The accurate characterization of the microstructure of fiber-reinforced polymer composites is crucial for quality control in manufacturing, material design, and robust performance prediction. Most of the characterization methods rely on the analysis of 2D or 3D images. However, the composites community lacks commonly shared best practices and a clear quantitative understanding of how different image processing approaches compare. This work presents a benchmarking exercise on image processing of fiber-reinforced composite materials to address this challenge. Processing three cross-section micrographs, acquired from a single unidirectional composite sample using typical yet distinct imaging protocols, 11 participants from 8 research institutions extracted fiber centroids and radii. The estimated fiber volume fraction (Vf) values for a single cross-section varied between participants from 0.42 to 0.65. The results highlight the sensitivity of different methods to factors like illumination inhomogeneities, pixel density, polishing-related surface defects, and fiber packing. Considering these observations, several best practices for image analysis are identified, providing critical insight into the methods’ sensitivities. To promote transparency and community uptake, the benchmark dataset, evaluation scripts, documentation, and algorithms that were open-sourced are made openly available through a dedicated website, paving the way toward more reliable microstructural analysis in composite materials and ultimately more standardized protocols.

Rotational molding, also known as rotomolding, is a widely used manufacturing process for composite tank liners. Developing this process to obtain high quality liners is usually a long and delicate step. The implementation of numerical simulation can facilitate and expedite its development. It is challenging to obtain information about polymer movement through experimental methods. In this paper, we present a two-dimensional thermo fluid simulation of rotomolding using the immersed boundary approach with the level set technique. Numerical simulation using the Eulerian approach with the finite element method with anisotropic mesh refinement and the immersed boundary method has proven to be a powerful tool for analyzing and optimizing the molding processes with the help of implicit boundary and adaptive anisotropic meshing techniques. The finite element method is a valuable tool that allows us to combine several physical elements. This approach enables us to identify critical process variables and optimize design choices. To verify our methodology, we first simulated a 2D cross section of the mold by incorporating a two phase flow problem involving the polymer/air interface.

Advanced manufacturing processes such as Tailored Fiber Placement (TFP) enable the fabrication of composite laminates with complex and spatially varying fiber architectures. These capabilities offer new opportunities for performance-driven structural design. However, most existing topology optimization approaches either neglect manufacturing constraints or decouple material distribution from fiber path generation, which leads to solutions that are not directly manufacturable. This work proposes a coupled topology optimization and fiber path design framework for composite laminates. Manufacturability is considered through a projection into a realizable design space. An unconstrained formulation is introduced for targeted deformation problems, avoiding artificial material removal and enabling more realistic laminate designs. The fiber volume fraction is incorporated as a continuous design variable, allowing local control of mechanical properties. To generate manufacturable fiber trajectories, a weighted streamline formulation is developed. This approach links fiber spacing to the local fiber volume fraction and ensures consistency between optimized fiber orientations and the resulting fiber paths throughout the optimization process. The proposed framework is validated through several numerical case studies involving single- and multi-layer composite laminates under bending loads. The results show excellent agreement with prescribed target displacements, with relative errors below 0.5%. Smooth and consistent fiber paths are obtained simultaneously. These results highlight the importance of coupling topology optimization and fiber path design, as well as integrating manufacturability considerations during the optimization process to avoid discrepancies between numerical designs and fabricated structures.

Understanding the interfacial interactions between molten short fiber-reinforced thermoplastics and pre-molded continuous fiber composite inserts during overmolding is essential for optimizing adhesion, stress distribution, and the mechanical performance of the final part. This study introduces a novel and streamlined numerical approach to model the formation of this complex interface during the overmolding process. A two-dimensional, two-phase flow model is developed by solving the Stokes equations in both the low-viscosity short fiber polymer suspension and the highly viscous thermoplastic composite phases. This strategy avoids the iterative fluid–structure coupling typically required by traditional fluid–solid interaction (FSI) models. To capture fiber–flow coupling effects within each phase, the model employs a modified constitutive equation that incorporates a fourth-order orientation tensor. This tensor represents the influence of fiber orientation on flow behavior and is computed by directly solving the Fokker–Planck equation using the Streamline-Upwind/Petrov–Galerkin (SUPG) finite element method, allowing dynamic tracking of fiber orientation over time. This study investigates the model’s ability to predict the deformation of composite inserts for different fiber volume fractions and orientations.The results demonstrate the model’s ability to capture coupled interfacial dynamics and fiber orientation evolution during overmolding. This highlights the model’s potential as a tool for advancing fiber-filled polymer processing research. Moreover, the approach provides a foundation for more sophisticated simulations of real-world overmolding scenarios involving fiber-reinforced thermoplastics.

