Pierre-Alain Boucard

Calendering governs the architecture and performance of dry composite cathodes, yet the coupled evolution of active material (AM), the carbon–binder domain (CBD), and pore pathways remains difficult to resolve. We develop a three-dimensional continuum–discrete framework representing AM particles by the discrete element method and the deformable viscoelastic CBD by the material point method. The model captures key experimental trends in structure and compaction while following the same evolving microstructure from mechanical loading through transport to electrochemical assessment. Densification increases AM connectivity and CBD surface coverage, generates heterogeneous CBD stress localization, and reveals substantial load transfer through the CBD. The AM force network becomes more interconnected and less anisotropic, whereas pore pathways become more tortuous and electrolyte flux more localized. Microstructure-informed electrochemical simulations showthat the resulting transport limitations constrain rate capability. The framework links cathode manufacturing, phase-resolved microstructure evolution, and functional performance.

In industrial applications, fine-scale simulations of bolted joints are often impractical due to the numerous nonlinearities in the vicinity of the bolt, which result in computationally expensive calculations, particularly during the early design stages. To address this, engineers typically replace detailed bolt models with simplified models built from a connector library available in commercial finite element (FE) solvers. This paper presents a nonlinear FE connector model, along with an identification methodology, designed to capture the full behaviour of a bolted assembly. The model is driven by key design parameters, such as bolt preload, friction coefficients, or elastoplastic properties of the materials used. The connector formulation separates the various mechanisms that influence the macroscopic behaviour of bolted assemblies. Axial behaviour is modelled by accounting for the effects of preload and axial stiffness, while tangential behaviour incorporates friction between the assembled plates, under the bolt head or nut, as well as plasticity in the bolt and potential contact between the screw and bore in case of extreme loads. The parameters for this connector are identified using a generic overlap joint. The connector model is implemented through a user-defined element subroutine in Abaqus/Standard ™. Comparative analysis of quasi-static responses from fine-scale full 3D simulations and those using the proposed connector across different bolted assemblies shows close agreement, with a significant reduction in computational time.

This paper offers an approach to deal with parametrized nonlinear strongly coupled thermo-poroelasticity problems. The approach uses the LATIN-PGD method and extends previous work in multiphysics problems. Proper Generalized Decomposition (PGD) allows the building of independent reduced-order bases for each physics. This point is particularly appropriate for thermo-poroelasticity problems whose physics present different dynamics. In parametrized problems dealing with material variability, a new computation is initialized with the result of a previous simulation to speed up the computation times. As a first step, the solver is validated on a standard benchmark in thermo-poroelasticity. The solver shows good performance even in the nonlinear frame. Then, the approach for parametrized problems is addressed on an academic problem and a more complex one, which is part of an industrial process. The results show that the method is effective and less time-consuming than naive approaches.

Stranded cables, composed of multiple twisted wires, exhibit high tensile strength and flexibility, making them essential in numerous industrial applications, such as mooring lines for offshore structures, overhead conductors, and cable-stayed bridges. The complex interactions between individual wire strands - primarily fretting-induced frictional contact and fatigue - pose significant challenges for numerical modeling. In this context, point-wise contact interactions between wires of different layers are often critical. This study presents a new beam-to-beam small-sliding point-wise contact element tailored for modeling stranded cables under small relative sliding conditions. Unlike traditional contact formulations, the proposed approach eliminates the need for repetitive, computationally expensive contact searches by assuming small sliding amplitudes between beams, which allows for predefined node pairing. The method, implemented within a large rotation wireframe finite element framework, offers enhanced computational efficiency and maintains robustness through a smooth evolution of the contact normal, thanks to nodal cross-sectional rotations. Numerical examples demonstrate the model’s effectiveness in handling arbitrary small sliding cases.

This paper offers an approach to deal with parametrized nonlinear strongly coupled thermo-poroelasticity problems. The approach uses the LATIN-PGD method and extends previous work in multiphysics problems. Proper Generalized Decomposition (PGD) allows the building of independent reduced-order bases for each physics. This point is particularly appropriate for thermo-poroelasticity problems whose physics present different dynamics. In parametrized problems dealing with material variability, a new computation is initialized with the result of a previous simulation to speed up the computation times. As a first step, the solver is validated on a standard benchmark in thermo-poroelasticity. The solver shows good performance even in the nonlinear frame. Then, the approach for parametrized problems is addressed on an academic problem and a more complex one, which is part of an industrial process. The results show that the method is effective and less time-consuming than naive approaches.

Moisture in the sensing coil of fiber-optic gyroscope (FOG) gives rise to bias drift. To explain and predict this phenomenon, one needs to quantify the strain along the fiber induced by moisture. In this paper, a full theoretical approach to determine the strain field into the sensing coil induced by a moisture loading is proposed. The approach consists in solving an analytical Fickian diffusion model in a semi-infinite medium, to implement a semi-analytical mechanical model of the moisture diffusion effect. The computed strain along the fiber is then compared with the distributed strain along the fiber measured using Rayleigh optical frequency domain reflectometry (Rayleigh-OFDR). Agreement between predicted and measured data demonstrate the validity of the proposed approach. Finally, a step function of $60\%RH$ (relative humidity) is shown to be equivalent to a thermal loading of $1 \ ^{\circ }C/min$ on $\Delta T = 15 \ ^{\circ }C$ and these loadings may induce an estimated bias of $0.1 \ ^{\circ }/h$ .

With railway interoperability, new trains are allowed to move on the French railway network. These trains may present different designs from standard trains. This work aims to complete the current approach for vehicle admission on the railway network, which is defined in technical baselines. Historically, computation rules for traffic conditions are based on simplified analytical works, which are considerably qualitative. They have evolved through feedback and experimental campaigns to comply with the track structure evolution. An efficient methodology based on numerical simulation is needed to evaluate railway vehicle admission to answer this issue. A perspective to update these computation rules is to evaluate the structural fatigue in the rail. That is to say, fatigue is caused by bending and shear stresses. The complexity of the railway system has led to an investigation at first of the vertical response of the railway track and quantifying its contribution to the rail’s stress response. In that sense, this paper investigates the vertical track response to a moving railway vehicle at low frequencies. For this purpose, a lightweight numerical model for the track, a multi-body model for the vehicle, and a random vertical track irregularity are proposed. More explicitly, the track model consists of a two-layer discrete support model in which the rail is considered as a beam and sleepers are point masses. The rail pads and ballast layer are modelled as spring/damper couples. Numerical results show a negligible effect of track inertia forces due to high track stiffness and damping. Nevertheless, this assumption is valid for normal rail stresses but not for ballast loading, especially in the case of sleeper voids or unsupported sleepers. Hence, the prediction of the mechanical stress state in the rail for fatigue issues is achieved through a static track model where the equivalent loading is obtained from a dynamic study of a simplified vehicle model. A statistical analysis shows that the variability of the vertical track irregularity does not influence the output variabilities like the maximum in time and space of the normal and shear stress.

The quadrupolar winding of the sensing coil of a fiber-optic gyroscope (FOG) is an essential technique to reduce the thermal bias drift of this sensor. This technique, which is based on orthocyclic winding, contains complex nonaxisymmetrical zones, for example layer transitions or crossovers. In this paper, a precise topological reconstruction of the sensing coil is proposed using X-ray computed tomography. Thanks to this reconstruction, the first layer role and its impact on the next layers are studied. Then, the quality of the winding is quantified using interest parameters to evaluate crossovers and layer transition fibers. Finally, winding defects, particularly the propagation of gaps from layer to layer that causes sinking fibers, are highlighted.