Dislocation Punching in Functionally-Graded Materials

A new dislocation punching model for a functionally graded material (FGM) subjected to a temperature change has been proposed, using Eshelby’s model. FGM, consisting of several layers, is deposited on a ceramic substrate. Two types of microstructures are examined for a layer: one consists of a metal matrix and ceramic particles and the other of a ceramic matrix and metal particles. An elastic energy is evaluated when plastic strain, in addition to thermal mismatch strain, is introduced in the metal phase. The work dissipated by the plastic deformation is also calculated. From the condition that the reduction in the elastic energy is larger than the work dissipated, a critical thermal mismatch strain to induce stress relaxation is determined. The magnitude of the plastic strain is also determined, when the relaxation occurs. The results of the present theory for a special case of FGM, i.e., the case of single interface coincide with those of our earlier work on a thin metal coating on ceramic substrate. The theory is applied to a model FGM consisting of mixtures of Pd and Al2O3 on an Al2O3 substrate.