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Abstract To develop a material with strong impact resistance, bending direction and in‐plane direction, the tensile and bending properties of sandwich films obtained by placing and re‐pressing a compression‐molded polypropylene sheet between two sheets of carbon‐fiber‐reinforced thermoplastics (CFRTPs) were evaluated. Three types of CFRTP were investigated, and thermoplastic nylon 66, polyurethane, and polyphenylene sulfite were used as the resin base materials to wrap the carbon fiber. Regarding the tensile properties of the sandwich films, the Young's modulus and maximum stress values were lower compared with those of the CFRTP sheets, regardless of the resin base material. However, improvements in elongation properties of 97%, 109%, and 156%, respectively were found, transforming the film into a softer and stronger film. Regarding the bending properties of the sandwich films, the Young's modulus and maximum stress values were higher compared with those of the CFRTP sheet. To examine the influence of the number of layers, the five‐layer sheet, in which the sandwich film was placed in two CFRTP sheets, exhibited inferior elongation properties to the three‐layer sheet during the tensile test. However, the results of the bending test found a significant improvement in Young's modulus of approximately 2.5 times and final strength of approximately three times. We anticipate that this material could be applicable to components requiring specific mechanical properties in both bending and in‐plane directions in future applications. Highlights CFRTP sandwich sheets were fabricated using a simple hot‐press method. The sandwich sheet showed improved mechanical properties in the in‐plane directions. Both the tensile modulus and the bending modulus have reached the GPa‐order. The sandwich film in question had particularly excellent bending properties. The sandwich film showed dependence on the number of layers. In‐plane elasticity of the films was evaluated using a falling ball test.

Highlights Sandwich films were prepared by inserting resin sheets between carbon fiber‐reinforced thermoplastic (CFRTP) sheets, and their tensile and bending strengths were evaluated. The CFRTP sheets used nylon 66, polyurethane, and polyphenylene sulfide as impregnating resins. The resin sheet used was polypropylene, a general‐purpose resin, combined with a composite material incorporating polyrotaxane and cellulose nanofibers as organic fillers. The sample containing both components showed a 134% improvement in Young's modulus compared to neat polypropylene. This study controlled the number of layers in the sandwich film and assessed the dependence of mechanical properties on layer count. The sandwich films demonstrated particularly good strength in the in‐plane direction, exhibiting excellent bending properties. Furthermore, using composite materials for the resins sandwiched between CFRTP sheets further enhanced mechanical properties. The film material, which can be prepared through simple press molding, is a lightweight material composed of light elements, and exhibits a Young's modulus in the gigapascal scale. CFRTP sheets using nylon 66 as the impregnating resin, the flexural modulus improved by approximately 5.8 times. Furthermore, by increasing the number of laminations, an additional improvement of 3.1 times was observed. This study also identified conditions for improving elongation properties. A new material was created using carbon fiber reinforced thermoplastics (CFRTP). Multilayered alternating films made of CFRTP and polymer composite were created. Corresponding multilayer films showed anisotropy in mechanical properties. Corresponding multilayer films exhibited excellent in‐plane elasticity. In‐plane elasticity showed a clear dependency on the number of layers. [ABSTRACT FROM AUTHOR]

To develop a material with strong impact resistance, bending direction and in‐plane direction, the tensile and bending properties of sandwich films obtained by placing and re‐pressing a compression‐molded polypropylene sheet between two sheets of carbon‐fiber‐reinforced thermoplastics (CFRTPs) were evaluated. Three types of CFRTP were investigated, and thermoplastic nylon 66, polyurethane, and polyphenylene sulfite were used as the resin base materials to wrap the carbon fiber. Regarding the tensile properties of the sandwich films, the Young's modulus and maximum stress values were lower compared with those of the CFRTP sheets, regardless of the resin base material. However, improvements in elongation properties of 97%, 109%, and 156%, respectively were found, transforming the film into a softer and stronger film. Regarding the bending properties of the sandwich films, the Young's modulus and maximum stress values were higher compared with those of the CFRTP sheet. To examine the influence of the number of layers, the five‐layer sheet, in which the sandwich film was placed in two CFRTP sheets, exhibited inferior elongation properties to the three‐layer sheet during the tensile test. However, the results of the bending test found a significant improvement in Young's modulus of approximately 2.5 times and final strength of approximately three times. We anticipate that this material could be applicable to components requiring specific mechanical properties in both bending and in‐plane directions in future applications. Highlights: CFRTP sandwich sheets were fabricated using a simple hot‐press method.The sandwich sheet showed improved mechanical properties in the in‐plane directions.Both the tensile modulus and the bending modulus have reached the GPa‐order.The sandwich film in question had particularly excellent bending properties.The sandwich film showed dependence on the number of layers.In‐plane elasticity of the films was evaluated using a falling ball test. [ABSTRACT FROM AUTHOR]

