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“Virtual PVD”: A Virtual Reality Approach to Explore PVD Magnetron Sputtering
No full textThe physical Vapor Deposition (PVD) surface treatment process con-sists of numerous steps involving of multi-physical and multiscale phenomena. i These phenomena are beyond the ability of human perception in their entirety which is a scientific challenge for learning PVD. The present article proposes a Virtual Reality (VR) approach dedicated to the PVD process learning and a pro-totype is developed with different modules. The virtual immersion includes two modalities. One ex-situ, in the surface treatment laboratory, at a real scale (1:1), allowing users to explore the process, the machine components, and to experi-ment with technical gestures such as handling the machine door or installing sub-strate-holder rods inside. The second modality is in-situ, enabling the user to fol-low the process steps immersed in an environment inaccessible to humans and multi-scale. These experiments help to understand the physical phenomena oc-curring thr
Clarifications about upscaling diffusion with heterogeneous reaction in porous media
Full text linkThe upscaling process of coupled (single- and two-species) diffusion with heterogeneous chemical reaction in homogeneous porous media is revisited in this work with several important clarifications following the article from Bourbatache et al. (Acta Mech 234: 2293-2314, 2023. https://doi.org/10.1007/s00707-023-03501-w). It is shown that the upscaled model obtained from the volume averaging method (VAM) or, equivalently, following an adjoint and Green’s formulation technique provides a closed model without any a priori assumption on the form of the solution for the pore-scale concentration involved in the spectral approach used in the periodic homogenization method (PHM) reported in the above reference. Through comparison with direct pore-scale simulations, the VAM model is shown to outperform the predictions of the average concentration and average flux profiles for the simple two-dimensional configuration considered in Bourbatache et al. (Acta Mech 234: 2293-2314, 2023. https://doi.org/10.1007/s00707-023-03501-w) in comparison with the model obtained from PHM in this reference. Finally, identification of the apparent effective diffusion coefficient from these pore-scale simulations, which serve as in silico experiments, proves that the correct dependence upon the Damkhöler number is the one predicted by the model obtained with VAM, in contradiction with the conclusion put forth in Bourbatache et al. (Acta Mech 234: 2293-2314, 2023. https://doi.org/10.1007/s00707-023-03501-w). The physical explanation lies in the corrective contribution of the reactive part to the apparent effective diffusion coefficient, which is positive and adds up to the pure intrinsic diffusive part. The discrepancy between PHM and VAM approaches is proved to originate from the choice of changes of variables in the pore-scale concentration used in the spectral approach while employing PHM. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2025
Simplifications of macroscopic models for heat and mass transfer in porous media
Full text linkWhen performing upscaling of transport phenomena in multiscale systems it is not uncommon that terms of different physical nature than those present at the underlying scale arise in the resulting averaged differential equations. For diffusive species mass transfer with heterogeneous reaction and conductive heat transfer, additional terms result from upscaling using the volume averaging method, which are classically discarded by means of orders of magnitude estimates. In this work, these two cases are revisited and it is shown that, for single and two-species diffusive mass transfer with heterogeneous nonlinear reaction, the additional term is exactly zero using Green's formula. This conclusion is shown to also be applicable when using the periodic homogenization method. Nevertheless, for heat conduction, with and without considering interfacial resistance, only the dominant conduction-corrective terms are shown to be zero also using Green's formula. In contrast, the contribution of the co-conduction-corrective terms may be relevant depending on the systems characteristics, the properties of the phases and the macroscopic boundary conditions. This is exemplified by performing numerical simulations in a non-symmetric unit cell. © 2025 Elsevier Lt
Experimental and numerical analysis of heat transfer and thermal deformation in small-dimension liquid mechanical seals
Full text linkThis paper presents an experimental and numerical analysis of heat transfer and thermal deformation in small-dimension (1.4 mm) liquid mechanical seals operating in an unstable dynamic tracking mode. The studied non-contacting mechanical seal is used in a liquid pump for turbojets. The study aims to estimate the values of pressure, temperature, and thermal deformations that can prevent excessive wear of the sealing rings and control the increase in leakage rate or power loss during operation. Experimental investigations were conducted under a nominal inner pressure of 0.7 MPa, across a wide range of rotational speeds (from 1000 to 6000 rpm), and at low Reynolds numbers (Re < 70). Two high-viscosity fluids, glycerol and engine oil, were used as sealing fluids. Rotational speeds and inner pressure were set as boundary conditions in the simulations. Temperatures measured by thermocouples during the experiments were used to compare with the simulation results. Simulations were performed using the computational fluid dynamics (CFD) software COMSOL. The two-dimensional numerical models accounted for thermal transfers and face seal deformations, coupled with the pressure field in the lubrication fluid. The effects of various sealing fluids and rotational speeds on the time-dependent behavior of temperature, displacement, and pressure within the thin liquid lubricant film were investigated. Subsequent comparisons between experimental and numerical results, particularly for temperature data measured by thermocouples under various operating conditions, demonstrated strong consistency. The greatest discrepancy observed was less than 1.2 °C. © 2025 The Author
Squeal occurrence classification using a harmonic balance vector signal model
Full text linkBrake squeal is an instability that generates self-excited limit cycles that, in real experiments, vary with time and operating conditions. To analyze test results, it is proposed to use a Harmonic Balance Vector (HBV) signal model, that combines the space-time decomposition of the Harmonic Balance Method, where spatial distribution of each harmonic is described by a complex vector and frequency is common to all sensors, with analytic signal methodologies, where quantities are assumed to be slowly varying in time. Synchronous demodulation and principal coordinate definitions are combined in a multistep algorithm that provides an HBV estimation.
