This paper introduces a novel bio-inspired design strategy based on the optimised topology of bird bone's joint to improve the strength-to-weight ratio and damage tolerance of composite T-joints. Better structuring the constituents' materials near the sharp bends results in redistribution of stress over a larger area and reduces the stress concentration. This is done by an integrally formed support structure that is spaced apart from the main body of the Tjoint in the vicinity of the bend using a Polyvinyl Chloride (PVC) foam. The support structure acts as a buttress across the bend and improves the performance of the T-joint. The T-joints are fabricated using wet l ay up process, from 2/2 twill TC35-carbon fibre fabric/SR5550 epoxy resin, and are subjected to quasi-static and fatigue bending, and quasi-static tensile pull-out tests. The quasi-static results reveal that the bio-inspired T-joint design has huge improvements compared to a conventional T-joint in the elastic stiffness (over 60%), peak load (over 40%) and absorbed mechanical energy (over 130%). There is only 3% weight increase in the bio-inspired T-joint compared to the conventional one. The fatigue results show a significant improvement for the bio-inspired design proving the efficiency of the novel bio-inspired design for both quasi-static and cyclic loadings.
A tough polyethersulfone (PES) membrane was utilized as a novel reinforcement to improve impact performance of a carbon/glass hybrid composite. The hybrid composite was made of a glass fibre/epoxy block that was sandwiched between two carbon fibre/epoxy blocks. The PES reinforced hybrid composite was compared with an unmodified hybrid composite and a glass reinforced aluminium (GLARE) laminate. During impact testing, results showed that incorporation of PES led to an increase in toughness with a reduction in damage propagation in the investigated composite panels. Furthermore, the results showed that for low impact energy levels (6 J, 12 J and 18 J), the addition of the PES membrane reduced the area of damage by an average of 67%, compared to the virgin laminate. By increasing the impact energy level (24 J and 32 J), fibre breakage was the dominant failure mode and the PES had a negligible effect on the impact performance. A comparable load bearing performance was observed with the hybrid composites and the GLARE laminate for the low energy levels (6 J, 12 J and 18 J). However, the GLARE laminate had a better performance during high energy impacts (24J and 32 J), due to the high ductility of the aluminium plates.
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