Enhanced Dynamic Energy Absorption in Carbon/Aramid Composite Tubes with Axially Graded Impedance

This study investigated the effects of carbon-aramid arrangement and strain rate on crush tube energy absorption. Round composite tubes, each consisting of three layers of fabric, were made using four different carbon-aramid hybridization schemes. Hand lay-up and compression bladder molding were used in the fabrication process. In two hybridization schemes, carbon-aramid fabrics were arranged to evaluate the effect of axially graded impedance relative to the tube impact end. Static crush and low-velocity impact (LVI) tests were conducted, and the force-displacement responses, energy absorption characteristics, and failure modes were compared. Test results revealed that energy absorption was 20% to 60% higher in the low-velocity impact test than in static crush, regardless of the hybridization schemes. In both tests, material arrangement played a surprisingly important role that was comparable to the tube carbon content in energy absorption. Maximum specific energy absorption of 26.21 kJ/kg was obtained in the hybridization scheme with the low impedance at the initiator end, with increasing impedance towards the impact end. This amount of specific energy absorption is almost equivalent to the other hybridization scheme that has twice the carbon fiber content. This scheme facilitated initial damage modes that favored progressive folding in the rest of the tube. This study presents the idea of enhancing the crashworthiness of crash boxes using axially graded impedance material arrangement. It is recommended that the idea be subjected to more testing for verification and potential commercialization.