Continuous Fiber-reinforced Thermoplastic Composites Research Articles

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.

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.

Exceptional mechanical performance by spatial printing with continuous fiber: Curved slicing, toolpath generation and physical verification

This work explores a spatial printing method to fabricate continuous fiber-reinforced thermoplastic composites (CFRTPCs), which can achieve exceptional mechanical performance. For models giving complex 3D stress distribution under loads, typical planar-layer based fiber placement usually fails to provide sufficient reinforcement due to their orientations being constrained to planes. The effectiveness of fiber reinforcement could be maximized by using multi-axis additive manufacturing (MAAM) to better control the orientation of continuous fibers in 3D-printed composites. Here, we propose a computational approach to generate 3D toolpaths that satisfy two major reinforcement objectives: (1) following the maximal stress directions in critical regions and (2) connecting multiple load-bearing regions by continuous fibers. Principal stress lines are first extracted in an input solid model to identify critical regions. Curved layers aligned with maximal stresses in these critical regions are generated by computing an optimized scalar field and extracting its iso-surfaces. Then, topological analysis and operations are applied to each curved layer to generate a computational domain that preserves fiber continuity between load-bearing regions. Lastly, continuous fiber toolpaths aligned with maximal stresses are generated on each surface layer by computing an optimized scalar field and extracting its iso-curves. A hardware system with dual robotic arms is employed to conduct the physical MAAM tasks depositing polymer or fiber reinforced polymer composite materials by applying a force normal to the extrusion plane to aid consolidation. When comparing to planar-layer based printing results in tension, up to 644% failure load and 240% stiffness are observed on shapes fabricated by our spatial printing method. We demonstrate the versatility of our approach through various complex load cases which demonstrate their successful implementation of continuous fiber printing in 3D.

Impact of weave architecture on the mechanical performance of carbon-aramid/PVB hybrid composites

Continuous fiber-reinforced thermoplastic composites having superior mechanical properties are preferred for lightweight architectures. Rising demands for enhanced mechanical performance under certain types of loadings have focused researchers toward the hybridization of composite materials. In this study carbon and aramid fibers were employed to produce hybrid fabrics by weaving in two different woven architectures, 1/1 plain and 2/1 twill. Polyvinyl butyral (PVB) matrix was reinforced with these woven fabrics and hybrid composites were fabricated by compression molding. Un-hybrid carbon and aramid composites were fabricated using PVB matrix, as control samples. Tensile characteristics of hybrid composites offered intermediate strain at failures of 0.5% due to the combined rigid and ductile natures of carbon and aramid, respectively. Flexural strength and absorbed impact energy (200 MPa and 97 kJ/m2) were higher for hybrid composites, and quick elastic recoveries were experienced in hybrid composites after impact. Plain woven reinforced hybridization had about 25% and 5% lower tensile and flexural characteristics respectively, as more interlocking zones of warp and weft yarns reduced strength. However, these interlocking zones positively contributed to impact performance by 11.5% higher energy absorption.

Robot-assisted laser additive manufacturing for high-strength/low-porosity continuous fiber-reinforced thermoplastic composites

Additive manufacturing (AM) of continuous fiber-reinforced thermoplastic composites (CFRTPCs) has become a hot area for both academia and industry. In this paper, a robot-assisted laser additive manufacturing (RLAM) technique is proposed, which involves utilizing a laser beam to heat the filament to a semi-molten state, followed by compacting it with a roller and bonding it layer by layer to create densely structured components. Firstly, an integrated framework of hardware, software, and control systems is presented. Then, the relationship between the processing parameters and the properties of the final specimens was examined. Finally, a process strategy was proposed to improve the forming accuracy. Due to the effective impregnation of continuous carbon fibers, the printed CFRTPCs using the LRAM process exhibit comparatively low porosity and superior mechanical performance. Specifically, the flexural strength, flexural modulus, and interlayer shear strength reached 584 MPa, 43.7 GPa, and 28.0 MPa, respectively. The prepared specimens boast a porosity of 0.19%, approaching levels achieved through autoclave processes. In addition, it was found that the dynamic offset of the yaw axis could be utilized to correct the deviation of the actual forming path due to the pultrusion force, thus making the position of the towpreg under the rollers controllable and improving the accuracy of the parts. This new method combines the advantages of industrial robotics and laser&roller-based continuous fiber additive manufacturing processes to enable high-performance additively manufactured large and complex CFRTPCs, which shows great potential for printing lightweight structures in the rail transit and aerospace industries.

