Simulation of hydrogen permeation through pure iron for trapping and surface phenomena characterisation

There is a need for numerical models capable of predicting local accumulation of hydrogen near stress concentrators and crack tips to prevent and mitigate hydrogen assisted fracture in steels. The experimental characterisation of trapping parameters in metals, which is required for an accurate simulation of hydrogen transport, is usually performed through the electropermeation test. In order to study grain size influence and grain boundary trapping during permeation, two modelling approaches are explored; a 1D Finite Element model including trap density and binding energy as input parameters and a polycrystalline model based on the assignment of a lower diffusivity and solubility to the grain boundaries. Samples of pure iron after two different heat treatments - 950C for 40 minutes and 1100C for 5 minutes - are tested applying three consecutive rising permeation steps and three decaying steps. Experimental results show that the finer grain microstructure promotes a diffusion delay due to grain boundary trapping. The usual methodology for the determination of trap densities and binding energies is revisited in which the limiting diluted and saturated cases are considered. To this purpose, apparent diffusivities are fitted including also the influence of boundary conditions and comparing results provided by the constant concentration with the constant flux assumption. Grain boundaries are characterised for pure iron with a binding energy between 37.8 and 39.9 kJ/mol and a low trap density but it is numerically demonstrated that saturated or diluted assumptions are not always verified, and a univocal determination of trapping parameters requires a broader range of charging conditions for permeation. The relationship between surface parameters, i.e. charging current, recombination current and surface concentrations, is also studied

Notch Fracture predictions using the Phase Field method for Ti-6Al-4V produced by Selective Laser Melting after different post-processing conditions

Ti-6Al-4V is a titanium alloy with excellent properties for lightweight applications and its production through Additive Manufacturing processes is attractive for different industrial sectors. In this work, the influence of mechanical properties on the notch fracture resistance of Ti-6Al-4V produced by Selective Laser Melting is numerically investigated. Literature data is used to inform material behaviour. The as-built brittle behaviour is compared to the enhanced ductile response after heat treatment (HT) and hot isostatic pressing (HIP) post-processes. A Phase Field framework is adopted to capture damage nucleation and propagation from two different notch geometries and a discussion on the influence of fracture energy and the characteristic length is carried out. In addition, the influence of oxygen uptake is analysed by reproducing non-inert atmospheres during HT and HIP, showing that oxygen shifts fracture to brittle failures due to the formation of an alpha case layer, especially for the V-notch geometry. Results show that a pure elastic behaviour can be assumed for the as-built SLM condition, whereas elastic-plastic phenomena must be modelled for specimens subjected to heat treatment or hot isostatic pressing. The present brittle Phase Field framework coupled with an elastic-plastic constitutive analysis is demonstrated to be a robust prediction tool for notch fracture after different post-processing routes

Hydraulic fracture behavior in the presence of hydrogen in notched miniature cylindrical specimens of a 42CrMo4 steel

The influence of internal hydrogen on the mechanical behavior of the 42CrMo4 steel grade has been evaluated by means of internal pressure fracture tests performed on hydrogen precharged notched cylindrical specimens. The notched cylindrical specimens were precharged in a 1 M H2SO4 solution + 0.25 g/l As2O3 for 3 h and 1.2 mA/cm2. Thereupon, hydraulic fracture tests were done under different ramps of pressure: 208, 100, 52, 35 and 25 MPa/h, respectively. Hydrogen content introduced into the notched cylindrical specimens (∼1 ppm) was determined by thermal desorption analysis (TDA), using a LECO DH 603 hydrogen analyser. Hydrogen damage was observed as testing time increased until 2 h. The burst pressure is reduced around 28 % while the Notch Mouth Opening Displacement decreased around 50 %. Hydrogen embrittlement susceptibility is discussed through the hydrogen embrittlement micromechanisms.The authors would like to thank the Spanish Government for the financial support received to perform the research projects RTI2018-096070-B-C33 and PID2021-124768OB-C21. L.B. Peral is grateful for his Margarita Salas Postdoctoral contract (Ref.: MU-21-UP2021-030) funded by the University of Oviedo through the Next Generation European Union

