A study on Overload Effects on Fatigue Crack Propqagation under Cyclic Loading using ESPI System

초록

For many fatigue-critical parts of machines and structures, load history under service conditions generally involves cyclic or variable amplitude loading, rather than constant amplitude loading. An accurate prediction of fatigue crack propagation life under variable amplitude loading requires a through 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 size is determined from the measured strain distribution. Analysis gives the overload effect factor for fatigue crack propagation life, which can be used to characterize the load interaction effect in load spectrum. The study proposes a crack propagation prediction model considering the overload effect. A comparative work proves that the prediction by the proposed model is in good agreement with the experimental results.