Behavior of a Novel Cyclic Olefin‐Based Hot‐Melt Adhesive in <scp>CFRP</scp> Adhesive Joints Compared to Conventional Epoxy‐Based Structural Adhesives

ABSTRACT A recently developed hot‐melt adhesive (HMA) based on cyclic olefin chemistry, supplied as a transparent, non‐tacky thermoplastic film with a distinctive polymer microstructure, was evaluated in this study. The aim was to compare the performance of the HMA with commonly used epoxy‐based structural adhesives in adhesively bonded composite joints. Composite single‐lap joints (SLJs) were used as test specimens, effectively representing adhesion quality and overall joint performance. Two epoxy‐based adhesives (paste and film forms) served as benchmarks, while the HMA was tested to highlight its advantages and limitations. All joints were evaluated under four‐point bending at various loading rates. Under static loading, the HMA showed comparable performance to the epoxy adhesives, although the failure mode shifted from delamination in epoxy joints to adhesive failure in HMA joints. Under high‐rate four‐point bending, the HMA demonstrated superior strength and toughness, reflecting its pronounced rate‐dependent behavior. Fatigue tests under four‐point bending were also conducted for all adhesive systems, and their performance was evaluated comprehensively. Furthermore, HMA SLJs initially tested under quasi‐static and fatigue loading were re‐bonded and retested under quasi‐static loading to assess performance after a second curing cycle, demonstrating the reusability advantage of the HMA. Overall, the study highlights that the HMA provides competitive static performance, enhanced high‐rate strength, and potential for re‐bonding, making it a promising alternative to conventional epoxy adhesives in composite joint applications. This work emphasizes the benefits of thermoplastic HMA in terms of mechanical performance, fatigue resistance, and reusability, supporting its adoption in advanced structural bonding of composites.