Youngs Modulus Determination for Spring Back Evaluation of Cold Formed Parts

Co-authors DŽUGAN Jan, PROCHÁZKA Radek

Cold forming of net shape or near-net shape manufacturing is progressive trend reducing material consumption and additional costs in material forming. If net shape or near-net shape manufacturing has to be attained, very high production accuracy has to be attained. The technology has to take into account a wide range of influencing parameters/properties. One of the critical issues is spring back especially in the case of cold forming. Nowadays, spring-back effect of cold parts is usually predicted using Finite Elements Analysis (FEA). To successfully predict spring-back effect, however, it is necessary to obtain relevant material data with highest accuracy possible. This is still the most problematic part of the whole problem. In this paper, the authors focus on Young modulus determination using three different methods and their subsequent comparison. First, standard method of tensile tests according to CSN EN ISO 6892-1 which gives the static modulus was considered with the use of mechanical extensometers as well as noncontact video and laser extensometer. Secondly, a variation of this method using digital image correlation to evaluate surface strains to calculate another version of static modulus was suggested. Last but not least, dynamic Young modulus was evaluated according to ASTM E1876-97 by analysis of free vibrations of a rectangular specimen after a special hammer strike.