Unidirectional CFRPs Research Articles

High-performance carbon fiber-reinforced epoxy resin composites based on novel, environmentally friendly, stability, and heat-moisture resistant nano emulsion encapsulated POSS sizing agent interface modification

Considering the development of CFRPs, addressing the challenge through the simplistic industrial operational methods to achieve high strength and toughness in carbon fiber-reinforced epoxy resin (EP) composites (CFRPs) is imperative. In this work, an innovative approach introduced to improve the strength and toughness of CFRPs by application of a nano emulsion encapsulated polyhedral oligomeric silsesquioxane (POSS) sizing agent (POE sizing agent). The employment of a POE sizing agent markedly enhanced the surface energy and roughness of carbon fibers (CF) as well as the interface properties of CFRPs. Furthermore, the 10-PCF (10 wt% POE sizing CF) reinforced EP unidirectional CFRPs demonstrated superior strength and toughness. Relative to the DCF (Desizing CF) reinforced EP unidirectional CFRPs, their interlaminar shear strength, flexural strength, and unnotched impact strength increased by 24.9 %, 37.8 %, and 45.6 %, respectively, reaching 99.8 ± 2.3 MPa, 1376.8 ± 21.6 MPa, and 94.9 ± 4.6 kJ/m2. Concurrently, the 10-PCF reinforced EP composite laminates exhibited outstanding impact resistance, minimal damage area, and enhanced compressive strength after impact. Additionally, the strength, bundling, and flexibility of the sized CF were maintained, ensuring the processability of CF. The utilization of POE sizing agent for strength and toughness improvement in CFRPs offers a straightforward and industrially feasible approach. This research opens up a novel strategy for high-performance CF and CFRPs preparation.

Determination of the optimal milling feed direction for unidirectional CFRPs using a predictive cutting-force model

Determination of the optimal milling feed direction for unidirectional CFRPs using a predictive cutting-force model

Tool wear prediction in edge trimming of carbon fiber reinforced polymer using machine learning with instantaneous parameters

Rapid tool wear occurs during the edge trimming of CFRP components due to the high strength and abrasive nature of the carbon fibers, leading to potential surface damage and delamination. This paper presents a hybrid approach by combining the machine learning technique and the physics-based kinematics model for tool wear prediction in edge trimming of CFRP. For edge trimming of unidirectional (UD) CFRP, the feature parameters of the machine learning models consist of the instantaneous fiber cutting angle, uncut chip thickness, and instantaneous radial force instead of the average force of a certain cutting period. The training data from UD CFRP is used to predict the overall radial force in edge trimming of multidirectional (MD) CFRP considering the nonuniform wear length distribution along the tool edge due to different fiber orientation angles of the UD layers. The machined surface, tool edge profile, and chip morphology were examined to demonstrate the nonuniform tool wear length and its effect on surface quality in edge trimming of MD CFRP. The tool wear monitoring in edge trimming of MD CFRPs with various lay-up configurations is achieved without the need for data training experiments on MD CFRP. The predictions from the machine learning methods are compared with experimental results in edge trimming of UD and MD CFRPs. As a result, the proposed method is able to reduce the experimental cost, considering the increased dimensionality if experimental data training of various fiber orientations of UD CFRP and various fiber lay-up configurations of MD CFRP is required.

Quantitative Evaluation of Porosity in Unidirectional CFRPs Using Laser Ultrasonic Method

A method for estimating the porosity of CFRPs based on measuring their acoustic impedances is proposed and experimentally implemented. The acoustic impedance of the test sample is derived from the magnitude of the antiderivative of an ultrasonic pulse reflected from the immersion-liquid–sample interface. The studied samples are unidirectional CFRPs with various volume contents of the matrix and filler. It has been established that the distribution of local porosity in the samples is uneven along the carbon fiber stacking plane. The value of porosity averaged over the results of optical–acoustic measurements with allowance for measurement errors is consistent with the X-ray tomography data. The method for estimating the value of porosity presented in this paper does not involve measuring the volume and mass of the object under study and can be used in diagnostics of complex shaped composite structures.

