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Opportunities from energy-loss near-edge fine structure analysis to track chemical and structural damage in zircon
No full textInternational audienceZircon (ZrSiO4) is the oldest-known mineral of Earth and an ubiquitous silicate in geochronology. More specifically, the accumulation of alpha decay damage in zircon over time significantly affects its physical and chemical properties, and can lead to a disturbance of the ages measured in this mineral. Therefore, analytical tools that enable comprehensive structural and chemical information at the nanoscale in this compound are highly sought after. In this context, we explore the electron energy-loss fine structures resulting from the excitation of O1s and Si2p core electrons in zircon, which are interpreted from ab initio calculations in a single-particle framework. An excellent agreement is obtained between the experimental and calculated fine structures, emphasizing the large distortion of the final electronic states induced by the core-hole potential. The O-K edge is particularly rich in information, with intense peaks dominated by O2p - Zr4d and O2p - Si3sp hybrids. This work suggests that the near-edge structures from the O1s and Si2p excitations accessible from electron energy-loss spectroscopy or X-ray absorption spectroscopy could be used as tools to follow, interpret and understand structural and chemical modifications in zircon subject to natural radiation damage. We illustrate the potential of this approach through the evolution of near-edge fine structures in a zircon sample that exhibits a locally amorphized zone formed by ultrafast laser excitation
Radial elastic heterogeneity in a high-modulus carbon fibre assessed by nano-indentation and micro-pillar compression
No full textInternational audienceUnderstanding the radial heterogeneity of carbon fibres is critical to optimising their performance in structural composites. In this study, we investigate the mechanical structure of a high-modulus PAN-based carbon fibre by combining instrumented nano-indentation (IIT) and micro-pillar compression (MCP). Nano-indentation mapping with 50 nm lateral resolution reveals a distinct layered skin–core structure. By combining IIT and MCP, we resolve for the first time the compressive modulus of individual radial layers within a single carbon fibre: a compliant core (110GPa at 0.45% compressive strain), a transitional middle layer, and a stiff outer skin (520 ± 100GPa, at 0.45% compressive strain). Our results confirm earlier indirect estimates and show that the skin modulus approaches that of highly oriented crystallites, whereas the core remains significantly softer due to misorientation. This integrated approach provides a robust framework for characterising anisotropic heterogeneous fibres and offers new insight into fibre-scale mechanical testing
Active learning - assisted experimental design for porous ceramic manufacturing
No full textNational audiencePorous alumina ceramics are fabricated using the sacrificial template method to investigate the impact of two different sphere sizes, PMMA porogen (D50 of 80 and 163µm) and volume fraction (up to 76 vol.%) on material properties. In order to screen the viable parameter space (where samples are mechanically resistant and permeable) efficiently and to leverage the possibility to manufacture several samples in parallel, a batch active learning algorithm coupled with a data-driven model based on Gaussian process classification is developed. Complementary, a Gaussian process regression (GPR) model is developed to predict permeability trends across the viable parametric space. Both models are tested and blind-validated experimentally using unseen data. The combination of GPC and active learning offers a powerful tool for generating effective experimental plans, particularly when investigating processes with large parametric spaces
A TMA and DSC study of the kinetics of the solid-state reaction in an Al<sub>2</sub>O<sub>3</sub>–Y<sub>2</sub>O<sub>3</sub> system
No full textInternational audienceThis study focuses on the kinetic analysis of the solid-phase reactivity of mixtures of Al2O3 and Y2O3 powders, introduced in stoichiometric proportions for the formation of the YAG phase (Y3Al5O12). Structural and microstructural analyses using XRD, TEM, STEM, and SEM provided a better understanding of the reaction mechanism of the formation of the YAG phase, which appears to be of a heterogeneous nucleation-growth type. The second part of this study focused on a kinetic analysis of these reactions, using the Kissinger model applied to data obtained by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). Activation energies equal to 560 kJ mol−1 for the formation of YAP and 660 kJ mol−1 for the formation of the YAG phase were obtained by both methods, meaning that the reaction should be limited by the diffusion of Y3+ ions
Microscale stored energy as a fatigue indicator for NiTi shape memory alloys via synchrotron X-ray diffraction
No full textInternational audienceAlthough fatigue is closely related to microstructural changes, current fatigue criteria for shape memory alloys (SMAs) fail to account for this information due to the lack of research on quantifying microstructural defects associated with fatigue. In this study, we introduce local stored energy as a quantifiable parameter that reflects microstructural evolution and demonstrate its effectiveness as a reliable fatigue indicator. Ex-situ synchrotron X-ray diffraction tests were conducted on a series of NiTi specimens subjected to cyclic loading and stopped at different fatigue stages. The results revealed inhomogeneous microstructures along the gauge section, characterized by residual R-phase accumulation, defect density, and residual stress in active zones. These microstructural changes, resulting from localized deformation, were quantified by local stored energy at the microscale via X-ray peak analysis. Consistent with these inhomogeneous microstructures, the distribution of local stored energy was uneven, with maximum values in active zones where fatigue cracks preferentially occur. As fatigue progressed, local stored energy in these zones increased, eventually stabilizing at a steady state. This steady state exhibited a negative correlation with fatigue lifetimes, where higher loading frequencies resulted in increased stored energy and shorter lifetimes. These findings validate local stored energy as a crucial fatigue indicator, paving the way for development of a physically-grounded fatigue criterion based on this quantity
