The local formability of AHSS sheet steels can be estimated by means of the relative average reduction of cross section area (or thickness) at fracture in flat tensile specimens. A 2D/3D characterization of tensile fracture shapes is performed with an optical stereo microscope for various typical fracture shapes. The initial width to thickness ratio (w0/t0) of flat tensile samples quantifies their non-proportionality behavior. A charpy like lower and upper shelf region with a highly scattered transition zone in between at a critical w0/t0 ratio is observed when plotting the fracture area or thickness reduction versus w0/t0 ratio. The higher the w0/t0 ratio of tensile specimens (samples wider, material thinner) the higher the local fracture strain level. The higher the material work hardening ability (n-value), the higher the critical w0/t0 ratio below which high scattering in thickness - and area reduction occurs. The local tensile fracture strain is therefore strongly dependent on specimen thickness, width and work hardening behavior. This is a severe drawback for a broader use of such tensile test based fracture strain measurements.
|Journal||IOP Conference Series: Materials Science and Engineering|
|Publication status||Published - 26 Nov 2019|
|Event||38th International Deep Drawing Research Group Annual Conference, IDDRG 2019 - Enschede, Netherlands|
Duration: 3 Jun 2019 → 7 Jun 2019