Crushing behaviour of carbon fibre lattice structures

Composite lattice truss core sandwich structures have been focus of investigation in recent years. In this paper, a recently-developed manufacturing method is presented to manufacture carbon fibre reinforced composites (CFRC) lattice truss sandwich panels using a combination of lost mould method and vacuum assisted resin infusion process (VARTM) technology in one manufacturing operation ensuring core and facesheets are connected integrally. Here, a fiber stitching operation was performed through a series of holes drilled into a salt slab (lost mould) ensuring that there are no fibre discontinuities in entire lattice structure. The dry fibre assembly was subjected to VARTM process to infuse resin into the vacuum system and allowed to cure. Following this method, columnar and pyramidal based topologically modified lattices were manufactured with different fiber volume fractions and relative densities. Quasi-static compression tests were conducted on the composite lattice specimens and their strength and failure modes were observed. The tests results showed that the columnar lattices offer specific strengths in the range of 41.5 – 109 MPa for a fixed fiber volume fraction of 0.14. The values were higher when fiber volume fraction in the columnar lattice members was increased to 0.37, there being in range of that 89.7 – 132.1 MPa. However, pyramidal lattices have shown that at a fiber volume fraction of 0.44, the structures exhibit comparable specific strength properties to those of the columnar lattices. The failure modes in the columnar lattices were buckling of the rods, crushing and fracture. Similar failure modes were observed in the pyramidal lattices, although the failure mode transitioned from buckling to splitting and fracture as the relative densities was increased. This manufacturing method offers significant potential for fabricating more complex lattice truss cores, providing the fiber are aligned in the direction of the trusses to give efficient strength capability.