Polymer Composite Parts Research Articles

Prediction of Flexural Properties of Additively Manufactured Short Fiber-Reinforced Polymer Composite Parts

Prediction of Flexural Properties of Additively Manufactured Short Fiber-Reinforced Polymer Composite Parts

Comparing Degradation Mechanisms, Quality, and Energy Usage for Pellet- and Filament-Based Material Extrusion for Short Carbon Fiber-Reinforced Composites with Recycled Polymer Matrices

Short carbon fiber (sCF)-based polymer composite parts enable one to increase in the material property range for additive manufacturing (AM) applications. However, room for technical and material improvement is still possible, bearing in mind that the commonly used fused filament fabrication (FFF) technique is prone to an extra filament-making step. Here, we compare FFF with direct pellet additive manufacturing (DPAM) for sCF-based composites, taking into account degradation reactions, print quality, and energy usage. On top of that, the matrix is based on industrial waste polymers (recycled polycarbonate blended with acrylonitrile butadiene styrene polymer and recycled propylene), additives are explored, and the printing settings are optimized, benefiting from molecular, rheological, thermal, morphological, and material property analyses. Despite this, DPAM resulted in a rougher surface finish compared to FFF and can be seen as a faster printing technique that reduces energy consumption and molecular degradation. The findings help formulate guidelines for the successful DPAM and FFF of sCF-based composite materials in view of better market appreciation.

METHODS OF QUALITY CONTROL FOR AEROSPACE PARTS, PRODUCED WITH 3D-PRINTING OUT OF COMPOSITE-REINFORCED POLYMERS

One of the features of parts, made from polymer composite materials, is that the part and material are both formed at once, when the part is being made. Complexity of interaction processes between matrix and reinforcing fiber makes it difficult to achieve prognosed characteristics of part due to possible imperfections of manufacturing processes and technology. Therefore, an important part of parts life cycle is quality control. Quality control can be destructive or non-destructive, the latter giving more information and insight on defects of the part itself and, possibly, at flaws in manufacturing technology. With the increase in popularity of use of additive manufacturing technologies, especially – FDM 3d-printing, in aerospace industry, there’s a need to improve the performance of parts. Benefits of FDM 3d-printing is the absence of need for specialized forming equipment and tools, especially for forming the parts with complex, topologically-optimized geometry and structure. One of the ways to improve printed parts performance and its physical properties is to use continuous fiber reinforcement. Because of need to control the state and position of the fiber in the part, quality control is also an important part of this type of additive manufacturing. Existing popular methods of quality control, used in polymer composite materials part manufacturing were reviewed. Also, the features and limitations, imposed by structure of printed parts and printing technology were reviewed as well, the differences of them and polymer composite parts made in traditional forming ways, were noted too. The destructive testing methods reviewed are tensile stress testing, bend testing and impact stress testing. The non-destructive quality control methods reviewed are visual, acoustic, radiological and ultrasound. Also, recommendations on their use on FDM 3d-printed parts were formed. As a result, visual and ultrasound methods were accepted as non-destructive methods of quality control, with need to perform destructive tests on sample parts as well. Also, as a promising method, thermography was proposed, yet because of the limitation of using it with high-temperature polymers, its utility is also limited.

Concave and convex small radius bending behavior of single and multiple layers reinforcement fabrics

Multilayer reinforcement fabrics are increasingly used for manufacturing structural polymer composites. In liquid molding processes, dry reinforcement fabrics are draped on a mold first, and infused with a liquid resin such as an epoxy in a subsequent manufacturing step. This presents major advantages in terms of operational flexibility and costs. However, draping multilayer reinforcement fabrics on complex mold geometries is challenging. Small radius mold corners constitute a major manufacturing challenge as they lead to variability in dry fabric positioning and resin-rich corners in polymer composite parts. Spring-back of fabrics bent over or into single curvature mold corners is a widespread industrial concern. However, contrary to draping over double-curvature surfaces, bending spring-back from convex or concave single-curvature corners has received very limited attention. No testing method is available. This paper quantifies reinforcement fabric bending spring-back. Single and multiple layer stacks were bent along three directions over convex and into concave 90° corners with five radii spanning 1.59 mm to 12.70 mm. In all cases, five replicated tests enabled variability quantification. Fabric stacks were also quantified using cantilevered bending tests for comparison purposes. Mold radius was found to affect the behavior to a larger extent than testing direction, number of layers or use of a binder.

