PSI - Issue 72

L.A.S. Maia et al. / Procedia Structural Integrity 72 (2025) 43–51

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particularly applied to simulate the bond between adherends by defining a cohesive zone along the interface. This zone is characterized by a traction-separation law that defines the relationship between stress (traction) and separation at the interface (de Oliveira and Donadon 2020). In the aerospace sector, adhesive joints are extensively used for lightweight bonding solutions, and CZM help engineers evaluate joint durability and design safer, more efficient structures (Nuhoğlu et al. 2023) . It is possible to enhance joint strength and/or improve stresses by modifying geometrical or material parameters, including adherend thickness ( t P ) and overlap length ( L O ), as well as implementing modifications such as chamfers and adhesive fillets (You et al. 2008). Mixed-adhesive joints, by combining multiple adhesives, have performance advantages over single-adhesive joints (Togar and Ozenc 2023). Given the higher shear stresses at the overlap edges, it is recommended to use a ductile and flexible adhesive at these locations while employing a stiff adhesive in the central region. Early studies (Raphael 1966, Semerdjiev 1970) used mixed adhesive joints to improve stress distribution and joint strength in high-modulus adhesives. Pires et al. (2003) and Fitton and Broughton (2005) demonstrated, via FEM and experimental work, that mixed adhesive joints outperform single-adhesive joints. Faria and Campilho (2024) conducted a numerical analysis using CZM to evaluate the tensile behavior of joggle tubular adhesive joints in composite adherends using a dual-adhesive technique. The research explored different dual-adhesive configurations to enhance maximum load capacity ( P m ), displacement at P m , and energy absorbed at failure ( E f ). The study confirmed that dual-adhesive joints can improve performance metrics over single-adhesive joints. Kurennov et al. (2023) presented a topological optimization model for a symmetric dual-adhesive joint with variable outer adherend thickness. The results offered insights into optimizing joint design, balancing the stiff and compliant adhesive sections for strength and efficiency. Hu et al. (2021) examined the mechanical behavior of single-lap joints with carbon fiber reinforced polymer (CFRP) laminates under low-velocity impact (LVI) and tensile-after-impact (TAI) tests. Using a FEM-based approach with CZM and the Hashin criterion, the study simulated damage progression within the adhesive and laminate layers. Results showed that impact energy significantly affected damage extent, while longer L O could not effectively improve impact resistance. Han et al. (2024) introduced a dual-adhesive joint approach to enhance load-bearing and stress distribution under impact loading by using a ductile adhesive, Araldite ® 2015, at the joint ends, and a brittle adhesive, Araldite ® AV138, at the middle. Experimental and FEM analyses under varying impact conditions showed a strong match with a three-parameter Gram-Charlier model. Findings indicated that residual joint strength decreased as the impact energy increased, with the AV138 showing greater sensitivity. This work investigates the impact behavior of DSLJ with steel adherends. It is possible to increase the impact performance of adhesive joints without making complex design changes, with the variation of geometry parameters and adhesive combinations. Impact-loaded DSLJ were analyzed by CZM. 2. Experimental and numerical details 2.1. Joint geometry The schematic representation of the DSLJ is illustrated in Fig. 1 (a). For the dual-adhesive portions, the length of each adhesive layer is related to L O , i.e., the stiffer adhesive occupies 2/3 of L O and is positioned in the middle section, while the more flexible adhesive at the overlap edges occupies 1/3 of L O (divided into two zones; Fig. 1 b). The main geometrical parameters are listed in Table 1.

a)

b)

Fig. 1. Illustration of the DSLJ (a) and detail of adhesive portions (b).