PSI - Issue 51

P.A.R. Ferreira et al. / Procedia Structural Integrity 51 (2023) 115–121 P.A.R. Ferreira et al. / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction Bonding of composite panels has several applications in aircraft construction (Hart-Smith, 2011). Although there are many geometric configurations for bonded joints, the single-lap joint (SLJ) is frequently studied; however, its geometry leads to an eccentric loading which results in peel stresses (  y ) at both ends of the bond line, reducing the joint’s strength ( P max ). Modifications to the SLJ allow for reducing the eccentric loading, one of these is the joggled lap joint (JLJ), allowing for coplanar substrates. Because of this, the JLJ is employed in the construction of aircraft wings (Taib et al., 2006). The geometry of the JLJ possesses similarities to the SLJ, like similar mode mixity. Therefore, comparisons between these two geometries are made (Liu et al., 2018). In this regard, Taib et al. (2006) compared the mechanical performance of both SLJ and JLJ in flat configurations and subjected to traction, the comparisons were numerical and employed the finite element method (FEM). The SLJ was found stronger and more compliant than the JLJ. The stress distributions in the JLJ present a higher peak at the vicinity of the knee. Then, the introduction of a spew (filling the knee cavity) was analyzed. The presence of the spew had a larger effect on the  y , which was significantly reduced, hence increasing P max (Taib et al., 2006). Although Taib et al. (2006) performed a parametric study involving knee length or curvature (please see Fig. 1), adherend thickness ( t P ), thickness of the adhesive layer ( t A ), and the effect of spew fillet, the joints studied were in a flat configuration and under traction. A comparison between flat and curved lap joints was performed by Liu et al. (2018), in which the SLJ and JLJ were the joint configurations studied. Thus, three curvature radii ( R ) were analyzed, 1000 mm, 2000 mm, and 3000 mm, all of which are used in aircraft fuselages. Also, experimental tests from SLJs were used to validate the numerical models and then expanded to the other joint configurations. In this case, FEM and cohesive zone modelling (CZM) were used in the numerical models, the latter allowed to obtain P max . The reported stress distributions were in agreement with those reported by Taib et al. (2006) for flat joints. Furthermore, P max seemed unaffected by the curvature radius; on the contrary, the smaller the radius the more complaint the joint was. In both of the aforementioned studies, the effect of varying t P and overlap length ( L O ) was not investigated. In this regard, Correia et al. (2020) performed a parametric study on curved SLJs using FEM and CZM to analyze how varying t P , L O , R , and adhesive type influence P max . Triangular cohesive laws were used for the CZM modelling, which are suitable for the studied adhesive types (Campilho et al., 2013). An improvement in P max was found for larger curvatures ( R ≥2000 mm) mostly for larger L O . The stress distributions in the bond line were influenced by R , where the peak stresses increase as R is reduced; thus, a flat joint is stronger than a curved one. In addition, ductile adhesives were found more suitable for curved joints because of their ability to distribute stresses along the bond line. Although studies involving curved joints are found in the literature, as described above, in these studies, the joints were subjected to traction, while aircraft structures are also subjected to pressure (Liu et al., 2018; Sforza, 2014) which should influence stress distributions and finally P m . In consequence, this work aims to evaluate the effect of pressure ( p ), R , L O , and t P in curved JLJ by using numerical analyses based on FEM and CZM. Carbon fiber reinforced polymer (CFRP) substrates and a ductile adhesive were considered for these analyses; these materials are often employed in aircraft fuselages. 2. Methods 2.1. Geometry and materials In this work, the effect of varying L O , t P , and R on curved joggle-lap joints (JLJ) is investigated through Finite Element Analysis (FEA). A schematic representation of the geometry is shown in Fig. 1.