Simulated end-of-life reuse of composites from marine applications using thermal reshaping of seawater-aged, glass fibre-reinforced acrylic materials

In this work, end-of-life reuse of continuous fibre-reinforced thermoplastic composites from marine applications has been simulated by thermally reshaping (reprocessing) seawater-aged materials. Specifically, resin-infused, V-shaped glass/acrylic composites were seawater-aged (60 °C; 170 h) and reprocessed in a heated hydraulic press (120 °C; 10 bar). Reprocessing promoted void collapse and increased short beam shear strengths. Unaged reprocessed materials retained 52 % and 57 % performance in flexural strength and modulus, (relative to virgin material), with corresponding retentions of 20 % and 62 % in the aged reprocessed materials, respectively. Ageing- and reprocessing-related flexural performance changes occurred due to mild matrix plasticisation and fibre misalignment, respectively.

A Novel Combining Method for Composite Groove Structure Fabrication

A composite groove structure with high specific strength and light weight has great potential in industrial application, but few studies on this have been carried out due to the fact that it is difficult to fabricate by one of the existing methods. The purpose of this work was to propose a novel method combining 3D printing and filament winding to manufacture the groove structure and study the link between its mechanical strength needs and fabrication parameters. Specifically, filament winding and 3D printing were used to fabricate the cylinder part and complex ring slot part of the groove structure, which is difficult to fabricate by winding. The combining method took advantage of the winding’s high efficiency and the printing’s high forming degree of freedom. The specimen was taken from the structure and submitted to a short beam test to determine its interlaminar shear strength, whereas thermal tests were carried out to evaluate its mechanical performance under high temperature. The interlaminar shear strength reached 6.694 MPa at a fiber orientation of 90°, a heating temperature of 245 °C and a thickness of 0.5 mm. The SEM photo showed some voids and gaps and typical failure in the failed specimen. DMA and TGA were carried out to investigate the performance under high temperature, from which the storage modulus lost half to 120 °C. Overall, the proposed combining novel method offers a new direction in the fabrication of continuous fiber-reinforced thermoplastic composites’ groove structure.

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.

Experimental and Numerical Study of Healing Effect on Delamination Defect in Infusible Thermoplastic Composite Laminates.

The integrity of delaminated composite structures can be restored by introducing a thermally-based healing effect on continuous fiber-reinforced thermoplastic composites (CFRTPC). The phenomenon of thermoplastics retaining their properties after melting and consolidation has been applied by heating the delaminated composite plates above their glass transition temperature under pressure. In the current investigation, the composite is comprised of Methyl methacrylate (MMA)-based infusible lamination resin combined with benzoyl peroxide initiator, which polymerizes into a Polymethyl methacrylate (PMMA) matrix. For the reinforcement, unidirectional 220 gr/m2 glass filament fabric was used. Delamination damage is artificially induced during the fabrication of laminate plates. The distributed delamination region before and after thermally activated healing was determined by using non-destructive testing with active thermography. An experimental approach is employed to characterize the thermal healing effect on mechanical properties. Experimentally determined technological parameters for thermal healing have been successfully applied to repair delamination defects on composite plates. Based on the compression-after-impact (CAI) test methodology, the intact, damaged, and healed composite laminates were loaded cyclically to evaluate the healing effect on stiffness and strength. During the CAI test, the 3D digital image correlation (DIC) technique was used to measure the displacement and deformation fields. Experimental results reveal the difference between the behavior of healed and damaged specimens. Additionally, the numerical models of intact, damaged, and healed composite laminates were developed using the finite element code LS-Dyna. Numerical models with calibrated material properties and tie-break contact constants provide good correlation with experimental results and allow for the prediction of the mechanical behavior of intact, damaged, and healed laminated plates. The comparison analysis based on CAI test results and modal characteristics obtained by the 3D Laser Doppler Vibrometer (Polytec GmbH, Karlsbad, Germany) proved that thermal healing partially restores the mechanical properties of damaged laminate plates. In contrast, active thermography does not necessarily indicate a healing effect.

