HAL-INSA Toulouse
Not a member yet
34325 research outputs found
Sort by
In-situ open-hole tensile testing and modeling of hybrid PEEK thermoplastic laminates under burn-through kerosene flame exposure
No full textInternational audienceThe objective of the present work is to investigate the thermo-mechanical behavior of open-hole hybrid carbon/ glass fiber reinforced PolyEther Ether Ketone (CG/PEEK) thermoplastic laminate subjected to the kerosene flame exposure (1100 • C and 116 kW/m 2 heat flux) in combination with tensile loading. A specialized flame testing bench has been developed, integrating a tensile mechanical loading and a kerosene burner, to induce in-situ firemechanical test conditions. The novel prototype has been employed to monitor the temporal evolution of several physical quantities in the range of fire exposure times up to 900 s, including back surface and through thickness temperature, open-hole deformation and swelling ratio of thickness. The mechanisms of fire-and mechanicallyinduced damage are examined through the fractographic analysis using tomography and microscopy. One-sided burn-through flame exposure causes the in-plane (4.0 K/mm) and through-thickness (40.1 K/mm) temperature gradients after 300 s. Compared to the virgin state, there is a considerable reduction in the equivalent stiffness (-67%) and axial strength (-55%) following a 900 s of flame exposure, indicating the severely damaged structural integrity. The modeling of the in-situ mechanical properties over multiple phase transition temperatures of the PEEK matrix is applied to characterize and ultimately predict the thermo-mechanical response of laminate under tensile loading in fire. The approach is based on the experimental measurement of mechanical properties over a wide temperature range (isothermal heating from the glass transition temperature to the PEEK matrix pyrolysis). The model shows a high degree of effectiveness in representing the in-situ open-hole tensile behavior of TP-based laminates under fire conditions as a function of flame exposure time.</div
Coupling quantum spin ice to matter on the centered pyrochlore lattice
No full textInternational audienceThe low-energy physics of quantum spin ice is known to support an emergent form of quantum electrodynamics (QED), where magnetic monopoles exist and the fine-structure constant is material dependent. In this article, we show how this QED is modified via a coupling to dynamical matter on the centered pyrochlore lattice, a structure that has recently been synthesized using metal-organic frameworks. Specifically, we study the low-energy properties of the S = 1 / 2 quantum XXZ model on the centered pyrochlore lattice, with a focus on the sign-problem-free region. At fourth order in degenerate perturbation theory, this model hosts a quantum spin liquid distinct from the well-known U(1) quantum spin ice on the pyrochlore because of the presence of dynamical matter in the ground state. Exact diagonalization results are consistent with this quantum spin liquid over an extended region of the ground-state phase diagram, although potential quantum critical points within this region could indicate a richer phase structure. Our work thus expands the physics of quantum spin ice in an experimentally motivated geometry, showing how the emergent QED can be coupled to dynamical matter at zero temperature
Modélisation et Optimisation des Performances Thermiques des Matériaux Bio et Géosourcés par Approche Multi-échelle : Apport à la Valorisation d'une Large Gamme de Co-produits Agricoles
No full textInternational audienceLes matériaux bio et géo-sourcés accompagnent la transition écologique du secteur du BTP. Ils améliorent le confort intérieur du bâti tout en diminuant son impact environnemental. De nombreux granulats végétaux, autres que la chènevotte utilisée dans le béton de chanvre, sont valorisables. Bien que largement disponibles grâce aux cultures implantées localement (tournesol, colza, lin, …), leur utilisation à grande échelle reste limitée. Leur comportement complexe est un des freins majeurs à leur développement. Ces travaux explorent de nouveaux champs disciplinaires pour lever plusieurs verrous. Il s’agit de comprendre les phénomènes physico-chimiques qui s’opèrent à différentes échelles et de développer des modèles prédictifs du comportement thermique. De l’échelle stratégique du granulat végétal à celle du matériau, l’analyse multi-échelle menée – via des techniques d’homogénéisation analytique- permet de prédire et d’optimiser le comportement thermo-hygrique de plusieurs types de matériaux, avant même l’étape de fabrication. Ces travaux doivent favoriser l’émergence d’économies locales basées sur des matériaux de construction sains, performants et écologiques. Leur utilisation à large échelle constitue indubitablement un levier stratégique pour atteindre la réduction des émissions de gaz à effet de serre visée par le Pacte Vert pour l’Europe, d’ici 2030
