Processing Of Thermoplastic Composites Research Articles

Resin percolation and intimate contact in fast processing of thermoplastic composites

Fusion bonding of thermoplastic composites (TPCs) requires intimate contact before polymer interdiffusion and solidification can establish an interlaminar bond. The lack of such intimate contact results in voids or disbonds. This study shows through cross-sectional imaging and scaling analysis that percolation flow, rather than squeeze flow, of resin through fibers is the dominant mechanism to achieve intimate contact in rapid TPC processes such as automated fiber placement (AFP) and welding. A 1D intimate contact model based on resin percolation, derived from Darcy’s Law, is presented and compared to experiments. While this model proved effective in comparing processing conditions by adeptly capturing trends, it under-predicted resin content in samples processed using AFP with low pressure. The model was extended to high processing rates, suggesting the importance of heated tools and high processing pressures on achieving intimate contact.. In-situ high-speed imaging and ex-situ microscopy revealed void size and morphology based on AFP processing parameters. The results of this study can guide fast processing of thermoplastic composites.

Application and thermal field analysis of multilayer thermal insulation in in-situ forming process of thermoplastic composites

Application and thermal field analysis of multilayer thermal insulation in in-situ forming process of thermoplastic composites

On PVDF composite prepared by single screw extruder: A statistical analysis of mechanical properties

The commercial processing of thermoplastics, using a single screw extruder (SSE) has been widely reported in the past three decades. But for the processing of thermoplastic composites, some studies have reported the loss of mechanical properties mainly due to the non-uniform blending of reinforcements in the main matrix. In this study, poly (vinylidene fluoride) (PVDF) matrix was prepared as wire filament forthe material extrusion in line with the sustainable development goal (SDG) followed by statistical investigations of attained mechanical properties. The result outlined the suitability of SSE for the fabrication of PVDF composite filament without significant loss of its mechanical properties. The best setting for the SSE observed as screw temperature 225 °C and a crew speed of 7 rpm.

CF/PEKK advanced pultrusion thermoforming process temperature field simulation

Advanced pultrusion molding technology is one of the composite molding processes. It has unique advantages in the automated manufacturing of long trusses and long beam components. Thermoplastic composites are becoming popular for research in many fields such as aerospace because of their room-temperature storage and secondary use. Since the temperature history is critical to the molding quality of thermoplastic composites, the temperature field variation of CF/PEKK composites in the advanced pultrusion thermoforming process has been explored in the context of studying the advanced pultrusion molding process of thermoplastic composites in this paper. By constructing a 3D model of the temperature field and setting up a complete solution scheme in ANSYS simulation software, the simulated temperature field data were obtained, and a real-time temperature monitoring platform was set up to obtain the measured temperature data, and the comparison showed that the two temperature profiles fit well, which proved the applicability of the model and solution scheme to this study.

Multi-scale finite element simulation of the thermoforming of a woven fabric glass fiber/polyetherimide thermoplastic composite

Understanding the thermoforming process for thermoplastic composites is of great importance to ensure the quality of the composite product but is difficult because of the complex material constitutive models and thermo-mechanical coupling in the thermoforming process. In this study, a woven fabric thermoplastic composite consisting of glass fiber and polyetherimide resin was thermoformed under one-sided cooling conditions. After the effective material properties are homogenized with newly developed, two-step asymptotic homogenization methods, and the temperature and pressure boundary conditions are measured experimentally, a 3D composite laminate sandwiched by interfacial layers and metal molds was finite element simulated in the macroscale. The simulated warpage, which was caused by the in-plane residual stresses, was consistent with the experimental results when reasonable tool–part interactions were considered. Subsequently, the temperature, displacement, strain, and stress were comprehensively discussed in terms of their spatial distribution, temporal evolution, and correlations with the others.

AEROPLAS – Desarrollo de componentes para la industria aeronáutica mediante tecnologías de bajo coste

The future of the aeronautical sector is oriented towards manufacturing lighter and more profitable structures and components, using more ecological materials and technologies, that allow reducing costs, weight and fuel consumption, with shorter manufacturing cycles, while increasing energy efficiency manufacturing. AEROPLAS project arises in this context, with the aim of contributing to the advanced manufacturing process of thermoplastic composites using low-cost technologies for the aeronautical industry. This study focuses on the replacement of aeronautical parts currently manufactured in thermosetting composite by thermoplastic ones, in two real components: cover panel and access door of the ventral fairing of A350, using two materials of different quality: LM-PAEK/CF semipreg (TenCate Cetex® TC1225) and PC/CF prepreg (ePreg245CHT/PC40). Through design and calculation, the stacking and part thicknesses necessary to cover the structural requirements of both components have been obtained, based on the data acquired from the characterization of the base materials. Two manufacturing processes have been studied and compared to obtain the new parts, selecting thermoforming and stamping as the most promising. Finally, the characterization of the pieces obtained has been carried out by means of non-destructive tests (visual inspection, ultrasonic verification, dimensional inspection using laser tracker) and destructive tests (pull-out strength on riveted joints [AITM1-0066], bearing strength [AITM1-0009], laminate tensile strength [AITM1-0007], fastened joints strength [AITM1-0067]).

