Fiber-reinforced Thermoplastic Composites Research Articles

Comparative analysis of eddy current pulsed thermography and long pulse thermography for damage detection in metals and composites

Eddy current pulsed thermography (ECPT) and long pulse thermography (LPT) are two emerging non-destructive evaluation techniques that have been recently used for sub-surface defect detection in both metallic and composite components. This paper provides a comparative analysis of these two methods by focussing on the detection of flat bottom holes (FBHs) in both aluminium and carbon fibre reinforced plastic samples. Principal component analysis was used for the post-processing of thermal data in order to enhance the detection of FBHs with various diameters and depths. Results showed that LPT had a better performance for detecting FBHs in low-thermally conductive materials such as carbon fibre-reinforced thermoplastic composites, whilst ECPT revealed a superior performance for detecting FBHs in materials with higher thermal and electrical conductivity such as aluminium.

Inverse procedure for mechanical characterization of multi-layered non-rigid composite parts with applications to the assembly process

In assembly process, non-rigid parts in free-state may have different forms compared to the designed model caused by gravity load and residual stresses. For non-rigid parts made by multi-layered fiber-reinforced thermoplastic composites, this process becomes much more complex due to the nonlinear behavior of the material. This paper presented an inverse procedure for characterizing large anisotropic deformation behavior of four-layered, carbon fiber-reinforced polyphenylene sulphide, non-rigid composite parts. Mechanical responses were measured from the standard three points bending test and the surface displacements of composite plates under flexural loading test. An orthotropic hyperelastic material model was implemented as a UMAT user routine in the Abaqus/Standard to analyze the behavior of flexible fiber-reinforced thermoplastic composites. Error functions were defined by subtracting the experimental data from the numerical mechanical responses. Minimizing the error functions helps to identify the material parameters. These optimal parameters were validated for the case of an eight-layered composite material.

Comparison of Low-Velocity Impact Damage Behavior of Unidirectional Carbon Fiber-Reinforced Thermoset and Thermoplastic Composites

This paper investigates the damage behavior of thermoset and thermoplastic fiber-reinforced composites. The specimens were subjected to low-velocity impacts (LVI) to produce barely visible impact damages (BVID). To compare the dependency of the matrix system and the laminate lay-up on the impact damage, four test series were set up. Therefore, laminates with an epoxy (EP) and a polyether ether ketone (PEEK) matrix in a quasi-isotropic (QI) [+45/0/-45/90]2s and an orthotropic (OT) fiber lay-up [0/90]4s were manufactured. To eliminate the influence of variant fiber systems, the thermoplastic tape and the thermoset prepreg contain similar carbon fibers (CF). After impact testing with three different impact energies, inner damages were investigated by using ultrasonic analyses. To get a deeper understanding of the interior damage mechanisms, cross sections of the damaged areas were examined via reflected light microscopy. By using these destructive and non-destructive test methods, significant differences in the damage behavior of composites with thermoplastic and thermoset matrix systems were identified for both laminate lay-ups.

Plastic droplet welding: bond strength between plastic freeforming structures and continuous fiber-reinforced thermoplastic composites

Plastic freeforming (PF) is an additive-manufacturing process for producing three-dimensional plastic parts based on 3D CAD data by applying plastic droplets in layers. This process is used to produce customer-specific and complex geometries (prototypes and small series) on organic sheets. A comparable serial process is the injection of a second component onto organic sheets by injection molding. A sufficient bond between the PF structure and the organic sheets is of particular importance for each application. If this is not guaranteed, the composite system cannot withstand the mechanical load and fails. The force exerted on the system can no longer be transmitted between the PF structure and the organic sheet. The organic sheet is made of glass fiber-reinforced polypropylene (PP). The connection between the organic sheet and the PF structure is achieved by welding the molten polymer droplets and the surface of the organic sheet. The PF structures are made of PP to ensure sufficient compatibility with regard to the weldability of the components. The processing of PP in the PF process is a challenge because PP is a semi-crystalline material. The shrinkage of semi-crystalline materials is significantly higher compared to amorphous materials. Due to the layered structure of the components, the shrinkage of the individual layers results in undesired warpage. The adhesive strength between the organic sheet and the PF structure is investigated by determining the bending strength in the 3-point bending test. The investigations include an optimization of the process parameters to maximize the adhesive strength. The experimental investigations show that an increase of the nozzle and build chamber temperature leads to a higher adhesive strength. In further investigations, the temperature of the nozzle shows no significant influence on the surface temperature despite the expected heat radiation. The surface temperature is almost only dependent on the temperature of the build chamber.

