Analysis of the mesoscopic high cycle multiaxial fatigue strength of fcc metals with crystal plasticity and generalized extreme values probability

Multiaxial high cycle fatigue modeling of materials is an issue that concerns many industrial domains (automotive, aerospace, nuclear, etc) and in wich many progress still remains to be achieved. Several approaches exist in the litterature: invariants, energy, integral and critical plane approaches all of there having their advantages and their drawbacks. These different formulations are usually based on mechanical quantities at the micro or meso scales using localization schemes and strong assumptions to propose simple analytical forms. This study aims to revisit these formulations using a numerical approach based on crystal plasticity modelling coupled with explicit description of microstructure (morphology and texture). This work has three steps: First, 2D periodic digital microstructures based on a random grain sizes distribution are generated. Multiaxial cyclic load conditions corresponding to the fatigue strength at 107 cycles are applied to these microstructures. Then, the mesoscopic Fatigue Indicator Parameters (FIPs), formulated from the different criteria existing in the literature, are identified using the FE calculations of the mechanical fields. These mesoscopic FIP show the limits of the original criteria when it comes to applying them at the grain scale. Finally, a statistical method based on extreme value probability is used to redefine the parameters of these criteria. These new criteria contain the sensitivity of the microstructure variability

Analysis of the mesoscopic high cycle fatigue strength of FCC metals with polycrystalline plasticity and extreme value probability methods

This study analyzes the influence of microstructure properties on the extreme value distributions of the fatigue indicator parameter (FIP) corresponding to the multiaxial HCF Dang Van criterion. The following loading cases are considered: uniaxial loading, proportional and non-proportional multiaxial loadings. The mesoscopic FIP determined from FE calculations on 2D polycrystalline synthetic aggregates using the ZeBuLoN code. The approach adopted in this work is to replace the RVE by random microstructure elements that can be considered as “statistical volume element” (SVE). A set of extreme values is constructed by determining the maximum value of the FIP for each SVE. The type of extreme value distribution is analyzed with a generalized extreme value function and is shown to follow a Gumbel type distribution. The shape factors of this distribution are compared for the different loading conditions. This comparison shows the limitations of the used criterion, especially in the case of multiaxial loadings. The effect of anisotropy on these distributions is finally investigated by comparing the results of two types of texture (isotropic and rolling). The introduction of a preferential texture reduces the shape factor and the criterion applied with the classic stress field becomes conservative, and also decreases the scatter parameter of the extreme value distributions of the FIP

Analysis of the multiaxial fatigue strength at the mesoscopic scale using 3D microstructure modeling and extreme value statistics

Fatigue life computing methods are generally based on putting into equation the mechanical quantities calculated at the micro or meso scale, the relevance of these selected quantities being validated by the capacity of the models to reproduce experimental results at the macroscopic scale. Although the scaling of the damage mechanisms involved in fatigue crack initiation processes are relatively well identified (grain scale, slip bands), their explicit consideration in fatigue criteria is still not well-developed. Furthermore, the existing methods do not consider the microstructure-sensitivity. The aim of this paper is to present the computational strategies developed to account for the microstructure-sensitivity in the calculation of fatigue strength. This work is based on three parts: (1) the development of 3D microstructure modeling tools (2) the analysis of the dispersion induced by the microstructure heterogeneities on the critical fatigue damage indicators and (3) the development of a statistical approach which provides a framework for analyzing calculation results in the HCF (High Cycle Fatigue) regime. In this background, a method of analysis based on the construction of statistical extreme value distributions from FEA calculation results was developed. The evolution of the scaling parameters of these distributions for different loading conditions informed us about the effect of non-proportional loading and microstructure. A design method based on these extreme value statistics is presented to obtain a new mesoscopic criterion sensitive to microstructure parameters. Finally, surface effects are discussed too

Micro-mechanical modelling of high cycle fatigue behaviour of metals under multiaxial loads

