Computational and experimental study of crack initiation in statistical volume elements

Fatigue crack formation and early growth is significantly influenced by microstructural attributes such as grain size and morphology. Although the crystallographic orientation is a primary indicator for fatigue cracking, the neighbourhood conformed by the first and second neighbour grains strongly affect the fatigue cracking driving force. Hence, two identical grains may result in different fatigue responses due to their interactions with their microstructural ensemble, which determines the fatigue variability. Naturally, macroscopic samples with millions of grains and thousands of competing microstructural neighbourhoods can effectively resemble a representative volume element in which fatigue failure may seem deterministic. However, when considering systems in which fatigue failure is controlled by hundreds or less of grains, fatigue failure is stochastic in nature and the samples are not a representative but a statistical volume. This work studies fatigue crack nucleation in micron-scale Ni beams that contain a few hundred grains. This work presents 3D crystal plasticity finite element models to compute stochastic distribution of fatigue indicator parameters that serve as proxies for crack nucleation in statistical volume elements. The integration of experiments with models provides a method to understand the irreversible deformation at the grain level that leads to fatigue cracking. Our results explain the role of grain morphology of crack nucleation distributio

Evaluation des moyens pour la réduction du taux de HAP dans un stock de matériaux

Lors de ce projet, nous nous sommes intéressés à la revalorisation de déchets de l’industrie pour reconstruire des routes. Ces matériaux ont été démontés et peuvent être utilisés pour faire d’autres choses telles que des bâtiments. Un problème se pose alors lorsque ces déchets sont pollués. Dans certains cas, on sait déjà qu’ils sont pollués, comme par exemple les déchets issus des industries chimiques. Mais dans d’autres cas, nous n’en n’avons pas connaissance. C’est d’ailleurs la difficulté qu’une entreprise peut rencontrer, en acceptant de prendre en charge un camion de déchets qui étaient en réalité pollué par des HAP, Hydrocarbures Aromatiques Polycycliques, issus de l’industrie du charbon. Il existe plusieurs classes de décharges, la classe 1 qualifiés de dangereux, la classe 2 qualifiés de non dangereux et la classe 3 qualifiés d’inertes. Les matériaux fortement chargés en HAP relèvent de la classe 1, de ce fait ils sont soumis à la législation pour être réutilisés. Pour être réutilisés, les taux limites sont fixés à 50mg/kg de HAP pour une utilisation à chaud et 500mg/kg de HAP pour une utilisation à froid. L’entreprise se retrouve donc avec un tas de déchets pollués, ne pouvant pas être traités ni mis en décharge car la mise en décharge couterait environ 15 millions d’euros pour un tas de 20 000 tonnes de déchets. Deux options sont alors possibles : on peut soit éliminer les HAP du tas avec une technique de traitement appropriée, soit diminuer la classe des déchets en dégradant les HAP afin de payer moins cher la mise en décharge. Afin de déterminer une technique de traitement adaptée, il faut d’abord identifier où se situent les HAP dans le tas ainsi que la concentration. Nous nous sommes donc intéressés aux techniques d’échantillonnage afin de doser les HAP dans le tas grâce aux méthodes analyses fines. Une fois cette étape réalisée, nous nous sommes attardés sur les voies de traitement physiques, chimiques et biologiques des HAP. Notre problème était que les techniques s’appliquaient à des sols pollués et non à des tas, nous avons donc dû isoler certaines techniques susceptibles de fonctionner dans notre cas. Certaines permettent de détruire les HAP, et d’autres les dégradent en des sous-produits moins dangereux, ce qui permet de descendre d’une classe de déchets pour la mise en décharge. Enfin, afin de parer à un éventuel achat de camion pollué, nous avons également réfléchi à des méthodes de terrain permettant de déterminer rapidement la présence ou pas des HAP dans un tas de déchets. Ainsi nous avons isolé des méthodes rapides de terrain pour détecter les HAP, telles que le PAK MARKER, qui est la méthode la plus utilisée aujourd’hui. Mais aussi les méthodes de la tâche au toluène, la spectroscopie infra-rouge ou le nez électronique qui existent également. Pour échantillonner notre tas, il semblerait que le concassage suivi de la méthode des quarts ou l’échantillonneur rotatif soient les méthodes les plus adaptées. Et enfin grâce au site du BRGM, nous pouvons proposer quelques techniques de traitement physiques telles que le traitement thermique continu, mais aussi les traitements chimiques comme le lavage ou l’oxydation chimique, et enfin des traitements biologiques, le biotertre et le bioréacteur, qui nécessitent encore quelques améliorations

