解理断裂前裂纹尖端变形与开裂的有限元模拟

对16MnR钢三点弯曲(3PB)裂纹试样进行了实验和有限元计算,模拟了裂尖开裂与钝化的构形和应力应变分布图.发现在临界载荷前,预裂纹尖端仅仅发生钝化;当载荷达到临界值时,开始有小裂纹起裂,随后钝化;再达到又一临界载荷时,小裂纹再次起裂,而后扩展,反复出现直至解理断裂发生.在模拟裂纹沿斜面起裂时,当小裂纹很短时,对对称面上的应力、应变和三向应力的分布影响比较小;只有小裂纹扩展到足够长并钝化到足够宽,才能够影响主裂纹的扩展及其前端应力、应变的分布.并针对采用有限元法在模拟裂纹扩展时所遇到的问题,探讨了模型的建立、网格的划分、断裂准则的应用以及网格重组技术的运用.

Simulation of deformation at and initiation of crack tip prior to cleavage fracture by means of finite element method

The configuration of initiation and blunting of the crack tip is simulated by means of experiment of 3PB and FEM calculation. The distribution of stress and strain at crack tip is calculated. The results show that before a critical load is reached,the crack tip is blunted only,and with the applied load increasing higher than the critical load,a short crack is initiated,extended at the precrack tip,and then blunted,When another critical load is reached,a short crack is again initiated and extended at the precrack tip and then is blunted.This process takes place repeatedly until the cleavage fracture is triggered. If the crack is short,its effect on the distribution of the stress ,the plastic strain,and the triaxiality in a symmetrical plane is little when the simulation of initiation of this short crack is performed in a inclined plane; Only if this short crack extends long enough and blunted wide enough,can it affect the principal crack extension and the distribution of stress and plastic strain. In connection with the problems encountered in the process of simulating crack extension with method of FEM,the problems such as model-building ,meshing,application of the fracture criterion,and the mesh-reconstruction are discussed,also.