Analysis of thermo-mechanical cracking in refractory coatings using variable pulse-duration laser pulse heating

The recent acquisition of a variable-pulse duration Nd:YAG laser, which allows a pulse duration as low as 0.5 ms, has resulted in initiation of coating adhesive failure in much better agreement with live fire tests. The variable pulse duration enables study of the varied thermal loading and the resulting wear and erosion behavior experienced by the cannon bore at various locations, which improves the fidelity of the laser test. The ability to independently vary the fluence supplied to the coating and the pulse duration affords insight into the processes leading to thermally induced wear and erosion. Finite-difference calculations of the heat flow in the coatings are presented to explain the temporal and depth-resolved temperature profile in the coating, and the implications of this profile for coating wear in thermal transient environments are discussed.