A new specimen for investigating shear fracture strain

In the automotive industry, the edge formability of a sheet metal part is usually defined by the Forming Limit Diagram despite its shortcomings. The success of the FLD can be explained by its easy applicability for dedicated FEM codes and physical measurements. However, the diagram covers a large range of strain paths of sheet metal parts, it does not fully specify the edge formability in the negative minor strain field, which is important for drawing operation with a small radius. This explains the great attention paid in the recent decade to the development of the shear test. Manufacturing the latest shear specimens (such as Butterfly or Smiley) is a significant cost and time-consuming process. In this paper, the applicability of a new flat shear specimen geometry was investigated, using finite element methods and physical measurements. Since the cracking can initiate on the boundary section of the flat specimen, first the effect of three different manufacturing methods (Wire EDM, laser cutting and drilling) were investigated. Based on the results a new flat specimen was created and optimized by finite element methods. The shear fracture strain of the new specimen was measured by an optical measurement system and the results were compared with the fracture strain of the smiley specimen.