The Effect Of Stress State On Damage Evolution And Fracture Of Metallic Materials

The effect of principal stress ratio on damage evolution of strip void has been analyzed by using finite element method in plane strain and plane stress. The results show that the void growth and coalescence behavior is different at various principal stress ratios σ₂/σ₁ in the case of the same stress triaxiality. This causes different crack growth paths and fracture strains. When the σ₂/σ₁, is larger then 1 , the maximum principal stress is σ₂ ,and the crack growth path determined by the void growth and coalescence tends to be vertical to the σ₂ direction. When σ₂/σ₁ is less then 1, the maximum principal stress is σ₁,, and the crack growth path determined by the void growth and coalescence tends to be vertical to the σ₁, direction. With increasing the principal stress ratio σ₂/σ₁, the increase rate of the void area fraction fα with the principal strain ε₁₁ increases, and the principal strain (ε₁₁)_f at fracture decreases. Therefore, when the effect of the stress state on the damage and fracture behavior of materials is analyzed and the mechanical model is established, not only the effect of stress triaxiality should be considered, but also the principal stress ratio.The effect of principal stress ratio on void damage evolution of round void has been analyzed by using finite element method in plane strain. The results show that the effect of stress state on damage evolution of round void strip void is weaker than that of strip void, the void growth and coalescence of the strip void is prone to occuring between big voids that their longer diameters are parallelling, growth is obviously anisotropic. The difference between void growths for the strip voids is large, and some big voids detemin the finial fracture of materials The growth and coalescence for the round voids mainly depends on the void distribution. The change of the void growth and coalescence with the stress state for the strip voids is larger than that for the round voids. The void growth and coalescence for the round voids changes in the case of large difference in the principal stress ratio.