Corner cutting accuracy for thin-walled CFRPC parts using HS-WEDM

Carbon Fiber-Reinforced polymer (CFRP) composite parts with thin-walled corners are in great demand in aircraft, cars, and precision instruments. Nonetheless, the fabrication of these parts is difficult due to their low stiffness. High-speed WEDM is an advanced technique for cutting thin CFRP components as it is a non-contact method for removing materials. Nonetheless, testing results demonstrate an unavoidable deformation in the thin-walled corners of the CFRP composite. The objective of this study is to improve the accuracy of corners in thin-walled CFRP composite parts. The research utilized a Taguchi L16 orthogonal array to investigate the influence of various process parameters, including pulse-on duration (Pon), pulse-off duration (Poff), and input current (I), as well as the parameter CFRP plate thickness (T), on corner inaccuracy. The CFRP thickness varied between 0.5, 1.0, 1.5, and 2.0 mm, and the corner angles examined were 30°, 60°, 90°, and 120°. Additionally, a second-order polynomial regression model was used to determine the correlation between the process parameters and corner inaccuracy at various corner angles. Also, a multi-response optimization technique using a composite desirability coupled with a generalized reduced gradient were used to find the optimal process combination across various CFRP thicknesses. According to the research findings, the most relevant process parameters impacting corner accuracy at different angles were the pulse-on duration and input current. To achieve accurate corners with different angles, the optimal process parameters were identified: Pon (40µs), Poff (15µs), and I (4A) for CFRP thicknesses 0.5 and 1.0mm, and Pon (45μs), Poff (30μs), and I (2A) for thicknesses 1.5 and 2.0mm.

Performance of delaminated CFRP composite under pure bending using two-dimensional digital image correlation

ABSTRACT Delamination is an interlaminar damage which may be pre-existing in multilayered fibre reinforced polymer composite parts due to manufacturing imperfections or generated by out of plane loading during service life. Its existence leads to significant reduction of structural integrity, strength and stiffness of the material. Hence, to study the effect of induced delamination on the performance of a composite under pure bending, a circular polytetrafluoroethylene (PTFE) film was introduced between the second and third plies of a sixteen layered carbon/epoxy laminate during fabrication. The bending tests were conducted in displacement control mode. The displacements and strains were measured through the thickness of the composite using two-dimensional digital image correlation. The damage modes were captured using CCD camera and the causes were explained. The flexural strength and modulus of composite were 329.74 MPa and 104.58 GPa respectively. The delaminated composite behaved as a single member without any crack within the elastic range. The existence of PTFE drastically reduced flexural stiffness of composite beyond the stress at 75.81% of its ultimate strength. The ± 45º plies offered low mechanical performance against the induced off axis loading. Hence, in these plies fibre breakage was higher. In the portion of PTFE, the strains were higher due to larger outward displacements produced by local buckling.

Active control of cure-induced distortion for composite parts using multi-zoned self-resistance electric heating method

High dimensional accuracy of the carbon fiber reinforced polymer (CFRP) composite parts has been a long-term challenge for manufacturers in the aerospace industry. Traditionally, the uneven curing temperature could aggravate the cure-induced distortion (CID) and should be avoided as much as possible. But even under an ideally uniform temperature field, the CID of curved parts still cannot be eliminated because of the anisotropic shrinkage nature of the CFRP laminate. In this work, a novel CID control method based on the multi-zoned heating methodology is proposed, which actively applies an optimized non-uniform temperature field in different zones of the part to counteract the CID influenced by geometric structures. The counteracting principle of the proposed method lies in that using the actively formed through-thickness temperature gradients in different zones generates numerous small local thermal deformations, and their combination can significantly reduce the overall CID of the CFRP part. A co-optimization framework combined with the numerical model and genetic algorithm is established to rapidly compute the optimized multi-zoned temperature field for the CFRP parts with arbitrary complex structures. A good agreement between the numerical and the previous experimental results shows the effectiveness of the numerical model, and the multi-zoned temperature field optimization case of a scaled air-intake CFRP part demonstrates the performance of the co-optimization framework. Finally, by using the multi-zoned self-resistance electrical heating method, the CID reduction of the proposed method is experimentally validated on a complex CFRP part, where the average displacement reduces by >60 % compared to that of the traditional oven process.

