Since the stress-strain curves are nonlinear, two parameters are required to describe the behabior of the coating. The elastic modulus (E) can be extracted from the linear region of the stress-strain curve while the nonlinear degree (ND) can be used to describe the change in elastic modulus at the beginning and the end of the curve. The results have indicated that coatings subjected to different processing routes will yield signatue E and ND values that can be used for both coating design and tracking reproducility and repeatability.
Investigations of plasma sprayed TBCs using an in-situ curvature sensor (ICP) and through recourse of post processing furnace thermal cycling test have shown that curvature-temperature relationship of APS YSZ coatings to be anelastic (nonlinear hysteresis in the loading-unloading curve associated with energy dissipation mechanisms). The curvature-temperature relations are converted to nonlinear stress-strain relations using a modified Ramburg-Osgood model and the relevant quantitative information extracted through a novel inverse analysis technique. Software solutions hav been developed for the analysis to enable rapid extraction of coating properties.