Material Strength Degradation Experiment and Statistical Expression Under Cyclic Loading

Abstract

Cyclic loading leads to material strength degradation gradually until fatigue fracture occurs. Material strength degradation path is significant to fatigue life prediction and/or fatigue reliability estimation. Since the stochastic attributes of material strength, fatigue damage and fatigue life, material strength degradation test data are the type of partially left-censored. It makes material strength degradation behavior description difficult. The present paper presents a method to estimate residual strength distribution after n times of cyclic stress application, in which the strength degradation information contained by the early failed specimens is converted to equivalent residual strength at the expected cycle number. The strength degradation information conversion is based on an assumption that the residual strength is normal distributed, and the residual strength data are roughly symmetrical to the median. Such obtained residual strength probability density function and strength degradation path can be applied to predict fatigue life and evaluate reliability.