Percorrer por autor "Sampaio, R. F. V."
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- Assembly of lightweight sandwich panels through joining by formingPublication . Sampaio, R. F. V.; Pragana, J. P. M.; Bragança, I .M F; Martins, P.A.F.This paper is focused on the assembly of lightweight sandwich panels built upon the patented ‘Opencell’ structure concept. The objective is to investigate the possibility of joining the connection members of the core to the adjoining skin sheet by plastic deformation at ambient temperature, instead of welding or adhesive bonding. The methodology draws from earlier developments of the authors in joining by forming using the mortise-and-tenon concept to experimentation and finite element modelling of the assembly process in unit cells that are representative of the sandwich panels. It is shown that replacing welding by joining by forming allows fabricating sandwich panels from sheet materials that are difficult or impossible to weld while preventing thermal cycles that are responsible for causing metallurgical changes, distortions, and residual stresses. Replacing adhesive bonding by joining by forming circumvents the need of surface preparation, time for the adhesive to cure and environmental compliance, among other requirements
- Double-flush riveting by punching and compressionPublication . Sampaio, R. F. V.; Larue, P.; Pragana, J. P. M.; Bragança, I. M. F.; Silva, C. M. A.; Martins, P. A. F.; Bragança, IvoThis paper presents a new double-flush riveting process to fabricate flat lap joints that can be easily integrated in progressive or transfer multistage tool systems. The process is based on a punching-compression sequence and the design methodology combines experimentation and finite element modeling followed by destructive peel testing. Special emphasis is placed on the identification and selection of punch-to-die clearances to produce tapered cut surfaces that are appropriate for subsequent compression of the solid rivets into double-flush riveted lap joints. Results confirm that rivet materials with lower mechanical resistance than the sheet materials allow fabricating double-flush riveted lap joints with flat surfaces on both sides in which the mechanical interlocking in the undercut area is obtained by plastic deformation of the rivets instead of the sheets. The utilization of aluminum sheets and copper rivets allows extending the process scope of application from structural to energy distribution parts in which the electrical resistance of joints is a critical design parameter.
- Macro-scale finite element simulation of wire-arc additive manufacturingPublication . Pragana, J. P. M.; Sampaio, R. F. V.; Bragança, I. M. F.; Silva, C. M. A.; Nielsen, C. V.; Martins, P. A. F.; Bragança, Ivo; SAGE Publications Ltd.This paper focuses on the development of a finite element computer software to perform macro-scale thermo-mechan ical simulations of wire-arc additive manufacturing (WAAM). The emphasis is placed on various aspects of computer implementation, such as modeling the heat source, incorporating an element birth approach to replicate material depos ition, and ensuring compatibility of solution time increments with the wire feed rate, travel speed of the heat source and melt pool volume. Thermal strains are also included due to their impact on residual stresses and distortions of the built parts after finishing material deposition. Experiments consisting of single bead, multi-layer deposition of AISI 316L stain less steel along linear paths are utilized to validate the predicted temperature distribution over time and evaluate the computed geometry and distortions of the deposited vertical walls after unclamping. Microstructure observations of samples extracted from the walls combined with finite element estimates of the temperature gradient help understand the influence of temperature history on the morphology and orientation of columnar grain growth.
- Thermal-electrical analysis of a novel interconnection for hybrid busbars in electric vehicle batteriesPublication . Costa, D. P. M. da; Kasaei, M. M.; Carbas, R. J. C.; Marques, E. A. S.; Sampaio, R. F. V.; Bragança, I. M. F.; Silva, L. F. M. da; Bragança, Ivo; ElsevierReliable and efficient busbar connections are critical for electric vehicle battery performance, yet conventional joining methods struggle with joining dissimilar materials such as copper and aluminum. This paper investigates a novel solution for joining hybrid copper-aluminum busbars using a technique called hole hemming, which eliminates the need for heating or additional elements. The focus is placed on the thermal-electrical performance of hole-hemming joints. Two configurations are studied: joints with and without branches. Numerical models analyse how sheet thickness affects temperature, electric current density, electric potential, and resistance, including models with cantered holes to study hole inclusion effects. Experimental tests are conducted on ma terial strips and unit cells to assess electrical resistance changes with temperature and the effect of Joule heating on joint configurations. Compression using a hydraulic press is applied to improve contact, leading to significant electrical resistance improvements (78 % reduction for branched joints and 36 % for branchless ones). Me chanical shear tests before and after compression show a peak shear load of 4.54 kN and 13.84 mm displacement for branched joints, with slightly lower values for branchless joints. Despite a minor decrease in mechanical performance after compression, the improved thermal-electrical performance of the joints outweighs this. The findings highlight the promising potential of hole-hemmed joints for enhancing hybrid busbar connections.