A uniform method for the characterization of shear fracture strain for high-strength steel sheets under quasi-static and crash loading

Abstract

In the conflict between lightweight design and crash safety of high-strength steel components failure models for crash simulation have to be calibrated precisely. To predict 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. In particular, asymmetric notched shear tensile specimens have proven useful for this purpose in previous investigations. Using this type of shear specimen, a characterization concept for shear loading in a wide strain rate range is presented for high strength steel sheets of different strength, ductility and sheet thickness in this contribution. Within a round robin test of different laboratories the influence of the degrees of freedom in the clamping area and the free clamping length on the kinematic of the specimens and on the deformation and failure behavior in the shear zone are investigated in detail. The main outcome is that the disadvantages of a fix clamping in terms of shear deformation, shear fracture and homogeneity of the shear zone can be compensated by a large free clamping length. An evaluation method based on digital image correlation (DIC) is presented, which enables an operator- and laboratory-independent determination of shear strains up to failure.