Publications

The present study intends to make possible the dynamic characterization of a non-reflective and opaque material using a laser shock test which must lead to the establishment of an equation of state and a constitutive law. The instrumentation used is a back-face velocity measurement by a green laser interferometry (VISAR). In this study, a metallic coating (aluminum) is added to the back-face of the non-reflective material to be characterized (here an elastomer). The influence of the back-face coating thickness on material characterization is studied experi­mentally and numerically. The experimental results indicate that, whatever the thickness of the metal coating, it is possible to determine the equation of state of the material using a simulation model. Limitations of the pro­ posed protocol are then finally discussed to get a constitutive law at loading up to 20 GPa. The role of a probable early damaging at the back-face of the sample and improvements proposals are given through numerical analysis of the shock tests.

In the present study a Discrete Element Method (DEM) is considered to model the dynamic behaviour and fragmentation mechanisms of alumina ceramic under high strain-rate shockless loading. GEPI (high-pulsed power) spalling experiments are simulated. The DEM allows to take into account the accurate propagation and interaction of stress waves within the samples upon calibration of microscopic bond parameters. The results indicate that a standard failure criterion can effectively represent the spalling phenomenon, though discrepancies with experimental data increase at higher strain rates. To address this, the study combines the DEM approach with a damage law, specifically the first and second order Kachanov damage law, to model crack initiation and propagation. Comparative analysis with experimental rear face velocity profiles validates the approach. The strain-rate sensitivity of the present DEM model is explored using loading pulses of increasing intensity that induce different strain-rate levels. This research demonstrates that the DEM approach can effectively model dynamic behaviour in brittle solids leading to a multiple fragmentation sensitive to the strain rate.

Polymer solution injection has emerged as a promising method for the remediation of NAPL (non-aqueous phase liquids)-contaminated aquifers. This technique enhances recovery efficiency by modifying viscous forces, stabilizing the displacement front, and minimizing channeling effects. However, there remains a significant gap in understanding the behavior of polymer solutions, particularly those with different molecular weights (MW), for mobilizing DNAPL (dense non-aqueous phase liquids) trapped in heterogeneous aquifers, especially within low-permeability layers. In this study, we address this gap by investigating the mobilization of DNAPL lenses confined by low-permeability layers through the injection of polyethylene oxide (PEO) polymers of varying MW. PEO solutions with MW of 5 M (million) and 8 Mg/mol displayed shear-thinning behavior for shear rates of 0.01 to 100 s-1, while the 1 Mg/mol solution showed shear-thinning below 10 s-1 and Newtonian behavior above. PEO solutions in porous media exhibit Newtonian behavior at low-to-moderate shear rates for all MWs, likely due to confinement-limited entanglement. Adsorption studies found non-significant PEO adsorption on soil surfaces, likely due to its large molecular size. Post-flushing of PEO-saturated columns with water led to notable permeability reductions attributed to viscous fingering. Column tests indicated a decrease of the residual DNAPL saturation with the capillary number (Ca), more sharply in low permeability soils. 2D cell tests identified three stages of DNAPL mobilization: initial stabilization, sharp recovery increase upon PEO arrival, and a final stabilization at residual saturation. The duration of each transition was found to be influenced by concentration. Numerical simulations accurately mirrored these stages and provided additional insights into PEO viscosity distribution and DNAPL mobilization patterns in heterogeneous media. The results highlighted that higher injection rates promote mobilization from the two low permeability layers surrounding the DNAPL bank from both sides and the upper zone, while lower rates mainly drive mobilization from the upper side. Using numerical simulations the performance of PEO injection on displacement of DNAPL in multiple lenses and various position of recovery points was evaluated.

Multiple software frameworks based on the Discrete Element Method (DEM) are available for simulating granular materials. All of them employ the same principles of explicit time integration, with each time step consisting of three main steps: contact detection, calculation of interactions, and integration of the equations of motion. However, there exist significant algorithmic differences, such as the choice of contact models, particle and wall shapes, and data analysis methods. Further differences can be observed in the practical implementation, including data structures, architecture, parallelization and domain decomposition techniques, user interaction, and the documentation of resources. This study compares, verifies, and benchmarks nine widely-used software frameworks. Only open-source packages were considered, as these are freely available and their underlying algorithms can be reviewed, edited, and tested. The benchmark consists of three common bulk processes: silo emptying, drum mixing, and particle impact. To keep it simple and comparable, only standard features were used, such as spherical particles and the Hertz-Mindlin model for dry contacts. Scripts for running the benchmarks in each software are provided as a dataset.

