Predictive Numerical Modeling of Foreign Object Damage

During service aircraft engines may suffer foreign object damage (FOD) from ingestion of small hard particles and then are subjected to a range of HCF-LCF cycles. Manufacturers are seeking to improve the FOD tolerance of engines at the design stage and thereby reduce the costs of ownership. A design methodology is therefore required with which to assess the loss of fatigue strength resulting from FOD on blades or vanes. This work describes progress in the prediction of the residual stresses left from the impact in a specimen which resembles a compressor blade. The FE package LS-DYNA has been used to analyse the problem. Initially different material models were considered, each including a strain rate dependence, and a calibration based on a tensile test was performed. The Bamman Damage (Mat 52) was then chosen and used in the numerical model of impact on an aerofoil leading edge. The model has proved capable of recreating the damage geometry and gives a valuable insight into the likely residual stress distribution around the notch. A subsequent fatigue analysis of the impacted blade has been run using the same material model. A methodology based on a posteriori analysis and comparison with post-impact fatigue experiments has been used to confirm the results obtained.