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Experimental study of two low tip-speed ratio micro wind turbines operating in tandem
No full textInternational audienceThis paper presents a parametric experimental study of a dual-rotor wind turbine system operating at low tip-speed ratios of the order of 1. The flow-field in the wake of such a multibladed-high solidity micro-scale windturbine is measured and characterized at distances up to 15Rt , with Rt = 70 mm the tip radius of the turbine.At the best operating point of a single rotor, the near wake presents on the one hand an axial velocity deficitof the order of 40% of the infinite upstream velocity and on the other hand an average tangential velocity ofthe order of 30% of it. The far wake recovery is almost achieved at 15Rt but tangential velocity of the orderof 10% remains. The performances of two identical corotating and counter-rotating wind turbines separatedby distances in the range 3Rt to 12Rt are then experimentally studied. The counter-rotating configurationgives 6% more power than the co-rotating configuration at the shortest distance 3Rt . However, the velocityfield analysis reveals notable interference between the front and rear rotors, degrading the performance ofthe first turbine. This study provides an experimental foundation that guides in d
Recent advances in the remelting process for recycling aluminium alloy chips: a critical review
No full textInternational audienceThis critical review examines advances in preprocessing and remelting processes for aluminium alloy chip recycling, emphasizing pre-treatment and remelting techniques that improve both resource recovery and material quality. Pre-treatment strategies, particularly cleaning methods and compaction are critically evaluated. Various cleaning methods, including centrifugation, ultrasonic solvent washing, extraction, and distillation are compared based on their ability to remove residual cutting fluids. Cold compaction, which augments chip density to approximately 2.5 g/cm³, significantly curtails oxidation losses and enhances metal recovery. During remelting, NaCl-KCl-based fluxes with limited fluoride additions (e.g., 3–7 wt% Na₃AlF₆) disrupt oxide networks but require careful dosage control to minimize furnace corrosion and environmental hazards. Moreover, mechanical stirring combined with suitable melting temperatures reduces porosity while enhancing melt purity. Future research should prioritize the development of low-energy cleaning methods, flux composition optimization, and scalable production techniques to further advance sustainable aluminium recycling
Direct and reverse 3D printing of geopolymer porous filters: a comparative study
No full textInternational audienceThis research delves into an in-depth exploration of two distinct approaches to additive manufacturing for creating 3D filters based on sodium geopolymers (GP): direct 3D printing through paste extrusion and reverse 3D printing using sacrificial polymeric templates. The investigation encompasses a comprehensive characterization of GP filters in both their fresh and hardened states. By employing rheology measurements during the fresh state analysis, a clear printability zone for formulations used in direct 3D printing is identified. In both printing methods, an extensive assessment of the structure and porosity of the resultant hardened GP filters is conducted, employing Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM) and 3D X-ray microtomography analyses. This study illuminates the distinct advantages and limitations associated with each manufacturing technique in the context of potential industrial applications of porous filters. Moreover, it underscores the potential for these filters to be further tailored for specific industrial uses through complementary chemical functionalization, thereby paving the way for innovation in the field of advanced filtration and environmental solutions.</div
Extended Intelligence for Rapid Cognitive Reconfiguration
No full textInternational audienceWith today‘s trend toward mass customization, fast and efficient reconfiguration of manufacturing systems is essential. New artificial intelligence and robotics developments play a key role in optimizing these processes. AI-driven reconfigurations are becoming increasingly effective because of real-time data from digital twins and intuitive interaction through extended reality. This article presents an approach that integrates digital twins and extended reality in a reconfigurable manufacturing use case, laying the foundation for AI-driven optimization. It highlights potential industrial benefits, such as increased flexibility and reduced downtime, and provides an outlook on future developments
Piezoelectric Polymer Characterization Setup for Active Energy Harvesting
No full textInternational audiencePiezoelectric polymers, such as poly(vinylidene fluoride) (PVDF), offer a sustainable alternative to traditional ceramic‐based energy harvesters, addressing concerns regarding environmental impact and resource scarcity. The energy harvesting ability of these PVDFs under various mechanical constraints has been widely investigated. To determine the power output of the material, most of the studies usually use the same electrical setup: the piezoelectric material is in series with a load resistor and the voltage is measured at the resistor's terminals. This usual “passive” method of measurement can underestimate the optimal value of energy harvesting ability. To accurately assess the energy harvesting potential of PVDF, a novel “active” measurement method is proposed. This method involves the simultaneous application of both mechanical and electrical stimuli to the PVDF film, enabling precise control and optimization of the energy harvesting process. To validate this approach, the structural and electrical properties of the stretched PVDF were initially characterized to produce a datasheet. Subsequently, the energy harvesting performance was investigated using both “passive” and “active” methods. The results demonstrated a significant enhancement in power output, with the “active” method yielding up to 3.2 times higher values compared with the “passive” method. This finding highlights the importance of employing advanced measurement techniques to accurately characterize the energy harvesting capabilities of piezoelectric materials
