Evaluation of sheet metal formability by tensile tests

The use of sheet metal forming simulations has reduced lead-times and costs for the development of new car bodies significantly. The accuracy of the simulations is to a large extent dependent on the quality of the material properties provided as input to the simulations. Improving the quality of the material properties is the key factor in order to further increase the accuracy of the simulations. This study is focused on the forming limit properties of sheet metal. A test procedure for determining the forming limit in plane was developed. The tests are carried out in a tensile testing machine. The test method enables a fast and easy determination of the forming limit and the results show small scatter. Furthermore, the influence of friction is eliminated. By modifying the specimen geometry, the test procedure can be applied to determine the complete left-hand side of the forming limit curve (FLC). The specimen geometry and the grip arrangements are essential in order to get successful tests. With inappropriate specimen design or insufficient clamping, fracture will not occur at the desired region of the specimen. The study involves both numerical and experimental work. Simulations were performed in order to find appropriate specimen design prior to testing and for performing parameter studies. One mild steel and one high strength steel was included in the study.