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Comparative Study of Nondestructive Mapping of Conformal-Coating Thickness on Microelectronics by Terahertz Time-of-Flight Tomography
No full textInternational audienceConformal coatings are used to protect microelectronic circuitry and increasingly optoelectronics and photonics from detrimental effects of the environment, such as moisture, dust, gasses, and mechanical abrasion. The conventional approach to determine the mean time to failure of conformally coated microelectronic components is usually labor-intensive and time-consuming. We recently showed (Shi et al., 2024) that the quasi-optical approach terahertz (THz) time-of-flight tomography (TOFT) could in principle be used to map conformal-coating thickness over a sample of dimensions on the scale of square centimeters. In this study, we employ THz TOFT to characterize several conformal-coating types on microelectronic test samples in a nondestructive and noncontact manner. This study extends previous work on acrylic conformal coatings. THz TOFT is shown to be effective in the thickness characterization of silicone and acrylic conformal coatings, but not nanometric atomic-layer-deposition metal-oxide coating, which is too thin for the technique
Static and Dynamic Aerodynamic Coefficients Evaluation on a Generic Fighter Configuration in ONERA Low Speed Wind Tunnels
No full textInternational audienceIn the field of NATO/STO Research Task Group AVT-351 dedicated to numerical methods for prediction of Stability and Control, wind tunnel tests have been carried out at ONERA to obtain reference values concerning aerodynamics under static and above all dynamic conditions in the low speed domain. First works did focus on the choice of the geometry. An overview of the process for the design of ONERA_DLR_M421 is presented. Then the experiments are detailed and major results are discussed
Adapted measurement method to assess mental workload in maintainability studies: industrial point of view
No full textInternational audienceIt is essential to ensure that the mental workload during a maintenance activity is not too high, in order to protect the integrity of maintenance operators and aviation safety. In particular, anticipating human error, which remains one of the consequences of the variability of the mental workload, leads us to define an appropriate method for measuring the mental workload during the maintenance activity. In the aviation industry and in the frame of mental workload assessment, subjective, objective, and physiological approaches will provide adequate solutions in a context always influenced by multiple constraints. Ultimately, these data will enable us to better anticipate the design of more robust and fault-tolerant systems that ensure the protection of operators' physical and mental integrity
Visual guidelines integration for automotive head-up displays interfaces
No full textInternational audienceDesigning automotive Head-Up Displays (HUD) interfaces requires careful consideration of visual guidelines to ensure safety. While specific safety guidelines exist, a general set of visual guidelines has not yet been established. Therefore, this research presents a comprehensive methodology to derive overall visual guidelines designed to project warnings on HUD interfaces. To this end, the present work focused on asking 20 test subjects for driving in various scenarios, while visual stimuli were projected on a specific HUD system, identifying drivers’ behavior patterns and reaction trends. These visual stimuli were based on already tested visual guidelines. The results obtained from this methodology show that it is possible to integrate all previous qualitative and quantitative visual guidelines, allowing for drivers faster reactions and better recognition of warnings. This integration enables determining the most and the least suitable way for presenting information in a specific HUD system concerning identification mistakes and reaction times. Moreover, these findings imply the feasibility of anticipating a driver’s comprehension of warnings in HUD interfaces
Stress-constrained topology optimization using the constrained natural element method
No full textInternational audienceThis paper presents a topology optimization framework to achieve volume minimization with Crossland fatigue constraints under proportional loading using the Constrained Natural Element Method. The local minimization problem is solved by means of the augmented Lagrangian method to deal with a large number of evaluation points. To suppress the numerical instabilities, a neighbor-based filter is proposed and compared to the widely used density filter. Furthermore, to circumvent the problem of stress singularity, several different relaxations of the constraints are also investigated. Compared with the topology optimization procedure based on the finite element method, the proposed method has the advantage of showing greater flexibility and convenience in discretization of complex design domains and the ability to maintain stable output under various discretization conditions
End-Region Losses in High-Power Electrical Machines: Impact of Material Thickness on Eddy Current Losses in Clamping Structures
