含热冲击预损伤的陶瓷基复合材料损伤本构模型

陶瓷基复合材料结构在服役过程中不可避免地经受热冲击(较高的热应力梯度)而产生热机械损伤, 因此, 建立含循环热冲击预损伤材料的损伤本构模型, 以描述材料在热机械载荷作用下的力学行为, 对材料结构损伤容限设计与结构完整性评估非常重要. 本文首先对经历了循环热冲击的材料进行单调拉伸损伤实验, 发现对于含循环热冲击预损伤的材料, 其弹性模量的下降与所施加的应变直接相关. 然后在连续介质损伤力学的框架下, 基于平面应力假设, 建立了含循环热冲击预损伤材料的损伤演化模型, 该模型所涉及的参数可通过一个偏轴(45$^\circ$)以及两个正轴(平行于两个主方向)的单调拉伸试验获得. 最后, 采用经典塑性理论对由基体损伤引起的非弹性应变进行了描述. 本文所提出的应变损伤宏观模型可以描述陶瓷基复合材料在热机械载荷作用下的损伤演化, 同时弥补了含预损伤的陶瓷基复合材料在机械载荷下损伤本构模型在理论及实验研究方面的不足. 

DAMAGE CONSTITUTIVE MODEL FOR THERMAL SHOCKED-CERAMIC MATRIX COMPOSITE1)

The ceramic-matrix composite (CMC) structure is inevitably subjected to cyclic thermal shocks in service, which induces the thermo-mechanical damage. Investigation of the damage constitutive model of the thermal shocked-CMC is of significance in the design and performance evaluation of such composites in aeronautical industry. In the present work, monotonic tensile damage tests were conducted for the thermal shocked-CMC. It is found that the degradation of elastic modulus for the thermal shocked-composites are directly related to the applied strain. Based on the framework of continuum damage mechanic, a nonlinear damage evolution model for the thermal shocked-CMC was proposed under plane stress assumption. The identification of the damage parameters involved in this model requires one off-axis (45$^\circ$), and two on-axis (parallel to tow directions) uniaxial tensile tests. Finally, the inelastic strain caused by matrix damage is described by classical plastic theory. The proposed strain damage macroscopic model can describe the damage evolution of CMC under thermo-mechanical loading, and also compensate the deficiency of the theoretical and experimental research for the damage evolution model of damaged-CMC under mechanical loading.