Effect of fiber volume fraction, fiber length and fiber tow size on the energy absorption of chopped carbon fiber–polymer composites

Abstract Composite materials have the potential to reduce the overall cost and weight of automotive structures with the added benefit of being able to dissipate large amounts of impact energy by progressive crushing. To identify and quantify the energy‐absorbing mechanisms in candidate automotive composite materials, modified test methodologies were developed for conducting progressive crush tests on flat‐plate composite specimens. The test method development and experimental setup focused on isolating the damage modes associated with the frond formation that occurs in dynamic testing of composite tubes. The Automotive Composites Consortium (ACC) is interested in investigating the use of chopped carbon fiber–reinforced composites as crash‐energy absorbers primarily because the low costs involved in their manufacture make them cost‐effective for automotive applications. While many in the past have investigated the energy‐absorption characteristics in various continuous fiber–reinforced composite materials, no literature is available on the energy‐absorption and crushing characteristics of chopped carbon fiber–reinforced composite materials. Hence quasi‐static progressive crush tests were performed on composite plates manufactured from chopped carbon fiber (CCF) with an epoxy resin system using compression‐molding techniques, and the effect of material parameters (fiber volume fraction, fiber length, and fiber tow size) on energy absorption was evaluated by varying them during testing. Of the parameters evaluated, fiber length appeared to be the most critical material parameter determining the specific energy absorption of a composite material, with shorter fibers having a higher specific energy absorption than longer fibers, possibly because of the increased concentration of stress raisers in the shorter fiber specimens, resulting in a larger number of fracture‐initiation sites. The combination of material parameters that yielded the highest energy‐absorbing material was identified. The test observations and trends established from this work would help support the development of low‐cost energy absorbers for the automotive industry. POLYM. COMPOS. 26:293–305 2005. Published 2005 Society of Plastics Engineers.