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.
High-strength, low-alloy transformation-induced plasticity (TRIP) steels are advanced multiphase steel grades that combine high-strength levels with an excellent ductility, making them ideally suited for application in crash-relevant parts of automotive car bodies. The enhanced plastic hardening and deformability are due to a complex interaction between the microstructural phases and to the transformation of metastable austenite to martensite during plastic deformation. During high-strain-rate loading, not only the material but also the transformation will be influenced by adiabatic heating. The impact-dynamic properties of CMnAl-and CMnSi-TRIP steels were determined in the range of 500 to 2000 s ÿ 1 using a split Hopkinson tensile bar (SHTB) setup. Bake-hardening treatments were applied to study the effect of strain aging. The experiments show that strain-rate hardening is superior to thermal softening: yield stresses, deformation, and energy dissipation increase with the strain rate. Phenomenological material models were investigated to describe the strain-rate and temperaturedependent behavior of TRIP steels. Both the Johnson-Cook model and an extended version of the Ludwig model were found to give good agreement with the experimental data.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.