Carbon Fiber Reinforced Polymers (CFRPs) are essential to the aerospace industry, offering superior strength-to-weight ratios. Currently, the manufacturing of primary structures via standard autoclave curing is a robust, mastered process that successfully minimizes defects, keeping porosity levels below critical thresholds (typically < 1 %). Consequently, porosity is generally not considered as an issue in standard, optimized production lines.However, this stability may be affected by emerging industrial paradigms aimed at increasing production rates and reducing costs. The shift toward accelerated manufacturing – characterized by rapid heating rates, shortened cure cycles and by new manufacturing processes – and the introduction of complex material architectures risk re-introducing significant porosity. In parallel, there is currently no numerical model capable of accurately predicting porosity formation and evolution under these complex conditions. Existing simulation approaches are typically macroscopic and rely on homogenized porous media assumptions, failing to capture the essential micro-scale interactions between bubbles and fibres.To address this gap, this study presents an extended, custom multi-physics Computational Fluid Dynamics (CFD) solver built upon an existing OpenFOAM framework. The goal is to provide the first predictive tool for void evolution within realistic microstructures. The numerical framework couples a two-phase compressible flow model with the complete thermo-chemo-rheological physics of thermoset curing.The solver is applied to 2D Representative Volume Elements (RVEs) of a prepreg ply. Simulations of a standard autoclave cycle demonstrated the solver's ability to capture micro-scale dynamics, showing how voids are compressed and transported during the resin viscosity drop before being frozen at gelation. A parametric study comparing 3-bars and 7-bars pressures confirmed the model's physical ability in predicting void volume reduction.While currently focused on mechanical compression, the tool is designed to support the development of future manufacturing cycles. Future work will incorporate moisture diffusion physics and includes experimental validation via X-ray micro-tomography and in-situ synchrotron monitoring.

For hydrogen application, one of the most important material property required is low gas permeability. In composite materials, this property depends on the materials but also on the processing parameters. In particular the residual porosity, but also the quality of the fiber/matrix interface, play a crucial role. This is particularly the case in composites involving a thermoplastic matrix with carbon fibers as the lack of reactive groups on the fiber surface can limit the level of interfacial interactions between the reinforcement and the matrix. In this study, the role of the interface is analyzed through the investigation of the hydrogen permeability of carbon fiber reinforced thermoplastics (CF/PVDF and CF/PPS) using different polymers and carbon fibers. The hydrogen permeability of the composites was measured, and a correlation with the crystallization behavior of the matrix on the fiber surface was identified. Hydrogen permeability decreases when the fiber favors matrix nucleation. Nucleation is improved by increasing the surface roughness of the carbon fiber.

Welding high-performance thermoplastics has gained popularity across various industries such as automotive, aerospace, and medical. Laser transmission welding (LTW) has emerged as an effective method for joining thermoplastic parts due to its precise control and high joint quality. PAEK (polyaryletherketone) are wide spreading over various industrial applications as a substitute to metals and thermosets when high durability and performance are required. Polyetherketoneketone (PEKK) is one of these PAEK and it has received less attention than PEEK until now. PEKK, being a semi-crystalline thermoplastic, requires additional care during processing due to its propensity to crystallize. This study presents both experimental and numerical investigations into LTW of PEKK molded parts, aiming to understand the influence of welding parameters and crystallinity on weld joint morphology and mechanical properties. PEKK plates, prepared in amorphous and semi-crystalline states, are subjected to LTW using a 975 nm diode laser. Material characterization confirms differences in crystallinity between the samples, which affect their thermal and optical properties, which are crucial for welding. Welding tests are conducted with varying laser power (between 75 and 95 W) and semi-transparent part thickness (2 and 4 mm). The morphology of joints is analysed. Assemblies undergo post-weld annealing treatment to examine its influence on weld crystallinity and consequent mechanical properties. Results reveal an anisotropic distribution of crystallinity within the heat-affected zone (HAZ). The depths of the molten layer (ML) and semi-crystalline layer (scL) vary with laser power and assembly type. A notable decrease in weld strength with laser power is highlighted, while annealing leads to enhanced crystallinity and improved weld strength. Despite variations, high weld strengths are achieved with annealing. Computational modelling elucidates the complex interplay between laser irradiation, temperature distribution, and crystallization kinetics observed experimentally. Overall, this comprehensive investigation provides valuable insights into optimizing LTW parameters for PEKK parts.

