Percorrer por autor "Pereira, A. M."
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- Analysis of manufacturing parameters on the shear strength of aluminium adhesive single-lap jointsPublication . Pereira, A. M.; Ferreira, J. M.; Antunes, F. V.; Bártolo, P. J.An experimental and numerical investigation into the shear strength behaviour of aluminium alloy adhesive lap joints was carried out in order to understand the effect of geometrical and manufacturing parameters on the strength of adhesive bonding joints, with the aim of optimizing shear strength. The adherend material used for the experimental tests was an aluminium alloy in the form of thin sheets, and the adhesive used was a high strength epoxy. Five surface treatments were studied. The surface treatments process using sodium dichromate-sulphuric acid etch (CSA) and abrasive polishing (AP) resulted in improved joint shear strength when compared to acetone cleaning (SW), caustic etch (CE), and Tucker's reagent etch (TR). The decrease in surface roughness was found to increase the shear strength of single-lap joints. An increase in adherend thickness and overlap length was found to increase shear strength which means that an increase in joint rigidity increases its strength. A numerical analysis was developed to explain the effect of the geometrical parameters on rotation angle, stress and strain fields, and failure load. An increase in adherend thickness and overlap length decreases the joint rotation angle, reducing the plastic strain peak and therefore increasing the failure load.
- Assessment of the fatigue life of aluminium spot-welded and weld-bonded jointsPublication . Pereira, A. M.; Ferreira, J. A. M.; Antunes, F. V.; Bartolo, P.J.In modern machinery and automobile structures weight reduction and increased durability are the main issues in design. In these applications, lap welded and/or bonded joints are widely used; therefore, tools are needed to accurately predict their fatigue life. This paper is concerned with the fatigue strength of single lap joints formed with thin plates of 6082-T6 aluminium alloy using a high strength two-component epoxy adhesive (Araldite 420 A/B from Hunstman). Experimental S–N curves were obtained for resistance spot-welded and weld-bonded lap joints. The fatigue lives of weld-bonded joints were significantly higher than those of resistance spot-welding joints. In addition, fatigue lives were predicted with Morrow's modified Manson–Coffin (M/M–C) and the Smith–Watson–Topper (S–W–T) damage equations. Elastic–plastic numerical models were developed, replicating the experimental work, in order to obtain local stress and strain fields. An acceptable agreement was obtained between the numerical predictions and the experimental results. The M/M–C damage equation diverged from experimental results for relatively long fatigue lives, while the S–W–T equation gave good predictions for all fatigue lives.
- Effect of process parameters on the strength of resistance spot welds in 6082-T6 aluminium alloyPublication . Pereira, A. M.; Ferreira, J. M.; Loureiro, A.; Costa, J. D. M.; Bártolo, P. J.In this study the microstructural and mechanical behaviour of resistance spot welds (RSW) done on aluminium alloy 6082-T6 sheets, welded at different welding parameters, is examined. Microstructural examinations and hardness evaluations were carried out in order to determine the influence of welding parameters on the quality of the welds. The welded joints were subjected to static tensile-shear tests in order to determine their strength and failure mode. The increase in weld current and duration increased the nugget size and the weld strength. Beyond a critical nugget diameter the failure mode changed from interfacial to pullout. Taking into consideration the sheet thickness and the mechanical properties of the weld, a simple model is proposed to predict the critical nugget diameter required to produce pull-out failure mode in undermatched welds in heat-treatable aluminium alloys.
- Effect of saline environment on mechanical properties of adhesive jointsPublication . Pereira, A. M.; Reis, P.N.B.; Ferreira, J.A.M.; Antunes, F.V.Literature reports very few works about the effect of corrosive environments on the mechanical properties of adhesive joints. Therefore, the present study intends to contribute for a better understanding of the effect of saline solution on the mechanical properties of single-lap adhesive joints. The specimens were manufactured using Docol 1000 high strength steel plates with 1 mm of thickness and Araldite® 420 A/B epoxy adhesive. The static shear strength of the joints was influenced by the exposure time in saline solutions only up to 120 h, and remained, after this period, nearly constant. In terms of fatigue strength, for 105 cycles, a decrease about 25% and 39% occurred in specimens immersed during 120 h in deionised water and saline solution, respectively, comparatively to the control samples.
- A Hybrid Processing Approach to the Manufacturing of Polyamide Reinforced Parts with Carbon FibersPublication . Silva, M; Pereira, A. M.; Alves, N.; Mateus, A.; Malça, C.The use of thermoplastic composites reinforced with long or continuous fibers underwent an amazing increase due to advantages such as good mechanical performance, high temperature resistance, recyclable and chemical stability when compared with simple thermosetting matrices. These advantages allowed for the replacement of thermosetting systems by composites that led to the discovery of new applications. However, the processing procedure of thermoplastics reinforced with prepregs yarns entails some technological and scientific challenges mainly due to its high viscosity that results in difficulty and complexity in impregnating the reinforcements. Concerning engineering components market requirements, the polyamide thermoplastic matrices reinforced with carbon fibers have a huge demand due to the versatility of the applications where they can be used. This work presents, therefore, the development of a low-cost device that combines the Fused Filament Fabrication (FFF) additive manufacturing technique together with the processing and consolidation of thermoplastic prepregs yarns for manufacturing parts made of polyamide reinforced with carbon fibers without need of post-processing operations. To evaluate the mechanical properties of the polyamide reinforced with carbon fibers, samples were manufactured and three point bending and tensile tests were done. From results it was demonstrated the very high structural strength to both bending and tensile loads of tested material.
- Influence of Superposition Length on Transverse Impact Response of Single-Strap Adhesive JointsPublication . Reis, P. N. B.; Ferreira, J. A. M.; Pereira, A. M.; Antunes, F. J. V.Adhesive joints are usually designed to carry in-plane loads, but in many cases they are also prone to transverse loading. On the other hand, the impact response of adhesive joints has received limited attention compared to quasi-static loading. Therefore, the present paper aims to study the influence of superposition length on transverse impact response of single-strap adhesive joints. For this purpose, low-velocity impact tests were performed using a drop weight-testing machine with a hemispherical impactor falling at the center of a bi-clamped specimen. The specimens were manufactured using Docol 1000 high-elastic limit steel, with 1.5 mm of thickness, and an Araldite® 420 A/B adhesive (Huntsman Advanced Materials, Everberg, Belgium). The collapse thresholds obtained were 61.6 J, 75.1 J, and 77.5 J, respectively, for adhesive joints with gap length of ℓo = 0, 10, and 20 mm. An adhesive fracture occurred for the three geometries and the cracks initiated at the corner of the joint where the deflection is higher. Joints with higher ℓo have higher impact energies, despite the lower bonding area, as consequence of the lower local deformation. A numerical study was developed and the zero gap (ℓo = 0) gives maximum peel stress.