Continuous Fiber-reinforced 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.

Damage identification and fracture behavior of 2.5D SiCf/SiC composites under coupled stress states

Continuous fiber-reinforced silicon carbide composites have received significant attention due to their high-temperature mechanical stability. However, their widespread implementation has been hindered by intricate fracture mechanisms and limited toughness. This study presents a real-time approach for identifying damage type in 2.5D SiCf/SiC composites and highlights the significant impact of minor eccentric loading angle on the fracture behavior and mechanical properties using acoustic emission (AE). Even a slight degree of eccentric loading angle can significantly alter the fracture behaviors, leading to a significant increase in fracture toughness. The fracture damage evolution law of 2.5D SiCf/SiC under varying eccentric loading angles was investigated with the help of the AE damage identification, fracture morphology and finite element analysis. These findings provide valuable insights for multi-axis stress analysis of 2.5D high-performance composites.

Z-printing of continuous fiber-reinforced thermoset composites: The process development, and mechanical properties evaluation

This study presents a process development and mechanical characterization for through-the-thickness yarns (TTYs) incorporated into continuous fiber-reinforced thermoset composites (CFTCs) using a 3D printing system with photopolymer curing technology. Two types of CFTCs were prepared with different ply orientations and placement of TTYs. The mechanical properties of the samples were evaluated through three-point flexural strength tests and numerical simulations. The experimental and numerical results exhibited acceptable agreement up to the first peak of the reaction force. The presence of TTYs reduced the maximum stress and altered the failure mechanisms, while improving resistance to delamination cracking. The energyabsorption capacity of the samples with TTYs was increased by 23% to 53%. However, the flexural strength of the samples decreased by 14% to 23% with the incorporation of TTYs due to the formation of small sections with low fiber content around TTYs and the concentration of von Mises stress.

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.

4D printing and programming of continuous fibre-reinforced shape memory polymer composites

This study demonstrates the use of fused filament fabrication (FFF) 4D printing (4DP) to print programmable continuous fibre-reinforced composite (CFRC) structures with exceptional strength and eco-friendly features. This research focuses on bio-shape memory polymer composites (SMPCs) and employs experiments to fabricate lightweight CFRC parts using FFF technology. Different types of continuous fibres, including carbon fibre (CF), aramid fibre (AF), and fibreglass (FG), are incorporated into a biopolymer matrix made of biodegradable polylactic acid (PLA). The study evaluates microstructure, mechanical properties, and shape memory properties of SMPCs, employing techniques like cold and hot programming. Continuous fibres significantly enhance mechanical properties, increasing strength by over 1027.5 % in tensile tests and nearly 497.3 % in three-point bending tests. The research also addresses shape recovery and fixity ratios in 4D-printed SMPCs, finding a decrease when continuous fibres are incorporated into PLA. Notably, FGPLA specimens achieve the highest shape recovery ratio of approximately 95 ± 1 % after pure PLA. These findings highlight the potential of 4D-printed CFRCs in various applications, from human-material interaction to mechanical and biomedical fields. They contribute to sustainability by reducing material consumption and waste, demonstrated through the creation of reusable and lightweight items like hooks, lockers, finger splints, and meta-composites.

Strain rate dependence of 3D printed continuous fiber reinforced composites

Fused Deposition Modeling (FDM), one of the most popular additive manufacturing technologies in polymer 3D printing, has been increasingly used in fabricating continuous fiber reinforced composites (CFRCs) in recent years. Intensive research has been conducted on the quasi-static mechanical properties of FDM made CFRCs and the corresponding failure mechanisms. However, limited research has been reported on the dynamic mechanical behavior of CFRCs fabricated using FDM. This paper presents a comprehensive experimental study to understand the deformation and load carrying capacity of FDM-fabricated continuous fiber reinforced Onyx (CFRO), with a focus on the dynamic tensile loadings up to strain rate of 100/s. The deformation and failure mechanisms of FDM-fabricated CFROs under dynamic loadings have been identified after microstructural analyses of fractured specimens. The effects of fiber type, fiber volume fraction, and strain rate on the tensile behavior have been revealed for Onyx reinforced by carbon fiber filaments (CFF), glass fiber filaments (GFF), and Kevlar fiber filaments (KFF). Empirical formulas have also been derived to describe the relationships between the elastic modulus, ultimate tensile strength (UTS) and fiber volume fraction. The results demonstrate that increasing the strain rate from 6.7 × 10−4/s to 100/s substantially enhances the UTS of all three types of printed CFRO.

