A new damage model and the prediction of elasto-plastic fatigue fracture

• For better predicting fatigue crack growth, a maximum shear stress model is proposed.
• This model accounts for the fracture surface interaction effects on the crack growth.
• Fracture surface is with asperities and can be considered in a form of factory roof.
• Fatigue crack growth rate is a function of effective stress intensity factor range.
• Model proposed can predict fatigue crack growth in steel pipes under complex loading.

In this study, the fatigue fracture of steel pipes, each consisting of an inclined semi-elliptical crack, subjected to axial loading is investigated both experimentally and theoretically. The inclined angle of the crack with respect to the axis of loading varies between 0° and 90°. On a microscopic scale, in fact, the fracture surface is not smooth indeed, as asperities, which are related to microstructure details, are developed. The mutual sliding interactions of these asperities result in a pressure and a frictional stress field between the fracture surfaces. In the present investigation, a new crack growth model, which accounts for the fracture surface interaction effects on the crack growth, is proposed. The fracture surface is considered in a form of a factory roof, with asperity height of h and wavelength of λ. Subsequently, this proposed model is applied to predict fatigue crack growth in steel pipes under complex stress states.