PSI - Issue 82

Celalettin Baykara et al. / Procedia Structural Integrity 82 (2026) 206–212 C. Baykara et al./ Structural Integrity Procedia 00 (2026) 000–000

211

6

• The 2 mm adhesive thickness consistently provided the most favorable performance, offering both high fatigue life and stable crack behavior. • 1 mm thickness performed comparably well at 0.4 and 0.45 kN, but showed more brittle failure at higher loads due to stiffness-induced edge stresses. • The 3 mm adhesive layer exhibited the lowest fatigue performance, particularly at 0.4 kN, where the adhesive nearly de-bonded entirely from the aluminum plate. This behavior is attributed to excessive compliance and poor adhesion at higher thicknesses, leading to interfacial failure. • For dissimilar metal joints such as DC01–aluminum, a moderate adhesive thickness (2 mm) balances stress transfer efficiency and fatigue life, and is recommended for fatigue-critical applications. • While KTL-coated DC01A steel exhibited cohesive failure across all specimens, the absence of surface treatment on aluminum substrates led to adhesive failure, underscoring the decisive role of chemical modification in improving bonding performance. Beyond its conventional function as a corrosion protection layer, the KTL process was shown in this study to substantially increase the surface energy of steel and to enable robust adhesive bonding. This redefinition of KTL as a functional interfacial treatment provides an innovative alternative for pre-bonding surface preparation of steel substrates and enriches the current body of knowledge with practical industrial relevance. These findings contribute to ongoing efforts in optimizing bonded joint design, especially for lightweight structural components subject to cyclic loading. Future studies will investigate the role of cure cycle, surface treatments, and real-time damage tracking in further enhancing fatigue resistance. Acknowledgement The authors gratefully acknowledge the financial support provided by The Scientific and Technological Research Council of Türkiye (TÜBİTAK) under the 2224-A – Support Programme for Participation in Scientific Meetings Abroad, which covered the conference participation expenses. References Abbasi, Mohammad, Ciardiello, Raffaele, Goglio, Luca. Backface strain as an index to detect damage initiation in composite single-lap bonded joints: Effects of adhesive type and joint dimensions. International Journal of Adhesion and Adhesives 2024;134. Azari, S., Papini, M., Spelt, J. K. Effect of surface roughness on the performance of adhesive joints under static and cyclic loading. Journal of Adhesion 2010; 86:742-764. doi:10.1080/00218464.2010.482430. Baykara C. Effects of single-lap joint at different adhesive thicknesses on fatigue strength of metals with different surface coatings. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 2023; 237(17):3987-4004 Baykara C. Fatigue analysis results of steel plates coated with different chemical methods and joined by single-lap joints with various adhesive thicknesses: Comparison in Wöhler curves. Afyon Kocatepe University Journal of Science and Engineering 2024;24(1):176-188. Baykara C, Teke IT, Ertas AH. Effects of the single-lap joint on fatigue strength of metals with different surface coatings: a numerical simulation. E3S Web of Conferences 2023; 402: Article Number: 11011. Beber, V. C., Fernandes, P. H.E., Schneider, B., Brede, M., Mayer, B. Fatigue lifetime prediction of adhesively bonded joints: An investigation of the influence of material model and multiaxiality. International Journal of Adhesion and Adhesives 2017;78():240-247. Biscaia, Hugo C., Coelho, Pedro, Conde, Fábio, D'Antino, Tommaso. Theoretical study on the bond performance of CFRP-to-steel single-lap shear tests with multiple debonding defects. Composite Structures 2024;345. Guo, Lei, Liu, Jianhua, Xia, Huanxiong, Li, Xiayu, Zhang, Xiumin, Yang, Hongfan, Yang, Ye. Effects of loading rate, temperature, and thickness on the tensile strength of precision adhesive joints. Polymer Testing 2022;109. Heidarpour, F., Farahani, M., Ghabezi, P. Experimental investigation of the effects of adhesive defects on the single lap joint strength. International Journal of Adhesion and Adhesives 2018;80():128-132. Kumar, S., Pandey, P. C. Fatigue life prediction of adhesively bonded single lap joints. International Journal of Adhesion and Adhesives 2011;31():43-47. Liu Z, Li S, Yu Y. CFRTP single-lap adhesive bonding and its mechanical performance enhanced by laser surface treatment: Finite element simulation and experimental validation. Opt Laser Technol 2025;181. Metehri A, Madani K, Campilho RDSG. Numerical analysis of the geometrical modifications effects on the tensile strength of bonded single-lap joints. Int J Adhes Adhes 2024;134. Saleema N, Sarkar DK, Paynter RW, Gallant D, Eskandarian M. A simple surface treatment and characterization of AA 6061 aluminum alloy surface for adhesive bonding applications. Appl Surf Sci 2012;261():742–748.