Prediction of fatigue damage accumulation of defective materials under variable amplitude loading

Abstract

The main goal of this attempt is to explore and analyze the behavior of a material containing artificial surface defect and solicited under variable amplitude cyclic loading. The observation and the follow-up of the loading history and the characterization of the damage accumulation were evaluated in the presence of an artificial surface defect. The results made it possible to highlight a strong nonlinearity of the damage accumulation. However, the absence of sequence effects encountered in a defect-free material has been found. In the perspective of developing an approach to evaluate the influence of the defects on cumulative damage under variable amplitude loading, this work consists of coupling a multiaxial fatigue criterion adapted to defective materials with a law of uniaxial damage solicited under variable amplitudes loading. A cumulative damage law has been used to analyze the validity of the proposed method. Introducing the equivalent multiaxial fatigue stress due to the presence of the defect allowed us to predict the residual lifetime of a defective material, and to find the effects of sequences usually observed for variable amplitude loading for the defect-free material. A coherent agreement is observed between the results predicted by the improved model and those obtained from the experimental investigations on specimens containing artificial surface defect subjected to purely alternating tension and torsion under increasing and decreasing load levels.