Predictive models for stable tearing crack growth due to overloading in fatigue

Stable tearing is a recurring process in which fatigue crack growth is interspersed by substantial jumps of crack growth, commonly at the central cross-section of the component while the crack front nearer the surface lags behind. These tearing bands have been observed to start very early during fatigue life and can make up the majority of the fatigue fracture surface. This paper presents the development of predictive models, in which the tongue-shaped stable tearing band is first idealised as trapezoidal shape, and then two alternative fracture criteria are formulated with the aid of the finite element (FE) method and the Forsyth stable tearing concept. Parametric solutions of the stress intensity factor at the front of the trapezoidal crack front are obtained using the FE method. Comparisons between the model predictions and experimental results indicate that both models produce satisfactory prediction of the stable tearing crack jump length in aluminium alloy coupons of varying cross-sectional thickness.