纳观尺度裂纹扩展微观机理的晶体相场法研究

Phase Field Crystal Simulation in Nano-scale for Crack Extension with Pre-deformation

采用晶体相场方法模拟不同预变形量的样品在单轴拉应变作用下的纳观裂纹扩展行为.观察纳观尺度的裂纹演化过程,结果表明:对于无预变形的样品,在拉应变作用下,由于裂口处应变集中,当应变量达到临界值时,裂口开始起裂并伴随位错出现,随着裂尖的前进位错伴随着裂尖而滑移.对于预变形的样品,在较小的临界应变值裂口起裂,且预变形量越大,裂纹越易起裂和扩展.在裂纹扩展早期阶段呈现出扩展-转向-扩展的长大特征,其本质是裂纹扩展由于裂尖附近的位错滑移受阻引起应变集中,造成主次原子晶面方向的原子键交替断裂,使得裂尖扩展沿[3,1]和[3,-1]方向交替改变而前进,裂纹边缘呈锯齿形状.样品的裂纹扩展后期出现显著的类似解理裂纹扩展行为,解理方向沿[3,1]和[3,-1]方向,且预变形量大的样品裂纹解理扩展更明显且扩展较快.

Crack propagation under tensile strain in samples with pre-deformation is simulated using phase field crystal （PFC） method. It shows that crack of sample without pre-deformation, under tensile strain, begins to crack due to strain concentration as strain reaches a critical value. For pre-deformed samples, crack starts to propagate at a less critical strain value, and the larger the predeformation, the faster and more obvious the crack growth. For samples with pre-deformation during early process of crack propagation, growth characteristics of expansion-turning direction-expansion are presented. The essence is that crack growth is extended by atomic bond alternative fracture in directions [√3,1] and [√3,-11 of primary and secondary atomic arrangement direction, which leads to zigzag edge of the crack. For samples with pre-deformation at later stage crack propagation present longer cleavage crack extension in directions along [√3,1 ] and [√3, - 1 ]. And the larger the pre-deformation of sample, the quicker the expansion of cleavage crack.