ABSTRACT
The present work is an extension of applying a previously developed fracture mechanics cracking damage model to predict the fatigue lifetime of un-notched round specimens made of a ferrite-pearlite 0.4C-70/30 carbon steel in the cases of (a) two-step fully reversed axial loading with low-to-high and high-to-low sequences and (b) repeated application of fully reversed two-step axial loading blocks. This model numerically simulates the collective behavior of growing short fatigue cracks originating from the specimen surface. The surface roughness is assumed resembling micro cracks of different sizes and locations along the minimum specimen circumference. Material grains of different phases, sizes and strengths are randomly distributed over that circumference. Possible activities of surface cracks are predicted against loading cycles till fracture occurs. Published experimental data on ferritic-pearlitic steel specimens in fully reversed variable amplitude loading were utilized. Different specimens were randomly configured and virtually tested. The present predictions are in a fair agreement with the corresponding experimental results.