Abstract
The fan blades and turbine blades in a jet engine are seriously damaged by high velocity impingements of various foreign objects, such as birds, sand, metallic fragments, and volcanic ash. The impingements of relatively small and hard objects form indentations on the surface of these blades, which result in a reduction of the fatigue life of these blades. Therefore, it is required that the indentation size produced by a high-velocity impingement of a small solid object are accurately predicted. In this study, an equation for prediction of indentation size formed by a high-velocity impingement of a solid sphere (EPIS) was developed via a theoretical model based on an expanding cavity model and energy conservation before and after impingement. The Johnson-Cook constitutive equation was employed to introduce effects of work hardening, strain rate hardening and thermal softening into the cavity model. As a result, the distribution of equivalent plastic strain, equivalent plastic strain rate, temperature and equivalent von Mises stress estimated using the expanding cavity model were in good agreement with the data obtained from the finite element analysis. In addition, it has been demonstrated that EPIS can accurately predict the radius of indentation formed on various metallic materials subjected to the impingement of a solid sphere with the radius of 1.5 mm at several impingement velocities in the range of 50-300 m/s.
