U形切口的有限断裂准则

Finite Fracture Mechanics Criterion for U-Notches

有限断裂力学准则综合了应力和能量参数,假设裂纹或切口端部有限裂纹长度的增长.特别地,该有限裂纹的长度不是材料的基本常数,而是与构件的结构有关.基于U形切口两种形式:点方式和线方式有限断裂准则,对文献中的铝合金U形切口三点弯曲断裂实验进行了分析验证.一方面基于材料的断裂韧度和抗拉强度,预测切口件断裂载荷;另一方面根据几组不同的切口根部半径及其对应的临界切口应力强度因子,同时估算材料的断裂参数:断裂韧度和抗拉强度.将点方式和线方式两种不同形式有限断裂准则的预测结果,与平均周向应力准则、最大周向应力准则以及文献中相关结果进行了比较得出:无论是预测断裂载荷还是估算材料断裂参数,线方式有限断裂准则,与文献中相关结果比较吻合,尤其是估算的断裂韧度精度较高.

Finite fracture mechanics criterion includes energy and stress parameters assuming a finite crack advancement ahead of the crack or notch tip.Especially,the finite crack advancement is not a material constant but a structural parameter.Based on the two different methods of finite fracture mechanics:point method and line method,the three-point bending experiments of alloy A1 in the literature were analyzed.On one hand,the values of fracture loads can be predicted according to the fracture toughness and tensile strength of the material.On the other hand,the fracture toughness and tensile strength can be calculated simultaneously by several groups of notch root radii and critical notch stress intensity factors.The results from finite fracture mechanics were compared with those from mean circumferential stress criterion,the maximum circumferential stress criterion and the data in the literature.It shows that the finite mechanics of line method is better at predicting fracture loads and calculating the fracture parameters,especially for the fracture toughness.