microstructure and fatigue performance of slm fabricated ti6al4v alloy after different stress relief heat treatments

Abstract The main interest in Additive Manufacturing (AM) technology relates to its ability to produce complex components with relatively reduced weight that are difficult to produce or cannot be produced by other conventional technologies. Selective laser melting (SLM) is extensively used, as one of the AM technologies to fabricate metallic parts. This advanced method allows to produce various parts with complex geometries with high three-dimensional (3D) accuracy from fusion powders in a layer-by-layer style. Ti6Al4V alloy is a widely used material for structural applications in aerospace and biomedical due to high specific fatigue strength. SLM processing makes this alloy attractive when weight reduction is a design objective. The SLM Ti6Al4V microstructure is influenced by process parameters and build orientation. The localized high energy input during very short interaction times leads to the formation of very fine structures and to the generation of internal stresses. Therefore, the SLM parts are heat treated to decrease or completely remove residual stresses. The present study aims at evaluating the effect of stress-relief heat treatments on the microstructure, the mechanical properties and the fatigue performance of SLM Ti6Al4V alloy. Ti6Al4V alloy specimens were manufactured according to the SLM process with an EOS M290 system. Post fabrications heat treatments at different temperatures (i.e. 740˚C vs. 900˚C) resulted in different structure and mechanical properties that were identified and measured. Fatigue testing of specimens with as-built surfaces was performed at room temperature on modified Schenk-type fatigue testing machine applying a pulsating plane bending (load cycle ratio R = 0) to the specimens at a frequency f = 15 Hz

Probing the electromagnetic response of dielectric antennas by vortex electron beams

Focused beams of electrons, which act as both sources, and sensors of electric fields, can be used to characterise the electric response of complex photonic systems, by locally probing the induced optical near fields. This functionality can be complemented by embracing the recently developed vortex electron beams (VEBs), made up of electrons with orbital angular momentum, which could in addition probe induced magnetic near fields. In this work we revisit the theoretical description of this technique, dubbed vortex Electron Energy-Loss Spectroscopy (v-EELS). We map the fundamental, quantum-mechanical picture of the scattering of the VEB electrons, to the intuitive classical models which treat the electron beams as superposition of linear electric and magnetic currents. We then apply this formalism to characterise the optical response of dielectric nanoantennas with v-EELS. Our calculations reveal that VEB electrons probe electric or magnetic modes with different efficiency, which can be adjusted by changing either beam vorticity or acceleration voltage, to determine the nature of the probed excitations. We also study a chirally-arranged nanostructure, which in the interaction with electron vortices produces dichroism in electron energy loss spectra. Our theoretical work establishes VEBs as versatile probes that could provide information on optical excitations otherwise inaccessible with conventional electron beams

Spatial and Temporal Variability of the Gamma Radiation from Earth's Atmosphere during a Solar Cycle

The Solar Maximum Mission satellite's Gamma Ray Spectrometer observed Earth's atmosphere for most of the period 1980-1989. Its 28deg orbit ensured that a range of geomagnetic latitudes (geomagnetic cutoff rigidities) was sampled. We measured the variation with time and rigidity of albedo gamma-ray lines at 1.6 MeV, 2.3 MeV and 4.4 MeV which are diagnostic of Galactic cosmic radiation penetrating the cutoff and of the secondary neutrons produced in the atmosphere. We found that the gamma-ray line intensities varied inversely with solar activity and cutoff rigidity, as expected. The line ratio (1.6 MeV + 2.3 MeV)/4.4 MeV was remarkably constant (close to 0.39) at all times and rigidities; the former two lines are produced by 5-10 MeV secondary neutrons causing excitation and de-excitation of 14N, while the latter is produced by more energetic (>20 MeV) neutrons inducing spallation. We infer that the shape of the secondary neutron energy spectrum is virtually constant everywhere and at all times. We also measured the intensity of the 0.511 MeV electron-positron annihilation line. This line too varies with solar cycle and cutoff rigidity, but its fall-off from low to high rigidity is less marked than that of the nuclear lines. This results from the energy dependences of the cross sections for positron production and for the hadronic processes which which produce secondary neutrons.Comment: 11 pages, 12 figs., J. Geophys. Res. in pres

Fatigue Strength of Nodular Cast Iron with Different Surface Conditions under Bending Loading

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Are UK E-waste recycling facilities a source of environmental contamination and occupational exposure to brominated flame retardants?