Squeeze-flow testing is a commonly used experimental method for characterising the flow behaviour of high-performance C-SMCs under typical compression moulding conditions. A European benchmark exercise involving 14 research institutes is currently being conducted to identify the sources of variability in squeeze flow testing results and to support the development of a standardised testing methodology. Experimental testing of five C-SMC materials has been completed using a well-defined testing procedure.This paper focuses on the data processing stage of the benchmark exercise, in which experimental data collected from all participants are processed and analysed to extract information on raw material variability, force–gap height relationships, and flow-front profiles. Qualitative assessment of these results is used to identify the critical sources of variability, which subsequently informs a more detailed statistical analysis.

While the use of composite materials increases the specific stiffness of structural parts, their manufacture using automated fiber placement processes such as Tailored Fiber Placement (TFP) allows for the addition of functionalization. An example of such a part is the hydrofoil, which can gain hydrodynamic performance if its shape adapts to the different loads encountered in the three modes of navigation. One method that can meet these requirements is passive functionalization. In this context, the development of digital design support tools is essential. Among them, topology optimization is a well-established method. This work focuses on the development of a strategy for optimizing the topology or the fiber density distribution of the part and the orientation of the fibers for composite materials with an objective function of path generating type allowing passive functionalization. A method for generating fiber trajectories for the TFP process is also presented. The topology optimization results of a cantilever type test case and a shell plate are shown and discussed.

During Liquid Composite Molding, a fibrous reinforcement is impregnated with liquid resin. Process design requires knowledge of the reinforcement permeability for fluid flow, but until recently, there has been no standard available for its measurement. In 2023, following decades of benchmarking activities and a standardization project, an ISO standard for the experimental characterization of in-plane permeability of fibrous reinforcements for liquid composite molding was finally published. It focuses on the experimental characterization of unsaturated in-plane permeability and specifies the requirements for test equipment, methods and data analysis. Given the deficiency of standardized procedures within the composites industry, this paper intends to provide an example of the steps towards standardization and summarizes lessons learned. It illustrates the research milestones that led to the establishment of the standard, promotes the standard by detailing its general content and notable features and finally gives explanations and reasoning behind the developed guidelines.

High-performance C-SMCs typically consist of long carbon fibre reinforcement with high fibre content and can be compression moulded at elevated temperatures and pressures to form parts with complex geometries. Squeeze flow testing has been increasingly adopted for experimentally characterising the flow behaviour of C-SMCs, but the reliability and repeatability of the testing results are low due to the lack of standardised methods. This paper presents a benchmarking exercise on C-SMC squeeze flow testing, jointly delivered by 14 European research institutes, with the objective of quantifying the variabilities in the testing results and identifying their sources.

Permeability is a fundamental property of porous media. It quantifies the ease with which a fluid can flow under the effect of a pressure gradient in a network of connected pores. Porous materials can be natural, such as soil and rocks, or synthetic, such as a densified network of fibres or open-cell foams. The measurement of permeability is difficult and time-consuming in heterogeneous and anisotropic porous media; thus, a numerical approach based on the calculation of the tensor components on a 3D image of the material can be very advantageous. For this type of microstructure, it is important to perform calculations on large samples using boundary conditions that do not suppress the transverse flows that occur when flow is forced out of the principal directions. Since these are not necessarily known in complex media, the permeability determination method must not introduce bias by generating non-physical flows. A new finite element-based method proposed in this study allows us to solve very high-dimensional flow problems while limiting the biases associated with boundary conditions and the small size of the numerical samples addressed. This method includes a new boundary condition, full permeability tensor identification based on the multiscale homogenization approach, and an optimized solver to handle flow problems with a large number of degrees of freedom. The method is first validated against academic test cases and against the results of a recent permeability benchmark exercise. The results underline the suitability of the proposed approach for heterogeneous and anisotropic microstructures.

