Carbon Fiber-reinforced Polyamide Research Articles

Polyamide 6/carbon fibre composite: An investigation of carbon fibre modifying pathways for improving mechanical properties

Carbon fibre-reinforced polyamide 6 (PA6) composites exhibit exceptional mechanical properties, making them a highly attractive material option for various industries. Their ability to combine the advantages of carbon fibres with the versatility of PA6 provides opportunities for lightweight, high-performance applications. This work presented the fabrication of a PA6/carbon fibre composition with carbon fibre was modified by two different chemicals: nitric acid and diglycidil ether bisphenol A (DGEBA). The tensile strength at break, flexural strength, Rockwell hardness and Izod impact were measured to compare the mechanical properties of composites based on the PA6 matrix with two different modified carbon fibres. The morphology of PA6-based composite with different modified carbon fibres was observed by scanning electron microscopy. The results showed that PA6 is more compatible with acid-modified carbon fibre than DGEBA-modified carbon fibre and unmodified carbon fibre. In comparison to composite materials containing unmodified carbon fibre and DGEBA-modified carbon fibre, composite containing acid-modified carbon fibre increase tensile strength (16–38% and 7–15%, respectively), flexural strength (18–66% and 51–70%, respectively), Izod impact (23–65% and 32–78%, respectively) and Rockwell hardness (50–400% and equivalence, respectively).

Effect of Flashlamp Heating System Parameters on the Wedge Peel Strength of Thermoplastic Carbon Fiber Tape in the Automated Tape Placement Process

Laser-assisted automated tape placement systems are currently the state of the art regarding thermoplastic tape placement. Flashlamp heating systems are rather new in this field of application and offer high energy density with low safety requirements and moderate costs compared to laser-assisted automated tape placement systems. In this study, the effect of processing parameters on interlaminar bonding of carbon fiber-reinforced polyamide 6 tapes is investigated using a flashlamp heating system. The temperature during placement is monitored using an infrared camera, and the bonding strength is characterized by a wedge peel test. The bonding quality of the tapes placed between 210 °C and 330 °C at a lay-up speed of 50 mm/s is investigated. Thermogravimetric analysis, differential scanning calorimetry, and micrographs are used to investigate the material properties and effects of the processing conditions on the thermophysical properties and geometric properties of the tape. No significant changes in the thermophysical or geometric properties were found. Moisture within the tapes and staining of the quartz guides of the flashlamp system have significant influence on the bonding strength. The highest wedge peel strength of dried tapes was found at around 330 °C.

A Comparison of Internal Mandrel Designs for Rotary Draw Bend Forming of Carbon-fibre/Thermoplastic (PA6) Tubular Structures

AbstractCarbon fibre reinforced thermoplastic tubular structures can be post-formed into desired curvatures via rotary draw bending (RDB) at elevated temperatures. During this process, a rigid internal mandrel is required to support the walls of the tubes to maintain their ovality and minimise unwanted geometrical distortions. This paper investigates four internal mandrel designs for post-forming carbon fiber reinforced polyamide 6 (CF/PA6) thermoplastic tubes. Mandrel designs include silicone rod, bullet, wire, and coil spring, were evaluated through RDB-forming experiments with [± 60°]4 CF/PA6 tubes formed to 90° bends. The designs were evaluated for their effectiveness on minimising distortions resulted from induced stresses during post-forming by measuring the post-formed tube diameter and extrados strains. The mandrel designs were also evaluated for their usability when integrated into the RDB process. Results from optical measurements and micro-computed tomography showed the spring mandrel outperformed others, producing tubes with the least geometrical distortions and no defects during the forming process. As compared to other designs, the spring mandrel is a reusable unibody design that is easy to assemble and remove from the tubes.

Static Behavior of a 3D-Printed Short Carbon Fiber Polyamide: Influence of the Meso-Structure and Water Content.

