In 2015, the transport sector contributed to nearly 30% of the total EU-28 greenhouse gas emissions. The figure decreases to 21% if international aviation and maritime emissions are excluded. The transport industry must therefore find solutions to reduce its impact on climate change.
A promising method to reduce the weight of vehicles and therefore to their CO2 emissions is to introduce components made of lightweight composite materials, in particular carbon fibre reinforced plastics. On medium size cars, weight savings as high as 35% can be achieved by replacing steel structures with structures made of composite materials, and so without any loss in mechanical performances (strength and stiffness). In addition, it has been shown that composites structures can potentially absorb more energy than metallic structures in crash situations. Higher energy absorption in crash yields higher safety of the occupants thanks to reduced deceleration loads.
Unfortunately, reliable simulation of the crash behaviour of composite structure has been identified as one the bottle necks for the introduction of composite materials in cars. With the aim of increasing the level of confidence in crash simulations, physical tests must be carried out in order to 1) extract relevant material properties to input to the simulation tools and to 2) validate the predictions of the numerical crash simulations.
In this work, a simple test method is developed to experimentally characterise the crushing behaviour of composites. The experimental results are compared the simulation results obtained from a project conducted in parallel to this thesis. The aim of the simulations is to pre-emptively predict the crushing behaviour of composite structures in order to optimise their design in terms of energy absorption and to reduce the number of physical tests which are associated with high costs. In addition, experimental methods are developed with the aim of extracting material parameters required as input to material models in simulation codes. It is important to carefully measure the mechanical response of composite materials under shear forces (shear forces are pairs of equal and opposing forces acting on opposite sides of an object, like the forces created when using a pair of scissors). Therefore, a methodology is proposed to characterise the shear response of composite materials and to calibrate crash models for composites from the measured shear response.