基于新型开口角隅试样的裂纹扩展研究

Research on Crack Propagation Based on New Opening Corner Specimen

局部开口区域会破坏整体结构的几何连续性而导致应力集中,引发疲劳裂纹的萌生和扩展。针对开口角隅区域的裂纹扩展和疲劳寿命预测问题,以实际工程中的开口结构为参照建立了新型小尺度开口角隅试样的三维模型。利用FRANC 3D对试样进行了裂纹动态扩展模拟并探讨了裂纹扩展数值计算中的影响因素,最终得到了裂纹长度与荷载循环次数以及应力强度因子间的关系曲线。研究表明:幂指数n=2、长浅形初始裂纹可承受更多的疲劳荷载循环次数,幂指数对裂纹扩展路径上应力强度因子计算的影响不大,而裂纹初始形状则会对其产生影响。裂纹前沿的形状在扩展过程中将逐渐由椭圆形演变成圆形,前缘线最终近似为一条直线。基于动态和准静态方法计算得到的裂纹扩展参数结果存在差异。稳定扩展阶段的Ⅰ型单一裂纹会在快速扩展阶段逐渐转化为混合型裂纹直至断裂失效。

The local opening area destroys the overall geometric continuity of the structure, leading to stress concentration and trigger the initiation and propagation of fatigue cracks. In order to solve the problem of crack propagation and fatigue life prediction in the opening corner area, a new three-dimensional model of small-scale called opening corner specimen was established with reference to the opening structure in actual engineering. The FRANC 3D was used to simulate the dynamic crack growth progress of the specimen and the influencing factors during crack propagation in the numerical calculation were discussed. Finally, the relationship curve between the crack length, the number of load cycles and the stress intensity factor were obtained. The results show that the power exponent n=2, the long and shallow initial shape of the crack could withstand more fatigue load cycles. The power exponent has little influence on the calculation of stress intensity factor on the crack propagation path, but the initial shape of the crack has influence on it. The shape of the crack front gradually changes from ellipse to circle in the process of crack propagation, and the crack front line finally approximates to a straight line. There are differences in the results of dynamic and quasi static methods to calculate the crack propagation parameters. In the rapid growth stage, the mode Ⅰ single crack during stable growth stage gradually transforms into mixed mode crack until fracture failure.