Investigations on the temperature-deformation behaviour of advanced high-strength steel sheets (AHSS) under shear loading from nearly isothermal to the adiabatic state

Abstract

Steel sheet materials tend to form adiabatic shear bands at high strain rates, leading to material separation. This phenomenon is used in adiabatic blanking processes, but it should be avoided in crash safety applications. This paper deals with investigations on the main influence parameters on adiabatic heating of advanced high strength steel sheets (AHSS) under shear loading. Focussing on the effect of applied strain rate, experimental investigations were carried out from quasi-static loading up to crash-relevant strain rates. Strain and temperature fields were recorded using a high-speed video camera and a high speed infrared camera, thus enabling a detailed analysis of the generated heat and the heat transport mechanisms in the deformed zones. The examination showed that the isothermal adiabatic transition under shear loading ranges between strain rates of 0,01 s-1 up to 50 s-1 for the investigated materials and thus at higher strain rates compared to tensile loading. This indicates an extreme strain localization in shear bands compared to necking zones at comparable strain rates. Consequently, larger temperature gradients occur in the shear zone, which significantly affect the heat transfer mechanisms. Furthermore, with increasing strain hardening, the isothermal-adiabatic transition region is also shifted to higher strain rates due to a slowdown of the strain and temperature localization process. Based on these results, local heating and the occurrence of adiabatic shear bands can be estimated without costly thermomechanical coupling finite element simulations (FE-Simulations).