TENSILE DUCTILITY AND FRACTURE OF SUPERPLASTIC ALUMINUM-SIC COMPOSITES UNDER THERMAL CYCLING CONDITIONS

The tensile and fracture creep behavior of aluminum-SiC composites has been evaluated under isothermal and cyclic heating conditions. The tr ue strain to fracture under thermal cycling conditions is shown to dec rease linearly with the logarithm of the applied stress. This trend is unexpected since the strain rate sensitivity exponent, m, is high (ty pical of superplastic materials) and constant over the range of stress es studied. The results obtained are explained by a fracture mechanics model in which the crack size increases by a strain-induced mechanism . The results are compared with similar behavior obtained in superplas tic ceramics.