Damage Parameter Assessment for Energy Based Fatigue Life Prediction Methods

Abstract

An energy-based method used to predict fatigue life and critical life of various materials has been previously developed, correlating strain energy dissipated during monotonic fracture to total cyclic strain energy dissipation in fatigue fracture. This method is based on the assumption that the monotonic strain energy and total hysteretic strain energy to fracture is equivalent. The fracture processes of monotonic and cyclic failure modes can be of stark contrast, with ductile and brittle fracture dominating each respectively. This study proposes that a more appropriate damage parameter for predicting fatigue life may be to use low cycle fatigue (LCF) strain energy rather than monotonic energy. Thus, the new damage parameter would capture similar fracture processes and cyclic behavior. Round tensile specimens machined from commercially supplied Al 6061-T6511 were tested to acquire LCF failure data in fully reversed loading at various alternating stresses. Results are compared to both monotonic and cyclic strain energy dissipation to determine if LCF strain energy dissipation is a more suitable damage parameter for fatigue life prediction.