Modelling Springback of Bent Hydroformed Dual- -

• Is a national laboratory within Department of Natural Resources Canada

– Relocated to Hamilton, Ontario in 2010

• Manages a national user facility for materials and manufacturing

– Pilot-scale processing facilities

– Performance assessment

– Microstructural characterization

– Computational engineering

• Has facilities in Hamilton, Ontario and Calgary, Alberta

• Has a mandate: To improve the competitive, social and environmental performance of Canadian industries that add value to minerals and metals

• Has programs in materials for transportation, pipelines, nuclear power and defense applications

Lightweighting of auto-body structures is a key objective in the materials for transportation program

• Fuel economy regulations of 54.5 mpUSg (eq. GHG) in 2025

• Significant lightweighting >30% by 2025

• One strategy is use of advanced high-strength steels and dual phase steels

• High strength, lower thickness, while retaining crash performance

• Seam-welded, dual-phase steel tubes are often bent and hydroformed

• Springback and its prediction is a key item in deployment of seam-welded dual phase tubes – problem introduced to Canmet by Variform

CanmetMATERIALS initiated a project on springback modeling of DP980 tubes

• Partners – Vari-Form and Arcerlor Mittal Tubular Products

• Funded by OERD (Office of Energy Research and Development), Department of Natural Resources Canada

• Initial proposal was to test tube material directly - can ignore work hardening - owing to tubing – 50-mm diameter, 2-mm thick DP980

• Initial proposal focused on material response and FE modeling

– kinematic hardening

Coiling of sheet and tube forming introduce residual stresses-

• Sheet and tube yield variation as high as ~50 MPa

• Residual stress at weld (ignored in current project)

• Need to use residual stress as initial condition is FE simulations

• Three-fold problem

 Initial hardening in tube

 Residual stresses in tube

 Material behavior

To model springback in DP980 tubes – starting FE mesh for tube must account for initial state owing to tube forming and material model must describe sheet material response

 Abaqus/Explicit + springback step in Abaqus/standard

 User-subroutine VDISP to “weld” edges

 Get residual stress and also work hardening

Cutting plane algorithm in Computational Inelasticity by Simo and Hughes

 Shell algorithm using the secant method (Benson and Schoenfeld)