Experimental and numerical study of the response of steel sheet Hopkinson specimens

Abstract
In recent years numerous studies on the high strain rate behaviour of sheet materials using split Hopkinson tensile bar set-ups have been reported in literature. For these experiments mostly dogbone-shaped specimens are used, however, widely divergent specimen dimensions can be found. In the presented study the influence of this specimen geometry on the test results is investigated experimentally and numerically. A series of Hopkinson tests on a steel sheet material using different specimen geometries is performed. An advanced optical technique is used to obtain the true distribution of the deformation along the length of the specimen. Important issues such as the contribution of the deformation of the transition zones to the total deformation and the (non)homogeneity of the strain in the specimen are thus determined. From the experiments it is clear that the influence of the specimen geometry on the observed behaviour cannot be neglected. The inconsistencies between the assumed and real specimen behaviour account for these differences. From finite element simulations, aspects not revealed by the experiments, such as the influence of the specimen geometry on the existence of non-axial stresses and their influence on the specimen behaviour, are obtained.