Comparative assessment of gas hydrate transportability at different scales
No full textInternational audienceA common challenge faced by oil and gas operators is the formation of gas hydrate blockages in production lines. There is no consensus on the methodologies and apparatus used to assess gas hydrate blockage risk, and extrapolating laboratory results to field conditions remains a significant challenge. This highlights the importance of comparing different techniques and experimental scales. This study aims to investigate the influence of key variables, such as shear, gas-liquid ratio, water cut, salinity, subcooling, gas composition, and wax content, on gas hydrate transportability at different scales. From an industrial perspective, the objective is to determine the most effective technique for translating laboratory data into field-scale applications. To this end, three experimental setups are employed: a high-pressure rheometer, a rock-flow cell, and a pilot-scale flow loop
Shear mechanical properties measurements at the surface scale: Enhanced performances of the micro-shear compression specimen
No full textInternational audienceAn intensive study combining experimental tests and numerical simulations was carried out to improve the understanding of the micro-shear test using the Micro-shear Compression Specimen (MCS). The results demonstrated good data reliability in the elastic regime up to the yield stress. However, the study also revealed that friction between the flat punch and the MCS significantly affects the plastic regime, and must therefore be accounted for to accurately extract shear mechanical properties. To overcome this limitation, two alternative methods were developed. The first one consists in compressing a new type of micro-shear compression specimen, featuring two perpendicular gauges forming a cross geometry (X-MCS). The second consists of applying multicycle loading to the conventional MCS. Both approaches successfully eliminated friction dependence in the plastic regime, in contrast to the classical method. Finally, the X-MCS geometry was applied to very high strain rate testing on fused silica. Thanks to the small gauge height of the X-MCS, it was possible to measure shear mechanical properties at a strain rate of 104 s−1, which was not achieved using conventional micropillar compression with our micromechanical setup. These methods provide a new pathway for extracting shear mechanical properties, which are critical in the field of tribology, where surfaces are subjected to intense shear deformation
DEM with Coarse Graining: Should Same Size Parcel receive more attention? Bridging the gap in the case of size-driven segregation
No full textInternational audiencehe Discrete Element Method (DEM) has gained significant popularity as a technique for simulating granular flows. However, its high computational cost has remained a primary limitation for decades. This limitation hinders its application in simulating realistic large-scale industrial scenarios. The Coarse Graining (CG) method addresses this issue by substituting physical particles with up-scaled particles, commonly referred to as parcels. Among CG techniques, the Same Size Parcel (SSP) approach is considered the most efficient, as it achieves the greatest reduction of constituents in poly-disperse media. Nevertheless, SSP is unable to simulate size-driven phenomena, such as segregation, which significantly restricts its applicability to systems with size heterogeneity. In this context, the present article introduces a novel local model that captures size-driven segregation during Coarse Grained — Same Size Parcel (CG-SSP) simulations when in dense regime. Preliminary results from flowing chute modeling indicate highly promising outcomes, suggesting a potential advancement towards the rapid simulation of poly-disperse, large-scale particle flows
Evaluation of global biotic resource consumption against absolute boundaries
No full textInternational audienceHuman activities rely on biotic natural resources to provide products and services necessary to meet human needs. This instrumental value is captured in life-cycle assessment through the “Natural resources” Area of Protection. Although several absolute boundaries have been proposed to safeguard biotic resources, it remains unclear whether these resources are currently used at a sustainable rate. This study addresses this question by evaluating global biotic resource consumption from 1995 to 2011 against suggested biotic resource boundaries, relying on Exiobase projections to assess the evolution beyond 2011. The assessment couples absolute boundaries with life-cycle impact assessment (LCIA) methods, enabling evaluation using consistent LCIA metrics. Five absolute boundaries and four LCIA methods were adapted to the Exiobase multiregional input-output model. Results show that most of existing boundaries are already transgressed, regardless of whether mass-based or LCIA-based control variables are applied. The wide range and normative nature of existing boundaries emphasize the need for harmonized, science-based boundaries to ensure the sustainable use of biotic resources