- Conference date: 13–17 June 2010
- Location: Pohang (Republic of Korea)
Dual‐phase (DP) steels are being used increasingly to make automotive panels because of their advantageous combinations of high ductility (for forming) and high strength (for service). However, their adoption has been limited because of failures during die tryout that are unpredicted by the usual methods of finite element modeling and forming limit diagrams. The failures, often called “shear failures” occur at regions of high curvature (low R/t) where sheet of thickness t is drawn over a tool radius R. Recent work revealed that the type of failure and the formability of DP steels depend not only on R/t, but also on strain rate, an effect derived from the propensity of these steels to locally heat in areas of high strain when strain rates are sufficiently high to limit heat transfer. The formability is reduced significantly by the thermal effect for rates greater than approximately 0.1/s. This result explains at least partially why forming limit diagrams, which are measured quasi‐statically (and thus isothermally) do not reflect the behavior of DP steels formed industrially (at typical strain rates of approximately 10/s). In order to apply laboratory test results of draw‐bend formability to industrial forming operations, the inputs to commercial finite element codes (constitutive equations, forming limits) must be adapted to the reality of the material (DP steel) and underlying physics (thermal effects on constitutive behavior). Toward this end, two procedures have been developed and tested, one numerical and one analytical. Together they predict similar forming limits and provide a path for understanding the applied formability of DP steels.
- Element formation
- Thermal effects
- Constitutive relations
- Finite element methods
Data & Media loading...
Article metrics loading...