Interface characterization and defect evolution of coated samples under thermal and pressure transients

Coatings are vital to the performance of gun tubes, as they protect the structural steel substrate from both the thermal and chemical affects of the hot, erosive, combustion gases. Gun tube coatings are often evaluated by the pulsed-laser heating experiment, though it does not include pressure affects. Live firing tests included all effects, but are expensive and difficult to conduct. Recognizing the short-comings of current evaluation techniques, a method was developed to evaluate interfacial properties by introducing an indentation induced flaw, and studying the flaws evolution under thermal and pressure transients.;The effects of severe thermal- and pressure-transients on coated substrates with indentation-induced, blister defects were then analyzed using experimental and finite element methods. Both explicit and implicit FEA approaches were used to assess the transient thermal- and stress-states and the propensity for fracture related damage and evolution, while undergoing uniform convective heating and pressure transients across the surface. Spherical indentations along with in-situ acoustic emissions, c-scans, and finite element modeling were utilized to induce the defects, and to quantify interfacial adhesion and cohesive zone properties. Preliminary results indicated complex interactions between the boundary conditions and their timing and the resulting propensity for damage birth and evolution. Given the need for robust coatings, the experimental and modeling procedures explored by this study will have important ramifications for coated tube designs and the evaluation of candidate materials.