A Study of Overload Effects on Fatigue Crack Propagation under Cyclic Loading Using ESPI System

摘要

For many fatigue-critical parts of machines and structures, load history under service conditions generally involves variable amplitude loading rather than constant amplitude loading. An accurate prediction of fatigue crack propagation life under variable amplitude loading requires a thorough evaluation of load interaction effects. In this study, fatigue tests under both constant and variable amplitude loading are carried out to investigate the overload effects on fatigue crack propagation of the notched specimens. Strain distribution around the crack tip before and after a tensile overloading is measured using ESPI (Electronic Speckle Pattern Interferometry) system. The size of plastic zone is determined from the measured strain distribution. The study proposes a crack propagation prediction model that incorporates the overload effect. The overload effect factor for fatigue crack propagation life is used to characterize the load interaction effect in load spectrum. A comparative work demonstrates that the prediction by the proposed model is in good agreement with the experimental results.