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The transverse permeability of fibrous reinforcement is one of the critical parameters that govern fabrication efficiency and production quality in several liquid composite molding process variants devised to achieve transverse impregnation of fibrous reinforcements. It is difficult to precisely measure and predict the transverse permeability, because it is simultaneously affected by diverse factors, for example, the geometric features of the test mold, nesting between fabric layers, and flow‐induced compaction of the fiber bed. In this article, the saturated transverse permeability of 2D woven glass fabrics is investigated using information provided by mesostructural geometric models reproducing the real textile architecture. These models are created by micro‐CT aided geometric modeling, a recently proposed technique to analyze three‐dimensional images obtained by X‐ray microtomography. They are called "material twins" because they reproduce with assessed accuracy the geometrical configuration of the textile preform, are representative of material variability, and allow performing numerical simulations of flow or mechanical properties. Computer simulations of steady state transverse flows in material twins were carried out to evaluate the transverse permeability and compared to experiments. Issues concerning material variability due to nesting and the accuracy of transverse permeability measurements were considered and discussed. A good agreement was obtained between numerical and experimental values of transverse permeability. Both approaches show a significant influence of the number of layers considered, which can be explained by nesting between adjacent plies. Numerical simulations also illustrate how nesting significantly affects material variability. [ABSTRACT FROM AUTHOR]

This study uses capillary flow porometry to investigate the porous structure of engineering fabrics used in high-performance polymer composites. This technique consists of applying air pressure to a previously wetted sample to progressively expel the liquid from the pores. A porometry testing device commonly employed to characterize filtration media was used as the principal tool for this investigation. Four types of fibrous fabrics made of glass and carbon fibers with different textile architectures have been experimentally characterized with a through-thickness setup. This allowed obtaining the pore size distribution inside the tested material. In all the cases studied, the porometry technique was able to detect in a reproducible way a bimodal pore size distribution reflecting the presence of both micropores (inside the fiber yarns) and mesopores (between the yarns). Moreover, experimental results indicate that the method can be used to study the influence of the textile pattern on the pore size distribution. Overall, the study shows that capillary flow porometry can give valuable information on the dual scale structure of fibrous reinforcements, which plays a critical role during the impregnation stage of Liquid Composite Molding processes. Because of its simplicity and speed of execution, the proposed approach appears to be a promising way to complement other sophisticated techniques already used for composites such as microscopy and X-ray microtomography. [ABSTRACT FROM AUTHOR]

Predicted evolution of the liquid height with an ideal falling-head setup (no outlet pressure drop and zero pressure at the sample bottom) for different permeability values. First, the mentioned limiting permeability value of HT ht is again chosen arbitrarily by the discussers (see previous point). Indeed, the proposed value of HT ht is solely based on the discussers' naked eye perception. [Extracted from the article]

Tomographic modeling of textiles is attractive for numerical investigation of composites due to its ability to reveal the internal architecture. However, reliability is notably dependent on geometrical modeling accuracy, which is still challenging. This paper addresses existing issues using a parametric approach that relies on statistical resampling and spatial autocorrelated prediction. The proposed strategy involves three stages: first, an explicit representation of each fiber tow is derived from the segmented images through statistical resampling in the parametric domain, which is subsequently mapped back to the physical domain according to known spatial autocorrelation. It allows depicting tow surfaces with varying levels of detail. Second, the tow trajectory is parameterized and subjected to a smoothing process, thereby identifying the local fiber orientation as its tangent vector. Finally, the normal cross-sections of tows are solved as intersecting implicit planes with a parametric tubular surface thanks to the parametric representation. This allows evaluating the spatial architectural variability in tows with notable waviness. Examinations were performed by contrasting the proposed approach with existing techniques. This new approach demonstrated better consistency with the ground truth while bringing additional benefits to the geometry reconstruction. [ABSTRACT FROM AUTHOR]

