Influence of foreign object damage (FOD) on the fatigue life of simulated Ti-6Al-4V airfoils

The fatigue behavior of Ti-6Al-4 V samples that have undergone foreign obje ct damage (FOD) was investigated. A unique test specimen configuration that replicates the leading edge of a typical fan blade was ballistically shot with 1.0 mm diameter glass spheres to simulate actual FOD. Samples were sho t at various incident angles to investigate the influence of impact angle o n fatigue strength. Two stress ratios were examined: R = 0.1 and 0.5. Attem pts were made to correlate the measured damage (macro-/microscopic) to the debit in fatigue strength. The FOD impact sites of fatigue samples were exa mined prior to testing via a scanning electron microscope (SEM); post-test examinations of the fatigue initiation sites were also performed on selecte d test samples. Subsurface or internal damage resulting from the FOD was al so investigated from precision micro-sectioning of selected samples. Oh-ang le impacts were found to be more detrimental than head-on (0 degrees) impac ts. Fatigue strength losses, some as high as 50%, showed little or no corre lation with leading edge thickness or depth of notch. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.