The crack closure phenomenon has attracted great attention in the prediction of
fatigue crack growth. The finite element analysis of fatigue crack growth has been conducted
by many researchers mainly emphasized on the technique implementation of the simulation. In
this paper the behavior of plasticity induced fatigue crack closure was analyzed by the
elastic-plastic finite element method for middle crack tension (MT) specimen. The material was
assumed as linear-kinematic hardening. The crack growth was simulated by releasing the
“bonded” node pairs ahead of crack tip in stepwise. The calculations focused on the effects of
load cases and crack length on crack opening/closure levels. For constant amplitude cyclic
loadings with different load ratios, the crack opening/closure levels increases for a while and
then decreases continuously, with the increase of crack length. For the loadings with invariable
maximum stress intensity factors (briefly the constant-K loading), however, the crack tip plastic
zone sizes at different crack lengths remain unchanged and the crack opening and closing load
levels normalized by the maximum load levels keep constants as well. The results indicate that
the crack length does not affect the relative opening and closure levels and numerical analysis
for the constant-K loading case should play a key role in characterizing the fatigue crack growth
behavior.