Application of micro-computed tomography for authentication of 3D printed composite parts

• Tomography analysis is used to study 3D printed fiber-reinforced composite parts. • The samples are different in infill printing direction and the presence of an outer wall. • Part identification methods are developed based on fibers, porosity, and printing features. • Frequency domain analysis captures distinguishing differences in CT datasets. • The result can be used for part authentication procedures for AM composite parts. Additive Manufacturing (AM) can apply unique customized printing patterns for each layer, which govern the microstructural features in a fiber-reinforced composite part. Non-destructive evaluation methods are used extensively to understand the defects and the microstructure of 3D printed composite parts. Considerable intellectual property is involved in designing and manufacturing composite parts, which needs to be protected using innovative methods. One of the concerns in this area is counterfeit parts made on high quality 3D printers, which need to be identified. This study aims to investigate and provide a part-authentication methodology for 3D printed composite parts by using the micro-computed tomography ( μ CT) scans of discontinuous fiber-reinforced polymer composite (FRPC) parts. The microstructure of FRPC contains fibers, matrix and porosity that are unique to the specimen and is a result of the printing parameters. Specimen A is printed with an infill direction of 90 ∘ and wall count of 3 and specimen B has the same infill direction but does not contain a wall boundary. A comparison between the different μ CT datasets of the specimens can identify the distinguishing features of the 3D printed composite part. The correlation developed across different μ CT datasets from extracted features and the metrics formulated can be used to quantitatively differentiate the composite specimens. Frequency domain analysis shows the most promising results by correctly identifying 3 out of the 6 datasets belonging to the same AM. A part identification and authentication method for AM composites will be useful for identifying genuine or counterfeit parts and protect intellectual property.

A Comparative Analysis of Chemical, Plasma and In Situ Modification of Graphene Nanoplateletes for Improved Performance of Fused Filament Fabricated Thermoplastic Polyurethane Composites Parts.

The limited number of materials and mechanical weakness of fused deposition modeling (FDM) parts are deficiencies of FDM technology. The preparation of polymer composites parts with suitable filler is a promising method to improve the properties of the 3D printed parts. However, the agglomerate of filler makes its difficult disperse in the matrix. In this work, graphene nanoplatelets (GnPs) were surface modified with chemical, low-temperature plasma and in situ methods, in order to apply them as fillers for thermoplastic polyurethane (TPU). Following its modification, the surface chemical composition of GnPs was analyzed. Three wt% of surface-modified GnPs were incorporated into TPU to produce FDM filaments using a melting compounding process. Their effects on rheology properties and electrical conductivity on TPU/GnPs composites, as well as the dimensional accuracy and mechanical properties of FDM parts, are compared. The images of sample facture surfaces were examined by scanning electron microscope (SEM) to determine the dispersion of GnPs. Results indicate that chemical treatment of GnPs with zwitterionic surfactant is a good candidate to significantly enhance TPU filaments, when considering the FDM parts demonstrated the highest mechanical properties and lowest dimensional accuracy.

Synthesis and characterization of flyash reinforced polymer composites developed by Fused Filament Fabrication

Fused filament fabrication (FFF) has seen an upsurge in its utilization towards development of tailored made materials of polymer base. The advancement and diversity in fabricating the polymer composite parts by using FFF has seen the embracement of this technology in wider aspects, ranging from automotive, aerospace, construction and has marched towards day to day requirements. This research article focuses on development of polymer composite; by using flyash (FA), an industrial waste produced during coal combustion, as reinforcement in Acrylonitrile butadiene styrene (ABS) matrix, to study the physical and mechanical properties. FA, which is primarily made up of metal oxides, plays an imperative role as reinforcement. Easily and abundantly available, FA is being used in several applications to reduce the landfills utilization and also helps the environment. In this study FA was added as reinforcement in 5 and 10 wt. % respectively to ABS matrix and was developed into filament of 1.75 mm diameter. The developed ABS + FA polymer composite using FFF, were analyzed for physical and mechanical properties as per American Society for Testing and Materials (ASTM) standards. Microstructure studies were carried out for the developed composite to understand their behavior in enhancing the dimensional accuracy and tensile strength with incremental addition of FA up to 10 wt%. Tensile strength was enhanced by 28.19% and 36.13% for ABS + 5wt. % FA and ABS + 10wt. % FA respectively. Dimensional stability was also enhanced. Similarly, surface roughness analysis was carried out and it was observed to reduce with addition of FA. The surface roughness measurements provided suitable results of decrement by 9.64% and 14.6% for ABS + 5wt. % FA and ABS + 10wt. % FA respectively. Overall, the usage of FA along with FFF, has paved a path in sustainable and green technology in manufacturing.