Predictive Thermal Modeling and Characterization of Ultrasonic Consolidation Process for Thermoplastic Composites

Abstract Ultrasonic consolidation (USC) of thermoplastic composites is a highly attractive and promising method to manufacture high-performance composites. This work focuses on USC of dry carbon fiber (CF) fabrics with high-temperature polyphenylene sulfide (PPS) films. Experimental trials to assess feasibility of the process are time-consuming. Consequently, a predictive thermal model would facilitate process parameters selection to reduce expensive trial-and-error approaches. This paper presents a 2D finite element model of samples under consolidation, incorporating equations for viscoelastic heating, matrix phase change, and material properties. Theoretical temperature profiles for nodes of interest were compared to the corresponding experimental temperature curves for various control parameters (i.e., weld time and vertical displacement of sonotrode) and showed good agreement during heating phase. It was found that welding time values below 1750 ms were insufficient to reach melting temperature, whereas weld times above 3000 ms led to the lowest average void content (2.43 ± 0.81%). More specifically, the time the material spent above melting temperature, i.e., residence time, was established as a parameter that could estimate cases resulting in better consolidation and lower void content (time above 2600 ms for void content below 2.5%). X-ray diffraction (XRD) characterization revealed that the USC process led to mostly amorphous PPS, due to the high cooling rates (70 °C/s to 108 °C/s). Overall, the thermal model and micro-structural outcomes confirmed the feasibility of the USC process for layered composites made from dry fabric and high-temperature thermoplastic films.

A Novel Multi-Region, Multi-Phase, Multi-Component-Mixture Modeling Approach to Predicting the Thermodynamic Behaviour of Thermoplastic Composites during the Consolidation Process.

In the processing of thermoplastic composites, great importance is attributed to the consolidation step, as it can significantly reduce the porosity of the semi-finished product and thus influence considerably the quality of the final component. This work presents an approach to modeling the thermodynamic behavior of composite materials during hot-press consolidation. For this purpose a multi-region, multi-phase and multi-component-mixture model was developed using the simulation toolbox OpenFOAM®. The sensitivity of the model was tested by varying the thermal parameters and mesh resolution, confirming its robustness. Validity of the model was confirmed by comparing simulation results to experimental data for (i) polycarbonate with 44% carbon fiber by volume and (ii) polypropylene with 45.3% glass fiber by volume. The simulation allows very precise estimation of when a particular temperature, such as the glass transition temperature or melting point, will be reached at the core of a composite. In relation to the total process time, maximum deviation of the simulation from the experimental data amounted to 2.84%. Therefore, the model is well suited for process optimization, it offers a basis for further model implementations and the creation of a digital twin.

Effect of filament winding process parameters on interlaminar performance for CF/PP thermoplastic composite

This paper focuses on the in-situ consolidation process of thermoplastic composites by winding, aiming to explore the influence of key process parameters on samples’ quality. During the consolidation of thermoplastic composites, they need to go through resin melting-bonding-consolidation process, in which each parameter affects the interlaminar bond strength. Through preliminary simulation and experiments, the process parameters were selected. In this paper, wound NOL ring samples made of carbon fiber reinforced polypropylene thermoplastic composite prepregs were obtained with a hot gas assisted filament winding equipment. The influence rule of winding temperature, winding tension and winding speed on the interlaminar shear strength were analyzed based on response surface methodology. Through the analysis, in the range of the experiments winding tension and temperature had more effect on the shear strength while speed’s influence was small. With the increase of tension and temperature, the interlaminar shear strength increased, but after reaching a certain value, the laminar shear strength decreased instead.

A Study of Manufacturing Process of Thermoplastic Composites

A Study of Manufacturing Process of Thermoplastic Composites

The synergistic steric hindrance effect in the preparation of polyether ether ketone composites by powder slurry method

AbstractThe preparation of continuous carbon fiber reinforced polyether ether ketone (PEEK) composites by the powder slurry method has many advantages, but the stability of PEEK suspension is required to be high. So far, there is a lack of in‐depth studies on the aqueous suspension of PEEK. In this study, two non‐ionic surfactants were selected for compounding. Then PEEK aqueous suspension and continuous carbon fiber reinforced PEEK composites were prepared. The stability mechanism of PEEK aqueous suspension with different surfactants was analyzed. Studies have shown that in the PEEK aqueous suspension, Triton X‐100 can help to infiltrate the PEEK powder. The steric hindrance of polyethylene glycol contributes to the stability of the suspension. The synergistic steric hindrance effect of the two surfactants can increase the stability time of PEEK suspension from 5 min to more than 50 min. The PEEK composites prepared by the powder slurry method has good quality stability, the fiber volume fraction is about 60%, the flexural strength of the composites can reach 1336 MPa, and the interlayer shear strength can reach 106 MPa. This study provides useful insights for the stability mechanism of PEEK aqueous suspension, and can guide the preparation process of thermoplastic composites by powder slurry method.

