Directional-to-isotropic transitions in metal/matrix composite joints

The mechanical behavior of transition joints between continuous-fiber metal /matrix composites and non-reinforced or discontinuously reinforced metalli c sub-elements is discussed. The broader themes are (i) the role of joint g eometry relative to the strength of the tensile and shear interfaces and (i i) the effect of particle reinforcement of the isotropic sub-element. The s tudy focuses on the deformation phenomena at the directional-isotropic tran sition and the relevant interfaces. Model joints were manufactured by press ure infiltration of molten A1-4.5%Mg into suitable preforms, a technique th at minimizes gross interfacial defects and the ensuing variability of joint strength. In general, joint strength increases with insertion ratio owing primarily to the contribution of shear at the lateral interfaces. Experimen tal results combined with finite-element analysis highlight the critical ro les of plastic constraint and stress concentrations arising from the geomet ry acid property mismatch. The plastic constraint can operate in two size s cales, one associated with the macroscopic dimensions of the transition, an d the other with the reinforcing particles, when present. Both effects incr ease the load-carrying ability of the joint - notably through the interface formed by the termination of the continuous fibers - with attendant implic ations for joint design. The mechanisms that initiate failure are discussed in the context of the stress and strain profiles near this interface in co mbination with data from other joint configurations. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.