Impact Torsion Experiments

Abstract

In 1936, the author, working under Professor W. Mason, attempted to obtain a complete torque-time curve for impulsive torsional fracture and thus to obtain quantitative information on both yield and rupture phenomena. The forces were measured by piezo-electric methods and recorded photographically against a uniform time base. The results (hitherto unpublished) showed that while the maximum stresses did not differ appreciably from the static values, the yield point was always greater when the straining rate was high (about 60 radians per sec.). In recent years the author has carried out a series of experiments at much lower speeds (4 radians per sec. and less) to explore the region between static and impact conditions. The lower speed has brought the upper yield well within the scope of the crystal gauge. Results from a range of mild steels show that both upper and lower yield points increase progressively with the rate of straining, and logarithmic plotting suggests that, for the steels tested, a transition from static to impact conditions takes place at a straining rate of about 1/10 radian per sec. or less.