微裂纹起裂扩展机理的晶体相场模拟

Phase field crystal Simulation of Nucleation and Propagation of Micro-cracks

【目的】研究初始晶向倾角为15°的样品分别在垂直和水平方向上,单轴拉应变作用下的纳观尺度裂口发射位错与裂纹扩展行为,了解韧性裂纹的生长特征和扩展规律,揭示纳米级韧性裂纹扩展机理及其对材料断裂的影响。【方法】采用晶体相场(PFC)方法观察15°晶向倾角下位错发射与裂纹扩展演化图及其对应的应力曲线图。【结果】垂直和水平不同方向拉应变作用下裂纹扩展方向不同,但裂纹都是韧性断裂模式扩展;当单轴拉应变作用达到临界值时,样品裂口开始发射滑移位错,随着外应力的增大,位错在滑移过程中留下一系列空位,空位长大连通形成裂纹并与主裂口相连,裂纹随着位错运动而扩展。【结论】在韧性裂纹扩展中,位错发射的运动对韧性裂纹扩展演化有重要影响。

【Objective】The samples with15°initial crystal orientations and crack propagation behavior of nano scale under uniaxial tensile strain are studied respectively in vertical and horizontal directions to understand the growth characteristics and propagation law of crack,and to reveal the mechanism of nano scale crack propagation and its effect on material fracture.【Methods】The phase field crystal(PFC)method are used to observe the dislocation emission,the crack propagation evolution and its corresponding stress curve of15°crystal orientations under uniaxial tensile strain in the different direction.【Results】The cracks are both propagation of ductile fracture mode in vertical and horizontal directions under uniaxial tensile strain.When the uniaxial tensile strain reaches the critical value,the sample begins to emit slip dislocations,and as the external stress increases,in the process of slipping the dislocations leave a series of vacancies,which grow up and form cracks,and then connect to the main crack.The crack expands with the dislocation movement.【Conclusion】In ductile crack propagation,the movement of dislocation emission has an important influence on the evolution of ductile crack propagation.