Browsing by Author "Silva, Carlos M. A."
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- Enhancing the performance of double-flush riveted joints through hybridization with adhesive bondingPublication . Alpendre, João M. B.; Rosado, Pedro M. S.; Sampaio, Rui F. V.; Pragana, João P. M.; Bragança, Ivo; Silva, Carlos M. A.; Martins, Paulo A. F.This paper explores the potential to enhance the mechanical performance of joints created through a new joining-by-forming technique called hybrid double-flush riveting. To achieve this, adhesive bonding is used to form hybrid lap joints with superior mechanical properties. The study focuses on high-strength steel sheets and starts by identifying the appropriate surface conditions necessary for producing strong adhesive-bonded joints. A similar strategy is applied to construct double-flush riveted joints, focusing on the geometric variables involved in the process. Hybrid joints are then created by integrating adhesive bonding with double-flush riveting, with the second carried out before or after curing is completed. The experimental development is supported by finite element analysis conducted with an in-house computer program. The mechanical performance of the hybrid joints is compared to that of purely adhesive-bonded and conventionally double-flush riveted joints through shear and peel destructive testing. Results demonstrate that hybrid joints ultimately provide greater joint strength for both solicitations. This allows showcasing the hybridization of double-flush riveting with adhesive bonding as an effective solution for applications where joint strength and continuity are essential.
- Exploring wire-arc additive manufactured rivets for joining hybrid electrical busbarsPublication . Rosado, Pedro M. S.; Sampaio, Rui F. V.; Pragana, João P. M.; Bragança, Ivo; Silva, Carlos M. A.; Martins, Paulo A. F.This paper presents a joining by plastic deformation process for fabricating hybrid electrical busbars made from copper and aluminum sheets. The process comprises the innovative use of wire-arc additive manufacturing to deposit copper rivets at specific locations on the copper sheets, the machining of slots with the required geometry in the aluminum sheets, and the compression of the copper sheets to force the rivets into the pre-machined slots of the aluminum sheets, creating form-closed mechanical interlocks. The work combines experimentation and finite element modeling to analyze the influence of the most significant process parameters, and the electrical performance of the hybrid busbar joints is evaluated and compared to that of conventional fastened joints at different service temperatures. Results demonstrate the effectiveness and potential advantages of the new joining by plastic deformation process for fabricating hybrid electrical busbars.
- Formability of wire-arc deposited AISI 316L sheets for hybrid additive manufacturing applicationsPublication . Pragana, João P. M.; Bragança, Ivo; Reis, L.; Silva, Carlos M. A.; Martins, P. A. F.This paper is focused on the formability of wire-arc additively manufactured AISI 316L stainless steel sheets with the purpose of analysing the feasibility of including this material in hybrid additive manufacturing chains involving sheet metal forming operations. Conventional tensile tests performed in specimens obtained from different orientations to the building direction were carried out to characterise the mechanical properties, the strain loading paths and the limiting strains at fracture. Microstructure observations combined with fractography analysis add insight to the results by establishing a link between the forming limits by fracture and the crack opening mechanisms. Results obtained for wrought commercial AISI 316L stainless steel sheets are included for comparison purposes and reveal that the additively manufactured sheets have a much stronger anisotropic behaviour and poorer formability due to their dendritic-based microstructure. Still, the forming limits obtained from the experiments allow concluding that the additively manufactured sheets can withstand large plastic deformations and, therefore, can be used in hybrid additive manufacturing routes.
- Groove stiffening of sheets by single point incremental formingPublication . Cristino, Valentino A. M.; Pragana, João P. M.; Bragança, Ivo; Silva, Carlos M. A.; Martins, PauloThis paper investigates the applicability of single point incremental forming to fabricate stiffening grooves in thin metallic panels. The work combines experimentation, finite element and analytical modelling to determine the required forces and the maximum allowable groove depths that can be produced without tearing. The analytical modelling is based on a framework that was previously developed by the authors and combines in-plane membrane stretching and fracture forming limits. Comparison of the results obtained by the analytical framework against experimental and finite element data proves its effectiveness to replicate the deformation mechanics of groove stiffening by single point incremental forming. Results also prove that groove stiffening by single point incremental forming is an easy and effective alternative to conventional reinforcement of thin metallic panels by welding or fastening of stringers.
- A joining by plastic deformation process to fabricate butt joints in copper-aluminium busbarsPublication . Pragana, João P. M.; Sampaio, Rui F. V.; Bragança, Ivo; Silva, Carlos M. A.; Martins, Paulo A. F.This paper presents a feasibility study on the fabrication of butt joints in copper-aluminium (hybrid) busbars by means of an innovative joining by plastic deformation process. The joints are obtained by cutting complementary fixing pairs consisting of fingers and grooves in the busbars and by subsequently upsetting the fingers, in position, to create a permanent interlocking with the grooves of an edge bent busbar. The presentation draws from the process working principle to the mechanical and thermo-electrical performance of the joints. Experimentation and numerical modelling give support to the presentation and demonstrate the effectiveness of the process to produce butt joints in hybrid busbars for power distribution systems.
