分子动力学模拟裂纹扩展及相关尺寸行为

运用分子动力学模拟方法研究原子弛豫对于裂尖场的影响,发现弛豫后裂尖离散非线性区半径约为150(A);如果原子区大于这一尺寸,连续介质力学的弹性场可以通过边界条件,有效影响原子尺度的裂尖行为.进一步研究表明:体心立方铁中,张开型裂纹在低温时为脆性解理扩展,并伴随裂尖层错和孪晶的形成;随着温度升高,裂尖层错和孪晶的形成逐渐减弱,在250 K左右发生脆韧转变;同时观察到裂尖位错发射.

Atomistic Simulation of Crack Propagation and Its Size-Dependent Behavior

In this paper the displacement distribution at the crack tip in bcc-iron is analyzed by using discrete atomistic simulation method. The results indicate that the radius of the nonlinear region at the crack tip region is about 150 ?, and the truncated distance of continuum elastic field is about 100 ? away from the crack tip. Based on these, the behavior of crack propagation at different temperature in bcc-iron is studied. The results show that at low temperature, the cleavage fracture occurs and the twin formation is cooperative process in brittle fracture. At high temperature, the twinning becomes weakened and vanishes at the brittle-to-ductile transition temperature(BDTT) accompanied dislocation nucleation, which is perpendicular to the crack surface. The BDTT that we have obtained is about 250 K, which is consistent with the experimental result.