Influence of Specimen Geometry on Split Hopkinson Tensile Bar Tests on Sheet Materials

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 present study the influence of this specimen geometry on the test results is investigated experimentally. An extensive 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. It is shown that inconsistencies between the assumed and real specimen behaviour account for these differences. For the TRIP steel considered in the study, accurate deformation values are only guaranteed if the length to width ratio of the central zone is larger than 1.25 and if the radius of the transition zone is sufficiently small.

Static and dynamic tensile behaviour of aluminium processed by high pressure torsion

“…For the dimensions of the tensile samples used here, deformation of the transitions zones of the sample, i.e. the shoulders, is limited [10]; the differences observed are mainly attributed to the slip in the clamps and a limited stiffness of the tensile device.…”

Determining the stress–strain behaviour at large strains from high strain rate tensile and shear experiments

“…The actual distribution of the deformation is dependent on both the specimen geometry and the constitutive behaviour of the material. If an appropriate specimen geometry is used, for metals showing significant hardening, the measured stress-strain curve is still a good representation of the real material behaviour because the error made by neglecting the strain in the shoulders is compensating for the non-homogenous strain in the gage section [3]. On the other hand, for metals with low strain hardening, such as Ti6Al4V, no compensation occurs and the calculated strain is an underestimation of the actual strain reached.…”

Finite-element analysis of errors on stress and strain measurements in dynamic tensile testing of low-ductile materials

“…Actually, this is not true and the sample shape and dimensions may influence these stress-strain relations. Several works interested in quantifying and correcting specimen geometry effects [2,5,12,[23][24][25][26][27][28][29][30][31][32][33].…”

“…Recently, Challita and Othman [34] investigated the case of doublelap bonded joints. Only Huh et al [12] and Verleysen et al [33] and Maringa [35] studied the case of dynamic tensile samples. In the last reference, this point is studied from an experimental point of view.…”