Continuous Fiber Reinforcement Research Articles

Advancing composite 3D printing: deep learning-optimized rheology-modified polymers with continuous carbon fiber reinforcement

Advancing composite 3D printing: deep learning-optimized rheology-modified polymers with continuous carbon fiber reinforcement

A review of 3D and 4D printable discontinuous and continuous fibre reinforcement polymers for soft robotics

A review of 3D and 4D printable discontinuous and continuous fibre reinforcement polymers for soft robotics

Ultra-high-rate Manufacturing of Thermoplastic Window Plug using Hybrid Overmolding

Highly loaded complex parts are machined from a solid block of metal by removing material through cutting, boring, drilling, and grinding to obtain the three-dimensional shape. Most cases, this involves removing as much as 80 percent of the material from a billet, which is time-consuming and inefficient considering the cost of the materials. Alternatively, these complex parts can be manufactured using hybrid overmolding process which involves injecting plastics over a reinforced substrate with continuous fiber-reinforcement eliminating subtractive machining or joining of multiple parts. The substrate is typically heated using an infrared (IR) oven and preformed over a solid mold to a three-dimensional shape using thermoforming. Injection overmolding material can also be reinforced with discontinuous fibers based on the design requirements. Both thermoforming and injection molding are matured automotive ultra-high-rate manufacturing processes. Adopting these technologies to aerospace requires advanced aerospace-grade thermoplastic material systems and developing the hybrid overmolding process that combines both thermoforming and injection molding processes. Material compatibility is one of the key enablers for the fusion across the overmolded interfaces. To demonstrate the overmolding technology for an aerospace application, Victrex AE250 low-melt polyaryletherketone (LM-PAEK) system reinforced with AS4 fibers and a 30% carbon fiber-reinforced polyetheretherketone (PEEK) were used to overmold aircraft window plugs to be used for cargo conversion of passenger aircraft. The fully automated overmolding process was demonstrated using KraussMaffei multi-robotic thermoforming and injection molding system. Thermal and mechanical test evaluations were employed to assess the material compatibility and overall part quality. Photomicrographs and flexure tests conducted on test samples extracted from the window plugs indicated satisfactory fusion across the overmolded interface and optimized holding of PEEK materials.

4D printing of liquid crystal elastomer composites with continuous fiber reinforcement

Multifunctional composites have been continuously developed for a myriad of applications with remarkable adaptability to external stimuli and dynamic responsiveness. This study introduces a 4D printing method for liquid crystal elastomer (LCE) composites with continuous fibers and unveils their multifunctional actuation and exciting mechanical responses. During the printing process, the relative motion between the continuous fiber and LCE resin generates shear force to align mesogens and enable the monodomain state of the matrix materials. The printed composite lamina exhibits reversible folding deformations that are programmable by controlling printing parameters. With the incorporation of fiber reinforcement, the LCE composites not only demonstrate high actuation forces but also improved energy absorption and protection capabilities. Diverse shape-changing configurations of 4D composite structures can be achieved by tuning the printing pathway. Moreover, the incorporation of conductive fibers into the LCE matrix enables electrically induced shape morphing in the printed composites. Overall, this cost-effective 4D printing method is poised to serve as an accessible and influential approach when designing diverse applications of LCE composites, particularly in the realms of soft robotics, wearable electronics, artificial muscles, and beyond.

In Situ Microscopy of Fatigue-Loaded Embedded Transverse Layers of Cross-Ply Laminates: The Role of an Inhomogeneous Fiber Distribution

Composites with continuous fiber reinforcement offer excellent fatigue properties but are tedious to characterize due to anisotropy and the interplay of fatigue properties, processing conditions, and the constituents. The global fiber volume content can affect both monotonic and fatigue strength. This dependence can increase the necessary testing effort even when processing conditions and constituents remain identical. This work presents an in situ edge observation method, enabling light microscopy during loading. As a result, digital image correlation can be employed to study local strains at cracking sites on the scale of fiber bundles. The geometric influence on fatigue damage is examined in non-crimp fabrics of glass and carbon fibers. Two epoxy resins (one modified by irradiation) are investigated to verify the geometric influence under changed polymer properties. The microscopy-based image correlation revealed that damage forms at very low global strains of only 0.2–0.3% in glass fiber-reinforced epoxy laminates. For carbon fiber-reinforced epoxy, laminate cracking was found to emanate mainly from regions containing stitching fibers. Across both reinforcements, irradiation treatment led to delayed cracks, emanating from interfaces. This detailed analysis of the damage formation is used as a basis for proposed applications of the in situ strain information.

