PSI - Issue 41

A.R.F. Soares et al. / Procedia Structural Integrity 41 (2022) 48–59 Soares et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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on composite materials (Naghipour et al., 2009), while others addressed wood, metals, sandwich structures, hybrid structures (bi-material) and structural adhesives (Stamoulis and Carrere, 2020). The MMB test is the only standardized mixed-mode test (per ASTM D6671/D6671M-06) to determine the interlaminar G C of composite materials. Plagianakos et al. (2020) experimentally analysed the interlaminar G C of graphite composite materials by the MMB test, to evaluate the effect of ageing by heat and humidity. The results were compared with analytical predictions and numerical predictions by the FEM, and some deviation was found in the tests. It was thus concluded that the MMB test is sensitive to geometric imperfections and/or the materials used. Arouche et al. (2021) investigated the influence of a layer of fibreglass mat inserted into an interface of a bi-material adhesive joint as a hardening mechanism to improve the performance of the structure. The fracture behaviour was evaluated by the MMB test. The results revealed a G C increase with the insertion of a fibreglass layer, and a relationship between G C and the roughness of the fracture surface was found. Stamoulis and Carrere (2020) investigated the fracture properties of a structural adhesive through the MMB test, where the influence of the mixed-mode ratio on the fracture strength of the joint was analysed. LEFM-based concepts were used to access G C . The MMB test was carried out at different speeds and mixed-mode ratios, and it was found that G C is influenced by both. It was also concluded that the test speed had a considerable impact on the fracture behaviour when close to mode II. A fracture criterion was also established that allowed obtaining adequate fracture envelopes for each mixed-mode ratio, whereby the calculation of G IIC was performed by interpolation. In this work, the main objective is to design, numerically model and experimentally validate an MMB test equipment to perform structural adhesive tests. Experimentally, it is intended to design and manufacture the MMB test equipment, and subsequently carry out the respective tests and data processing leading to the validation of the equipment for testing adhesives. The numerical work consists of creating the geometry of the equipment in software and carrying out the respective simulations, in order to optimize the geometry of the MMB test equipment. Another objective of this work is to validate the equipment with experimental tests. 2. Methods 2.1. Problem statement and objectives The main objective of this work is to design, numerically model and experimentally validate an MMB test equipment for structural adhesive tests, considering the study and critical analysis of existing equipment. In particular, it is intended to carry out a comparison between the base equipment for the study, developed by Chaves (2013) and the improved equipment. The numerical work consists of creating the geometries of the different components of the equipment in software and carrying out the respective simulations for structural validation. Experimentally, the intention is to manufacture the designed equipment and carry out the respective tests. The end result should be an equipment that enables obtaining various mixed-mode combinations, using a single equipment and the same type of test specimen, for further application in the design of bonded joints. 2.2. Requirements After defining the objectives for this work, it is important to define the equipment requirements that the development of this work imposes: • Compatibility and easy attachment to the testing machine;

• Simple and compact configuration; • Versatile, practical and intuitive; • Easy assembly and configuration of the equipment; • Good surface finish that increases the lifespan of the equipment; • Use of calibrated pins to eliminate friction; • Use of pins that promote quick assembly and disassembly; • Parts made of high tensile strength steel; • High strength connecting, fastening or guiding components; • Equipment design by the finite element method (FEM) to optimize stiffness;