Mechanical analysis of unidirectional glass fibre reinforced epoxy composite joints manufactured by adhesive bonding and co-curing techniques

• Effective surface treatment: roughening both A-sides of thin composite adherents improved shear strength by 38.2%. • Co-curing increases strength: co-cured single lap joints showed a 49% increase in shear strength compared to adhesive joints • Optimal adhesive thickness: An adhesive layer of 2 mm yielded the highest joint strength; 1 mm, 4 mm, and 8 mm showed lower performance. • Fracture behaviour in co-curing: co-cured joints with thin adherent failed by debonding, and thick ones by delamination, supporting higher shear capacity. • Flexural performance: a hybrid beam with adhesive and co-cured joints sustained full flexural load; failure began in the upper spar cap. The finite element model accurately predicted structural behaviour and supports full-scale design. The use of epoxy powder in composite laminate fabrication may provide an efficient and alternative solution to traditional resin infusion techniques for manufacturing thick and complex composite parts in the aerospace, automotive, and marine industries. This study demonstrates the feasibility of this technology for joining of unidirectional glass fibre-epoxy composite parts with desired mechanical strength through co-curing process. The effectiveness of co-curing techniques for joining thin and thick composite laminates were assessed and compared with adhesive joints. The challenges and parameters relating to both manufacturing methods were discussed. The results showed that co-curing bonding is an effective bonding method alongside adhesive joints. The co-curing joints showed a 49% higher shear strength than optimised adhesive joints. To further demonstrate the effectiveness of the results, one beam, with co-curing and adhesive bonding joints, was manufactured as a demonstrator of a bowfoil. The beam was then tested under four-point bend tests to characterise the flexural strength and damage propagation area. The results revealed that both bonding types withstand the ultimate loads, with the composite part failing. A finite element model was proposed, and its accuracy was verified against the test results, with an average difference of 8.9% in ultimate fibre direction strain.