考虑闭合效应和三维应力约束的表面裂纹扩展模拟

Numerical simulation of surface crack propagation considering the crack closure effects and the three-dimensional stress constraints

假定承受Ⅰ型常幅载荷下的表面裂纹在扩展中的形状保持为半椭圆,利用N ewm an半椭圆表面裂纹应力强度因子公式计算应力强度因子。提出了等效厚度的概念,利用穿透直裂纹的研究结果,考虑表面裂纹扩展中塑性致闭和三维应力约束效应。基于E lber模型建立了三维表面裂纹扩展模型。数值模拟了表面裂纹扩展过程,研究了裂纹形状变化及规律,计算了裂纹扩展寿命。将计算结果与有关试验结果进行了对比,吻合较好。

It is assumed that the shape of the surface crack keeps semi-ellipse during propagation under mode-Ⅰ loading. Then the stress intensity factor along the semi-elliptical crack front can be evaluated by use of the Newman and Raju＇s formula. An equivalent thickness conception is proposed to consider the crack closure effects and the three-dimensional stress constraints along the crack front by use of the theory obtained for the straight through thickness crack. Based on the Elber＇s fatigue-crack-closure theory, a surface-crack-propagation model is developed to simulate crack propagation numerically, investigate the evolution of the shape-ratios and calculate the fatigue life. It shows good agreements to compare the numerical predictions with the available experimental results.