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Caractérisation rapide de propriétés en fatigue d'un composite stratifié sous sollicitations hors plan et de compression à partir d'essais d'auto-échauffement
No full textDue to their technological maturity, laminated composites now enable the design of complex and optimized parts, some of which require fatigue justification with the aim of achieving long service lives. However, this poses a major challenge for the design of composite parts, as the visco-elasto(plastic) nature of organic matrices limits loading frequencies to around ten Hz. In this context, the objective of the study is to propose a methodology based on self-heating to rapidly characterize the fatigue properties of a unidirectional carbon/epoxy laminate subjected to in-plane compression and out-of-plane shear loading. To address this issue, experimental campaigns were conducted to characterize the failure scenarios of laminates under targeted cyclic loadings. The configurations of interest were also subjected to thermomechanical analyses, primarily based on infrared measurements. The analysis strategies developed for processing self-heating tests allow access to the source term associated with energy dissipation. This characterization is complemented by a modeling of the resin’s role in dissipation, thereby establishing the link between its nonlinear viscoelastic behavior and the fatigue response.Grâce à leur maturité technologique, les composites stratifiés permettent aujourd’hui de concevoir des pièces complexes et optimisées, dont certaines nécessitent une justification en fatigue, avec la volonté de viser des durées de vie importantes. Cependant, cela représente un défi majeur pour le dimensionnement des pièces composites, car la nature visco-élasto(-plastique) des matrices organiques limite les fréquences de sollicitation à une dizaine de Hz. Dans ce contexte, l’objectif de l’étude est de proposer une méthodologie basée sur l’auto-échauffement pour caractériser rapidement les propriétés de fatigue d'un stratifié de plis unidirectionnels carbone-époxy soumis à des sollicitations de compression dans le plan et cisaillement hors plan. Pour répondre à cette problématique, des campagnes expérimentales ont été menées afin de caractériser scénario de ruine des stratifiés soumis aux sollicitations cycliques ciblées. Les configurations d’intérêt ont également fait l’objet d’analyses thermomécaniques, reposant principalement sur des mesures infrarouges. Les stratégies d’analyse développées pour l’exploitation des essais d’auto-échauffement permettent d’accéder au terme source associé à la dissipation énergétique. Cette caractérisation est complétée par une modélisation du rôle de la résine dans la dissipation, établissant ainsi le lien entre son comportement viscoélastique non-linéaire et la réponse en fatigue. L’ensemble de ces travaux permet de proposer des méthodologies de dimensionnement en fatigue à partir d’essais d’auto-échauffement
On the risk of fatigue failure of structural elements exposed to bottom wave slamming – Impulse response regime
No full textInternational audienceThis study aims to investigate whether fatigue damage induced by bottom wave slamming can be a failure mode, important to consider when sizing a marine structural element. The body exposed to wave impacts is assumed to have a shape and structural arrangement such that the duration of wave-impact loads is short relative to the structure's vibratory response time. In this dynamical regime, fatigue is found to be a potentially important failure mechanism: accounting for the risk of failure due to fatigue damage may result in design constraints that are significantly more conservative than those based on the risk of ultimate strength exceedance. The role of fatigue damage depends on the elevation of the body. It is predominant for low elevations, for which slamming events are frequent. Since this study aims to provide general insight, the specific details of the body, such as its shape and structural arrangement, are not specified. Instead, a general framework is used for the analysis. The way forward to address a specific case study, possibly including the effects of forward and seakeeping motions, is briefly explained
A Müller approach for reachability
No full textThis paper presents an approach to deal with the prediction of dynamical systems in case of interval uncertainties. These uncertainties can be both on the initial state vector, on the timedependent inputs and on the evolution function. The approach is based on the Müller theorem often used in an interval context to perform predictions of cooperative systems. We show here that the Müller approach can be used for general non-cooperative systems. We also show the benefit we can obtain by using a conditioning approach in order to reduce the pessimism.</div
Numerical study of hydrodynamic performance of a heaving buoy wave energy converter in regular waves using the CEL method
No full textInternational audienceWave energy converters (WECs) operating in ocean environments are subject to highly unsteady hydrodynamic loads that significantly influence their performance and structural stability. This study investigates the nonlinear interaction between regular waves and a heaving buoy, with a focus on wave-induced pressure distribution, dynamic response, and energy absorption characteristics. A Coupled Eulerian-Lagrangian (CEL) approach is employed to capture the transient fluid-structure interaction, including wave slamming and pressure amplification effects. The simulation results reveal pronounced pressure peaks on the buoy surface, particularly at wave incidence (90 • ) and leeward sides (180 • ), reaching up to 1.75 times the nominal hydrostatic pressure. The vertical displacement response is validated against experimental data from the literature, showing strong agreement in amplitude and phase. Additionally, a parametric analysis is conducted to assess the influence of buoy geometry and density on key performance indicators such as the Response Amplitude Operator (RAO) and Capture Width Ratio (CWR). This study integrates the CEL in Abaqus/Explicit, enabling simultaneous resolution of fluid dynamics, structural deformation, and pressure fields without the need for external co-simulation. The results offer new physical insights into wave loading mechanisms and provide a computationally efficient tool for optimizing the design and survivability of WECs in realistic sea states
