Conventional Carbon Fiber Reinforced Plastics Research Articles

Crashworthiness design of novel CFRP functionally-graded conical square structures with variable circumscribed diameters

Crashworthiness design of novel CFRP functionally-graded conical square structures with variable circumscribed diameters

AFP tool path planning for manufacture of variable stiffness composites

Variable stiffness composites (VSC) demonstrate enhanced mechanical properties compared to conventional carbon fiber reinforced plastics (CFRP). Finite element analysis (FEA) is used to optimize layup directions, which need to be transformed into viable tool paths for automated fiber placement (AFP) processes. Manufacturing defects such as wrinkles, gaps, and overlaps should be handled. In this study, a novel path planning algorithm is developed for variable steering in AFP. The fiber directions are clustered and for each cluster a reference curve is fitted as B-Spline, where manufacturing constraints are considered. The proposed tool path planning approach is successfully demonstrated in a case study.

Research on the mechanical and water-repellent properties of bionic carbon fiber reinforced plastic composites inspired by coelacanth scale and lotus leaf

Carbon fiber reinforced plastic (CFRP) laminates are widely used in vessel side plate, underwater propeller, and submarine oil pipeline because they possess superior specific strength and hydrophobicity compared with metal materials. However, conventional CFRP laminates are limited by insufficient mechanical properties and incompetent water-repellent performance. Herein, a biomimetic double-helicoidal superhydrophobic laminate (BDHSL) was designed and manufactured through a method combining hot press forming and two-step spraying. The BDHSL was composed of double-helicoidal (inspired by coelacanth scale) carbon fiber prepreg and SiO2-based coating with multiscale hierarchical structures (inspired by lotus leaf), which displayed excellent mechanical properties and water-repellency. Besides, mechanical tests were carried out systematically. Remarkably, the peak impact force of the BDHSL at the impact energy of 20 J was 2865.25 N, which increased by 136.88% compared with traditional unidirectional laminate (UL 1209.56 N). Meanwhile, the finite element simulation was conducted using 3D Hashin's failure criteria. The simulation results showed that the predicted stress-deflection curve for four types of laminates correlated well with experimental results. Moreover, the water contact angle of BDHSL reached approximately 156.5°, which indicated its superhydrophobicity. What is more, the durability and water-repellency of the SiO2-based coatings were investigated, which further confirmed its potential underwater applicability. The investigations in this work offer a promising way to effectively design and fabricate exquisitely structured CFRP laminates with hierarchically textured coatings that are more suitable for various marine applications under practical conditions, such as offshore oil drilling platform, autonomous underwater vehicle, high-speed ship, and so forth.

Nonlinear behavior mechanism of change in electrical resistance on 3D printed carbon fiber / PA6 composites during cyclic tests

The aim of this paper is to investigate the cause of nonlinear behavior mechanism of change in electrical resistance of 3D printed carbon fiber reinforced plastics (CFRP) due to tensile loading. The electrical resistance change method is a nondestructive testing method that helps detect strain and damage. In previous research for electrical resistance change method applied to 3D printed CFRP, the change in electrical resistance is different compared with the one of conventional CFRP. The behavior makes health monitoring difficult, and the phenomenon needs to be clarified. In this research, we focused on the electrode fabrication method and viscoelasticity effect during cyclic tests. Polishing and laser processing are used as surface treatments for electrode fabrication. Consequently, the treatments are found to affect the reverse piezo-resistivity. In addition, the decrease in electrical resistance depends on the test speeds of cyclic test. The viscoelasticity is found to affect the nonlinear behavior.

Variable thickness design for composite materials using curvilinear fiber paths

Carbon fiber reinforced plastic (CFRP) laminates are often used in a quasi-isotropic manner, such as in cross-ply lamination; thus, the mechanical properties of the CFRP cannot be fully exploited. In this study, we proposed a carbon fiber design method, which uses fiber orientation and thickness as the lamination parameters, where the fiber orientation is determined using the principal stress direction and the fiber thickness is determined by iterative calculations of the maximum stress theory using the bisection method. The method also accounts for manufacturability by considering fiber bundles and modifies the fiber orientation and thickness accordingly. As a result of implementing this method, the weight of wing plate model was reduced by approximately 5% with a failure index of approximately 0.7 compared with that using the constant thickness linear lamination model. Thus, the weight can be reduced while maintaining the strength, which may be useful for further weight reduction of conventional CFRP parts.

