Continuous Fiber Reinforcement Research Articles

Carbon-fiber reinforced polymer composites: A comparison of manufacturing methods on mechanical properties

Carbon-fiber reinforced polymer composite materials are used throughout industry for their excellent mechanical properties; in particular, these composites boast high specific stiffnesses and specific strengths. However, current limitations on manufacturing, which vary greatly based on the technology that is utilized, restrict access to composite materials in a variety of applications. Traditional wet hand-layups offer a large diversity of viable constituent materials, but the fabrication geometry is limited and the manual process is time-consuming. In contrast, fiber 3D-printing (F3DP) allows for the production of complex geometries and requires little manual labor. In this study, laminates with continuous carbon fiber reinforcement printed using a commercially-available 3D printer are compared to carbon fiber fabric-resin composites produced using manual layup techniques. Cross-ply [0,90,0,90,0]T laminates were fabricated and subject to mechanical testing in uniaxial tension and flexure. After normalization with respect to fiber volume fraction, we found that the tensile strength and stiffness of cross-ply carbon fiber composites manufactured using F3DP were higher than the tensile strength and stiffness of cross-ply specimens manufactured by a traditional hand-layup method; however, the hand-layup specimens exhibited higher strength and stiffness in flexure. The difference in material properties evident between the two fabrication methods suggests that each has its own suitable application. We anticipate that further studying the failure response of printed, fiber-reinforced composite materials to various loading modalities will give insight into potential areas of improvement for F3DP material selection and printing processes, particularly relating to void reduction. On a broader scale, comparing and analyzing the mechanical properties of composite laminates produced in these various methods will provide perspective on the viability of novel additive manufacturing methods for large-scale production and industrial applications.

Experimental studies for the additive manufacturing of continuous fiber reinforced composites using UV-curing thermosets

The economical production of lightweight structures with tailor-made properties and load-adapted geometry is limited using conventional technologies. Additive manufacturing processes offer a high potential to meet these requirements, where the established solutions are based primarily on thermoplastics matrix systems. From a process-technological point of view, thermoplastics enable simplified processing, but only a limited range of applications for high-performance components. These limitations are due to their comparatively low heat resistance, low melting temperatures and limited adhesion to embedded reinforcing fibers. In contrast, thermosets show high potential for realization of high- performance lightweight structures with adaptable properties. The present work employs a UV-curing thermoset resin for the impregnation of a continuous filament strand for 3D printing. The main challenge is to reconcile the crosslinking reaction of the thermoset and the process velocity during impregnation and cure. The liquid polymer must provide low initial viscosity to impregnate the filaments and a sufficiently high cure rate and dimensional stability after discharge from the print head to ensure sufficient bonding strength to the substrate. To demonstrate feasibility, a prototypic print head with UV-LED activation was designed and implemented. With a robot-guided printing platform, the 3D-deposition of continuous fiber-reinforcements without additional supporting structures can be realized. To derive initial process parameters, reaction and thermos-mechanical properties are determined by rheometer measurements. Impregnation and cure behavior of the glass fiber reinforced resin is investigated. The presented results provide a reliable process window and a straightforward process monitoring method for further enhancement of the conceived 3D printing process.

Impacts of thermoplastics content on mechanical properties of continuous fiber-reinforced thermoplastic composites

Continuous fiber reinforcements are widely used to enhance mechanical properties of composite materials, but the impregnation of continuous fiber reinforcements with thermoplastics is a challenge due to high melt viscosity of the thermoplastic matrix. One of promising routes to improve the impregnation is to prepare commingled yarns with continuous matrix filaments and reinforcement fibers. In this study, we investigate mechanical properties of commingled yarns comprising different ratios of continuous glass fibers and polypropylene filaments, and of the composite plates made up of fabrics woven by the commingled yarns with a different polypropylene content. We found that undistributed or bunched glass fibers occur at high PP contents (>50 wt%), inducing an inhomogeneous mixing of the continuous reinforcement fibers and polypropylene filaments, which resultantly leads to abrupt changes in mechanical properties of both commingled yarns and resulting composites. Notably, the inhomogeneous distribution of continuous glass fibers in the commingled yarn at high PP contents gives rise to unexpected viscoelastic characteristics of resulting composites although impregnation of continuous glass fibers with polypropylene matrix is enhanced as the absolute amount of the polymer matrix increases.