This study explores the influence of post-weld annealing on friction stir welded (FSW) carbon fiber reinforced thermoplastic (CFRTP) in woven laminate form. Field advancement occurs in three key areas including furthering the understanding low-melt polyaryletherketone (LMPAEK) welding/processing, effects of post-weld annealing on CFRTP joints, and determining feasibility for friction stir welding (FSW) of thermoplastics reinforced with continuous carbon fibers. High temperature annealing just below LMPAEK's melting point improved ultimate tensile strength by up to 30% and weld toughness by up to 91%. Improvements to mechanical performance result from increases in joint crystalline content from 14.09% in non-annealed joints to 27.91% in joints subject to 280 ◦ C annealing. Annealing does not reduce porosity in the weld zones, rendering necessary further improvements to the FSW process for CFRTP joints. Further analysis also indicates that despite its slight molecular modifications, LMPAEK has highly similar crystalline structure and response to thermal treatment compared to PEEK. [ABSTRACT FROM AUTHOR]

This article investigates the use of nickel electroplated carbon fiber (Ni‐CF) fabric to enhance the electromagnetic interference (EMI) shielding capability of carbon fiber reinforced thermoplastics (CFRTs), particularly for automotive and aerospace applications. The study examines the influence of nickel electroplating parameters of carbon fiber on the morphologies of carbon fiber fabrics. Ni‐CF reinforced polyamide 6 (Ni‐CF/PA 6) was prepared by the film‐stacking method. The flexural properties analysis demonstrates a 21.1% increase in flexural strength for Ni‐CF/PA 6 composites compared to as‐received carbon fiber reinforced PA 6 (CF/PA 6) composites. Additionally, the introduction of nickel layer significantly improves the EMI shielding efficiency of CF/PA 6 composites, with the average shielding efficiency increasing from 23.5 to 31.6 dB within the X‐band and Ku‐band frequency ranges. Scanning electron microscope (SEM) analysis confirms that the nickel layer enhances the interfacial bonding between the PA 6 matrix and the Ni‐CF, which is attributed to the micro cone‐shaped structures of the nickel layer. Overall, the electroplating method effectively modifies the carbon fiber surface, resulting in composite laminates with enhanced mechanical properties and superior EMI shielding efficiency. These findings provide valuable insights for the development of advanced carbon fiber reinforced composites with improved functionalities in various applications. Highlights: The electroplating method is used to process the nickel electroplated carbon fiber fabrics.The introduction of micro cone‐shaped structure nickel on the fiber surface by electroplating provides the mechanical interlocking between carbon fiber and matrix.The nickel electroplated carbon fiber can significantly increase electromagnetic interference shielding capability of carbon fiber reinforced thermoplastic composites. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced thermoplastics (CFRTP) have increasing use in aerospace structures due to improved process-ability and weldability. In this study, lap joints between carbon fiber reinforced low-meltpolyaryletherketone (LMPAEK) are formed by friction stir welding (FSW). This study presents novelty by applying FSW to continuous carbon fiber composites in woven laminate form. FSW disrupts the fibers in the weld zone and distributes fragments as small as several microns in length. Thermal analysis shows that the weld zones degrade at 40°C cooler temperatures than the base laminate material due to enhanced polymer mobility surrounding the disrupted carbon fibers. Though optimized joints have regions of over 9% porosity, tensile strengths of up to 73.8 MPa retains up to 50% joint efficiency of a comparable short carbon fiber reinforced composite. CFRTP also requires lower processing forces during FSW than metals, and the power consumption of 67 W during the traverse period for strength optimized welds retains energy efficient characteristics. [ABSTRACT FROM AUTHOR]

