Publications

The 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 thro

Predictive dynamic simulations of virtual machining rely on accurate representation of eigenmodes and damping factors. Historically, the modeling of flexible workpieces requires experimental updating of general modal properties, especially due to a simplified definition of fixtures. In the present work a substructuring-based approach for a virtual machining simulation is developed. It is demonstrated on a vibration-prone boring of a thin-walled automotive workpiece. Fixture-affected zones are modeled via MacNeal-type approach. This enables for addressing the influence of clamping in the mechanical modeling of dynamics, and for creating specific models of typical fixture configuration. During simulation vibrations occur on similar frequencies to those observed on real machining. Resulting surface defects follow alike patterns in simulation and experiment.

Brake squeal is an instability that generates self-excited limit cycles which vary with time and operating conditions in real experiments. To analyze test results, it is proposed to use a Harmonic Balance Vector (HBV) signal model. It combines Harmonic Balance Method and analytic signal methodologies. From the Harmonic Balance Method, one uses the space-time decomposition where spatial distribution of each harmonic is described by a complex vector and frequency is common to all sensors. From analytic signal, one keeps the assumption that quantities are slowly varying in time. Synchronous demodulation and principal coordinate definitions are combined in a multistep algorithm that provides an HBV estimation. On an industrial brake test matrix, HBV estimation is shown to be robustly applicable. The HBV signal being slowly varying, time 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 that associate to each time sample the 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 squeal occurrences is first discussed showing pressure and amplitude dependence. The effect of amplitude on both frequency and shape is next 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.

Polymethyl methacrylate (PMMA) is a benchmark brittle material for dynamic crack propagation studies. Despite extensive research, significant inconsistencies persist in reported fracture parameter values, complicating the establishment of a consensus on their sensitivity to the cracking regime. This study aims to rigorously determine these properties while identifying the origins of these discrepancies. To minimize microbranching effects that can strongly influence fracture surface roughness, crack propagation was restricted to subcritical velocities using a strip-band-specimen (SBS) geometry and a dedicated experimental setup. This approach ensured a quasi-steady propagation regime with minimal inertial effects. Dynamic toughness was evaluated using resistance curves constructed from Williams series expansion and displacement fields obtained via digital image correlation (DIC). Fracture energy was assessed through two complementary methods: a global energy balance and an indirect analytical approach based on Irwin’s generalized relation. Two distinct propagation regimes were identified: a stable regime (90 – 180  $$\hbox {m}.\hbox {s}^{-1}$$ m . s - 1 ) with smooth fracture surfaces and an unstable regime (180 – 320  $$\hbox {m}.\hbox {s}^{-1}$$ m . s - 1 ) characterized by the emergence of conical microstructures, followed by a transition to fully disrupted propagation beyond 320  $$\hbox {m}.\hbox {s}^{-1}$$ m . s - 1 , marking the onset of microbranches. A key outcome of this study is the validation of global fracture energy estimation through the local approach, and vice versa, allowing the derivation of one fracture property from the other – an unprecedented achievement for PMMA in dynamic crack propagation. This was made possible by the experimental setup and specimen geometry, which effectively minimized parasitic effects such as inertia and microbranching. Additionally, the findings confirm a strong correlation between surface roughness and the evolution of fracture energy from the earliest stages of dynamic propagation.

Pharmaceutical tablets must meet a number of requirements and among them, the mechanical strength plays an important role. The diametral compression test is generally used to evaluate it but can generate unstable failures. Thanks to load–unload cycles applied to the tablets subjected to a DCT test, it was shown that the concept of equivalent linear elastic fracture mechanics usually, can be successfully applied to the Mode I fracture behavior. Within this framework, the equivalent elastic crack growth resistance, commonly called resistance curve (R-curve), of the studied material was obtained and revealed the development of a Fracture Process Zone (FPZ) which is symptomatic of a quasi-brittle behavior. Moreover, the cyclic loading applied during the fracture test revealed the existence of a second dissipative mechanism leading to residual crack opening which seems to be mainly caused by friction phenomenon in the FPZ.

The porous-cracked microstructure of plasma sprayed ceramics coatings directly influences their macroscopic mechanical response. A 3D micromechanical model based on the discrete element method (DEM) is developed to reproduce their behavior. 3D observations are conducted with FIB-SEM nano-tomography and image analysis is used to extract and discretize the microstructure. A modeling strategy is developed to incorporate both pores and cracks into the model while preserving the computation performance. The lattice nature of DEM is used for the modeling of crack thickness that are smaller than the discrete element size. A method to compute the crack thickness from gray level images is proposed. Virtual quasi-static tests are performed on a sample of yttria-stabilized-zirconia. The results are in accordance with the literature data, such as the anisotropy and the non-linear behavior. The model is helpful to precisely investigate the role of the microscopic components, and micro-cracking on the macroscopic failure.

Wear of vitrified alumina wheels is a major research issue. Although extensive experimental work has been presented in the scientific literature, wheel manufacturers and grinding users are still unable to predict the expected grinding ratio of their operations. This work presents a novel multiscale approach that integrates the mechanical behavior of vitrified bonds with the stochastic nature of grain location. The new multiscale model integrates a DEM microscale model (μSM) and a randomization of the μSM (RμSM) of the wheel. The μSM simulates the stress field in the region of the wheel in contact with the workpiece, while RμSM accounts for the actual and random location of the alumina grits. This approach drastically reduces computational time and effectively determines the actual number of grains lost under a set of given grinding conditions. The model successfully predicts the detachment of complete clusters of abrasive grains from the bonds, with a large degree of agreement with experiments considering the deviation introduced by the micro-cutting edges that modify the hypothetical spherical geometry of the Discrete El­ ements (DEs). This is the first model to predict the volumetric wear of grinding wheels. The results will be useful for informing the future analysis of grinding operations affected by volumetric wear.

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.