In August 2005, National Highway Traffic Safety Administration
(NHTSA) proposed to increase the roof strength requirement under
Federal Motor Vehicle Safety Standard (FMVSS) 216 from 1.5 to 2.5
times unloaded vehicle weight (UVW). To meet the new requirement
with a minimum impact on vehicle weight and cost, the automotive
community is working actively to develop improved roof
architectures using advanced high strength steels (AHSS) and other
lightweight materials such as structural foam. The objective of
this study is to develop an optimized steel-only solution with low
material and part-manufacturing costs.
Since the new regulation will present a particular challenge to
the roof architectures of large vans, pickup trucks and SUVs due to
their large mass and size, a validated roof crush model on a
B-Pillar-less light truck is utilized in this study. Optimized
steel-only solutions are investigated with the application of CAE
optimization technology and AHSS including dual phase (DP) steels
up to 980 MPa tensile strength and boron steel for hot stamped
parts. HyperStudy® optimization software and LS-DYNA® nonlinear
finite element software are utilized together to search for the
optimal design. Steel inserts are designed and added at critical
locations to improve the load-carrying capacity. Material and gauge
optimizations are also performed on key roof components to minimize
the vehicle weight while meeting the enhanced roof crush load
requirement. The optimized steel-only solutions are compared to the
alternative designs using nylon inserts.