An approach to design high-performance unidirectional CFRPs based on a new sensitivity analysis model

The modification of the material parameters (MPs) of different types of fibers and matrices is an important task when designing high-performance unidirectional carbon fiber reinforced plastics (UD-CFRPs). The focus of this study is the computational analysis of the MPs variability, as well as deterministic sensitivity of fiber and matrix to design new types of high-performance UD-CFRPs. The prediction model of the mechanical properties of higher precision UD-CFRPs is established based on a cross-scale finite element (FE) method, while the experimental results make clear that the prediction models are in good agreement. Modeling and solving the sensitivity analysis model of the MPs of fiber and matrix are carried out entirely in MATLAB using the input and result sample set. A method of the variable parameter amplitude is first proposed to verify the sensitivity indices. Simultaneously, different types of high-performance UD-CFRPs are designed based on the sensitivity analysis model. In addition, the MPs of UD-CFRPs are verified using the cross-scale FE prediction model, and the verification results indicate that the proposed design approach is accurate and efficient. This study shows the most influential MPs of fiber and matrix, which contribute to the design of higher-performance UD-CFRPs.

Theoretical modeling for the exit-delamination morphology of the unidirectional CFRPs

Accurate exit-delamination morphology (i.e., shape and size) is of great significance both to evaluate and to control for the delamination during the drilling of carbon fiber-reinforced plastics. However, the morphology of the exit delamination in different fiber orientations is still difficult to precisely predict. In this paper, a theoretical model is established based on the classical bending theory of beam and the linear elastic fracture mechanics for determining the exit-delamination morphology. Based on this theoretical model, the accurate exit-delamination morphology can be precisely predicted. The results show that the exit-delamination zone is near to the elliptical shape, and its size decreases with the increasing of the cutting speed but increases with the increasing of the feed speed. Both the Zhang model and the beam theory model can predict the exit determination morphology. The beam theory model can reflect effectively the influences of the cutting speed and the feed speed on the exit delamination.

Drill-exit temperature characteristics in drilling of UD and MD CFRP composites based on infrared thermography

This paper presents a comprehensive study on the complex drill-exit temperature characteristics in the drilling of unidirectional (UD) and multidirectional (MD) CFRPs using a state-of-art microscopy infrared imaging system. For the first time, temperature variation and distribution at drill exit have been revealed in full detail, associated with the CFRP material properties and drilling conditions. Results suggest that the actual drill/CFRP interactions have critical but similar effects on the drill-exit temperatures for UD and MD CFRPs. Specifically, three distinct cutting regions with varying temperature characteristics are evident when the main cutting edge is acting on the drill exit material. In all cases, the temperature distribution features elliptical shape, of which the eccentricity depends on the lay-up sequence and the drilling depth. In addition, the real-time temperature profiles and 2D/3D maximum temperature distribution maps are created with high visualization. With the aid of those findings, the relationships between drilling temperature maxima, their locations and drilling depths have been discovered and temperature effects on drill-exit damages have been elucidated for the first time. MD CFRP is proven more difficult to achieve high drilling qualities at certain fiber cutting angles than UD CFRP due to the associated temperature effects. Such important knowledge enables the identification of the heat affected zones and subsequently informs strategies for reducing the negative temperature effects.

Calculation and design of lattice cylindrical shells manufactured of unidirectional CFRPs

The work is devoted to numerical simulation of the stationary stress-strain state of lattice cylindrical shells made of unidirectional carbon fiber reinforced plastics and to their optimal design. After averaging stiffness characteristics of lattice structure, the displacement and stress formulations for continuum anisotropic equivalents of lattice shells are given on the basis of classical relations of 3D theory of elasticity. While using a special fast pseudo-spectral algorithm, the solutions to problems of axial compression of anisogrid shells are obtained and compared one to another. The algorithm provides exponential decrease of error of approximation and requires small computational resources. Using this algorithm we have found the optimal geometrical parameters of structure ensuring its bearing capacity under given non-uniform loads.

