CONCLUSIONS
The present work is an extension of applying a previously developed
fracture mechanics cracking damage model to assess the fatigue lifetime
of un-notched round specimens made of a two phase ferrite-pearlite
0.4C-70/30 carbon steel alloy 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. The model simulates collective behavior of growing short fatigue
cracks originating from the specimen surface roughness. The model is
applied on different specimens with surface grains randomly configured
in terms of their phase, size, strength and included crack size. The
model identifies the development of possible activities of surface short
cracks against loading cycles due to the application of the analyzed
constant and variable amplitude loading. Comparison of published
experimental fatigue lifetimes on ferritic-pearlitic steel specimens in
fully reversed variable amplitude loading and the corresponding
prediction shows fair agreement.