Enhanced Model for Describing Total Fatigue Rate Curve considering Stress Ratio Effects

Abstract

An enhanced fatigue crack growth model is proposed to approximate fatigue crack growth rate in all three regions of fatigue rate curve. The model uses Collipriest's crack driving force for accounting stress ratio effect on fatigue crack growth. Seven fatigue crack growth models, namely Priddle, Mcevily, Weertman, Collipriest, Broek, Walker and Forman are examined. Performance of the crack driving force of these models in depicting stress ratio effects in fatigue crack growth rate is evaluated by fitting a lowess curve in transformed FCG data. Non-uniform B-spline is used to describe fatigue rate curve which allows local movements of the fatigue crack growth data that can be matched well in the vicinity without extending their effects to distant parts of the curve. Experimental FCG data of Al 2024 T351 from literature are used for validation of the model.