The knowledge of the mechanical behavior of a 3D-printed material is fundamental for the 3D printing outbreaking technology to be considered for a range of applications. In this framework, the significance, reliability, and accuracy of the information obtained by testing material coupons assumes a pivotal role. The present work focuses on an evaluation of the static mechanical properties and failure modes of a 3D-printed short carbon fiber-reinforced polyamide in relation to the specimen's unique meso-structural morphology and water content. Within the manufacturing limitations of a commercially available printer, specimens of dedicated combinations of geometry and printing patterns were specifically conceived and tested. The specimens' meso-structure morphologies were investigated by micro-computed tomography. The material failure mechanisms were inferred from an analysis of the specimens' fracture surfaces and failure morphologies. The outcomes of the present analysis indicate that each test specimen retained proper mechanical properties, thereby suggesting that they should be accurately designed to deliver representative information of the underlying material beads or of their deposition layout. Suggestions on the adoption of preferred test specimens for evaluating specific material properties were proposed.

Analysis of the machining process of short carbon fiber-reinforced polyamide additive manufactured parts

In recent years, additive manufacturing technologies have revolutionized the production of parts, particularly in the aeronautical sector. This new manufacturing paradigm has created significant challenges and opportunities for researchers in materials and manufacturing processes. One important aspect is the development of optimal strategies for finishing-oriented machining of parts produced through additive manufacturing.This article focuses on the analysis of reinforced polyamide materials and the integration of large-scale additive manufacturing using Big Area Additive Manufacturing (BAAM) technology, along with robotic systems for subtractive machining. The aim is to explore the potential of integrating additive and subtractive processes to produce high-quality, large-scale components.The study examines the production and subsequent machining of reinforced polyamide parts using BAAM technology, showcasing the advantages and promising results observed. By combining additive manufacturing with subtractive machining, this research contributes to the ongoing advancements in the field of manufacturing, particularly in relation to reinforced polyamide materials. The findings presented in this article shed light on the potential of integrating additive and subtractive processes in the manufacturing industry, paving the way for more efficient and high-quality production methods.

Achieving gradual failure under bending by the layering design of 3D printed continuous fiber reinforced composites

A variety of methods have emerged to tailor the mechanical properties of 3D-printed continuous fiber-reinforced thermoplastic composites (CFRTCs) through geometry design or manufacturing parameters. However, the potential to achieve customized failure behavior is not exploited. In this study, the effect of different layer orders on load bearing and failure of 3D-printed CFRTCs is investigated. Carbon fiber-reinforced polyamide composites with six layer orders were prepared and the mechanical response in 4-point bending was investigated. We show that the failure behavior ranges from catastrophic to pseudo-ductile, and we distinguished four typical stress-strain responses. We found that the location and the thickness of matrix-only layers strongly influence the failure. For the latter, we present a linear relationship to the ductility index which shows that toughness can be increased with thicker matrix layers. Our results facilitate the design of CFRTCs with customizable failure behavior, thus contributing to safer applications.

Very high cycle fatigue assessment of thermoplastic-based hybrid fiber metal laminate by using a high-frequency resonant testing system

The prolonged fatigue lifetime of fiber metal laminates (FML) compared to monolithic metals is a key aspect for safety-relevant components, where detailed knowledge about the fatigue properties up to the very high cycle fatigue (VHCF) regime is necessary. For thermoplastic-based FMLs, offering formability, recyclability, and mass production due to short consolidation cycle times, this knowledge needs to be established.In this study, FML containing AA6082 sheets and unidirectional glass and carbon fiber-reinforced polyamide 6 was investigated. Fatigue tests up to max. 109 cycles were conducted on a servo-hydraulic and a high-frequency resonant fatigue testing system with frequencies of 10 Hz and 1,000 Hz. Frequency-induced self-heating was evaluated and limited using air-cooling to maintain the matrix properties. Fatigue progress was monitored through high-speed optical deformation analysis.Compared to HCF loads, VHCF loads lead to reduced crack and delamination occurrence. Changes in microstructure are dominated by singular crack initiation and propagation within the aluminum. The FML’s S-N curve shows a significant flattening from the HCF to the VHCF regime, simplifying the predictability of the fatigue life. By using post-stretching, the VHCF strength can be increased by over 60 %, making this thermoplastic-based FML a considerable competitor in the field of FML.

