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Mechanical properties of carboxymethyl cellulose aerogels and cryogels
No full textInternational audienceAbstract Lightweight and highly porous carboxymethyl cellulose (CMC) aerogels were prepared from CMC solutions via non-solvent induced phase separation, followed by supercritical CO 2 drying. Direct freeze-drying of CMC solutions was used to obtain “cryogels” for comparative analysis. The influence of CMC concentration and of drying method on the morphology, density, porosity and mechanical response of CMC aerogels and cryogels under uniaxial compression were evaluated. Two methods were used: direct data collection from the machine sensors and the digital image correlation (DIC) technique. It was demonstrated that DIC method is more precise; video-monitoring of the changes in sample shape and dimensions was also performed. Nominal stress–strain dependences were constructed, and compressive modulus, yield stress, absorbed energy and sample volume evolution under compression were analyzed as a function of density and material morphology. The elastic recovery of cryogels is slightly higher than that of aerogels at the similar density. The “equivalent” Poisson’s ratio (at 50% strain) was nearly zero for cryogels, while for aerogels it was non-zero and decreased with increasing density. The difference in the mechanical response of aerogels vs cryogels was attributed to their different morphology
Group Equivariant Morphological Networks
No full textInternational audienceClassical mathematical morphology on images relies on two translation equivariant operators which are often considered as the non-linear counterparts of convolution. Observing the development of convolutional neural networks, mathematical morphology is transitioning to a deep learning framework. This paper is an attempt 1 to build theoretical foundations to adapt mathematical morphology to group equivariant deep learning. The proposed theory generalizes existing framework of translation equivariant morphological operators by considering a special case of group morphology, introduced by Roerdink in the early 2000s, and deriving it in the context of non-Abelian group actions. A theoretical aperture is given by i) a generalized expression of H-operators, proposed by Heijmans in the early 90s, for group equivariance and ii) a group equivariant version of a recent smooth approximation of morphological operators by Hermary et al. The theoretical results lead to the proposition of several group equivariant morphological layers. Finally, the proposed layers are assessed using the Fashion-MNIST dataset in the case of translations and 90 • rotations. The experiments show that the proposed morphological networks, trained only with upright samples, classify rotated images without a loss of performance.</div
Influence of steel substrate behavior on the deformation and cracking of Zn–Al–Mg coatings on galvanized steel sheets
No full textInternational audienceThe objective of this study is twofold: (i) to comprehensively describe the deformation modes of zinc coatings depending on their crystallographic texture and (ii) to investigate the effect of Lüders banding occurring in the steel substrate on the coating deformation and cracking modes. Microscopic characterization and mechanical tests were conducted on three types of galvanized steel: a mild steel substrate and a high-strength low-alloy (HSLA) steel substrate known to exhibit the Lüders banding phenomenon, and a dual-phase steel substrate. The results reveal a direct correlation between the coating texture, plastic deformation modes, and the mechanical behavior of the respective substrates. Digital Image Correlation (DIC) was employed to measure the strain fields and characterize strain localization phenomena resulting from Lüders banding. The strain field measured on the galvanized substrate specimens showed that Lüders band propagation leads to accelerated plastic deformation and cracking in the Zn–Al–Mg coating. Finite element simulations were performed by considering the real coating microstructure and incorporating the macroscopic behavior of the substrate. The simulation results demonstrate that slip and twinning activities of the coating grains are strongly influenced by the underlying substrate behavior.L’objectif de cette étude est double : (i) décrire de manière exhaustive les modes de déformation des revêtements de zinc en fonction de leur texture cristallographique et (ii) étudier l’effet des bandes de Lüders se développant dans le substrat en acier sur les modes de déformation et de fissuration du revêtement. Une caractérisation microscopique et des essais mécaniques ont été réalisés sur trois types d’acier galvanisé : un substrat en acier doux, un substrat en acier à haute résistance et faiblement allié (HSLA) connu pour présenter le phénomène de bandes de Lüders, et un substrat en acier à microstructure biphasée (Dual-Phase). Les résultats révèlent une corrélation directe entre la texture du revêtement, les modes de déformation plastique et le comportement mécanique des substrats respectifs. La corrélation d’images numériques (DIC) a été utilisée pour mesurer les champs de déformation et caractériser les phénomènes de localisation associés aux bandes de Lüders. Les champs de déformation mesurés sur les éprouvettes de substrat galvanisé montrent que la propagation des bandes de Lüders entraîne une accélération de la déformation plastique et favorise la fissuration dans le revêtement Zn–Al–Mg. Des simulations par éléments finis ont été réalisées en considérant la microstructure réelle du revêtement et en intégrant le comportement macroscopique du substrat. Les résultats de la simulation démontrent que les mécanismes de glissement et de maclage au sein des grains du revêtement sont fortement influencés par le comportement mécanique du substrat sous-jacent
Évolution de la microstructure lors du fluotournage d'Inconel 718 et d'alliage d'aluminium 2219
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Coupling grain growth, fluid flow, and anisotropic mechanical behavior at the track scale through thermo-fluid-metallurgical-mechanical simulations
No full textInternational audienceDuring the laser powder bed fusion (L-PBF) process in metal additive manufacturing, the formation of columnar dendritic microstructures induces an anisotropic mechanical behavior which is key in understanding the development of stresses and defects such as hot cracking (solidification cracking). As the grain structure directly results from heat transfer and fluid flow in the melt pool, the objective of this study is to concurrently address fluid dynamics, grain structure formation and stress build-up in L-PBF process simulation, focusing on investigating defect formation through thermal-metallurgical-mechanical simulations. This study presents a coupled thermo-fluid-solid numerical model and a grain growth simulation framework for L-PBF, incorporating a two-step partitioned approach [1] to separately resolve fluid flow, grain structure evolution and solid mechanics at each time increment. Thermo-hydrodynamics in melt pool is simulated within a level-set based finite element framework. Grain structure evolution is modeled using a Cellular Automaton (CA) method, which simulates growth within the mushy zone. Concurrently, stress evolution is studied using a crystalline elasto-viscoplastic (CEVP) model, considering slip systems of individual grains to understand stress distribution based on crystallographic orientation. Already applied in the simpler context of multiple laser scan lines on a substrate [2], this approach is applied to L-PBF, at the scale of several adjacent tracks, to investigate the mechanisms driving stress generation, with a particular focus on structural effects. This involves analyzing non-uniform deformations within individual grains, intra-granular texture evolution, and the inherent intergranular stresses that develop during solidification. The insights obtained from these analyses are expected to contribute to the establishment of a refined criterion for predicting hot cracking. References [1] Zhang Shaojie, Guillemot Gildas, Gandin Charles-André, Bellet Michel, A partitioned two-step solution algorithm for concurrent fluid flow and stress-strain numerical simulation in solidification processes, Computer Methods in Applied Mechanics and Engineering 356 (2019) 294-324, doi.org/10.1016/j.cma.2019.07.006 [2] Li Zixuan, Bellet Michel, Gandin Charles-André, Upadhyay Manas, Zhang Yancheng, Metallurgically-driven thermomechanical analysis of multiple side-to-side laser melting on a 316L substrate, submitted to Additive Manufacturing, Februa
Invariant Extended Kalman Filter for State Estimation of a Robot With an IMU on an Inclined Plane
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How are the data from the OZCAR RI critical zone observatories used by local stakeholders?
