A Tangential Model for Fatigue Crack Growth Rules

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.