Continuous CF/PA6 Composite Aircraft Window Frame Manufactured via a Novel Winding Compression Process.

Using fiber-reinforced polymer composite to replace metal in window frames has become a trend in aircraft manufacturing to achieve structural weight reduction. This study proposes an innovative winding compression molding process for continuous production of aircraft window frames using continuous carbon fiber-reinforced polyamide 6 thermoplastic composite filaments (CF/PA6). Through process parameter optimization, the production cycle of CF/PA6 composite window frames was controlled within 5 min, with an ultra-low porosity of 0.69%, meeting aviation application standards. Combining mechanical property experimental tests and finite element analysis, the mechanical performance of window frames made from three different materials was compared and evaluated. In the hoop direction, the mechanical performance of the continuous CF/PA6 thermoplastic window frames were significantly higher than that of chopped CF/epoxy compression molding window frames and aluminum alloy window frames. In the radial direction, the maximum strain occurred at the corner with the highest curvature of the frame due to the absence of fiber reinforcement, resulting in weak pure interlayer shear. Nevertheless, the thermoplastic CF/PA6 winding compression molded window frame still exhibited a high resistance to crack propagation and damage, as evidenced by the absence of any detectable sound of microdamage during testing with a 9000 N load. It is believed that achieving a further-balanced design of hoop-radial performance by appropriately introducing radial ply reinforcement can lead to a significant weight reduction goal in the window frame. The findings in this study provide an innovative process reference that can be universally applicable to high-speed and near-net-shape manufacturing without material waste of continuous fiber-reinforced thermoplastic composite products.

A machine learning approach to characterise fabrication porosity effects on the mechanical properties of additively manufactured thermoplastic composites

The investigation of the mechanical properties of additively manufactured (AM) composite has been the focus of several research over the past decades. However, testing constraints of time and cost have encouraged the exploration of more pragmatic methods such as machine learning (ML) for predicting these characteristics. This study builds on experimental investigations of the flexural, tensile, compressive, porosity, and hardness properties of 3D printed carbon fibre-reinforced polyamide (CF-PA) and carbon fibre-reinforced acrylonitrile butadiene styrene (CF-ABS) composites, proposing the application of ML for predicting these mechanical properties. A comprehensive comparative analysis of various machine learning approaches was executed, with a resultant accuracy ranging between 80 and 99%. The results unveiled the superior predictive performance of ensemble tree learners and the K-NN regressor algorithms when temperature and porosity are selected (based on correlation analysis) as predictors for material hardness and strength in tension, compression, and flexion. In particular, the model built on the extra-tree regressor algorithm demonstrated a remarkably robust fit, with R-squared evaluation scores of 0.9993 and 0.9996 for CF-PA and CF-ABS, respectively. This work develops a ML model that relates porosity to the other mechanical properties of AM composites and the prediction models’ exceptional accuracy, along with their precise alignment with experimental data, provide invaluable insights for the autonomous control and data-driven optimization of the structures.

Experimental Characterization of Screw-Extruded Carbon Fibre-Reinforced Polyamide: Design for Aeronautical Mould Preforms with Multiphysics Computational Guidance

In this research work, the suitability of short carbon fibre-reinforced polyamide 6 in pellet form for printing an aeronautical mould preform with specific thermomechanical requirements is investigated. This research study is based on an extensive experimental characterization campaign, in which the principal mechanical properties of the printed material are determined. Furthermore, the temperature dependency of the material properties is characterized by testing samples at different temperatures for bead printing and stacking directions. Additionally, the thermal properties of the material are characterized, including the coefficient of thermal expansion. Moreover, the influence of printing machine parameters is evaluated by comparing the obtained tensile moduli and strengths of several manufactured samples at room temperature. The results show that the moduli and strengths can vary from 78% to 112% and from 55% to 87%, respectively. Based on a real case study of its aeronautical use and on the experimental data from the characterization stage, a new mould design is iteratively developed with multiphysics computational guidance, considering 3D printing features and limitations. Specific design drivers are identified from the observed material’s thermomechanical performance. The designed mould, whose mass is reduced around 90% in comparison to that of the original invar design, is numerically proven to fulfil thermal and mechanical requirements with a high performance.

