The energy-absorbing characteristics of Novel tube-reinforced sandwich structures

This thesis presents the findings of a research study investigating the energy-absorbing characteristics of the foam sandwich cores reinforced with aluminium, steel and carbon fibre-reinforced polymer (CFRP) cylindrical tubes under quasi-static and dynamic loading conditions. Initial testing focused on establishing the influence of the length and inner diameter to thickness ratio (D/t) of the tubes on their specific energy absorption (SEA) characteristics. Following this, individual aluminium, steel and CFRP tubes were embedded in a range of foams with varying densities and the SEA was determined. The effect of increasing the number of tubes on the energy-absorbing response was also studied. In addition, preliminary blast tests were conducted on a limited number of sandwich panels. It has been shown that the stiffness of the foam does not significantly enhance the energy-absorbing behaviour of the metal tubes, suggesting that the density of the foam should be as low as possible, whilst maintaining the structural integrity of the part. Tests on the CFRP tube-reinforced foams have shown that the tubes absorb greater levels of energy with increasing foam density, due to increased levels of fragmentation. Values of SEA as high as 86 kJ/kg can be achieved using a low density foam in conjunction with dense packing of tubes. The SEA values of these structures compare very favourably with data from tests on a wide range of honeycombs, foams and foldcore structures. The crushing responses of the structures were predicted using the finite element method Abaqus and the predictions of the load–displacement responses and the associated failure modes are compared to experimental results. It is proposed that these models can be used for further parametric studies to assist in designing and optimising the structural behaviour of tube-reinforced sandwich structures