Recipe to Strengthen Continuous Fiber Reinforced 3D Printed Parts

Today, the design of polymer parts by additive manufacturing subjected to large stress has undergone a clear advance with the new concept of continuous fiber-reinforced thermoplastic composites (CFRTPC). The optimization of fiber alignment is the main asset to improve strength and has been widely discussed by the research community. In this work, the effect of the intercalation of the polymeric matrix (ONYX) between layers of continuous fiberglass reinforcement has been analyzed in shear specimens. Onyx is nylon mixed with short carbon fibers. The results show how inserting polymeric layers among the continuous fiber ones improves the shear strength up to 25% and the stiffness modulus up to 18%.

Fabrication of a 3D Printed Continuous Carbon Fiber Composite Grid Stiffened Structure Using Induction Heating.

In aerospace applications, composite grids have been widely utilized to enhance the strength of large thin-shell components. Recently, a growing focus has been on the research of 3D printing continuous fiber-reinforced thermoplastic composites. The 3D printing method offers various advantages over traditional molding processes, including a simpler process, higher material utilization, and lower manufacturing costs. However, the use of 3D printing for manufacturing continuous fiber-reinforced composite structures presents challenges, such as a high occurrence of defects within the structure and insufficient mechanical properties. These limitations hinder its widespread application. To address these issues, this study proposes a method for treating 3D-printed composite grid structures using induction heating. Initially, the induction heating mechanism of 3D-printed composite grids was analyzed by studying the impedance at the junction, including direct contact resistance and dielectric hysteresis loss. Subsequently, the impact of induction heating treatment on internal defects was explored by observing micro morphologies. The results show that the combination of induction heating and vacuum pressure effectively reduces porosities within the 3D-printed carbon fiber composite grids. Additionally, 3D-printed composite grid-stiffened PLA structures were fabricated with induction heating, and the bending and impact tests were conducted to evaluate their mechanical properties. The results indicate that using a grid-unit size of 4 mm leads to significant increases in bending strength and modulus of the grid-stiffened structure, with improvements of 137.6% and 217.8%, respectively, compared to the neat PLA panel. This demonstrates the exceptional mechanical enhancement efficiency of the 3D-printed lightweight composite grids.

Research Status of and Prospects for 3D Printing for Continuous Fiber-Reinforced Thermoplastic Composites.

Continuous fiber-reinforced thermoplastic composites (CFRTPCs) have advantages such as high specific strength, high specific modulus, corrosion resistance, and recyclability and are widely used in the fields of aerospace, rail transit, new energy, and so on. However, traditional methods for preparing CFRTPCs, such as placement and molding, rely more on forming molds, resulting in high manufacturing costs and a slow response speed, which limits the promotion and application of the new generation of CFRTPCs with complex configurations and designable performance. Three-dimensional printing can efficiently create products with multiple materials, complex structures, and integrated functions, introducing new ways and opportunities for the manufacturing of CFRTPCs. However, poor mechanical properties are the bottleneck problem in achieving 3D printing of CFRTPCs. This paper summarizes the research status of the fused deposition modeling (FDM) 3D printing process and the corresponding mechanical properties of CFRTPCs. The focus is on analyzing the influences of the FDM process parameters, such as the material type, printing temperature, speed parameters, layer thickness, scanning space, stacking direction, and fiber volume content, on the mechanical properties of CFRTPCs. Finally, the main problems and future prospects of current CFRTPCs-FDM are analyzed and forecasted, providing new references and ideas for 3D printing of high-performance CFRTPCs.

Global Continuous Toolpath Planning with Controllable Local Directions

Toolpath planning for Continuous fiber reinforced thermoplastic composites (CFRTPCs) 3D printing is a challenging task, which is vital to decrease the process complexity. In this paper, we propose a global continuous path planning method for CFRTPCs. First, for the set of 2D connected regions generated by slicing, we establish an optimized print sequence with a minimum idle stroke under interference constraints. Second, a continuous Zigzag path generation algorithm with controlled deposition direction is constructed for each 2D connected region, and path optimization is used to lessen the uneven deposition spacing. Finally, A separation axis theorem is used to prevent interference during the printing process, and we use a genetic algorithm to choose the connection points between 2D paths in a given spatial printing sequence to make the minimum idle stroke, creating a global continuous path with controllable deposition direction. The method proposed in this paper can provide the ability to customize the local deposition path direction and ensure the continuity of the global path to avoid interference and reduce the post-processing workload, so it is suitable for continuous path planning and multi-physics field optimization of complex structures, which can fully utilize the advantages of high-performance fibers to improve the customization ability and the performance of the fabricated parts for 3D printing and provide support for the manufacturing of high-performance structures in different fields.