La Responsabilité Elargie des Producteurs (REP) pour les Articles de Sport et de Loisirs (ASL) a été instaurée en France depuis le 1er janvier 2022. ...

The Cauer ladder network (CLN) method can accelerate eddy current field analysis of electromagnetic devices in the time domain by reducing the order of the finite element (FE) model. To control its accuracy, the reduction error should be estimated without conducting the FE analysis. In this study, we extend the estimation method in the frequency domain developed in a previous study to time-domain analysis. The proposed method is also extended to a multiport system. Numerical examples illustrate that the proposed error estimation method is effective.

The Cauer ladder network (CLN) method, as proposed by Kameari et al. (2018), has been extensively studied to construct a reduced model of magneto-quasistatic (MQS) Finite Element (FE) models. In this case, this method enables the construction of an equivalent electrical circuit based on resistances and inductances as well as a reduced basis where the solution of a reduced problem is sought. In this article, we propose to extend the applicability of the CLN method to the development of reduced models for FE electro-quasistatic (EQS) models. It appears that the derivation of the reduction of an EQS model is not similar to the one of an MQS model. After development, the process of reduction using CLN leads to consider two electrical circuits based on the cascade association of resistances and capacitances. Each circuit is associated with a reduced basis constructed by applying the self-adjoint Lanczos method. The reduced solution to the EQS problem is got by first solving the circuit equations to determine the voltages and the currents at the terminals of the resistances and capacitances. Then, the approximated solution of the FE EQS model is got by a linear combination of the vectors of the two reduced bases weighted by the currents (or the voltages) previously calculated. An error estimator is also derived, enabling to calculate the distance between the reduced solution and the FE solution without solving the FE model. The proposed approach has been applied on an industrial application, a resin-impregnated paper bushing, in order to evaluate the accuracy in function of the size of the reduced bases as well as the efficiency in terms of computation time.

Operating temperatures of electrical machines are known to cause various effects on magnetic performances and losses. On the one hand, reversible contributions may reduce iron losses through temporary lowering of conductivity, which in turn reduces eddy-current losses. On the other hand, when specific thermal conditions are met, the time-temperature combination may lead to irreversible changes of the magnetic material properties. This latter phenomenon, the so-called magnetic aging, need to be addressed to further improve energy efficiency, predict and reduce heat-dissipated iron losses. These service conditions indeed lead to changes in the microstructure of the electrical steels. Thus, iron losses suffer from these structural modifications as well as long exposure to constant operating temperatures; magnetic aging results from carbides precipitation and impacts the magnetization of these steels. The present paper hence explores a multi-scale approach, coupling the Johnson-Mehl-Avrami-Kolmogorov (JMAK) precipitation kinetics with a static Jiles-Atherton (J-A) model of magnetic hysteresis for a non-oriented soft ferromagnetic Fe-Si steel. Based on an experimental analysis for temperatures ranging from 160°C to 200°C, the applicability of the chosen approaches will be explored and a parameter-based modeling of magnetic aging will be proposed and proved to be in good agreement with measurement data.

Transforming daily chores into game-like activities has long been a tantalizing promise. Whether it is completing homework, washing dishes, or even filing taxes, many of these tasks have been incorporated into serious games or gamified interventions. Yet, the question remains: why do such efforts often fall short, leaving mundane tasks as unappealing as ever? In this article, we argue that the literature on game interventions could benefit from a methodological shift to better understand the impact of game mechanics on human psychology. We illustrate this point by presenting two experimental protocols that isolate game elements, providing a clearer understanding of their effects on the desired outcomes. The results of both studies are not disclosed here, as our focus is solely on the protocols themselves.

Assessing mental workload is essential for optimizing the design of complex systems, particularly in aeronautical maintenance, where operators' activities serve as a crucial safety barrier to ensure optimal system safety levels. One of the roles of human factors in maintainability is, therefore, to anticipate maintenance activities and human behavior from the start of the design cycle. This study pursues a dual objective: firstly, to identify relevant for evaluating mental workload in an industrial maintenance environment, and secondly, to determine which of these indicators correlate with performance degradation. Ten participants performed five maintenance tasks of varying complexity on a helicopter, involving the removal, installation of components and a detailed inspection. Subjective measures (NASA-TLX), performance metrics (completion time), and cardiovascular data (heart rate, heart rate variability) were analyzed. We observed longer completion times and higher NASA-TLX scores for complex maintenance conditions. Regarding cardiovascular data, the results in the time domain of heart rate variability follow a similar trend compared to two other types of measurements. These results will be discussed in depth in this article. This study represents a further step in the multidimensional measurement of mental workload in maintenance within a realistic industrial context.