Effect of High Fiber Content on Properties and Performance of CFRTP Composites

Continuously reinforced thermoplastic composites are widely used in structural applications due to their toughness, light weight, and shorter process cycle. Moreover, they provide flexibility in design and material selection. Unlike thermoset composites, continuous fiber content to maximize mechanical properties in thermoplastic composites has not been well investigated. In this paper, three thermoplastic systems are investigated to study the optimum content of continuous fiber reinforcement. These systems include carbon fiber/polyphenylene sulfide (PPS), glass fiber/PPS, and glass fiber/high-density polyethylene (HDPE). Tapes were made at several fiber contents, and samples were compression molded and tested using thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile, 3-point flexure, and short-beam shear tests. Results revealed that higher fiber content led to an increase in the glass transition and melt transition temperatures of the polymer. Some mechanical properties increased with fiber content and then began to decrease upon further addition of fibers, while other properties, such as ductility and interfacial bond strength, decreased with more reinforcement. Furthermore, the optimum fiber contents to maximize mechanical properties are different for different properties and different materials.

Development and Evaluation of a Novel Method for Reinforcing Additively Manufactured Polymer Structures with Continuous Fiber Composites

Additively manufactured polymer structures often exhibit strong anisotropies due to their layered composition. Although existing methods in additive manufacturing (AM) for improving the mechanical properties are available, they usually do not eliminate the high degree of structural anisotropy. Existing methods for continuous fiber (cF) reinforcement in AM can significantly increase the mechanical properties in the strand direction, but often do not improve the interlaminar strength between the layers. In addition, it is mostly not possible to deposit cFs three-dimensionally and curved (variable–axial) and, thus, in a path that is suitable for the load case requirements. There is a need for AM methods and design approaches that enable cF reinforcements in a variable–axial way, independently of the AM mounting direction. Therefore, a novel two-stage method is proposed in which the process steps of AM and cF integration are decoupled from each other. This study presents the development and validation of the method. It was first investigated at the specimen level, where a significant improvement in the mechanical properties was achieved compared to unreinforced polymer structures. The Young’s modulus and tensile strength were increased by factors of 9.1 and 2.7, respectively. In addition, the design guidelines were derived based on sample structures, and the feasibility of the method was demonstrated on complex cantilevers.

Fabrication of Cellular Composite Structures with Continuous Fiber Reinforcement and Different Infill Patterns Using Fused Filament Fabrication

Additive manufacturing (AM), also known as 3D printing, is a process of creating three-dimensional objects with complex geometries that is utilized in various engineering applications. Continuous carbon fiber (CCF) is a high-performance material that offers a range of benefits in terms of strength, weight, and durability. Fused filament fabrication (FFF) is a type of AM that uses a thermoplastic filament as a material with which to create a three-dimensional object, and it has been widely used in various applications, as it enables the faster, cheaper, and more customizable production of parts and products. Lightweight cellular composite structures consists of small, repeating unit cells that are interconnected to form a larger structure, and they are employed in high engineering applications. In this study, cellular composite structures were fabricated using FFF technology, considering two types of infill paths design (grid and triangular) manufactured at three infill density levels (20%, 40%, and 60%). After the fabrication process, tensile and flexural properties were experimentally investigated, and the influence of the infill pattern and density on the cellular composite parts were studied. The achieved results demonstrated that the infill design pattern and its density had great influence on the mechanical properties of the cellular structure. The obtained results also showed that the lightweight cellular composite parts had great potential for use in structural applications.

Tensile behaviour of continuous carbon fibre reinforced composites fabricated by a modified 3D printer

This study aims to highlight the impact of low-volume (7.5%) continuous carbon fibre reinforcement in three different polymer matrices and the effects of post-processing under hot pressing on the mechanical properties of the structures. A fused deposition modelling (FDM) printer’s print head was modified to directly extrude the polymer matrix and continuous carbon fibre tow together. Both pure and carbon fibre-reinforced samples were cured under hot pressing at 100 °C and 10 kN pressure for 15 min. All samples underwent tensile and hardness tests, and the microstructure of fractured samples was analysed using a scanning electron microscope. The results indicate that continuous carbon fibre reinforcement and hot pressing are crucial for enhancing the mechanical performance of 3D-printed objects.

Bending Strength of Continuous Fiber-Reinforced (CFR) Polyamide-Based Composite Additively Manufactured through Material Extrusion.