Automotive front lighting evolved towards high definition beams. To create such function, up to several light source per square millimeters are involved. The current trend tends to replace multiple LED designs with only one high luminance LED. The 10W-optical power emitted by this optoelectronic source induces high energy density that requires to be thermally managed. Moreover, when this LED is integrated within its optical system, the radiation concentration can lead to the system self-heating, leading to early damage or failure. The strategy adopted in this paper to avoid the component failure consists in developing an accurate and robust multi-physics simulation to predict heat transfer in a LED lighting system. In this paper, the validation of a high luminance LED thermo-optical coupling model is achieved by comparing numerical simulations with experimental results. The full optical characterization of LED has been performed to build its opto-thermal model. Then, an experimental set-up has been designed and consists in positioning a black plate in front of the LED, to capture its self-heating induced by light energy absorption using infrared thermography. The agreement between thermo-optical simulation and IR thermography is fair, which reinforces the use of the model with an error lower than 10%.

Automotive front lighting is evolving towards digital and adaptive high definition beams. To create such functions, multiple LED designs are replaced with new LED concepts using only one high luminance LED. Light concentration emitted from this optoelectronic component generates a high density of energy which must be thermally managed. Indeed, optical performance and reliability of components are directly linked to the LED temperature. Thus, to optimize cooling system, accurate and efficient numerical models must be developed. The validation of these models are based on comparison with experimental data. In this paper, an infrared camera was used to measure quantitatively the temperature of a high luminance LED emitting area and was then compared to 3D thermal simulations.

Nowadays, injection stretch blow molding (ISBM) process represents the most employed technology to produce plastic bottles. An important step of this process is the heat conditioning stage which is performed within infrared ovens by the use of powerful halogen lamps. Homogenizing the temperature distribution along and inside the preform at the end of this conditioning stage is one of the key parameters to determine the final quality of the bottle (thickness, mechanical properties, transparency...). In this research work, a numerical software has been developed to simulate recycled PET (rPET) preforms infrared heating inside the industrial ISBM ovens, where both rotation and translation of the preform across different heating modules occur. In addition, the presence of a fan system involving a forced convective condition inside the ovens is also considered using a Computational Fluid Dynamics (CFD) approach instead of using a conventional heat transfer coefficient.

Relatively recent citizen's consciousness about plastic pollution forces industrial actors of packaging to re-invent their shaping processes and materials. Specifically, for plastic bottle industry shaping, classical Polyethylene Terephthalate (PET) material is little by little replaced by recycled PET (rPET). The change in material composition due to recycling loops leads to an inevitable adaptation of the Injection Stretch Blow Molding (ISBM) process used to shape bottles at a satisfactory production rate. Indeed, rPET contains contaminants which modify its optical properties, so the heating stage becomes material-dependent and unstable regarding the polymer supplier. The approach adopted in this article is to build a numerical model able to simulate the infrared heating of rPET preforms, sensitive enough to predict changes in temperature due to the recycling rate. To do so, the optical properties of 50% and 100% rPET are measured by spectrometry and implemented in the simulation. Thermal radiative heat transfer between infrared lamps and rPET preforms is simulated by ray tracing method using an in-house software so-called RAYHEAT. Then, the result of the infrared ray tracing computation is used as the input heat source for thermal simulation by commercial software COMSOL Multiphysic (R) in order to simulate the temperature distribution of the preform. The numerical results are then confronted to experimental ones obtained on a research Stretch Blow Molding pilot, instrumented with thermography. The results show that the temperature obtained at the end of a classical heating cycle of the 100% recycled grade is 8 C higher than the virgin one. Also, simulations confirm that this difference is attributed to changes in optical properties. Finally, heating 100% rPET at a sufficient forming temperature is about 8% less energy consuming than for virgin PET.

In order to assess the impact of the thermal degradation of PEEK on the consolidation of composite preforms, an impregnation model taking into account degradation is proposed. It includes a viscosity model based on a double Arrhenius law describing the viscosity increase due to degradation. The implementation of this viscosity model into an impregnation model allowed to define an intrinsic processing window for the manufacturing of CF/PEEK composites based on a criterion of irrecoverable viscosity level. The simulation shows a good correlation with the experimentally measured porosity rates of commingled preforms. It predicts the absence of impregnation when increasing the consolidation time or the processing temperature from 380 to 410 °C. Above 410 °C or when increasing the pressure, however, a discrepancy is observed between the model and the simulation. This discrepancy is attributed to a change in the degradation kinetics resulting from a change in oxygen access.

Variabilities in polyamide 6 (PA6) composite manufacturing by liquid processes can occur due to polymerization, crystallization, and flow through a fibrous preform. Numerical simulations of the process predicting the kinetics can facilitate manufacturing optimization. This study proposes an efficient modeling approach that can be integrated in current simulation discretization methods such as the finite volume method (FVM) while considering the interaction between PA6 polymerization and crystallization. Using polymerization and crystallization models issued from the literature, a previous study determined Hillier coupling method to be able to predict PA6 kinetics. A simpler and more efficient coupling will be introduced and adapted to account for process variability. It was integrated into an FVM framework for process simulation of injection showcasing the capabilities of the model to predict potential crystallization discrepancies.