Dual nozzle 3D printing strategy to improve the surface quality of continuous glass fiber reinforced polyamide 6 composites

AbstractA dual‐nozzle 3D printing technique was proposed to prepare continuous glass fiber reinforced PA6 (CGF/PA6) composites with sandwich structure. Short glass fiber reinforced PA6 filament was used for printing the surface layer and CGF/PA6 filament was used for inner part to provide high‐mechanical performance. Morphology of CGF/PA6 filament and the properties of printed composites samples were investigated. Printing process parameters were systematically optimized. The results showed that when CGF/PA6 part thickness of the composites samples was 2.8 mm, the flexural strength and flexural modulus, notched impact strength and interlaminar shear strength of the printed products can reach 275.4 MPa, 10.8 GPa, 168.2 kJ/m2, and 26.5 MPa, respectively. The dual‐nozzle 3D printing strategy in this work was of great significance for the precision fabrication of continuous fiber reinforced thermoplastic composites (CFRTPC), which can be widely used in aerospace, automotive, wind turbine blades, shipbuilding, and other industrial fields due to their excellent mechanical properties and ability to resist vibration and corrosion.

Tailorable mechanical and energy absorption behaviors of 3D printed continuous hybrid fiber reinforced composites

Abstract3D printing of continuous fiber‐reinforced thermoplastic composites (CFRPCs) has expanded potential structural application in recent years. However, it is still challenging to tailor the mechanical and energy absorption properties of 3D‐printed composites to fulfill the requirements for critical application conditions. Herein, hybrid fiber (HF) reinforced composites have been prepared by 3D printing of CFRPCs and investigated on the mechanical and energy absorption behaviors. Continuous virgin carbon fibers (CF), Kevlar fibers (KF) (130 Deniers (D), and 200 Deniers (D)) and E‐glass fibers (GF) were used as reinforcing fibers to produce hybrid and non‐hybrids composites. Hybrid composites with different combination of CF + GF, CF + 130D KF, and CF + 200D KF showed tailorable behaviors, such as flexural modulus (16,691.74, 20,372.38, and 19,017.44 MPa), tensile modulus (15,022.6, 16,269.41, and 15,320.58 MPa). And energy absorption behaviors of CF + 130D KF and CF + 200D KF were tailored in both tensile (18,865.25 and 20,302.07 N‐mm, respectively) and bending (3594.54 and 3570.80 N‐mm, respectively) tests compared to other composites which will be ideal for energy absorption applications. Moreover, CF + GF showed tailored strength which could be used in the need of high stiffness. SEM images were providing strong evidence to resist the fracture and breakage patterns, by tailoring the stiffness and elongation properties of fibers in hybrids specimens. Furthermore, positive hybrid effects of CF + KF hybrids in tensile and bending tests were also showing an ideal match of toughness and flexibility. In future, these cost and weight effective hybrids will have potential to apply in aerospace and automobile.

Quantifying the influence of reinforcement architecture on the planar mechanical properties of 3D-printed continuous fiber-reinforced thermoplastic composites

Quantifying the influence of reinforcement architecture on the planar mechanical properties of 3D-printed continuous fiber-reinforced thermoplastic composites

Evaluation of thermal and mechanical properties of continuous fiberglass reinforced thermoplastic composite fabricated by fused deposition modeling

AbstractFused deposition modeling (FDM) is utilized to fabricate continuous fiber‐reinforced thermoplastic composites (CFRTPCs) and can be considered an alternative to conventional processes. In present study, the specimens are 3D printed in Markforged Mark Two composite 3D printer by considering Onyx as matrix material and fiberglass as reinforcing material. Thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) of Onyx and fiberglass materials are done to investigate their thermal stability and composition. The effect of infill pattern and fiber orientation on tensile and drop impact properties are examined. The TGA results show that the initial decomposition in Onyx is higher compared to fiberglass due to more evaporation of moisture content in Onyx. The FTIR analysis confirmed that the spectrum for both materials is same within the range of wave number from 4000 to 1500 cm−1. The tensile test results represent that the specimen with triangular infill pattern and 0°/90° fiber orientation resulted in maximum tensile strength of 148.01 MPa and the drop impact test results showed that the triangular infill pattern with 0°/90° fiber orientation absorbs maximum impact energy which is 14.90% and 8.98% higher compared to honeycomb and rectangular pattern respectively. Further, the fracture behavior study is carried out based on the optical images of fractured specimens.

