热环境下FGM壳的振动特性及裂纹扩展分析

发布时间：2018-02-25 01:18

本文关键词： 振动特性 FGM壳热环境物理特性热应力　出处：《南昌航空大学》2015年硕士论文　论文类型：学位论文

【摘要】：本论文以功能梯度材料(FGM)壳为研究对象,基于有限元离散分层思想建立壳结构动力学模型,研究热环境下FGM的物理特性,探讨热环境对FGM壳动力学特性的影响以及和含裂纹FGM壳在热冲击下的裂纹扩展及损伤疲劳寿命估算。首先,分析FGM在不同温度场影响下的物理特性变化规律,探讨物理特性变化使FGM壳初始刚度矩阵线性变化而引起的振动特性改变;然后,研究了热环境下均匀、线性高温引起的FGM壳非线性变形,及其内外的温度梯度产生的热应力,分析了热应力、热变形引起的FGM壳刚度变化和几何参数变化;综合考虑初始刚度矩阵、初始位移矩阵和热应力矩阵,结合几何边界条件和物理特性参数探讨了热力耦合下的FGM壳的振动特性;最后,基于XFEM理论,对含裂纹FGM壳在热冲击下情况下的裂纹扩展及损伤疲劳进行研究,在给定裂纹位置和裂纹尺寸时,利用均匀温度场下得到的材料物理特性和最大热应力,及其第一阶热力耦合固有频率加载的交变载荷简化热冲击,仿真裂纹扩展过程,利用不考虑加载史的寿命估算方法初步估算FGM壳热损伤疲劳寿命。通过数值计算,得出了不同体积分数指数FGM物理特性在均匀温度场和线性温度场下的变化规律;研究了不同温度场下材料物理特性对FGM圆柱壳振动特性的影响规律,综合考虑了均匀温度场下热应力,热力耦合对FGM壳的影响规律和线性温度场下热应力,热力耦合对FGM壳的影响规律。结果表明,热环境下FGM的物理特性发生了一系列的变化,物理特性的变化尤其是弹性模量的改变对FGM壳的振动特性具有明显的影响。热力耦合下FGM壳的模态频率比单纯考虑材料物理特性影响下模态频率大;而且温度越高两条曲线之间的间隔越大。均匀温度环境产生的热应力对结构的固有频率起主导作用。
[Abstract]:In this paper, the dynamic model of the shell structure is established based on the idea of finite element discrete stratification, and the physical properties of the FGM in the thermal environment are studied by taking the functionally graded material (FGM) shell as the research object. The effect of thermal environment on the dynamic characteristics of FGM shells and the crack propagation and damage fatigue life estimation of FGM shells with cracks under thermal shock are discussed. Firstly, the variation of physical properties of FGM under different temperature fields is analyzed. The vibration characteristics of FGM shell caused by the linear change of initial stiffness matrix caused by the change of physical characteristics are discussed. Then, the nonlinear deformation of FGM shell caused by uniform and linear high temperature in thermal environment and the thermal stress caused by temperature gradient inside and outside are studied. The changes of FGM shell stiffness and geometric parameters caused by thermal stress and thermal deformation are analyzed, and the initial stiffness matrix, initial displacement matrix and thermal stress matrix are considered synthetically. The vibration characteristics of FGM shell under thermal coupling are discussed by combining geometric boundary conditions and physical parameters. Finally, based on XFEM theory, the crack propagation and damage fatigue of cracked FGM shell under thermal shock are studied. When the crack position and crack size are given, the physical properties and maximum thermal stress of the material obtained under uniform temperature field, and the alternating load loaded with the first order thermodynamic coupling natural frequency, are used to simplify the thermal shock and simulate the crack propagation process. The thermal damage fatigue life of FGM shell is estimated by using the life estimation method without considering the loading history. By numerical calculation, the variation of physical properties of FGM with different volume fraction exponents under uniform and linear temperature fields is obtained. The effects of material physical properties on the vibration characteristics of FGM cylindrical shells under different temperature fields are studied. The thermal stress under uniform temperature field, the influence of thermal coupling on FGM shells and the thermal stress under linear temperature field are considered synthetically. The results show that a series of changes have taken place in the physical properties of FGM in thermal environment. The variation of physical properties, especially the change of elastic modulus, has an obvious effect on the vibration characteristics of FGM shells. The modal frequencies of FGM shells under thermal coupling are larger than those of FGM shells with only considering the physical properties of materials. The higher the temperature, the larger the interval between the two curves. The thermal stress produced by the uniform temperature environment plays a leading role in the natural frequency of the structure.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34

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