42nd International Deep Drawing Research Group Conference - IDDRG 2023

In the conflict between lightweight design and crash safety of high-strength steel components failure models for crash simulation have to be calibrated precisely. Especially the negative strain rate effect concerning the shear failure strain of high-strength steel sheets as well as the fact that ductile shear failure occurs immediately and without previous necking are safety-critical aspects. For an accurate prediction of shear failure strains in a wide strain rate range shear experiments must be performed from quasi-static up to crash-relevant strain rates of about 100 s-1. For this notched shear tensile specimens are frequently used, however, with the tendency to produce early failure in the notch region. Different investigations in the past propose optimized shear zone geometries with delayed or without notch failure. Though, the influence of the free length between the grips and the type of clamping also have a pronounced influence on the deformation and failure behavior of the widely used asymmetrical notched shear tensile specimens.
In this contribution a characterization concept for shear loading in a wide strain rate range based on asymmetrical notched shear tensile specimens is presented for high strength steel sheets of different strength, ductility and sheet thickness. The influence of the number of degrees of freedom in the clamping area and of the free length between the grips on the kinematic of the specimens and on the deformation and failure behavior in the shear zone are investigated in detail. As a result, shear deformation and shear fracture is supported by a clamping with translational degrees of freedom in horizontal direction or by an increase in the free length between the grips. As an experimental determination of shear failure strains evaluation strategies with and without optical measurement techniques are proposed. For this reason, a uniform method for the strain rate dependent characterization of steel sheet metals under shear loading is developed and the status of standardization is presented.