金属材料疲劳裂纹扩展速率Paris模型中材料常数的相关性

金属材料疲劳裂纹扩展速率是工程应用中进行损伤容限设计、疲劳寿命评估的一项重要力学性能指标。Paris模型是疲劳裂纹扩展速率最常用的表达形式,该模型认为疲劳裂纹扩展速率随裂纹前缘应力强度因子范围的变化呈幂函数关系,涉及到两个材料常数C和m。本研究借助部分文献中的试验数据,分析合金钢、铜合金、钛合金、铝合金等不同金属材料疲劳裂纹扩展速率Paris模型中材料常数C和m的关系。结果表明:Paris模型中材料常数C和m的关系可用m=alnC+b线性模型来描述,且不受试样取样方向、焊缝位置、试验环境等因素影响;但不同应力比对该模型的线性度有一定影响,尤其是当应力比为负值时,影响较为显著;不同金属材料常数C和m线性模型的斜率并不相等,其影响因素有待于进一步系统研究。分析结果可为金属材料在工程中的疲劳设计与应用提供参考。

Pertinence of Material Constants in Paris Model for Fatigue Crack Propagation Rate of Metallic Materials

Fatigue crack propagation rate of metallic materials is an important index of mechanical property, which is employed for damage tolerance design and fatigue life assessment in engineering application. Paris model is the most popular expression for fatigue crack propagation rate, and the relation of fatigue crack propagation rate and stress intensity factor range at the crack front is believed to meet a power-function rule in the model. The model involves in two material constants of C and m. In this paper, based on some test data published in some literatures, the relationships between material constants of C and m in Paris model for fatigue crack propagation rate of metallic materials of alloy steels, copper alloy, titanium alloy and aluminum alloy were analyzed. The results indicated that the constants of C and m of different types of metallic materials satisfied good linear relationship, namely m=alnC+b, which was not affected by specimen sampling orientation, weld position, and test environment. Stress ratios had great influence on the linear relationship, especially when the stress ratio value was negative. The slopes of the linear models for different metallic materials were not equivalent and the influencing factors should be further researched systematically. The analyzing results would provide reference for fatigue design and application in engineering.