SN5150,
Are you sure that strength-to-weight is the only parameter of interest? What about stiffness? For spaceframe structures that are extremely stiff (fully constrained truss-type frames), strength-to-weight becomes the limiting parameter, as long as buckling has been adequately addressed. Metals with the highest strength-to-weight ratio are maraging steels and several metastable Beta titanium alloys. These metals will also have appreciable ductility, fracture toughness, and yielding behavior under dynamic events like rollovers, crashes, etc. Composite structures based on toughened epoxies reinforced with carbon fibers, aramid fibers, or S glass fibers (S is structural glass vs. the normal Electical glass) will all have high strength to weight ratios, but will not show similar fracture toughness, ductility, or yield behavior. Aerospace and high performance racing applications still use honeycomb sandwich construction (skins of fiber-reinforced epoxy laminated over a honeycomb core of aluminum or nomex) for crash structures, which can be difficult to integrate into an open frame architecture-- they are distinctly closed, monocoque structures. Anyway, you should be able to get some preliminary information on strength and density from Matweb, or perform a keyword search on Eng-tips for maraging steel to find additional information in this area.
