Influence of an optical strain rate controlled tensile testing method on mechanical properties of sheet metals

Abstract. Precise material characterization is a key factor not only for representative finite-element-analysis (FEA) in production technology, but also for product development in general. Hereby, the tensile test is of particular importance, as it can be used to determine the most relevant material parameters. These are used to ensure a better process and tool design but therefore material behavior has to be determined to a high level of precision [1]. Especially in the field of metal forming, strain rate sensitive material properties like work hardening, yield point or tensile strength need to be measured at constant strain rate to provide coherent data for material models in numerical forming simulations [2]. Current testing procedures control the strain rate with a feedback control, in which various measuring systems can be used. From this comes the necessity to investigate the influence of a strain rate controlled tensile testing procedure compared to a conventional crosshead-displacement controlled one. Thus, in the scope of this study, an optical strain rate controlled (OSRC) tensile test procedure with a digital image correlation (DIC) system, and a universal testing machine (UTM) was developed. The resulting mechanical properties and the evolution of the strain rate during the test of the steel DP600 (CR330Y590T-DH) and DC05 (CR4) were analyzed at a nominal strain rate of 0.4 %/s. In addition, the results obtained from displacement strain rate controlled (DSRC) tensile tests were compared. The results demonstrate that OSRC testing method enables the measurement of mechanical material properties at a higher level of precision in terms of constant strain rate compared to DSRC procedure.