Acta mater. 45, 3401-3417, 1997


E. Weissenbek¹²³, H.E. Pettermann¹², S. Suresh¹

¹Department of Materials Science, Massachusetts Institute of Technology, Cambridge, MA
²on leave from Institute of Lightweight Structures and Aerospace Engineering,
TU Wien, Vienna, Austria
³present address: BMW Entwicklungszentrum Steyr,
Steyr, Austria

Abstract - The elasto-plastic deformation due to thermal and mechanical loading of layered metal-ceramic composites with compositionally graded interfaces is analyzed using detailed finite element models. The model material considered is a Ni-Al2O3 layered system with a compositionally graded interface. The analyses consider planar geometries with perfectly periodic arrangements of the constituent phases, by recourse to new classes of square-packing and hexagonal-packing unit cell formulations for the graded material. Also considered are graded phase arrangements within which large numbers of microstructural units of the two phases are randomly placed within the unit cell. It is found that square-packing arrangements provide the best possible bounds for the thermal strains and coefficient of thermal expansion (CTE) of the graded multilayer, among the different unit cell models examined; however, no unique bounds could be identified for mechanical loading. The numerical predictions of thermal and mechanical response are compared with those provided by the mean-field approach involving an incremental Mori-Tanaka analysis and by the simple rule-of-mixture approximations. The former method provides a stiffer mechanical response than the finite-element unit cell models. The finite element predictions of bending CTE due to thermal excursions match the overall trends observed experimentally for the Ni-Al2O3 graded system, and further provide quantitative prediction of the temperature for the onset of plastic flow in the graded material.