Determining Mode I Fracture Energy for Bonded Joints Having Different Adhesive Thicknesses

• Published in: Journal of failure analysis and prevention
• Main Authors: Ali, Ahmed Mohamed Jubartalla, Benyahia, Faycal, Alsuhaibani, Zeyad, Bouiadjra, Bel Abbes Bachir, Dean, Aamir
• Format: Journal Article
• Language: English
• Published: 23.08.2025
• ISSN: 1547-7029; 1864-1245
• DOI: 10.1007/s11668-025-02257-w

The bonded composite repair technique has been widely used to extend the life of cracked structures, such as aircraft and wind turbine structures. After repair, the growth of the crack is significantly slowed until the patch begins to lose its effectiveness. To maintain a low rate of crack growth, the patch repair needs to be replaced once a critical level of adhesion damage (separation) is reached. The objective of this research is to determine the cohesive zone model (CZM) parameters for simulating mode I damage initiation and propagation in different thicknesses of Araldite®2015 structural adhesive. First, mode I load–displacement curves were obtained experimentally using double cantilever beam (DCB) tests. Next, the corresponding fracture toughnesses (GIc) were calculated using the compliance-based beam method (CBBM), which does not require measuring the crack length during testing. Finally, finite element analysis (FEA) was used to predict the progression of adhesion damage using three different softening laws: triangular, trapezoidal, and exponential. The study found that mode I fracture energy is the same for adhesive thickness between 0.20 and 0.30 mm, but then increases by 27% when the adhesive thickness becomes 0.35 mm. Numerically, the results showed good agreement across all softening shapes, with the trapezoidal law being considered the most computationally efficient.