Demonstration of computer vision for void characterisation of 3D-printed continuous carbon fibre composites

Microstructural void formation during the processing of continuous fibre-reinforced polymer composites are a significant limitation of processes such as 3D printing, as voids inhibit resultant mechanical properties. Traditional optical microscopy approaches to void characterisation are tedious and are prone to errors due to non-ideal but realistic image conditions, including low contrast typical of microscopic images. This paper proposes a novel application of automated computer vision image processing techniques (i.e. a contrast-limited adaptive histogram equalisation (CLAHE) algorithm and Otsu's method) for detailed void characterisation of continuous fibre-reinforced composites. Microstructural void fraction was determined for both unidirectional and bi-axial laminates of a variety of thicknesses. The void characterisation by computer vision was shown to produce comparable results with manual contrast/brightness control, but with significantly less standard deviation. The computer vision software used in void characterisation is made freely available online at https://github.com/Xiao-ying/VoidDetector.

Assessment of mechanical properties and shape memory behavior of 4D printed continuous fiber-reinforced PETG composites

Additive manufacturing (AM) has transformed composite structure production with continuous fiber-reinforced composites (CFRCs). Integrating shape memory polymers (SMPs) into AM enables 4D printing, holding promise across industries. Despite SMP brittleness at low temperatures, most studies focus on high-temperature shape memory behavior. Polyethylene Terephthalate Glycol (PETG), known for good printability, shape memory, and room temperature flexibility, is reinforced with carbon fiber in this study and its chemical and thermo-mechanical properties are systematically evaluated. The investigation extends to assessing the influence of printing parameters on CFRC printability and mechanical properties to identify optimal settings. Mechanical property enhancement is significant, especially with 7% carbon fiber, resulting in 474% and 386% improvement in tensile and flexural modulus, respectively. Shape-recovery tests at room temperature show 98% recovery for pure PETG and 94% for composites. PETG CFRC's high mechanical properties, room temperature flexibility, and promising shape recovery position them for potential load-bearing applications in various industries.

The role of printing parameters on the short beam strength of 3D-printed continuous carbon fibre reinforced epoxy-PETG composites

It is well known that printing parameters strongly affect the mechanical performance of 3D printed parts. This work explores the role of i) extruder temperature, ii) print speed, and iii) layer height on the interlaminar strength of 3D-printed continuous fibre-reinforced composites. The carbon fibre-reinforced thermoset filament is printed concomitantly with polyethylene terephthalate glycol (PETG) thermoplastic filament in a single nozzle, characterising a continuous fibre co-extrusion (CFC) process. There is a significant variation in the short beam strength for composites printed with different parameters. The load–displacement curves have a similar pattern, with clear load peaks followed by a plastic zone. Optical micrographs and computed tomography (CT) scans reveal that the microstructure is dependent on the printing parameters. Image analysis elucidates the various mechanisms of void formation. Following the application of a three-way ANOVA and statistical tests to quantify the effects and interactions among variables, the analysis concludes that the extruder temperature has the highest influence, followed by print speed and layer height. When considering all possible interactions between the factors, the interaction between print speed and layer height is the most impactful.