Innovative Tool for Improving Surface Quality in Single Point Incremental Forming: A Comparison with Hemispherical Tools
No full textInternational audienceSingle Point Incremental Forming (SPIF) has emerged as a flexible and cost-effective technique for producing complex sheet metal parts. However, its industrial application is often limited by issues related to surface quality. This study examines the impact of tool geometry on the surface integrity of the AA6061-T6 aluminum alloy. The research novelty lies in the innovative eccentric tool with a variable radius (ETVR), which we compare to two conventional hemispherical tools with radii of 5 mm and 10 mm. Truncated cones were formed under the same process conditions, and their quality was assessed by measuring surface roughness and microhardness along the cone’s generatrix in both the rolling direction and the transverse direction. Additionally, microchip analysis and visual inspections were conducted. The results reveal distinct differences in the surface morphology, evolution of roughness, and distribution of microhardness among the three tools. The SS5 tool produced the highest level of hardening but also resulted in significant surface deterioration. In contrast, the SS10 tool generated smoother surfaces with moderate hardening, while the ETVR tool struck a balance between surface uniformity and enhanced hardness. Statistical analyses, using t-tests, confirmed the significance of these findings. This study offers new insights into tool design for SPIF, highlighting the trade-offs between surface quality and material strengthening
Enhancing security requirements specification with SECRET-SCORE: A template-driven and ontology-based approach
No full textInternational audienc
On the application of the T-coercivity method for the Helmholtz problem with sign-changing coefficients
No full textTo solve transmission problems with sign-changing coefficients, one can apply the T-coercivity method, which imposes specific mesh conditions near the interface to ensure optimal convergence rates for the finite element approximation. This method was initially proposed and analyzed for the quasi-static case. The aim in this work is to extend it and prove its convergence for the case of non-zero frequency. Additionally, we check its convergence for a general compact perturbation and outline key ideas for a 3D polyhedral interface. Our theoretical results are validated through a numerical test
Research on data storage with a focus on AI on the Edge
No full textInternational audienceDeploying ML/AI algorithms on the edge is necessary for applications (e.g., security and surveillance, industrial IoT, autonomous vehicles, healthcare use cases, ...) requiring low latency, data privacy or reduced costs. However, most edge devices are not equipped with powerful memory systems to process such applications. The objective of this presentation is to show some optimization venues to unlock the memory/storage bottleneck of some ML/AI algorithms mainly from a learning perspective to deply them on low-resource devices.The speaker will first present some past contributions on different topics related to storage systems, then he will focus on some edge AI related storage optimization and conclude with some perspectives
Analysis of microcracking processes in microconcrete under confined compression utilising synchrotron-based ultra-high speed X-ray phase contrast imaging
No full textInternational audienceIn the present study, microconcrete (MC) samples were exposed to dynamic quasioedometric compression (QOC) tests and visualised in-situ by the means of MHz synchrotron X-ray phase-contrast imaging in the ESRF synchrotron in order to analyse the damage mechanisms governing the mechanical behaviour of concrete under high-strain-rate confined compression. To do so, small cylindrical samples were placed in polymeric confinement cell and dynamically compressed along their axial direction using SHPB (Split-Hopkinson Pressure Bar) set-up available in ID19 beamline in the European Synchrotron Radiation Facility (ESRF).The damage process was visualized with MHz X-ray phase-contrast imaging along with an ultra-high-speed camera operating at a recording frequency approximately 1 Mfps (million frames per second i.e., 880 ns interframe time). The axial stress and strain temporal profiles were obtained from standard Kolsky's (SHPB) data processing. In addition, data of radial stress and strain within the sample were deduced from non-linear analysis of the mechanical behaviour of the polycarbonate confining cell instrumented with a strain gauge. Finally, the onset and growth of microcracking observed from the equatorial zone of large spherical pores is correlated with deviatoric and pressure measurements showing how the pore collapse process develops during the applied mechanical loading.</p
The non-intrusive reduced basis two-grid method applied to sensitivity analysis
No full textInternational audienceThis paper deals with the derivation of Non-Intrusive Reduced Basis (NIRB) techniques for sensitivity analysis, more specifically the direct and adjoint state methods. For highly complex parametric problems, these two approaches may become too costly ans thus Reduced Basis Methods (RBMs) may be a viable option. We propose new NIRB two-grid algorithms for both the direct and adjoint state methods in the context of parabolic equations. The NIRB two-grid method uses the HF code solely as a “black-box”, requiring no code modification. Like other RBMs, it is based on an offline-online decomposition. The offline stage is time-consuming, but it is only executed once, whereas the online stage employs coarser grids and thus, is significantly less expensive than a fine HF evaluation. On the direct method, we prove on a classical model problem, the heat equation, that HF evaluations of sensitivities reach an optimal convergence rate in L∞(0, T ; H10(Ω)), and then establish that these rates are recovered by the NIRB two-grid approximation. These results are supported by numerical simulations. We then propose a new procedure that further reduces the computational costs of the online step while only computing a coarse solution of the state equations. On the adjoint state method, we propose a new algorithm that reduces both the state and adjoint solutions. All numerical results are run with the model problem as well as a more complex problem, namely the Brusselator system