Browsing by Author "Branco, Ricardo"
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- Low-Cycle Fatigue Behaviour of AISI 18Ni300 Maraging Steel Produced by Selective Laser MeltingPublication . Branco, Ricardo; Costa, José; Berto, Filippo; Razavi, Seyed; Ferreira, José; Capela, Carlos; Santos, Luís; Antunes, FernandoSelective laser melting has received a great deal of attention in recent years. Nevertheless, research has been mainly focused on the technical issues and their relationship with the final microstructure and monotonic properties. Fatigue behaviour has rarely been addressed, and the emphasis has been placed on high-cycle regimes. The aim of this paper is, therefore, to study, in a systematic manner, the cyclic plastic behaviour of AISI 18Ni300 maraging steel manufactured by selective laser melting. For this purpose, low-cycle fatigue tests, under fully-reversed strain-controlled conditions, with strain amplitudes ranging from 0.3% to 1.0%, were performed. After testing, fracture surfaces were examined by scanning electron microscopy to identify the main fatigue damage mechanisms. The analysis of results showed a non-Masing material, with a slight strain-softening behaviour, and non-linear response in both the elastic and plastic regimes. In addition, this steel exhibited a very low transition life of about 35 reversals, far below the values of conventional materials with equivalent monotonic mechanical properties, which can be attributed to the combination of high strength and low ductility. The total strain energy density, irrespective of strain amplitude, revealed itself to be a quite stable parameter throughout the lifetime. Finally, the SEM analysis showed for almost all the tested samples cracks initiated from the surface and inner defects which propagated through the rest of the cross section. A ductile/brittle fracture, with a predominance of brittle fracture, was observed in the samples, owing to the presence of defects which make it easier to spread the microcracks.
- Quasistatic and fatigue behavior of an AISI H13 steel obtained by additive manufacturing and conventional methodPublication . Garcias, José F.; Martins, Rui F.; Branco, Ricardo; Marciniak, Zbigniew; Macek, Wojciech; Pereira, Cândida; Santos, CyrilThis work aims to compare the mechanical behavior of an AISI H13 steel obtained by additive manufacturing with that obtained by conventional manufacturing methods. The average values of the ultimate tensile strength (UTS) and ductility obtained for the specimens produced by the conventional method were equal to 658 MPa and 18%, respectively, which compares with 503 MPa and 0.75% registered for the selective laser melting (SLM) specimens. Inversely, the average hardness value determined for the SLM specimens was higher, 450 HV, than the observed for the conventional, 200 HV. In addition, the maximum applied stress corresponding to a fatigue limit's endurance of 2 × 106 cycles was equal to 340 and 85 MPa for conventional and SLM specimens, respectively. Therefore, from a fatigue design point of view, it was possible to infer that σmax/UTS = 0.17 for the SLM specimens tested. Porosity and lack of fusion influenced the static and the fatigue strength negatively in the SLM specimens.