Development of a new cyclic shear test setup for characterizing thin metallic foils

Abstract

Recent developments aimed at reducing cumulative CO2 emissions in the energy sector and e-mobility are leading to an increase in the production volumes of formed components made from thin metallic foils used for alternative energy supply concepts. Thus, components such as bipolar plates in fuel cells and a variety of parts in e-motors and batteries are being manufactured in ever higher quantities and thinner material thicknesses. As a consequence, this leads to increased challenges regarding the feasibility and robustness of required production processes. Finite Element Analysis in fact do represent a useful tool in this context to predict and to optimize expected outcome of forming processes virtually at an early stage of development. The prediction accuracy of such simulation codes thereby significantly depends on the precision of modelling the sheet metal material behavior, which is derived from special characterization methods. However, classical approaches to mechanical characterization usually tend to fail in case of thin metallic foils, especially when the structural stability of the specimen becomes an important factor for the validity of the characterization test. The cyclic shear test, for example, is used to determine the hardening behavior of the material to be characterized, but appear unsuitable for metallic foil investigations unless a special anti-wrinkling device is used. Current anti-wrinkling devices proposed in literature must be attached directly to the deforming area of the specimen and cause further weaknesses. Attaching such devices to prevent the specimen from wrinkling requires remarkable skills of the operator to avoid deforming of the specimen even before testing. Against this background, this paper presents a novel experimental setup, which increases the structural stability of the cyclic shear specimen and thus prevents wrinkling. Structural stability of specimen is enhanced by curving the gauge area of the specimen to drastically suppress the tendency to wrinkle. As a proof of concept FE-simulations with LS-Dyna were performed in this study to verify this novel idea and to design a suitable experimental setup.