Fiber reinforced thermoplastic composites have shown to be attractive for industry as they can be reused, reshaped, welded and repaired, while keeping mechanical properties on par with thermoset composites. Since thermoplastics usually have high melt viscosities unsuitable for liquid composite molding processes, in-situ synthesis of PA6 from ε-caprolactam is considered. Its reactive mix has low viscosity which allows impregnation. However, the coupled crystallization and polymerization affects the resin viscosity and its flow is altered by the dual-scale permeability of the fiber preform. Thus, to predict the local differences in the thermoplastics properties, a coupled polymerization crystallization model needs to be integrated in the LCM processing simulation at representative scales. This study aims to propose a reliable simulation of the resin flow through a fibrous preform. Hence, viscosity measurements on the reactive mix are achieved using a rheometer with parallel-plate geometry, aiming to associate a viscosity model with the Hillier coupled polymerization-crystallization model previously determined by Vicard. The full chemorheological model will then be integrated into a simulation of LCM process in OpenFOAM®, an open source CFD software in order to follow the extent of the synthesis in the resin flow during the process. As a future work, simulations including microscale tow information extracted from a real textile specimen will permit to investigate the effect of permeability and double scale porosity in fibrous preforms on the final polymerization rate and crystallinity.

The effects of PEEK degradation on consolidation of commingled semi-finished products have been investigated. Two commingled semi-finished products provided by two different suppliers have been studied and compared to a powdered fabric based on the same PEEK grade. Both were manufactured from aligned AS4 carbon and PEEK yarns but the first product referred as the NCF1 has a lower commingling level than the second one identified as the NCF2. Contrary to what could be expected, under the same processing conditions, consolidation of the NCF1 and the NCF2 systematically results in a high porosity content, above 10%. Fourier Transform Infrared spectrophotometry (FTIR) in ATR mode and Gel Permeation Chromatography (GPC) have shown small molecular structure modifications of PEEK yarns compared to the raw material, such as a shift of molar mass distributions towards lower molar mass and the appearance of C-H absorption bands attributed to non-aromatic alkanes. These modifications have been attributed to sizing of PEEK filament. Calorimetric (DSC) and rheological analyses have demonstrated that the presence of sizing in the semi-finished products have huge consequences on the degradation kinetics. The crystallization temperature decreases and the viscosity increases significantly. This acceleration of the degradation kinetics is the reason of the poor consolidation behavior during composite manufacturing. The conditions of melt spinning extrusion under which the neat PEEK is transformed into filament are therefore a key factor of PEEK degradation.

PEEK yarns are used for commingled yarn based preforms in order to manufacture high performance thermoplastic composites. In a previous work, characterizations of PEEK commingled yarns revealed degradation, causing poor consolidation of final composites. The sizing applied onto the yarn surface in the melt spinning was identified as a degradation factor. Thus, the aim of this work is to assess the effect of different melt spinning parameters: extrusion, sizing and draw ratio, on PEEK integrity and its degradation process. Yarns at different stages of melt spinning were characterized through various techniques. For all yarns, degradation was identified during further transformation, in the molten state, inducing a decrease of the crystallization temperature and an increase of viscosity due to crosslinking. Extrusion initiates degradation earlier without changing the PEEK decomposition process. Sizing is responsible for an acceleration and modifications of degradation steps. (C) 2021 Elsevier Ltd. All rights reserved.

The effects of poly(ether ether ketone) (PEEK) degradation on consolidation of commingled preforms have been investigated. Contrary to what could be expected, under the same processing conditions, consolidation of the preforms systematically results in a high porosity content, above 10%. Fourier Transform Infrared spectrophotometry (FTIR) and Gel Permeation Chromatography (GPC) have shown small molecular structure modifications of PEEK yarns compared to the raw material. These modifications have been attributed to sizing of PEEK filament. Calorimetric (DSC) and rheological analyses have demonstrated that the presence of sizing in the preforms have huge consequences on the degradation kinetics. The crystallization temperature decreases and the viscosity increases significantly. This acceleration of the degradation kinetics is the reason of the poor consolidation behavior during composite manufacturing. The conditions of melt-spinning under which the neat PEEK is transformed into filament are therefore a key factor of PEEK degradation.

