Local Temperature Development in the Fracture Zone during Uniaxial Tensile Testing at High Strain Rate: Experimental and Numerical Investigations

Abstract

The quality of simulation results significantly depends on the accuracy of the material model and parameters. In high strain rate forming processes such as, e.g., electromagnetic forming or adiabatic blanking, two superposing and opposing effects influence the flow stress of the material: strain rate hardening and thermal softening due to adiabatic heating. The presented work contributes to understanding these influences better by quantifying the adiabatic heating of the workpiece during deformation and failure under high-speed loading. For this purpose, uniaxial tensile tests at different high strain rates are analyzed experimentally and numerically. A special focus of the analysis of the tensile test was put on identifying a characteristic time- and position-dependent strain rate. In the experiments, in addition to the measurement of the force and elongation, the temperature in the fracture region is recorded using a thermal camera and a pyrometer for higher strain rates. Simulations are carried out in LS-Dyna using the GISSMO model as a damage and failure model. Both experimental and simulated results showed good agreement regarding the time-dependent force-displacement curve and the maximum occurring temperature.

Deep drawing of DC06 at high strain rates

“…As already mentioned, the material characterisation from [1] and [8] provides the basis for the numerical investigations. Here, the determined material properties are initially verified by tensile tests at a strain rate 𝜀̇ = 50 s -1 .…”

“…The method is based on measuring auxiliary test parameters and using them as input data for the parameter identification in an inverse simulation. More recently, the identified material data was refined and supplemented with values considering more moderate strain rates (10 -1 s -1 to 10 2 s -1 ) [8].…”

“…In this context, the punch acceleration and the punch force are measured in order to characterize the process. The research results presented in [1] and [8] will be used to model the process numerically. This will provide deeper knowledge of high-speed deep drawing and enable a more comprehensive verification of the determined material parameters for strain rates in the range of up to 𝜀̇ = 100 s -1 .…”

“…Figure 2. Input parameters for numerical tensile test: Strain rate dependent flow curves (a), instability and failure strain for GISSMO-model (b) and geometry of the specimen (c) according to[8] …”