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This work proposes a novel deformable self-clinching fastener for producing hidden lap joints suitable for both structural and electric power distribution applications. The fastener, characterized by an axisymmetric concave shape, is employed to fabricate hybrid busbar joints between electrically conductive strips of different materials and thicknesses. The self-clinching process with the new deformable fastener involves machining dovetail holes in both conductors and applying a squeezing force to the fastener to create a form-closed mechanical joint. The work encompasses both experimental investigations and numerical modeling using finite element analysis and is carried out on unit cells made from aluminum and copper conductors, which are representative of the joining process. The investigation evaluates force requirements, conducts destructive testing, and performs thermo-electric characterization of the new joints to conclude on the suitability of the new deformable self-clinching fastener for electric power distribution applications. Results indicate that while copper fasteners necessitate greater squeezing forces, they offer superior mechanical and thermo-electrical performance compared to aluminum fasteners in hybrid busbar joints. [ABSTRACT FROM AUTHOR]

This paper presents an upset geometry sequence to determine the fracture forming limits in a wide variety of strain loading paths ranging from uniaxial compression to equibiaxial tension. The strains at fracture in principal strain space are obtained by combination of digital image correlation and experimental evolutions of the compression force versus time, and their representation in the effective strain versus stress triaxiality space is accomplished by means of a new analytical framework that uses the instantaneous slope of the strain loading paths. Modeling of the experimental strains at fracture by means of an uncoupled ductile fracture criterion built upon combination of the Cockcroft-Latham and McClintock criteria and fractography analysis using a scanning electron microscope allow understanding and characterizing the crack opening modes by shear and tension as well as the uncertainty region inside which mixed crack opening modes are observed. Results confirm that the overall philosophy and objectives underlying the new upset geometry sequence for determining the fracture forming limits in bulk forming resemble those of the Nakajima test that is commonly used in sheet forming. [ABSTRACT FROM AUTHOR]

This paper is focused on hybrid busbars made from aluminum and copper with the purpose of analyzing the influence of temperature on the electric performance of the joints. The methodology involves the fabrication of fastened, friction stir spot welded, sheet-bulk compressed, and injection lap riveted unit cells that are representative of the different types of hybrid busbars joints, the development of a special purpose laboratory apparatus for thermo-electrical measurements, and numerical simulation with a finite element computer program developed by the authors. Results are a step forward in understanding the variation of the electrical resistance of hybrid busbars with temperature and allow concluding that an increase above 30% is expected when the temperature in service reaches the limiting value defined by the IEEE standard for metal-clad switchgear. [ABSTRACT FROM AUTHOR]

This paper is focussed on the mechanical and formability characterisation of wire-arc additive manufactured (WAAM) AISI 316-L stainless-steel tubes. The methodology to be presented involved carrying out tension and ring hoop tension tests on specimens extracted from the tube longitudinal, transverse and inclined directions. The force evolutions, acquired from the load cells, and the strain measurements, retrieved from digital image correlation and from thickness measurements along the cracks, allowed obtaining the stress-strain curves, the strain paths and the onset of failure by fracture for the three different tube directions. Special attention was paid to the ring hoop test, which was revisited to determine the appropriateness of using ring specimens with one or two dumbbell geometries. The originality of using the ring hoop tension test in WAAM tubes with strong anisotropic behaviour allowed obtaining strain loading paths that range from plane strain to pure shear deformation conditions. Resort to commercial AISI 316-L stainless-steel tubes during the presentation is included for reference purposes. [ABSTRACT FROM AUTHOR]

Additive manufacturing is proposed as a novel alternative to coin blank's production routes based on rolling, blanking and edge rimming. The presentation draws from laser powder bed fusion of cylinders, slicing into individual coin blanks by electro discharge machining and surface preparation by polishing, to coin minting in a laboratory press-tool system. Special emphasis is given to material deposition and coin minting due to the originality of producing coin blanks with complex intricate contoured holes and to the necessity of subjecting the additive manufactured coin blanks to extreme compressive stresses that are typical of coin minting. Numerical and experimental results confirm the excellent performance of the additive manufactured coin blanks. The new design layouts included in the additive manufactured coin blanks open the way to produce high value-added singular collector coins, which are disruptively different from those available in the market nowadays. [ABSTRACT FROM AUTHOR]

This 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. [ABSTRACT FROM AUTHOR]