This paper shows the three-point bending strength analysis of a composite material consisting of polyamide doped with chopped carbon fiber and reinforced with continuous carbon fiber produced by means of the material extrusion (MEX) additive manufacturing technique. For a comparison, two types of specimens were produced: unreinforced and continuous fiber-reinforced (CFR) with the use of carbon fiber. The specimens were fabricated in two orientations that assure the highest strength properties. Strength analysis was supplemented by additional digital image correlation (DIC) analysis that allowed for the identification of regions with maximum strain within the specimens. The utilization of an optical microscope enabled a fractographic examination of the fracture surfaces of the specimens. The results of this study demonstrated a beneficial effect of continuous carbon fiber reinforcement on both the stiffness and strength of the material, with an increase in flexural strength from 77.34 MPa for the unreinforced composite to 147.03 MPa for the composite reinforced with continuous carbon fiber.

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.

An Analytical Friction Model for Handling and Spreading of Carbon Fiber Tows for Composite Prepregging Applications

Abstract A novel co-extrusion system for continuous fiber-reinforced thermoplastic composites in filament and narrow-tape format was designed, fabricated, and tested. The new modified pultrusion process, called In Situ Impregnation, impregnates continuous dry fiber reinforcement tows in situ with thermoplastic matrix for applications ranging from 3D printing using robotic manipulation to automated fiber placement. The technical goal of the system is to directly co-extrude and impregnate a reinforcement fiber tow (carbon) with thermoplastic matrix injected by an extruder fed with thermoplastic pellets. This approach uses inexpensive materials instead of “prepreg” tow in order to streamline the additive manufacturing process, cut costs for advanced composites manufacturing, and deliver fully customizable fiber orientation. The purpose of this paper is to discuss analytical modeling of friction and fiber tensioning in the system which allows for the full impregnation of the fibers. Experiments were conducted on a working pultrusion system where load was adjusted through the tensioning system to better understand the amount of friction throughout the system, the magnitude of tension in the fiber tow, and to validate the models. The resulting friction model can be used by machine designers to estimate the tension in tows, ropes, fibers, etc. in similar tensioning devices, and estimate automated system specifications such as motor requirements. A brief description of the new manufacturing process is also provided. Future work includes commercialization of the technology, automation of the manufacturing system, and further modeling work to predict fiber spreading behavior based on geometric factors.

Water Diffusion in Additively Manufactured Polymers: Analysis of the Capillary Effect

Additive manufacturing (AM) is an advanced manufacturing method that produces objects by sequential layering. Material extrusion AM (MEAM) with continuous-fibre reinforcement is becoming more widely used in naval structures, which are exposed to the marine environment. However, the water diffusion process and the effect of water ageing on the mechanical performance of AM materials are not yet well understood because of their complex internal structure, caused by defects generated during manufacturing. Current research on diffusion is mostly based on experimental methods for conventionally manufactured materials without considering AM-induced defects. The objective of this study is to explore how the defects inherent to MEAM affect water diffusion in a composite material by the capillary effect. Results from a numerical study of capillary flow in MEAM polymer are applied as a boundary condition in the subsequent finite-element analysis. The study illustrates that flow in the capillary reaches the steady state quicker compared to the saturation time in the matrix, predicted by Fick’s diffusion equation. It is demonstrated that the capillary effect can significantly affect the water diffusion in MEAM parts and reduce the saturation time to one-third compared to the case without accounting for this effect.

G-code generation for deposition of continuous glass fibers on curved surfaces using material extrusion-based 3D printing

Improving the mechanical properties of 3D printed parts produced through a material extrusion-based 3D printer with continuous fibers (carbon, glass, and aramid) has been a focal point for numerous researchers. Given the layered nature of additive manufacturing (AM) processes, wherein parts are built up layer by layer, most studies involve the deposition of continuous fibers onto a 2D surface. Cases involving curved surfaces have employed robots with high degrees of freedom. This research introduces a method for depositing continuous glass fibers onto curved surfaces, implemented on a cost-effective material extrusion-based 3D printer. The presented approach involves G-code modification, the incorporation of a rotating axis for the nozzle, and the application of computer-aided design and manufacturing techniques. Experimental results affirm the efficacy of this method for depositing continuous fibers onto curved surfaces. The developed technique enables the production of free-form composite shells with a thermoplastic matrix and continuous fiber reinforcement. Lastly, through 3D scanning of the printed sample and subsequent comparison with the 3D model, the degree of surface form deviation and tolerance is determined. The maximum deviation identified in this study is 0.1 mm, a tolerable amount considering the inherent characteristics and behaviors of thermoplastic materials (shrinkage and warpage) during production processes.