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On an industrial brake test matrix, the method is shown to be robustly applicable. The HBV signal being slowly varying, sub-sampling reduces the volume of test data by two orders of magnitude. Limit cycle frequency, amplitude and shapes can thus be added to the parallel coordinates containing operating parameters: pressure, velocity, temperature, torque, disk position, disk/bracket distance, ... This opens a path to a range of analyzes otherwise difficult to perform. Classification of occurrences is first discussed showing pressure and amplitude dependence. The effect of amplitude on both frequency and shape is then demonstrated. The entry and exit of instability when parameters change are then analyzed by proposing a transient root locus built from test. Thus squeal test results are related to the classical complex eigenvalue analysis. Intermittent growth/decay events are shown to be correlated with wheel position. Furthermore, distance measurements indicate that disk shape variations of a few microns play a clear parametric role. Parametric testing and clustering are then used to map the instability region and its edges. Pressure is shown to have an effect dominating other variations. Prospective uses of these results to combine test results and finite element models are discussed last
Comparison of Major Wood Hygro-Thermal Modification Technologies Paves the Way for a Generalized Mass Loss Kinetic Model
No full textBibliographic data about dry mass loss coming from different thermal and hygrothermal modification processes versus time were collected in this work and analyzed together. The data sets were collected from 2 experimental campaigns involving different modification technologies: (A) spruce wood hygro-thermally modified under superheated steam conditions performed at relative humidity ranging from 35 to 92% at temperatures ranging from 110 to 170 °C; and (B) poplar wood samples thermally modified with Thermo-vacuum® technology performed at temperatures ranging from 150 to 240 °C. For both processes, conversation rates master curves at 150 °C were identified on the experimental points using the time-temperature and the time-temperature-humidity superposition method. The two master curves were then compared and a generalized kinetic model able to predict the mass losses when modifying wood at different temperatures and relative humidity implemented. A kinetic model is expressed with a master curve composed of 2 kinetic stages. That model can predict the mass variation occurring during any hygrothermal modification whatever the temperature applied and the environment medium relative humidity
Detection of Low-Velocity Impact Damage in Woven-Fabric Reinforced Thermoplastic Composite Laminates by Deep-Learning Classification Trained on Terahertz-Imaging Data
No full textTerahertz (THz) imaging is gaining attention as a nondestructive testing technique for assessing damage due to its high axial resolution and nonionizing nature, presenting a promising alternative to conventional methods such as ultrasound and X-ray imaging. Its practical implementation, however, remains limited by the reliance on expert interpretation and the frequent need for validation using supplementary techniques such as X-ray microcomputed tomography (µCT), particularly for complex damage modes. This study focuses on woven-fabric-reinforced thermoplastic composites subjected to low-velocity impact, which typically causes barely visible impact damage (BVID). The damage is subtle yet critical, potentially leading to failure under subsequent loading. The multilayered and spatially distributed characteristics of BVID make it especially challenging to identify. To overcome these challenges, this work integrates deep learning with pulsed THz time-of-flight tomography (TOFT) imaging to enable automated damage detection in composite laminates. In contrast to existing research that mainly targets delamination using A- or C-scan data, this study emphasizes the detection of low-velocity impact damage by leveraging THz B-scans, which offer nondestructive depth-resolved cross-sectional imaging. The training dataset is labeled by correlating THz TOFT scans with X-ray CT images used as ground truth. A transfer learning approach, based on convolutional neural network (CNN) architectures, is employed for binary classification to distinguish damaged from undamaged regions. The resulting classifier achieves over 95 % accuracy, demonstrating the viability of this method for industrial applications such as quality assurance and in-service inspection of composite structures
Micromechanics-Informed Neural Networks for Periodic Homogenization of Thermocondcutive Behavior in Unidirectional Composites with Cylindrically Orthotropic Graphite Fibers
