应变控制的热机械疲劳行为的数值模拟

根据高温合金材料的力学性能，以弹粘塑性本构模型为基础，用数值模拟方法研究材料的热机械疲劳循环特性，模型将应变分为弹性应变、温度应变和粘塑性应变三部分，认为材料在高温循环载荷下呈现明显的弹粘塑性特征，根据虚位移原理建立轴对称体的弹粘塑性计算有限元格式，对于循环机械载荷和循环温度载荷，程序中采用了增量法迭代求解，在非线性项中不仅考虑了机械载荷增量的影响，同时也考虑了温度增量的影响，根据应变控制热机械疲劳的特点，发展了应变增量法的有限元计算方法、通过数值模拟，得到材料在各种循环载荷下的应力—应变响应，数值模拟较好地反映了粘塑性变形过程以及温度变化的效应，所描述的不可逆系统在某一时刻的状态完全由当时的状态参数、内变量、承载时间及塑性应变累积量决定，对带缺口试件的模拟结果显示了程序对复杂轴对称结构进行热机械疲劳计算的有效性。

NUMERICAL SIMULATION OF THERMOMECHANICAL FATIGUE BEHAVIOR UNDER STRAIN CONTROLLED CONDITION

A numerical simulation is performed for investigating thermome chanical fatigue (TMF) behavior of materials. The method is based on the elasto- viscoplastic constitutive model and the mechanical behavior of high temperature alloys. It is considered that the alloys present clearly elasto-viscoplastic cha racteristics under high temperature themomechanical cycles, and so that the stra in is divided in three parts: elastic strain, thermal strain and viscoplastic st rain. According to the virtual displacement theory, a dispersion form of the fi nite element method is obtained with the axial symmetry. The increment me thod is used to deal with the dynamically mechanical and thermal loading. In the non-linear part of the program, both the mechanical effects and the temperatur e effects are considered. In order to compare the numerical results with the test results, a strain controlled increment method is developed. The stress -strain hysteresis loops of a 316L steel under different themomechanical fatigu e loading are simulated.It is shown that the simulation is in good agreeme nt with the experimental data. In describing a non-reversible system with this m odel, the process is fully decided by the status parameters, intrinsic variables , loading time and cumulative plastic strain. The numerical simulation of the V - notched specimen shows the effectiveness of the program dealing with complex axi al-symmetrical problems.