PSI - Issue 39

M.R.M. Aliha et al. / Procedia Structural Integrity 39 (2022) 393–402 Author name / Structural Integrity Procedia 00 (2021) 000–000

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1. Introduction Many high tech and modern components and industries, such as aerospace, civil, and automotive engineering, have always been particularly interested in joining structural and engineering parts with adhesive. This is due to the advantages and benefits of such a joining method over more traditional methods like welding. Adhesively bonded joints have a good share of the market for manufacturing advanced products due to benefits such as high strength, fatigue and stiffness, low cost and low weight, and the ability to join both similar and dissimilar parts. After curing and during life service, some structural adhesives may act as brittle materials. In the presence of structural defects, adhesively bonded joints are more susceptible to sudden fracture. Understanding the failure and fracture propagation mechanisms in these joints is therefore critical for the safe use of adhesive bonded components in practical applications [1]. The interfacial fracture may be studied using the fracture mechanics framework, which defines the intensity of the stress/strain field using quantities such as the stress intensity factor. The critical values of such parameters are frequently used to describe the fracture behavior of adhesively bonded joints as mechanical characteristics. Several studies have utilized experimental methodologies and testing specimens to determine the load-bearing capability or fracture energy of such components. A well-known test setup for the tensile type or mode I fracture investigation of the adhesively bonded joints is the double cantilever beam (DCB). There are several testing techniques and specimens for mode II fracture investigation of bonded joints, including edge notch flexural (ENF), which has been widely utilized by numerous researchers to assess shear-type fracture energy. Other test samples for assessing and researching mixed-mode I/II fracture in these components have been offered. A well-known test designed for the tensile-shear type investigation of adhesively bonded joints is the mixed mode bending (MMB) specimen [2-4]. The aforementioned testing techniques have several challenges and shortcomings, such as the inability to introduce the complete range of mode mixities, the need for complicated testing jigs and fixtures to execute the tests, high cost of testing, occurrence of large deformations during the test, non-linearity due to lever weight and curvature, and the enormous size of the test specimen [5,6]. Aliha and colleagues have recently presented a new testing method for evaluating the behavior of adhesively bonded joints that is simple and effective. This new specimen is named bi-material inclined notch short bend beam (BI-SBB). Simple geometry, simplicity of testing using a traditional three-point bend fixture, creating entire ranges of mode mixity from pure mode I to pure mode II, occurrence of small deformations during the test, low cost of testing, and needing small amounts of materials are some of the benefits of the suggested BI-SBB specimen [7]. The stress intensity factors of the BI-SBB specimen have already been determined by the authors for different mode I and II mixities and different adherent materials. The direction of fracture initiation and the path or trajectory of fracture growth in the BI-SBB specimen is also another important and interesting subject that has not been studied yet. Therefore, the crack initiation angles and mixed mode I/II fracture propagation paths in the adhesively bonded joints are investigated numerically in this study by using the BI-SBB specimen. 2. Novel Mixed mode I/II test specimen for adhesively bonded joints Figure 1 depicts general schematics of the BI-SBB specimen. The specimen's overall dimensions are L = 54 mm, W = 15 mm, t = 5 mm, and d = 0.4 mm. The materials used to create the BI-SBB specimen on the left and right sides of the adhesive can be similar or dissimilar. To make the proposed BI-SBB specimen, Alumina ceramic and Aluminum metal alloy (Al) were selected for bonding with an epoxy adhesive. The mechanical properties of the chosen materials are shown in Tables 1 and 2. The state of mode mixity is changed mainly by altering the crack inclination angle ( α ) and crack length ( a ) shown in Figure 1. By increasing α from zero, the state of crack tip deformations switches from mode I opening (tensile) to mode II sliding (shear). The authors showed that this specimen can introduce full ranges of mode mixities from pure mode I to pure mode II [7].