FGH97粉末高温合金缺口试样小裂纹闭合特性数值模拟

采用有限元方法研究了FGH97粉末高温合金缺口试样小裂纹的塑性诱导裂纹闭合效应，分析了网格单元尺寸、缺口形式及外载大小、应力比和本构模型对裂纹闭合的影响，同时采用Walker公式计算裂纹扩展速率，并和试验结果进行对比以考察有限元方法的准确性。结果表明:当前塑性区尺寸大于10倍裂纹尖端网格单元尺寸时，裂纹闭合程度会趋于收敛；缺口形式在裂纹闭合未稳定前会产生影响，外载荷将决定闭合程度的稳定值；应力比的增大会降低裂纹闭合程度直至消失；相对于理想弹塑性本构模型，多线性弹塑性本构模型对网格的依赖性较低。缺口试样小裂纹扩展试验结果表明:考虑裂纹闭合效应之后，裂纹扩展速率计算结果与试验符合良好。 

Numerical simulation of small crack closure characteristic of the notched FGH97 powder metallurgy superalloy specimen

Plasticity-induced crack closure (PICC) effect of small crack of notched FGH97 powder metallurgy superalloy specimen was investigated by finite element method (FEM). The influences of five principle factors, namely mesh element size, notch profile, load level, stress ratio and the constitutive model, on crack closure were analyzed. Crack propagation rate was predicted via Walker formula and compared with the test results to confirm the accuracy of FEM. The results show that crack closure level tends to converge if the size of forward plastic zone is ten times bigger than the element size around the crack tip; notch profiles affect crack closure in the closure transient zone, the load determines the crack closure stabilization level; crack closure level decreases with the increase of stress ratio till disappearance; compared with perfectly elastic-plastic constitutive model, the multi-linear elastic-plastic constitutive model shows much less dependency on mesh element size. The predicted crack propagation rate in consideration of crack closure fits well with test results.