PSI - Issue 61

João C.M. Santos et al. / Procedia Structural Integrity 61 (2024) 79–88 Santos et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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materials of any thickness, and eliminate the need for drilling, which results in no stress concentrations at these points. With the most innovative adhesives, it is now possible to join most dissimilar materials, such as metals, plastics, or glass. In addition, adhesive connections are associated with lower manufacturing costs, higher fatigue resistance and high vibration damping capability (Petrie 2007). However, adhesive joints also present numerous disadvantages, such as the need for careful preparation of the adherends, a very long curing time, repair difficulties, among others (Romano et al. 2020). Various joint configurations have been proposed and used by designers. One of the most widely used geometries is the single-lap joint (SLJ), due to the simplicity of its manufacturing process (Öztoprak and Gençer 2023). This configuration has a major drawback: when subjected to tensile loads, the asymmetry of the stress transfer lines causes deflection of the joint, leading to peel stresses (  y ) at the edges of the overlap, which has a detrimental impact on its performance (Hart-Smith 1973). Aiming to overcome the aforementioned limitations, several adhesive joint configurations have been suggested, as is the case of the double-lap, scarf, stepped, among others (Petrie 2008). Over the years, various approaches have been proposed for adhesive joint strength prediction, including theoretical analyses such as Volkersen ’ s early formulation (Volkersen 1938) or numerical approaches, essentially relying on the Finite Element Method (FEM) (de Sousa et al. 2017). Currently, one of the most recognized and widely adopted methods is CZM. In combination with FEM and employing fracture mechanics concepts, this method allows for an accurate prediction of the adhesive joints’ strength. Using the CZM method it is possible to simulate the onset and propagation of cracks or delamination in composite materials, or to analyze cohesive and interfacial defects (Saeedifar et al. 2017). Several researchers have studied adhesive joints applied in the context of naval structures. Alderucci et al. (2022) experimentally analyzed the effects of different surface patterns produced by mechanical engraving on composite or aluminum adhesive joints. Four types of patterns were considered for the overlap joints (no engraving, pattern 0°, pattern 45° and pattern 45°X). The Al/Al joints showed higher strength in the 45° and 45°X patterns, while the specimen with the 0° pattern showed less strength than the "no pattern" specimen. The Al/composite joints showed higher strength when manufactured with some kind of pattern. In conclusion, in naval applications where lightweight materials need to be joined, the existence of grooves can help improve the mechanical strength of the adhesive joint. Ulus et al. (2022) performed a study of the fracture and dynamic mechanical behavior of hybrid adhesive joints after long-term ageing in seawater. The aim was to develop mode I and mode II delamination resistance and glass transition temperature ( T g ) data for basalt fiber reinforced polymers (BFRP)-aluminum hybrid joints. In addition, the adhesive was reinforced with Halloysite nanotubes to enhance fracture toughness and to slow down water absorption. After exposure, the adhesively bonded reinforced joints exhibited 36% higher fracture resistance than the non-exposed bonded joints. Darla et al. (2023) presented a study evaluating the strength of the connection between an aluminum hub and a carbon fiber reinforced polymer (CFRP) propeller blade profile for marine applications. The adhesive Araldite ® 2011 was used to bond the components, and the assembly was subjected to axial thrust conditions. The authors also carried out a numerical study given the difficulty in assessing the strength of the experimental joint due to the complex geometry and concluded that the bonded joint specimens between the aluminum hub and the CFRP propeller blade profile were influenced by the prolonged duration of ageing at the interface between the aluminum hub and the adhesive, resulting in joint failure at lower load. The present work numerically studies, by CZM, an adhesive joint applied in a canoeing boat, namely the hull/deck joint. The numerical workplan includes the currently used joint configuration and adhesive in the analysis, while different joint configurations and adhesives were also tested. 2. Materials and methods 2.1. Joint geometries In this work the goal is to optimize a bonded joint employed in kayak manufacturing. Given the complexity of the structure, it was decided to reduce the study of the adhesive joint to just one section of the vessel (Fig. 1 a). Fig. 1 (b) shows the sectional view of the section that will be analyzed. The red line refers to the hull while the blue line refers to the deck of the kayak. Currently the two parts are bonded considering a butt joint configuration (Fig. 1 c). In addition