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Energy-absorption capability of multi-axial warp-knitted FRP tubes

With fibre-reinforced plastics (FRPs) being adopted widely in many fields, low manufacturing cost with high mechanical property is urgently required. Unfortunately, traditional composite structures and manufacturing methods are very labour-intensive and not cost-effective for wide commercial applications. Therefore, multi-axial warp knitting (MWK) is attractive as a new reinforcement form in composite structures because it incorporates textile structural property and the automated pultrusion process. Additionally, this fabric, made by connecting several fibre layers by stitching yarns, is considered to enhance the property through the thickness, which also raises questions as to its effect on energy absorption. In this study, several forms of glass and carbon MWK FRP tubes fabricated by pultrusion process, which have circular or square cross-section geometries, were axially crushed by quasi-static, high compressive speed or impact crash tests to determine the energy-absorption capabilities. It is found that the energy-management capacities of FRP tubes involved in different MWK fabrics are different both in the typical load/displacement response and in terms of specific energy absorption. The cross sections were observed microscopically to clarify the effect of the constitution and the position of MWK fabric.