Knowledge of deformation limit states is the basic presumption for the proposal of all forming operations at stampings production. Deformation limit states of given material are greatly influenced by forming temperature, stress state and strain rate. Regarding the fact that common types of steel sheets are not formed under higher temperatures, size of limit deformation depends mainly on the stress state and the strain rate. For the technical community is the dependence of deformation limit states on the stress state commonly marked as forming limit diagram (FLD) and there are many experimental and numerical methods how to obtain so-called forming limit curve (FLC). Problem about strain rate on the deformation limit state is not so frequently discussed and in mostly cases it is just focused only on the research zone for uni-axial stress state. In this paper is evaluated influence of strain rate on the deformation limit state of TRIP steel at different stress states (from uni-axial up to bi-axial stress state). At experiment there is used pneumatic device which was designed and assembled at TU of Liberec and which makes possible to achieve the impact velocity of punch up to 30 ms-1. Deformation analysis of tested samples was carried out by modern contact-less system ARAMIS in combination with high-speed (HS) cameras Photron SA3 which enables to scan processes under frequency up to 100 kHz. Results of experiments are presented by forming limit diagrams for chosen strain rates and by examples of deformation distribution on tested samples.Keywords: Plastic Deformation, Stress, Strain Rate, Deformation Limit State, Optical Analysis, HS Cameras
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