The effect of preforming and infusing bindered and unbindered carbon non-crimp-fabrics on the final quality of composites parts

Vacuum infusion (VI) is a liquid moulding process used to manufacture fibre-reinforced polymer composite parts. The VI process for non-crimp fabric (NCF) preforms is one of the most promising processes for improving the quality and cost efficiency of traditional processes using prepregs and autoclave curing. An understanding of the preform thickness behaviour in the compaction, wetting, and curing stages is necessary to optimise the overall process and obtain high-performance composite parts. In this study, the influence of the material, preforming, and infusion parameters on the thickness of four different carbon NCF laminates were investigated. The preforming behaviour includes the influence of the NCF composition, such as the presence of an organic binder or the number of compaction steps. Infusion was characterised using dielectric analysis (DEA). The properties of the resulting composites were analysed in terms of the fibre volume fraction (FVF) and porosity, as measured using X-ray computed tomography (CT). The main consequence of the outcome of the present study is that, from a manufacturing point of view, downward through-thickness resin infusion offers benefits in terms of thickness, FVF, and porosity tolerance. In addition, the acquired results allow for the identification of the main settings for an optimised consolidation strategy, which could be used for manufacturing NCF composite parts.

Технологические основы обработки полимеркомпозитных деталей гибким абразивным инструментом

There are presented investigation results of polymer-composite parts abrasion. The dependences for the definition of surface roughness at polymer-composite material hydro-abrasive cutting are shown. The results of theoretical and experimental investigations of hydro-abrasive cutting processes are presented. A procedure for their carrying out, tool and equipment used is described. The results of experimental investigations on polymer-composite parts preparation to splicing are shown. A procedure for designing a technological process of polymer-composite parts abrasion is offered.

Infiltration behavior of liquid thermosets in thermoplastic powders for additive manufacturing of polymer composite parts in a combined powder bed fusion process

AbstractPolymer‐based multimaterial additive manufacturing (AM) has developed into one of the most promising technologies of recent times. A processing concept was developed in previous studies, which targets the implementation of reactive liquids in a thermoplastic powder‐bed for the creation of multimaterial polymer composite parts. This process aims to be the first AM process of its kind to fully utilize the potentials of both thermoplastic and thermoset polymers simultaneously. A highly important aspect for this process is the investigation of the infiltration behavior of the reactive liquids within the powder bed, since premature or delayed curing of the liquids could lead to deviations from the intended geometry as well as process errors due to material protrusions. This investigation presents an experimental and a mathematical approach to describe and predict the time which a droplet needs to completely infiltrate the powder bed. The results showed, that the experimental setup is viable to observe the droplet height over time at temperatures of up to 105°C and infiltration times below 500 ms. The mathematical model proved to be a powerful approximation to describe the infiltration behavior of a reactive liquid within a thermoplastic powder bed once a material‐specific form factor is determined for each powder material. Through the process of elimination, the independence of the form factor was demonstrated for different powder parameters like the particle size. A theory is presented, which correlates the form factor to the microstructural shape and surface condition of the particles based on SEM images.

Research progress in manufacturing multifunctional polymer composite materials based on fused deposition modeling technology

3D printing technology, also known as additive manufacturing technology, is based on materials, mechanical control, computer-assisted design and other multi-cross disciplines. 3D printing enables fabrication of complex structure materials which cannot be fabricated by traditional methods. Fused deposition modeling (FDM) is one of the most well-known 3D printing technologies due to its merits like cost-effectiveness, simple in equipment and ease of operation, which has been widely used in aerospace, medical and auto industry. This review introduced the overall layout, development and planning of 3D printing technologies. This review also systematically summarized the characteristics and classifications of common 3D printing technologies, and mainly focused on the principles, advantages and requirements for the FDM technology. Especially, we aim to outline the basic requirements of polymer that suitable for FDM printing and introduce the applications of carbon-based polymer composite materials in the FDM manufacturing process. In addition, recent advances of FDM printing in fabrication of functional polymer composite materials and parts, including biomedical, electrical and thermal conductive polymer composites are reviewed in detail. The prospects for the research and applications of FDM towards manufacturing of high-performance and multifunctional polymer composite materials are proposed. At last, the challenges and key problems that need to be solved in FDM processing are considered and prospected.

