ELASTOPLASTIC ANALYSIS OF THERMAL CYCLING - LAYERED MATERIALS WITH COMPOSITIONAL GRADIENTS

Elastoplastic analyses are presented for the cyclic thermal response i n multi-layered materials which comprise layers of fixed compositions of a metal and a ceramic, and a compositionally graded interface. Anal ytical solutions for the characteristic temperature at which the onset of thermally induced plastic deformation occurs are derived for the l ayered composite. Solutions for the evolution of curvature and thermal strains, and for the initiation of plastic yielding are also obtained for different combinations of the geometry, physical properties and c ompositional gradation for both thermoelastic and thermoplastic deform ation. Finite-element formulations incorporating continuous and smooth spatial variations in the composition and properties of the graded la yer are used to simulate the evolution of thermal stresses, the accumu lation of plastic strains, and the development of monotonic and cyclic plastic zones at the interfaces, edges and free surfaces of different layers during thermal cycling. Engineering diagrams detailing the eff ects of compositional gradients are also presented for optimizing ther mal residual stresses, layer geometry, acid plastic strain accumulatio n.