Comparison of the low and high/very high cycle fatigue behaviors in Ni microbeams under bending

The present work demonstrates a micromechanical technique to investigate the low cycle fatigue (LCF) behavior of Ni microbeams under fully reversed bending loadings. The technique extends the range of measured fatigue lives from the previously reported technique for high and very high cycle fatigue (HCF/VHCF) characterization in the same microbeams. The results highlight significant differences in the slope of stress and strain-life behavior and crack propagation rates that differ from an average of 10–12 m/cycle in HCF/VHCF to an average of 10–8 m/cycle in LCF. These results, in addition to postmortem fractography work, suggest that the mechanisms follow the conventional mechanisms of crack tip stress intensification in the LCF regime. This is in stark contrast to the void-controlled mechanisms that were previously identified in the HCF/VHCF regime. These results demonstrate that the transition in governing mechanisms from void-controlled to conventional mechanisms is highly influenced by the size effects present in the microbeams

Evolution of porewater composition through time in limestone aquifers: Salinity and D/H of fluid inclusion water in authigenic minerals (Jurassic of the eastern Paris basin, France)

International audiencePast water circulations can significantly reduce the porosity and permeability of marine limestones. This is particularly the case in the Middle (Bathonian/Bajocian) to Upper (Oxfordian) Jurassic limestones from the eastern border of the Paris Basin. The knowledge of the timing, the temperature and composition of paleowaters is essential to model the hydrological evolution in this area where the Callovian–Oxfordian claystones are studied for the storage of nuclear wastes. In this way, fluid inclusions hosted in low-temperature (< 60°C) authigenic calcite, quartz and celestite crystals were analyzed by Raman spectroscopy and mass spectrometry to determine the chlorinity and D/H ratios. Chlorinity measurements (mmol Cl per liter of water) in fluid inclusions trapped in authigenic crystals during the late Jurassic/early Cretaceous period revealed unexpected high values, up to 3800 mmol l− 1, indicating that brines were involved in some of the diagenetic crystallization processes. By contrast, fluid inclusions in calcite cements of Cenozoic age within the Oxfordian limestones have low Cl concentration (less than 150 mmol l− 1), thus showing that a dilution event caused by water infiltrations during the Cretaceous uplift of this part of the basin has flushed out the original saline porewater. By coupling δD of fluid inclusion with δ18O of calcite crystals, we estimate that calcite precipitation occurred at temperatures between 25 and 53°C. The hydrogen isotope composition of calcite-forming water is different between the Middle Jurassic (δD ranging from − 20 to − 35.8‰V-SMOW) and the overlying Oxfordian limestone (δD from − 59.5 to − 44.8‰V-SMOW). Present-day groundwaters are also of distinct composition on both sides of the Oxfordian claystones, indicating that limestone aquifers underwent independent hydrologic evolutions since the early diagenetic Jurassic cementation

A computational and experimental comparison on the nucleation of fatigue cracks in statistical volume elements

The failure of micron-scale metallic components presents significant variability as a result of their size being comparable to microstructural length scales. Indeed, these components do not represent the bulk of the material but correspond to statistical volume elements (SVEs). This work investigates the role of SVEs on fatigue crack nucleation with a novel comparison between microbeam experiments and microstructure-sensitive simulations. We recreate multiple microstructural computational realizations to estimate fatigue crack nucleation lives and orientations by means of physics-based crystal plasticity models. We demonstrate a unique approach to validate microstructure sensitive models and quantify the fatigue crack stochasticity associated with small volumes

Mutation Rate Switch inside Eurasian Mitochondrial Haplogroups: Impact of Selection and Consequences for Dating Settlement in Europe

