Fiber-reinforced Thermoplastic Composites Research Articles

Linear viscoelasticity of anisotropic carbon fibers reinforced thermoplastics: From micromechanics to dynamic torsion experiments

The link between experimental characterization and the constitutive behavior of an anisotropic linear viscoelastic unidirectional carbon fiber-reinforced thermoplastic composite is explored using micromechanics modeling. Dynamic torsion tests were conducted at 1 Hz over a wide temperature range, from the glassy to the rubbery states of the polymeric matrix, on both the pure matrix and the composite, for various cutting angles relative to the fibers. A two-step modeling procedure in the frequency domain is presented to predict and validate the effective behavior of the composite. The first step involves FFT-based homogenization, which maps the microstructure and constituent behaviors to effective transversely isotropic viscoelastic properties. The second step consists of finite element simulations using the effective behavior calculated from homogenization as input to replicate the experiments. A comparison between experimental results and model predictions across the entire temperature range is performed. The modeling predictions show good accuracy at low temperatures, where the matrix is in the glassy state. At high temperatures, where the matrix is in the rubbery state, the predicted behavior becomes too soft. As the phase contrast increases and the ratio of matrix bulk modulus to shear modulus rises significantly, the impact of fiber arrangement on the effective properties becomes more pronounced.

Detecting Multi-Scale Defects in Material Extrusion Additive Manufacturing of Fiber-Reinforced Thermoplastic Composites: A Review of Challenges and Advanced Non-Destructive Testing Techniques.

Additive manufacturing (AM) defects present significant challenges in fiber-reinforced thermoplastic composites (FRTPCs), directly impacting both their structural and non-structural performance. In structures produced through material extrusion-based AM, specifically fused filament fabrication (FFF), the layer-by-layer deposition can introduce defects such as porosity (up to 10-15% in some cases), delamination, voids, fiber misalignment, and incomplete fusion between layers. These defects compromise mechanical properties, leading to reduction of up to 30% in tensile strength and, in some cases, up to 20% in fatigue life, severely diminishing the composite's overall performance and structural integrity. Conventional non-destructive testing (NDT) techniques often struggle to detect such multi-scale defects efficiently, especially when resolution, penetration depth, or material heterogeneity pose challenges. This review critically examines manufacturing defects in FRTPCs, classifying FFF-induced defects based on morphology, location, and size. Advanced NDT techniques, such as micro-computed tomography (micro-CT), which is capable of detecting voids smaller than 10 µm, and structural health monitoring (SHM) systems integrated with self-sensing fibers, are discussed. The role of machine-learning (ML) algorithms in enhancing the sensitivity and reliability of NDT methods is also highlighted, showing that ML integration can improve defect detection by up to 25-30% compared to traditional NDT techniques. Finally, the potential of self-reporting FRTPCs, equipped with continuous fibers for real-time defect detection and in situ SHM, is investigated. By integrating ML-enhanced NDT with self-reporting FRTPCs, the accuracy and efficiency of defect detection can be significantly improved, fostering broader adoption of AM in aerospace applications by enabling the production of more reliable, defect-minimized FRTPC components.

Development of the forming limit diagram for fiber-reinforced thermoplastic composites and its temperature effect

The aim of this study is to investigate the formability properties of thermoplastic composite sheets and to develop a forming limit diagram (FLD) for them under ambient and elevated temperatures. Polypropylene thermoplastic composite sheets reinforced with unidirectional continuous glass fibers in a four-layer 0–90 layup were used in this research. Experimental findings demonstrate that the failure of samples at room temperature is more similar to brittle failure and occurs suddenly, whereas at elevated temperatures, the failure resembles ductile failure and occurs gradually. Employing the Nakajima method, a forming limit diagram for the composite material was successfully established at both ambient and elevated temperatures. The resultant forming limit diagrams illustrate an augmented strain tolerance of the material at elevated temperatures. Notably, despite the increased depth of stretch observed at elevated temperatures in comparison to ambient conditions, a concomitant reduction in the force requisite to induce deformation is evident.

