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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.

Barely visible impact damage (BVID) occurs in composite laminates subjected to low-velocity impact. They can then exhibit significant effect on mechanical performance of laminates. Previously, it is shown, analytically and experimentally, that BVID occurs at a critical energy level and below this energy level there is no induced damage. However, repeated impact may cause BVID even below the critical energy level. This paper is a novel investigation that deals with the cyclic behaviour of quasi-isotropic glass/epoxy laminated composites under indentation, which is a quasistatic version of low-velocity impact. In particular, this study aims to investigate the ply thickness effect on matrix crack-induced delamination damage in the case of laminated composites under cyclic quasi static indentation loadings. The effect of different parameters, such as load level and ply thickness, on the damage evolution were here investigated. Tests were performed according to the ASTM 7136 standard. Since the glass layer was translucent, it was also possible to visually inspect the matrix delamination during the tests. The laminates were subjected to load levels lower than the critical load level, while there was no evidence of damages when samples were indented just once. However, by increasing the number of cycles, matrix crack-induced delamination appeared in the samples. In brief, it was observed that the ply thickness and energy level have significant effects on the intensity of the induced damage.

This paper investigates low-velocity impact response of Quasi Isotropic (QI) hybrid carbon/glass fiber reinforced polymer composites with alternate stacking sequences. Cross-ply woven carbon and glass fibers were used as reinforcing materials to fabricate sandwiched and interlayer hybrid composites. For comparison, the laminates containing only-carbon and only-glass fibers were also studied. Drop weight test was used to impact the samples. The images captured by a normal camera demonstrated that localized damages (delamination) existed within plies. The hybrid laminates had smaller load drops, smaller maximum deflection, and higher maximum load compared to the single fiber laminates. In addition, carbon outside interlayer hybrid laminate showed the highest maximum load and energy absorption, showing the significant dependence of the impact performance on hybridization and stacking sequence. It was concluded that a hybrid composite would help improve impact performance of laminated composites compared to non-hybrid composites if they are properly designed.

Joints and interfaces are one of the key aspects of the design and production of composite structures. This paper investigates the effect of adhesive–adherend interface morphology on the mechanical behavior of wavy-lap joints with the aim to improve the mechanical performance. Intentional deviation from a flat joint plane was introduced in different bond angles (0°, 60°, 90° and 120°) and the joints were subjected to a quasi-static tensile load. Comparisons were made regarding the mechanical behavior of the conventional flat joint and the wavy joints. The visible failure modes that occurred within each of the joint configurations was also highlighted and explained. Load vs. displacement graphs were produced and compared, as well as the failure modes discussed both visually and qualitatively. It was observed that distinct interface morphologies result in variation in the load–displacement curve and damage types. The wavy-lap joints experience a considerably higher displacement due to the additional bending in the joint area, and the initial damage starts occurring at a higher displacement. However, the load level had its maximum value for the single-lap joints. Our findings provide insight for the development of different interface morphology angle variation to optimize the joints behavior, which is widely observed in some biological systems to improve their performance.