Electrothermally controlled origami fabricated by 4D printing of continuous fiber-reinforced composites

Active origami capable of precise deployment control, enabling on-demand modulation of its properties, is highly desirable in multi-scenario and multi-task applications. While 4D printing with shape memory composites holds great promise to realize such active origami, it still faces challenges such as low load-bearing capacity and limited transformable states. Here, we report a fabrication-design-actuation method of precisely controlled electrothermal origami with excellent mechanical performance and spatiotemporal controllability, utilizing 4D printing of continuous fiber-reinforced composites. The incorporation of continuous carbon fibers empowers electrothermal origami with a controllable actuation process via Joule heating, increased actuation force through improved heat conduction, and enhanced mechanical properties as a result of reinforcement. By modeling the multi-physical and highly nonlinear deploying process, we attain precise control over the active origami, allowing it to be reconfigured and locked into any desired configuration by manipulating activation parameters. Furthermore, we showcase the versatility of electrothermal origami by constructing reconfigurable robots, customizable architected materials, and programmable wings, which broadens the practical engineering applications of origami.

Characterization of mechanical properties, efficiency, and design considerations for the additive manufacturing of hybrid composites with continuous fibers

The integration of continuous fibers into additively manufactured plastic components greatly enhances their mechanical properties. Nonetheless, a challenge lies in the limited adaptability of these properties to specific loading scenarios. To address this issue, present research aims to exploit the hybridization of additively manufactured composites, combining diverse fiber materials within a single component. Specifically, fabricating continuous fiber-reinforced hybrid composites through material extrusion enables high flexibility in adapting local fiber materials. To further the understanding of the effects of hybrid fiber reinforcement in additively manufactured plastic parts, this study investigates how distinct stacking sequences in hybrid and non-hybrid PA6-based composite components, reinforced with carbon and glass fibers, affect deformation and failure behavior. Mechanical properties are assessed using tensile, flexural, and impact tests, in conjunction with an analysis of cost and weight efficiency. The results unveil a distinct correlation between stacking sequences and the mechanical properties of additively manufactured composites. While the hybrid samples predominantly exhibit slight negative hybrid effects, a positive hybrid effect of 96.4 % is achieved in terms of impact toughness with an optimized stacking sequence. With the exception of impact strength, specimens reinforced solely with carbon fibers frequently demonstrate a remarkable ratio between mechanical properties, weight, and cost, whereas hybrid composites exhibit a balanced compromise across all tested mechanical properties. Building upon the obtained results, three comprehensive design approaches are introduced and applied, demonstrating the new design possibilities arising from the combination of hybrid composites and additive manufacturing. The developed design approaches and material combinations can be used for a wide range of lightweight construction 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.

Micron-sized SiC particles reinforced TC4 composites: Mechanical properties and strengthening mechanisms

SiC fiber, W fiber, C fiber and other continuous fiber-reinforced titanium matrix composites (TMCs) have limited their application prospects due to their anisotropy, interface reaction, and high costs. In contrast, the SiC particles (SiCp) reinforced TMCs are of particular interests due to their ease of fabrication, lower costs, and isotropic properties. Micron-sized SiCp reinforced TC4 (Ti-6Al-4V) composites (SiCp/TC4) were synthesized via spark plasma sintering (SPS). The microstructure and mechanical properties of SiCp/TC4 composites have been investigated. The results showed that SiCp/TC4 composites exhibite a typical Widmanstatten structure composed of plate α, grain boundary α phase, and intercrystalline β phase. TiC particles formed via the reaction of SiCp with the TC4 matrix distributed at grain boundaries. In the meanwhile, a small amount of Ti5Si3 have been observed around the β phase. The strength of the composites increased continuously with the increase of SiCp contents. Due to effects of grain refinement and load transfer strengthening and solution strengthening from C, O and Si elements, the composites of 0.5 wt% SiCp/TC4 has achieved a high yield strength and an ultimate tensile strength of 1053 MPa and 1144 Mpa, which are higher than TC4 matrix for 33.5% and 27.1%. SiCp/TC4 composites have widespread application prospects in aerospace, military and automotive industries.

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.