Investigations into the impacts of regulated electrical and electronic waste (e-waste) recycling activities on urban environments in Europe remain rather scarce. In this study, dust samples taken both inside and outside of five UK e-waste recycling facilities were analysed for concentrations of polybrominated diphenyl ethers (PBDEs), novel brominated flame retardants (NBFRs), and hexabromocyclododecane (HBCDD). Average concentrations of ∑BFRs in dust inside and outside UK e-waste recycling facilities were 12,000 ng/g and 180 ng/g, with median concentrations of 7500 ng/g and 85 ng/g, respectively. BDE-209 and decabromodiphenyl ethane (DBDPE) were the most abundant BFRs in both indoor and kerb dust, making a combined contribution to ∑BFRs of ~90 % on average. While four out of the five studied e-waste facilities showed a lack of significant impact on BFR contamination in surrounding environment, one of the studied e-waste recycling facilities was identified as a likely source of BFR contamination to UK urban environments, with industrial activities as another potential source of NBFRs. Occupational exposure of UK e-waste recycling workers to BFRs via dust ingestion was generally lower than that estimated for e-waste recyclers from other countries, but was comparable to BFR exposure via dust ingestion of UK office workers. Our estimates suggested that health burdens posed by dust ingestion of BFRs were minimal for UK e-waste recycling workers.</p

Determination of the wind pressure distribution on the facade of the triangularly shaped high-rise building structure

Methods for determination of the wind pressure distribution on the facade of the atypically shaped high-rise building structure will be shown. The standard Eurocode 1 [1] does not mention recommendations for calculation of wind pressure distribution on the facade for the most cases of buildings having an irregular cross-section. Analysed object has a shape of the equilateral triangle. For the determination of the pressure distribution two methods were used. Experimental analysis was carried out in the boundary layer wind tunnel and second approach was performed by numerical simulation of wind flow using computational fluid dynamics (CFD) software based on the finite volume method. Both methods used scaled model of the structure. For the wind tunnel experiment, 16 points of interests around an object were monitored in steady wind flow and from those points, results of external pressure coefficients from 2 directions of wind flow were obtained. In conclusion comparison of results of both methods will be shown

Influence of nitriding on the fatigue behavior and fracture micromechanisms of nodular cast Iron

