Fatigue Life Prediction of Steel Alloys under Uniaxial Random Loading using Stress-Based Approach

In this paper, fatigue life of various steel alloys undergoing uniaxial random loading conditions are evaluated using stress-based damage models. Critical plane based models of Findley, Macha and Carpinteri-Spagnoli (CS)evaluate fatigue damage with different plane orientation definitions and material constants. Findley and Macha models utilize linear integration of shear and normal stress components while CS employs a nonlinear combination of shear and normal stresses acting on the critical plane to calculate fatigue lives. Findley model describes critical plane as a plane in which maximum magnitude of damage due to both shear and normal stress components takes place. Critical plane in the Macha model is determined based on the average value of principal stress directions. CS defines the angle between normal vector of the critical plane and the weighted mean direction of the maximum principal stress as a critical plane orientation. The rainflow cycle counting technique is applied to discretize random block loading spectra and to determine the number of reversals over block loading histories. The accumulated damage over peak-valley events is then calculated based on the Miner-Palmgren linear damage rule. Capability of stress-based damage models for assessment of steel samples is discussed in terms of model descriptions.