Automatic selection of inducing points in sparse Gaussian process for approximations of finite element analyses
No full textInternational audienceGaussian process regression (GPR) is a widely used regression model, but it has poor scalability. Sparse approximation methods improve scalability by using in- ducing points to approximate the GPR, but determining the optimal number and placement of these points is challenging. This article presents a method to esti- mate the necessary number of inducing points for accurate predictions of finite element method (FEM) analyses using approximate GPR. The approach lever- ages the proper orthogonal decomposition (POD) technique, using its modes to determine the inducing points. POD has previously been combined with GPR to provide computationally efficient predictions for the full solution field across un- seen variable combinations, treating spatial components separately via reduced basis functions. However, this work treats the spatial component as a variable within the GPR approximation, allowing continuous spatial predictions. This en- sures that the covariance in the spatial dimension is captured by a single GPR. The method is applied to simulations of a three-span, post-tensioned concrete girder bridge. Results demonstrate that the proposed method identifies a suf- ficient number of inducing points for approximate GPR to achieve predictive accuracy comparable to full GPR, but with half the training time. Furthermore, approximate GPR achieves accuracy similar to POD with GPR, while slightly reducing predictive variance in specific areas. This approach ensures computa- tional efficiency without significant loss in accuracy, making it a valuable tool for scalable regression in engineering applications.<br /
An Immersed Boundary Method for pressure-based compressible solvers with applications to free-convection flows, acoustic wave propagation and thermal plasma
No full textInternational audienceImmersed Boundary Methods (IBM) are a practical class of methods that enable fluid computations in complex geometry while keeping a structured mesh. Most of the existing IBM have been developed in the framework of incompressible solvers, despite their significant interest to perform simulations in more complex configurations requiring a compressible solver. In the last years, pressure-based solvers met a growing interest to perform numerical simulations of compressible flows, due to their attractive features, as removing the stability condition on the acoustic time step, and being asymptotically preserving of the incompressible regime when the Mach number tends to zero. As this class of compressible solvers share many common features with classical projection methods for incompressible flows, our objective in this paper is to present an adaptation of an efficient and accurate IBM developed for an incompressible solver by Ng et al. in [1] to a pressure-based compressible solver recently published by Urbano et al. in [2]. The proposed algorithm benefits of the attractive properties of the original IBM proposed in [1] while being able to undertake simulations in much more complex configurations. In particular, we will present validations and illustrations of the proposed solver in various configurations as free-convection flows, acoustic waves propagating in a variable section pipe or interacting with a solid obstacle, as well as the description of a thermal plasma during an electric arc discharge in a gas
Performance of Sewer Concretes with Calcium Sulpho-Aluminate Cement and Portland Cement Blends: Field and Laboratory Studies
No full textInternational audienceThis paper discusses the performance of calcium sulpho-aluminate (CSA) cement and a Sulphate-Resisting Portland Cement (SRPC) with a fly ash (FA) additive (i.e., a SRPC + FA binder system) in a ‘live’ sewer environment; it deepens the understanding of their deterioration mechanisms by using a laboratory test for simulated sewer conditions. It also studies the role of an iron-based additive (‘Hard-Cem®’, HC) in improving the performance of SRPC + FA concrete under a biogenic acid attack. The performance of 0.4 w/b concrete specimens of the three binders (CSA, SRPC + FA, and SRPC + FA + HC) with calcite aggregates in sewer exposure was assessed by visual observation, measurements of mass and thickness changes, and microstructural analysis for approximately 25 months. The laboratory test, i.e., the Biogenic Acid Concrete (BAC) test, was used to study the deterioration mechanisms of these binders in terms of leaching solution pH and standardised cumulative leached calcium and aluminium. The results indicate that CSA concrete had improved performance in the sewer environment, showing no mass loss and only about one-third of thickness lost in the SRPC + FA concrete over a 25-month exposure period in the sewer environment. The BAC test results complemented the field observations. The iron-based additive in sewer concrete slightly reduced mass loss, likely due to its better resistance to abrasion and erosion, but not due to any chemical influence, since it does not participate in hydration or dissolution reactions. The findings imply that CSA cement may represent a suitable alternative binder for concrete sewer construction. They also suggest that a surface hardener has limited benefits, except when it is under abrasive conditions. Further investigation is required, especially since CSA contains high amounts of sulphate, the effect of which is not well understood