Effect of carbon nanotubes on the interlaminar and fracture properties of carbon fiber/epoxy composites

The average properties of carbon fiber reinforced plastics (CFRPs) depend on the extent of interaction between the fiberand matrix. Any means, therefore, to modify either of the two constituents of CFRPs is the key to design the composite.Carbon nanotubes (CNTs) are often used to tailor the interface/interphase in conventional CFRPs either by mixing thenanotubes in matrix or by growing them on the surface of fiber. However, the incorporation of nanotubes, by either means, may affect the mechanical performance of the matrix and that of the composite as a whole. Experiments are carried out toassess the effect of CNT dispersion on the rate sensitivity of matrix, and the effect of CNT grafting on the averagemechanical properties of laminated composites. For better dispersion and interfacial interaction of nanotubes with matrix,molecular level designing of nanotubes is carried out by way of functionalization. It is found that the ultimate strength ofepoxy composites increases with applied loading rate, and that neat epoxy is more rate sensitive than CNT based epoxynano composites. Significant enhancements are also observed in the interlaminar and fracture properties of CFRPs after theincorporation of grafted nanotubes in the composite.

Capability of a grinding wheel reinforced in hoop direction with carbon fiber

Abstracat Efficient and precise grinding is essential as a finishing process in a number of fields. Performance of a grinding wheel made of carbon fiber reinforced plastic (CFRP) whose fiber orientation was aligned along the circumferential direction was investigated. This wheel was observed to have smaller expansion due to the centrifugal force and thermal stress as well as higher stability against chatter vibration than both conventional steel wheels and CFRP wheels having different fiber orientations. Dimensional parameters were determined based on the safety analysis of the interface between CFRP and steel. Finally, the wheel was prototyped and tested.

Effects of machining conditions on the hole wall delamination in both conventional and ultrasonic-assisted CFRP drilling

The need of carbon fiber–reinforced plastics (CFRP) has been driven by the increasingly wide applications in many industrials including sports, transportation, and energy. However, until now, the poor machinability of CFRP can be still considered the key problem and the most urgent machining-induced issue can be the delamination damage in the drilling process. Although many efforts have been paid to investigate this topic, most of them investigated the delamination at either the hole entrance and the exit. Very few of these studies focused on the internal delamination defects on the hole wall, although these internal defects can be as important as the entrance and exit defects. To fill this gap, this paper investigated the condition effects (feed rate, spindle speed, ultrasonic vibration of drills, and the workpiece support strategy) on the delamination in CFRP drilling, with the special focus on the internal delamination damage on the inside hole walls. Based on both the experimental and theoretical analysis, the effectiveness of the back supports and the variable feed rates was investigated as well. Considering few published studies reported the delamination on the hole wall, the key findings in this paper are expected to be meaningful to deepen the understanding of CFRP drilling and helpful to provide some industrial guidance.

Preparation of carbon fibers coated with epoxy sizing agents containing degradable acetal linkages and synthesis of carbon fiber-reinforced plastics (CFRPs) for chemical recycling