Surface modification processes are increasingly used to fully exploit material potential in fatigue critical applications because fatigue strength is sensitive to surface conditions. Nitriding is extensively adopted with ferrous materials because it forms a hard and strong surface layer and a system ofsuperficial compressive residual stresses. Fatigue, however, is strongly dependent also on defects and inhomogeneity. When nitriding is applied to nodular cast iron (NCI), the relatively thin hardened layer (about 300 μm) contains graphite nodules (diameter of the order of 30 μm), casting defects and a heterogeneous matrix structure. The paper presents and discusses the influence of nitriding on the fatigue response and fracture mechanisms of NCI. A ferritic NCI and a synthetic melt with different content of effective ferrite were initially gas-nitrided. Then, (i) structural analysis of nitrided layers, (ii) fatigue testing with rotating bending specimens, and (iii) fatigue fracture surface inspection were performed. Performance and scatter in fatigue performance is discussed by selective inspection of fracture surfaces and identification fracture micromechanisms. A semiempirical model explains observed trends in test results and is used for the process optimization.Процессы модификации поверхности все более широко применяются для полного раскрытия возможностей материала в условиях высоких усталостных нагрузок, поскольку на усталостную прочность влияет состояние поверхности. Азотирование широко используют для обработки железосодержащих материалов, поскольку оно создает прочный поверхностный слой и поверхностные остаточные сжимающие напряжения. Усталость также существенно зависит от дефектов и неоднородности. При азотировании чугуна с шаровидным графитом в относительно тонком упрочненном слое (примерно 300 мкм) присутствуют шаровидные включения графита (диаметр порядка 30 мкм), дефекты литья и неоднородная структура основы. Рассматривается влияние азотирования на характеристики усталости и механизмы разрушения чугуна. Сначала проводили газовое азотирование ферритного чугуна и синтетического расплава с различным содержанием активного феррита. Затем выполняли структурный анализ азотированных слоев; испытание на сопротивление усталости путем кругового изгиба образца; контроль поверхности усталостного разрушения. Эффективность и разброс усталостных характеристик оценивали путем выборочного контроля поверхностей разрушения и идентификации микромеханизмов разрушения. Полуэмпирическая модель используется для оценки результатов испытаний и оптимизации процесса

Nuclear and Mitochondrial Circulating Cell-Free DNA Is Increased in Patients With Inflammatory Bowel Disease in Clinical Remission

Background: The role of cell-free DNA (cfDNA) in the pathogenesis of inflammatory bowel disease (IBD) has been recently suggested. The aim of this study was to analyze circulating cfDNA and deoxyribonuclease (DNase) activity in IBD patients in clinical remission. Materials and Methods: Plasma and serum were obtained from 72 patients with Crohn's disease and 28 patients with ulcerative colitis. Total cfDNA, nuclear DNA (ncDNA), mitochondrial DNA (mtDNA) and DNase activity were measured. Results: IBD patients showed higher levels of both ncDNA and mtDNA compared to healthy controls. Concentration of ncDNA was higher in males compared to females, including patients and healthy controls. However, unlike males higher amount of ncDNA was found in female IBD patients compared to healthy controls. DNase activity was significantly lower in male IBD patients compared with healthy controls. In addition, there was a negative correlation between DNase activity and ncDNA levels in male IBD patients. Conclusions: Herein we present increased amount of circulating ncDNA and mtDNA in IBD patients in clinical remission. Thus, unlike total cfDNA, circulating ncDNA and mtDNA might not represent the optimal biomarkers of disease activity. This is also the first report on sex difference in circulating ncDNA levels, possibly associated with lower DNase activity in males.publishedVersio

Effect of commercial crossing of Šumavska sheep with selected meat breeds on carcass characteristics of lambs

Evaluation of the effect of commercial crossing of Šumavska sheep (S) with selected meat breeds (Suffolk (SF) and Texel (T) on basic carcass and non-carcass traits of lambs was carried out on an organic farm in Proseč in the Pardubice region. Four different genotypes were included in the experiment: SF x S (n = 9), S (n = 11), SF x (T 75 S 25) (n = 12) and S x (T 75 S 25) (n = 14). All lambs in the study were males. The highest daily gain (0.166 kg/day), carcass yield (43.96 %) and proportion of muscle and fat in the left leg (79.25 %) were found in crossbreds SF x (T 75 S 25) while in this group was the highest proportion of meat breeds. In contrast, in purebred lambs of Šumavská sheep the lowest daily gain (0.122 kg/day), carcass yield (37.71 %) and proportion of muscle and fat in left leg (74.47 %) were found. The best conformation score and the lowest fatness score (2.22) were found in crossbreds SF x S. On the other hand in purebred lambs of Šumavska sheep the worst conformation score (4.91) was found. However in this group relatively very favorable fatness score (2.27) was also found. The results of the experiment indicate that use of commercial crossing of ewes of Šumavská breed with rams of meat breeds had a positive effect on the most of the monitored carcass traits