Because of the high viscosity and poor fluidity of thermoplastic resin, it is easy to form voids in thermoplastic composites fabricated by traditional methods. The introduction of ultrasonic vibration into the fabrication of thermoplastic composites promotes the flow of thermoplastic resin and improve the quality of thermoplastic composites. In this study, continuous carbon fiber-reinforced polyamide 6 (CF/PA 6) composites were fabricated by ultrasonic vibration. The effects of ultrasonic amplitude and welding time on the temperature variations of the CF/PA 6 stack during the fabrication process were studied. Experimental results show that increasing the ultrasonic amplitude and welding time can increase the fiber volume fraction and decrease the void content of CF/PA 6 composites. The maximum fiber volume fraction is around 49.6%, and the minimum void content is around 0.09%. Meanwhile, the average diameter of single carbon fiber in CF/PA composites decreases from 7 μm of as-received carbon fiber to 6.03 ± 0.04 μm of composites fabricated at the welding time of 15 s and the ultrasonic amplitude of 90 μm. Additionally, the flexural strength of composites is improved within a limited window, while the flexural modulus increases with the increase of ultrasonic amplitude and welding time due to more compact CF fabrics in the composite laminates. The obtained maximum flexural modulus of CF/PA 6 composite laminates can reach up to 31.8 ± 3.9 GPa. The failure mode of composites is sensitive to the ultrasonic vibration parameters. [ABSTRACT FROM AUTHOR]

Injection compression molding technique with self‐resistance electric heating provides an effective way to fabricate continuous carbon fiber reinforced thermoplastics (cCFRTs) components, but it may also have a significant impact on the properties of the components by inducing undesirable effects. It is necessary to understand the manufacturing process and minimize the introduction of undesirable factors. Thus, this work is to investigate the influence of process parameters (i.e., melt temperature, current intensity, holding pressure, and holding time) on the impregnation quality and mechanical properties of cCFRTs. The results show that fiber fabrics cannot be uniformly distributed in all cCFRTs, resulting in a thick polymer layer on the top of all cCFRTs. Moreover, the fiber distribution shows insensitive to the processing parameters. The increase of melt temperature, the decrease of current intensity and the extension of holding time are conducive to reduce void content and the frequency of macro void; While excessive holding pressure cannot reduce void content due to serious overflow of resin. Meanwhile, the effect of processing parameters on the mechanical properties and fracture morphology of the sample was also determined. The findings show that the flexural strength of the sample is 106.7 ± 0.8 MPa using the optimal processing parameters. [ABSTRACT FROM AUTHOR]

The mechanical properties of open-hole tensile (OHT) specimens made of 3D-printed continuous carbon-fiber-reinforced thermoplastics (CFRTPs) were investigated. The stacking sequence of the OHT specimens were [0/90]2s, and the as-printed specimens possessed higher porosity (15.19%) than conventional fiber reinforced composites. The OHT tests demonstrated that the tensile modulus and fracture strength of the as-printed specimens exhibited 36.7 ± 0.3 GPa and 226.0 ± 9.0 MPa, respectively. To evaluate the effects of voids on the OHT properties, the 3D-printed CFRTPs were hot-pressed, where fiber orientation and porosity (3.41 ± 0.10%) were improved. Additionally, the tensile modulus was increased to 45.1 ± 0.8 GPa, which is 23% higher than the as-printed specimens, even though the fracture strength were comparable or lower than that of as-printed specimens. To validate such OHT properties, a numerical multiscale model was introduced, with a microscale periodic unit cell (PUC) analysis for determining the effective tensile moduli and mesoscale extended finite element method (XFEM) analysis for OHT properties. In the PUC analysis, we considered a two-scale numerical model including a fiber-resin scale with fiber orientation for effective tensile moduli of a CFRTP filament, and filament-void scale for those of a CFRTP laminate. The porosity and fiber orientation were measured by X-ray computed tomography and digital microscopy observations, and the porosity for the 0° specimen were 14.86%. By substituting the effective tensile moduli of the filament-void scale and those of the fiber-resin scale into the XFEM, respectively, the stress-strain responses of the computational OHT models were found to be in good agreement with those of the experimental results of as-printed and hot-pressed CFRTP, respectively. Both the OHT models showed that the Weibull criterion was satisfied without significant delamination at the failure strain, corresponding to the brittle failure mode due to fiber breakage, which agreed reasonably well with the experimental observations. [ABSTRACT FROM AUTHOR]