Additively manufactured vacuum grippers for the flexible handling and assembly of hairpin coils in electric motor production

Hairpin technology has recently become the predominant winding technology for the manufacturing of stators used in electric traction motors. In contrast to conventional winding techniques, the manufacturing process chain is based on rectangular wire which is bent into a three-dimensional U-shape – so-called hairpin coils. These hairpin coils have to be individually gripped and assembled to form the stator winding. There can be hundreds of hairpin coils in a single stator, which can also differ in shape. Therefore, gripping and moving the individual hairpin coils is a challenging task in terms of flexibility and cycle time. This paper presents an approach to meet the outlined requirements using additively manufactured vacuum grippers. A concept is investigated in which the vacuum is generated in a conventional vacuum ejector and fed to the vacuum gripper via hose lines. In contrast, the concept of a functionally integrated vacuum gripper manufactured by a new laser-sintering process with automated continuous fibre reinforcement is presented. Based on the laser-sintering process, a lightweight vacuum gripper with an integrated vacuum ejector can be manufactured in a single process step without additional costs for purchased parts. After a review of the state of the art in both hairpin-specific and additively manufactured lightweight grippers, experimental test series are carried out concerning the vacuum quality and the grip strength of the different vacuum gripper designs. Pull-off tests show that high holding forces of several Newtons are possible proving the basic usability of vacuum grippers for hairpins, even though the achievable vacuum quality of the functionally integrated vacuum gripper is lower than that of the conventional ejector. Comparison of the novel approaches with a conventional mechanical hairpin gripper regarding weight, production costs and production time show promising improvements.

Optimization of Thermoplastic Pultrusion Parameters of Jute and Glass Fiber-Reinforced Polypropylene Composite.

Thermoplastic pultrusion is a suitable process for fabricating continuous unidirectional thermoplastics with a uniform cross-section, high mechanical properties due to continuous fiber reinforcement, low cost, and suitability for mass production. In this paper, jute and glass fibers were reinforced with a polypropylene matrix and fabricated using the thermoplastic pultrusion process. The volumetric fraction of the composite was designed by controlling the filling ratio of the reinforcing fiber and matrix. The effects of molding parameters were investigated, such as pulling speed and molding temperature, on the mechanical properties and microstructure of the final rectangular profile composite. The pulling speed and molding temperature varied from 40 to 140 mm/min and 190 to 220 °C, respectively. The results showed that an increase in molding temperature initially led to an increase in mechanical properties, up to a certain point. Beyond that point, they started to decrease. The resin can be easily impregnated into the fiber due to the low viscosity of thermoplastic at high temperatures, resulting in increased mechanical properties. However, the increase in molding temperature also led to a rise in void content due to moisture in jute fiber, resulting in decreased mechanical properties at 210 °C. Meanwhile, un-impregnation decreased with the increase in molding temperature, and the jute fiber began to degrade at high temperatures. In the next step, with varying pulling speed, the mechanical properties decreased as the pulling speed increased, with a corresponding increase in void content and un-impregnation. This effect occurred because the resin had a shorter time to impregnate the fiber at a higher pulling speed. The decrease in mechanical properties was influenced by the increase in void content and un-impregnation, as the jute fiber degraded at higher temperatures.

Damage evolution model and failure mechanism of continuous carbon fiber-reinforced thermoplastic resin matrix composite materials

