第 1 部 (23) 分子動力学法によるき裂先端近傍の塑性変形解析

概要

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The mechanical behaviors around a crack tip for a system including both a crack and two tilt grain boundaries under cyclic loading are examined using a molecular dynamics simulation. The grain boundary has the lowest grain boundary energy among all tilt grain boundaries. A structural transition from bcc to hcp occurs around the crack tip during the first loading in order to relax stress concentration. Edge dislocations emitted from the crack tip move to the slip direction of α-Fe. Then, two dislocation pile-ups near the grain boundaries are formed after the edge dislocations reach the grain boundaries, because they cannot move beyond the grain boundaries. During the first unloading, the edge dislocations emitted from the crack tip return to the crack tip and disappear in the system. We observe that not only the crack does not propagate in the cleavage plane of α-Fe but also several vacancies are generated along the slip direction from the crack tip during cyclic loading. Conclusively, we suggest the fatigue crack growth mechanism for the initial phase of the fatigue fracture. That is, the fatigue crack propagates due to coalescence between the crack and vacancies which are caused by the emission and absorption of the dislocations.
一般社団法人日本機械学会の論文
2003-03-27