Effect of single-fiber properties and fiber volume fraction on the mechanical properties of Ioncell fiber composites

The present study concentrates on a series of experiments and numerical analyses for understanding the effects of fiber volume fraction ( VF) and draw ratio ( DR) on the effective elastic properties of unidirectional composites made from an epoxy resin matrix with a continuous fiber reinforcement. Lyocell-type regenerated cellulose filaments (Ioncell) spun with DRs of 3, 6, and 9 were used. In accordance with the specimens in situ, the fibers were modeled as slender solid elements, for which the ratio between the diameter and length was taken to be much less than unity and deposited inside the matrix with the random sequential adsorption algorithm. The embedded element method was thereafter used in the numerical framework due to its computational advantages and reasonable predictions for continuous fiber reinforced composites. Experiments and numerical investigations were carried out, the results of which were compared, and positive trends for both fiber VFs and DRs on the effective properties were observed. The presented experimental and numerical results and models herein are believed to advance the state of the art in the mechanical characterization of composites with continuous fiber reinforcement.

The re‐manufacture and repairability of poly(ether ether ketone) discontinuous carbon fibre composites

AbstractA major limitation of carbon fibre‐reinforced polymers is their unsuitability for repair and recycling processes due to the common employment of thermoset resin matrices and continuous fibres. Advanced thermoplastic discontinuous fibre moulding compounds (DFMCs) now offer an alternative for high‐performance components. Although DFMCs cannot match the raw performance of continuous fibre reinforcement, compression‐moulding techniques developed at the University of Exeter enable poly(ether ether ketone) (PEEK) matrix DFMCs to challenge the mechanical properties of aluminium in thick‐section components, an application area outside the scope of thermoset composites. This previous research also identified that PEEK DFMC components are far less likely to suffer significant breakage of the fibres during fracture, suggesting that the material is highly suited to repair through simple remoulding, using heat and pressure to re‐melt and consolidate the resin along the fracture path returning it to its original strength and stiffness. This offers an exciting capacity for repair and recyclability. This paper investigates this further, utilising a series of three‐point bending samples loaded to fracture before being reheated and pressurised then tested again. Multiple reprocessing approaches are investigated, including the use of additional material to act as repair packs, re‐pressing to induce significant flow and simple remoulding. This study shows that composites can be repaired with minimal loss of mechanical performance even when significant fracture occurs. The application of repair packs actually increases performance, reaching a flexural modulus of ca 80 GPa after three fracture cycles and a maximum bending stress of ca 900 MPa. © 2021 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Micromechanical modeling of time-dependent and nonlinear responses of magnetostrictive polymer composites

The overall time-dependent and nonlinear responses of two-phase magnetostrictive polymer composites are obtained by coupling micromechanical analysis for magnetoelastic coupled composites with a time-integration algorithm for thermorheologically complex materials. The nonlinear magnetoelastic behavior is due to large magnetic driving fields while the nonlinear viscoelastic response is associated with stress and temperature. Because of the material nonlinearity of these constituents, linearized constitutive relations are first defined for obtaining the trial overall responses of the magnetostrictive composites followed by an iterative scheme in order to correct errors from linearizing the nonlinear responses. The presented micromechanical formulation is applicable to magnetostrictive composites reinforced by continuous fiber, particle, and lamina reinforcements. The predicted responses of the composites are first validated with the experimental data available in the literature. Numerical results are then presented for the magnetostrictive composites with 1–3, 0–3, and 2–2 connectivity in terms of their strain and magnetic flux density responses. Time-dependent and nonlinear behaviors show the different degrees of the dependency on microstructural geometry, reinforcement volume fraction, environmental temperature, and loading rate of magnetic and mechanical inputs.

