A NEW MODEL OF FUNCTIONALLY GRADED COATINGS WITH A CRACK UNDER THERMAL LOADING

A new model for fracture analysis oaf functionally graded materials (FGMs) with arbitrarily varying material properties under thermal loading is developed. The FGM is modeled as a multilayered medium and in each layer both shear modulus and thermal conductivity are assumed to be a linear function of the depth and are continuous on the subinterfaces. To make the crack problem tractable, thermal expansion and conductivity of the FGMs are supposed to have the same form. With this new model, the crack problem of a functionally graded coating bonded to a homogeneous substrate under steady-state thermal loading is investigated. Employment of the Fourier integral transform technique reduces the problem to a system of Cauchy singular integral equations that are solved numerically. Thermal stress intensity factors (TSIFs) are obtained for various forms of thermal conductivity or expansion. The results reveal that the present model is very efficient and in the frame of the present model both the form of thermal conductivity/expansion and that of its derivative can influence the TSIFs significantly.