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

Geometrical Scaling Effects in the Mechanical Properties of 3D-Printed Body-Centered Cubic (BCC) Lattice Structures

This paper investigates size effects on the mechanical response of additively manufactured lattice structures based on a commercially available polylactic acid (PLA) polymer. Initial attention is focused on investigating geometrical effects in the mechanical properties of simple beams and cubes. Following this, a number of geometrically scaled lattice structures based on the body-centered cubic design were manufactured and tested in order to highlight size effects in their compression properties and failure modes. A finite element analysis was also conducted in order to compare the predicted modes of failure with those observed experimentally. Scaling effects were observed in the compression response of the PLA cubes, with the compression strength increasing by approximately 19% over the range of scale sizes investigated. Similar size-related effects were observed in the flexural samples, where a brittle mode of failure was observed at all scale sizes. Here, the flexural strength increased by approximately 18% when passing from the quarter size sample to its full-scale counterpart. Significant size effects were observed following the compression tests on the scaled lattice structures. Here, the compression strength increased by approximately 60% over the four sample sizes, in spite of the fact that similar failure modes were observed in all samples. Finally, reasonably good agreement was observed between the predicted failure modes and those observed experimentally. However, the FE models tended to over-estimate the mechanical properties of the lattice structures, probably as a result of the fact that the models were assumed to be defect free

Thermal and mechanical properties of thermoplastic cassava starch/beeswax reinforced with cogon grass fiber

The aim of this paper is to investigate the effect of cogon grass fiber (CGF) on the thermal and mechanical properties of thermoplastic cassava starch (TPCS)/beeswax matrix. The alteration of TPCS/beeswax reinforced with cogon grass fiber was performed by incorporating various amount of CGF (0,10,20,30,40 wt.%) into the polymer matrix. The samples were then evaluated using thermogravimetric analysis and tensile test. The findings showed that the thermal properties of the composite were slightly improved as the CGF content increase. The mechanical test showed that the tensile strength and tensile modulus increased with the addition of the CGF. However, the elongation at break showed a decreased pattern following the increasing content of CGF compared to the 0% of fiber content. In general, the findings from this study have shown that the TPCS/beeswax reinforced with the CGF composite has improved the functional properties of the composites compared to the TPCS matrix