A numerical model is proposed to simulate significant yarn slippage and unweaving in woven fabrics using the Arbitrary Lagrangian Eulerian (ALE) method. Woven fabrics were modeled at the yarn scale using 1D ALE elements with additional slip displacement degrees of freedom (DOF). The relatively weak bending stiffness of the yarn was included using a rotation-free approach. A weave kinematic constraint between crossing yarns allowed an efficient description of the deformation modes due to the yarn assembly such as in-plane shear. In particular, normal compaction at weave points was taken into account using an additional crimp amplitude DOF and couplings of the fabric’s cohesion with the normal and lateral compaction were considered. To deal with yarn unweaving, a specific void-ALE 1D element was developed in order to avoid remeshing, time-step reduction (explicit scheme) and early deactivation of the weave kinematic constraint. To demonstrate the capabilities of this numerical model, common characterization tests such as in-plane and out-of-plane pullouts, which induced unweaving were simulated. Finally, a first forming simulation on a hemisphere was performed to verify whether the cohesion of the fabric remained well represented in situations without loss of cohesion before simulating forming on a prismatic punch involving significant yarn slippage.

A numerical model of packing applied to rigid objects is presented. It aims at describing a random stack of polymer composite chips in order to model the packing step of an existing recycling technique. The geometric properties of the stack play a major role in the mechanical properties of the recycled products. Short, simple and effective geometric descriptors of the stack are proposed. Their ability to differentiate random stacks is illustrated with an example. Then, a validation is proposed based on experimental data obtained from a bench specially designed for this work. The tests consist in the free fall of square chips. Finally, the developed model is compared to other models (free fall and packing of fibers) in order to enforce its relevance in the simulation of packing of rigid objects.

This work aims to introduce a groundbreaking approach by directly computing the Fokker–Planck equation, providing a mesoscopic scale orientation indicator based on the 2D-probability density function (PDF) of the fibers’ orientation state. Unlike conventional methods that rely on pre-averaged quantities and closure approximations, our method offers enhanced accuracy and information preservation. The model’s enhanced accuracy can be served as a foundational tool for future studies, enabling the development of comprehensive models describing the fluid-flow coupling problem with precision. Consequently, this advancement facilitates the simulation of real-case scenarios, such as the dynamic motion of fibers during the injection phase of molten thermoplastics within a mold cavity. The novelty of this work lies in its application of the Streamline-Upwind/Petrov–Galerkin (SUPG) finite element method, on both orientation and physical spaces. Our model shows the potential to improve the understanding and prediction of fiber behavior in industrial applications, offering valuable insights into process optimization and design. Implemented within a finite element framework, a comprehensive investigation is conducted into the effects of mesh refinement, time scheme, and time stepping on the computational modeling of the PDF evolution, aiming to strike an optimal balance between model precision and computational efficiency. The validation tests were conducted for the case of simple shear flow to examine the influence of the interaction coefficient CI and the fiber shape factor λ on the resolution of the probability distribution function. The numerical results demonstrate the evolution of fiber orientation over time under Poiseuille flow conditions.

This study focuses on the analysis of the directionality of saturation of materials with bimodal pore size distributions. The material studied is an anisotropic carbon interlock with highly contrasted dual-scale porosity, with heavy warp and light weft tows. Experimentally, 6 configurations are tested using injection combined with dielectric sensors to measure saturation times and unsaturated lengths. The experimental results show that this material has a high contrast in dual-scale porosity and the unsaturation is anisotropic. In parallel, a two-phase flow in porous media continuum model is developed within the OpenFOAM® toolbox of libraries to simulate the transient impregnation. The need to use a tensorial relative permeability and its alignment with the saturated permeability is analyzed by a numerical multiphase mesoscale flow model. The combined experimental and numerical analysis paves the way for a methodology to analyze the saturation of various bimodal pore size distribution materials.