It has been explored that thin ply would improve the mechanical performances of carbon fiber reinforced epoxy composites laminate. It has not been known whether there are similar effects on thermoplastic composites. In this article, carbon fiber reinforced polyamide 6 (CF/PA6) unidirectional fabrics with two thicknesses of 0.045 and 0.105 mm were used to fabricate the unidirectional laminate (UDL). Tensile and bending behaviors of the UDL were recorded with a digital image correlation (DIC) system, their damage macro‐morphologies were observed with high‐speed camera during loading. The fracture microstructures of the samples were observed with SEM and optic microscope. The results showed that the tensile and bending strengths of the samples with 0.045 mm thick are 79.8% and 24.8% higher than that with 0.105 mm thick. Thinning ply can inhibit the crack expanding, and the time from crack originating to fracture of the sample is larger than that of the thick ply one. Morphologies of the fractures revealed that the crack mainly expanded in the matrix along the loading direction for thin‐ply laminate, while the crack developed in the fiber cluster for thick‐ply laminate. The results also revealed that the mechanical properties of the laminate can be improved obviously by using thin‐ply. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastics (CFRP) with the matrix of thermoplastic resin called as carbon fiber reinforced thermoplastics (CFRTPs) has been widely used in the industrial fields. Recently, a thermoplastic epoxy resin (TP-EP resin) has been developed as the matrix of CFRTP and carbon fiber reinforced TP-EP strands (CF/TP strands) molded by pultrusion method began to be used as tension rods for infrastructure under water absorption. On the other hand, an accelerated testing methodology (ATM) for predicting statistically long-term creep and fatigue strengths of CFRP was established by the authors. This study examines the prediction of statistical life time for these developed CF/TP strands at creep and fatigue tension loadings under the wet condition of water absorption with comparison to similar prediction under a dry condition by using our developed ATM. First, the static, creep, and fatigue tensile strengths of CF/TP strands were measured statistically at various constant temperatures under wet and dry conditions. The statistical long-term creep and fatigue tensile strengths for CF/TP strands under wet and dry conditions are predicted by substituting the measured data into the formulations of these strengths on our developed ATM. Finally, the influences of water absorption on the statistical long-term creep and fatigue strengths of CF/TP strands are cleared. In particular, the degradation of relaxation modulus of matrix TP-EP resin with increasing of elapsed time is accelerated with the water absorption, and the degradation of creep strength of CF/TP strand with increasing of elapsed time is also accelerated with the water absorption in the similar manner of matrix resin. On the other hand, the fatigue strength of CF/TP strand decreases scarcely with water absorption although this fatigue strength depends remarkably on the number of cycles to failure. [ABSTRACT FROM AUTHOR]

In the conventional process of thermoplastic composites, a heating stage from the external heat source usually consumes a large amount of energy. To solve this problem, self‐resistance electric (SRE) heating of carbon fiber‐reinforcement was introduced to form a continuous carbon fiber reinforced polyamide 6 (CF/PA 6) composite based on film stacking technique in this paper. The temperature distribution was first measured to verify the temperature uniformity for SRE heating process. X‐ray photoelectron spectroscopy (XPS) was used to assess effects on the chemical properties of carbon fibers from SRE heating and conventional convective heating. To evaluate forming quality by SRE heating, the physical properties, crystallinity, and mechanical properties of CF/PA 6 composites were measured. The results show that the forming time and energy consumption of SRE heating process are significantly reduced compared with that of the traditional heating process because of fast heating/cooling rate. While fast heating/cooling rate of SRE heating process leads to a higher void content, which finally results in a slightly lower flexural strength and impact properties of composite laminates. It is clear that SRE heating technique is one of the energy‐ and cost‐effective ways to fabricate continuous carbon fiber reinforced thermoplastic composites although the forming quality is still improved in future investigation. [ABSTRACT FROM AUTHOR]