Effect of fiber reinforcement on the open hole tensile strength of 3D printed composites

Initially, Fused Deposition Modeling (FDM) based 3D printed parts are only used as prototyping rather than the functional components. However, due to new advancements in the FDM process and its ability to add continuous fibers into the polymer parts, FDM made part can now be used as functional parts. Composites fabricated from the FDM process can be used in aerospace and automotive applications. Still, the applications of FDM made parts are limited due to the lack of critical information about the reliability and mechanical properties of the components. Therefore, in the present investigation, the effect of fiber reinforcement on the open hole tensile strength of the FDM printed part is investigated. Onyx as a polymer matrix material and HSHT (High Strength High Temperature) fiberglass as a continuous fiber reinforcement are used for the study. It is observed that the fiber reinforcement into the polymer matrix significantly increases the open hole tensile strength, but it also increases the specimen weight and printing time.

Interlaminar shear behavior of continuous and short carbon fiber reinforced polymer composites fabricated by additive manufacturing

This study investigates the interlaminar shear behavior of 3D printed CFRP composites fabricated by fused deposition modeling (FDM) through a combined experimental and numerical study. Short beam shear (SBS) tests were performed to quantitatively characterize interlaminar shear strength (ILSS) of 3D printed continuous and short CFRP composites. Numerical simulations incorporating the extended finite element method (XFEM) and cohesive zone model (CZM) were conducted to rationalize the experiments. Two different combinations of continuous and short carbon fiber reinforcements were studied. The first composite layup made of 48 layers of continuous CFRP filaments was used to determine the intrinsic ILSS of the fully continuous CFRP composites. The second composite layup composed of 24 layers of continuous CFRP filaments and 24 layers of short CFRP filaments was used to determine the ILSS of the continuous and short CFRP composites. The average ILSS of these two composite layups were measured to be about 40.9 MPa and 24.4 MPa, respectively. Four distinct stacking sequences were implemented to examine the effect of stacking sequence of the continuous and short CFRP layers on the ILSS. The ILSS exhibited a significant sensitivity to the stacking sequence. The ILSS tends to increase with the number of the consecutive short CFRP layers. A failure mode transition from a brittle matrix cracking of short CFRP layers to cracking in the interface between the continuous and short CFRP layers was observed. The failure mode transition is attributed to the enhanced fracture strength and toughness of the short CFRP layers due to the increase in layer thickness.

Review on process model, structure-property relationship of composites and future needs in fused filament fabrication

This paper presents the state-of-the-art of additive manufacturing of composites for processing functional, load-bearing components. A general overview of different additive manufacturing methods is provided, and specific attention is focused on fused filament fabrication-based composites processing. Different process modeling strategies are summarized, and key aspects of these models are discussed. Significant results such as thermal and fluid flow characteristics, effects of nozzle geometry on melt flow, fiber orientation, bead spreading, and solidification, the formation of residual stresses, and deformation behavior are discussed from computational modeling perspective. The scientific advancement, model limitations, and future modeling needs are prescribed reviewing the current works. A general overview of material development in nano-micro-macro-scale reinforcement is also presented. Different length-scales of reinforcement has its own challenges and promises. The continuous fiber reinforcement has a great potential for being the next-generation composites manufacturing technology. However, the challenges in reducing the void content, better bonding between the fiber–matrix, and layer-layer adhesion, and process uncertainty are some of the key areas yet to advance. Based on the current limitations on computational modeling, materials development, and process modeling studies, future research needs and recommendations are provided.