Mechanical Characterization of Polylactic Acid, Polycarbonate, and Carbon Fiber-Reinforced Polyamide Specimens Fabricated by Fused Deposition Modeling

This paper investigates the mechanical behavior of polylactic acid (PLA), polycarbonate (PC) and carbon fiber-reinforced high-temperature polyamide (PAHT-CF) specimens fabricated by fused deposition modeling (FDM). PC and PAHT-CF are considered engineering grade materials that exhibit good mechanical properties, suitable for rapid prototypes and functional parts fabrication. PLA, a popular, commonly used FDM material, has been included in this work for comparison purposes. The purpose of the present study is to provide comprehensive experimental data on the materials’ critical properties since limited data is available in the existing literature and there is a lack of comparative analysis regarding the three materials. Mechanical characterization has been carried out on the basis of tensile, three-point bending, impact and creep tests. Measurements of hardness, density and porosity were conducted, and the specimens’ morphology was examined through microscopy. The results showed that the highest strength and flexural modulus of elasticity were observed for the PAHT-CF specimens followed by PC and PLA. PC specimens exhibited the highest impact resistance followed by PAHT-CF and PLA. The highest stage II creep resistance was achieved by PAHT-CF followed by PC and PLA. The optical and scanning electron microscopy images revealed that specimens’ quality depends on the printing parameters.

Effect of nozzle wear on mechanical properties of 3D printed carbon fiber-reinforced polymer parts by material extrusion

A widespread problem of manufacturing processes is represented by the occurrence of tool wear that can lead to both poor surface finish and poor mechanical properties in the workpiece. This issue affects also additive manufacturing technologies such as the material extrusion technique. In this process, the wear mechanisms of the extrusion nozzle can be severe, in particular when materials with a high abrasive capacity, such as carbon fiber-reinforced polymers, are 3D printed. Despite the significance of this problem, scientific literature lacks systematic evaluations of nozzle wear and its correlation with parts mechanical properties. In this framework, the present paper aims at investigating the effect of the nozzle wear evolution on the mechanical properties of additively manufactured parts in short carbon fiber-reinforced polyamide. To this purpose, 3D printing processes were performed. The time dependence of the nozzle wear was analyzed by interrupting the additive manufacturing process at fixed time intervals. To analyze the effect of nozzle wear on the mechanical performances of printed parts, tensile specimens were 3D printed and tested at room temperature. A reduction in mechanical performances of the printed samples and a worsening in the surface quality were observed with increasing the nozzle wear. Optical microscopy investigation and X-ray computed tomography were used to monitor the external and internal nozzle wear evolution. The surface roughness measurements were performed to evaluate the surface quality of the 3D printed parts. Furthermore, the scanning electron microscopy was used to observe the three-dimensional topography of the longitudinal sections of filament in Carbon PA, at different printing time values, and fractured surfaces of tensile samples. This study can help to better understand nozzle wear and to predict tool service life for industrial applications. In addition, it can prompt future studies focused on the reduction of tool wear.

Fatigue Life Prediction for Injection-Molded Carbon Fiber-Reinforced Polyamide-6 Considering Anisotropy and Temperature Effects.

