疲劳裂纹扩展规律的正切模型

A Tangential Model for Fatigue Crack Growth Rules

为了用解析方法合理地描述疲劳裂纹扩展的三个阶段,提出了一种新的疲劳裂纹扩展模型——正切模型。该模型驱动力使用应力强度因子幅值K,能够描述裂纹扩展的三个阶段,且只有四个参数需要确定。通过非线性拟合确定疲劳裂纹扩展正切模型中的四个参数。研究了门槛值Kth和失稳值Kf与应力比R的关系,以及四个参数对裂纹扩展速率的影响。最后比较了试验值、九参数模型和正切模型在疲劳裂纹扩展速率曲线和裂纹扩展长度变化曲线等方面的差别,发现正切模型结果与试验数据较为吻合。该模型描述的裂纹扩展长度变化曲线能够较好地用于疲劳寿命评估。

A new fatigue crack growth model called as tangential model is presented to describe the three phases in fatigue crack growth process,i.e.threshold,stable and unstable phase.The tangential model,in which stress intensity factor ΔK is taken as driving force,has only four parameters to be determined.The parameters can be obtained with a nonlinear fitting approach.Relationships between threshold ΔKth and stress ratio R,and relationship between failure value ΔKf and R are investigated respectively.Sensitivity analysis of fatigue crack propagation rate to the four parameters is carried out.Finally,comparison of crack propagation rate and a-N curve among experimental data,nine parameters model and the tangential model shows that the tangential model agrees well with experimental results.It is concluded that the tangential model can rationally describe the three fatigue crack growth phases and the crack length propagation in fatigue life assessment.