车削表面及微观结构影响小裂纹形核扩展概率模型

Probabilistic Model of Small Crack Nucleation and Propagation Considering Turning Surface and Microstructure Influence

关键词:  表面粗糙度  残余应力  材料微观结构  小裂纹形核扩展  萌生寿命

Key words:  Surface roughness  Residual stress  Material microstructure  Small crack nucleation and propagation  Initiation life

摘要:

车削试件疲劳行为受表面状态及材料微观结构影响显著。为提高对车削件初始寿命及分散性的预测精度，将车削表面粗糙度、残余应力及材料微观结构作为输入参数，提出综合考虑以上因素影响的随机小裂纹形核扩展概率模型。针对高温合金X材料，在开展试验的数据基础上，识别刀痕深度、残余应力及晶粒尺度随机分布参数，并建模，进而识别了晶体塑性本构、小裂纹形核及扩展模型参数。对高温合金X盘坯不同晶区取样等直棒试件宏观裂纹的萌生过程仿真结果表明：当前模型各晶区仿真寿命抽样分布±2σ区间全覆盖相应试验寿命，且寿命均值在试验寿命均值1.1倍分散带内。此外，模型仿真的萌生裂纹宏观形貌与试验观测断口形貌相仿。

Abstract:

The fatigue behavior of turning specimens is significantly affected by surface state and material microstructure. In order to improve the prediction accuracy of initiation life and its dispersion of turning components， a probabilistic model of random small crack nucleation and propagation was proposed with turning surface roughness， residual stress and material microstructure taken as input parameters. For superalloy X material， the random distribution parameters of turning tool path depth， residual stress and grain size were identified and modeled based on the experimental data. Then， parameters of the crystal plastic constitutive model and the small crack nucleation and propagation model were identified. The simulation results of macroscopic crack initiation process of superalloy X uniform-cross-section bar specimens with different grain size show that the ±2σ range of simulation life sampling distribution in each grain region by the present model fully covers the corresponding test lives， and the average simulation life is within the 1.1 times dispersion zone of the average test life. In addition， the macroscopic morphology of the initiation cracks simulated by the proposed model is quite similar to that observed in the specimen’s fracture.