| The destruction of engineering material is often closely relative to the crack evolution, while the essential factors of crack expansion are the stress, the strain and the micro-structure change of the material in the region of the crack tip area. Based on microscopy view, to study the influence that is along with the micro-structure change of the material around crack tip is not only the subject keeping up with development of fracture mechanics but also one of the hot issues.In the view of metallography, ductile fracture of metallic materials is mainly influenced by void nucleation, growth and coalescence. Much is known about the mechanism, accompanying nucleation of voids by second phase particles that separate from interface, or splinter, which grows and expands due to plastic deformation of surrounding and substrate material. It is the nucleation, growth and coalescence of the micro-void that causes crack expansion for ductile material. Therefore, it is a acceptable way to simulate the process of ductile fracture at the crack tip by G-T-N model which is with a view to void effect.In this thesis, the model of three-point bending specimen is adopted. After creating macroscopic mechanical model, nonlinear finite element analysis software ABAQUS is utilized to simulate the crack process of ductile material. Then it is indicated that the traditional macroscopic fracture mechanics is somehow limited, and the real stress field in the crack tip as well as essential cause for crack expansion of metal ductile fracture isn't illustrated. By creating mesoscopic mechanical model, it is achieved to track and simulate the crack expansion progress of the ductile material based on the G-T-N model. The crack tip stress filed, the plastic strain filed and the distribution of the void percentage in the crack expansion process are calculated and analyzed. As a result, the law and process that the crack tip material is being gradually deteriorated until destroyed is clearly demonstrated.
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