Determination of nonlinear properties of thermal sprayed ceramic coatings via inverse analysis

Abstract

A robust procedure to estimate nonlinear mechanical properties of thermally sprayed (TS) ceramic coatings is introduced. Such a method is valuable particularly for TS coatings since each may possess unique properties depending upon its processing condition. Traditionally, their responses have been assumed as linear elastic (isotropic or anisotropic) except in very high temperature environments where softening may occur. However, recent inspections revealed their properties to be more accurately characterized as nonlinear elastic. It appears their distinctive morphology consisting of cracks and interfaces are responsible for such a response. In this work, a versatile procedure to identify nonlinear properties of thermally sprayed coatings is developed. First, a suitable stress–strain model is proposed and then a nonlinear bi-material beam solution is derived. Afterward, an inverse analysis technique is utilized to process the measured curvature–temperature to extract the unknown parameters. Prior to implementing in actual specimens, a detailed simulation study is performed to verify the method’s accuracy as well as robustness. This computational analysis closely replicates deposition processes of TS coatings. With the successful verification, actual curvature measurement of TS yttria-stabilized zirconia (YSZ) coating is used to determine the nonlinear properties. The estimated results clearly reveal a significant nonlinearity of the TS coating. The main advantage of this procedure is that it requires essentially no specimen preparation and allows continuous measurements after TS deposition. Furthermore, the data interpretation does not require complex computational models and calculations. This streamlined process makes the present method attractive when evaluations of many specimens are required. The present procedure can be also extended to identify nonlinear properties of other coatings/films on substrates.