超长寿命双重S-N曲线模型的研究

Research on Ultra-Long Life Duplex S—N Curve Model

基于某些高强度钢、钛合金等特殊金属材料由于破坏机理(表面和内部破坏)的不同而表现出的双重S—N(应力—寿命)曲线特性,以高碳铬轴承钢为试验材料进行旋转弯曲疲劳的试验研究,用Basquin,Langer和三参数模型分别描述其S—N曲线关系,并且应用常规最小二乘法、广义极大似然法分别研究其概率S—N曲线模型。结果表明:在区分破坏机理的情况下,试验数据较好地服从对数正态分布;从试验数据的拟合效果和可靠性设计出发,三参数模型更能有效地描述这些特殊金属材料的双重S—N曲线关系,并且更宜采用广义极大似然法描述其概率S—N曲线模型,以避免常规最小二乘法受试验数据局部统计特征影响而给出偏于非安全的估计。

Based on some special metal materials, such as high strength steel, titanium alloy, and so on, which represent the character of duplex S--N （stress-life） curves due to the difference of the fracture mechanism （surface and internal fracture mode）, high carbon-chromium bearing steel is used for the rotary bending fatigue test research. Its S--N curve relation is described respectively by Basquin, Langer and three-parameter model. Its probabilistic S--N curve model is researched respectively by conventional least square method and general maximum likelihood method. Test results show that the test data follow the logarithm normal distribution better based on differentiating the fracture mechanism. Taking the fit effect and reliability design into account, three-parameter model is better for describing the duplex S---N curves relation of special metals. Simultaneously, it is discovered that its probabilistic S--N curve model should be described by general maximum likelihood method. It can avoid the possible non-conservative predictions of the conventional least square method, which is resulted from the influence of local statistical characteristics of the testing data.