Influence of hydrogen on the hydraulic fracture behavior of a 42CrMo4 steel welds: Effect of the prior austenite grain size

The influence of hydrogen on the mechanical behavior of a quenched and tempered 42CrMo4 steel has been evaluated by means of high internal pressure fracture tests carried out on hydrogen precharged notched cylindrical specimens. The notched cylindrical specimens were precharged in a 1 M H2SO4 + 0.25 g/l As2O3 solution for 3 h with 1.2 mA/cm2. Hydraulic fracture tests were performed at different loading rates. Hydrogen embrittlement resistance increased with grain size refinement although the fine grained specimen had a higher hydrogen content than the coarse grained one. Fractographic analysis showed hydrogen enhanced decohesion fracture was less pronounced with decreasing grain size. Hydrogen embrittlement susceptibility is discussed in terms of the prior austenite grain size (PAGS) and the operative fracture mechanisms.The authors would like to thank the Spanish Government for the financial support received to perform the research projects TED2021-130413B-I00 and PID2021-124768OB-C21. This work was supported by the Regional Government of Castilla y León (Junta de Castilla y León) and by the Ministry of Science and Innovation MICIN and the European Union Next Generation EU/PRTR (MR5W.P3) and PRTR (MR4W.P2). L.B. Peral is grateful for his Margarita Salas Postdoctoral contract (Ref.: MU-21-UP2021-030) funded by the University of Oviedo through the Next Generation European Union

Parameter Optimisation in Selective Laser Melting on C300 Steel

Additive manufacturing (AM) of metallic materials is increasingly being adopted in numerous sectors, such as biomedicine, aerospace or automotive industries, due to its versatility in the creation of complex geometries and the minimisation of material waste when compared to traditional subtractive methods. In order to ensure a reliable operation of these parts, however, an in-depth study of the effect of additive manufacturing on mechanical properties, including tensile, fatigue and fracture resistance, is necessary. Among the vast number of methods and materials, this project is focused in one of the most promising techniques for the industry: Selective Laser Melting (SLM) for the production of a tools steel, in particular C300 steel components for the automotive sector. The main objective of this paper is to optimise some of the key parameters in the printing process, such as laser power, laser speed and hatch spacing. These variables are essential to obtain parts with good resistance. To that purpose, tensile tests were performed in 3D printed specimens, and then elastoplastic properties were extracted, organised and analysed through a design of experiments for the subsequent output fitting using the response surface methodology.This research was funded by: INVESTUN/22/BU/0003 // BU-002-P20 // MU-21-UP2021-030

A genome-wide association study follow-up suggests a possible role for PPARG in systemic sclerosis susceptibility

Introduction: A recent genome-wide association study (GWAS) comprising a French cohort of systemic sclerosis (SSc) reported several non-HLA single-nucleotide polymorphisms (SNPs) showing a nominal association in the discovery phase. We aimed to identify previously overlooked susceptibility variants by using a follow-up strategy.<p></p> Methods: Sixty-six non-HLA SNPs showing a P value <10-4 in the discovery phase of the French SSc GWAS were analyzed in the first step of this study, performing a meta-analysis that combined data from the two published SSc GWASs. A total of 2,921 SSc patients and 6,963 healthy controls were included in this first phase. Two SNPs, PPARG rs310746 and CHRNA9 rs6832151, were selected for genotyping in the replication cohort (1,068 SSc patients and 6,762 healthy controls) based on the results of the first step. Genotyping was performed by using TaqMan SNP genotyping assays. Results: We observed nominal associations for both PPARG rs310746 (PMH = 1.90 × 10-6, OR, 1.28) and CHRNA9 rs6832151 (PMH = 4.30 × 10-6, OR, 1.17) genetic variants with SSc in the first step of our study. In the replication phase, we observed a trend of association for PPARG rs310746 (P value = 0.066; OR, 1.17). The combined overall Mantel-Haenszel meta-analysis of all the cohorts included in the present study revealed that PPARG rs310746 remained associated with SSc with a nominal non-genome-wide significant P value (PMH = 5.00 × 10-7; OR, 1.25). No evidence of association was observed for CHRNA9 rs6832151 either in the replication phase or in the overall pooled analysis.<p></p> Conclusion: Our results suggest a role of PPARG gene in the development of SSc

