The effects of processing variables on the energy absorption of composite crash structures
Environmental pressures are driving automotive manufacturers towards light weight cost efficient structures. Composite materials have been shown to display high specific energy absorption levels thus offering opportunities for mass reduction over conventional steel structures. Whilst composites display these specific advantages, the mechanisms by which energy is absorbed are more complex and are preventing widespread acceptance of composite structures. This work aims to further scientific understanding of the crushing process and provide realistic data for a wide range of processing conditions and commonly used materials. The main objectives of this study were to quantify the effect of industrial manufacturing conditions on the crush performance of composite structures, and to correlate the performance to a number of in-plane laminate properties. The manufacturing parameters considered are constituent material related (mould temperature, post-cure time and resin composition), interlaminar toughness related and process related (amount of binder and voidage). The work presented in the thesis reports the results of axial crushing experiments, in-plane and inter-laminar testing performed on composite parts made from glass reinforced polyester and vinylester resins. The preforms were made from 2 fabrics; a continuous filament random mat and a 0/90° non crimp fabric. All parts were produced by resin transfer moulding (RTM) under conditions which were representative of medium volume industrial processing. Constituent material results demonstrate clear advantages associated with the use of vinylester resin and that while relationships between all in-plane properties and the crush performance can be observed, the ultimate compressive stress is the most reliable indicator of this performance. Interlaminar toughness enhancement shows great promise for tailoring of the crush curve and increase in energy absorption of non-crimp fabrics. Results for the processing work are directly applicable to existing manufacturing and demonstrate the potential for real reductions in cycle time and increase in properties.