Plane strain formability analysis of automotive body structures using DYNA2D

At the early design phase, formability evaluation of automotive panels is usually needed before the complete geometry is defined in order to differentiate between design alternatives. The designs of these panels at early phases are rapidly changing with few defined sections. This creates the need for fast formability evaluation techniques with minimum geometric definition, modeling, analysis time and effort to effectively guide the design for manufacturability process. This paper introduces the plain strain approach as a tool for formability prediction of automotive body structural panels at early design phases. The plane strain approach was introduced based on the assumption that for a certain section location of a stamped panel member, the minor strains are relatively small and negligible in comparison with the major in-section strains. For automotive panels this approach can save time, cost and effort in analyzing sheet metal formability, since only few sections of the entire panel need be analyzed. It is also the most logical approach, when only few sections are defined and their geometries are rapidly changing. During analysis, the state of plane strain can be easily induced on a narrow strip of the sectional analysis model, through the use of symmetry and boundary conditions. The accuracy and applicability of the plane strain approach was investigated by comparing the DYNA2D analytical results with the measured results of actual automotive body side panels. The results of the study were satisfactory and suggested that the plane strain approach can be used to evaluate the formability of the panel members with fairly constant cross-section along the length. When the members have cross-sectional variation along the length, several sections are needed to obtain meaningful results. For the plane strain approach to achieve accurate strain distribution over an entire simulated section, the geometric modeling of the draw bead is necessary.