基于裂纹闭合效应的疲劳裂纹扩展特性研究

Research on Crack Growth Characteristics Based on Crack Closure Effect

依据线弹性力学理论对30NCD材料的裂纹扩展特性进行了研究,研究表明Paris公式能够很好地描述疲劳裂纹稳定扩展阶段的疲劳裂纹扩展速率da/d N与应力强度因子幅度ΔK之间的关系,稳定扩展段的疲劳裂纹扩展参数m=2.5~4,与绝大多数金属材料的疲劳裂纹扩展参数m=2~4的统计结果相符;NASGRO公式能较好地描述该材料从疲劳裂纹门槛值到高速裂纹扩展速率范围内的3种应力比的da/d N与ΔK关系。由裂纹闭合效应获得的有效应力强度因子范围与da/d N的关系表明:3种应力比下的所有数据都较好地关联在同一曲线上,裂纹闭合是引起应力比和裂纹扩展速率相关的主要原因,随着应力比增加,裂纹闭合程度减弱。

Based on the linear elasticity fracture mechanics theory, the fatigue crack growth characteristics of 30NCD were studied. The results show that the Paris＇ law can accurately describe the relation of the crack growth rate da/dN versus the range of the stress intensity factor △K at the steady crack growth stage. At the steady growth stage, the crack growth parameter m =2.5 -4 , which is consistent with the known statistical result that the crack growth parameter m =2-4 for most metallic materials. The NASGRO equation can properly describe the relation of da/dN versus for three stress ratios ranging from the fatigue crack growth threshold to high crack growth rate region for 30NCD. The effective stress intensity factor versus da/dN curves at three stress ratios were determined by the crack closure effect. All test data obtained at three stress ratios correlated well. Crack closure is the major factor in correlating stress ratio and crack growth rate, and the ratio increasing. degree of crack closure decreases with the stress