Improving the joint strength of thermoplastic composites joined by press joining using laser-based surface treatment

Fibre-reinforced thermoplastic composites (TPC) provide an automated and cost-effective solution for their use in lightweight structures in series production. The combination of different material configurations allows the design of highly stress tolerant components. Previous studies demonstrated that the combination of TPC sheets, TPC hollow profiles and injection moulding compounds is even suitable for crash-relevant automotive parts. All three components are combined during the injection moulding process. To prevent collapse, the part must remain in a consolidated state and cannot be preheated. However, this results in poor adhesion between the hollow profile, the bulk material, and the TPC sheet. Previous studies have shown that the bonding strength between the hollow profile and the injection moulding compound can be increased by surface pre-treatment using laser structuring and plasma technology. In this work, laser structuring is employed to enhance the bonding strength between the hollow profile and the TPC sheet. Microscopy analysis is used to investigate the resulting surface morphology. Subsequently, single-lap-shear (SLS) specimens are produced by pressing the TPC sheets onto the flat part. The resulting bonding strengths are then evaluated by tensile shear tests. The study analyses the impact of various pre-treatment parameters on the bonding strength. Furthermore, it investigates the effect of sheet temperature on the bonding strength, including specimens without pre-treatment. Finally, the results of the surface treatment of hollow composite profiles are discussed.

An Improved Mampel Model of the Non-Isothermal Crystallization Kinetics of Fiber-Reinforced Thermoplastic Composites.

Fiber-reinforced thermoplastic composites (FRTPs) are gaining increasing attention and widespread use in engineering applications due to their high specific strength and stiffness, excellent toughness, and recyclability. The mechanical properties of these composites are closely tied to their crystallization process, making it crucial to accurately describe this phenomenon. Existing theoretical models for analyzing the non-isothermal crystallization of thermoplastic composites often face challenges relating to the complexity of obtaining multiple parameters and the difficulty of achieving a final relative crystallinity of 1. To address these issues, this paper introduces a novel functional form of the crystallization rate parameter K(T), tailored for engineering applications, and proposes an improved Mampel model. This model assumes K(T) to be zero before the onset of crystallization and also to be linearly dependent on temperature thereafter, ensuring that the final relative crystallinity reaches 1. The model requires only two easily accessible parameters: the initial crystallization temperature (Ts) and the linear slope (k). The simplicity of the model makes it particularly well suited to engineering applications. This provides a straightforward and effective tool for describing the non-isothermal crystallization kinetics of fiber-reinforced thermoplastic composites.

Base-free trifluoroacetylation: From methyl glucopyranoside to cellulose nanofibers

Trifluoroacetic anhydride (TFAA) reacts smoothly with low molecular weight carbohydrates and cellulose nanofibers (CNFs) under base-free conditions. Methyl α- and β-d-glucopyranoside were used as model compounds to optimize reaction conditions, which were then applied to lyophilized CNFs for surface modification. ATR-IR spectroscopy and powder X-ray diffraction were employed to characterize the modified CNFs. Trifluoroacetylation for 4 h yields a degree of substitution (DS) of 0.4 acyl groups per anhydroglucose unit while maintaining a crystallinity index near 50 %. DS values were quantified by gravimetry, acid–base titration after saponification, and a novel approach utilizing solution 19F NMR spectroscopy which offers greater accuracy than the other techniques. This study presents an efficient, base-free method for derivatizing carbohydrates as well as surface functionalization of CNFs with trifluoroacetyl groups, potentially expanding their application in fiber-reinforced thermoplastic composites.

Coupled heat transfer–crystallization analysis in continuous carbon fiber-reinforced thermoplastic composites 3D printing: simulation and experimental validation

AbstractThis study proposes an advanced progressive numerical modeling approach to investigate heat transfer phenomena occurring in the 3D printing of continuous carbon fiber-reinforced co-polyamide (Copa) composites. The material extrusion process is simulated using element activation techniques and active cooling methods, while thermal boundary conditions are updated during the printing process. Differential Scanning Calorimetry (DSC) tests are conducted on composite and neat polymer samples to include the crystallization behavior, where the Hoffman–Lauritzen model is employed for crystallization modeling based on the input data from DSC tests. It is demonstrated that the proposed modeling approach, coupled with the Hoffman–Lauritzen crystallization model, accurately predicts the thermal history of the composite extrudate post-deposition. In the case of a neat polymer, the results of the developed FEM model align well with existing literature. Experimental in-situ temperature measurements utilizing thermal vision agree very well with the predictions of the heat transfer model developed for 3D printing of continuous fiber-reinforced Copa composites, demonstrating the model's capability to predict temperature profiles during printing.

