Design and Evaluation of an in-Plane Shear Test for Fracture Characterization of High Ductility Metals

Abstract

Fracture characterization of automotive metals under simple shear deformation is critical for the calibration of advanced fracture models employed in forming and crash simulations. In-plane shear fracture tests of high ductility materials have proved challenging since the sample edge fails first in uniaxial tension before the fracture limit in shear is reached at the center of the gage region. Although through-thickness machining is undesirable, it appears required to promote higher strains within the shear zone. The present study seeks to adapt existing in-plane shear geometries, which have otherwise been successful for many automotive materials, to have a local shear zone with a reduced thickness. It is demonstrated that a novel shear zone with a pocket resembling a “peanut” can promote shear fracture within the shear zone while reducing the risk for edge fracture. An emphasis was placed upon machinability and surface quality for the design of the pocket in the shear zone. A mild steel and two high strength aluminum alloys were tested using both conventional and modified shear geometries with digital image correlation techniques utilized for strain measurement. The modified geometry increased the equivalent fracture strains of the low and medium ductility aluminum alloys by a respective 24% and 41% relative to the conventional geometry. For the mild steel, the conventional shear geometry failed prematurely at the edges. Edge failure still occurred in the modified geometry but achieved an equivalent strain magnitude of over 300% which is a 62% increase relative to the conventional geometry.