一种结合晶体塑性及扩展有限元的短裂纹扩展模拟方法

A short crack growth simulation method using crystal plasticity combining with extended finite element method

多晶金属材料的疲劳短裂纹扩展过程受到晶粒尺寸、晶体取向和晶界阻碍等微观组织影响,导致裂纹扩展速率呈现明显的波动特征;在相同应力强度因子下,短裂纹扩展速率比长裂纹扩展速率高,基于长裂纹扩展模型预测短裂纹扩展过程往往得到偏危险的结果。因此,结合晶体塑性与扩展有限元,本文提出了一种反映微观组织影响的短裂纹扩展模拟方法,并通过粉末高温合金FGH96疲劳短裂纹扩展原位试验进行验证。以电子背散射衍射(EBSD)检测结果为输入,建立短裂纹扩展细观有限元模型,表征晶粒尺寸、晶体取向影响;将晶体塑性引入扩展有限元法,基于滑移系本构及塑性切应变率表征晶界阻碍影响。结果表明:该方法可有效描述短裂纹扩展速率的波动特征,短裂纹扩展寿命预测精度得到显著提高。

The short crack growth process of polycrystalline metal materials is affected by the microstructure such as grain sizes,crystallographic orientations and grain boundary blocks,which results in the crack growth rate showing obvious fluctuation characteristics.With the same stress intensity factor,the growth rate of short crack is higher than that of long crack,which makes the prediction of short crack growth process based on long crack growth model often get dangerous results.Therefore,combined with crystal plasticity and extended finite element method,a short crack growth simulation method reflecting the effect of microstructure was proposed in this paper,and the in situ test of fatigue short crack growth of powder superalloy FGH96 was verified.Using EBSD test results as a input,a mesoscopic finite element model of short crack growth was built to characterize the effects of grain sizes and crystallographic orientations.The crystal plasticity was introduced into extended finite element method to characterize the effect of grain boundary block based on slip system constitutive and plastic shear strain rate.The results show that the proposed method can effectively describe the fluctuation characteristics of short crack growth rate,and the prediction accuracy of fatigue short crack growth life is significantly improved.