Browsing by Author "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.
- 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.
- 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.