Study on creep damage and crack growth for TC11 under complex stress loading

复杂应力下TC11蠕变损伤及裂纹扩展研究

School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China

Received: 23 June 2020

Abstract

In order to investigate the creep damage and creep crack growth of TC11, we established the finite element model based on ductility exhaustion constitutive model. This paper uses the uniaxial creep test of TC11 at 500℃ as a reference and studies the effect of initial crack dimensions on crack growth of CT specimen and surface crack specimen. The initial crack length of CT specimen has a significant effect on creep crack growth of TC11 material. The larger the initial crack length, the higher the crack growth rate, the crack tip equivalent stress and the crack tip stress triaxiality. The initial crack length has a greater influence on creep crack growth for deep crack specimens(a₀/W=0.6, a₀/W=0.7) than that for shallow crack specimens(a₀/W=0.3, a₀/W=0.4, a₀/W=0.5). When the stress intensity factor K_π/2 at the deepest location of surface crack is the same, the crack growth length of each specimen in the depth direction at the same time is approximately twice as much as that in the length direction. With the increase of initial crack size, the crack growth rate of surface crack decreases gradually. And the effect of initial crack length on crack growth is greater than that of initial crack depth.

摘要

为探究TC11材料的蠕变损伤和蠕变裂纹扩展特性，以500℃下TC11的单轴蠕变试验为参考，基于考虑孔洞长大的延性耗竭蠕变损伤本构关系，建立有限元模型，研究了初始裂纹长度对CT试件裂纹扩展的影响以及初始裂纹尺寸对表面裂纹扩展的影响。研究表明：初始裂纹长度显著影响TC11材料CT试件的蠕变裂纹扩展行为，其值越大裂纹扩展速率、裂尖等效应力、裂尖应力三轴度越大，且初始裂纹长度对深裂纹试样（a₀/W=0.6，a₀/W=0.7）裂纹扩展特性的影响明显大于对浅裂纹试样（a₀/W=0.3，a₀/W=0.4，a₀/W=0.5）的影响；当表面裂纹最深处的应力强度因子K_π/2相同时，各试件在同一时刻深度方向的扩展量近似为长度方向扩展量的2倍，随着初始裂纹尺寸的增大，表面裂纹的扩展速率逐渐减慢，且初始裂纹长度对裂纹扩展的影响要大于初始裂纹深度对裂纹扩展的影响。