Quasi-static and Dynamic Torsion Testing of Ceramic Coatings Using High-speed Photography

A novel experimental procedure for the testing of ceramic coatings in quasi-static and dynamic torsion is presented. The tests were performed on a Kolsky bar apparatus modified for torsion loading. High-speed photography was used to take snapshots of the surface of the specimen gage during loading, and digitally correlated to determine the full displacement and strain fields. Microand nanoAl2O3/TiO2 and WC/Co coatings on thin aluminum substrates were tested. The specimens contained porosity and cracking prior to testing, that resulted from the coating process. This damage was found to be significant and resulted in low shear moduli and strengths. The damage mechanisms of the coatings with respect of the substrate were determined.