Issue 43

F. Berto et alii, Frattura ed Integrità Strutturale, 43 (2018) 1-32; DOI: 10.3221/IGF-ESIS.43.01 23 In SLM-processed samples, fatigue cracks were observed to initiate on severe surface intrusions due to the high roughness induced by the process itself as shown in Fig. 27. Such intrusions are covered by an oxide layer which was formed during the stress-relief heat treatment and non-cleaned up by the grinding treatment. The number of potential crack initiation intrusions is thought to be much higher in smooth samples than in the sharp V-notch specimen where there is the possibility that no such critical surface defects occur in the small region near the notch tip. As discussed in section 4.2 the SED is able to treat in simple and unified way internal defects and notches providing a sound approach for fracture and fatigue assessment of components weakened by defects and notches of any shape. Some preliminary results are reported in Refs. [138-140]. One of the future aim will be to combine AM with thin film deposition [141-143] reaping these technologies’ advantages while bypassing their limitations. The final aim should be to fully equip parts with mechanical and electrical properties that are conventionally not achievable, not in costs nor in performance introducing key surface properties ranging from corrosion to scratch resistance, hydrophobicity all the way to enhanced flow characteristics. In summary, the following three points should be accurately considered: simulation based design, property prediction of additive manufactured parts and thin film deposition. All fields together will enable novel digital materials and designs, their direct conversion into physical parts as well as the guarantee of their compliance through properly defined and tailored failure criterions. This interdisciplinary and integrative research will streamline the digital manufacturing workflow all the way from the idea to the final product and will enable designers and engineers to better transform their ideas into reality. Hybrid Metal & Extrusion Bonding Finally, the last potential application of the SED approach that authors want to present in this manuscript is Hybrid Metal & Extrusion Bonding (HYB) [144-147]. The HYB process, developed by Professor Øystein Grong, Engineers Ulf Roar Aakenes and Tor Austigard, is a revolutionary way to achieve bonding without melting base material, thus belonging to cold welding processes. A comprehensive work about the HYB process has been done in Ulf Aakenes’ PhD thesis [146], with following images extracted from that work. To remember is that this first approach is only focused on similar welding, in this case Al alloys. The idea is to force an extruded plasticized Al (AA6082-T4) wire between two Al plates (AA6082-T6) in a butt join configuration, Fig. 28. The result is an achieved bonding performed by scratching and subsequently restoring the lattice action of the FM. Inside the spindle extruder, at above say 275°C, the FM is submitted to a work hardening process that increases its hardness enough to scrape a thin layer of the BM and overtake the sufficient pressure to promote the joint. A steel scraper was implemented to reshape a V-groove with oxide-free surfaces soon before the aluminum injection, due to back-annealing occurring inside the spindle chamber. Figure 28: HYB configuration used for similar Al-Al welding. After years of tests and upgrades, Fig. 29 finally shows the complete workbench used in the experimental activity. The process was performed at room temperature, the heat generated belongs only to the strain work inside the spindle extruder. Two plates of 4mm 6082-T6 Al alloy were used in the experiments.