Fabrication of continuous carbon fiber reinforced polyamide 6 composites by means of self‐resistance electric heating

AbstractIn the conventional process of thermoplastic composites, a heating stage from the external heat source usually consumes a large amount of energy. To solve this problem, self‐resistance electric (SRE) heating of carbon fiber‐reinforcement was introduced to form a continuous carbon fiber reinforced polyamide 6 (CF/PA 6) composite based on film stacking technique in this paper. The temperature distribution was first measured to verify the temperature uniformity for SRE heating process. X‐ray photoelectron spectroscopy (XPS) was used to assess effects on the chemical properties of carbon fibers from SRE heating and conventional convective heating. To evaluate forming quality by SRE heating, the physical properties, crystallinity, and mechanical properties of CF/PA 6 composites were measured. The results show that the forming time and energy consumption of SRE heating process are significantly reduced compared with that of the traditional heating process because of fast heating/cooling rate. While fast heating/cooling rate of SRE heating process leads to a higher void content, which finally results in a slightly lower flexural strength and impact properties of composite laminates. It is clear that SRE heating technique is one of the energy‐ and cost‐effective ways to fabricate continuous carbon fiber reinforced thermoplastic composites although the forming quality is still improved in future investigation.

Optical fiber multiparameter sensor for real‐time monitoring of thermoplastic composites during in situ consolidation process

AbstractTemperature and strain are important parameters in the in situ consolidation process of thermoplastic composites and have been monitored based on optical fiber Bragg gratings. A special polyimide fiber grating (PFBG) is used in this article. PFBG can monitor temperatures up to 400°C and strains up to 40,000 με. The wavelengths of the PFBGs are obtained by wavelength demodulation system and fast digital signal processing with field programmable gate array. Temperature and strain in auto fiber placement process of thermoplastic composites are monitored accurately according to wavelengths. During the whole consolidation process, temperatures have been monitored with the accuracy of 0.1°C in the range of 100–250°C and strains have been monitored with the accuracy of 1 με in the range of −250 to 500 με. The validity and correctness of the results have been validated by the thermocouple and the strain gauge.

Thermal degradation behaviour of natural fibres at thermoplastic composite processing temperatures

Natural fibres have been identified as a potential substitute for mineral fillers in thermoplastic matrix composites for automotive applications. However, natural fibres are known to be susceptible to thermal degradation at relatively low temperatures. This paper focuses on the characterisation of the thermal and mechanical degradation of date palm and coir fibres as part of an evaluation of their potential as a reinforcement for polypropylene composites. The thermal degradation of the fibres and the resultant volatiles produced have been analysed for a range of typical polypropylene processing temperatures. The effect of the thermal degradation of the fibres on their mechanical performance has also been evaluated using single fibre tensile testing. The results indicate that processing temperatures should be minimised as much as possible and certainly kept below 200°C.

On differences and similarities between static and continuous ultrasonic welding of thermoplastic composites

Continuous ultrasonic welding is a promising high-speed and energy-efficient joining method for thermoplastic composite structures. Our aim was to identify and understand differences between the static and continuous ultrasonic welding process for thermoplastic composites. In particular, melting of the interface, consumed power and energy density, temperature evolution at the weld interface, and optimum welding conditions for both types of processes were investigated. This was done for three combinations of welding force and vibrational amplitude, parameters which are known to have a significant effect in both welding processes. Our results showed that for the continuous process the amount of non-welded area under the sonotrode remains constant, while for the static process the amount of non-welded area gradually decreases to zero. Additionally, the optimum vibration times and welding speeds in both processes are similar.

Measurement and prediction of residual strains and stresses during the cooling of a glass fibre reinforced PA66 matrix composite

The forming process of thermoplastic composites inevitably leads to the development of residual stresses. This study proposes a model to predict the residual stresses at the ply scale of a thermoplastic composite laminate. It accounts for the heat transfer, crystallization kinetics and mechanical behaviour of the laminate. The model is applied to the cooling of a polyamide 66 (PA66) matrix reinforced with continuous glass fibres. The Stress Free Temperature is considered as the starting point of stresses accumulation within each ply and its identification is discussed. The curvatures of [904/04] laminates and their evolution with temperature are recorded with a digital image correlation technique. They are compared to the curvatures predicted by the model, which permits to validate it. The predicted stresses distribution is then discussed. Finally, the model is compared to the Classical Lamination Theory, demonstrating the interest of the developed model.

