Effect of impact velocity and impact angle on residual stress fields caused by foreign object damage

In order to study the residual stress induced by foreign object damage (FOD), the distribution of residual stress caused by the impact of a hard spherical body was measured via the sin²ψ technique, using synchrotron X-ray. A steel sphere was impacted onto a flat surface of a Ti-6Al-4V alloy from an angle of either 90° or 45°, at a velocity of 180 m/s. The same sphere was also quasi-statically pressed into the surface. In the cases of right-angled impact and quasi-static indentation, a compressive residual stress was extensively distributed inside the generated crater. No remarkable difference in residual stress distribution was noted between the dynamic case and the quasi-static case. However, at an impact angle of 45°, a tensile residual stress that is more detrimental to fatigue strength was widely distributed inside the crater. Outside of the craters, tensile stress was generally observed in all cases.