Impregnating fibrous preforms through thickness has become a main feature of some liquid composite molding process variants. Thus, the evaluation of transverse permeability is critical to optimize the fabrication and reduce manufacturing defects. Some problems connected with the design of testing devices need to be addressed to perform a reliable characterization. In this study, the efficiency of a typical one‐dimensional testing device to measure transverse permeability is evaluated numerically and experimentally. The paper introduces a novel methodology to identify the optimal mold configuration and evaluate the flow pattern inside the mold cavity. A dimensionless number called the "fill coefficient" is also proposed to evaluate quantitatively the effect of the mold structure on the transverse flow pattern. The measured transverse permeability is shown to increase with lower fill coefficients for saturated and unsaturated flows. The intrinsic transverse permeability is obtained when the fill coefficient is equal to one. The proposed methodology is verified by experiments performed in an existing tool. This confirms that the measured transverse permeability can be significantly affected by the above mentioned factors. [ABSTRACT FROM AUTHOR]

A stochastic method is introduced to characterize the dual-scale geometry of textile reinforcements in composites. The fiber tows are identified automatically from X-ray microtomographic scans with a machine learning algorithm, quantifying the error of the procedure. The tow geometry is then used to construct a stochastic model as a Gaussian Random Process which permits quantification of the uncertainty in the measurements of microscale fiber volume fraction. The hyperparameters of the model are calibrated with a custom-built multi-objective evolutionary algorithm. The approach is illustrated by the analysis of a vinyl-ester composite reinforced with a glass fiber non-crimp fabric. [ABSTRACT FROM AUTHOR]

Volumetric image-based modeling of textile reinforcements and composites is favored over ideal geometric modeling because of its ability to represent complex structures in sufficient detail. Although several approaches were devised, there is still a scarcity of dedicated tools capable of effectively transferring pertinent information from images to high-fidelity models. This work presents the open source project, PolyTex , a Python-based object-oriented application that establishes a streamlined and reproducible workflow for such tasks. Dual kriging serves as the foundational theory for the parametric approach developed to represent, simplify, and approximate the morphology and topology of fiber tows. The code takes two types of input, either an explicit representation of tow geometry using point clouds or implicit representations, such as image masks representing fiber tows separately with grayscale values. Tailored APIs allow for smooth integration between PolyTex 's modeling capabilities and the simulation environments offered by OpenFOAM and Abaqus. Case studies on virtual testing of textile permeability were presented to demonstrate this capability. The modular and object-oriented design makes PolyTex a highly reusable and extensible tool that allows users to create a customized pipeline. [Display omitted] • A parametric geometry modeling scheme is introduced to create digital material twins. • The newly created tool, PolyTex, establishes a streamlined and reproducible workflow. • Customized APIs were developed to integrate PolyTex with OpenFOAM and Abaqus. • Virtual permeability testing cases demonstrated its ability and the proposed method. • PolyTex is publicly available as an open-source project with detailed documentation. [ABSTRACT FROM AUTHOR]

• The temperature of a pipe filled with beads and heated with air flowing through the granular bed is investigated. • A damping function is combined with the nakayama-kuwahara turbulence model to improve the accuracy of temperature predictions. • Suggestions to improve the pipe wall thermal uniformity are provided. Placing granular materials inside empty channels with coolant or heat transfer fluids flowing through is an effective way to increase the heat transfer rate to the wall. Although this approach has been used in different engineering fields, a particular goal is seldom considered in some applications, namely the temperature uniformity of the bounding wall. As temperature varies along the flow direction, a non-uniform temperature field appears on the wall. This bears consequences in some applications such as in electronics, battery cooling or composite manufacturing. In the present study, the uniformity of the wall temperature is investigated numerically for a typical cylindrical pipe filled with monodisperse ceramic beads and heated by air flow. Numerical simulations based on Reynolds-averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) are performed to analyze the heat transfer to the bounding wall. Because of the uncertainty mentioned in the literature, the applicability of an empirical model reflecting additional sources of production and dissipation of turbulent energy due to beads is firstly evaluated. By comparing the numerical predictions of temperature fields with experimental data, a damping function is needed to adjust these additional source terms to better fit experimental data for bulk Reynolds numbers between 100 and 700. A parametric study is then conducted to assess the effect of various parameters on the wall temperature uniformity. Results shows that wall materials of low volumetric heat capacity and a reduced wall thickness greatly shorten the duration to reach thermal uniformity. A less pronounced enhancement also exists for larger thermal conductivity of the wall material. However, using beads of lower volumetric heat capacity does not have a major influence on the uniformity of the wall temperature. [ABSTRACT FROM AUTHOR]