Fractographic evaluation of welded joints of PPS/glass fiber thermoplastic composites

Joints obtained by resistance welding of polyphenylene sulphide (PPS) laminates reinforced with bidirectional glass fiber (GF) fabrics were investigated by fractographic analyses. The welded joints were tested under lap shear loading at room temperature. The fracture surfaces were analyzed by scanning electron microscopy (SEM) technique. Electric resistance welding technique uses the matrix flow property, when the thermoplastic is heated above the softening temperature (for amorphous polymers) or above the melting temperature (for semicrystalline polymers), to promote the welding between the laminates. Fractographic aspects of the studied fracture surfaces show that the interfacial adhesion of matrix/heating element was efficient, with the presence of intralaminar and interfacial failures. The intralaminar failure was predominant in laminates with higher values of shear strength (9.6 MPa). On the other hand, interfacial failure was predominant in laminates with lower values of shear strength (1.9 MPa). The mechanical performance measured for the welded joints was attributed to the polymer chains interdiffusion mechanism in the welding region as well as to the good polymer anchoring in the mesh of heating element. The fractographic analyses performed proved to be an adequate tool because provide information to evaluate the quality of welding process of thermoplastic composites.

Styrene-Free, Partially Biobased Resin System for Thermoplastic Composites. I. Rheological Properties and Preliminary Panel Fabrication

For the first time ever, a styrene-free, biobased formulation suitable for infusion processing of thermoplastic composites is reported. Biobased polylactide (PLA) is soluble in methyl methacrylate ...

Effect of preheat treatment on carbon fiber surface properties and fiber/PEEK interfacial behavior

In this work, the effect of preheat treatment on surface properties of carbon fiber (CF) and interfacial properties of CF‐reinforced polyether ether ketone (CF/PEEK) composites was investigated in detail. The sized T700SC CFs were preheated based on practical thermoplastic composites processing conditions. The obvious mass loss was obtained due to the sizing agent degradation. Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy demonstrated that the concentration of sizing agents and activated carbon atoms decreased apparently for preheated fibers. Preheat treatment had negligible effect on tensile strength. Transcrystallinity structures were observed at fiber/PEEK interfaces using polarizing microscope and they had similar transcrystallinity density before and after preheat treatment. The microbond test was performed to determine interfacial shear strength (IFSS) between fibers and PEEK matrix. The IFSS increased from 40.16 to 46.32 MPa by 15.34%, which was against the trend of activated carbon atoms. Furthermore, the mechanisms of interfacial adhesion enhancement were discussed. The sizing layer became weak interface region because of poor chemical bonding between sizing agents and PEEK. Removing sizing via preheat treatment could enhance the interfacial adhesion. POLYM. COMPOS., 40:E1407–E1415, 2019. © 2018 Society of Plastics Engineers

Dry Electrostatic Spray Coated Towpregs for Thermoplastic Composites

Though the processing steps for the manufacture of thermoplastic composites present little difficulty when compared to those for thermoset composites, it is not cost effective as a result of difficulty in accomplishing thorough infusion of resin into fibers and fibrous structures. Tremendously high viscosity for thermoplastic resin leads to numerous problems in the manufacturing process of thermoplastic composites. Pre-impregnation processes such as melt impregnation or solution impregnation, tend to form a stiff towpreg that cannot be used for any textile preforming operation. Powder coating can be a destined to be a cost effective as well as efficient processing technology to produce a flexible towpreg. A method for production of flexible towpregs for thorough infusion of resin into fibers using electrostatic spray gun, which involves powder coating a bundle of filaments is described. During the powder coating process using electrostatic spray gun, powder particles fetched by a conveying air stream, from a fluidizing hopper, are charged in the high voltage corona discharge by ion bombardment and transported to the fiber tow through the combination of electrostatic, aerodynamic and gravitational forces. Aerodynamic forces have the obligation to carry the powder particles to the tow where electrostatic forces dominate and cause the adherence of powder particles to the potentially grounded tow. After the powder deposition, tow is made to pass through convective oven where powder particles glue to the reinforcement as a result of partial liquefaction of the powder. The towpreg formed is then wound by the take up device. Take up device is equipped with dancer arm which ensures constant line tension and thereby consistent powder deposition. The effects of process variables of the electrostatic spray process such as corona voltage, fluidizing air pressure, conveying air pressure, distance of gun from tow and tow velocity on maximum powder deposition are investigated and reported.