An Ultrasonic Evaluation of Damage in Cermets

Cermets are hard ceramic-metal composites with predominant ceramic phases and are finding increasing applications. It is important to understand the evolution of damage and the failure modes in these materials under dynamic loading conditions in order to design them for impact resistant applications. In this investigation a plate impact recovery technique [1,2] is used to subject cermet specimens to a single step compressive pulse of known amplitude and duration. This technique has the advantage of applying sufficiently high stress levels to initiate damage and yet providing controlled amounts of energy input to avoid catastrophic failure of the material. Ultrasonic velocity and attenuation studies are carried out on the recovered specimens to asses the evolution of damage under stress wave loading. Optical microscopy and image processing techniques are used to quantify the extent of damage in the recovered samples. Techniques such as ultrasonic measurements could prove to be useful in predicting damage levels in materials subjected to dynamic loading. The material chosen for study is a boron carbide-aluminum cermet [3].