An analysis of high cycle multiaxial fatigue behaviour is conducted through the numerical simulation of polycrystalline aggregates using the finite element method. The metallic material chosen for investigation is pure copper, which has a Face Centred Cubic (FCC) crystalline microstructure. The elementary volumes are modelled in 2D using an hypothesis of generalised plane strain and consist of 300 equi-probability, randomly oriented grains with equiaxed geometry. The aggregates are loaded at levels equivalent to the average macroscopic fatigue strength at 1E7 cycles. The goal is to compute the mechanical quantities at the mesoscopic scale (i.e., average within the grain) after stabilization of the local cyclic behaviour. The results show that the mesoscopic mechanical variables are characterised by high dispersion. A statistical analysis of the response of the aggregates is undertaken for different loading modes: fully reversed tensile loads, torsion and combined in-phase tension–torsion. Via the calculation of the local mechanical quantities for a sufficiently large number of different microstructures, a critical analysis of certain multiaxial endurance criteria (Crossland, Dang Van and Matake) is conducted. In terms of material behaviour models, it is shown that elastic anisotropy strongly affects the scatter of the mechanical parameters used in the different criteria and that its role is predominant compared to that of crystal plasticity. The analysis of multiaxial endurance criteria at both the macroscopic and mesoscopic scales clearly show that the critical plane type criteria (Dang Van and Matake) give an adequate estimation of the shear stress but badly reflect the scatter of the normal stress or the hydrostatic stress

Altered protein O-GlcNAcylation in placentas from mothers with diabetes causes aberrant endocytosis in placental trophoblast cells

From Springer Nature via Jisc Publications RouterHistory: received 2021-05-28, accepted 2021-09-27, registration 2021-10-06, pub-electronic 2021-10-19, online 2021-10-19, collection 2021-12Publication status: PublishedAbstract: Women with pre-existing diabetes have an increased risk of poor pregnancy outcomes, including disordered fetal growth, caused by changes to placental function. Here we investigate the possibility that the hexosamine biosynthetic pathway, which utilises cellular nutrients to regulate protein function via post-translationally modification with O-linked N-acetylglucosamine (GlcNAc), mediates the placental response to the maternal metabolic milieu. Mass spectrometry analysis revealed that the placental O-GlcNAcome is altered in women with type 1 (n = 6) or type 2 (n = 6) diabetes T2D (≥ twofold change in abundance in 162 and 165 GlcNAcylated proteins respectively compared to BMI-matched controls n = 11). Ingenuity pathway analysis indicated changes to clathrin-mediated endocytosis (CME) and CME-associated proteins, clathrin, Transferrin (TF), TF receptor and multiple Rabs, were identified as O-GlcNAcylation targets. Stimulating protein O-GlcNAcylation using glucosamine (2.5 mM) increased the rate of TF endocytosis by human placental cells (p = 0.02) and explants (p = 0.04). Differential GlcNAcylation of CME proteins suggests altered transfer of cargo by placentas of women with pre-gestational diabetes, which may contribute to alterations in fetal growth. The human placental O-GlcNAcome provides a resource to aid further investigation of molecular mechanisms governing placental nutrient sensing

Structural characterization of the of inorganic and organic hydrotalcites

Layered double hydroxides are versatile materials used for intercalating bioactive molecules, both in pharmaceutical and cosmetic fields, with the purpose of protecting them from degradation, enhancing their water solubility to increase bioavailability, and/or obtaining modified release properties. Hydrotalcite is commercially available in its carbonate form, which is usually transformed into the nitrate form and finally exchanged by organic anions to obtain or regulate bioactivity or photo-activity effects (1). In this study all the steps of these transformations were characterized from the structural viewpoints by X-ray powder diffraction (XRPD) and automated electron diffraction tomography (ADT). ADT allowed shedding light on the nitrate position and conformation inside LDH. XRPD demonstrated at first that the presence of carbonate impurities is able to drive the intercalation of organic molecules into LDH, since CO32- contaminated samples tend to assume d-spacings roughly multiple of LDH-CO3 d-spacing. Finally XRPD was employed at in situ conditions to unravel the structural transformation occurring during the substitution of carbonate by nitrate ion and of the nitrate ion by organic anions. The carbonate-nitrate substitutions resulted to be very rapid (only few seconds) and only the use of a fast area detector, coupled to synchrotron radiation, allowed obtaining reliable patterns to perform XRPD refinement of the disordered structure at the sub-second time resolution. The nitrate-organic substitution resulted slower and depending on the chemical properties of the organic molecules