A review of Long fibre thermoplastic (LFT) composites

ABSTRACTLong fibre-reinforced thermoplastic or long fibre thermoplastic (LFT) composites possess superior specific modulus and strength, excellent impact resistance, and other advantages such as ease of processability, recyclability, and excellent corrosion resistance. These advantages make LFT composites one of the most advanced lightweight engineering materials and enable their increasing use in various applications. This review paper summarises the research and development work that has been conducted on LFT composites since their initial development. Different aspects of LFTs, such as process development, fibre orientation distribution (FOD), fibre length distribution (FLD), and their effects on the mechanical properties of LFT composites are described. The characterisation of the FOD and FLD in the LFT composites using advanced imaging technology such as high-resolution 3D micro-CT scanning technique is summarised. Research and development of LFT hybridisation and LFT additives are also discussed. Finally, conclusions are made and the future outlook of LFT composites is given.

Syntactic core composite sandwich (SCCS) with thermoplastic foam and expanded glass granulate core

Ultra light, highly porous materials arranged as a sandwich structure with thermoplastic fiber reinforced composites (TP-FRC) as a cover layer have very good physical and mechanical properties. An essential prerequisite for the production of hybrid material composites is therefore the provision of material compatible and cost effective manufacturing processes. The lightweight potential of such a syntactic core composite sandwich (SCCS) with thermoplastic and expanded glass granules was examined with the aim of a mass production. After developing a manufacturing strategy, various samples are prepared and their mechanical properties are evaluated by performing bending tests and examination of micrographs.

CARACTERIZACIÓN DE UNIONES ADHESIVAS ENTRE COMPOSITES TERMOPLÁSTICOS REFORZADOS CON FIBRA CONTINUA (CFRTP) Y CAUCHO VULCANIZADO BAJO UNA SOLICITACIÓN DE CARGA A CIZALLA

El objetivo de este articulo es estudiar y proponer una metodologia para ensayar y caracterizar uniones adhesivas entre sustratos rigidos formados por materiales compuestos de matriz termoplastica reforzados con fibra continua (CFRTP) y goma vulcanizada bajo una solicitacion de carga a cizalla. La UE se comprometio en establecer reglas mas estrictas respecto a las emisiones de CO2 en la industria de automocion, lo que ha derivado en que los principales fabricantes de coches se centren en una politica de reduccion de peso del cuerpo del vehiculo mediante el uso de materiales CFRTP. Por lo tanto, se debe estudiar el comportamiento de estos nuevos materiales bajo distintos tipos de uniones. El ensayo definido en este documento se basa en un concepto de probeta single lap sobre la que se aplica una carga de cizalla con el fin de obtener las cargas maximas y analizar los diferentes tipos de fallos producidos. La metodologia definida se ha aplicado en una amplia gama de probetas fabricadas con diferentes combinaciones de materiales para confirmar que la metodologia puede ser usada como guia generalizada para caracterizar toda la variedad de combinaciones de uniones adhesivadas de goma-CFRTP, independientemente de los materiales y aditivos utilizados.

Finite element analysis of the residual stress of automotive wheel made of long glass fiber-reinforced thermoplastic composite

To increase the simulation accuracy, a finite element analysis method for the prediction of the residual stress distribution in the injection molded wheel made of the long glass fiber-reinforced thermoplastic composite (LGFT) is studied, and a simulation method of the wheel bending fatigue test considering the residual stress distribution is investigated in this paper. First, the in-cavity residual stress is calculated using the molding simulation method. Then the residual stress relaxation process is analyzed and the final residual stress distribution is obtained. With the residual stress as the initial stress, the structural simulation of the LGFT wheel under the bending load is performed. To evaluate the influence of the residual stress on the LGFT wheel, an additional simulation without considering the residual stress is conducted. The result shows that the interior stress considering residual stress is much higher than that without considering residual stress. To verify the simulation accuracy of these two cases, the high-stress area locations in the simulation results are compared with the damage locations in physical bending fatigue test. The result illustrates that the simulation result considering the residual stress accords with the experimental result better. Therefore, the simulation result of the residual stress is reasonable, and it is necessary to consider residual stress in the simulation of the LGFT wheel.