Online monitoring of pre-crack initiation in carbon fiber-reinforced thermoplastic composites by an ultrasonic cutting tool using high-speed optical imaging and infrared thermography

The ultrasonic-assisted manufacturing process is a promising machining approach for composite materials as it exerts less force, making it ideal for the aerospace and automotive sectors. This work reports about the pre-crack initiation in carbon fiber reinforced (CF)/ poly-ether-ether-ketone (PEEK) composite under ultrasonic frequency at room temperature. An iron-based cutting tool matching the system’s resonance frequency (20 kHz) was used to perform the ultrasonic pre-cracking. In this novel work, the pre-cracking of CF-PEEK is considered as the initial step for a complete fiber layer separation, which holds the key for circularity options in high-performance aerospace composites. State-of-the-art high-speed camera and infrared thermography were combined to monitor the crack initiation and propagation. By online monitoring, the different stages involved in the pre-cracking process, its temperature evolution, and consequently the dissipated energy during pre-cracking under ultrasonic frequency were evaluated. The results showed that oscillation amplitude had a significant influence on the determined pre-crack depth and measured global temperature and energy compared to cutting force. The measured global temperature data indicates that pre-cracking occurred in the solid state with a temperature well below the glass-transition temperature of PEEK. However, the local temperature at the contact between the sample and sonotrode could have been much higher during ultrasonic cutting which needed further investigation. The computed global dissipated energy and temperature were only reliable at the pre-crack initiation site due to the limitation in the infrared thermography system.

Hygrothermal effects on the durability of resin‐infused thermoplastic E‐glass fiber‐reinforced composites in marine environment

AbstractThis paper presents a comparative assessment of hygrothermal effects on the mechanical and thermomechanical properties of resin‐infused thermoplastic E‐glass fiber‐reinforced composites (FRC) in the marine environment. The thermoplastic FRCs were immersed in seawater at two different aging temperatures, that is, 35 and 70°C. The quasi‐static tests were conducted on unaged and aged FRCs, followed by scanning electron microscopy (SEM) to determine the effect of the marine environment on the mechanical properties and damage progression. The specimens immersed at 70°C showed a significant drop of 46.7%, 39.7%, 22.6%, and 16% in mechanical properties (tensile, compression, flexural, and ILSS) mainly due to plasticization, matrix cracking, and fiber/matrix debonding. The specimens immersed at 35°C showed a reduction in tensile, compressive, and flexural strength of 10%, 14.7% and 1.9% respectively, with no significant effect on ILSS. In addition, dynamic mechanical analysis (DMA) reveals that prolonged aging induces an increase in glass transition temperature due to polymerization reactions. This work is intended to reveal the effect of extreme marine environment on the resin‐infused thermoplastic FRC and to provide a useful reference for their potential structural applications in the marine industry.Highlights Influence of aging conditions on the long‐term performance of FRCs. Hygrothermal aging leads to an increase in the glass transition temperature. The marine environment degrades mechanical properties of FRCs by up to 50%. Matrix cracking and fiber‐matrix debonding evolved as dominant failure modes.