Costs and benefits of automation for astronomical facilities

The Observatorio Astrof\'isico de Javalambre (OAJ{\dag}1) in Spain is a young astronomical facility, conceived and developed from the beginning as a fully automated observatory with the main goal of optimizing the processes in the scientific and general operation of the Observatory. The OAJ has been particularly conceived for carrying out large sky surveys with two unprecedented telescopes of unusually large fields of view (FoV): the JST/T250, a 2.55m telescope of 3deg field of view, and the JAST/T80, an 83cm telescope of 2deg field of view. The most immediate objective of the two telescopes for the next years is carrying out two unique photometric surveys of several thousands square degrees, J-PAS{\dag}2 and J-PLUS{\dag}3, each of them with a wide range of scientific applications, like e.g. large structure cosmology and Dark Energy, galaxy evolution, supernovae, Milky Way structure, exoplanets, among many others. To do that, JST and JAST are equipped with panoramic cameras under development within the J-PAS collaboration, JPCam and T80Cam respectively, which make use of large format (~ 10k x 10k) CCDs covering the entire focal plane. This paper describes in detail, from operations point of view, a comparison between the detailed cost of the global automation of the Observatory and the standard automation cost for astronomical facilities, in reference to the total investment and highlighting all benefits obtained from this approach and difficulties encountered. The paper also describes the engineering development of the overall facilities and infrastructures for the fully automated observatory and a global overview of current status, pinpointing lessons learned in order to boost observatory operations performance, achieving scientific targets, maintaining quality requirements, but also minimizing operation cost and human resources.Comment: Global Observatory Control System GOC

Análisis de la seguridad integral en los centros educativos de enseñanza obligatoria de España

El presente estudio analiza el Nivel de Seguridad Integral (NiSI) de los centros educativos de enseñanza obligatoria de España, como continuación de un trabajo de investigación anterior. Para la recogida de datos se ha aplicado el Cuestionario de Autoevaluación EDURISC a una muestra de 273 centros educativos de toda España, realizando, también, 12 estudios de caso y celebrando cuatro grupos de discusión. El análisis de los resultados evidencia las principales fortalezas y debilidades que presentan los centros en materia de seguridad, destacando las deficiencias detectadas en: suscripción de seguros escolares y extraescolares, mantenimiento de las instalaciones, accesibilidad, tránsito y circulación interior y exterior, medidas de protección contra el robo y la intrusión, custodia de documentación y prevención del riesgo físico del alumnado. En este sentido, es necesario seguir trabajando en pro de la seguridad de los centros educativos, adoptando y aplicando adecuadas medidas preventivas y paliativas, para mejorar los Niveles de Seguridad Integra

Food and nutrition security discursive frames in the context of the Spanish economic crisis

[EN] The recent economic crisis in Spain has provoked a number of food and nutrition security (FNS) impacts that have fuelled a fragmented landscape of food-related debates, although these have not taken the form of a coherent and allembracing public discussion on national food security. This paper is an inductive analysis of such debates, mostly based on media coverage, in an attempt to disentangle the different discourse frames on FNS in Spain, and the role played by the economic crisis in the shaping and underpinning of such frames. For this purpose a frame matrix was constructed, paying particular attention to the stakeholders governance claims in order to confront frame-specific problems. Results show how stakeholders have used elements of the crisis to underpin or reinterpret their core arguments. 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