The effect of fibre length and matrix modification on the fire performance of thermoplastic composites: The behaviour of PP as an example of non-charring matrix

The fire performance of fibre-reinforced polypropylene (PP) was investigated with respect to fibre length and modification of the matrix. Fibre lengths of 3 mm, 12 mm, and continuous fibres were used as reinforcements. E-glass continuous fabrics were melt impregnated with PP and consolidated via compression moulding. E-glass fibre-reinforced PP pellets of 3 and 12 mm were compression moulded. Cone calorimetry tests with incident radiant fluxes of 20, 30 and 35 kW m−2 were used to investigate the fire properties of PP glass fibre composites. Results showed that continuous glass fibre reinforced PP exhibits the best fire performance at 20 kW m−2, while 3-mm fibre has the best performance at 35 kW m−2; 12-mm fibre-reinforced PP exhibitedthe lowest performance in comparison with 3-mm and continuous glass fibre reinforcement. Melic-anhydride (MA)-modified PP was found to increase the heat release rate (HRR) by up to 44% and time to ignition by up to 10% depending on the heat flux applied in comparison with unmodified PP. The glass fibre-reinforced composite made with MA-modified PP has 5–12% lower mean HRR and similar time to ignition in comparison with glass fibre composite made by unmodified PP. This suggests improved fibre adhesion plays a role of the fire performance of glass fibre-reinforced PP.

Design of binder jet additive manufactured co-continuous ceramic-reinforced metal matrix composites

Ceramic-reinforced metal matrix composites (MMCs) display beneficial properties owing to their combination of ceramic and metal phases. However, the properties are highly dependent on the reinforcing phase composition, volume fraction and morphology. Continuous fiber or network reinforcement morphologies are difficult and expensive to manufacture, and the often-used discontinuous particle or whisker reinforcement morphologies result in less effective properties. Here, we demonstrate the formation of a co-continuous ceramic-reinforced metal matrix composite using solid-state processing. Binder jet additive manufacturing (BJAM) was used to print a nickel superalloy part followed by post-processing via reactive sintering to form a continuous carbide reinforcing phase at the particle boundaries. The kinetics of reinforcement formation are investigated in order to develop a relationship between reactive sintering time, temperature and powder composition on the reinforcing phase thickness and volume fraction. To evaluate performance, the wear resistance of the reinforced BJAM alloy 625 MMC was compared to unreinforced BJAM alloy 625, demonstrating a 64 % decrease in the specific wear rate under abrasive wear conditions.

Influence of component design on features and properties in thermoplastic overmoulded composites

Thermoplastic composite overmoulding is an integrated process to manufacture components with combined continuous and short fibre reinforcements. These components benefit from high intrinsic mechanical properties, geometric complexity and low production cycle times. In this study, ribbed plates were manufactured by overmoulding short-fibre CF/PPS (carbon fibre/polyphenylene sulphide) material onto continuous woven-fibre CF/PPS flat preforms. Specifically, the effects of the rib geometry and flow length on the process-induced features were investigated using optical microscopy. The bonding at the overmoulded interface was evaluated via quasi-static tensile rib pull-off tests. Results indicate that both the bond strength and corresponding failure type vary with rib geometry. However, the effects of the specimen position along the flow length are only significant towards the end path. The implications of certain rib designs are discussed both qualitatively and quantitatively, based on feature development at the overmoulded interface during manufacture.

Consolidation and compression of deformable impregnated fibrous reinforcements: Experimental study and modeling of flow-induced deformations

Continuous fiber-reinforced thermoplastic composites can be produced by compression or consolidation processes at a temperature above the thermoplastic melting temperature. High production rates or high fluidity thermoplastic (TP-HF) viscosities can lead to large in-plane displacements of the fibrous network during the process. The same mechanisms appear when viscous toughened thermosets resins are used. One can assume that the in-plane displacements occur when the liquid thermoplastic flow sets the deformable fibrous reinforcement in motion. The composite material being manufactured is therefore subjected to a hydro-mechanical coupling between a liquid flow and a deformable continuous fibre reinforcement. Within this context, the in-plane flow-induced deformations during transverse consolidation are investigated in this study. An experimental setup is used in order to localize and quantify fibre tow displacements and large strains as a transient full-field measurement. Then, in order to identify the driving forces occurring during consolidation, these induced deformations are taken into account in the modeling. The fibrous reinforcement properties are redefined locally based on the measured full-field strains. The comparison of experimental and modeling results shows that the local in-plane drag force peaks mainly drive the onset of the fibrous architecture deformation.