New epoxy resins containing degradable acetal linkages were synthesized by the addition reaction of bisphenol-A (BA) and epoxy-functionalized vinyl ethers containing hydrophilic oxyethylene chains, 2-(vinyloxy)ethyl glycidyl ether (VEGE) and 2-[2-(vinyloxy)ethoxy]ethyl glycidyl ether (VEEGE). Carbon fibers were applied with the obtained degradable epoxy resin-based sizing agents (designated as BA-VEGE and BA-VEEGE) in ordinary (1.4 ~ 2.2 wt%) or excess (6.4 ~ 13.4 wt%) amounts. Interfacial adhesion between the carbon fibers applied with the degradable epoxy resin-based sizing agents and matrix resins (bisphenol-A-type epoxy resin) was evaluated by the microdroplet method. Carbon fibers with both degradable epoxy resins as a sizing agent showed improved adhesive properties compared with the desized carbon fibers. Using the degradable sizing agent-applied carbon fibers, carbon fiber-reinforced plastics (CFRPs) were prepared by laminating prepreg sheets and heating them under pressure. The tensile properties of the CFRPs with [0]50 lay-up did not depend on the structure of the sizing agents, but the tensile strength decreased as the amount of sizing agent used increased. On the other hand, the tensile properties of the CFRPs with [0/90]12S lay-up were not dependent on the structure or volume of sizing agents used. The impact toughness of the CFRPs was evaluated by the charpy impact test. When an ordinary volume of sizing agent was applied, the CFRPs with degradable epoxy resin-based sizing agents exhibited higher levels of impact strength than the commercial sizing agent-based CFRPs. However, applying an excessive volume of sizing agent to carbon fibers led to a decline in impact strength. The degradation reaction was conducted under acidic conditions by the treatment of HCl at room temperature or 70 °C. CFRPs with degradable epoxy resins as sizing agents in ordinary volumes were barely decomposed due to insufficient degradable regions in the CFRP components. However, the CFRPs applied with excess degradable sizing agents decomposed and carbon fibers were recovered. The new epoxy resins containing degradable acetal linkages were synthesized and used as sizing agents for carbon fibers. Using the degradable sizing agent-applied carbon fibers, the carbon fiber-reinforced plastics (CFRPs) were prepared via laminating prepreg sheets and heating them under pressure. The mechanical properties of the obtained CFRPs were comparable with those of the conventional CFRPs. With the treatment of acidic conditions, the CFRPs with the degradable sizing agents on carbon fiber surface were decomposed and the carbon fibers could be recovered.

Preparation and Mechanical Properties of Graphene/Carbon Fiber-Reinforced Hierarchical Polymer Composites

Conventional carbon fiber-reinforced plastics (CFRP) have extensively been used as structural elements in a myriad of sectors due to their superior mechanical properties, low weight and ease of processing. However, the relatively weak compression and interlaminar properties of these composites limit their applications. Interest is, therefore, growing in the development of hierarchical or multiscale composites, in which, a nanoscale filler reinforcement is utilized to alleviate the existing limitations associated with the matrix-dominated properties. In this work, the fabrication and characterization of hierarchical composites are analyzed through the inclusion of graphene to conventional CFRP by vacuum-assisted resin infusion molding.

Deburring drilled holes in CFRP composites with large pulsed electron beam (LPEB) irradiation

The generation of burrs is one of the most common problems affecting carbon fiber reinforced plastic (CFRP) machining processes. However, it is difficult to develop machining processes that generate no burrs. To overcome the limitations of conventional CFRP composite deburring methods, we propose a new process for deburring drilled holes in CFRP composites based on large pulsed electron beam (LPEB) irradiation. We evaluated the deburring performance as we independently varied the three major controllable parameters that affect energy transfer during LPEB irradiation, namely the acceleration voltage, solenoid voltage, and number of pulses. We optimized the irradiation process to improve the accuracy of the shapes of the holes, and reduced the sizes of the burrs by 97%. We evaluated deviations in the shapes of the holes from perfect circles by measuring their diameters. As our deburring process reduced these deviations by 93%, it significantly improved the dimensional accuracy of the holes. We hypothesize that the deburring mechanism starts with evaporation of the resin that coats the carbon fibers evaporates. This leaves the uncut carbon fibers exposed so that they can be detached by the LPEB irradiation. We obtained high quality, burr-free drilled holes by applying the proposed LPEB deburring method.

