裂纹尖端压缩应力对闭合和扩展特性影响的数值模拟

Numerical Simulation of Effects of Compressive Stress around Crack Tip on Closure and Propagation Characteristic

关键词:  粉末高温合金  裂纹扩展  裂纹闭合  裂纹尖端压缩应力  寿命预测

Key words:  Powder metallurgy superalloy  Crack propagation  Crack closure  Crack tip compressive stress  Life prediction

摘要:

为了研究FGH97粉末高温合金的塑性诱导裂纹闭合现象，采用有限元方法分析了FGH97紧凑拉伸试样的裂纹扩展和裂纹闭合效应，考察了裂纹尖端单元尺寸、本构模型和节点释放周期对闭合比的影响，提出了修正闭合比和修正有效应力强度因子范围的概念，同时进行了寿命预测并和试验结果进行对比。结果表明:随着裂纹尖端单元尺寸从40μm减小至3μm，闭合比逐渐增大至收敛。各向同性硬化模型的闭合比约为0.51，随动硬化模型的闭合比约为0.44，Chaboche模型的闭合比约为0.48，闭合比的大小可以用裂纹尖端压缩应力区域尺寸反映。随着节点释放间隔周期数的增加，压缩应力区域尺寸和闭合比逐渐降低。裂纹扩展试验结果表明:根据修正有效应力强度因子范围进行寿命预测，与试验结果偏差为3.86%。

Abstract:

In order to study plasticity-induced crack closure (PICC) effect of FGH97 powder metallurgy superalloy， crack propagation and PICC effect of FGH97 compact tension specimen were analyzed by finite element method (FEM). The effects of element size around crack tip， constitutive model and number of cycles between each node release on crack closure ratio were examined， and the concepts of corrected crack closure ratio and corrected effective stress intensity factor range were proposed， crack propagation life was predicted and compared with test results. The results show that crack closure ratio rises until convergence with refinement of element size around crack tip from 40μm to 3μm. Crack closure ratio of isotropic hardening model is about 0.51， the value of kinematic hardening model is about 0.44， and for Chaboche model crack closure ratio is about 0.48， the value of crack closure ratio can be reflected by the size of crack tip compressive stress zone. The size of crack tip compressive stress zone and crack closure ratio tend to decrease when the number of cycles between each node release increases. The results of crack propagation tests show that the error between predicted life based on corrected effective stress intensity factor range and test life is 3.86%.