3D morphological analysis of local elastic fields in a cementitious material

The linear elastic fields occurring in a cementitious material are numerically computed and analyzed in order to determine the spatial arrangement between the microstructure and high- stress regions in the matrix. The microstructure is obtained by segmentation of a mortar sample microtomography whereas fields are evaluated on the 3D image grid using the FFT algorithm for both hydrostatic and shear strain loading. Different contrasts, i.e. ratios of the Young moduli between aggregates and matrix are considered: 10−8, 3, 100, 1000 and 104. Various components of the stress tensor are successively analyzed, corresponding to the component "parallel" to the applied loading and invariant components. Regions of stress concentration are correlated to the skeleton by influence zone of the aggregates phase. Moreover, when hydrostatic strain loading is applied, the highest values of the von Mises component of the stress tensor are both on the aggregates skeleton and at low distance from aggregates. Similar analysis of the local fields are carried out on a simulated microstructure made of boolean random polyhedra and compared with results on the real mortar microstructure

Influence of the multiscale distribution of particles on elastic properties of concrete

International audienceThe mechanical role of the shape of the aggregates, and their spatial distribution in concrete materials is examined. The effect on the macroscopic mechanical response as well as on the local stress fields are investigated by numerical means, making use of a recently developed Poisson-polyhedra model in which the aggregates have polyhedral shapes. Comparison is made with previous microstructure models of spheres. Full-field computations are carried out on large volume size using Fourier methods. The field maps are used to determine zones of highest stress. Furthermore, the scale separation hypothesis for the computation of the elastic properties is investigated using numerical calculations on various multiscale microstructures. Finally, numerical predictions for the elastic properties are compared to experimental measurements, and the results discussed

Estimation of creep strain and creep failure of a glass reinforced plastic by semi-analytical methods and 3D numerical simulations

International audienceGlass reinforced plastics based on polyvinyl chloride (PVC) is a material of choice for construction applications, such as pipes. The lifetime of pipes may be limited by creep failure and polymers exhibit a viscoelastic response that depends on the time of loading. In this paper, homogenization methods are designed to upscale the viscoelastic properties of a composite material made of chopped glass fibers with random orientations and PVC. The estimates of the Mori–Tanaka scheme and 3D numerical computations for creep strains and creep failure are compared, validating the Mori–Tanaka model as a practical tool to predict the effect of fiber length and volume fraction of fibers on creep strain and creep failure. In particular, it appears that, for a given creep load, the lifetime of the material is increased if the volume fraction of fibers increases or if the length of fibers decreases, as long as the failure mode is fiber breakage

Estimation of local stresses and elastic properties of a mortar sample by FFT computation of fields on a 3D image

International audienceThis study concerns the prediction of the elastic properties of a 3D mortar image, obtained by micro-tomography, using a combined image segmentation and numerical homogenization approach. The microstructure is obtained by segmentation of the 3D image into aggregates, voids and cement paste. Full-fields computations of the elastic response of mortar are undertaken using the Fast Fourier Transform method. Emphasis is made on highly-contrasted properties between aggregates and matrix, to anticipate needs for creep or damage computation. The Representative Volume Element, i.e. the volume size necessary to compute the effective properties with a prescribed accuracy, is given. Overall, the volumes used in this work were sufficient to estimate the effective response of mortar with a precision of 5%, 6% and 10% for contrasts ratio of 100, 1000 and 10000, respectively. Finally, a statistical and local characterization of the component of the stress field parallel to the applied loading is carried out

Complications and revisions after semi-constrained total elbow arthroplasty: a mono-centre analysis of one hundred cases.

Background The complication rate after total elbow arthroplasties is higher than for other arthroplasties. Purpose The purpose of this study was to evaluate the complications and revision rate after 100 semi-constrained total elbow arthroplasties from various types of aetiologies performed in our university hospital. Methods One hundred linked semiconstrained total elbow arthroplasties were performed and were reviewed with 24 months minimum follow-up. Indications were rheumatoid arthritis (45), trauma (33), revisions (16) and others (6). Results At five years average follow-up (range, 2–11), the complication rate was 37 %. Most frequent complications were ulnar nerve involvement (9 %) and triceps insufficiency (7 %). Five implants were aseptically loosed. The infection rate was 4 % with loosening of the implant in two. Four fract humerus proximal or distal to the stem. The radial nerve was injured in two cases. Failure of the locking system of the prosthesis was noted in one case and a fracture of the ulnar component was found in another patient. A revision surgery was performed in 13 cases (13 %). At follow-up 94 prostheses were still in place and the survival rate was 98 % at five years and 86 % at ten years. Conclusion Total elbow arthroplasty remains a difficult procedure with sometimes a high rate of complications necessitating revision procedures. Selection of the patients, a rigorous surgical technique, and a systematic follow-up are prerequisite to limit this incidence

Singular magnetic anisotropy in the nematic phase of FeSe

FeSe is arguably the simplest, yet the most enigmatic, iron-based superconductor. Its nematic but non-magnetic ground state is unprecedented in this class of materials and stands out as a current puzzle. Here, our NMR measurements in the nematic state of mechanically detwinned FeSe reveal that both the Knight shift and the spin-lattice relaxation rate 1/T_1 possess an in-plane anisotropy opposite to that of the iron pnictides LaFeAsO and BaFe2As2. Using a microscopic electron model that includes spin-orbit coupling, our calculations show that an opposite quasiparticle weight ratio between the d_xz and d_yz orbitals leads to an opposite anisotropy of the orbital magnetic susceptibility, which explains our Knight shift results. We attribute this property to a different nature of nematic order in the two compounds, predominantly bond-type in FeSe and onsite ferro-orbital in pnictides. The T_1 anisotropy is found to be inconsistent with existing neutron scattering data in FeSe, showing that the spin fluctuation spectrum reveals surprises at low energy, possibly from fluctuations that do not break C_4 symmetry. Therefore, our results reveal that important information is hidden in these anisotropies and they place stringent constraints on the low-energy spin correlations as well as on the nature of nematicity in FeSe.Comment: Submitted version. More recent version and Supplementary Information (24 pages) available upon reques

