Advanced use of a split Hopkinson bar setup for the extended characterization of multiphase steel sheets

Abstract. In this paper some highlights are presented of an integrated numerical and experimental approach to obtain an in-depth understanding of the high strain rate behavior of materials. This is illustrated by an investigation of the multiphase TRansformation Induced Plasticity (TRIP) steel. ‘Classic’ high strain rate tensile experiments using a split Hopkinson tensile bar setup are complemented with strain rate jump tests, tensile tests at elevated temperatures and interrupted experiments. High strain rate compression and three-point bending experiments are performed on the steel sheets as well. The results reveal the excellent energy-absorption properties in dynamic circumstances of TRIP steels. Advanced experimental setups using the Hopkinson principle provide indeed tools for validation of the material and structural properties of TRIP steel

Static and impact-dynamic characterization of multiphase TRIP steels

In this study, results are presented of an extensive experimental program to investigate the strain rate dependent mechanical properties of various Transformation Induced Plasticity (TRIP) steel grades. A split Hopkinson tensile bar setup was used for the high strain rate experiments and microstructural observation techniques such as LOM, SEM and EBSD revealed the mechanisms governing the observed behavior. With elevated testing temperatures and interrupted tensile experiments the material behavior and the austenite to martensite transformation is investigated. In dynamic conditions, the strain rate has limited influence on the material properties. Yet an important increase is noticed when comparing static to dynamic conditions. The differences in strength, elongation and energy absorption levels observed between the investigated materials can be attributed to their chemical composition. Adiabatic heating during high strain rate deformation tends to slow down the strain induced martensitic deformation. The elongation of the ferritic and austenite constituents is found to be strain rate dependent and the strain induced martensitic transformation occurs gradually in the material

Influence of specimen geometry on split Hopkinson tensile bar tests on sheet materials

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