Synthesis of Multilayered DLC Films with Wear Resistance and Antiseizure Properties.

Diamond-like carbon (DLC) films have attracted considerable interest for application as protective films in diverse industrial parts. This is attributed to their desirable characteristics, such as high hardness, low coefficient of friction, gas-barrier properties, and corrosion resistance. Antiseizure properties, in addition to wear resistance, are required during the die molding of polymer and polymer-matrix composite parts. Graphite films can be easily peeled because the vertically stacked graphene sheets are bonded via weak van der Waals forces. The present study demonstrates the fabrication of multilayered DLC/Cu films, where the Cu film functions as a catalyst for the formation of a graphite-like layer between the DLC and Cu films. The DLC/Cu film was synthesized on a Si (100) substrate via plasma-enhanced chemical vapor deposition and magnetron sputtering. The peelability, wear resistance, microstructure, texture, and cross-section of the film were experimentally analyzed. The results indicated a variation in the peelability with the deposition conditions of the Cu film that comprised particles with diameters of several nanometers. The DLC film at the interface in contact with the Cu film was transformed into a graphite-like state i.e., graphitized. The surface of the multilayered film exhibited antiseizure properties with the peeling of the upper DLC film. The multilayered film also exhibited wear resistance owing to the repeated appearances of a new DLC film. It is expected that the wear-resistant films with antiseizure properties demonstrated in the present study will be utilized in various industrial sectors.

Small-diameter optical fibre sensor embedment for ambient temperature cure monitoring and residual strain evaluation of CFRP composite laminates produced by vacuum-assisted resin infusion

Out of autoclave (OoA) processing techniques, such as liquid composite moulding techniques (LCM) and, particularly, the vacuum-assisted resin infusion (VARI) technique, are being used, with increasing success, in replacement of prepreg/autoclave technologies to produce structural aircraft/aerospace polymer composite parts, due to its better cost effectiveness and competitiveness. This work aims to embed Fibre Bragg grating (FBG) sensors to monitor the VARI manufacturing of carbon fibre reinforced polymer (CFRP) composites and evaluate the associated phenomena: ambient curing and post curing reactions and resulting residual strains. The curing kinetics of the epoxy resin system alone was initially studied through isothermal differential scanning calorimetry (DSC) tests and applying the isoconversional Friedman method, and further studied by strain monitoring during ambient curing and post curing resorting to FBG sensors. The FBG sensors in the CFRP laminates were able to detect a subtle increase of strain as infusion of the CFRP started and to measure decreasing strain as resin filled in the dry fabric layers. Subtle strain decrease revealed forming crosslink bonds. Compressive strains measured by the FBG sensors during post curing show that further crosslink takes place. A comparison of resultant residual strains was made between specimens with embedded FBG sensors on small-diameter optical fibres (SDOF) and on large-diameter optical fibres (LDOF).

A review of factors that influence the fracture toughness of extrusion-based additively manufactured polymer and polymer composites

Fracture toughness, is a critical aspect of a component’s strength and structural integrity. In additive manufacturing (AM) of polymers and polymer composites, the fracture toughness of the manufactured part is influenced by the bonding between the layers which is dependent on the material, geometric and processing parameters. Known factors that influence the bond strength and interfacial adhesion in 3D printed parts can be broadly divided into three main categories; 1) deposition related conditions (direction, nozzle size and geometry, temperature), 2) solidification related conditions (heat transfer, molecular movement, crystallinity and void formation) which also play a major role in defining properties and 3) composition and rheological behavior of the resins and the fiber microstructure (content, orientation and surface treatment). In this review, we identify factors that have been reported to influence interface bonding in 3D printed polymer and polymer composite parts. We discuss best practices, as recommended in the reported literature, to address fracture behavior and strategies to improve fracture toughness and structural integrity. Due to the layer-by-layer nature of 3D printed parts, which makes them orthotropic, most AM studies are mainly focused on application of Mode I and mixed mode loading to characterize interlaminar fracture toughness. Intralaminar and translaminar toughness behavior have mostly remained untouched or scarcely discussed in the AM literature. Our focus is to specifically address fracture toughness of 3D printed polymer composites made using the fused filament fabrication (FFF) additive manufacturing method. The material, process and geometric parameters used in FFF will impact the adhesion between layers and hence the fracture toughness and structural integrity. The review identifies the parameters that play key roles and discusses the mechanisms put forth by various researchers that influence the fracture toughness behavior under various modes of fracture. Important gaps in the literature are identified and the future outlook of AM using the FFF process is discussed.