The effects of anisotropy and temperature of short carbon fiber-reinforced polyamide-6 (CF-PA6) by the injection molding process were investigated to obtain the static and fatigue characteristics. Static and fatigue tests were conducted with uniaxial tensile and three-point bending specimens with various fiber orientations at temperatures of 40, 60, and 100 °C. The anisotropy caused by the fiber orientations along a polymer flow was calculated using three software connecting analysis sequences. The characteristics of tensile strength and fatigue life can be changed by temperature and anisotropy variations. A semi-empirical strain-stress fatigue life prediction model was proposed, considering cyclic and thermodynamic properties based on the Arrhenius equation. The developed model had a good agreement with an R2 = 0.9457 correlation coefficient. The present fatigue life prediction of CF-PA6 can be adopted when designers make suitable decisions considering the effects of temperature and anisotropy.

Experimental Investigation of Mechanical Properties of Additively Manufactured Fibre-Reinforced Composite Structures for Robotic Applications

AbstractThis study explores the variation in mechanical properties of additively manufactured composite structures for robotic applications with different infill densities and layer heights using fused deposition modelling (FDM). Glass fibre-reinforced polyamide (GFRP), and carbon fibre-reinforced polyamide (CFRP) filaments are used, and the specimens are printed with 20%, 40%, 60% and 100% infill density lattice structures for tensile and three-point bending tests. These printed samples are examined in the microscope to gain more understanding of the microstructure of the printed composites. To characterise the mechanical properties, a set of tensile and three-point bend tests are conducted on the manufactured composite samples. Test results indicate the variations in tensile strength and Young’s modulus of specimens based on the printing parameters and reveal the tensile and bending behaviour of those printed composite structures against varying infill ratios and reinforcing fibres. The experimental findings are also compared to analytical and empirical modelling approaches. Finally, based on the results, the applications of the additively manufactured structure to the robotic components are presented.

Product, process, property, and performance (PPPP) relationship of 3D-Printed polymers and polymer composites: Numerical and experimental analysis

Understanding the external and internal factors during an additive manufacturing (AM) process is crucial, as they can significantly affect the final product's performance. Efforts have been made to unwind the product, process, property, and performance (PPPP) relationships. The conventional experimental approaches can lead to boundless runs, resulting in exorbitant costs for research and development. Hence, developing, adapting, and validating numerical models is essential to achieving the desired performance of 3D-printed products with lesser resource utilization. In this study, numerical and experimental techniques were used to perform the PPPP relationship assessment on material extrusion 3D-printed parts. Three infill designs (rectangular, triangular, and hexagonal), with layer heights (0.1 mm, 0.125 mm, and 0.2 mm), and three different materials (carbon fiber-reinforced polyamide-6 (PA6-CF), polyamide-6 (PA6), and acrylonitrile butadiene styrene (ABS)), were selected for the investigation. Taguchi's design of experiments (DOE) method was used to limit the number of numerical simulations and experimental runs. A thermomechanical numerical model was utilized to perform the material extrusion process simulations and mechanical performance prediction of the specimens. Subsequently, the samples were 3D-printed and tested mechanically to validate the numerical simulation results. The dimensional, distortion, and mechanical analysis performed on numerical simulation results agreed well with the experimental observations.

Atomistic Modeling of the Effect of Temperature on Interfacial Properties of 3D-Printed Continuous Carbon Fiber-Reinforced Polyamide 6 Composite: From Processing to Loading.

The combination of continuous fiber-reinforced thermoplastic composites (CFRTPCs) and the continuous fiber 3D printing (CF3DP) technique enables the rapid production of complex structural composites. In these 3D-printed composites, stress transfer primarily relies on the fiber-resin interface, making it a critical performance factor. The interfacial properties are significantly influenced by the temperatures applied during the loading and forming processes. While the effect of the loading temperature has been extensively researched, that of the forming temperature remains largely unexplored, especially from an atomistic perspective. Our research aims to employ molecular dynamics simulations to elucidate the effect of temperature on the interfacial properties of continuous carbon fiber-reinforced polyamide 6 (C/PA6) composites fabricated using the CF3DP technique, considering both loading and forming aspects. Through molecular dynamics simulations, we uncovered a positive correlation between the interfacial strength and forming temperature. Moreover, an increased forming temperature induced a notable shift in the failure mode of C/PA6 under uniaxial tensile loading. Furthermore, it was observed that increasing loading temperatures led to the deterioration of the mechanical properties of PA6, resulting in a gradual transition of the primary failure mode from adhesive failure to cohesive failure. This shift in the failure mode is closely associated with the glass transition of PA6.

