An Experimental Study on Fatigue Crack Propagation under Cyclic Loading with Multiple Overloads

초록

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 distributions 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 distributions. The study proposes a crack propagation prediction model that incorporates the overload ratio effect. A comparative work for the overload ratio effect demonstrates that the prediction by the proposed model is in good agreement with the experimental results. This prediction of fatigue crack propagation including multiple overloads using proposed model show also a good agreement with test results.