Fiber-reinforced Thermoplastic Composites Research Articles

Injection over-molding warpage prediction of continuous fiber-reinforced thermoplastic composites considering yarn reorientation

The injection over-molding process combines thermo-stamping of continuous fiber reinforced thermoplastic (CFRTP) laminates and injection of plastic onto the surface of the CFRTP insert. A challenge for this process is to predict the warpage due to the influence of CFRTP insert. This work proposed a simulation method for predicting the warpage considering yarn reorientation induced in the thermo-stamping. In detail, the geometry and yarns reorientation of the deformed CFRTP inserts in thermo-stamping were calculated by a hybrid lamination model. Then the local thermo-mechanical properties were calculated according to the directions of reorientated yarns. Finally, the geometric and material information of CFRTP insert were imported into injection analysis, especially warpage prediction. The simulation method was validated by experiments on centrally injected bilayer plate and stiffened square box. This work highlights the importance of anisotropy induced from thermo-stamping on the final warpage of injection over-molded composite parts.

Tunable soft–stiff hybridized fiber-reinforced thermoplastic composites using controllable multimaterial additive manufacturing technology

As a revolutionary manufacturing technology, material extrusion exhibits great potential for fabricating thermoplastic composites. However, the application of controllable multiple-thermoplastic materials for producing a tunable soft–stiff hybridized fiber-reinforced thermoplastic composite (CCFRTP-TSSH) based on material extrusion has yet to be extensively studied. Thus, this study proposes a controllable multimaterial additive manufacturing process for integrating continuous carbon fibers (CCF) as reinforcement for the thermoplastic structures. Structural reinforcement and tunable soft–stiff hybridization were achieved by adopting thermoplastic polyurethane (TPU) and polylactic acid (PLA) as the soft and stiff materials, respectively. Additionally, the mechanical properties of the CCFRTP-TSSH specimens were systematically investigated and discussed based on various process parameters, such as nozzle temperature, layer thickness, and supporting resin volume ratio (SRVR). The experimental results revealed that the layer thickness had a significant influence on the tensile properties, followed by the SRVR and nozzle temperature, wherein the highest tensile strength obtained was 90.89 MPa. Moreover, the bending strength depends on both the layer thickness and loading direction, with the largest bending strength of 65.96 MPa. Furthermore, the influence of SRVR on various fusion interfaces, e.g., PLA/ TPU, PLA/CCF, and PLA/PLA, was analyzed using scanning electron microscopy, including the influence of process parameters on the wall thickness of the stiff and soft resins, to realize an enhanced tunable soft–stiff hybridization. Ultimately, several distinct components, including a thin-walled hollow cylinder, round table, and a socket for a limb prosthetic, were fabricated to demonstrate the feasibility and accuracy of the proposed method. Therefore, this study presents a novel approach for the integrated manufacturing of soft–stiff hybridized composites, particularly in the field of wearable devices.

Multiscale viscoplastic modeling of recycled glass fiber-reinforced thermoplastic composites: Experimental and numerical investigations

One of the main challenges facing fiber-reinforced polymer composites is the lack of options for end-of-life recycling. The environmental impact of waste materials disposed of at landfill sites, by incineration, or by erratic dispersion in the environment is accelerating the need to find innovative solutions to increase the value of recycled materials. This research aims to investigate the relationship between microstructural parameters and the mechanical properties of a recycled thermoplastic composite material. The latter is processed by thermocompression molding of a polyamide (PA66) matrix reinforced with chopped glass strands. An innovative approach is proposed to link the local microstructure of the composite to the mechanical behavior of the recycled material. It exploits an experimental characterization of the material microstructure using optical microscopy and X-ray micro-computed tomography (mCT). The experimental findings are implemented into a numerical modeling strategy to mimic the flexural behavior, based on a micromechanical approach coupling mean and full-field analysis. The region of interest is reconstructed from detailed 3D images using a modified random sequential adsorption (MRSA) algorithm, while other regions are modeled as homogenized macro-scale continua. Furthermore, the abilities of the proposed approach are proven by incorporating the viscoplastic behavior of the random heterogeneous material induced by the polymer matrix. The originality of the present research consists of the multi-scale FE analysis and the experimental validation for the viscoplastic behavior of the recycled composite material, taking into account influences from the microstructure.

