料的界面定义是什么？包括哪些部分？

复合材料的界面是指基体与增强物之间化学成分有显著变化的、构成彼此结合的、能起载荷传递作用的微小区域。

界而通常包含以下几个部分：基体和增强物的部分原始接触而；

基体与增强物相互作用生成的反应产物，此产物与基体及增强物的接触面；

界而的效应

(1) 传递效应

界面能传递力，即将外力传递给增强物，起到基体和增强物之间的桥梁作

用。

(2) 阻断效应结合适当的界面有阻止裂纹扩展、屮断材料破坏、减缓应力集中

的作用。

(3) 不连续效应

在界面上产生物理性能的不连续性和界面摩擦出现的现象，如抗电性、电感应性、磁性、耐热性、尺寸稳定性等。

(4) 散射和吸收效应

光波、声波、热弹性波、冲击波等在界而产生散射和吸收，如透光性、隔热性、隔音性、耐机械冲击及耐热冲击性等。

(5) 诱导效应

一种物质(通常是增强物)的表面结构使另一种(通常是聚合物基体)与之接触的物质的结构由于诱导作用而发生改变，由此产生一些现象，如强的弹性、低的膨胀性、耐冲击性和耐热性等

界面效应是任何一种单一材料所没有的特性，它对复合材料具有重要的作

用。界面效应既与界面结合状态、形态和物理?化学性质有关，也与复合材料各组分的浸润性、相容性、扩散性等密切相关。

4 ?复合材料界面具有哪些效应？

复合材料界面效应有：

1、传递效应：界面可将复合材料体系屮基体承受的外力传递给增强相，起

到基体和增强相之间的桥梁作用。

2、阻断效应：基体和增强相之间结合力适当的界面有阻止裂纹扩展、减缓

应力集小的作用。

3、不连续效应：在界面上产生物理性能的不连续性和界面摩擦岀现的现

象，如抗电性、电感应性、磁性、耐热性和磁场尺寸稳定性等。

4、散射和吸收效应：光波、声波、热弹性波、冲击波等在界而产生散射和吸

收，如透光性、隔热性、隔音性、耐机械冲击性等。

5、诱导效应：一种物质（通常是增强剂）的表面结构使另一种（通常是聚合

物基体）与之接触的物质的结构由于诱导作用而发生改变，由此产生一些现象，如强弹性、低膨胀性、耐热性和冲击性等。

5?聚合物基复合材料、金属基复合材料、陶瓷基复合材料界面有哪些特点？都有哪些优化设计的方法？

（1）＞聚合物基复合材料界面界面结合有机械粘接与润湿吸附、化学键结合等。聚合物基体复合材料改性方法

%1颗粒增强体在热塑性聚合物基体加入两性相溶剂（增容剂），则能使液晶微纤与基体间形成结合良好的界面

%1纤维增强体复合材料界而改善

a）纤维表面偶联剂

b）涂覆界面层

c）增强体表面改性

（2）、金属基复合材料界面

金属基体在高温下容易与增强体发生不同程度的界而反应，金属基体多为合金材料，在冷却凝固热处理过程屮还会发生兀素偏聚、扩散、1*1 溶、相变等。

金属基复合材料界面结合方式有化学结合、物理结合、扩散结合、机械结合。总的來讲，金属基体复合材料界面以化学结合为主，有时也会出现几种界而结合方式共存。

金属基体复合材料的界面有3种类型：第一类界面平整、组分纯净，无屮间相。第二类界面不平直，由原始组分构成的凸凹的溶解扩散型界面。第三类界面屮含有尺寸在亚微米级的界面反应物。

金属基复合材料的界面控制研究方法：

1）对增强材料进行表而涂层处理在增强材料组元上预先涂层以改善增强材料与基体的浸润性，同吋涂层还应起到防止发生反应的阻挡层作用。

2）选择金属元索改变基体的合金成分，造成某一元索在界面上富集形成阻挡层来控制界面反应。尽量避免选择易参与界面反应生成脆硬界面相、造成强界而结合的合金元素

3）优化制备工艺和参数金属基体复合材料界面反应程度主要取决于制备方法和工艺参数，因此优化制备工艺和严格控制工艺参数是优化界面结构和控制界面反应的有效途径。

（3）、陶瓷基复合材料的界面

陶瓷基体复合材料指基体为陶瓷材料的复合材料。增强体包括金属和陶瓷材料。界面结合方式与金属基体复合材料基本和同，有化学结合、物理结合、机械结合和扩散结合，其屮以化学结合为主，有吋几种结合方式同吋存在。陶瓷基体复合材料界而控制方法

1）改变基体元素

2）增强体表面涂层