Augmenting mode-II fracture toughness of carbon fiber/epoxy composites through carbon nanotube grafting

Systematic experimental investigation is carried out to characterize the effect of carbon nanotubes (CNTs) grafting on the average mechanical properties and mode-II fracture toughness of carbon fiber reinforced plastics (CFRPs). Two growth strategies are used in a chemical vapor deposition (CVD) reactor to ensure uniform coverage of both sides of fiber fabric with CNTs. Improvement in interlaminar shear strength of CFRP due to incorporation of CNTs is found to be sensitive to the uniformity of grafted CNTs on the fabric surface. It is shown that the use of optimum CNT grafting strategy on the fiber surfaces leads to a significant improvement in flexural properties and mode-II fracture toughness of conventional CFRPs. However, the use of CNT grafted laminas in the composite laminate does not alter the response of CFRP under the uniaxial tensile loading. Scanning electron microscopy (SEM) analysis of failed composite coupons after mode-II testing reveals that different failure mechanisms operate in composite laminate fabricated with or without the use of CNT grafted laminas.

Development of recyclable carbon fiber-reinforced plastics (CFRPs) with controlled degradability and stability using acetal linkage-containing epoxy resins

Recyclable carbon fiber-reinforced plastics (CFRPs) with controlled degradability and stability were developed by adding bisphenol A (BA)-type epoxy resins containing acid-degradable acetal linkages (BA-CHDMVG) to the matrix resins of CFRPs. BA-CHDMVG was synthesized by the reaction of the hydroxyl groups of BA with vinyl ether containing a glycidyl group (cyclohexane dimethanol vinyl glycidyl ether (CHDMVG)) and added to conventional BA-type epoxy resins (jER828 and jER1001). The acetal linkage-containing CFRPs (BA-CHDMVG-based CFRPs) were prepared using a mixture of these epoxy resins as the matrix. The obtained CFRPs exhibited almost the same tensile and thermal properties as those of the conventional BA-based CFRP (BA-based CFRP). One of the BA-CHDMVG-based CFRPs, (BA-CHDMVG)40-(jER1001)60-based CFRP (content in the matrix resin: BA-CHDMVG, 40 wt%; jER1001, 60 wt%), underwent smooth degradation through hydrolysis of the acetal linkages incorporated into the matrix resin upon treatment with 0.1 mol l−1 hydrochloric acid in a tetrahydrofuran (THF)/water (9/1 v/v) mixed solvent for 24 h at room temperature to produce strands of carbon fibers. On the other hand, there was no change in the appearance of the same BA-CHDMVG-based CFRP board upon acid treatment in water with no organic solvent. To determine their stability against aqueous acid, the BA-CHDMVG-based CFRP boards were immersed in 0.1 mol l−1 aqueous acetic acid solution at room temperature for 30 days and then subjected to tensile testing. The BA-CHDMVG-based CFRPs after the acid treatment exhibited almost the same tensile properties as those of the BA-CHDMVG-based CFRPs before the acid treatment. These results indicate that the BA-CHDMVG-based CFRPs are stable toward acid in the normal living environment, such as acid rain. Recyclable carbon fiber-reinforced plastics (CFRPs) with controlled degradability and stability were developed by using acid-degradable acetal linkage-containing epoxy resin (BA-CHDMVG). The obtained BA-CHDMVG-based CFRPs exhibited almost the same tensile and thermal properties as those of the conventional BA-based CFRPs and underwent smooth degradation through hydrolysis with the treatment of hydrochloric acid in a tetrahydrofuran (THF)/water (9/1) mixed solvent. On the other hand, in the absence of organic solvents, the BA-CHDMVG-based CFRPs have sufficient stability toward acid in the normal living environment.

超軽量熱防御材 LATS の熱機械特性

The outer wall of re-entry vehicles is covered with heat shield materials in order to protect them from severe aerodynamic heating. An ablator is a type of heat shield material effective for re-entry vehicles. In particularly an ablator made of Phenolic carbon fiber-reinforced plastics (CFRP) is known to possess superior resistance against severe aerodynamic heating. Okuyama laboratory has been studying the lightweight ablator series for transfer vehicle systems (LATS). From the past research results, it was confirmed that the heat-resistant performance of this LATS is equivalent to high-density ablator material made of that CFRP. However, we do not confirm those details about the temperature dependency of the mechanical property of this heated LATS. In this research, we compared the elastic modules of the LATS and a conventional heavy density CFRP which were heated. We could identify that the reduction phenomenon of the elastic modulus of the CFRP occurs from approximately 600K, this phenomenon of the LATS happens from after a heating start. Moreover, we were able to find out that we can predict the temperature dependency of the elastic modulus of LATS using the Arrhenius equation.

