PSI - Issue 83

R.J.B. Rocha et al. / Procedia Structural Integrity 83 (2026) 179–186

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1. Introduction AM, commonly known as 3D printing, refers to a group of techniques capable of building components through the successive deposition of material layers, using a three-dimensional (3D) model (Gibson et al. 2021). AM has emerged as a substitute of traditional subtractive methods, which remove material of a solid block to shape an object, due its less material waste generation, creation of parts with complex geometries, and fast structural optimization (Kumar and Prasad 2021). These characteristics reduce the time-to-market (Dilberoglu et al. 2017). AM began in the 1980s with Hideo Kodama’s 1981 conceptual development, followed by Charles Hull’s invention of stereolithography in 1984 and the 1987 commercial launch of the SLA-1 printer (Pragana et al. 2021). The ISO/ASTM 52900 standard classifies all AM processes according working principle and material into seven categories (Izdebska- Podsiadły 2022) . Material Extrusion (MEX), also known as Fused Deposition Modelling (FDM), is the most widely used technique due to its low operational cost and ease of handling (Bikas et al. 2016). In this technique, a thermoplastic filament is heated and extruded through a nozzle, producing a part layer by layer directly from a 3D model. The part integrity is function of the material moisture, nozzle temperature, bed temperature, infill pattern, layer thickness, and print speed (Izdebska Podsiadły 2022) . The FDM technology remains largely constrained to small-scale components because of limited interlayer adhesion, slow and uneven solidification, difficulty maintaining precise nozzle temperatures, long fabrication times, and the inherently small layer thickness achievable (Ali et al. 2023). These limitations of FDM printers leads to segmentation of large parts which are typically joined by bolts, hooks, welding or adhesives (Frascio et al. 2025). Adhesive bonding is the most effective joining method for FDM AM parts due to its advantages, such as more uniform stress distribution, reduced structural weight, compatibility with dissimilar materials, excellent damping properties, and cost-effectiveness ratio (Naat et al. 2025). The performance of adhesive joints in FDM‑manufactured components is governed by process related factors, although anisotropy and layer roughness exert a significant influence on joint strength (Spoerk et al. 2018, Brancewicz-Steinmetz et al. 2021). Leicht et al. (2020) investigated the effects of pre- and post-treatments on AM SLJ, revealing that atmospheric plasma treatment (pre-processing) and surface modification (post-processing) can raise joint strength up to 27 MPa, while printing orientation has a minor effect. The role of joint geometry has also been highlighted by Khosravani et al. (2023). Experimental comparisons between SLJ and SJ indicated that introducing steps at the overlap substantially enhances the fracture load, with joints featuring uniform step sizes exhibiting the highest strength. Adhesive selection and curing conditions further influence joint behavior. Kamer (2025) investigation into ABS and PLA SLJ bonded with different adhesives showed that curing at 80°C for 1 h maximized the tensile strength. Under these conditions, the ABS joints reached failure loads between 1386 and 1744 N, while PLA joints achieved 2690 to 3375 N. The bonding behavior of polycarbonate (PC) adherends has been experimentally and numerically explored by Öztürk et al. (2024). In the numerical approach, PC adherends were modeled as isotropic and the adhesive layer by CZM. The printing angle and overlap length ( L O ) strongly affected the joint strength, with failure loads ranging from 1586 N ( L O = 12.5 mm, 90°) to 4115 N ( L O = 25.4 mm, 0°). The close agreement between experimental and numerical results (1.34-11.98% deviation) confirmed the suitability of the numerical approach in predicting the joint performance. Ribeiro et al. (2025) conducted an experimental and a numerical study. Scarf joints were examined using various polymers (ABS, PETG, PLA) and adhesives. Results indicated that the adherend material, adhesive type, and scarf angle collectively govern joint strength, stiffness, and energy absorption. PLA bonded with the Araldite ® 2015 provided the highest strength and stiffness, whereas the Sikaforce ® 7752 offered superior energy absorption for longer L O . The investigation showed that the application of the numerical model with CZM method accurately predicted the joints’ mechanical behavior. Numerous studies have examined adhesive joints using AM adherends. However, few have focused on 4PB. In this work, the flexural behavior of adhesively bonded joints produced from AM thermoplastics is investigated using a 4PB test configuration. Specimens manufactured from PLA, PETG, and ABS were bonded using two structural adhesives, Araldite ® 2015 and Sikaforce ® 7752. Both SLJ and SJ geometries were considered. The experimental testing data were interpreted with the support of numerical simulations based on CZM.