An Investigation of Printing Parameters of Independent Extrusion Type 3D Print Continuous Carbon Fiber-Reinforced PLA

Fused filament fabrication (FFF) technology is highly favored by various industries as the simplest and most commonly used technology in additive manufacturing. The embedding of continuous fiber-reinforced thermoplastic composites (CFRTC) is a great help to compensate for the mechanical properties of FFF-printed specimens. In this paper, the optimal printing parameters of printed specimens containing continuous carbon fiber-reinforced PLA were investigated by the Taguchi method, full factorial analysis, and the tensile test. Fiber printing layer thickness and fiber printing speed are significant factors. After excluding the influence of fiber overlap, the optimal printing parameters were obtained. When the thickness of the fiber printing layer is 0.05 mm, the speed of the fiber printing nozzle is 250 mm/min, and the temperature of the fiber printing nozzle is 210 °C, the maximum tensile stress of the sample is 189.52 MPa. In this paper, the maximum tensile stress of the specimen printed by different printing parameters can be doubled, which shows the influence of printing parameters on the mechanical properties of the specimen. Compared with the specimen using pure PLA printing, the increase was 703.5%. Then the failure mechanism of 3D-printed CFRTC specimens with different layer thicknesses was investigated by using microstructural morphology and tensile fracture interfacial property analysis. The influence of layer thickness parameters on the interfacial bonding force was revealed. Through analysis, it is found that the lower the thickness of the specimen printing layer, the better the interface bonding force of the specimen, and the minimum layer thickness suitable for FFF independent extrusion printer is found.

The Relationship Between Fiber Bundle Size and Mechanical Performance of Additively Manufactured Continuous Carbon Fiber Reinforced Thermoplastic Composites.

Additively manufactured continuous fiber-reinforced thermoplastic (CFRTP) composites are still in the early stages of reaching competitive mechanical properties compared with conventional composites. The main reason for this is that their mechanical properties are limited due to weak interlayer strength, porosity, and low fiber fraction. Therefore, the effects of many parameters, such as layer thickness, temperature, printing speed, and fiber fraction, have been extensively studied to improve mechanical properties. With a different perspective on these parameters, this study aimed to investigate the effect of fiber bundle size on the mechanical properties of CFRTP composites. For this purpose, 3K and 6K fiber bundle filaments with the same fiber volume fractions (∼41%) were produced utilizing a polymer impregnation setup. CFRTP samples were printed using fused deposition modeling with polylactic acid as the matrix. The mechanical properties were investigated via three-point bending, interlaminar shear strength (ILSS), and tensile tests. The results showed that fiber bundle size does not particularly influence tensile strength but dominates flexural and ILSS performance. Although increased flexural strength and modulus were observed, the bundle size effect was much more dominant in ILSS tests, and 6K bundle size samples with the same fiber fraction showed much higher strength.

Strength analysis of carbon fiber reinforced PEEK composites with heat resistant sizing agents

Continuous Fiber Reinforced Thermoplastic Composites (CFRTPCs) are known for their demand in high-tech industries due to their excellent mechanical, thermal and chemical performance. However, poor adhesion interaction between carbon fiber (CF) and high-performance polymers such as PEEK tend to influence the mechanical modulus of the composite parts in a negative way. In the current work, a number of PAA-based sizing agents modified with various fillers were used for CF surface treatment in order to improve adhesion. Thus, the wettability of the sizing agents was studied, as well as the free surface energy using the Owens-Wendt method. The calculated energy values were used to determine the work of adhesion between the sizing agents and PEEK. The adhesive connection between the CF treated with the sizing agents and PEEK was examined by the single fiber pull-out testing. Furthermore, the most promising samples were used for CF, on the basis of which towpreg composites samples were obtained to study its physico-mechanical properties. Results suggested that the values of the strength characteristics of the composites are comparable to the values measured for composites based on commercially available materials.