Axi-symmetric compression of solid cylinders: Part I. Slow loading conditions

Abstract

The analytical and experimental methods of determining the compressive yield stress of materials have been reviewed briefly. Using aluminium, EN 24 steel, lead and a tin-lead eutectic alloy, the areas of applicability of the Cook and Larke method (including its modified form for strain-rate sensitive materials) and the ring compression test have been delineated. Under conditions of sliding friction, both the methods give similar values for the coefficient of friction. Under sticking or near-sticking friction conditions, the modified Cook and Larke method is more accurate, because the interpretation of the ring compression test ignores the strain-rate sensitivity of the flow stress. Within the experimental range, the coefficient of friction and the interface friction factor were unaffected by the changes in the strain level, strain rate, grain size and efficacy of lubrication. Under slow loading conditions, the effect of specimen dimensions on the flow stress could be attributed entirely to a change in the frictional contribution. The strain and/or strain-rate hardening behaviour, as well as the grain size dependence of the flow stress of the different materials, were consistent with earlier well-known results.