Abstract
The mechanical behaviors around a crack tip for a system including both a crack and two tilt grain boundaries under uniaxial tension are obtained using a molecular dynamics simulation. The Johnson potential for α-Fe is used in this analysis. Three kinds of the grain boundaries are examined. The <110>{112} grain boundary has the lowest grain boundary energy among all tilt grain boundaries. The <110>{111} grain boundary is one of the grain boundaries which have local-maximum grain boundary energy. The <110>{332} grain boundary has grain boundary energy between the preceding two grain boundaries. In a system including both the crack and the <110>{112} grain boundaries, not only a phase transition from bcc to hcp but also ductile deformation occurs around the crack tip in order to relax stress concentration. Dislocations emitted from the crack tip are observed and two dislocation pile-ups near the grain boundaries are formed. Moreover the phase transition domain at the crack tip changes to twin deformation after the elapse of time. In a system including both the crack and the <110>{111} grain boundaries, a new crack is generated at the grain boundaries and intergranular fracture occurs. In a system including both the crack and the <110>{332} grain boundaries, dislocations are emitted not only from the crack tip but also from contact points of a free surface and the grain boundary, then complex dislocation structure is formed.