No full textInternational audienceHigh-power electrical machines often utilize clamping structures composed of various materials with specific geometric dimensions to secure the stator laminations. These structures are exposed to end-region magnetic flux, which induces eddy currents, leading to significant power losses that reduce the machine's efficiency. This study systematically investigates the impact of clamping plate thickness on eddy current losses across different materials and operating frequencies. A simplified experimental configuration was established to validate the numerical model developed using 3D Finite Element Method (FEM). This model was used to calculate the eddy current losses and analyze the influence of plate thickness under various conditions. A comprehensive parametric analysis was performed, revealing critical insights into the relationship between material properties, plate thickness, and loss generation. The findings indicate that while thinner plates exhibit higher current density, thicker plates provide a larger volume for current flow, resulting in varying loss patterns depending on the material's electrical and magnetic properties. The study's results offer valuable guidance for optimizing clamping structure designs in high-power electrical machines by selecting materials and thicknesses that minimize losses while maintaining mechanical integrity.</div
Analyse numérique de l'endommagement dynamique à l'échelle de la microstructure par simulation discrète
No full textNational audienceLa méthode des éléments discrets est utilisée pour étudier l’influence de la mésostructure de matériaux fragiles sur leur comportement à rupture face à des sollicitations dynamiques. Des essais de traction uniaxiale sont simulés en considérant différentes conditions initial, notamment via l’utilisation d’un champ de vitesse initial hétérogène. Cela permet d’atteindre de grandes vitesses de déformation tout en assurant l’équilibre des forces. Une augmentation de la contrainte maximale à rupture est mise en évidence, ainsi que la transition d’une fragmentation simple à une fragmentation multiple
Effect of shear rate on early Shewanella oneidensis adhesion dynamics monitored by deep learning
No full textInternational audienceUnderstanding pioneer bacterial adhesion is essential to appreciate bacterial colonization and consider appropriate control strategies. This bacterial entrapment at the wall is known to be controlled by many physical, chemical or biological factors, including hydrodynamic conditions. However, due to the nature of early bacterial adhesion, i.e. a short and dynamic process with low biomass involved, such investigations are challenging. In this context, our study aimed to evaluate the effect of wall shear rate on the early bacterial adhesion dynamics. Firstly, at the population scale by assessing bacterial colonization kinetics and the mechanisms responsible for wall transfer under shear rates using a time-lapse approach. Secondly, at the individual scale, by implementing an automated image processing method based on deep learning to track each individual pioneer bacterium on the wall. Bacterial adhesion experiments are performed on a model bacterium (Shewanella oneidensis MR-1) at different shear rates (0 to1250 s−1) in a microfluidic system mounted under a microscope equipped with a CCD camera. Image processing was performed using a trained neural network (YOLOv8), which allowed information extraction, i.e. bacterial wall residence time and orientation for each adhered bacterium during pioneer colonization (14 min). Collected from over 20,000 bacteria, our results showed that adhered bacteria had a very short residence time at the wall, with over 70 % remaining less than 1 min. Shear rates had a non-proportional effect on pioneer colonization with a bell-shape profile suggesting that intermediate shear rates improved both bacterial wall residence time as well as colonization rate and level. This lack of proportionality highlights the dual effect of wall shear rate on early bacterial colonization; initially increasing it improves bacterial colonization up to a threshold, beyond which it leads to higher bacterial wall detachment. The present study provides quantitative data on the individualdynamics of just adhered bacteria within a population when exposed to different rates of wall shear
Identification of friction coefficient between uncoated carbide tool and Ti-6Al-4V alloy under different lubrication conditions
No full textInternational audienceDuring machining, the friction between the tool and the workpiece (cutting face and flank face) is a significant tribological phenomenon because it strongly influences the cutting operation. Indeed, higher friction leads to an increase of cutting forces, a greater heat generation, a premature tool wear and a surface degradation. This study focuses on tool (WC/Co)/workpiece (Ti-6Al-4V) friction under different cooling conditions (dry, emulsion, cryogenic). Determining the friction coefficient requires numerical simulations to separate the tribological phenomena. For this purpose, several modeling methods are compared (Lagrangian, CEL, and ALE). Experimental tests revealed that the friction coefficient depends not only on the sliding velocity but also on lubrication modes. Specifically, the lowest friction coefficient is obtained under cryogenic condition. Adhesive phenomena on the WC/Co pin are observed in the friction zone, particularly at high sliding velocities
A numerical model for investigating the effect of material and process parameters on the running of flash sintering
No full textInternational audienceFlash sintering of ceramic powders is a complex process that involves electric, thermal and mechanical phenomena. Modelling should help to better understand and control it, with a view to producing safe and homogeneous parts. A finite element model that couples all relevant phenomena, including the densification and shrinkage of the sintering material, has been worked out for this purpose. This model is used here to investigate the flash sintering of disk-shaped parts. Particular attention is paid to the appearance and growth of heterogeneities within the part, known as hot spots, which are highly dependent on material and process parameters. Leads are provided for limiting the development of such heterogeneities