Influence of Adhesive Variation and Inserts on The Strength of CFRP-to-CFRP Single Lap Bonded Joint

This study aims to compare the adhesion properties of single lap joints fabricated from carbon fiber-reinforced vinyl ester composites, focusing on the effects of different adhesives and inserts. The research involved evaluating six adhesives: an aerospace-grade epoxy, two acrylic adhesives, two epoxy resins, and a vinyl ester resin. The substrates, produced via vacuum-assisted resin infusion with unidirectional carbon fiber and vinyl ester resin, were bonded using these adhesives. The impact of three inserts—3D-printed polylactic acid (PLA) nets with 0.2 mm and 0.4 mm hole spacings, and an e-glass chopped strand mat (CSM)—on the tensile properties of the SLJ was examined. Finite Element Analysis (FEA) predicted stress distributions in the joints. The results identified vinyl ester adhesive as the most suitable due to its superior lap shear strength and stiffness. Although all inserts reduced lap shear strength and modulus compared to specimens without inserts, the CSM insert showed the best performance among the inserts. The study highlights the importance of matching adhesive material to the resin used in the composite substrate, enhancing mechanical strength through better cross-linking reactions. The findings offer valuable insights for improving the design and performance of adhesively bonded joints in carbon fiber-reinforced vinyl ester composites, especially in applications requiring high strength and durability.