Open AccessLocal fracture strain measurement in AHSS uniaxial flat tensile tests considering specimen geometry and fracture morphology
Author(s) -
P. Larour,
Leopold Wagner,
A. Felbinger,
J. Angeli
Publication year - 2019
Publication title -
iop conference series. materials science and engineering
Language(s) - English
Resource type - Journals
eISSN - 1757-899X
pISSN - 1757-8981
DOI - 10.1088/1757-899x/651/1/012016
Subject(s) - materials science , ultimate tensile strength , composite material , fracture (geology) , formability , tensile testing , charpy impact test , strain hardening exponent
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 (w 0 /t 0 ) 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 w 0 /t 0 ratio is observed when plotting the fracture area or thickness reduction versus w 0 /t 0 ratio. The higher the w 0 /t 0 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 w 0 /t 0 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.