能量法分析纳晶材料裂纹的萌生

An energy approach to account for crack initiation in nanocrystalline materials

利用能量守恒定律分析了纳晶材料裂纹在三晶交处的萌生,分别推导了纳晶材料中的特定旋转变形能、晶界滑移能、晶界扩散能,并运用最大等效裂纹能量释放率准则来判断纳晶材料裂纹萌生。结果表明:特定旋转变形、晶界扩散均能松弛裂纹尖端的应力,阻碍裂纹的生长;而晶界滑移使得晶界位错在三晶交处堆积,造成三晶交处的应力集中,促使裂纹的生长;稳定状态下,外力做的功等于由特定旋转变形、晶界滑移、晶界扩散造成的能量耗散。

An energy balance method to calculate the initiation of crack at triple junctions in nanocrystalline materials is developed.In the steady state of crack initiation,work done by an applied stress is considered to be dissipated as heat by specific rotational deformation,grain boundary sliding and diffusion.The stress field at crack tips,the energies of rotational deformation,grain boundary sliding and grain boundary diffusion are calculated.The special rotational deformation and grain boundary diffusion can significantly contribute to the relaxation of the crack tip stress and hinder the growth of the crack.At the same time,grain boundary sliding can induce the stress concentration at triple junctions and then promote crack propagation.The maximum equivalent crack energy release rate criterion is proposed to judge the crack initiation of nanocrystalline materials.