多轴载荷作用下马氏体耐热钢中微孔洞演化行为的模拟研究

Mechanistic Modelling of Micro-void Growth Behavior in Martensitic Steels under Multiaxial Loading Conditions

微孔洞演化包括孔洞成核、生长和聚合三个阶段,是影响金属材料韧性断裂的重要因素.为了分析P91马氏体耐热钢中的塑性滑移对微观孔洞扩展的影响,论文提出了一种基于晶体塑性有限元的微观力学计算模型,量化了应力三轴度、洛德参数和晶体取向对微孔洞演化行为的影响.结果表明,在相对较高应力三轴度条件下,随着应力三轴度的增大,含孔洞马氏体块的等效应力-应变响应呈现出快速软化的特征,同时孔洞体积分数随着等效应变的增加而快速增加.对于给定的应力三轴度,胞元的聚合应变在[111]取向时最小,在[110]取向时最大.孔洞聚合开始时,低应力三轴度下孔洞形状趋向于椭球状,而较高应力三轴度时孔洞横向略鼓.在一定的应力三轴度和洛德参数范围内,在孔洞聚合和孔洞坍塌两种胞元失效状态之间存在着一个条带状过渡状态,在[100]晶体取向时,当洛德参数L=-1时条带最宽.论文揭示了P91马氏体耐热钢中微孔洞演化的基本机制,分析了晶体取向、应力三轴度和洛德参数对微孔洞演化的影响.这些发现为P91马氏体耐热钢的韧性损伤模型的进一步发展提供了微观理论基础.

Micro-void evolution,including nucleation,growth and coalescence,is usually considered an important intrinsic factor affecting the ductile fracture behavior of metal materials.This work aims to investigate the effect of crystallographic plastic slip on the evolution of micro-voids in P91 martensitic steels.To this purpose,a crystal plasticity-based micromechnical finite element model is proposed.The influences of stress triaxiality,Lode parameter,and crystallographic orientation on micro-void evolution are quantified.The results indicate that under relatively high stress triaxialities,with the increase of stress triaxiality,the equivalent stress-strain response of the voided martensitic blocks exhibits a rapidly softening characteristic,and the void volume fraction increases rapidly with increasing equivalent strain.For a given stress triaxiality and the three crystallographic orientations examined,the critical strain for the onset of void coalescence in the martensitic block has the minimum value for the[111]orientation and the maximum value for the[110]orientation.At the beginning of void coalescence,the void shape tends to be ellipsoidal under relatively low stress triaxialities,while the void shape becomes slightly bulged under relatively high stress triaxialities.Over a certain range of stress triaxiality and Lode parameter,it is found that a band of transition state exists between the two failure states of void coalescence and void collapse in the phase diagram for failure.For the[100]orientation of interest,the band widths are different under different Lode parameters,and the largest width occurs at the Lode parameter L=-1.This work reveals the underlying mechanisms of micro-void evolution in P91martensitic steels,and highlights the importance of crystal orientation,stress triaxiality,and Lode parameter for the evolution of micro-voids.These findings provide a microscopic physical foundation for the development of ductile damage modelling for martensitic heat-resistant steels.