EFFECT OF THE MODE OF OVERLOAD ON THE BEHAVIOUR OF FATIGUE CRACK PROPAGATION

The effects of different modes of overload, including tensile, compressive, tensile-compressive and compressive-tensile, on the behaviour of fatigue crack propagation in LY12 A1 alloy were investigated. From a study of the changes in micro-morphology, the plastic zone size and strain distribution around the crack tip and the fracture analysis before and after various overloading, it is suggested that various modes of overload produce different influences on FCP, and the retardation behaviour of FCP after tensile overloading may be described as a combination effect of several factors acting on the crack tip and its surrounding region. A general mechanism of the effect of tensile overload on FCP behaviour is proposed.