Comparative Analysis of Water-Induced Response in 3D-Printed SCF/ABS Composites under Controlled Diffusion

Additive manufacturing (AM) or 3D-printing of fiber-reinforced composites (FRCs) has garnered significant interests for its versatility in creating intricate parts and rapid prototyping due to cost-effectiveness. Although short fiber-reinforced thermoplastic composites are challenging to manufacture, their mechanical properties can be easily tailored by adjusting fiber type, orientation, and volume fraction. However, void formation during printing is a key issue, impacting mechanical properties and facilitating water ingression, affecting long-term durability. This work studies water diffusion characteristics and the associated hydro-aging of 3D-printed short carbon fiber (SCF)/acrylonitrile butadiene styrene (ABS) composites with controlled water diffusion. Effects of material type (ABS and SCF/ABS), 3D-printing path (horizontal and vertical filament orientation), and diffusion surface (uni-directional and bi-directional diffusion) on water diffusion coefficient and maximum water absorption level are characterized to ensure the long-term durability of 3D-printed ABS and SCF/ABS composites. Baseline representative volume element-based finite element (RVE-FE) diffusion models were developed based on micro-computed tomography (micro-CT) image analysis to understand water diffusion characteristics. This work proves that the SCF/ABS composite is more resistive to hydro-aging than neat ABS due to the SCFs’ hydrophobic nature. SCF/ABS composites, while providing distinct advantages over pure ABS in terms of mechanical properties, could also be more effective against water environments.

Enhanced interlayer strength in 3D-printed PA12 composites via electromagnetic induction post-processing

Weak interlayer strength remains a critical limitation in the application of material extrusion 3D-printed parts. Herein, a non-contact method, electromagnetic induction post-processing, is proposed to address this issue. This method aims to enhance the weak interlayer strength of 3D-printed PA12 samples by introducing Fe3O4 particles for induced heat generation under alternating magnetic fields. The heat generation characteristics, surface morphology, crystallization behavior, and interlayer performance of 3D-printed samples subjected to induction post-processing are systematically investigated. The results indicate that a remarkable improvement in the interlayer strength of 3D-printed PA12 samples can be achieved through induction post-processing. Tensile strength along the Z-direction (perpendicular to the printing plane) exhibits a distinct increase of 218.3 %, while interlayer tear strength can rise by 328.1 %. Improvement in interlayer strength results from heat generation driving interfacial resin diffusion. Additionally, induction post-processing results in localized surface smoothing and a slight reduction in the crystallinity of the 3D-printed sample. Compared to traditional methods like in-oven heat treatment (annealing), induction post-processing offers higher efficiency by circumventing the initial constraints of heat transfer. Furthermore, the concept of selective induction heating (SIH) is proposed to achieve non-contact, localized heating by adjusting the composition of thermoplastics during printing. SIH holds good promise for applications in 3D-printed continuous carbon fiber-reinforced thermoplastic composites, including mold-free forming, complex surface welding, and repair (particularly in narrow and inaccessible areas).

An anchor-inspired interface for improving interfacial properties of carbon fiber-reinforced high-performance thermoplastic composites

Carbon fiber-reinforced thermoplastic composites are promising materials with many application prospects. However, surface inertness of CFs weakens the interfacial properties of these composites. Therefore, in this study, an anchor-inspired structure was designed and grafted onto CFs by using an anchor-inspired segmented copolymer, comprising of polyimide as the “chain” and polyhedral oligomeric silsesquioxane (POSS) as the “anchor”. In combination with atom transfer radical polymerization with the advantage of controllable molecular weight, degree of polymerization of the anchor-shaped structure with the best compatibility with poly (phthalazinone ether nitrile ketone) (PPENK) resin was pre-determined through molecular dynamics simulations, which reduced the experimental costs. The results of X-ray photoelectron spectroscopy indicated the successful connection of the numerous anchor-shaped structures to the CFs. Compared to composite made of origin fibers and PPENK, the interfacial shear strength at the microscopic level and interlaminar shear strength at the macroscopic level of grafted CF and PPENK composite increased by 184.9 % and 44.2 %, respectively. This is mainly attributed to the synergistic effect of mechanical interlocking and interfacial interaction between the anchor-shaped structure and the PPENK resin. This study serves as a feasible path to enhance the interfacial adhesion of composites by designing an anchor-shaped structure of organic macromolecules and inorganic nanoparticles on CFs.

Mechanical, Dielectric and Flame-Retardant Properties of GF/PP Modified with Different Flame Retardants.

