A cantilever beam method for evaluating Young’s modulus and Poisson’s ratio of thermal spray coatings |
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Authors: | E F Rybicki J R Shadley Y Xiong DJ Greving |
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Affiliation: | (1) Mechanical Engineering Department, KEH L-185, The University of Tulsa, 600 South College Avenue, 74104 Tulsa, OK, USA |
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Abstract: | Young’s modulus and Poisson’s ratio for thermal spray coatings are needed to evaluate properties and characteristics of thermal
spray coatings such as residual stresses, fracture toughness, and fatigue crack growth rates. It is difficult to evaluate
Young’s modulus and Poisson’s ratio of thermal spray coatings be-cause coatings are usually thin and attached to a thicker
and much stiffer substrate. Under loading, the substrate restricts the coating from deforming. Since coatings are used while
bonded to a substrate, it is desirable to have a procedure to evaluate Young’s modulus and Poisson’s ratio in situ.
The cantilever beam method to evaluate the Young’s modulus and Poisson’s ratio of thermal spray coat-ings is presented. The
method uses strain gages located on the coating and substrate surfaces. A series of increasing loads is applied to the end
of the cantilever beam. The moment at the gaged section is calcu-lated. Using a laminated plate bending theory, the Young’s
modulus and Poisson’s ratio are inferred based on a least squares fit of the equilibrium equations. The method is verified
by comparing predicted values of Young’s modulus and Poisson’s ratio with reference values from a three-dimensional finite
ele-ment analysis of the thermal spray coated cantilever beam. The sensitivity of the method is examined with respect to the
accuracy of measured quantities such as strain gage readings, specimen dimensions, ap-plied bending moment, and substrate
mechanical properties. The method is applied to evaluate the Young’s modulus and Poisson’s ratio of four thermal spray coatings
of industrial importance. |
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Keywords: | cantilever beam method elastic modulus mechanical properties Poisson’ s ratio |
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