ENERGY ABSORPTION CHARACTERISTICS OF AUTOMOTIVE-TYPE BEAM STRUCTURES IN HIGH-SPEED CRUSH TESTING

As part of a larger study on automotive lightweight materials / low-carbon vehicles, the University of Warwick's WMG evaluated the energy-absorption characteristics of an automotivetype U-beam structure in 3-point bending and high-speed crush testing. Variants evaluated include thermoplastic composite (laminates produced from unidirectional (UD) tapes of 60% fiber fraction by weight E-glass-reinforced polyamide 6 (PA6-GF60)), structural steel (DP600), and structural aluminum (AA5754)). The composite materials were hot stamp-molded at 100150 bar in a 60-sec cycle in a high-speed compression press. Owing to the higher fiber fraction and orientation of the reinforcements, there was very little flow forming of the materials during the molding cycle. The thermoplastic composite laminates performed well in the crush tests, with superior specific properties (notably improved strength to weight and specific energy absorption) vs. the metallic options. Additionally, failure mode for the composites was considered beneficial vs. that of the metals as material was removed from the crush zone once it was no longer able to absorb additional energy (rather than being folded back in the metallic beams). Although for a highly loaded structural application alternative polymer matrices (other than PA 6) would likely be used, the beam geometry was an ideal way to evaluate high-speed crush characteristics and energy absorption of pure composite and pure metallic components side-by-side. Further, the method used to produce the composite beams (UD tape layup plus high-speed hot stampforming) offers interesting opportunities for producing highly complex, void-free composite components with high levels of design flexibility, since fiber orientation can be varied greatly on each ply. Given the rapid molding cycle, this method would be of particular interest for mediumto-high-volume production of structural composite parts. The following paper provides detailed study parameters and results and discusses future work that might be considered based on the interesting outcomes seen in the initial study. Auto Industry Need to Lose Weight It is well known to this audience that automakers in many parts of the world face very challenging fuel economy and even more demanding greenhouse-gas emissions targets that have already begun phasing in and will become more severe over the next 12 years. In Europe, especially, failing to meet these targets is not an option since non-compliance carries very significant financial penalties so significant that they literally could put automakers out of business. Hence, the auto industry is engaged like never before in efforts both to find ways to extract higher efficiency out of internal combustion engines, seek alternative powertrain options and find new ways to take significant mass out of vehicle bodies. This has led to considerable interest in lightweight materials such as aluminum, magnesium, and composites. For the composites industry, this represents opportunities to make significant inroads into vehicle-critical applications that have never before been possible in any significant volumes.