Fracture strength of alumina fiber reinforced aluminum wire with and without a torsional pre-strain

The influence of torsion applied prior to tensile testing on the fracture s trength of Nextel(TM) 610 alumina continuous-fiber reinforced aluminum matr ix composite wire is investigated. It is shown that internal stresses that develop in the composite upon twisting exert a dominant influence on the de rived failure criteria, which exceeds that of fiber misalignment resulting from the gradual inclination during twisting of the fibers with respect to the wire axis. Al low and intermediate levels of twisting up to a surface s hear strain of 10%, fracture occurs when the sum of externally applied and internal stresses reaches locally the fracture stress of the untwisted mate rial. For higher surface shear deformations, two possible fracture-stress v s surface shear strain dependencies are predicted, depending on the general fracture behavior of the composite qualified in terms of damage tolerance. Experiment shows that the fracture strength of the reinforced wire used in this study follows the behavior ascribed to a nondamage-sensitive material . (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All ri ghts reserved.