Abstract: Finite element calculation and analysis have been performed to investigate the stress triaxiality constraint level and other features in the crack tip fields of various specimens geometries with different crack depths in plane stress case. The results showed that the crack tip constraint intensity for plane stress is in bettor agreement with that required by the HRR solution and independent essentially from specimen geometries, crack depths and materials states. Therefore, the validity of J-dominance of crack tip fields is ensured and the critical value of J integral at crack growth initiation can be considered as the material constant, which can be used to characterize and compare the fracture toughness for different materials states in the case of same crack tip constraint. And the viewpoints have been verified by experimental results.

Key words: 裂纹, 启裂准则, 应力