Vacuum assisted resin infusion (VARI) is a composite manufacturing process, in which a fibrous reinforcement is laid out in a mold, and then sealed under a vacuum bag. The preform is compressed under vacuum and a liquid polymer resin is infused into the mold cavity. A characterization of compressibility and permeability is required to get accurate predictions of infusion times and thickness of final parts. A new experimental methodology is developed to simultaneously characterize the preform expansion and permeability of fibrous reinforcements during infusion. It is implemented in a one‐dimensional rectangular workbench by impregnating the preform with silicone oil. Pressure sensors measure the liquid pressure, and the reinforcement thickness is acquired by linear variable displacement transducers (LVDTs). The flow rate is also recorded with a scale. The expansion of the wetted reinforcement and permeability can be modeled by power laws as a function of pressure and fiber volume content, respectively. For isotropic preforms, a single experiment provides all the information needed to simulate the flow and predict the infusion time, the thickness and pressure. To validate this new characterization approach, the results of two infusions are successfully compared with numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract As a soft material with an almost negligible bending stiffness, a membrane may easily lose its mechanical stability. To capture its entire instability process, intensive computation is required, especially in the case of short wave length. The objective of this paper is to construct an efficient model to simulate and study the instability phenomena of circular membranes. By using the method of Fourier series with slowly variable coefficients in the circumferential direction, a new family of one-dimensional reduced finite elements are developed to study the three-dimensional problems. The nonlinear system is solved by the Asymptotic Numerical Method(ANM), which is reliable and efficient for tracing the bifurcation points and post-buckling equilibrium path compared with other classical non-linear solution algorithms. The accuracy and efficiency of the reduced model is verified by simulating the instability phenomena in stretched annular membranes and a compressed circular plate. The relation between critical loads and bifurcation patterns and the evolution of stress components in the entire wrinkling process are discussed. This study provides new simulation schemes to explore the instability in circular membranes under complex loadings and boundary conditions. [ABSTRACT FROM AUTHOR]

• A novel validation procedure for gasoline particulate filter (GPF) modelling is developed. • It relies on kinematic similarity between digital and magnified twins of a GPF porous wall. • It makes use of additive manufacturing and falling head permeability measurements. • The relative difference between numerical and experimental permeabilities is less than 20%. • It is a reliable and affordable validation procedure for flow modelling in micro-scale porous media. The validation of a numerical model used to predict the permeability of the microporous wall of a coated gasoline particulate filer is arduous due to multiscale effects. To circumvent this, an experimental "magnified twin" approach based on kinematic similarity is proposed. It consists of (1) printing magnified porous wall sections by fused filament additive manufacturing; and (2) characterizing their permeability using a modified falling head permeability measurement device and testing procedure. A detailed approach is also proposed to select the appropriate scaling factor to produce the samples by 3D printing. Comparison between numerical, semi-analytical, and experimental predictions of the impact of coating amount and degree of uniformity on wall permeability is presented. Despite the inherent sensitivity of permeability to pore space characteristics, a very good agreement is reported between simulations and experiments with a 19.3% mean discrepancy for the seven magnified structures tested. The proposed procedure is a relatively easy-to-implement and inexpensive method that may find many applications in the field of porous media. [ABSTRACT FROM AUTHOR]