Simulation of blood flow in human arteries as porous media

peer reviewedThe porous flow model studies the blood flow in a curve shape. This study has addressed simulations of blood flow in a porous media through an elbow artery; two-dimensional (2D), have been investigated. The blood flow is supplied with diameters such as (300 and 500 µm). The outputs from numerical simulations have presented the details of blood flow patterns and the local distribution of blood flow along the artery. The effects of permeability concerning the variations in the Reynolds number (Re = 0.1, 1 and 5) and changing porosity levels have been discussed. Different vessel diameters were studied to show the velocity distribution inside the vessel. Results are presented in variations of velocity distributions and local variations of flow rates through the vessel dimensions. Outputs compare with the available data, and a good agreement find. The study potentially evaluates the role of porosity and flow conditions when the body is subject to diseases

Estimation du comportement thermo-viscoélastique effectif des pièces composites obtenues par impression 3D-FDM

peer reviewedDans le but d’estimer le comportement effectif des pièces obtenues par le procédé de fabrication FDM pour le cas des matériaux composites à fibres courtes on a visé une méthodologie permettant la mise en place d’une procédure d'homogénéisation analytique en thermo-viscoélasticité de façon analogue à celle des matériaux élastiques linéaires ; la prise en compte de la variation des paramètres qui déterminent l’état particulier des fibres dans le filament est achevé grâce à l’introduction des fonctions de distribution obtenues via l’analyse statistique de la microstructure. La procédure d'homogénéisation a été évaluée en comparant ses prédictions aux calculs basés sur la FFT en champ complet et des résultats des essais pour des échantillons traités en autoclave, pour enlever les porosités à l'échelle des couches du filament imprimé

ESTIMATING THERMOMECHANICAL RESIDUAL STRESSES IN FDM 3D PRINTED COMPOSITE PARTS

peer reviewedWe implemented a two-step methodology to estimate the residual stresses induced by the FDM manufacturing process in 3D printed composite parts. The first step consisted in an analytical thermo-viscoelastic homogenization procedure to derive the effective behavior of the filament. The second step consisted in a coupled thermomechanical structural analysis of the part. The homogenization procedure was assessed by comparing its predictions to full-field FFT-based computations. The structural analysis was assessed by comparing its predictions to experimental results

Mean-Field Approximations in Effective Thermo-viscoelastic Behavior for Composite Parts Obtained via Fused Deposition Modeling Technology

editorial reviewedAiming to estimate the effective behavior of the parts obtained by fused deposition modeling (FDM) in the case of short fiber composite materials, the Mean-field homogenization procedure, introduced in linear elasticity, is here extended to linear thermo-viscoelasticity. The variation of the parameters describing the state of the fibers inside the printing filament is represented by introducing appropriate distribution functions obtained through the statistical analysis of the microstructure. The validation of the procedure is achieved by comparing its predictions with calculations based on full-field Fast-Fourier-Transform homogenization and experiments results from samples treated in autoclave to remove layer-scale porosities from the printed filament

Multiscale Homogenization in Short-Fiber Reinforced Thermostable Polymers : On the Estimation of Residual Stresses in FDM-3D Printed Composite Parts

This thesis deals with the study of residual stresses in a polymer matrix composite part obtained using the High Temperature Fused Deposition Modeling (HT-FDM) manufacturing process. This type of 3D printing uses high performance polymers as the primary material. During the printing process, several types of defects are observed due to the strong thermal gradient that the part under construction undergoes, generally representing the lack of dimensional accuracy with respect to the 3D model used to encode the printing paths. This distortion is in fact a residual deformation associated with residual stresses in the part in response to the temperature distribution during printing until each point of the material reaches room temperature. Estimating residual stresses in a printed polymer composite is not trivial because the material contains multiple scales of heterogeneity. If we want to treat the multiscale problem in a deterministic way using a generic computational method such as Finite Element Analysis (FEA), we observe that the phenomenon of scale separation imposes characteristic mesh sizes that are beyond the scope of a reasonable computational approach in terms of time versus current computational resources, and in such an approach we have to take into account that the cost of simulations increases exponentially due to the total volume of the part studied. For this reason, we propose a methodology based on homogenization in the mechanics of materials \cite{Bornet01, Mura1987, milton2002theory} to trace back to the macroscopic behavior, which allows to consider the printed part as represented by a continuous model that, at the scale of the observer, behaves equivalently to its heterogeneous counterpart, which we treat through a two-stage homogenization methodology. The first scale, the microscale, is treated using a mean-field homogenization method described in a previous publication by the authors \cite{Suarez22_1}, where the estimation is obtained by extending conventional mean-field homogenization methods (derived from the Eshelby problem in the context of thermoelasticity) using the extension of the correspondence principle \cite{Mandel66} in continuous temperature variations for a thermo-viscoelastic material known as \textit{thermorheologically simple}, and using a probabilistic description of the microstructural parameters associated with the fibers. It should also be mentioned that we have dedicated a chapter to the estimation of the effective behavior in the case of \textit{thermorheologically complex} materials by a model reduction technique of the mean-field homogenization problem being already published in \cite{Suarez2023}. The mesoscale is treated by a full-field numerical homogenization method based on conventional finite elements, the calculation of the effective thermo-viscoelastic properties is carried out by steady-state dynamic simulations over a frequency space relevant to the part's operating conditions of the part, and then undergoes an identification procedure according to \cite{JALOCHA15}, which maintains a conventional representation of the functions characterizing the material's response in an experimental identification context. After checking the quality of the approximations obtained with purely numerical comparisons, we compare what we have obtained with physical reality. The reference experiment is that of cooling a thin plate obtained by superimposing unidirectional printing layers, the orientation of the layers being [0,0,90,90]. The part is cooled in the printing chamber and the deflection of the plate is measured, as a consequence of the temperature evolution and the asymmetric distribution of the porosities aligned in the printed layers. The objective is therefore to predict the plate deflection using a numerical model with properties obtained using the methodology proposed in this thesis. Since we are confronted with reality, several experimental measurements have been carried out to identify the necessary parameters, as well as microtomographic analysis of the two characteristic scales

