F Kazerooni - Graduate student, Department of Mechanical Engineering, Persian Gulf University, Bushehr, Bushehr ۷۵۱۶۸
M.R Golbahar Haghighi - Associate Professor, Department of Mechanical Engineering, Persian Gulf University, Bushehr ۷۵۱۶۸
G.R Ahmadzadeh - Visiting Professor, Department of Mechanical Engineering, Ryerson University, Toronto, Ontario M۶L N۲B Canada

In this paper, fatigue life of various steel alloys undergoing uniaxial random loading conditions are evaluatedusing 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 modelsutilize linear integration of shear and normal stress components while CS employs a nonlinear combination of shearand normal stresses acting on the critical plane to calculate fatigue lives. Findley model describes critical plane as aplane in which maximum magnitude of damage due to both shear and normal stress components takes place. Criticalplane in the Macha model is determined based on the average value of principal stress directions. CS defines the anglebetween normal vector of the critical plane and the weighted mean direction of the maximum principal stress as acritical plane orientation. The rainflow cycle counting technique is applied to discretize random block loading spectraand to determine the number of reversals over block loading histories. The accumulated damage over peak-valleyevents is then calculated based on the Miner-Palmgren linear damage rule. Capability of stress-based damage modelsfor assessment of steel samples is discussed in terms of model descriptions.

Fatigue life, stress-based criterion, critical plane, uniaxial random loading, cycle counting