Browsing by Author "Cardoso, M.G."
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- Effect of material hybridization on the strength of scarf adhesive jointsPublication . Alves, D.L.; Campilho, R.D.S.G.; Moreira, R.D.F.; Silva, F.J.G.; Cardoso, M.G.Adhesively-bonded joints have become more efficient due to the improvement of adhesives’ characteristics. On the other hand, with the use of composites in structures it is possible to reduce weight. Due to this, new techniques are being explored, including adhesively-bonding different materials. Nowadays, in many high performance structures, it is necessary to combine composite materials with other light-weighted metals such as aluminium or titanium. This work reports on an experimental and numerical study for hybrid scarf joints between composite and aluminium adherends, and considering different values of the scarf angle (α). The numerical analysis by Finite Elements (FE), using the software Abaqus®, enabled the obtainment of peel (σy) and shear stresses (τxy), which are then used to discuss the strength between different joint configurations. Cohesive zone modelling (CZM) was used to predict the joint strength and the results were compared to the experiments for validation. The joints’ behaviour was highly dependent on α, and CZM were validated for the design process of hybrid scarf joints.
- Evaluation of T-joints in aluminium structures under different geometriesPublication . Moreira, F.J.P.; Campilho, R.D.S.G.; Cardoso, M.G.; Silva, Francisco J. G.The adhesive bonding technique is nowadays very popular in industrial applications, and is gradually replacing other more traditional bonding methods (fastened, welded and riveted joints) due to some advantages. However, its application supposes accurate methods for strength prediction. As a result, the techniques to predict the strength of adhesive joints has highly evolved. The eXtended Finite Element Method (XFEM) is a recent innovation implemented over the (Finite Element Method) FEM that enables crack growth to be modelled. However, its application to adhesive joints is still scarce. This work consists of an experimental and XFEM analysis of aluminium alloy T-joints, adhesively-bonded with three adhesive types. A parametric study is undertaken regarding the curved adherends’ thickness (tP2), with values between 1 and 4 mm. The adhesives Araldite® AV138 (strong but brittle), Araldite® 2015 (less strong but moderately ductile) and the Sikaforce® 7752 (with the smallest strength but highly ductile) were tested. A comparative analysis between the different joints conditions was undertaken by plotting peel (σу) and shear (τxy) stresses. The XFEM predictive capabilities were tested with different damage initiation criteria. It was found that, provided that the modelling conditions are properly set, accurate numerical results can be found.
- Fracture envelope estimation of a structural adhesive by dedicated fracture testsPublication . Nunes, F.A.A.; Campilho, R.D.S.G.; Cardoso, M.G.; Silva, F.J.G.Cohesive zone modelling (CZM) is widespread for the strength analysis of bonded joints. The fracture toughness (GC) is required to use CZM. A scarcely studied mixed-mode test is the Asymmetric Tapered Double-Cantilever Beam (ATDCB), which merges a Tapered Double-Cantilever Beam (TDCB) adherend with a Double-Cantilever Beam (DCB) adherend. This work addresses the ATDCB test to estimate the fracture envelope of a structural adhesive. TDCB and End-Notched Flexure (ENF) tests were also performed to acquire the tensile (GIC) and shear fracture toughness (GIIC), respectively. Numerically, mixed-mode CZM laws were constructed based on the obtained data, and the results were compared with experiments, to validate the CZM laws and the mixed mode propagation criterion. As a result, the best damage propagation criterion for mixed mode was estimated and validated.
- A new structural two-component epoxy adhesive: Strength and fracture characterizationPublication . Cardoso, M.G.; Pinto, J.E.C.; Campilho, R.D.S.G.; Nóvoa, P.J.R.O.; Silva, Francisco J. G.; Ramalho, L.D.C.In the past decades, adhesive technology has been useful in order to solve numerous issues related with conventional joining techniques (bolting, riveting and welding). Several advantages of adhesive bonding can be pointed out, such as low weight (relevant in the automotive and aeronautical industries), capability to resist to adverse environmental conditions, lower manufacturing costs and possibility to join different materials. To predict crack propagation of an adhesive joint by advanced fracture mechanics-based techniques such as cohesive zone models (CZM) it is not enough to know the traditional mechanical properties, such as Young’s modulus (E), shear modulus (G), tensile strength (σf) and shear strength (τf). Actually, it is also mandatory to estimate the tensile (GIC) and shear fracture energies (GIIC). The purpose of this work is to carry out the mechanical and fracture property characterization of a new structural two-component epoxy adhesive. With this purpose, four tests which were conducted: tensile testing to bulk specimens, shear testing with thick adherend shear tests (TAST), double-cantilever beam (DCB) and end-notched flexure (ENF). With these tests, it was possible to determine the mechanical and fracture properties of the adhesive in tension and shear. Different data reduction methods were evaluated for the fracture properties. The test results agreed with the data provided by the manufacturer and will enable the design of bonded structures with this adhesive.