With the rapid development of electronic information technology, higher requirements have been put forward for the dielectric properties and load-bearing capacity of materials. In continuous glass fiber-reinforced thermoplastic composites, polypropylene matrix is a non-polar polymer with a very low dielectric constant and dielectric loss, but polypropylene is extremely flammable which greatly limits its application. Aiming at the better application of flame retardant-modified continuous glass fiber-reinforced polypropylene composites (FR/GF/PP) in the field of electronic communication, the effects of four different kinds of flame retardants (Decabromodiphenyl ethane (DBDPE), halogen-free one-component flame retardant (MONO), halogen-free compound flame retardant (MULTI), and intumescent flame retardant (IFR)) on the properties of FR/GF/PP were compared, including the mechanical properties, dielectric properties and flame-retardant properties. The results showed that among the FR/GF/PP, IFR has the highest performance in mechanical properties, MULTI has better performance in LOI, DBDPE and IFR have better performance in flame retardant rating, and DBDPE and IFR have lower dielectric properties. Finally, gray relational analysis is applied to propose an approach for selecting the optimal combination (flame retardant type and flame-retardant content) of comprehensive performance. In the application exemplified in this paper, the performance of IFR-3-modified GF/PP is optimized.

Lessons learned from the sustainable recycling process of a wind blade made with a new thermoplastic resin

The use of thermoplastic resins instead of thermoset ones in wind turbine blade manufacturing is being investigated and validated in a global scale due to some theoretical improvements such as costs saving during production, shorter cycle’s time and a better circular recovery of the raw materials at the End of Life. The initial objective of this paper was to manufacture and test a small wind turbine blade (SWTB) glass fiber-reinforced thermoplastic (GFRT) resin composites, recycle it, and use the products obtained from the recycling process (fibers and resin) to remanufacture a new thermoplastic SWTB. But loss of fibers higher than estimated during the recycling process made to get away from the original aim of testing both blades (1st and 2nd recyclable blades). At least, some lessons learned were obtained to improve future developments. Nevertheless, this study provides an example of how to recycle a small WT blade and to remanufacture it using the same raw materials.

Energy transfer and release during the fracture of UD fiber-reinforced thermoplastic composites

This study delves into the complex dynamics of energy transfer and release during the fracture of unidirectional (UD) fiber-reinforced thermoplastic composites. Conducted through meticulous experimental observations and rigorous energy analysis, the research presents groundbreaking conclusions on the fracture toughness and energy conversion efficiency of UD carbon fiber composites under various loading conditions. A prominent focus is on how these mechanical properties are intricately linked to the sample’s fiber orientation angles and the external conditions applied during testing.The work employed tapered double cantilever beam (TDCB) as the far-field boundary to investigate the energy changes, transfer, and conversion processes during the crack propagation of unidirectional fiber reinforced thermoplastics (UDFRTPs) structures. It was found that throughout the entire propagation process, blunt extension occurs first followed by inertial extension. This is because in the initial stage of crack propagation, the stored elastic energy in the structure is relatively small, making the crack tip prone to blunting. This continuous blunting impedes the release of internal strain energy in the structure, with blunt extension accounting for a very small proportion of the entire fracture process. When the internal strain energy in the structure continues to increase to a certain extent, the blunting of the crack tip cannot prevent the release of a large amount of elastic energy inside the structure. At the same time, the excess released strain energy converts into kinetic energy and continually impacts the blunted region at the crack tip. At this point, the propagation transitions into the inertial extension stage, which occupies a significant portion of the entire fracture process.

Lignocellulosic abaca fibre-reinforced thermoplastic composites as future sustainable structural materials: a bibliometric analysis and literature review

Lignocellulosic abaca fibre-reinforced thermoplastic composites as future sustainable structural materials: a bibliometric analysis and literature review

Recent Trends of Recycling and Upcycling of Polymers and Composites: A Comprehensive Review

