Discussion of the Forces Acting in Tension Impact Tests of Materials

Abstract

Abstract A method of measuring the forces acting on a specimen during a tension impact test is described briefly in this paper. In this method a dynamometer is used in tests made in a rotary impact testing machine in which impact velocities up to approximately 200 fps can be attained. The method of computing force-time relations prevailing in a specimen subjected to tension impact is described from the standpoint of the theory of the propagation of elastic and plastic strain. The method is applied to a specific material to illustrate the computing procedure. A theoretical stress-time diagram has been computed for a specimen of SAE 1020 cold-rolled steel 0.300 in. diam and 8 in. long for an impact velocity of 150 fps. This computation has been made (a) on the basis that the dynamometer is rigid, and (b) on the basis of a dynamometer mounted in a manner approximately equivalent to that in the actual equipment. The diagrams are for the stress-time relations at the fixed end of the specimen. The computed curves are compared with an experimental force-time diagram obtained on the same material. The general shape of the experimental diagram is quite similar to the theoretical diagram computed on the basis of a nonrigid dynamometer.