四参数全范围da/dN曲线测定方法研究

4-Parameter Full Range Crack Growth Rate Curve

机械结构设计的损伤容限分析,需要使用材料疲劳裂纹扩展速率曲线性能。在总结传统疲劳裂纹扩展曲线的基础上,本文讨论了四参数全范围da/dN曲线公式;基于断裂力学原理,分别给出了此公式中材料裂纹扩展门槛值ΔKth,断裂韧性K1C和张开函数f的测定方法;利用多元线性回归法对试验数据进行了曲线拟合,得到了四参数全范围da/dN曲线公式的参数估计式;将此公式运用于不同应力比下的裂纹扩展速率试验数据拟合,通过试验数据的拟合结果可以看出:四参数全范围da/dN曲线公式,能够充分有效合理地表征全范围裂纹扩展速率的物理特性和宏观数据规律,且参数估计简便,拟合精度高;从而验证了四参数全范围da/dN曲线公式的有效性和合理性,并将得到广泛应用。

Damage tolerance analyses of mechanical structure design require some information on fatigue crack growth rate curve of the material. In order to address this need, a four-parameter curve, which describes the full range of fatigue crack growth rate, was adopted to represent the test results of fatigue crack growth rate based on the conventional method. The approaches of determining the material′s fatigue crack growth threshold value ΔK_(th), the fracture toughness K_C and the opening function f in this four-parameter curve were presented respectively by means of fracture mechanics principles. The parameters of the four-parameter full range da/dN Forman curve formula were estimated by using the multivariable linear regression and the parameter estimation formulae were derived. The four-parameter da/dN curves obtained were then used to fit the fatigue crack growth rate data under different stress ratios. From the fitting results of test data, it is evident that the fitting curves can effectively, adequately and logically depict the physical characteristics and the phenomenological quantitative laws of the full range of crack growth rate. The parameters in the models can be estimated expediently and easily, and the calculated curves are consistent with the experimental data. This demonstrates the validity and rationality of the four-parameter da/dN curve. It is concluded that the methods presented in this paper will have a wide application.