Recycling of carbon fiber-reinforced thermoplastic and thermoset composites: A review

Carbon fiber (CF) reinforced thermoplastic and thermoset composites are on the rise for research and new technologies, consequently, the use by many industries for applications in diverse areas. The principal methodologies and technologies for reusing and recycling these composites and possible applications are reviewed based on available in the information in the existing scientific literature. This review aims to present the possibilities of recycling, reuse and application of these composites reinforced with CF. The composites show a high added value due to the cost of the raw material and the technology involved in its development, which deserves attention for its possible recycling, and thus, and closed-loop economy. Given the current concern for the environment, the future disposal of waste based on CF reinforced thermoplastic and thermoset composites deposited in sanitary landfills and incinerated are unlikely to continue. It is expected that with the new carbon-fiber reinforced-polymer (CFRP) waste management guidelines, most industries, and scientific research will develop viable and profitable methodologies for the reuse and recycling of this waste and that can be inserted into the economy for the manufacture of new components for the most diverse sectors automotive industry.

A review on carbon fiber-reinforced hierarchical composites: mechanical performance, manufacturing process, structural applications and allied challenges

The utilization of carbonaceous reinforcement-based polymer matrix composites in structural applications has become a hot topic in composite research. Although conventional carbon fiber-reinforced polymer composites (CFRPs) have revolutionized the composite industry by offering unparalleled features, they are often plagued with a weak interface and lack of toughness. However, the promising aspects of carbon fiber-based fiber hybrid composites and hierarchical composites can compensate for these setbacks. This review provides a meticulous landscape and recent progress of polymer matrix-based different carbonaceous (carbon fiber, carbon nanotube, graphene, and nanodiamond) fillers reinforced composites’ mechanical properties. First, the mechanical performance of neat CFRP was exhaustively analyzed, attributing parameters were listed down, and CFRPs’ mechanical performance barriers were clearly outlined. Here, short carbon fiber-reinforced thermoplastic composite was distinguished as a prospective material. Second, the strategic advantages of fiber hybrid composites over conventional CFRP were elucidated. Third, the mechanical performance of hierarchical composites based on carbon nanotube (1D), graphene (2D) and nanodiamond (0D) was expounded and evaluated against neat CFRP. Fourth, the review comprehensively discussed different fabrication methods, categorized them according to performance and suggested potential future directions. From here, the review sorted out three-dimensional printing (3DP) as the most futuristic fabrication method and thoroughly delivered its pros and cons in the context of the aforementioned carbonaceous materials. To conclude, the structural applications, current challenges and future prospects pertinent to these carbonaceous fillers reinforced composite materials were elaborated.

Development of a Novel Hybrid Manufacturing Technology For Continuous Fiber-Reinforced Thermo-Plastic Composites

Abstract In this study, we present a novel approach for the production of continuous fiber-reinforced thermoplastic composites by combining injection molding and additive manufacturing. After exploring the design requirements, we manufactured inserts via continuous fiber-reinforced 3D printing, then we used them as reinforcement for injection-molded samples. Improper fiber placement can cause warpage as the continuous fibers prevent shrinking; however, warpage can be compensated with the insert geometry. The reinforcement resulted in an increase of about 30% in the properties tested.