As a new composite material with high strength, toughness, and heat resistance, the continuous fiber-reinforced polyaryl ether sulfone ketone (PPESK) thermoplastic resin matrix composite (CFRP) has a wide temperature range, which is attributed to the complex temperature sensitivity of the matrix. The failure evolution characteristics under different conditions are not clear yet, which significantly limits its development and application to high-precision equipment. In this work, in order to deeply explore the full three-dimensional (3D) multi-scale multi-physics damage evolution mechanism of the CFRP over a wide temperature range, macroscale cross-temperature stretching/bending experiments, computer tomography (CT) scanning, and microscale scanning electron microscopy (SEM) are performed to effectively capture the overall damage morphology and local fiber/matrix damage failure characteristics of the material. The results show that the reinforcement with continuous fibers increases the tensile strength of the CFRP by 14–45 times and its bending strength by 2–6 times compared to those of the PPESK matrix in the cross-temperature domain. Moreover, the main failure mechanism of the CFRP in the cross-temperature domain is matrix crushing and fiber fracture at room temperature and fiber fretting slip and matrix viscous flow at high temperatures. This further explains the deformation mechanism of the CFRP, which can maintain its stability at high temperatures (low elongation at break: 1%–1.2%). The unique trans-temperature regional energy evolution and continuous fiber reinforcement of the material matrix resin PPESK lay the synergic stability of the high temperature performance and damage morphology of the CFRP. In particular, a cell model is constructed to further reveal the damage evolution characteristics of the matrix, fiber, and interface of the CFRP at the micro-scale. Combined with the failure mode theory and the performance degradation mechanism of composite materials, the temperature influence factor is introduced to formulate a multi-scale full 3D temperature-dependent damage evolution constitutive model of the CFRP over a wide temperature range. The constitutive model of the CFRP is incorporated in finite element software, and the simulation results are compared with the experimental ones for validation. The results show that the model developed in this work can effectively characterize the complex mechanical damage morphology and progressive failure characteristics of the CFRP over a wide temperature range.

Fabrication and tunable reinforcement of net-shaped aluminum matrix composite parts via 3D printing

Advanced materials, such as metal matrix composites (MMCs), are important for innovation, national security, and addressing climate change. MMCs are used in military, aerospace, and automotive applications because of their exceptional mechanical and thermal properties, however adoption has been slow due to costly and onerous manufacturing processes. A new process using fused filament fabrication 3D printing has been developed to make net shape MMCs without tooling or machining. The process involves printing an alumina preform and then using pressure-less infiltration with a molten aluminum alloy to form the composite. Arbitrary shapes can be formed in this process—a brake lever and a flange are demonstrated—and the properties can be tuned by varying the ceramic infill geometric pattern and ceramic loading. By using 35 vol% continuous fiber reinforcement over 800 MPa strength and 140 GPa modulus are achieved for the aluminum composite, 3.4 × and 2 × the matrix aluminum properties.

Deformation-dependent electrical resistivity of fiber-reinforced nanocomposites: A concentric cylindrical model approach

Fiber-reinforced composites have seen growing demands and widespread use in a variety of fields, including aviation, civil engineering, and the automobile industry. Fiber-reinforced composites must be monitored by nondestructive methods because of their tendency to have complicated and often visually undetectable failure mechanisms. Incorporating self-sensing capabilities into composites through nanofiller modification to leverage the piezoresistive effect is one approach for monitoring these materials. In this method, electrical resistivity is a function of mechanical strains, allowing for intrinsic self-sensing. To date, predictive modeling efforts in this field have mostly concentrated on microscale piezoresistivity. Research on modeling resistivity changes in macroscale fiber–matrix material systems has been limited, and even less research has been conducted to evaluate the impact of continuous fiber reinforcement. To bridge this gap, an analytical model that predicts changes in the resistivity of a material system with nanofiller-modified polymer and continuous fiber reinforcement is proposed. The cornerstone of this strategy is the establishment of an electrical concentric cylindrical model. We begin by defining our domain, which consists of concentric cylinders representing a continuous reinforcing fiber surrounded by a nanofiller-modified matrix. Next, the system is homogenized such that we can predict the change in the axial and transverse resistivity of the concentric cylinders. It is envisaged that the results herein presented will serve as a stepping stone towards the creation of a laminate theory of piezoresistivity.

A review of fused filament fabrication of continuous natural fiber reinforced thermoplastic composites: Techniques and materials

AbstractThe combination of continuous natural fiber and fused filament fabrication (FFF) 3D printing enables the manufacturing of low carbon emitting, environment friendly, lightweight, and high strength biomass composites with designated geometry characteristics. In current literature, reviews associated with continuous fiber 3D printing primarily cover synthetic fibers, such as carbon fiber, Kevlar, and glass fiber. Very few pieces of literature on the FFF printing of continuous natural fibers are available. Techniques/methodologies for incorporating continuous natural fiber reinforcements in FFF is an emerging field of research. A comprehensive review and discussion on current progress and the future prospects of continuous natural fiber 3D printing would be beneficial to its development. This article summarizes the current research status of continuous natural fiber 3D printing, including information on printing techniques, materials, and the influence of printing parameters on composite properties, so as to provide reference for the future development of FFF technology using continuous natural fiber and thermoplastic composites.