Deformation behavior of model MMC scarf joints

The mechanical response of metal interlayers constrained between two fiber- reinforced MMC (metal-matrix composites) sub-elements was investigated. The fibers were polycrystalline Al2O3, discontinuous at the joint, embedded in Al-4.5Mg, that was continuous through the joint and constituted both the c omposite matrix and the interlayer material. The specimens were produced by pressurized melt infiltration and comprised interlayers oriented from 0 to 75 degrees relative to the plane normal to the fiber axis. Analytical and finite element models were developed and compared with experimental results in order to elucidate the deformation behavior of these interlayers and to identify the key factors controlling joint performance. Two predominant re gimes were identified in this manner. Joints in the intermediate angle rang e (45 +/- 15 degrees) exhibit limit load behavior and develop large strains prior to failure, whereas joints at lower (less than or equal to 15 degree s) and higher (75 degrees) angles show only modest plasticity. The models s uggest that the latter group could, in principle, develop large strains and Limit loads, but this behavior is precluded by the intervention of failure owing to debonding in the lower angle joints, and to composite fracture in the highest angle ones. The analysis further reveals that the constitutive behavior of the metal in the interlayer exhibits substantial hardening rel ative to that of the monolithic matrix processed in the same manner. The re asons for this behavior are discussed. The models set the stage for future work to elucidating failure criteria for interlayers in these joint configu rations. (C) 2000 Elsevier Science S.A. All rights reserved.