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Abstract
Heavily drawn wires (80/99·7% R.A.) were fractured at temperatures between 20°c and − 100°c at various strain rates. An unusual morphology of fracture resulted in all cases, even when plastic strain or necking preceded fracture. Specimens broke into three pieces, viz. two wire ends, with conical fracture surfaces, and a cylindrical chip with re-entrant conical fracture surfaces and with a small hole where the apices of these cones met. Despite some resemblance to a ductile shear failure, evidence shows that the fracture is of ‘brittle’, presumably cleavage, type and that the morphology results from crack-branching (Congleton and Petch 1987). The conditions at fracture are eminently favourable for crack-branching because of (i) the high stress level (∼20% of the theoretical), (ii) the low effective surface energy for fracture, and (iii) the highly preferred crystallographic texture which provides (III) planes of low effective surface energy in suitable orientations for propagation of the branched cracks.
