Local formability assessment of AHSS steels with shear cut tensile tests

Abstract

Abstract As an alternative to the ISO16630 hole expansion test, the punched tensile test is increasingly popular for edge crack characterization of AHSS advanced high strength steels. In this investigation the reduction of area as well as thickness reduction at fracture in the vicinity of left/right sample edge fracture sides has been determined by means of light optical microscopy according to the Hance local formability test methodology for 10% to 40% cutting clearance in (both sided) sheared cut vs. spark eroded or milled edge conditions. An edge crack index has been defined based on the tensile sample fracture shape. Local formability tensile properties based on area reduction or average thickness reduction are more sensitive to edge condition than Axx fracture elongation values. The determination of the reduction of area at fracture is however challenging due to projection issues. The % thickness reduction at minimum thickness as well as at left/right thickness in cut edge vicinity may offer some additional information about edge crack initiation and final fracture. The shear punch edge quality (punch and die tool wear, target vs. actual clearance) should be closely monitored for accurate reproducible testing results.