Internal damage evaluation of composite structures using phased array ultrasonic technique: Impact damage assessment in CFRP and 3D printed reinforced composites

The application of non-destructive techniques for the evaluation of internal damage in composite materials is a challenge due to their complexity. The aim of this study is to analyse the ability of ultrasonic technique to identify and evaluate manufacturing defects and internal damage in composite laminates. Artificial object inclusions of different shapes, sizes and materials were embedded in carbon fibre reinforced epoxy (CFRP) laminates. Comprehensive investigation of non-destructive evaluation using phased array ultrasonic testing to trace and characterize the embedded defects is presented. Phased array ultrasonic technique was able to precisely locate most of the artificial inclusion in the composite laminates. Nerveless, the shape and size of the inclusions were not accurately determined due to the high signal attenuation and distortion characteristics of the carbon fibre epoxy composite.Furthermore, a major concern affecting the efficient use of composite laminates is their vulnerability to low velocity impact damage. The dynamic behaviour of composite laminates is very complex as there are many concurrent phenomena during composite laminate failure under impact loading. Thus, the practicality of the previous results is demonstrated by the evaluation of impacted carbon fibre reinforced epoxy laminates using ultrasonic testing. The influence of laminate thickness and impact energy on impact damage is also investigated. The performance of phased array ultrasonic testing for the inspection of composite laminates with barely visible impact damage is evaluated. In addition, fibre-reinforced thermoplastic composites are becoming more significant in industrial applications due to their excellent mechanical performance and potential recycling. In this study, impact damage in 3D printed continuous glass fibre reinforced thermoplastic laminates is also analysed. Phased array ultrasonic testing is performed and the amount of damage is quantified in terms of delaminated area.

A new methodology for rapidly assessing interfacial bonding within fibre-reinforced thermoplastic composites

A new testing methodology is presented for determining the adhesion strength and failure at composite interfaces. An automated bonding evaluation system (ABES) has been adapted to process and test thermoplastic sandwich composites formed with various natural solid phase materials such as wood. Composites can be rapidly formed and then tested in situ over a range of temperatures to provide information on interfacial adhesion and shear strength between the thermoplastic and the substrate. This methodology is demonstrated for HDPE, PP, PLA and TPU composites comprising wood as solid phases. The interfacial properties depend on processing and testing temperatures, individual thermoplastic phase properties, and wood species. It is expected that this new test method will have applicability in thermoplastic composite design, manufacture and service life predictions for reinforced or filled thermoplastics.

Development and validation of extrusion deposition additive manufacturing process simulations

The process simulation tool Additive3D has been developed in Abaqus© 2017 to model the Extrusion Deposition Additive Manufacturing (EDAM) process for fiber-reinforced thermoplastic composites. This additive manufacturing (AM) method encompasses material deposition processes where geometries are constructed layer by layer and the resulting layer properties are highly anisotropic.The goal is to predict final deformed shapes and residual stresses of printed geometries due to the printing process and the material anisotropy. The resulting design tool allows to assess the outcomes of the printing process based on the part geometry, the printing material and the position control parameters.Material properties were characterized, and validation experiments, without additional calibration, show an excellent agreement between modeled and measured part deformation states with relative deviations below 7%. Due to the physics-based nature of the developed simulation tools, the simulations can be extended to account for different part scales, printing materials and printing histories.

Improving mechanical properties of continuous fiber-reinforced thermoplastic composites produced by FDM 3D printer

The main purpose of this research is to bolster mechanical properties of the parts, produced by an extrusion-based 3D printer, or fused deposition modeling machine, via increasing the content of continuous fiber yarn to its practical limit. In-melt continuous glass fiber yarn embedding was applied as a reliable and consistent method for simultaneous impregnation to produce continuous fiber-reinforced thermoplastic composites in the fused deposition modeling process. It is well known that the main weakness in the fused deposition modeling 3D printed products is their low strength compared to the manufactured ones by conventional methods such as injection molding and machining processes. This characteristic can be related to both inherent weakness of thermoplastic materials and poor adhesion between the deposited rasters and the layers. Although various attempts have been performed to tackle this issue, it is widely believed that using continuous fibers is the most effective method to serve this purpose if a reliable and consistent method is implemented. Since the mechanical properties of continuous fiber-reinforced composites directly depend on the content of fiber volume, maximizing the fiber content as well as producing an integrated part was assumed as the main objective. In this work, an analysis of various patterns of raster deposition was conducted, followed by the experiments and verification. The effective parameters on the fiber yarn volume, such as fiber yarn diameter, fiber yarn laying pattern, extrusion width, layer height, and flow percentage, were investigated and their optimal values were reported. The attained experimental results showed that, for polylactic acid-glass fiber yarn reinforced composite, with the extrusion width of 0.3 mm, the layer heights of 0.22 mm, flow percentage of 0.43, and the rectangular laying pattern, approximately 50% fiber-volume content can be achieved which resulted in tensile yield strength and modulus of 478 MPa and 29.4 GPa, respectively. There was an excellent agreement between these experimental results and predicted theoretically values by rule of mixture.

