Verification of Linear Dependence of Plastic Zone Size on J-Integral for Mixed-Mode Loading

Abstract

Determination of fatigue crack growth characteristics under shear-mode loading is a rather complicated problem. To increase an efficiency and precision of such testing, special specimens enabling simultaneous propagation of shear cracks under II, III and II+III loading modes started to be used rather recently. However, a description of crack growth rate in terms of appropriate fracture mechanics quantities demands a precise assessment of plastic zone size under various shear-mode loading levels. This contribution is focused on the numerical elasto-plastic analysis of stress-strain field at the crack tip in specimens made of a pure polycrystalline (ARMCO) iron loaded by mixed mode II+III. The dependence of plastic zone size on theJ-integral value described the wide region of loading. The results reveal that formixed mode II+III the small scale yielding conditions are fulfilled in the region where plastic zone size is smaller than 1/10 of the total crack length.