- Joining of hybrid busbars for e-mobility: an economic and environmental studyPublication . Pragana, João P. M.; Sapage, Miguel S. T.; Sampaio, Rui F.V.; Bragança, Ivo; Ribeiro, Inês; Silva, Carlos M. A.; Martins, PauloThis paper presents a model to evaluate and analyze the costs of joining hybrid (copper-aluminum) busbars when different production processes are deployed. The process-based cost model (PBCM) is built upon the subdivision of the production cycle in three different stages related with the fabrication or purchase of auxiliary joining elements, preparation of the individual copper and aluminum conductors, and final joining of the hybrid busbars. The total cost per hybrid busbar is obtained by converting the major physical, human, and financial resources associated with the production cycle into itemized costs that make use of the expenses in materials, labor working hours, number and usage time of machines and tools, among other production costs. Application of the PBCM is illustrated with three different joining processes and enriched with a life cycle assessment (LCA) focused on the environmental performance of hybrid busbars throughout its fabrication, service use and end of life. The combined economic and environmental sustainability analysis of joining hybrid busbars allows concluding that despite conventional fastening being the cheaper process it has the highest environmental impact due to the use of bolts, nuts and washers made from galvanized medium carbon steel. Injection lap riveting arises to be the most well-balanced process in terms of production cost and environmental impact.
- Multi-planar injection lap rivetingPublication . Sapage, Miguel S. T.; Pragana, João P. M.; Sampaio, Rui F.V.; Bragança, Ivo; Silva, Carlos M. A.; Martins, PauloThis paper is focused on multi-planar hybrid busbars made from copper and aluminum for electric energy distribution systems. The objective is to provide an overview of its assembly by injection lap riveting in multidirectional tools and to compare the electrical performance of its joints against that of conventional (in-plane) busbars. The injected lap riveted joints require a dovetail ring hole and a countersunk hole to be first machined in the overlapped copper and aluminum sheets and then to inject the semi-tubular rivets by compression through the lined-up holes in order to fix the sheets in position. In this work, the injection of the semi-tubular rivets was carried out in a laboratory multidirectional tool set that converts the vertical press stroke into two-orthogonal horizontal movements by means of cam slide units consisting of compression punch holders and sliding wedge actuators attached to the upper bolster. Experimental results obtained for a multi-planar, three-conductor, rake-shaped elbow of a hybrid busbar system allow concluding that while the required compression force is proportional to the number of injected lap riveted joints, the electrical performance is non-proportional due to changes in the distribution of electric current density. Numerical simulation with finite elements gives support to the discussion and allows readers to recognize the pitfalls of designing busbar joints exclusively based on mechanical requirements.
- Resistance element welding of sandwich laminates with hidden insertsPublication . Calado, Francisco N.; Pragana, João; Bragança, Ivo; Silva, Carlos M. A.; Martins, Paulo A. F.This paper presents a new resistance element welding process capable of producing invisible lap joints between steel-polymer-steel composite laminates. The process involves pre-drilling a flat-bottom hole in each laminate to remove the polymer core and one of the steel sheets, and positioning a cylindrical insert inside the two adjoining holes for subsequent resistance welding. Finite element modeling is utilized to construct the weldability lobe and to identify the parameters that lead to the formation of acceptable joints. Experimental results confirm the applicability of the process to produce invisible lap joints without signs of material protrusions or local indentations resulting from squeezing the polymer out to create contact between the steel sheets. Destructive peel and shear tests allow determining the maximum forces that the joints can safely withstand and comparing their performance against alternative joined by forming lap joints in which the mechanical interlocking is also hidden inside the laminates.
- A self-clinching fastener for hidden lap jointsPublication . Sampaio, Rui F. V.; Pragana, João; Bragança, Ivo M. F; Silva, Carlos M. A.; Martins, P. A. F.This paper presents a new self-clinching fastener to connect two sheets (or plates), made from similar or dissimilar materials, placed over one another by means of a mechanical form-closed joint that is hidden inside the sheets. The development of the fastener, the definition of its main design variables and the identification of its workability limits are carried out by means of a combined experimental and numerical simulation work based on finite elements. It is shown that self-clinching by pressing the two overlapped sheets against each other to displace material around the annular groove of the fastener shank and create undercuts in both sheets requires an appropriate choice of the design variables. Wrong values of the design variables resulting in lack or excess of material displaced by plastic flow gives rise to inappropriate lap joints that cannot be used in production. The new proposed fastener allows, for the first time ever, joining by forming with the use of auxiliary elements that are harder than the sheet materials to fabricate invisible joints with no material protrusions in applications requiring minimum installation space
- An upset geometry sequence for determining the formability limits in bulk formingPublication . Silva, Carlos M. A.; Sampaio, Rui F. V.; Pragana, João P. M.; Bragança, Ivo M. F.; Bragança, Ivo; Martins, Paulo A. F.This paper presents an upset geometry sequence capable of providing strain loading paths from uniaxial compression to biaxial stretching. Combination of digital image correlation and experimental force vs. time evolutions allows determining the fracture strains and the instantaneous slope of the strain loading paths at the instant of cracking in principal strain space. Fractography using scanning electron microscopy helps identifying the crack opening modes corresponding to the different fracture strains. Results show that the proposed upset geometry sequence allows creating a new testing methodology for bulk forming similar to that of sheet forming with the widely used Nakajima test.