Isolated arthroscopic Bankart repair vs. Bankart repair with “remplissage” for anterior shoulder instability with engaging Hill-Sachs lesion: a meta-analysis

INTRODUCTION: Arthroscopic "remplissage" of a Hill-Sachs lesion (HSL) associated with a Bankart repair (BR) has been recently introduced as a surgical option to treat chronic anterior shoulder instability. The purpose of this study was to analyze the current literature comparing results of isolated BR versus BR+remplissage in the treatment of anterior shoulder instability with engaging HSL. HYPOTHESIS: BR+remplissage are superior to isolated BR in the management of anterior shoulder instability with engaging HSL. MATERIAL AND METHODS: Four electronic databases were searched for original, English-language studies comparing BR vs. BR+remplissage procedures. During the inclusion process we used international Preferred Reporting Items for Systematic review and Meta-Analysis (PRISMA) guidelines and the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) checklist. Our data were extracted from the text, tables and figures of the selected studies. RESULTS: Three comparative studies were identified, which included 146 patients; 74 of them underwent isolated BR, and 72 BR+remplissage procedure. The isolated BR results in significantly higher risk of recurrence and redislocation. There was no significant difference in the rates of reoperation and time to return to sport between the two procedures. Rowe and UCLA scores were lower in the isolated BR group compared with the BR+remplissage group. DISCUSSION: This meta-analysis demonstrates the superiority of BR+remplissage procedure vs. isolated BR in the management of anterior shoulder instability with engaging HSL and with up to 25% glenoid bone loss regarding redislocation rate, recurrent instability and functional scores. A comparison between postoperative range of motion and particularly external rotation was not able to be formally assessed in this study

Periprosthetic shoulder infection: an overview

Periprosthetic shoulder infection (PSI) is rare but potentially devastating. The rate of PSI is increased in cases of revision procedures, reverse shoulder implants and co-morbidities. One specific type of PSI is the occurrence of low-grade infections caused by non-suppurative bacteria such as Propionibacterium acnes or Staphylococcus epidemermidis.Success of treatment depends on micro-organism identification, appropriate surgical procedures and antibiotic administration efficiency. Post-operative early PSI can be treated with simple debridement, while chronic PSI requires a one- or two-stage revision procedure. Indication for one-time exchange is based on pre-operative identification of a causative agent. Resection arthroplasty remains an option for low-demand patients or recalcitrant infection

Predicting leakage of the VERCORS mock-up and concrete containment buildings - a digital twin approach

EDF operates a nuclear power generation fleet made up of 56 reactors. This fleet contains 24 reactors designed as double-walled concrete containment building. The inner concrete containment vessel has no metallic liner and is a prestressed reinforced concrete building. The inner concrete containment vessel is designed to withstand a severe accident, in terms of mechanical and sealing behaviour. The tightness of the containment is tested every 10 years, by carrying out a pressurization test and by measuring the leak rate. The leak rate is required to be below a regulatory threshold to continue operation of the concrete containment building for the next ten years. Ageing of concrete due to drying, creep and shrinkage leads to increase prestress loss and then leak rate with time. For some containment buildings, the leak rate gets closer to the regulatory threshold with time, so important coating programs are planned to mitigate and limit the leak rate under the regulatory threshold. Therefore, it is very important for EDF to have a concrete containment building leak rate prediction tool. To address this issue, an important research program around a 1/3 scale concrete containment building mock-up called "VERCORS" have been launched at EDF. The mock-up is heavily instrumented, and its materials (concrete, prestressing cables) have been widely characterized and studied. An important numerical effort has also been made to implement structural computations of the mock-up and to capitalize these computations as well as their post-processing (so as to compare automatically with the monitoring data) in what can be called a digital twin of the mock-up. This digital twin is now used to predict the leakage of VERCORS mock-up before yearly pressure test, and also to optimize the repair programs on the real containments

Magnetic and structural properties of the iron silicide superconductor LaFeSiH

The magnetic and structural properties of the recently discovered pnictogen/chalcogen-free superconductor LaFeSiH ($T_c\simeq10$~K) have been investigated by $^{57}$Fe synchrotron M{\"o}ssbauer source (SMS) spectroscopy, x-ray and neutron powder diffraction and $^{29}$Si nuclear magnetic resonance spectroscopy (NMR). No sign of long range magnetic order or local moments has been detected in any of the measurements and LaFeSiH remains tetragonal down to 2 K. The activated temperature dependence of both the NMR Knight shift and the relaxation rate $1/T_1$ is analogous to that observed in strongly overdoped Fe-based superconductors. These results, together with the temperature-independent NMR linewidth, show that LaFeSiH is an homogeneous metal, far from any magnetic or nematic instability, and with similar Fermi surface properties as strongly overdoped iron pnictides. This raises the prospect of enhancing the $T_c$ of LaFeSiH by reducing its carrier concentration through appropriate chemical substitutions. Additional SMS spectroscopy measurements under hydrostatic pressure up to 18.8~GPa found no measurable hyperfine field