Effect of Biaxial Work Hardening Modeling for Sheet Metals on the Accuracy of Forming Limit Analyses Using the Marciniak-Kuczyński Approach

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 high-strength steel sheet with a tensile strength of 590 MPa for a strain range from initial yield to fracture. Tubular specimens were fabricated by roller bending and laser welding the as-received flat sheet materials. Many linear stress paths in the first quadrant of the stress space were applied to the tubular specimens to measure the forming limit curve (FLC), forming limit stress curve (FLSC), and forming limit plastic work per unit volume (FLPW) of the as-received sheet material in addition to the contours of plastic work and the directions of the plastic strain rates. Differential hardening behavior was observed; the shapes of the work contours constructed in the principal stress space changed with an increase in plastic work. The observed differential hardening behavior was approximated by changing the material parameters and the exponent of the Yld2000-2d yield function as functions of the reference plastic strain. Marciniak-Kuczyński-type forming limit analyses were performed using both the differential hardening model and isotropic hardening models based on the Yld2000-2d yield function. It was found that the material model that is capable of reproducing both the work contours and the directions of the plastic strain rates measured for a strain range close to the fracture limit can give a more effective constitutive model for accurately predicting the FLC, FLSC, and FLPW.T. Hakoyama JSPS Research Fellow (Doctoral Course Students),

Advanced constitutive modeling and application to industrial forming processes

“…C and L have a structure, which is consistent with the macroscopic symmetry of the material. Finally, when yield is defined conventionally with an offset strain of a fraction of a percent, it leads to yield surface shapes in agreement with experiments [10,11]. Under the isotropic hardening assumption, the yield surface only expands because it is controlled by one parameter, the reference stress σ R or, equivalently, the effective strain, ϕ .…”

“…The effective (or accumulated) strain always increases, Yld2000-2d (a) Figure 2. Experimental of iso-plastic work contours for DP590 steel approximated by Yld2000-2d (reprinted from [11] with permission from Springer).…”

Nonlinear stress path experiment using mild steel sheet for validation of material model

“…For details of the servo-controlled tension-internal pressure testing machine used in the experiment, see [3]. For details of the measurement method of the axial and circumferential strain components, 𝜀𝜀 𝜙𝜙 and 𝜀𝜀 𝜃𝜃 , the axial radius of curvature, 𝑅𝑅 𝜙𝜙 , and the calculation method of the axial and circumferential stress components, 𝜎𝜎 𝜙𝜙 and 𝜎𝜎 𝜃𝜃 , see [20].…”

Measurement of Biaxial Deformation Behavior and Material Modeling for HI-PVC Using Multiaxial Tube Expansion Test

“…The genetic algorithm method (GA method) was used to determine the exponent M and the six coefficients 𝛼𝛼 𝑖𝑖 (i=1~6) of the Yld2000-2d yield function so that the evaluation function f shown below was minimized [7]:…”