Design technique of highly efficient technological processes for preparation of polymeric composite parts for adhesive bonding

This paper presents the results of technological machining of polymer composite parts with the flexible flap wheels for further adhesive bonding. The peculiarities of polymer composite materials and their application field are revealed. Constructions that use polymer composite material parts are described.The article identifies the process of gluing parts made of polymer composites, as well as features of ensuring the strength of the adhesive joint after mechanical processing of bonded parts.Methodology of modes processing selection and structural-geometric tool parameters for the processing of surface parts under the adhesive bonding is elaborated. Theoretical studies of processing the polymer composite parts with the help of flap wheels are conducted. The surface roughness model is developed. A considerable amount of experimental research has been carried out. The tools for machining and cutting modes are selected. The strength of the glue connection of the details processed by the flap wheels is examined. To compare the durability of the received glue connections and the combinations executed according to the factory technology, the reference surfaces of the samples used at comparative control of quality sanding are investigated. The theoretical and experimental results are compared. Their high convergence is established. The adequacy of the theoretical dependence in compliance with the Fisher criterion is checked. Effective methodology for designing highly efficient technological processes tested in industrial conditions is presented. It allowed to reduce the processing time in more than 2 times, while providing the high strength adhesive bonds.

Towards intelligent CFRP composite machining: Surface analysis methods and statistical data analysis of machined fibre laminate surfaces

Many carbon fibre reinforced polymer composite parts need to be edged trimmed before use to ensure both geometry and mechanical performance of the part edge matches the design intent. Measurement and control of machining induced surface damage of composite material is key to ensuring the part retains its strength and fatigue properties. Typically, the overall surface roughness of the machined face is taken to be an indicator of the amount of damage to the surface, and it is important that the measurement and prediction of surface roughness is completed reliably. It is known that the surface damage is heavily dependent on the fibre orientation of the composite and cutting tool edge condition. This research has developed a new ply-by-ply surface roughness measurement methods using optical focus variation surface analysis and image segmentation for calculating areal surface roughness parameters of a machined carbon fibre composite laminate. Machining experiments have been completed using a polycrystalline diamond edge trimming tool at increasing levels of cutting edge radius. Optical surface measurement and µ-CT scanning have been used to assess machining induced surface and sub-surface defects on individual fibre orientations. Statistical analysis has been used to assess the significance of machining parameters on Sa (arithmetic mean height of area) and Sv (areal magnitude of maximum valley depth) areal roughness parameters, on both overall roughness and ply-by-ply fibre orientations. Empirical models have been developed to predict surface roughness parameters using statistical methods. It has been shown that cutting edge degradation, fibre orientation and feed rate will significantly affect the cutting mechanism, machining induced surface defects and surface roughness parameters.

Preparation of short CF/GF reinforced PEEK composite filaments and their comprehensive properties evaluation for FDM-3D printing

Fused deposition modeling (FDM) has been successfully applied to fabricating short fiber reinforced polymer composites parts. However, due to the intrinsically limited mechanical properties of matrix polymers, there is critical need to develop fiber reinforced high-performance thermoplastic composites for FDM-3D printing to expand engineering applications. In this work, the potential of FDM-3D printing short carbon fiber (CF) and glass fiber (GF) reinforced high-performance PEEK composites has been investigated. Composite filaments with fiber contents of 5 wt%, 10 wt% and 15 wt% were prepared using extrusion process and characterized by micromorphology observation; and thermal properties testing demonstrated its better thermal stability than pure PEEK. The performance evaluation of printed CF/GF-PEEK parts was focused, including mechanical properties, microstructure, surface quality and porosity. The results indicate that the addition of CF/GF to PEEK can significantly enhance the tensile and flexural strength at the cost of ductility. Lower fiber content of 5 wt% is conducive to increasing mechanical properties, improving surface quality and reducing porosity of printed CF/GF-PEEK. GF/PEEK has better interfacial bonding than CF/PEEK due to the different surface treatments on fibers. Furthermore, microstructure observation suggests that fibers aligned along the printing orientation can strengthen the properties, while pores lead to performance degradation of 3D printed CF/GF-PEEK.