Influence of Raster Orientation and Feeding Rate on the Mechanical Properties of Short Carbon Fiber-Reinforced Polyamide Printed by Fused-Filament Fabrication

Influence of Raster Orientation and Feeding Rate on the Mechanical Properties of Short Carbon Fiber-Reinforced Polyamide Printed by Fused-Filament Fabrication

Measuring the interlaminar fracture toughness of thin carbon fiber/polyamide6 composites using adhesively bonded stiffeners

The present work investigates the interlaminar fracture toughness of a thin unidirectional carbon fiber-reinforced/polyamide6 (CF/PA6) composite laminate. Aluminum (Al) stiffening beams are adhesively bonded on both sides of the thin laminate to avoid undesirable large deformations during the subsequent double cantilever beam tests. Experimentation with various surface treatment techniques and different adhesives is presented, from which it is concluded that the mode I fracture toughness of the CF/PA6 laminate is always higher than the fracture toughness of the adhesives used. Consequently, the crack initiates at the Al–composite interface. A finite element (FE) model is proposed, and quantitative results for the fracture toughness of the laminate are provided (e.g., GIc,ini=2.1N/mm). Overall, the study highlights the challenges in the adhesive joining of stiffening beams to CF/PA6 surfaces, ways to improve adhesion, and the FE simulation as an alternative to determining the interlaminar fracture toughness of such thin laminates.

Enhancement of flexural properties of carbon fiber-reinforced polyamide 6 via oriented crystallization of polyamide 6 among carbon fibers

The effect of the crystalline structure of polyamide 6 (PA6) among carbon fiber (CF) on the mechanical properties of PA6/CF composites was explored using two types of PA6 with different spherulite sizes. Infrared (IR) spectroscopy showed that intra/intermolecular interactions were nearly equivalent for the two types of PA6. The viscoelasticities in the molten state were almost identical; that is, the molecular weights of the PA6s were comparable. The mechanical properties of the PA6 matrix with smaller spherulites (PA6a) in PA6/CF were superior to those of the PA6 matrix with larger spherulites (PA6b). Polarized light microscopy, wide-angle X-ray scattering, and polarized Raman spectroscopy revealed oriented crystals of PA6a in the PA6a/CF composite and random crystals of PA6b in the PA6b/CF composite. Therefore, the superior mechanical properties of PA6/CF are due to the oriented crystal chains of PA6, which support the overall stress transfer in composites.

Mode I, mode II and mixed mode I-II delamination of carbon fibre-reinforced polyamide composites 3D-printed by material extrusion

Continuous carbon fibres can greatly improve the properties of 3D-printed polymer parts made by material extrusion. However, like all laminated composites, 3D-printed parts are susceptible to delamination damage. In addition, the printing process does not include a consolidation at high temperatures and pressure, unlike conventional manufacturing methods, which can lead to poor interlayer cohesion. Due to the combination of the susceptibility to delamination and a weak interface, the assessment of the interlaminar properties of 3D-printed parts is critical. This work experimentally investigates the delamination behaviour of carbon fibre-reinforced polyamide laminates under mode I, mode II and mixed mode I-II loading, using the double cantilever beam (DCB), end-loaded split (ELS), end-notched flexure (ENF) and mixed-mode bending (MMB) tests. An interlaminar fracture toughness at crack initiation of 1.5 kJ/m2 was found in mode I, 2.1 (ELS) and 1.8 (ENF) kJ/m2 in mode II, and 1.0 kJ/m2 in mixed mode I-II with GII/Gtotal = 0.5. Several analytical and numerical models are employed to validate the experimental results. Scanning electron microscopy revealed the micro-mechanical origins of the crack in the different loading configurations.