Low Velocity Impact Behavior of 3D Hollow Core Sandwich Composites Produced with Flat-Knitted Spacer Fabrics

Impact failure of newly-designed textile composites from three-dimensional integrated weft-knitted spacer fabrics (3D-IWK-SF) was aimed to be investigated under drop weight loading. Using a computerized flat knitting machine, three different 3D-IWK-SF as the composite reinforcements varied in their cross-sectional shapes, were produced from E-glass yarns. The produced fabrics were then impregnated with unsaturated polyester resin via the vacuum assisted resin transfer molding (VARTM) which eventually results in 3D integrated spacer weft-knitted sandwich composites (3D-IWK-SC). For comparing the results, an additional core/sheet sandwich composite composed of the same sheet and the polyurethane foam core was also fabricated. From the resulted values of contact force, it was concluded that 3D-IWK-SC of V-shaped crosssection had the highest resistance against low velocity impact load. On the other hand, the evaluated damaged area of both Vshaped 3D-IWK-SC and the foam core sandwich composites were lower than the other samples. Moreover, it was observed that matrix crack-formation in face-sheets of all samples as well as transversely propagated cracks at the connecting layers of 3D-IWK-SCs were of dominant failure modes under drop weight impact test, while no sign of face-core de-bonding were observed for all type of 3D-IWK-SCs.