R-lineage mitochondrial DNA represents over 90% of the European population and is significantly present all around the planet (North Africa, Asia, Oceania, and America). This lineage played a major role in migration “out of Africa” and colonization in Europe. In order to determine an accurate dating of the R lineage and its sublineages, we analyzed 1173 individuals and complete mtDNA sequences from Mitomap. This analysis revealed a new coalescence age for R at 54.500 years, as well as several limitations of standard dating methods, likely to lead to false interpretations. These findings highlight the association of a striking under-accumulation of synonymous mutations, an over-accumulation of non-synonymous mutations, and the phenotypic effect on haplogroup J. Consequently, haplogroup J is apparently not a Neolithic group but an older haplogroup (Paleolithic) that was subjected to an underestimated selective force. These findings also indicated an under-accumulation of synonymous and non-synonymous mutations localized on coding and non-coding (HVS1) sequences for haplogroup R0, which contains the major haplogroups H and V. These new dates are likely to impact the present colonization model for Europe and confirm the late glacial resettlement scenario

Imaging and multi-omics datasets converge to define different neural progenitor origins for ATRT-SHH subgroups

Atypical teratoid rhabdoid tumors (ATRT) are divided into MYC, TYR and SHH subgroups, suggesting diverse lineages of origin. Here, we investigate the imaging of human ATRT at diagnosis and the precise anatomic origin of brain tumors in the Rosa26-Cre$^{ERT2}$::Smarcb1$^{flox/flox}$ model. This cross-species analysis points to an extra-cerebral origin for MYC tumors. Additionally, we clearly distinguish SHH ATRT emerging from the cerebellar anterior lobe (CAL) from those emerging from the basal ganglia (BG) and intra-ventricular (IV) regions. Molecular characteristics point to the midbrain-hindbrain boundary as the origin of CAL SHH ATRT, and to the ganglionic eminence as the origin of BG/IV SHH ATRT. Single-cell RNA sequencing on SHH ATRT supports these hypotheses. Trajectory analyses suggest that SMARCB1 loss induces a de-differentiation process mediated by repressors of the neuronal program such as REST, ID and the NOTCH pathway

Single-cell transcriptomics reveals shared immunosuppressive landscapes of mouse and human neuroblastoma

BACKGROUND High-risk neuroblastoma is a pediatric cancer with still a dismal prognosis, despite multimodal and intensive therapies. Tumor microenvironment represents a key component of the tumor ecosystem the complexity of which has to be accurately understood to define selective targeting opportunities, including immune-based therapies. METHODS We combined various approaches including single-cell transcriptomics to dissect the tumor microenvironment of both a transgenic mouse neuroblastoma model and a cohort of 10 biopsies from neuroblastoma patients, either at diagnosis or at relapse. Features of related cells were validated by multicolor flow cytometry and functional assays. RESULTS We show that the immune microenvironment of MYCN-driven mouse neuroblastoma is characterized by a low content of T cells, several phenotypes of macrophages and a population of cells expressing signatures of myeloid-derived suppressor cells (MDSCs) that are molecularly distinct from the various macrophage subsets. We document two cancer-associated fibroblasts (CAFs) subsets, one of which corresponding to CAF-S1, known to have immunosuppressive functions. Our data unravel a complex content in myeloid cells in patient tumors and further document a striking correspondence of the microenvironment populations between both mouse and human tumors. We show that mouse intratumor T cells exhibit increased expression of inhibitory receptors at the protein level. Consistently, T cells from patients are characterized by features of exhaustion, expressing inhibitory receptors and showing low expression of effector cytokines. We further functionally demonstrate that MDSCs isolated from mouse neuroblastoma have immunosuppressive properties, impairing the proliferation of T lymphocytes. CONCLUSIONS Our study demonstrates that neuroblastoma tumors have an immunocompromised microenvironment characterized by dysfunctional T cells and accumulation of immunosuppressive cells. Our work provides a new and precious data resource to better understand the neuroblastoma ecosystem and suggest novel therapeutic strategies, targeting both tumor cells and components of the microenvironment

Genetic alterations of ALK in high-risk neuroblastoma patients: a SIOPEN study

Background: In neuroblastoma (NB), the ALK receptor tyrosine kinase can be constitutively activated either through genomic amplification or activating point mutations. We studied ALK genetic alterations in high-risk NB patients to determine their frequency and prognostic impact.N/