Composite bars having a low density foam core - in a reaction injection sheath for use as self-supporting automobile bumper with impact recovery

摘要

A self-supporting bar with good recovery from impact damage is made as a hollow profile produced by reaction injection moulding (RIM) around a core of cellular material. For lightweight beams, joists, etc., but esp. for automobile bumpers with intrinsic recovery from a 4 km/h impact test. Easier to mould than a channel profile, esp. if internal bracing ribs are also then required. The neutral axis of the profile is central, resulting in less stress variation under torsion. The low cavity pressures (approx. 10 bar) of RIM allow relatively low density compressible cores to be used compared with those necessary for inclusion in conventional injection moulded sheaths using materials requiring injection at e.g. 1000 bars.