The degradation of different semi-finishedproducts carbon/poly(ether ether ketone) (PEEK) and its impact on consolidation quality have been studied. Fourier Transform Infrared spectrophotometry (FTIR) in ATRmode and calorimetric analyses have demonstratedinitial degradation of semi-finished. FTIR measurements have allowed to detect spectral modifications, with the appearance of C-H and O-H absorption bands attributedtonon-aromatic alkanes and degradation products such as phenols and benzoic acid respectively.DSC thermograms have shown important modifications of melting temperature during cyclic treatments at 400°C for all of the semi-finished matrices.The melting temperature decrease with the number of cycle and this decrease is different between the semi-finished products. The porosity measurements of consolidated parts have allowed to classify the different semi-finished productsand correlate this to degradation. The first results seems to demonstrate that semi-finished product such as the stretch-broken commingled have an important degree of degradation whereas the powdered fabrichave a small one.This behaviour may be due to extremeconditions of NCF spinning which initiate degradation.

This study focuses on the characterization of the in-plane shear response of a novel powder-impregnated, non-consolidated PA66/glass semipreg to evaluate its forming behaviour. The effects of temperature and rate on the behaviour of the semipreg and the preconsolidated material were investigated using bias-extension tests. Results obtained show an increase in shear stress with decreasing temperature and increasing rate, with the semipreg exhibiting a lower sensitivity to the test speed. An increase of the flow distance to impregnate the yarns, due to intra-ply sliding mechanisms specific to the powder-impregnated semipreg, is observed. A model based on a hypoelastic approach with temperature and rate dependence is proposed to represent the material behaviour. Isothermal simulations of the bias-extension test are conducted. Results show a good agreement between the model and experimental data in terms of force and shear angle prediction.

This paper proposes a novel experimental-numerical approach for radiation heat transfer in semi-crystalline thermoplastics. The proposed experimental and numerical approaches were analyzed here for the case of IR heating of linear polyethylene (PE). The challenges for radiation transport in semi-crystalline polymers may be categorized into the two main aspects: optical heterogeneity in polymer medium due to semi-crystalline nature and, semi-transparency in certain type of such polymers, like PE. In this study, we address the temperature dependence in the thermo-optical properties of semi-crystalline thermoplastics concerning its effect as a thermal radiation parameter for radiation heat transfer modeling of such type of polymers. The temperature dependence in the optical properties of PE, namely transmittance and reflectance characteristics, were experimentally analyzed under heating condition and, the temperature-dependent thermo-optical properties of PE was determined. The experimental analyses showed that the change in the thermo-optical properties under heating is related to change in the optical scattering behavior in PE medium since it is strongly affected by its crystalline structure. The radiation heat transfer model was built based on optically homogeneous medium assumption at which the change in the amount of radiative energy absorbed by the PE medium under heating was introduced without modeling how the light scatters inside of the medium. Thus, the effect of optical scattering on the absorption characteristics of PE under varying temperature was taken into account without modeling the spatial distribution of the scattered light intensity at microscopic level, which offers computationally cost-effective numerical solutions. The accuracy of the numerical model was analyzed performing IR heating experiments where IR thermography and thermocouples were employed for the surface temperature measurements. Due to the semi-transparent nature of PE, an experimental method was developed for IR thermography of PE and its accuracy was analyzed. The experimental-numerical comparisons showed that the temperature field on PE can be closely predicted using its temperature-dependent thermo-optical properties. Thanks to the adopted comparative case study, it was demonstrated how the temperature field predictions may deviate from the experimental thermal measurements due to the ignorance of this temperature dependence. Considering any type of monochromatic or polychromatic radiation source, the combined experimental-numerical approach proposed here may be adopted for temperature field predictions and non-invasive surface temperature measurements on the radiatively heated semi-crystalline thermoplastics.-

This study proposes a modelling strategy to simulate the heating stage during the production of thermoplastic composite tapes. Impregnation using a slurry powder technique with carbon fibres and PEKK (PolyEther-Ketone-Ketone) requires a heating step, to evaporate the aqueous phase and melt the polymer powder. These phenomenon are highly temperature dependant justifying the need to characterise heat transfer within the IR oven. In the literature, most models refer to clear lamps with Lambertian emission. In this study, tubular lamps with a coating on the back side (i.e. integrated reflector) are used. This integrated reflector greatly modifies the lamps spatial emission, therefor the lamp can no longer be modelled using a cylinder with Lambertian emission. This study proposes an adaptation of the radiosity method to predict spatial emission of the lamp without explicitly accounting for the reflector in terms of radiative exchange. The emission of the lamp was characterised by inverse analysis combining experimental results with numerical simulation using the commercial software –COMSOL Multiphysics®. Mots Clés : Rayonnement, analyse inverse, optimisation