A critical assessment of notched tensile tests for formability mapping of AHSS sheets

Abstract

Abstract The influences of specimen geometry during the determination of local ductility have recently been investigated, using the fracture surfaces of standardized tensile tests specimens. Among the shortcomings of these specimens was the rather undefined strain path to failure, i.e. uniaxial tension followed by a deviation towards a more or less pronounced plane strain path, and the varying fracture angle, often hampering accurate image acquisition of the fracture surface. Notched tensile tests are currently used during damage model calibration for sheet metal for crash simulation. These samples exhibit a defined strain path to fracture and the notch triggers fracture predominantly perpendicular to the tensile direction. These kind of specimens have therefore been suggested as alternative to standardized tensile test specimens. However, several issues need to be addressed for notched tensile specimens as well, in addition to being an undesired additional test during e.g. quality control. These include again geometric considerations as well as the effect of different fracture types on the resulting measures of local fracture strain.