Exposure to blue light reduces antimicrobial resistant Pseudomonas aeruginosa isolated from dog ear infections

Introduction: Pseudomonas aeruginosa is a leading cause of canine otitis externa. Enrofloxacin is often applied topically to treat this condition, although recalcitrant and recurring infections are common. There is evidence that exposure to blue light (400–470 nm) has a bactericidal effect on P. aeruginosa and other microorganisms.Methods: In the present study, we tested the biocidal effect of blue light (375–450 nm), alone or in combination with enrofloxacin, against six isolates of P. aeruginosa from dogs with otitis externa (5 of which were resistant to enrofloxacin).Results: Treatment of planktonic cell cultures with blue light resulted in significant (p < 0.5) reductions in Colony Forming Units (CFU) for all seven strains tested, in some cases below the limit of detection. The greatest bactericidal effect was observed following exposure to light at 405 nm wavelength (p <0.05). Exposure to blue light for 20 min usually resulted in a greater reduction in Pseudomonas aeruginosa than enrofloxacin treatment, and combination treatment typically resulted in the largest reductions in CFU. Analysis of the genome sequences of these strains established that enrofloxacin resistance was likely the result of a S466F substitution in GyrB. However, there was no clear association between genotype and susceptibility to blue light treatment. Discussion: These results suggest that blue light treatment, particularly at 405 nm wavelength, and especially in combination with enrofloxacin therapy, could be an effective treatment for otherwise recalcitrant canine otitis externa causedby Pseudomonas aeruginosa. It may also provide a way of extending the usefulness of enrofloxacin therapy which would otherwise be ineffective as a sole therapeutic agent

A direct examination of the dynamics of dipolarization fronts using MMS

Energy conversion on the dipolarization fronts (DFs) has attracted much research attention through the suggestion that intense current densities associated with DFs can modify the more global magnetotail current system. The current structures associated with a DF are at the scale of one to a few ion gyroradii, and their duration is comparable to a spacecraft's spin period. Hence, it is crucial to understand the physical mechanisms of DFs with measurements at a timescale shorter than a spin period. We present a case study whereby we use measurements from the Magnetospheric Multiscale (MMS) Mission, which provides full 3-D particle distributions with a cadence much shorter than a spin period. We provide a cross validation amongst the current density calculations and examine the assumptions that have been adopted in previous literature using the advantages of MMS mission (i.e., small-scale tetrahedron and high temporal resolution). We also provide a cross validation on the terms in the generalized Ohm's law using these advantageous measurements. Our results clearly show that the majority of the currents on the DF are contributed by both ion and electron diamagnetic drifts. Our analysis also implies that the ion frozen-in condition does not hold on the DF, while electron frozen-in condition likely holds. The new experimental capabilities allow us to accurately calculate Joule heating within the DF, which shows that plasma energy is being converted to magnetic energy in our event

EurOP2E – the European Open Platform for Prescribing Education, a consensus study among clinical pharmacology and therapeutics teachers

Purpose Sharing and developing digital educational resources and open educational resources has been proposed as a way to harmonize and improve clinical pharmacology and therapeutics (CPT) education in European medical schools. Previous research, however, has shown that there are barriers to the adoption and implementation of open educational resources. The aim of this study was to determine perceived opportunities and barriers to the use and creation of open educational resources among European CPT teachers and possible solutions for these barriers. Methods CPT teachers of British and EU medical schools completed an online survey. Opportunities and challenges were identified by thematic analyses and subsequently discussed in an international consensus meeting. Results Data from 99 CPT teachers from 95 medical schools were analysed. Thirty teachers (30.3%) shared or collaboratively produced digital educational resources. All teachers foresaw opportunities in the more active use of open educational resources, including improving the quality of their teaching. The challenges reported were language barriers, local differences, lack of time, technological issues, difficulties with quality management, and copyright restrictions. Practical solutions for these challenges were discussed and include a peer review system, clear indexing, and use of copyright licenses that permit adaptation of resources. Conclusion Key challenges to making greater use of CPT open educational resources are a limited applicability of such resources due to language and local differences and quality concerns. These challenges may be resolved by relatively simple measures, such as allowing adaptation and translation of resources and a peer review system