Tensile mechanical properties of composite materials with continuous fiber produced by additive manufacturing

Additive manufacturing of composites parts reinforced with continuous fibers is emerging as a versatile process, capable of producing complex computer-aided design models by fabricating parts adding material layer by layer. Fused deposition modelling using polymeric materials has been used to produce prototypes, with the constraint of the strength of the material. Recently, the use of continuous fiber reinforcement has provided an alternative for the production of load-bearing functional parts. Current international standards for the characterization of composite materials from mechanical tests are established for parts manufactured by conventional methods, such as, manual molding, injection or coatings. Moreover, the standards do not specify procedures for composite materials produced by additive manufacturing. The objective of this work is to evaluate the performance of the reinforced composite materials produced by additive manufacturing for tensile tests under ISO and ASTM standards, and compare the results in terms of the topology of the material configuration. Average values of the tensile strength for composite materials having a triangular nylon matrix reinforced with fiberglass were obtained within the range of 205 MPa to 234 MPa, with deformations no greater than 0.020 mm. These values are higher than the strength provided by additive manufacturing using materials such as polylactic acid and acrylonitrile butadiene styrene.

Shape optimization of a control arm produced by additive manufacturing with fiber reinforcement

Additive manufacturing makes possible to overcome the limitations of subtractive manufacturing and supposes a transformation with respect to the traditional processes, allowing to manufacture complex geometries by controlled deposition of material. In the automotive industry, the application of continuous fiber reinforcement, in combination with shape optimization for additive manufacturing, can produce parts with higher mechanical performance. This paper reports the shape optimization problem of a suspension control arm to be produced by additive manufacturing with fiber reinforcement, using finite element analysis. First, the current material, loading conditions and constraints to which the control arm is subjected were determined, considering its traditional design. Then, a numerical model of the part was developed considering its current material and shape to obtain the total deformation and von Mises stress distributions. Afterwards, the new material model was defined, and the shape optimization was performed with the goal of maximizing stiffness. Finally, the results from the optimization process were validated by manufacturing and testing the part.

Tensile Performance of Fused Deposition Modeling PA 6 Polymer Composites With Nanoparticle Reinforcement and/or Continuous Fiber Reinforcement

AbstractFused deposition modeling (FDM) printing of continuous fiber reinforced polymers had been a challenge until about 5 years ago. With the reinforcement of continuous fiber, the mechanical properties of FDM printed polymers are improved by leaps and bounds. In this paper, we aim to investigate the possibility of further improvement in the mechanical properties of three-dimensional (3D) printed continuous fiber reinforced polymers by adding nanoreinforcements to the polymer matrix. Kevlar fiber is selected as the continuous fiber reinforcement, nylon 6 (PA 6) is selected as the polymer matrix material, and carbon nanotubes (CNTs) or graphene nanoplatelets (GNPs) nanoparticles are selected as the nanoreinforcements. In the experiment, CNT or GNP nanoparticles are first mixed with nylon 6 pellets to make nanocomposites, the nanocomposites are then extruded into filaments for 3D printing, and finally, both Kevlar filament and nanocomposite filament are fed through the printing nozzle and deposited on the platform. Tensile specimens are directly printed from pure PA 6 and three types of nanocomposites, namely, CNT/PA 6, GNP/PA 6, and GNP-NH2/PA 6, as well as Kevlar fiber reinforced PA 6 and three types of Kevlar fiber reinforced nanocomposites. The results indicate that although Kevlar fibers dominate the enhancement of mechanical properties for the printed composite materials, the existence of GNP nanofillers also provide a noticeable contribution to the enhancement of tensile strengths and moduli, while the effect of CNTs is much less pronounced.

