Percorrer por autor "Costa, José D."
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- Fatigue Failure from Inner Surfaces of Additive Manufactured Ti-6Al-4V ComponentsPublication . Jesus, Joel de; Ferreira, José António Martins; Borrego, Luís; Costa, José D.; Capela, CarlosSelective laser melting (SLM) is an additive manufacturing process for producing metallic components with complex geometries. A drawback of this process is the process-inherent poor surface finish, which is highly detrimental in materials submitted to fatigue loading situations. The goal of this work is to analyze the fatigue behavior of Ti-6Al-4V specimens with internal axial channels under the following different conditions: hole drilled, hole as manufactured, and hole threaded M4 × 0.7. All the cases studied showed a lower fatigue performance as compared with solid samples due to the surface roughness and geometry effect that produced a surface stress concentration leading to a reduction in fatigue strength. The fractography revealed that crack initiation occurred from the internal surface in all specimens with internal channel mostly from defects as unfused particles and lack of fusion zones, while for the solid specimens crack initiation was observed from the external surface due to insufficient fusion defect. The application of the Smith-Watson-Topper energy-based parameter was revealed to be a good tool for fatigue life prediction of the different series studied.
- Fracture Toughness of Hybrid Components with Selective Laser Melting 18Ni300 Steel PartsPublication . Lima Santos, Luís; Jesus, Joel De; Ferreira, José M.; Costa, José D.; Capela, CarlosSelective Laser Melting (SLM) is currently one of the more advanced manufacturing and prototyping processes, allowing the 3D-printing of complex parts through the layer-by-layer deposition of powder materials melted by laser. This work concerns the study of the fracture toughness of maraging AISI 18Ni300 steel implants by SLM built over two different conventional steels, AISI H13 and AISI 420, ranging the scan rate between 200 mm/s and 400 mm/s. The SLM process creates an interface zone between the conventional steel and the laser melted implant in the final form of compact tension (CT) samples, where the hardness is higher than the 3D-printed material but lower than the conventional steel. Both fully 3D-printed series and 3D-printed implants series produced at 200 mm/s of scan rate showed higher fracture toughness than the other series built at 400 mm/s of scan rate due to a lower level of internal defects. An inexpressive variation of fracture toughness was observed between the implanted series with the same parameters. The crack growth path for all samples occurred in the limit of interface/3D-printed material zone and occurred between laser melted layers.
- Influence of Tool Geometry and Process Parameters on Torque, Temperature, and Quality of Friction Stir Welds in Dissimilar Al AlloysPublication . Manuel, Neves; Beltrão, Daniel; Galvão, Ivan; Leal, Rui M.; Costa, José D.; Loureiro, AltinoIn the current investigation, the influence of the tool geometry, the position of the materials in the joint, the welding speed on the temperature and torque developed, and on the quality of the welds in dissimilar and tri-dissimilar T joints were analysed. The aluminium alloys used were AA2017-T4, AA6082-T6, and AA5083-H111 and the friction stir welds were performed with identical shoulder tools, but with either a pin with simple geometry or a pin with progressive geometry. Progressive pin tools proved to be a viable alternative in the production of dissimilar and tri-dissimilar welds, as they provide a larger tool/material friction area and a larger volume of dragged material, which promotes an increase in the heat generated and a good mixing of the materials in the stir zone, although they require a higher torque. Placing a stronger material on the advancing side also results in a higher temperature in the stir zone but requires higher torque too. The combination of these factors showed that tools with a progressive pin provide sound dissimilar and tri-dissimilar welds, unlike single-pin tools. The increase in the welding speed causes the formation of defects in the stir zone, even in tri-dissimilar welds carried out with a tool with a progressive pin, which impairs the fatigue strength of the welds.
- Nugget Formation and Mechanical Behaviour of Friction Stir Welds of Three Dissimilar Aluminum AlloysPublication . Manuel, Neves; Galvão, Ivan; Leal, Rui M.; Costa, José D.; Loureiro, AltinoThe aim of this research was to investigate the influence of the properties of the base materials and welding speed on the morphology and mechanical behavior of the friction stir welds of three dissimilar aluminum alloys in a T-joint configuration. The base materials were the AA2017-T4, AA5083-H111, and AA6082-T6 alloys in 3 mm-thick sheets. The AA6082-T6 alloy was the stringer, and the other alloys were located either on the advancing or retreating sides of the skin. All the T-joint welds were produced with a constant tool rotation speed but with different welding speeds. The microstructures of the welds were analyzed using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, and the electron backscatter diffraction technique. The mechanical properties were assessed according to micro-hardness, tensile, and fatigue testing. Good quality welds of the three dissimilar aluminum alloys could be achieved with friction stir welding, but a high ratio between the tool's rotational and traverse speeds was required. The welding speed influenced the weld morphology and fatigue strength. The positioning of the skin materials influenced the nugget morphology and the mechanical behavior of the joints. The joints in which the AA2017 alloy was positioned on the advancing side presented the best tensile properties and fatigue strength.