Natural fibre-reinforced thermoplastic composites from woven-nonwoven textile preforms: Mechanical and fire performance study

Partially and fully biodegradable natural fibre – reinforced composites have been prepared using a novel patented woven-nonwoven technology. Natural fibres included jute and sisal, whereas the matrices were of synthetic polymers derived from petroleum (polypropylene (PP)) or natural (polylactic acid (PLA)) resources. The physical, mechanical and flammability properties of these partially and fully biodegradable composites have been studied and compared with those of similarly produced glass-fibre reinforced PP and PLA composites with a view to enabling their use in automotive applications. Mechanical test results showed that the tensile and flexural moduli of the PLA composites were higher than respective PP composites. In comparison, sisal composites have higher tensile and flexural moduli than jute composites. The fire performance of the composites studied by cone calorimetry showed that while natural fibre reinforcement had no effect on time-to-ignition, peak heat release was significantly reduced. PLA composites had lower burning propensity compared to respective PP composites.

CAE method for compression molding of carbon fiber-reinforced thermoplastic composite using bulk materials

There has been great interest in using fiber-reinforced polymer composites to develop lightweight components for automotive applications. Compression molding of carbon fiber (CF) reinforced thermoplastic is one of the preferred processes, as it offers the opportunity to maintain a longer fiber length and higher volume production. We have developed a unique computer aided engineering (CAE) method by utilizing viscoelastic structural analysis to accurately predict the warpage behavior of fiber-reinforced thermoplastic material under the compression molding process from a bulk charge format. A prototype structure with complex geometry was designed and manufactured for validation purposes. The fiber orientation and warpage results from both the CAE and actual part were compared to verify the accuracy of the CAE method. Additional studies related to the charge footprint effect were also conducted for the compression molding process on the same materials. The developed method and tools are expected to help in expediting the development of lightweight carbon fiber-reinforced thermoplastic parts.

Micro-scale model for a multi-scale modeling approach of thermoplastic fiber reinforced polymers

Thermoplastic fiber reinforced composites (TPFRCs) are becoming more important due to the potential of short part cycle times and recyclability. One major problem of these materials is process stability. During processing, unwanted distortions appear due to residual stresses on different scales. The prediction of these distortions and stresses would reduce the cost of TPFRCs and would assist in achieving a higher market share. For the prediction of the residual stresses, a new multi-scale simulation approach is required. The research presented in this paper is a contribution to the micro-scale model. A method for the representation of the thermoplastic matrix in a 2D micro-scale model is developed. With this, the a solid as well as a semi-liquid state of the polymer which appear during thermoforming can be represented.

Effects of KMnO4 Treatment on the Flexural, Impact, and Thermal Properties of Sugar Palm Fiber-Reinforced Thermoplastic Polyurethane Composites

Global warming has had a great impact on environmental changes since the last decade. Eco-friendly industrial products are of great importance to sustain life on earth, including using natural composites. Natural fibers used as fillers are also environmentally valuable because of their biodegradable nature. However, compatibility issues between the fiber and its respective matrix is a major concern. The present work focused on the study of the flexural, impact, and thermal behaviors of environmentally friendly sugar palm fibers (SPF) incorporated into a composite with thermoplastic polyurethane (TPU). Two techniques (extrusion and compression molding) were used to prepare these composites. The fiber size and dosage were kept constant at 250 µm and 30 wt.% SPF, respectively. The effects of potassium permanganate (KMnO4) treatment on the flexural, impact, and thermal behaviors of the treated SPF with 6% NaOH-reinforced TPU composites were investigated. Three different concentrations of KMnO4 (0.033%, 0.066%, and 0.125%) were studied for this purpose. The characterization of the flexural and impact properties of the new TPU/SPF composites was studied as per American Society for Testing Materials ASTM standards. Thermogravimetric analysis was employed for thermal behavior analysis of the TPU/SPF composites. The best flexural strength, impact strength, and modulus properties (8.118 MPa, 55.185 kJ/m2, and 262.102 MPa, respectively) were obtained with a 0.033% KMnO4-treated sample. However, all flexural strength, impact strength, and modulus properties for the KMnO4-treated samples were lower than the sample treated only with 6% NaOH. The highest thermal stability was also shown by the sample treated with 0.033% KMnO4. Therefore, this method enhanced the thermal properties of the TPU/SPF composites with clear deterioration of the flexural and impact properties.

