晶粒取向对过载下疲劳裂尖塑性区的影响

Effect of grain orientation on plastic zone of fatigue crack tipunder overload

为了厘清过载形式及裂尖晶体的晶粒取向对裂尖塑性区和疲劳性能的影响,采用基于晶体塑性有限元的子模型方法对裂尖塑性区进行了分析。首先,构建了具有随机微结构的多晶代表性体积单元模型并对其中的Chaboche模型与晶体塑性循环本构模型参数进行了识别。然后,应用子模型方法对裂尖位置进行了不同特征的晶粒取向分析以总结不同滑移系下的累积剪切应变。最后,结合过载行为对比了不同晶粒取向下的裂尖过载效应。结果表明,在拉伸过载、拉伸-压缩过载与压缩-拉伸过载中,拉伸过载均对抑制裂纹起主导作用。此外,应力集中倾向于发生在“硬”晶粒内,而应变集中往往位于“软”晶粒内,其中应变集中的晶粒取向趋势主要集中在反极图中的[001]方向。当裂尖晶体的晶粒取向倾向于“软晶粒”时有利于进一步优化拉伸过载的裂纹延迟效应。

To clarify the effect of overload forms and grain orientations of crack tip crystals on plastic zone and fatigue properties of crack tip,the sub model method based on crystal plasticity finite element was used to analyze the plastic zone of crack tip.Firstly,the polycrystalline representative volume element model with random microstructures was constructed and the parameters of Chaboche model and crystal plastic cyclic constitutive model were identified.Then,the sub model method was used to analyze the grain orientations with different characteristics at the crack tip location to summarize the cumulative shear strains under different slip systems.Finally,combined with the overload behavior,the overload effect of crack tip with different grain orientations was compared.The results show that the tension overload plays a leading role in restraining cracks in the tension overload,tension-compression overload and compression-tension overload.In addition,the stress concentration tends to occur in“hard”grains,while the strain concentration tends to occur in“soft”grains.The grain orientation trend of strain concentration mainly focuses on the[001]direction in the reverse pole figure.When the grain orientation of the crack tip crystal tends to“soft”grains,it is beneficial to further optimize the crack delay effect of tension overload.