Mean-field descriptions for the viscoelastic response of thermorheologically complex reinforced solids

peer reviewedMean-field descriptions for the thermo-viscoelastic response of reinforced solids undergoing small deformations but large temperature changes are presented. The descriptions follow from an approximate homogenization scheme that identifies macroscopic internal variables with low-order statistics of the microscopic internal variable fields as a result of a variational model reduction. Unlike descriptions based on the correspondence principle, these descriptions can account for thermorheologically complex constitutive laws with multiple internal times and/or temperature-dependent stiffnesses, and can provide information not only on the macroscopic response but also on the statistics of the microscopic mechanical fields; it is further demonstrated that the descriptions can even accommodate a special class of hereditary laws often employed for polymeric materials. Simple expressions for material systems with elastically rigid but thermally dilatant reinforcements are provided. By way of example, reduced descriptions are presented for a special class of material systems for which the thermomechanical response can be computed exactly by means of the correspondence principle. In the case of isotropic particle-reinforced solids under hydrostatic loadings, the reduced descriptions can reproduce the exact response identically; in the case of transversely isotropic fiber-reinforced solids subject to monotonic coolings, the reduced and exact descriptions provide indistinguishable macroscopic strains and stresses for the entire range of temperature drops and cooling rates considered

Estimation des contraintes résiduelles dans des pièces composites imprimées 3D HT-FDM. Estimation of residual stresses in printed composite (SPC) parts

peer reviewedCe travail, résultat d’une thèse doctorale en collaboration de l’université d’Aix-Marseille et l’Université du Luxembourg, possède la finalité d’utiliser les outils de la mécanique des solides et la mécanique computationnelle dans la prédiction des contraintes internes dans les pièces composites obtenus par une procédure d’impression HT-FDM (High Temperature Fused Deposition Modeling). Le travail considère le problème multiéchelle par une procédure d’homogénéisation à deux étapes ; en combinant des techniques d’homogénéisation en champ moyen à description probabiliste des paramètres microstructuraux, avec des approches par champ complet pour l’estimation du comportement macroscopique, tout en gardant une représentation mathématique du matériau qui est fidèle au comportement réel du polymère, en conclusion, on cherche une prédiction du comportement thermo-viscoélastique effective d’une pièce imprimé avec une représentation mathématique qui est sensible aux variations dans la cinétique des charges mécaniques et thermiques. Et en fin en présentant un scénario fiable et plausible du prototypage virtuel en impression 3D

Mean-Field Approximations in Effective Thermo-viscoelastic Behavior for Composite Parts Obtained via Fused Deposition Modeling Technology

International audienceAiming to estimate the effective behavior of the parts obtained by fused deposition modeling (FDM) in the case of short fiber composite materials, the Mean-field homogenization procedure, introduced in linear elasticity, is here extended to linear thermo-viscoelasticity. The variation of the parameters describing the state of the fibers inside the printing filament is represented by introducing appropriate distribution functions obtained through the statistical analysis of the microstructure. The validation of the procedure is achieved by comparing its predictions with calculations based on full-field Fast-Fourier-Transform homogenization and experiments results from samples treated in autoclave to remove layer-scale porosities from the printed filament