Computational simulation of the relaxation of local stresses due to foreign object damage under cyclic loading

In this study, the phenomenon of residual stress relaxation from foreign object damage (FOD) is numerically simulated using a hybrid explicit implicit finite-element method. The effects of cycle fatigue loadings on stress relaxation were studied. FOD is first simulated by firing a 3 mm cube impacting onto a plate made of titanium alloy Ti-6Al-4V at 200 m s. The FOD impact produces two distinct stress concentrations: one is compressive directly beneath the impact site; the other is tensile around the outer edge of the impact. The plate was then assumed to be subjected to a cyclic fatigue loading. The stress relaxation was investigated under a range of stress ratios and maximum applied stresses. Two different material models were considered for the simulations, namely an elastic perfectly plastic model and a non-linear kinematic hardening model.