Thermal residual stresses in plates and coatings composed of multi-layered and functionally graded materials

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In this paper, thermal residual stresses in multi-layered and compositionally graded plates and coatings were analyzed. Systematic studies on effects of different material combinations, including the compositional gradient, the elastic modulus, the coefficient of thermal expansion, and the number of layers in the case of multi-layered materials on the magnitude and distribution of residual stresses were conducted. Geometry changes of plates and coatings due to these residual stresses were also investigated. It was found that the distribution and magnitude of thermal residual stresses within a plate can be adjusted by controlling the compositional gradient and selecting a proper combination of ceramic and metal constituents. When the compositional gradient of a plate is such that a rapid change in volume fraction and properties occurs near the ceramic face and a gradual change near the metal face, a residual compressive stress is produced on both faces of the plate. However, when the rapid change in volume fraction and properties occurs near the metal face and the gradual change near the ceramic face, a residual tensile stress is generated on both faces of the plate. Minimum residual stresses are obtained when the plate has a linear compositional gradient. As for compositionally graded coatings, the magnitude of the residual stresses on the surface of the coating cannot be decreased by introducing a compositional gradient. The gradient coating only alters the characteristics of the residual stress distribution.