Detection of delaminations in AS4/PEEK composite plates using highly nonlinear solitary waves

We experimentally investigate a non-destructive evaluation (NDE) technique to detect defects in an AS4/PEEK fiber-reinforced thermoplastic composite using highly nonlinear solitary waves (HNSWs). HNSWs are generated using an experimental setup of a granular crystal sensor composed of a one-dimensional chain of steel beads. The granular chain is vertically aligned and placed in contact with the surface of the laminated composites containing a defect through the depth of their thickness. The influence of the defect and the defect location in AS4/PEEK is examined by analysing the characteristics (i.e., delay and amplitude) of the reflected HNSWs. Experimental results demonstrate the capability of the proposed HNSW-based NDE scheme in identifying defects in AS4/PEEK laminated composites, offering a low-cost and robust alternative to existing NDE methods.

Processing and Mechanical Properties of Basalt Fibre-Reinforced Thermoplastic Composites.

Basalt fibre is derived from volcanic rocks and has similar mechanical properties as glass fibre. However, poor fibre-matrix compatibility and processing issues are the main factors that have restricted the mechanical performance of basalt fibre-reinforced thermoplastic composites (BFRTP). In this work, basalt continuous fibre composites with polypropylene (PP) and polycarbonate (PC) matrices were studied. The composites were processed by compression moulding, and a processing study was conducted to achieve good quality composites. For the BF-PC composites, the optimisation of material preparation and processing steps allowed the polymer to impregnate the fibres with minimal fibre movements, hence improving impregnation and mechanical properties. For BF-PP composites, a compatibiliser was required to improve fibre-matrix compatibility. The compatibiliser significantly improved the tensile and impact strength values for short BF-PP composites and continued to increase at 40 wt%. Furthermore, the analytical modelling of the Young’s moduli indicated that the induced fibre orientation during processing for short BF-PP composites and unidirectional (UD) BF-PC composites had better stress transfer than that of UD BF-PP composites.

Joining of Fibre-Reinforced Thermoplastic Polymer Composites by Friction Stir Welding—A Review

The objective of the current work is to show the potential of the friction stir welding (FSW) and its variants to join fibre-reinforced thermoplastic polymer (FRTP) composites. To accomplish that, the FSW technique and two other important variants, the friction stir spot welding (FSSW) and the refill friction stir spot welding (RFSSW), are presented and explained in a brief but complete way. Since the joining of FRTP composites by FSSW has not yet been demonstrated, the literature review will be focused on the FSW and RFSSW techniques. In each review, the welding conditions and parameters studied by the different authors are presented and discussed, as well as the most important conclusions taken from them. About FSW, it can be concluded that the rotational speed and the welding speed have great influence on heat generation, mixture quality, and fibre fragmentation degree, while the tilt angle only has residual influence on the process. The reduction of internal and external defects can be achieved by adjusting axial force and plunge depth. Threaded or grooved conical pins achieved better results than other geometries. Stationary shoulder tools showed better performance than conventional tools. Regarding the RFSSW, it has not yet been possible to deepen conclusions about most of the welding parameters, but its feasibility is demonstrated.

Molecular Dynamics Simulation on the Effect of Self-Resistance Electric Heating on Carbon Fiber Surface Chemical Properties and Fiber/PP Interfacial Behavior.

Carbon fiber-reinforced thermoplastic (CFRT) composites have been dramatically employed in the automotive field on account of their superior performances, such as being light weight and high-strength. Self-resistance electric (SRE) heating provides a solution to the problem of high energy consumption in the conventional process of CFRT composites. The effect of SRE heating on the surface chemical properties of carbon fiber (CF) was investigated by X-ray photoelectron spectroscopy (XPS). XPS analysis suggests that the C-O-C epoxy group, the CF surface, would be degraded after SRE heating with strong current intensity, while there are weak changes in the content of -C-OH, -C-O-C-, -C-NH2 and -COOH groups with current intensity. The interfacial bonding properties and the radial distribution function (RDF) of CF–PP interfaces were carried out by molecular dynamics (MD) simulation. The simulation results show that the adhesion between the PP and the E44 sizing agent is weaker than that between CF and PP. There are no interaction modes between the PP and E44 sizing agent except van der Waals and electrostatic adsorption. The presence of the E44 sizing agent does not change the bonding mechanism at the interface of CF/PP.

