A Spatially-resolved Synchrotron Diffraction Method for Evaluating Impact-induced Residual Stresses

Abstract

Turbine engine fatigue failures associated with foreign object damage (FOD) are thought to be driven, in part, by the impact-induced residual stresses. The present work summarizes the use of spatially-resolved synchrotron X-ray diffraction to quantify the residual stresses, residual elastic Poisson strain, and plastic strain of simulated FOD in a Ti-6Al-4V alloy. A 300 × 300 µm low-divergence synchrotron source provides adequate spatial resolution for the interrogation of impact craters 2–6 mm in diameter, while still sampling a sufficient number of grains for monochromatic polycrystalline diffraction experiments. The observed residual stresses are compared to continuum- based numerical predictions. Both the formation of microcracks at high impact velocities (300 m/s), and the Bauschinger-induced fatigue relaxation of the initial residual stresses must be taken into account to adequately address the driving force for fatigue failure.