Recently, the Innovative Composite Center of Kanazawa Institute of Technology developed a thermoplastic epoxy resin (TP-EP). Resin-impregnated carbon fiber reinforced TP-EP (CF/TP) strands molded by pultrusion were developed by Komatsu Matere Co., Ltd., for use as tension rods. This study examines the prediction of the statistical life time for these developed CF/TP strands under cyclic tension loading with comparison to our earlier report of similar predictions for carbon fiber reinforced thermoset epoxy resin (CF/TS) strands having a thermoset epoxy resin (TS-EP) as a matrix. First, test methods for static and fatigue strengths at elevated temperatures were developed for CF/TP strands. Second, static and fatigue tensile strengths of CF/TP strands were measured statistically at various constant temperatures under a constant strain rate and frequency. The master curves of statistical fatigue tensile strengths for CF/TP strands were constructed by substituting the measured data into the formulations of these strengths based on the matrix resin viscoelasticity. The fatigue strength characteristics of CF/TP strands were discussed through comparison to those of CF/TS strands with thermosetting epoxy resin as the matrix. [ABSTRACT FROM AUTHOR]

Evaluating the internal geometry of carbon fiber reinforced plastics is important to predict its mechanical properties and fracture behavior. In this study, we employed two different commercially available image processing software – AVIZO and 3D-Bon to analyze the fiber orientation distribution (FOD) of the chopped carbon fiber tape reinforced thermoplastics (CTT) by processing the imaged volume observed from an X-ray computed tomography (CT) system. To clarify the capability of the CT observation and subsequent analysis, the elastic modulus of CTT was estimated analytically based on the FOD data. Meanwhile, the experimental results were selected as the reference value for qualification. The local FOD, which was obtained from an individual observation, presented local anisotropy and stochastic dispersion of the fiber strands, while we found that the representative FOD of CTT can be acquired by performing CT observation and analysis on more than 15 samples. The statistical analysis and cross section observation were performed to validate the reliability of multi-sample observation. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced thermoplastic (CFRTP) has a good electromagnetic shielding property due to its higher conductivity and broad absorption frequency bandwidth while presenting high specific strength and stiffness, their easy process-ability, cost-effectiveness, and recyclability. In the present study, laminated CFRTP made of carbon fiber-polyamide 6 unidirectional tape (UD tape) were fabricated with different laminate configurations and arrangements (unidirectional, bidirectional, and quasi–isotropic) and then were compared with randomly chopped-tape CFRTP. Thereafter, estimated electromagnetic interference shielding effectiveness (EMI-SE) using Simon formalism and flexural properties of CFRTP were evaluated. The result showed a remarkable total EMI-SE of 31–44 dB in the Ultra High Frequency (UHF) range and strongly correlated with the laminate configuration of CFRTP. Whereas, randomly chopped-tape CFRTP has a lower total EMI-SE of 23–27 dB in the same frequency range. In addition, the flexural test result showed the flexural strength and modulus are strongly influenced by the tape layer configuration in the laminated CFRTP. Moreover, microscopy analysis was also conducted to verify the interlaminar structure and fiber-to-fiber contact in the composite. In conclusion, laminated CFRTP made of UD tape can be considered as electromagnetic interference shielding material for both functional and structural applications. [ABSTRACT FROM AUTHOR]

Recently, a thermoplastic epoxy resin (TP-EP) was developed at the Innovative Composite Center of Kanazawa Institute of Technology. Resin-impregnated carbon fiber reinforced TP-EP (CF/TP) strands molded by pultrusion were developed for use as tension rods by Komatsu Matere Co. Ltd. This study examines the prediction of the statistical life time for these developed CF/TP strands under creep tension loading with comparison to similar prediction for CF/TS strands having a thermoset epoxy resin (TS-EP) as matrix described in our earlier report. First, a test method for creep strength and static strength at elevated temperatures was developed for CF/TP strands. Second, the static tensile strengths of CF/TP strands were measured statistically at various constant temperatures under a constant strain rate. The statistical creep failure times under tension loading for CF/TP strands were predicted at a constant temperature by substituting the statistical static strengths into the formulation based on the matrix resin viscoelasticity. Third, the validity of predicted results was clarified by comparison with the creep failure times measured statistically using creep tests for CF/TP strands. Finally, the relation between the failure probability and creep failure times for CF/TP strands at various loads and temperature conditions was discussed by comparing the result of CF/TS strands with those for thermosetting epoxy resin as the matrix. [ABSTRACT FROM AUTHOR]

