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- Joining by forming of additive manufactured 'mortise-and-tenon' jointsPublication . Silva, Diogo F. M.; Bragança, Ivo; Silva, Carlos; Alves, Luís; Martins, PauloThis article is aimed at extending the 'mortise-and-tenon' joining concept commonly utilized in corner or tee joints to lap joints in which one sheet is partially placed over another without any change in their shape. The approach makes use of wire arc additive manufacturing to fabricate the tenons and allows various shapes and thicknesses to be made from a wide range of metallic materials. Upset compression of the tenons is utilized to mechanically lock the two sheets being joined. Experimental and finite element simulation works performed with monolithic (aluminium-aluminium) and hybrid (aluminium-polymer) 'unit cells' consisting of a single lap joint are utilized to investigate the deformation mechanics and the feasibility of the new proposed joining process. Tensile-shear loading tests were carried out to determine the maximum force that the new proposed joints are capable to withstand without failure. Pull-out forces of approximately 8 and 6 kN for the monolithic and hybrid joints allow concluding on the potential of additive manufactured 'mortise-and-tenon' lap joints to connect sheets made from similar and dissimilar materials.
- Joining aluminium profiles to composite sheets by additive manufacturing and formingPublication . Baptista, R. J. S.; Pragana, João; Bragança, Ivo; Silva, Carlos; Alves, Luís; Martins, PauloThis paper explores the application of the 'mortise-and-tenon' concept for joining hollow section aluminium profiles to composite strips or sheets. Wire arc additive manufacturing is combined with joining by forming to fabricate the tenons and to obtain the mechanical interlocking with the mortises available in the strips (or sheets). The workability limits are established by means of an analytical model that combines plastic deformation, instability and fracture. Experimental and finite element modelling are utilized to develop the overall joining process and to validate the round 'mortise-and-tenon' design resulting from the analytical model. Pull-out and shear destructive tests are carried out to evaluate the overall strength of the joints and results allow concluding that the new joints can easily and effectively replace existing solutions based on welding, fastening or adhesive bonding. The proposed joining process also circumvents the need to design extra fixing and interlocking features in low cost hollow section aluminium profiles for easy assembling.
- Joining by forming of metal-polymer sandwich composite panelsPublication . Pragana, João; Contreiras, Tomás R. M.; Bragança, Ivo; Silva, Carlos; Alves, Luís; Martins, PauloThis article presents new joining-by-forming processes to assemble longitudinally two metal-polymer sandwich composite panels perpendicular to one another. Process design draws from an earlier development of the authors for metal sheets to new concepts based on the combination of sheet-bulk forming with mortise-and-tenon joints. Selected examples obtained from experimentation and finite element modelling give support to the presentation. A new three-stage joining by the forming process is capable of producing mechanically locked joints with larger and stiffer flat-shaped heads than those fabricated by alternative single- or two-stage solutions. Failure in the new three-stage joining by the forming process is found to take place by cracking instead of disassembling after unbending the flat-shaped head of the joint back to its original shape. The required forming forces to produce the new metal-polymer joints are below 15 kN, allowing them to be an effective, easy-to-implement alternative to existing solutions based on adhesive bonding, welding and mechanical fastening.