Forming and cutting at high strain rates Part 1: Experimental data and FE-model for an inverse material characterization of DC06 at high strain rates

Abstract

High-speed processes can lead to significant technological advantages like an increased formability, reduced springback or an improved quality of cutting edges. For conventional forming processes, quasi-static conditions are a good approximation and numerical process optimization is state of the art. However, there is still a need for research in the field of material characterization for high-speed forming and cutting processes. Production technologies with high velocities leads to high strain rates and the dependency of strain hardening and failure behavior on the forming velocity cannot be neglected. Therefore, the data of the material behavior at high strain rates is required for modelling high velocity processes. The challenge here is the measurement of relevant process quantities due to short process time that requires a very high sampling rate and the limited size and accessibility of the specimen. In this context, an inverse method for determining material characteristics at high strain rates was developed. The approach here is the measurement of auxiliary test parameters, which are easier to measure and then used as input data for an inverse numerical simulation. Two devices were implemented for different ranges of strain rates: a pneumatically driven device for strain rates up to 1.000 1/s and an electromagnetically driven accelerator for strain rates up to 100.000 1/s. The method developed by Psyk et al. is presented in detail in "Determination of Material and Failure Characteristics for High-Speed Forming via High-Speed Testing and Inverse Numerical Simulation". https://doi.org/10.3390/jmmp4020031. In order to test and comprehend the inverse method for material characterization the experimental data and the FE-model (LS-Dyna) are presented in case of the electromagnetically accelerated unit. The experimental data are the displacement curve of the hammer and the recorded elastic strain curve of the measuring body for determining the force. The FE-model contains the whole test setup (hammer, specimen, measuring body) and the determined flow curves as well as the data for the damage behavior.