A Facile Molding Method of Continuous Fiber-Reinforced Thermoplastic Composites and Its Mechanical Property.

The mechanical properties of continuous fiber-reinforced thermoplastic (C-FRTP) composites are commonly lower than those of continuous fiber-reinforced thermosetting plastic (C-FRP) composites. We have developed a new molding method for C-FRTP. In this study, pre-impregnated materials were successfully prepared by polymer solution impregnation method and, finally, C-FRTP was fabricated. The viscosity of the thermoplastic matrix was decreased to approximately 3dPa×s, the same level of epoxy, and the fiber volume fraction was increased from approximately 45 to 60%. The cross-section of specimens were polished by an ion milling system and impregnation condition was investigated by scanning electron microscopy (SEM). The micrographs suggested that thermoplastic polymer was impregnated to every corner of the fiber, and no void was found on the cross-section. It revealed that void-free composites with perfect mechanical properties can be manufactured with this new molding method. All specimens were submitted to a mechanical measuring equipment, and the mechanical properties of the composite specimens were investigated. Mechanical analysis revealed that tensile property and flexural property of C-FRTP were enhanced up to the same level with C-FRP.

Hybrid Printing Method of Polymer and Continuous Fiber-Reinforced Thermoplastic Composites (CFRTPCs) for Pipes through Double-Nozzle Five-Axis Printer.

The most widely used 3D process, fused deposition modeling (FDM), has insufficient interlayer adhesion due to its layer-by-layer forming method. A support material is also essential for the hollow parts and cantilevers. Moreover, the polymer materials used have limited mechanical properties. These issues have restricted the application of FDM in high-performance fields. Continuous fiber-reinforced thermoplastic composites (CFRTPCs) have high mechanical properties and have recently become the focus of research in the field of 3D printing. This paper, using pipe parts as an example, proposes a hybrid of pure polymer (pure PLA used) and CFRTPC (flax fiber pre-impregnated filament) material to develop a printing method based on the outstanding mechanical properties of CFRTPC material. After studying the printing path planning algorithm, the CFRTPC filament is laid along the axial and radial directions on the surface of the polymer base to improve the printed parts’ properties. The method feasibility and algorithm accuracy are verified through the development of five-axis printing equipment with a double nozzle. Through the printed sample’s tensile, compression and bending tests, the results show that the tensile, compressive and bending properties of PLA pipe can be significantly enhanced by laying CFRTPC filament along the axial and radial directions of the pipe. To summarize, the introduction of CFRTPCs greatly improved the mechanical properties of the printed parts, and the implementation of our method provides an effective way to solve the defects of the FDM process.

A DMA-Based Approach to Quality Evaluation of Digitally Manufactured Continuous Fiber-Reinforced Composites from Thermoplastic Commingled Tow

Direct digital manufacturing of continuous fiber-reinforced thermoplastics exhibits the potential to relieve many of the constraints placed on the current design and manufacture of composite structures. At present, the additive manufacturing of continuous fiber-reinforced thermoplastics is demonstrated to varying extents; however, a comprehensive investigation of manufacturing defects and the quality of additively manufactured high fiber volume fraction continuous fiber-reinforced thermoplastic composites is limited. Considering the preliminary nature of the additive manufacturing of continuous fiber-reinforced thermoplastics, composites processed in this manner are typically subject to various manufacturing defects, including excessive void content in the thermoplastic matrix. Generally, quality evaluation of processed composites in the literature is limited to test methods that are largely influenced by the properties of the continuous fiber reinforcement, and as such, defects in the thermoplastic matrix are usually less impactful on the results and are often overlooked. Hardware to facilitate the direct digital manufacturing of continuous fiber-reinforced thermoplastic matrix composites was developed, and specimens were successfully processed with intentionally varied void content. The quality of the additively manufactured specimens was then evaluated in terms of the measured maximum storage modulus, maximum loss modulus, damping factor and the glass transition temperature by means of dynamic mechanical analysis (DMA). DMA allows for thermomechanical (i.e., highly matrix sensitive) evaluation of the composite specimens, specifically in terms of the measured elastic storage modulus, viscous loss modulus, damping factor and the glass transition temperature. Within the tested range of void contents from roughly 4–10%, evaluation by DMA resulted in a distinct reduction in the maximum measured storage modulus, maximum loss modulus and glass transition temperature with increasing void content, while the damping factor increased. Thus, the results of this work, which focused on the effect of void content on DMA measured properties, have demonstrated that DMA exhibits multi-faceted sensitivity to the presence of voids in the additively manufactured continuous fiber-reinforced thermoplastic specimens.