Review of fracture characterization by delamination and debonding of polymer composite materials and bonded interfaces subjected to high temperature
No full textInternational audiencePolymer composite materials and bonded composites are now widely used in the design of major aircraft components due to their high specific properties and feasibility for joint assembly. Nevertheless, there are fire-related risks, which can significantly alter their thermal behaviour. High temperatures directly influence the thermochemical and mechanical degradation of composites and bonded layers, leading to the apparition of damage phenomena such as delamination or interfacial cracking at the interface, and debonding at the bonded layer. The characterisation of delamination and debonding in temperature remains critical to ensuring the integrity of aeronautical structures. This review aims to describe the mechanics leading to delamination and debonding as a consequence of thermomechanical loading. A recompilation of experimental tests used to characterise the mechanical properties of composite interfaces and bonded layers is provided. The adaptation of standard tests to high-temperature conditions is discussed, along with key findings from the literature. Limited research has focused on the characterisation of fracture properties at elevated temperature due to the challenges associated with conducting experimental tests and analysing the resulting data. Finally, a discussion about the main findings and the need for further advancements in delamination and debonding characterisation at high temperatures is presented
Determination of effective diffusion properties based on 3D FIB/SEM images of clays
No full textInternational audienceThis article presents a numerical approach aiming to estimate the effective diffusion properties of clay using real 3D images obtained through Focused Ion Beam and Scanning Electron Microscopy (FIB/SEM). A description of the original FIB/SEM procedure, specifically developed for observing remoulded clays at the particle scale, is presented. Image processing allowed the reconstruction of a micro-volume extracted from a clay sample subjected to an oedometric loading with an effective vertical stress of 1000 kPa. Numerical calculations of effective diffusivity were performed on the real 3D images using periodic homogenization technique. The results revealed anisotropy in the diffusion phenomena of the studied clay: the effective diffusion coefficient is lower along the direction of the mechanical loading and higher in the plane normal to the stress axis. These findings are consistent with quantitative pore orientation results obtained through image processing, where it was shown that, after mechanical loading, the pores tend to orient towards the plane normal to the axis of the effective vertical stress. These results demonstrate that incorporating the real geometry of clay microstructure into diffusion property calculations allows for a better consideration of the complexity of the clay fabric in relation to mechanical loading
Scapula and clavicle kinematics during wheelchair fencing: a preliminary study
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Turbulent transport of sea-spray in the coastal region
No full textInternational audienceA realistic three-dimensionnal large-eddy simulation is performed for the study of turbulent transport of sea spray aerosol in the coastal region of Le Croisic, France. A new transport model for the aerosol is implemented in the ARPS code. Simulation results are compared with field measurements, both for the mean wind field and aerosol concentration. The numerical results fit well with the observations. The mean vertical concentration profile takes an exponential shape when the data is averaged over sufficiently long timeframe, whereas the 15min averaged profiles vary and deviate from the theory. The transport of the aerosols is analyzed in relation to the sea-land transition and the changes in thermal stability of the atmosphere during the diurnal cycle. Turbulence is found to play an important role in the mixing of aerosols in the unstable surface layer. The turbulent vertical transport of aerosols is enhanced through convective cells over the land during the day, whereas, at night, aerosols remain trapped near the surface and are transported over appreciable horizontal distances under quasi-neutral or stable thermal conditions
A comprehensive investigation of the tribological behaviour of α, α+β, and β titanium alloys against a steel counterpart
No full textInternational audienceThe tribological behaviour of three different natures of titanium alloys, the α (T50), α+β (Ti-6Al-4V) and β (Ti-5553), against a steel ball counterpart was investigated for different surface conditions produced by surface severe plastic deformation (SSPD) at room and cryogenic temperatures.Friction led to the formation of various oxides that acted as third bodies and resulted in different wear regimes referred to as stages I, II, and III. Stage I, the initial abrasive regime under which TiO2-anatase formed, was the only characteristic of the β Ti-5553 alloy behaviour. In addition, stages II and III were observed for the α T50 and α+β Ti-6Al-4V alloys. Stage II is characterised by an increase in the coefficient of friction (COF) associated with the formation of hard TiO2-rutile. Stage III corresponds to the formation of Fe-oxides induced by the steel ball abrasion. While the COF remained steady during stage III for T50, the presence of β-phase in the Ti-6Al-4V destabilised periodically the Fe-oxide layer during stage III and generated repeated sharp drops in the COF values.Despite increasing hardness and roughness of the treated surfaces, SSPD did not modify the overall mechanisms of abrasion and improved only slightly the tribological properties