Axi-symmetric compression of solid cylinders: Part II. Rapid loading conditions

Abstract

Cylinders of EN 24 steel and commercial aluminium were compressed at 0.2 and 10.0 s^-1 (rapid loading conditions). The temperature rise due to plastic deformation increased with strain rate and was significantly more in steel than in aluminium. The shape of the observed true stress-true strain curves was similar to the temperature rise-true strain plots. In steel, beyond a certain strain, the flow stress decreased with increasing strain, but in aluminium, a direct relation between the observed true stress and the true strain existed over the entire deformation range. Under rapid loading conditions the ring compression test was more reliable than the Cook and Larke method. In both materials, in specimens of constant diameter up to a true strain of 30%-40%, the compressive yield stress, σ_o, was proportional to H^1/8, where H is the instantaneous height of the specimen. Beyond this strain level, σ_o increased with the diameter-to-height ratio (as seen during slow loading). The various factors that can influence the shape of the observed true stress-true strain curves have been considered. Semi-empirical equations have been developed which ensured that the friction-corrected data covering four to five decades of strain rate superimposed fairly well, following suitable temperature or temperature and strain-rate corrections.