Forming Limit Analyses of 590 MPa High Strength Steel Sheet Using Differential Work Hardening Model

Abstract

A servo-controlled tension-internal pressure testing machine with an optical 3D deformation analysis system (ARAMIS®, GOM) was used to measure the multiaxial plastic deformation behavior of a 590MPa high strength steel sheet for a range of strain from initial yield to fracture. Tubular specimens were fabricated from the sheet sample by roller bending and laser welding. Many linear stress paths in the first quadrant of stress space were applied to the tubular specimens to measure the forming limit curve (FLC) and forming limit stress curve (FLSC), in addition to the contours of plastic work and the directions of plastic strain rates. It was found that the shapes of the measured work contours changed with the increase of work hardening (plastic work). The observed differential work hardening (DWH) behavior was approximated by changing the material parameters and the exponent of the Yld2000-2d yield function (Barlat et al, 2003) as a function of the equivalent plastic strain. The FLC and FLSC calculated using the Marciniak-Kuczyński-type (M-K) approach with the DWH model were in good agreement with the measurement.