In the context of environmental transition, the environmental impact of composite parts manufacturing has to be improved as well as the impact of each step of the life cycle. However, a lack of data makes this improvement difficult as few studies have focused on the environmental impact of the manufacturing process of composite parts by giving detailed inventory data and an associated environmental assessment. Thus, this paper aims to propose a comprehensive gate-to-gate environmental analysis of a manufacturing process used in the aerospace industry: the thermo-stamping of carbon fibre reinforced polyphenylene sulfide (C/PPS) composite parts. A methodology based on the life cycle assessment framework is used to quantify and analyse the environmental impact of thermo-stamping parts. First, a complete description of the manufacturing process is proposed to define the studied system boundaries. The manufacturing process is divided into unit processes representing each step of production. Linked to this description, a balance of all the consumptions and waste of materials and energy (inventory flows) is established for each unit process. As a result of the study, each inventory flow is then modelled as a function of the process parameters using data collected from laboratory-scale experimental measurements, databases, and literature. These inventory data models allow computing inventory data of different manufacturing scenarios and C/PPS composite parts. Furthermore, the gate-to-gate environmental assessment of a case study part is presented using the models developed in this paper. C/PPS over-consumption and energy consumed during heating and stamping were identified as unit processes and inventory flows contributing most to the environmental impact of part manufacturing.

Fibre tow slippage in conventional reinforcement forming is a major defect which can be turned into an additional degree of freedom in preforms made by Tailored Fibre Placement (TFP). Controlling slippage of reinforcing fibre tows, which are deposited on a conventional reinforcement using the TFP technology, is an advantage which enlarges the preform design space Fial et al. (2018). Moreover, when TFP is used to locally reinforce a conventional reinforcement, slippage of the deposited fibre tow during forming, is required depending on its orientation relative to the conventional reinforcement layout to avoid defects. Therefore, characterizing the friction behaviour of the reinforcing fibre tows is necessary to take advantage of its slippage as an additional degree of freedom. In this paper, an analytical friction model describing the interactions of the fibre tows with the backing material and the stitching yarn in TFP preforms is developed based on pull-out experiments. A parametric study allows expressing the parameters of the analytical friction model as function of the stitching parameters.

In the Resin Transfer Molding (RTM) process, a polymeric resin is injected inside a dry preform to fill the gaps around and inside the fiber tows.Simulating this process at the scale of the tows is challenging because of the computational cost associated to solving a three-dimensional dual-scale flow problem.In this work, a novel Dual-Scale Skeleton model (DSS) is introduced, capable of solving a dual-scale flow problem at an affordable computational cost.The three-dimensional geometry of a multi-layer layup, consisting of inter-tow channels and permeable tows, is replaced by a skeletonized representation of the original subdomains.Dual-scale flow is modeled using a Reynolds-Darcy finite elements formulation.The model is validated numerically and its application is demonstrated over a few test cases.The adoption of the DSS model allows one to simulate complex dual-scale flow problems over large domains at a reduced computational cost when compared to full 3D solutions.

The main idea behind “Quilted Stratum Process” (QSP ® ) is to create a flat blank made of unidirectional/woven thermoplastic prepreg patches instead of using uniformly shaped prepreg stack as is the case with standard thermostamping process. Thus, using QSP ® ; one can manufacture components with complex geometries by using nearly rectangular patches while still maintaining a short cycle time similar to the standard thermostamping process. The use of near-rectangular patches results in a significant material saving which is a necessity for a sustainable product development. During standard thermostamping and/or QSP ® ; the consolidation phase plays a key role in the strength and quality of the final product. This becomes even more important in the case of unidirectional thermoplastic prepregs where mechanisms such as transverse squeeze flow can impact not only the in-plane dimensions of the prepreg but also the fibre orientations within the prepreg. This work presents a unified modeling approach that combines a novel pinching shell element, a new elasto-plastic constitutive model for pinching shell in order to provide a unified solution to simulate both forming and consolidation-flow using a shell-based approach. This unique unified approach of simulating forming and consolidation provides a set of additional outputs such as the through-thickness stress, final deformed shape of the plies including the squeeze flow effect and the changes in the orientation of fibres within the plies during and after the process. This work finally demonstrates how this information can help the manufacturers to design better tooling based on the outcomes of the numerical process simulation in order to achieve a desired product quality. Additionally, one can also steer the final fibre orientation which results from the initial position of the patch, its forming and squeeze flow.