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- PublicationThe role of microstructural evolution on the fatigue behavior of additively manufactured Ti–6Al–4V alloy(Elsevier, 2022-11-24)The fatigue behaviour of additively manufactured Ti–6Al–4V via Laser Powder Bed Fusion (L-PBF) was evaluated in three different conditions, as-built, heat-treated and hot isostatically pressed (HIP'ed). Fractography analysis interpreted together with the S–N curves indicates that fatigue failure in as-built and heat-treated conditions where <0.2% porosity was present, was mainly driven by early-stage crack growth. However, crack initiation was determined to be the main controlling factor for fatigue deformation of HIP'ed samples. Moreover, a strong correlation between the impact energy and fatigue limit was found. The findings were based on detailed microstructural and crystallographic characterization, as well as mechanical testing. The as-built and heat-treated conditions exhibited poor fatigue response in comparison to HIP'ed which is largely attributed to the lower levels of porosity identified. Even though similar levels of porosity are present in as-built and heat-treated samples, improvement in fatigue limit was determined in the heat-treated condition due to phase transformation and microstructural coarsening leading to reduction in micro-strain.
- PublicationThe Study on Microstructural Evolution During Post-processing of Additively Manufactured Ti64(Springer, 2022-02-07)The effect of furnace heat treatments to 850 °C, on the evolution of microstructure in Ti–6Al–4V alloy produced via selective laser melting (SLM), was studied using optical microscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Columnar prior-β grains in the build direction with lamellar α-martensite laths contained within the prior-β grains were determined. α-martensite laths present in the as-built microstructure had thicknesses around 236 nm while the heat-treated microstructure showed an α-lath thickness values of around 1.8 μm. Based on XRD analysis, upon heat treatment the formation of β-phase was determined with associated peaks around 41° and 58°, corresponding to (110) and (200) planes, respectively.
33Scopus© Citations 1
- PublicationHierarchical RVE-based multiscale modelling of non-linear heterogeneous materials using the finite volume method(Begell House, 2022)This paper describes the development of a hierarchical multiscale procedure within the finite volume OpenFOAM framework for modelling the mechanical response of non-linear heterogeneous solid materials. This is a first development of hierarchical multi-scale model for solid mechanics to use the finite volume discretisation method. In this computational procedure the information is passed between the macro and micro scales using representative volume elements (RVE), allowing for general, non-periodic microstructures to be considered. Each computational point at the macro scale is assigned an RVE with prescribed microstructural features. The overall macro response accounts for the microstructural effects through the coupling of macro and micro scales, i.e., the macro deformation gradient is passed to the RVE and in turn, the homogenised micro stress-strain response is passed back to the macro scale. The incremental total Lagrangian formulation is used to represent the equilibrium state of the solid domain at both scales and its integral equilibrium equation is discretised using the cell-centred finite volume (FV) method in OpenFOAM. The verification of the model is demonstrated using both 2D and 3D simulations of perforated elastic-plastic plates subjected to tensile loading.
- PublicationImpact of print bed build location on the dimensional accuracy and surface quality of parts printed by multi jet fusion(Elsevier, 2021-10)Multi Jet Fusion (MJF) is one of the newly developed additive manufacturing techniques, based on the use of powder bed fusion technology. It provides the opportunity to build up 3D, complex polymer geometries, without the need for support structures. This study evaluates the effect of build location across a 380 × 284 mm2 build plate, on both the dimensional accuracy and surface quality of polyamide 12 (PA12) parts printed using the MJF technique. The cube test samples were printed at each of the four corners and the center of the build plate. Dimensional deviations were determined using optical metrology measurements, while surface deviations were measured using 2D tactile and 3D optical profilometers. The density and the degree of crystallinity of the samples were determined using the Archimedes method and Differential Scanning Calorimetry analysis, respectively. Moreover, the morphology of the internal polymer surfaces was evaluated using Scanning Electron Microscopy. It was concluded that while overall printed part dimensions and crystallinity homogeneity were relatively uniform across the build plate, some variations were observed. Parts printed in particular, closer to the front of the build plate exhibited higher porosity, higher surface roughness along with the highest level of geometry deviation, compared with the CAD drawing. This is likely to be associated with some non- uniformities in heating and cooling of the PA12 polymer parts across the build plate.
101Scopus© Citations 4
- PublicationNiO/ZrO2 nanocomposites as photocathodes of tandem DSCs with higher photoconversion efficiency with respect to parent single-photoelectrode p-DSCs(Royal Society of Chemistry, 2021-08-20)The nanocomposites of nickel oxide (NiO) and zirconia (ZrO2) (NZNCs) are particularly effective photocathodic materials in p-type dye-sensitized solar cells (p-DSCs) and tandem DSCs (t-DSCs). The t-DSCs obtained from P1-sensitized NZNC as photocathode and nanostructured titania (TiO2) sensitized with squaraine VG10-C8 as photoanode display overall efficiencies of ca. 2% at their best and, more importantly, produced photocurrents that surpassed systematically the values obtained from the parent devices having one photoelectrochemical interface. Such a finding is a consequence of the diminished resistance of the electrolyte the thickness of which is systematically smaller in t-DSCs with respect to parent DSCs with a single photoelectrochemical junction and same interelectrodic separation. The results here reported demonstrate that a careful combination of photoelectroactive electrodes can lead to an increase in current density of more than 15% in the t-DSC with respect to single-junction DSCs employing the same photoelectrodes provided that the whole thickness of the t-DSC is the same as in the single photoelectrode DSC and the photoelectrodes in the t-DSC do not incur in short-circuit phenomena through the electrolyte. For the successful realization of t-DSCs another important aspect is the complementarity of the absorption properties of the chosen colorants with the sensitized electrodes having similar absorbance in their respective ranges of optical absorption. The latter condition in t-DSCs makes possible the achievement of photoactivity spectra with a uniform efficiency of conversion in the whole visible range. For the attainment of efficient t-DSCs the two different photoelectrodes from parent DSCs (i.e. the devices at a single photoeletrochemical interface), should generate anodic and cathodic photocurrent densities with very similar values. Such a matching of photocurrents requires a careful selection of the thickness values for the photoelectrodes especially in case of materials with considerably different characteristics of charge injection. The approach here considered is a promising one for the assembly of quasi-transparent photoelectrochemical tandem devices operating as smart windows that convert light into electrical power.
86Scopus© Citations 2