Exploiting cyclic softening in continuous lattice fabrication for the additive manufacturing of high performance fibre-reinforced thermoplastic composite materials

Continuous lattice fabrication (CLF) was recently introduced as a new additive manufacturing (AM) technology capable of printing continuous fibre-reinforced thermoplastic composites along desired trajectories in three-dimensional space. In a systematic attempt to maximize the mechanical properties of the printed extrudate by minimizing the residual void content, this study investigates the thermal deconsolidation behaviour observed in pultruded unidirectional fibre-reinforced thermoplastic composite material when it is reheated above its melting point and exposed to ambient pressure. Fibre decompaction, generally accepted to be the primary cause for deconsolidation in fibre-reinforced thermoplastics, was investigated to assess the influence of cyclic softening of the fibrous media on the residual void content of the extruded material. The magnitude and rate of fibre decompaction were observed to decrease with the number of consolidation-deconsolidation cycles to which the material was subjected. A model was developed to predict the degree of deconsolidation in the CLF process as a function of temperature, processing speed, and processing history. Based on the deconsolidation behaviour observed, a multi-stage pultrusion module was designed that exploits cyclic softening and was demonstrated to reduce the residual void content of the printed extrudate by over 80%.

Effect of thermal properties on laser cutting of continuous glass and carbon fiber-reinforced polyamide 6 composites

ABSTRACTThe single mode fiber laser cutting of two types of continuous fiber-reinforced thermoplastic composites (TPC) with polyamide 6 (PA6) matrix and a fiber content of 60 wt% was investigated: a glass fiber-reinforced composite (PA6/GF60) and a carbon fiber-reinforced composite (PA6/CF60). Preliminary, the thermal properties of the composites were analyzed to derive the cutting mechanisms. Thermogravimetric Analysis (TGA) showed decomposition onset temperatures of 457.6°C for the PA6 matrix and 737.3°C for the carbon fibers, while no thermal decomposition of the glass fibers was detected up to 1,000°C. In consequence, the single mode fiber laser cutting of the PA6/GF60 composites required a significantly higher number of cutting cycles in conjunction with an increased heat affected zone (HAZ) as compared to the PA6/CF60 composites. Analysis of the HAZ and the mechanical properties of the laser cut composites by optical microscopy and uniaxial tensile testing showed an anisotropy and dependency on the laminate structure. However, the obtained mechanical properties of the laser cut composites were found comparable to their water jet cut counterparts.

A non-destructive optical experimental method to predict extinction coefficient of glass fibre-reinforced thermoplastic composites

The aim of this paper is to develop a cost-effective, efficient and fast experimental optical method to predict the optical properties (extinction coefficient) of semi-transparent glass-fibre-reinforced polymer composites. The extinction coefficient takes into account the effects due to the absorption and the scattering phenomena in a semi-transparent component during the laser processes, i.e. TTLW (Through-Transmission Laser Welding). A laser as light source and a reflex camera equipped with a macro lens as a measuring device are used in the present method. It is based on the measuring of the transmission of light through different thicknesses of samples. The interaction between the incident laser beam and the semi-transparent composite is examined. The results are presented for the case of a semi-transparent composite reinforced with unidirectional glass fibre. A numerical method, ray tracing, is used to validate the experimental results. The ray tracing method is suitable for characterizing the light-scattering in semi-transparent materials.

Effects of Styrene-Acrylic Sizing on the Mechanical Properties of Carbon Fiber Thermoplastic Towpregs and Their Composites.

Thermoplastic towpregs are convenient and scalable raw materials for the fabrication of continuous fiber-reinforced thermoplastic matrix composites. In this paper, the potential to employ epoxy and styrene-acrylic sizing agents was evaluated for the making of carbon fiber thermoplastic towpregs via a powder-coating method. The protective effects and thermal stability of these sizing agents were investigated by single fiber tensile test and differential scanning calorimetry (DSC) measurement. The results indicate that the epoxy sizing agent provides better protection to carbon fibers, but it cannot be used for thermoplastic towpreg processing due to its poor chemical stability at high temperature. The bending rigidity of the tows and towpregs with two styrene-acrylic sizing agents was measured by cantilever and Kawabata methods. The styrene-acrylic sized towpregs show low torque values, and are suitable for further processing, such as weaving, preforming, and winding. Finally, composite panels were fabricated directly from the towpregs by hot compression molding. Both of the composite panels show superior flexural strength (>400 MPa), flexural modulus (>63 GPa), and interlaminar shear strength (>27 MPa), indicating the applicability of these two styrene-acrylic sizing agents for carbon fiber thermoplastic towpregs.