中文摘要：

带缺陷的高强度X80管线钢基体相α—Fe裂纹顶端的变形机理对于揭示该材料的失效机理是非常重要的．采用嵌入原子方法（EAM）描述原子间作用势，由大型分子动力学并行软件LAMMPS（Large-scale Atomic／Molecular Massively Parallel Simulator），建立足够大的模型以避免边界对位错发射与运动的影响，对中心裂纹板施加远场应力载荷，获得了裂尖发射位错的临界应力强度因子．模拟结果显示，在远场应力作用下，裂纹尖端出现了间歇性发射出位错的现象，即，首先在裂尖沿[111]晶向发射出首个位错并运动约至38个晶格间距后，再由裂尖发射出后继的位错，随着位错的不断发射，裂纹尖端出现明显的钝化现象，并伴随着裂尖不断往前推进．该过程清楚的揭示了的裂纹韧性扩展机理．

英文摘要：

The deformation mechanism near crack tip for the matrix phase of high strength pipeline steel XSP with defects,α-Fe, is great significant to investigate the failure behavior for this material. The Embedded Atom Method （EAM） potentials are adopted to characterize the interatomic interactions of α-Fe. To avoid the effects of boundary on the emission and move of dislocations, a big enough molecular dy- namic model is setup through the LAMMPS（Large-scale Atomic/Molecular Massively Parallel Simula- tor, in which a central cracked plate under remote stress is included, and the critical stress intensity fac- tor when a dislocation emitted is obtained. The simulation results showed that, under the remote stress, the intermittent dislocation emission came up around the crack tip, i.e. the first dislocation emitted along the [111]crystalline direction, the subsequent dislocation did not emitted until the first one overcame a distance of 38 crystal lattice. Accompany with the crack tip moving ahead, an obvious blunting of the crack with the repeated dislocation emission was investigated. The process reveals the mechanism of ductile crack growth clearly.