No full textA micromechanics-informed neural network framework is developed for homogenization of periodic unidirectional thermoconductive composites with cylindrically orthotropic fibers. The framework hard-imposes the steady-state governing heat conduction equations within the network architecture, enabling accurate capture of singular heat flux fields at the fiber center that are challenging for conventional approaches. In contrast, continuity and periodicity conditions are enforced via boundary collocation points in the loss function. Validation against finite element simulations across a wide range of fiber volume fractions shows that accurate and converged temperature distributions can be achieved after 9000 training epochs using 8-16 harmonic terms. Additional higher-order harmonics are difficult to train reliably and may degrade predictions. While strong agreement is observed in the matrix heat flux distributions, noticeable discrepancies persist in the fiber phase due to varying ability to capture the singular heat flux fields. Furthermore, uniform collocation points converge faster than random points during solution refinement. Finally, transfer learning is employed to accelerate training for new configurations, allowing the network to achieve comparable accuracy after only 2000 training epochs, which is substantially fewer than the 9,000 epochs required when training from scratch
FMCW THZ radar and X-ray analysis of wood properties: A comparative study
Full text linkWood is a material valued for its mechanical properties and sustainability. It exhibits substantial variability in density due to its growth being influenced by the external environment. The measurement of its local properties is therefore crucial for various applications such as in the construction and transport industries. X-ray attenuation densitometry measurement is a well-established method, but it uses ionizing radiation which can pose hazards to human health. Its cost is significant in terms of investment and consumables. Terahertz (THz) technology, being non-ionizing and promising, emerges as an alternative for density imaging. Therefore, this study employs THz frequency modulated continuous wave (FMCW) radar, a novel approach, to assess its ability to predict local density in a pool of 110 samples from diverse wood species, with different thicknesses, and a wide density range (from 111 kg m�� 3 to 1086 kg m�� 3) representative of the natural variability of wood density — both at the local scale of growth rings and at a global scale. The beating signal of the FMCW radar was modeled by considering the crossed medium as uniform, to extract both the optical index and the absorption coefficient. Additionally, the local density was measured using an X-ray industrial timber scanner as a reference for the actual local density. Results reveal strong correlations between density and THz parameters. However, the study highlights limitations in the THz modeling, such as wood vessel scattering, thickness influence, potential polarization effect, or non-uniformity of the medium between earlywood and latewood
A Normative Data Approach to Define Proximal Junctional Kyphosis
No full textStudy design:
Multicentric retrospective study of prospectively collected data.
Objective:
Based on normative data from a cohort of asymptomatic volunteers, this study sought to determine the rate of abnormal values of proximal junctional angles (PJA) in adult spinal deformity (ASD) surgery patients, and compare it with PJK rate.
Summary of Background Data:
Proximal junctional kyphosis (PJK) definition does not take the vertebral level into account.
Methods:
This study included 721 healthy volunteers and 824 ASD surgery patients with 2-year postoperative follow-up. Normative values for each disc and vertebral body between T1 and T12 were analyzed, then normative values for PJA at each thoracic level were defined in the volunteer cohort as the mean±2 standard deviations. PJA abnormal values at the upper instrumented vertebra (UIV) were compared with Glattes’ and Lovecchio’s definitions for PJK in the ASD population at two years.
Results:
Mean age was 37.7±16.3 in the volunteer cohort, with 50.5% of females. Mean thoracic kyphosis (TK) was -50.9±10.8°. Corridors of normality included PJA greater than 20° between T3 and T12. Mean age was 60.5±14.0 years in the ASD cohort, with 77.2% of females. Mean baseline TK was -37.4±19.9°, with a significant increase after surgery (-15.6±15.3°, P<0.001). There was 46.2% of PJK according to Glattes’ versus 8.7% according to Lovecchio’s and 22.9% of kyphotic PJA compared to normative values (P<0.001).
Conclusion:
This study provides normative values for segmental and regional alignment of thoracic spine, used to describe abnormal values of PJA for each level. Using level-adjusted PJA values allows a more precise assessment of abnormal proximal angles and question the definition for PJK.
Level of evidence:
I