Browsing by Author "Moreira, R.D.F."
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- Adhesive selection for hybrid spot-welded/bonded single-lap joints: Experimentation and numerical analysisPublication . Marques, G.P.; Campilho, Raul; Silva, F.J.G. da; Moreira, R.D.F.The applications of adhesive joints are increasing in various industrial applications because they offer several advantages over traditional methods. The combination of adhesive bonding with spot-welding enables some advantages over adhesive joints such as increased stiffness, and higher static and fatigue strength. This work relates to the adhesive selection for single-lap adhesive joints by the bonding and hybrid (bonded and welded) techniques with different overlap lengths (LO). The adhesives are the brittle Araldite AV138®, and the ductile Araldite® 2015 and Sikaforce® 7752. The experimental results were compared against a Finite Element (FE) study coupled with Cohesive Zone Modelling (CZM). The results validated the numerical technique and also showed varying strength improvements of the hybrid joints over bonded joints depending of the adhesive.
- Bonded structures improvement by the dual adhesive techniquePublication . Ferreira, C.L.; Campilho, R.D.S.G.; Moreira, R.D.F.A common technique to reduce stress gradients in adhesive joints is to use the dual adhesive technique, which has proven to reduce peak stresses in single-lap joints. However, other joint configurations could benefit from this technique. This work experimentally and numerically evaluates stepped-lap dual-adhesive joints (DAJ) between aluminum adherends, for various overlap lengths (LO), and carries out a detailed comparison with stepped-lap single-adhesive joints (SAJ) with the same individual adhesives (Araldite® AV138 and Araldite® 2015). The joint behavior was predicted by cohesive zone modelling (CZM) with a triangular law. The analysis of the results is presented in the form of failure modes, stress analysis, maximum load (Pm) and energy required to failure (U). It was concluded that, in general, CZM presented precise predictions and are a valuable tool for the design of both SAJ and DAJ. However, no significant increase in strength was achieved with DAJ, although using more ductile adhesive can promote better DAJ results.
- 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.
- Parametric Study of the Reinforcement Geometry on Tensile Loaded Scarf Adhesive RepairsPublication . Moreira, R.D.F.; Campilho, RaulThe recent enhancements in structural adhesives technology enabled the use of adhesive joints and repairs in several industrial fields. The scarf repair is the most efficient because of suppression of peel (σ) and shear (τ) peak stresses, arising from the tapered adherend edges. The repair of structures that have the requirement of flush surfaces is one of the major applications of the scarf geometry. This work is a numerical study on the ultimate tensile strength of two-dimensional (2D) scarf repairs of aluminum structures with external doublers as reinforcements. Two adhesives were considered: the brittle epoxy Araldite® AV138 and the ductile epoxy Araldite® 2015 (Huntsmann, Basel, Switzerland). The numerical analysis by finite elements (FE) was performed in Abaqus® (Dassault Systèmes, Vélizy-Villacoublay, France) and used cohesive zone models (CZM), thus enabling the strength prediction of the repairs. Validation of this methodology with scarf repair experiments was performed previously. The influence of the main reinforcement geometric parameters is studied for the two adhesives, such as doubler thickness and edge geometry. This work enabled to conclude that the repairs’ strength can be optimized by a significant amount by a careful selection of the doubler geometry, and that the results are dependent on the adhesive ductility.
- Strength improvement of adhesively-bonded scarf repairs in aluminium structures with external reinforcementsPublication . Moreira, R.D.F.; Campilho, RaulAdhesively bonded techniques are an attractive option to repair aluminium structures, compared to more traditional methods. Actually, as a result of the improvement in the mechanical characteristics of adhesives, adhesive bonding has progressively replaced the traditional joining methods. There are several bonded repair configurations, as single-strap, double-strap and scarf. Compared with strap repairs, scarf repairs have the advantages of a higher efficiency and the absence of aerodynamic disturbance. The higher efficiency is caused by the elimination of the significant joint eccentricities of strap repairs. Moreover, stress distributions along the bond length are more uniform, due to tapering of the scarf edges. The main disadvantages of this technique are the difficult machining of the surfaces, associated costs and requirement of specialised labour. This work reports on an experimental and numerical study of the tensile behaviour of two-dimensional (2D) scarf repairs of aluminium structures bonded with the ductile epoxy adhesive Araldite® 2015. The numerical analysis, by Finite Elements (FE), was performed in Abaqus® and used cohesive zone models (CZM) for the simulation of damage onset and growth in the adhesive layer, thus enabling the strength prediction of the repairs. A parametric study was performed on the scarf angle (α) and different configurations of external reinforcement (applied on one or two sides of the repair, and also different reinforcement lengths). The obtained results allowed the establishment of design guidelines for repairing, showing that the use of external reinforcements enables increasing α for equal strength recovery, which makes the repair procedure easier. The numerical technique was accurate in predicting the repairs’ strength, enabling its use for design and optimisation purposes.