Affiliations: Sandia National Laboratories, PO Box 5800, Mailstop 0889, Albuquerque NM 87185-0889, USA | Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Menlo Park CA 94025, USA | Lufthansa Technik AG, HAM WR 124, Weg beim Jäger 193, 22335 Hamburg, Germany | Lawrence Berkeley National Laboratory, Mailstop 62-203, 1 Cyclotron Road, Berkeley CA 94720, USA
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.
