THERMAL-STRESSES IN BICOATED STRUCTURES

The thermoelastic problem of a three-phase concentric sphere subject to phasewise uniform temperature variations is solved exactly. With this solution, the cool-down stresses in a metallic structure with plasma-sprayed oxidation- and thermal-barrier coatings are determined. In this context, the relevance of several control parameters is examined, including the Poisson ratios of both coatings and the substrate temperature during deposition. The thin-film approximation to the subject problem is derived, and it is shown that the response of the two barrier layers is essentially uncoupled. In particular, the thermoelastic properties of the intermediate layer have a negligible effect on the stresses in the outermost layer. It is then concluded that the most relevant stress-control variable is the substrate deposition temperature.