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.