Ultrasonic welding of fiber-reinforced thermoplastic composites: a review

Ultrasonic welding of fiber-reinforced thermoplastic composites: a review

Investigation of the shear properties of 3D printed short carbon fiber-reinforced thermoplastic composites

Short fiber-reinforced 3D printed components are high performance materials with a wide range of potential applications in various industries ranging from aerospace to automotive. Mechanical characterization of 3D printed short carbon fiber polyethylene terephthalate and acrylonitrile butadiene styrene parts are presented under the application of shear load in this study. The anisotropy properties of both composite and polymer materials were investigated by printing samples at two different orientations, using fused deposition modeling (FDM) technique. The fabricated samples were subjected to tensile and shearing loads while 2D digital image correlation (DIC) was used to measure full-field strain on the specimen. The obtained results revealed a noticeable anisotropy in shear properties as the function of printing orientation. Moreover, it found that using carbon fiber-reinforced PET results in higher elastic modulus, tensile, and shear strengths up to 180%, 230%, and 40% compared to ABS.

Bending behaviour of thermoplastic composites in melt: A data-driven approach

The resistance to bending of continuous fibre-reinforced thermoplastic composites at processing temperature is an important predictor of wrinkle formation during the stamp forming process. This resistance can be quantified with experiments and approximated with models. However, current models are validated with one, or at most two, thermoplastic composites. Hence, it is not known whether these models generalise to other thermoplastic composites. This data-driven study proposes a rate- and temperature-dependent bending model derived from the experimental data of 10 very different thermoplastic composites. The multivariate data structure was analysed with a Tucker decomposition, together with bootstrapping and cross-validation, to reveal the important generalisable trends, and discard irrelevant features. The most suitable Tucker model could be parametrised to yield a four-parameter model, which approximates the deformation, rate, and temperature dependence, respectively using a linear, a power law, and an Arrhenius-type relation. The four-parameter model was validated with experimental data from four other thermoplastic composite materials. It can describe the measured rate- and temperature-dependent bending behaviour of a wide range of thermoplastic composites.

Impact behaviour and non destructive evaluation of 3D printed reinforced composites

The widespread additive manufacturing technology for producing components having complex geometries has increased the attention towards new reinforced materials, whose internal structure can be designed ad hoc on the required mechanical performance. Moreover, fused deposition modelling (FDM) technology allows the building of continuous fibre-reinforced thermoplastic composites. Due to this innovative technology, there is a lack of knowledge mainly about the impact behaviour of these materials, also considering that the main demand comes from the transportation field (automotive, aircraft, etc.), where the impact event is always possible.Thus, the aim of this research is the investigation of the impact behaviour of specimens obtained by continuous fiber fabrication technique, where Onyx and nylon white filaments were used as matrices and glass fibres for reinforcement. Onyx is a nylon mixed with short carbon fibres. An extensive non-destructive evaluation was performed on the specimens subjected to impact tests to assess the impact damage tolerance of these materials and to measure the damage extension as well. Nevertheless, considering that different non-destructive techniques were employed, the research aims also to suggest the most suitable and reliable technique to detect damage, mainly by on-site inspection.