No full textInternational audienceThe long-term observatories of the OZCAR Critical Zone Research Infrastructure (https://www.ozcar-ri.org/ ) were initially set up to answer scientific questions of local interest to society. To answer these questions, a series of variables documenting meteorological conditions, hydro-geochemistry of surface water or aquifers, land surface fluxes and soils, as well as land use and practices are collected, sometimes over several decades. In the context of open science, these data are shared according to the FAIR (Findable, Accessible, Interoperable, Reusable) principles. However, a recurring question is the usefulness of making this data available and the use made of it by local stakeholders or citizens. To answer this question, observatory managers were asked to provide information on - The measured variables from their observatory used by local actors, - The stakeholders who use their data- The type of data used (raw data or data already transformed/digested by scientists) - The type of interactions they have with stakeholders.The results of the consultation show that the data is primarily used in universities or as part of initial training. Long-term involvement in the study-areas has also led to the establishment of long-lasting relationships with stakeholders (e.g. local authorities, hydropower companies, river basins management authorities, water agencies, Regional Natural Parks, state agencies (e.g. forest managers), associations, farmers and the public. Often, but not always, these stakeholders make direct use of the data produced by the observatories included in OZCAR RI. Qualified data from several monitored sites are used to manage the drinking water supply of several towns or municipalities, flood warning systems (in this case in near-real time or in a a posteriori analysis of problematic episodes), quantify water resources (quantity, quality), understand soil quality, or monitor wetland restoration. Nevertheless, in the face of increasingly strong and frequent pressures and disturbances, local stakeholders are increasingly questioning critical zone observatories to obtain data, trends and projections on the impact of climate change or land use. This information will help them to draw up regulatory documents and make decisions on the future habitability of their areas. Scientists are also called upon to provide scientific mediation and make the results of their research accessible to non-specialists. In addition to data, decision-makers, elected representatives and the public expect scientists to provide them with indicators that can be used more directly than raw data. In order to provide satisfactory responses to these new needs, it is necessary to co-construct the various actions, which requires time and a strong investment by scientists and stakeholders. As a result, new missions and new jobs are emerging, making observatories meeting places for local stakeholders and scientists. Observatories are becoming places, named Living Labs, where knowledge and research questions can be co-constructed, where citizens can be involved in metrology (participatory science), in order to better respond to the challenges of the Earth's habitability in the various areas
Impact of seasonal malaria chemoprevention timing on clinical malaria incidence dynamics in the Kedougou region, Senegal
No full textInternational audienceSeasonal malaria chemoprevention (SMC) with sulfadoxine-pyrimethamine and amodiaquine is recommended by the World Health Organization since 2012 for clinical malaria prevention in children in the Sahelian region of Africa. In Senegal, SMC implementation began in 2013 and is given to children under 10 years old. This study aimed to describe clinical malaria incidence in the general population during routine SMC implementation and to analyse how SMC timing impacted clinical malaria dynamics in eligible children. We conducted an ecological study in the Kedougou region of Senegal in 27 villages included in the Bandafassi Health and Demographic Surveillance System (HDSS). We calculated weekly Plasmodium falciparum malaria incidence by age group using malaria case data recorded by community health workers and health-posts, and population denominators obtained from Bandafassi Health and Demographic Surveillance System. We used negative binomial generalized additive multilevel models to analyse the incidence of clinical episodes in children under 10 years during the expected SMC prophylactic period and at the end of the transmission period. Malaria incidence was strongly seasonal with a high transmission period starting in June. Children under SMC presented an overall lower incidence compared to older children and young adults. Among children eligible for SMC, the incidence was lowest for approximately 3 weeks after treatment administration and increased subsequently, suggesting a gradual loss of protection. At the end of the high transmission period, a higher malaria incidence was recorded from the 3 rd to 6 th week after the week of administration of the fourth (final) SMC round. While protecting children under 10 years, SMC warrants adjustment to reduce exposure before the next round, to increase protection of 5–9 years, and to cover the high transmission period completely. The addition of a 5 th round of SMC in 2023 was necessary to cover the end of the transmission season, but individual-level studies are required to ensure that drug efficacy and adequate dosing are maintained