Permethylated Cyclodextrins with Thiol Groups as Stabilizing Agents for Catalytic Water‐Soluble Platinum Nanoparticles
No full textInternational audienceIn this study, water‐soluble colloidal platinum nanoparticles (Pt NPs) have been stabilized with novel thiolated cyclodextrins (CD‐SH) and their catalytic performance has been investigated. We varied the size of the CD cycle (α‐CD/β‐CD), the degree of thiolation (one or two thiol groups per CD), and the CD/Pt molar ratio (0.5; 0.2; 0.1; 0.05) to find the best performing water‐soluble, air‐stable hydrogenation catalyst. An organometallic approach for the Pt NP synthesis resulted in the formation of small well‐dispersed NPs of 1–2 nm in size, as shown by TEM. XPS analysis confirmed the formation of a Pt−S interaction, rationalizing the strong NP stabilization by a small quantity of CD‐SH, while preserving the NP catalytic properties. Only 0.1 equivalent of CD‐SH was enough to obtain a promising hydrogenation activity with preserved stability of the colloidal dispersion. Performing catalysis in biphasic conditions allowed simple separation of the products and reuse of the catalyst five times without deactivation
A Linear Complementarity based MPC for Aerial Physical Interaction
No full textInternational audienceThis paper presents a general MPC-based control framework that includes the linear complementarity problem (LCP) for modeling the interaction forces of a mobile robot. To validate our approach, two case studies are considered: (i) an aerial robot that should reach a target point placed on a frictionless surface; and (ii) an aerial robot that should lift a cable-suspended mass, switching from a slack to a taut cable condition. The simulation results confirm the validity of our approach, and the ability of the LCP to model the interaction forces for an aerial platform
Optimizing quasi-dissipative evolution equations with the moment-SOS hierarchy
No full textInternational audienceWe prove that there is no relaxation gap between a quasi-dissipative nonlinear evolution equation in a Hilbert space and its linear Liouville equation reformulation on probability measures. In other words, strong and generalized solutions of such equations are unique in the class of measure-valued solutions. As a major consequence, non-convex numerical optimization over these non-linear partial differential equations can be carried out with the infinite-dimensional moment-SOS hierarchy with global convergence guarantees. This covers in particular all reaction-diffusion equations with polynomial nonlinearity
Cofactor engineering for improved production of 2,4-dihydroxybutyric acid via the synthetic homoserine pathway
No full textInternational audience(L)-2,4-dihydroxybutyrate (DHB) is a versatile compound that can serve as a precursor for the synthesis of the methionine analog 2-hydroxy-4-(methylthio)butyrate and new advanced polymers. We previously implemented in Escherichia coli an artificial biosynthetic pathway for the aerobic production of DHB from glucose, which relies on the deamination of (L)-homoserine followed by the reduction of 2-oxo-4-hydroxybutyrate (OHB) and yields DHB by an enzyme-bearing NADH-dependent OHB reductase activity. Under aerobic conditions, using NADPH as a cofactor is more favorable for reduction processes. We report the construction of an NADPH-dependent OHB reductase and increased intracellular NADPH supply by metabolic engineering to improve DHB production. Key cofactor discriminating positions were identified in the previously engineered NADH-dependent OHB reductase ( E. coli malate dehydrogenase I12V:R81A:M85Q:D86S:G179D) and tested by mutational scanning. The two point mutations D34G:I35R were found to increase the specificity for NADPH by more than three orders of magnitude. Using the new OHB reductase enzyme, replacing the homoserine transaminase with the improved variant Ec.AlaC A142P:Y275D and increasing the NADPH supply by overexpressing the pntAB gene encoding the membrane-bound transhydrogenase yielded a strain that produced DHB from glucose at a yield of 0.25 mol DHB mol Glucose −1 in shake-flask experiments, which corresponds to a 50% increase compared to previous producer strains. Upon 24 h of batch cultivation of the most advanced DHB producer strain constructed in this work, a volumetric productivity of 0.83 mmol DHB L −1 h −1 was reached