AN EXPERIMENTAL-TECHNIQUE FOR SHEAR TESTING AT HIGH AND VERY HIGH-STRAIN RATES - THE CASE OF A MILD-STEEL

A new experimental technique is reported in this paper. The new techni que is based on direct impact of a long rod on a modified double shear specimen which is supported by a Hopkinson tube. Application of the H opkinson tube and optical extensometer makes it possible to determine a whole history of the specimen deformation: tau(t), GAMMA(t), GAMMA(t ) or tau(GAMMA), GAMMA(GAMMA). A flat MDS specimen is loaded directly by a projectile with the impact velocity from approximately 1 to appro ximately 200 m s-1. The nominal strain rates vary accordingly from 10( 3) to 10(5) s-1. The main advantages of this technique lie in (a) dire ct impact on an MDS specimen which practically eliminates the risetime period which occurs in the incident bar and transmitter tube configur ation, and (b) application of an optical extensometer for non-contact direct measurement of the shear strain as a function of time GAMMA(t). An account is given of preliminary experiments in which the upper and lower yield stresses of low alloy steel XC18 were determined at shear strain rates from 10(-4) to 5 x 10(4) s-1. The experimental results a re compared with those from the other literature sources. A brief disc ussion is offered on possible sources of pseudoviscosity and rate sens itive threshold stress.