Finite element modeling of plasticity-induced crack closure due to occasional mode II loading on mode I fatigue crack growth

• We model the effect of single mode II loading on mode I fatigue crack growth.
• After single mode II loading ΔCTOD exhibits initial drop and subsequent recovery.
• Plasticity-induced closure can cause a small retardation for mode I crack growth.

Plasticity-induced fatigue crack closure associated with occasional mode II loading was simulated for two-dimensional middle-crack tension geometry by using the finite element method. When a single mode II cycle was superposed onto the steady-state mode I crack growth, the range of crack tip opening displacement, ΔCTOD, exhibited the initial drop and subsequent recovery under plane strain condition. On the other hand, under plane stress condition, ΔCTOD exhibited the initial jump and drop right after the single mode II loading, and then it showed the recovery. The present results indicate that occasional mode II loading can cause a small retardation for mode I crack growth due to the enhanced plasticity-induced closure.