Interlaminar and translaminar fracture toughness of 3D‐printed continuous fiber reinforced composites: A review and prospect

AbstractFracture toughness is a critical parameter in the evaluation of a component's structural integrity and damage tolerance. For 3D‐printed continuous fiber reinforced composites (CFRCs) based on the fused deposition modeling (FDM) technique, the fracture behavior differed from that of composites manufactured by traditional processes due to the presence of voids and interfaces at different scales, receiving significant attention. Recently published research attempted to apply various testing standards (for other materials) to investigate the fracture behavior of 3D‐printed CFRCs. In these results, the fracture toughness of CFRCs was influenced by the manufacturing parameters dependent on structural porosity and interfacial bonding quality. This paper reviewed fracture toughness measurement standards compatible with CFRCs, factors influencing fracture behavior, and methods improving the fracture toughness of CFRCs. Lastly, this review explored limitations in current studies focused on fracture toughness measurement of 3D‐printed CFRCs and future perspectives for the fabrication of 3D‐printed CFRCs with improved fracture toughness.Highlights This review focuses on fracture toughness measurement standards compatible with 3D‐printed continuous fiber reinforced composites (CFRCs). The manufacturing parameters influencing fracture behavior and methods improving fracture toughness were summarized. This review explores limitations in current studies focused on fracture toughness measurement of 3D‐printed CFRCs.

Effects of cellular crossing paths on mechanical properties of 3D printed continuous fiber reinforced biocomposite honeycomb structures

3D printing continuous fiber reinforced composite (CFRC) has the advantages of manufacturing complex shapes and short production cycles. Due to the anisotropic mechanical properties of continuous fibers, the printing path of the fibers determines the properties of the printed CFRCs. In this paper, a series of novel cellular crossing paths were proposed to print continuous ramie fiber reinforced biocomposite honeycomb structures (CFHSs). The compression, bending, and tensile tests were performed to analyze the effects of cellular crossing paths on the mechanical properties of CFHSs. An assessment method was presented for analyzing the comprehensive mechanical properties of CFHSs printed by different printing paths. The results showed that the CFHSs printed by no-crossing path (Path-1), single-crossing path (Path-3), and double-crossing path (Path-4) exhibited better compression, bending, and tensile properties, respectively. In addition, the samples printed by Path-3 were the most outstanding in the assessments of comprehensive mechanical properties, the comprehensive performance assessment score was 1.5 times that of the single-crossing path (Path-2, minimum score). Thus, an appropriate cellular crossing path could be selected according to the structural load-bearing state, thereby providing higher mechanical properties.

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.

Fabrication of a novel continuous fiber 3D printed thermoset all-composite honeycomb sandwich structure with polymethacrylimide foam reinforcement

Continuous fiber-reinforced composite (CFRC) 3D printing provides attractive solutions for integrated fabrication of all-composite honeycomb sandwich structures. However, weak matrix strength and insufficient interlayer bonding degrade the performance of 3D-printed thermoplastic honeycomb sandwich structures. The curing-mold-dependent thermoset honeycomb sandwich structures are challenging to fabricate integrally by 3D printing. This study addressed these issues by filling the honeycomb cells with lightweight polymethacrylimide (PMI) foam during 3D printing, achieving co-curing support and enhanced performance of the integrally 3D-printed honeycomb sandwich structures. The novel foam-reinforced structure was studied using three-point bending tests and compared to the foam-free bonding-based structure. With a minor weight gain (9.48 %), the PMI foam reinforcement increased the peak load capacity of the honeycomb sandwich structure by 198.31 % (4.32 kN). The specific bending stiffness and the specific core shear strength were increased by 49.32 % and 165.69 %, respectively. Finally, the failure flow maps and stress state were analyzed to reveal structural failure modes and PMI foam reinforcing mechanisms.

Comparison of three algorithms generating virtual microstructures in terms of the degree of randomness

The degree of randomness of fibre arrangements within the resin area is of great importance to the composites’ micro-distribution of stress and strain. A new algorithm, hard-core model & random shaking model, is developed to generate the unidirectional continuous fibre-reinforced composites. Another two algorithms, the random sequential expansion model and the initially periodic shaking model are presented and improved to generate the representative volume element microstructures. Statistical analyses are performed to compare these representative volume element microstructures generated by different algorithms at different fibre volume fractions. A quantitative approach is first applied to provide the exact degree of randomness of both virtual and real microstructures. Results of qualitative and quantitative analyses show that the novel algorithm is capable of generating statistically equivalent fibre distributions to real continuous fibre-reinforced composites.

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.