CFRP円筒材のねじり疲労特性に及ぼす積層構成の影響

Application of carbon fiber reinforced plastics (CFRP) pipes to torque transmission shafts makes it possible to improve automotive driving performance as well as fuel efficiency. A modified simultaneous multi ply winding method was developed as a new forming method for CFRP pipes using prepregs. The CFRP pipes formed by the method have fewer initial flaws, such as voids and fiber waviness. It resulted in 20 % increase in the static torsional strength than conventional CFRP pipes formed by a filament winding method. In this study, effects of stacking sequence on the torsional fatigue properties of the CFRP pipes formed by the modified method were investigated. Torsional fatigue tests were conducted under load control. All tests were conducted at the test frequency f=1 Hz, the maximum applied torque Tmax=1.0 kNm and the stress ratio R=0.1. [902/-45/+45]6 and [90/-45/90/+45]6 pipes were formed to investigate effects of lamination angle difference between adjacent plies. Maximum lamination angle difference of the [90/-45/90/+45]6 pipe is smaller than that of the [902/-45/+45]6 pipe. When the CFRP pipes had smaller lamination angle difference, the initiation and growth of the delamination from the prepreg end in the innermost layer were delayed because interlaminar stress was reduced. Moreover, [(90/-45/90/+45)6/90] pipes were formed to investigate effects of an application of a 90° layer on the innermost layer. As the result, the delamination hardly initiated since the shear stress on the prereg end was reduced. Consequently, the fatigue life of the [(90/-45/90/+45)6/90] pipes increased seven-fold than that of the [902/-45/+45]6 pipes due to improvement of delamination resistance under cyclic torsional loading.

Compensating Deviations During Flexible Pin-type Moulding of Spatially Curved CFRP by Using 3D-Surface Detection

Laminating carbon-fiber-reinforced plastic (CFRP) traditionally uses rigid moulds. This process means that customising CFRP components is expensive since the costs of each rigid mould are allocated fully to only one associated CFRP. Therefore, using form-flexible moulds is beneficial, because it would eliminate the conventional restriction that each CFRP geometry needs one single rigid mould. The costs of one flexible mould would be allocated to all produced CFRP components. Thus, the more CFRP laminated on this single form-flexible mould, the less the CFRP is affected by mould costs. Creating form-flexible moulds by using pin-type tooling results in a discrete pin accumulation. To achieve the required continuous laminating surface, an interpolation layer is placed on the pins. However, compared to conventional CFRP moulds, normally made by CNC-milling, pin-type tooling complicates accuracy achievement. This is due to the fact that the elastic, silicone-like interpolation layer as well as several tolerances or inaccuracies within the mould mechanics, as an assembly, accumulate into the range of millimeters. Instead of using more accurate pin-type moulds, which is associated with increasing costs, this paper introduces an approach to integrate 3D surface detection methods into the process of form-flexible moulding of spatially curved CFRP using pin-type tools, which maintains costs and increases accuracy. The developed control loop compensates deviations dynamically and results in accuracies in the same range as parts produced using CNC-milled rigid moulds.