A novel leaf inspired hydrogel film based on fiber reinforcement as rapid steam sensor

Intelligent hydrogel films with bilayer structures are promising materials as smart devices. Although the design of bilayer hydrogels with excellent mechanical properties, tough interfacial adhesion and rapid shape deformation is important, their construction in simple route is still challenging. In this work, inspired by leaf structure, an extremely simple casting strategy is established for preparing bilayer intelligent hydrogel films with bacterial cellulose (BC) for reinforcement. Driven by active diffusion of aqueous NIPAM/clay pre-gel solution into BC network, a tough fiber reinforced Gel@BC bilayer hydrogel with double network interface could be directly fabricated. The as-prepared Gel@BC bilayer hydrogel possessed exceptional mechanical properties since BC acted as the continuous reinforcement phase like vein of the leaves. The interfacial toughness reached ~102 J/m2 because the PNIPAM/clay nanocomposite hydrogel was filled into BC network to form the double network structure at the interface. Due to the anisotropic swelling induced by bilayer structure, the Gel@BC bilayer hydrogel provided remarkable rapid temperature-induced tunable shape transformation and exhibited a reversible bending behavior. In particular, the non-swelling characteristic of BC is beneficial for the mechanical stable and shape deformation of Gel@BC even in hot environment. This simple continuous fiber reinforcement strategy provides significant guidance for fabricating biomimetic actuators with applications in soft robotics such as bionic stomata for environment regulation and circuit switch as steam detectors.

Reinforcement of continuous fibers for extruded wood-flour/HDPE composites: Effects of fiber type and amount

Continuous-fiber reinforced WPCs were prepared using an extruder with a special die. The effects of the amount (1–7 bundles) and type of fiber (aramid rovings and yarns and carbon and glass yarns) on the mechanical properties of WPCs were studied. The addition of continuous fibers increased the tensile, flexural and impact strength of the composites by up to 47.3%, 83.1% and 713.4%, respectively. The damping ratio analysis revealed that the interfacial bonding of glass-yarn reinforced WPCs was the best among the tested samples. Adding continuous fibers to WPCs at a low volume fraction can promote their use as load-bearing engineered materials.

Flexural properties of three-dimensional printed continuous wire polymer composites

ABSTRACTRecently, continuous fibre reinforcement has been combined with three-dimensional (3D) printing to create stiffer printed components. This study investigates the effect of wire volume fraction, type of polymer matrix, and wire treatment on the flexural properties of 3D printed continuous wire polymer composites (CWPCs) through a design of experiment study. CWPC samples were printed using a modified, open-source 3D printer. The flexural properties were measured and compared to non-reinforced samples. An analytical model was developed to describe the stress distribution across unidirectional CWPCs as a function of the geometrical printing parameters, reinforcement dimensions, and material properties. Sample failure analysis was performed to investigate failure modes and offer insight into further enhancement of the composite’s properties.

The evolution of thermoplastic composites: The road to highest lightweight potential in mass production

Thermoplastic composites with continuous fibre reinforcements, sometimes also referred to as organosheets, come with excellent weight-specific mechanical properties such as strength and stiffness. Moreover, these materials are tough and allow short cycle times in part production. Also fuelled by the rapid development of Hybrid Moulding (forming & over-injection moulding in one operation), these materials are now starting to replace more traditional materials such as aluminium and steel. But there is still room for further improvement: the new group of neolaminates marketed under the brand name W8SVR from Huesker Synthetic are made completely from thermoplastic UD tapes, and have the potential to further improve the weight/performance ratio of thermoplastic composites, increase surface smoothness and reduce waste, according to Huesker Synthetićs Michel Jansen.