This review article gathers the most recent recycling technologies for thermoset and thermoplastic polymers. Results about existing experimental procedures and their effectiveness are presented. For thermoset polymers, the review focuses mainly on fibre-reinforced polymer composites, with an emphasis on epoxy-based systems and carbon/glass fibres as reinforcement, due to the environmental concerns of their end-of-life management. Thermal processes (fluidised bed, pyrolysis) and chemical processes (different types of solvolysis) are discussed. The most recent combined processes (microwave, steam, and ultrasonic assisted techniques) and extraordinary recycling attempts (electrochemical, biological, and with ionic liquids) are analysed. Mechanical recycling that leads to the downgrading of materials is excluded. Insights are also given for the upcycling methodologies that have been implemented until now for the reuse of fibres. As for thermoplastic polymers, the most state-of-the-art recycling approach for the most common polymer matrices is presented, together with the appropriate additivation for matrix upcycling. Mechanical, chemical, and enzymatic recycling processes are described, among others. The use of fibre-reinforced thermoplastic composites is quite new, and thus, the most recent achievements are presented. With all of the above information, this extensive review can serve as a guide for educational purposes, targeting students and technicians in polymers recycling.

Mechanical performances of continuous carbon fiber reinforced PEEK (polyether ether ketone) composites printed in a vacuum environment

Continuous fiber-reinforced thermoplastic (CFRTP) composites have attracted significant attention in various industries due to their exceptional mechanical properties and lightweight nature. Various methods have been applied to improve the mechanical properties of parts produced by fused deposition modeling (FDM), such as printing in a vacuum environment. Vacuum is utilized during printing to minimize heat transfer by convection, improve interfacial bonding, and reduce void formation. This study investigates the effects of vacuum and process parameters on the mechanical and microstructural properties of continuous fiber-reinforced thermoplastic composites. The goal was to investigate the effects of the printing parameters in a vacuum environment and therefore, enhance the mechanical properties. CFRTP test specimens were produced under various vacuum levels and processed at nozzle temperatures, heated bed temperatures, and printing speeds. Three-point bending tests were conducted to evaluate the flexural properties, and microstructural analysis was performed using optical microscopy. The results demonstrate the positive influence of vacuum on flexural performance and highlight the importance of controlling parameters, such as nozzle temperature and heated bed temperature for achieving enhanced mechanical properties. This study provides valuable insights into the production of higher mechanical properties of CFRTP composites and contributes to advancements in their manufacturing.

Novel thermoplastic matrix resin with low processing temperature and good interfacial strength for carbon fiber-reinforced polyethersulfone

Owing to the increased demand for carbon fiber-reinforced thermoplastic composites with excellent recyclability, there is a need to improve the interfacial bonding between the fiber and matrix. Hydroxy-functionalized polyethersulfone (PES), i.e., PES-OH, and epoxy resin (ER) were included to impart functionality to PES. A mixture of PES, PES-OH, and ERs with a weight ratio of 8:1:1 reduced the Tg by −18% compared with 100% PES. The enhancement of the interfacial properties increased the interlaminar shear, tensile, compressive, and residual compressive strengths by 50%, 22%, 43%, and 25%, respectively. This study can contribute to the development of carbon fiber composites for future mobility.

Enhanced mechanical performance of bamboo fiber/polypropylene composites via micro-nano reinforcing strategy

Developing high-performance plant fiber-reinforced thermoplastic polymer composites using environmentally friendly and cost-effective methods remains a significant challenge. In this study, we present a novel micro-nano strategy for producing robust short bamboo fibers (BFs) reinforced polypropylene (PP) composites (SBFPCs) without the need for chemical modification. Our approach involves the utilization of purified short micron BFs, which is surface-coated with holocellulose nanofibers (HNFs) extracted from bamboo parenchyma cells (BP). Through conventional injection processing, the resulting SBFPCs demonstrate remarkable mechanical enhancements with just a 0.2 wt% addition of HNFs compared to control samples. Notably, the mechanical properties of our SBFPCs surpass those of most reported short plant fiber-reinforced thermoplastic composites. The superior mechanical performance of our SBFPCs can be attributed to several factors, including the use of purified micron BFs with optimal aspect ratios as the primary reinforcement phase, enhanced interfacial mechanical interlocking between BFs and the PP matrix facilitated by the addition of HNFs, and the potential dispersion of HNFs within the PP matrix at submicron or nanoscale as a secondary reinforcement phase. This study highlights the promising application of SBFPCs in engineering areas with stringent mechanical requirements.