典型结构件的振动疲劳分析

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典ຫໍສະໝຸດ Baidu结构件的振动疲劳分析
图清单
图 1.1 基础激励振动疲劳试验装置 ........................................................................................ 4 图 1.2 铝合金疲劳裂纹扩展曲线及实物图.............................................................................. 4 图 1.3 复合膜材料疲劳寿命曲线............................................................................................ 5 图 1.4 有机塑料的 S-N 曲线 ................................................................................................... 5 图 1.5 LY12CZ 铝合金动态疲劳 S-N 曲线............................................................................. 6
南京航空航天大学 硕士学位论文 典型结构件的振动疲劳分析 姓名：廉政 申请学位级别：硕士 专业：飞行器设计 指导教师：王轲 2010-12
南京航空航天大学硕士学位论文
摘
要
常规静疲劳寿命的分析方法已经形成一套独立的系统，且在工程应用上已经比较成熟。但 是在实际环境中，结构发生的破坏主要是由振动所造成的。仅用静疲劳的思想已经无法全面的 解释在振动条件下的失效，因为它忽略了结构动态特性的变化在振动过程中的关键作用。为此 本文以振动条件下，结构动态特性变化及其对疲劳特性和寿命的影响为分析目标并采用飞机结 构中常见的典型结构件为分析对象，基于 MSC.patran&nastran 及 fatigue 平台, 建立典型结构件 的动力学模型，完成动态特性与疲劳寿命估算，通过与实验结果进行比较，提出一种以频率为 主要分析参量的共振疲劳全寿命方法。论文主要工作包括： 1. 以飞机上广泛应用的铆接件为分析对象，完成在一定约束条件下结构的模态实验，并 利用模态识别软件 Ideas 进行频率和振型的识别。为后面章节的动力学模型的建立及响应分 析和疲劳寿命估算奠定基础。 2. 以结构件的第一阶固有频率为初始的激振频率，完成跟踪结构固有频率下的振动疲劳 实验。研究了共振条件下结构寿命变化规律以及固有频率的动态变化情况。结果表明，结构 动力学特性对疲劳寿命具有重要的影响，固有频率随疲劳过程单调递减。 3. 建立了典型结构件有限元动力学模型，并通过模态实验结果验证有限元模型的有效 性，以 Ftigue 软件为计算平台，依托静疲劳的思想对修正后的有限元模型进行振动疲劳寿命 的估算。计算结果表明，同等应力条件下，静疲劳寿命要比振动疲劳寿命要大的多。 4. 考虑频率变化对结构损伤的影响，提出了以频率为主要分析参量的共振疲劳全寿命方 法。通过合理简化及假设，采用 ABAQUS 有限元软件模拟结构裂纹的动态扩展过程即频率 的动态下降过程，并对各个阶段进行动态分析，采用 SN 法，损伤容限法相结合的方式估算 了在振动条件下结构的疲劳全寿命。算例分析表明该方法是有效的，为振动疲劳寿命分析提 供了参考。
关键词：振动疲劳，典型结构件，固有频率，模型修正，频率变化，裂纹扩展
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典型结构件的振动疲劳分析
Abstract
At present, the conventional analytical methods of static fatigue has been formed a separate system, and in engineering applications are quite ripe. But in actual environment, the project structure is often working in the environment of the vibration loads, the principal loss of structure is caused by vibration. Only use the idea of static fatigue can not compeletly explain the vibration conditions of failure，because it omits the key role of the changes of frequency . As a result, we take the common typical structure of aircraft as analyzing objects. Futhermore, we use the finite element software of MSC.patran&nastran and fatigue as a platform building dynamic models to study its’dynamic features and fatigue life. This paper put forward a method which considers frequency as a main factor to predict the life of structure. All works of this paper includes: First, we choose unidirectional stiffened plate and linking slab which are widely used in aircraft as objects to complete the structural vibration fatigue experiments under resonant excitation, realizing band motivation of the incentive frequency tracking structure inherent frequency and studying structure life change rule and the dynamic change of natural frequency by the resonance conditions. Results show that structural dynamic characteristics have important influence on fatigue life and nature frequency with the fatigue process is drab degressive. Futhermore, all works Based on the MSC. Patran&nastran platform, establishing the typical structure finite element dynamic model to complete the modal analysis and validate the finite element model is correct. And we use the amended model to analysis structure dynamic response, so as to realize the fatigue life calculation. Moreover, considering frequency variation of structure damage effect, this paper puts forward the frequency as the main parameters of resonance fatigue longevity methods. Through reasonable simplification and assumptions, using the finite element software of ABAQUS to simulate the dynamic structure crack propagation (named frequency of dynamic decreasing process), dynamic analysis is studied on each stages. SN method and damage tolerance are picked to simulate the progress of Adopt SN method, damage tolerance is done by the way under the condition of simulation timely resonance fatigue life. The example shows that the method is simple and reasonable and provides reference for vibration fatigue analysis. Key words : vibration fatigue; typical structure; natural frequency; model modification; frequency change; crack propagation
图 3.1 连接板结构及尺寸 .................................................................................................... 15 图 3.2 1.6mm 加筋板结构及尺寸........................................................................................... 15 图 3.3 实验系统安装示意图................................................................................................. 16 图 3.4 ideas 中的识别模型 .................................................................................................... 16 图 3.5 第一阶振型及频率 ..................................................................................................... 17 图 3.6 第二阶振型及频率 ..................................................................................................... 17 图 3.7 第三阶振型及频率 ..................................................................................................... 17 图 3.8 第一阶振型及频率 ..................................................................................................... 17 图 3.9 第二阶振型及频率 ..................................................................................................... 17 图 3.10 第三阶振型及频率 ................................................................................................... 17 图 3.11 加筋板实验系统安装示意图..................................................................................... 18 图 3.12 连接板实验系统安装示意 ........................................................................................ 18 图 3.13 软件控制界面.......................................................................................................... 19 图 3.15 加筋板配重 ............................................................................................................. 21 图 3.16 连接板配重.............................................................................................................. 21 图 3.17 加筋板实验系统装夹 ............................................................................................... 21 图 3.18 连接板的实验系统装夹 ............................................................................................ 21 图 3.19 加筋板应变片黏贴位置............................................................................................ 22 图 3.20 连接板应变片黏贴位置 ............................................................................................ 22 图 3.21 实验系统的操作流程................................................................................................ 23 图 3.22 1.6mm 定应力应变寿命关系 ..................................................................................... 23 图 3.23 1.6mm 定应力载荷寿命关系 ..................................................................................... 24 图 3.24 1.6mm 定应力频率寿命关系 ..................................................................................... 24 图 3.25 2mm 定载荷载荷寿命历程........................................................................................ 25 图 3.26 2mm 定载荷应变寿命历程........................................................................................ 25