ROLLING CONSOLIDATION OF METAL-MATRIX COMPOSITES

Transverse rolling of metal matrix composite precursor wires is propos ed as a consolidation technique for making sheets. Rolling in the tran sverse direction to the fiber orientation is analytically shown to be feasible, and longitudinal rolling results in fiber breakage. Plastici ty analysis is conducted using Hill's general yield criterion for anis otropic materials and the associated Levy-Mises equations modified for plane strain conditions. The slab method is used to calculate the str esses in the material, and the effects of rolling parameters on the pr incipal stress ratio are investigated. At the microscopic level, an el astic-plastic finite element formulation and a computation procedure a re presented. Individual fibers are modeled to determine the stress st ate around each fiber. The principal stress ratio is suggested as a pa rameter that determines the tendency for void formation due to debondi ng and fiber breakage; finite element analysis is used to determine th e effects of the principal stress ratio on the fiber-matrix interfacia l stresses in the micromechanics model. The analysis determines the de formed mesh, plastic zone propagation and the stresses at the interfac e as a function of volume fraction and principal stress ratio. Interfa cial stresses are assumed to be responsible for debonding during the d eformation of metal matrix composites. This assumption and the results of the analysis provide guidelines for defining the level of the biax ial stress field in the plane transverse to the fibers during rolling that will minimize interfacial fiber-matrix stresses. (C) 1997 Elsevie r Science Ltd. All rights reserved.