The effects of molding conditions on the flexural strength of textile carbon fiber reinforced polycarbonate laminates were assessed. Choosing the temperature and pressure conditions appropriately during hot-press molding using carbon fiber textile layers and polycarbonate films can produce void-free, high interfacial adhesion in textile carbon fiber reinforced polycarbonate laminates. Those characteristics were confirmed from observing the cross-sections of carbon fiber reinforced polycarbonate laminates and measuring the interlaminar shear strength. A suitable molding condition can raise the flexural strength of carbon fiber reinforced polycarbonate laminates to a level predicted from the measured flexural strength of textile carbon fiber/epoxy laminates by assuming carbon fiber micro-buckling in the compression side of specimens. [ABSTRACT FROM AUTHOR]

The application of laser ultrasound for nondestructive testing of carbon fiber-reinforced plastics (CFRP) and carbon fiber-reinforced thermoplastics (CFRTP) is shown. Laser-generated excitation creates a three-dimensional, thermoelastic zone which emits ultrasound waves during expansion and contraction. In order not to exceed the damage threshold of the material to be tested usually only a low-energy density and therefore a weak excitation of ultrasound waves can be achieved. For instance, the use of a YAG laser type with a wavelength around 1 µm leads to a very low absorption in the matrix of CFRP while the absorption in the fibers is very high. As a consequence the excitation is often destructive. To solve this problem, we describe the successful introduction of a spatial light modulator to laser ultrasound allowing for tailored spatial energy distributions for efficient nondestructive excitation of ultrasound waves within CFRP or CFRTP. [ABSTRACT FROM AUTHOR]

In this study, a carbon fiber-reinforced thermoplastic (CFRTP) laminate has been drilled and the drill-hole quality was evaluated. Drill-holes were introduced into the laminate by two 5.9 mm diameter step drills to simulate low and high quality machining processes. Defects from manufacturing of the laminate as well as resulting from the machining process were identified and classified by different imaging techniques on representative images. It became obvious, that burr formation is the dominant but not exclusive type of damage in drilled CFRTP in contrast to delamination in case of CFRP. Subsequently, 4-point-flexure and tensile tests have been performed with initial and differently drilled samples to characterize the starting material as well as to determine the influence of the different drill-hole qualities on the mechanical performance and failure behavior. These tests showed that there is no critical influence of the drill-hole quality on the open-hole tensile and flexure strength of the applied CFRTP. [ABSTRACT FROM AUTHOR]

Continuous carbon fiber reinforced poly-ether-ether-ketone (CCF/PEEK) composites have attracted significant interests in mission-critical applications for their exceptional mechanical properties and high thermal resistance. In this study, we additively manufactured CCF/PEEK laminates by the Laser-assisted Laminated Object Manufacturing technique, which was recently reported by the authors. The effects of laser power and consolidation speed on the flexural strength of the CCF/PEEK composites were studied to obtain the optimal process parameters. Hot press postprocessing was performed to further improve the mechanical properties of the composites. Various fiber alignment laminates were prepared, and the flexural and tensile properties were characterized. The hot press postprocessing 3D printed unidirectional CCF/PEEK composites exhibited ultrahigh flexural modulus and strength of 125.7 GPa and 1901.1 MPa, respectively. In addition, the tensile modulus and strength of the composites reached 133.1 GPa and 1513.8 MPa. The results showed that the fabricated CCF/PEEK exhibited superior mechanical performance compare to fused filament fabrication (FFF) printed carbon fiber reinforced thermoplastics (CFRTP). • Continuous carbon fiber reinforced PEEK composites were additively manufactured by LA-LOM. • Effects of process parameters on mechanical properties of the composites were investigated. • Hot press postprocessing was performed to further improve the mechanical properties. • The tensile and flexural properties of the composite laminates were characterized. [ABSTRACT FROM AUTHOR]