Impact resistance of TiC-based cermets

The present article describes a comparative study of the impact resistance of two commercial TiC/Ni cermets and an armor-grade alumina, each in the form of plates backed by thin steel sheets. Performance is assessed on the basis of the ballistic limits of the targets and, below the ballistic limit, on the magnitude and the shape of the back-sheet deflection profile. The operative damage and deformation mechanisms are characterized via optical and scanning electron microscopy on plugs of material recovered from the impact site. We find that, over the range of conditions probed by the present experiments, the cermets exhibit ballistic performance comparable to that of the alumina on an areal density basis yet suffer significantly less extended cracking and fragmentation. Furthermore, for both of the cermets and the alumina, failure at the highest velocities occurs via shear plugging, thereby producing cylindrical plugs with diameter somewhat greater than that of the projectile. Complementary finite element simulations of impulsively loaded steel sheets show that the magnitude and the shape of the deflection profile are dictated by the size of the loading patch. Upon comparison of the simulations with experimentally-measured profiles we find that the inferred effective radius over which the impact load is transmitted from the striker-plate to the backing sheet is broadly consistent with the observed radii of ejected plugs. Furthermore, this radius generally decreases with increasing projectile velocity. On this basis, we suggest that the combination of the maximum back-sheet deflection and the shape of the deflection profile provides a useful measure of the efficacy of the plates in spreading the impact load and mitigating the effects of the impact on back-sheet deflection.