Isothermal crystallisation ATP process for thermoplastic composites with semi-crystalline matrices using automated tape placement machine

Continuous fibre-reinforced thermoplastic composites based on semi-crystalline thermoplastic matrices, such as PA, and PP, have been most commonly used for thermoplastic automated tape placement (ATP). However, the fluidity of the matrix and rapid cooling rate also result in some intractable defects owing to the high peak temperatures of the nip point and compaction pressures of the roller, such as warpage, matrix squeeze-out, and fibre or ply waviness. Hence, a method for controlling the substrate temperature to achieve isothermal crystallisation in the ATP process was proposed, and the effect of isothermal temperatures on the structure and performance of the laminates was studied. The results revealed that the optimised process not only reduced the defects but also ensured the bonding strength and improved mechanical properties at a low peak temperature of the nip point. • An in-situ solidification approach for thermoplastic composites integrates isothermal crystallisation and ATP process. • Modifying the performance of ATP parts using low-cost thermoplastic composites with semicrystalline matrices. • Reducing defects such as matrix squeeze-out, in-plane and out-of-plane waviness, and warpages. • Improving the bonding strength and overall bending properties.

Numerical Simulation and Experimental Validation of Hybrid Injection Molded Short and Continuous Fiber-Reinforced Thermoplastic Composites.

In-situ thermoforming and overmolding of continuous fiber-reinforced thermoplastic composites by hybrid injection molding enables the mass production of thermoplastic lightweight structures with a complex geometry. In this study, the anisotropic mechanical behavior of such hybrid injection molded short and continuous fiber-reinforced thermoplastics and the numerical simulation of the resulting mechanical properties under flexural loading were investigated. For this, the influence of the volume flow rate between 25 and 100 cm3/s during injection molding of a PP/GF30 short fiber-reinforced overmolding material was studied and showed a strong effect on the fiber orientation but not on the fiber length, as investigated by computer tomography and fiber length analysis. Thus, the resulting anisotropies of the stiffness and strength as well as the strain hardening investigated by tensile testing were considered when the mechanical behavior of a hybrid test structure of short and continuous fiber-reinforced thermoplastic composites was predicted by numerical simulations. For this, a PP/GF60 and PP/GF30 hybrid injection molded test structure was investigated by a numerical workflow with implemented injection molding simulation data. In result, the prediction of the mechanical behavior of the hybrid test structure under flexural loading by numerical simulation was significantly improved, leading to a reduction of the deviation of the numerically predicted and experimentally measured flexural strength from 21% to 9% in comparison to the isotropic material model without the implementation of the injection molding data.

Manufacturing and Analysis of Overmolded Hybrid Fiber Polyamide 6 Composite.

Currently, fiber-reinforced thermoplastic composites are widely applied in structural applications. It has great potential to replace metal structures and provides advantages in weight reduction. In this study, the pretensioned unidirectional carbon fiber was overmolded by Polyamide 6 contained 30%wt of glass fibers (PA 6-30GF). Process parameters such as injection pressure, melting temperature, duration of carbon fiber cryogenic treatment, and fiber pretension were optimized to maximize the flexural strength, impact strength, and interlaminar properties of the hybrid composite. The relationship between factors and responses was analyzed using Box–Behnken design (BBD) from response surface methodology (RSM) and analysis of variance (ANOVA). Three levels were assigned for each factor. There were 27 experimental trials carried out, and a significant regression for the coefficient between the factors was derived. The BBD and ANOVA analysis demonstrate that the predicted values from the model are in satisfactory correlation with the experimental results. The optimum responses found were achieved by setting the following injection molding parameters: melting temperature of 278 °C and injection pressure of 122 bar. Carbon fiber, as a unidirectional reinforcement, should be immersed in liquid nitrogen for 10 min and mounted on the mold in a pretensioned state with a force of 100 N. The combination of these parameters can produce an optimum flexural strength of 248.6 Mpa, impact strength of 173.4 kJ/m2 and an ILSS of 30.4 Mpa.