Novel test method for accurate characterization of intralaminar fracture toughness in CFRP laminates

A novel initial crack insertion method, “intralaminar film insertion method”, was proposed to investigate the fracture toughness of unidirectional carbon fiber reinforced plastic (CFRP) laminates when the crack propagates inside the ply and not in the interlayer resin-rich area. Here, a release film was inserted inside a single lamina during the resin impregnation process of prepreg manufacturing. Mode I intralaminar fracture toughness tests were carried out for conventional CFRP laminates and interlayer toughened CFRP laminates. For comparison, two conventional methods were used to introduce initial cracks. One is the “interlaminar film method”, where a release film is inserted between two prepreg plies during the lay-up process. The other is the “machined slit method”, where a slit notch is machined in parallel to the layer of CFRP laminates. It was demonstrated that the proposed “intralaminar film method” can correctly evaluate the intralaminar fracture toughness of both conventional CFRP laminate and interlayer toughened CFRP laminate from the initial value to the propagation value. For this range, it was also found that the intralaminar fracture toughness of interlayer toughened CFRP laminate was the same as that of conventional CFRP laminate. Thus, the intralaminar fracture toughness was not influenced by interlayer toughening.

A toughening and strengthening technique of hybrid composites with non-woven tissue

The hybrid composite materials with non-woven tissue (NWT) are developed to improve the mechanical properties of conventional fiber reinforced plastic (FRP) composite materials. From the previous works we can see that the interleaving of the non-woven carbon tissue (NWCT) layer largely increases the Mode II interlaminar fracture toughness, while it does not significantly change the Mode I interlaminar fracture toughness. In addition, compared with conventional carbon fiber reinforced plastic (CFRP) composites, the hybrid composites with NWCT have high reliability and high strengthening effect for mechanical properties under tensile static and fatigue loadings. The impact damage mechanism of low-energy range for the hybrid composites with NWCT was also investigated under quasi-static indentation loading. The mechanism of the NWCT interleaving's effect was clarified based on the observation of damage. As the CFRP and hybrid composites with the indentation damage failed by shearing under the compressive fatigue loading, it was effective that the propagation of shear cracks in the hybrid composites were prevented by NWCT located between the CFRP layers. It was found that the Mode II interlaminar fracture is predominant in the delamination by the indentation loads. The purposes of this study of hybrid prepreg with NWT are (i) to increase the interlaminar properties (the fracture toughness and strength), (ii) to improve the mechanical properties (tensile strength and stiffness) and reliability, while maintaining a low cost, (iii) to propose an interlayer hybrid concept with NWT as a “Toughening and Strengthening Technique”. Namely, this concept is designed to introduce a tough and strong interlayer at the positions of typical premature composite failure. A production technique to decrease voids in NWT is exhibited by comparing two types of hybrid laminates. The mechanical properties of the hybrid composites were measured, and then the validity of the present technique was confirmed.

A new vibration damping CFRP material with interlayers of dispersed piezoelectric ceramic particles

In this paper, the author summarizes the previous works on the passive damping of carbon-fiber reinforced plastic (CFRP) cantilever beams using: (1) interleaving of viscoelastic thermoplastic films, (2) surface-bonded piezoelectric ceramics, and (3) dispersed PZT particles interlayers. Introducing polyethylene-based film interlayers between composite plies resulted in a significant increase in the vibration loss factor. It is also shown that the vibration damping of CFRP laminates can be improved passively by means of resistively shunted, surface-bonded piezoelectric ceramic, PbZrO 3–PbTiO 3 (PZT) sheets. In particular, the author developed an original method to enhance vibration damping of CFRP laminates via dispersed PZT particles interlayers. All these damping methods can be jointly used to improve the damping of CFRP laminates/structures. The usefulness of the damping concepts dealt in this work is verified through an application of the method to the actual design of robotic arm. The robotic arm designed and manufactured using damping CFRP materials showed an excellent vibration damping in comparison with those made with conventional CFRP and aluminum materials.

3006 グリーンコンポジットの熱伝導率(S40-2 グリーンコンポジットの機能性評価と新規開発,S40 バイオマス由来材料の成形加工と特性評価)

Bamboo fiber-reinforced "green" composites were fabricated by using a conventional hot pressing method. Their insulating properties were evaluated by the value of thermal conductivity, which was measured using a hot wire method. It was demonstrated that thermal conductivity of bamboo fiber reinforced "green" composites is smaller than that of conventional GFRP (glass fiber reinforced plastics) and CFRP (carbon fiber reinforced plastics). The thermal conductivity of "green" composites was significantly influenced by their density as observed in woods.