Wavelength and Pulsewidth Dependences of Laser Processing of CFRP

As the use of CFRP material becomes widespread in various industries, achieving high-speed cutting with less pulse energy and minimal thermal damage is one of the important issues for laser-based processing. Among the various parameters in laser processing, we have focused on wavelength from UV (266nm) to NIR (1064nm) and pulsewidths from 100 fs to 20ns in order to investigate cutting efficiency in terms of ablated mass per irradiated laser energy and corresponding heat affected zone (HAZ). Samples used in our experiments were uni-directional CFRPs with thickness from 140μm to 250μm or 1.3 mm-thick cross CFRPs. We measured time to cut the samples and ablated volume in order to estimate cutting efficiency in mg/kJ. Also we observed SEM images of the processed samples to evaluate HAZ. In general, shorter wavelength and shorter pulsewidth resulted in higher cutting efficiency and less thermal damages. These results could contribute to optimize the machining of CFRP composite materials.

An Investigation of Cutting Mechanisms and Strain Fields during Orthogonal Cutting in CFRPs

Fiber-reinforced plastics (FRPs) are typically difficult to machine due to their highly heterogeneous and anisotropic nature and the presence of two phases (fiber and matrix) with vastly different strengths and stiffnesses. Typical machining damage mechanisms in FRPs include series of brittle fractures (especially for thermosets) due to shearing and cracking of matrix material, fiber pull-outs, burring, fuzzing, fiber-matrix debonding, etc. With the aim of understanding the influence of the pronounced heterogeneity and anisotropy observed in FRPs, “Idealized” Carbon FRP (I-CFRP) plates were prepared using epoxy resin with embedded equispaced tows of carbon fibers. Orthogonal cutting of these I-CFRPs was carried out, and the chip formation characteristics, cutting force signals and strain distributions obtained during machining were analyzed using the Digital Image Correlation (DIC) technique. In addition, the same procedure was repeated on Uni-Directional CFRPs (UD-CFRPs). Chip formation mechanisms in FRPs were found to depend on the depth of cut and fiber orientation with pure epoxy showing a pronounced “size effect.” Experimental results indicate that in-situ full field strain measurements from DIC coupled with force measurements using dynamometry provide an adequate measure of anisotropy and heterogeneity during orthogonal cutting.

見掛けの横弾性係数を考慮した一方向CFRPの圧縮強度予測

Compressive strength of unidirectional CFRP was estimated based on a model of column buckling on elastic foundation. It was shown that the compressive strength based on the column buckling model coincided with the compressive strength based on the fiber kinking model for high fiber volume fraction of the unidirectional CFRP. Apparent shear modulus of a carbon fiber in the in-phase buckling was calculated by the shear and bending deformation of the composite. The apparent shear modulus was decreased depending on the ratio of kink band length to the fiber diameter. Compressive strengths of unidirectional CFRPs were estimated by considering the apparent shear modulus. The estimated results for various types of unidirectional CFRP showed good agreement with the experimental results. Upper and lower limit of the compressive strengths of the unidirectional CFRPs were found out theoretically.

On the fatigue life prediction of CFRP laminates using the Electrical Resistance Change method

The electro-mechanical response (Electrical Resistance Change method) as a damage index of quasi-isotropic Carbon Fiber Reinforced (CFRPs) laminates under fatigue loading was investigated. The effect of dispersed Multi-Wall Carbon Nanotubes (MWCNT) into the epoxy matrix was additionally evaluated and compared with neat epoxy CFRPs. The longitudinal resistance change of the specimens was monitored throughout the fatigue experiment. Three different stress levels were tested. The frequency and the ratio ( R) of the minimum applied load (stress) to the maximum applied load (stress) were kept constant for the different stress levels. The temperature of the specimen was also monitored throughout the process in order to deduce its effect on the electrical resistance of the specimen. The electrical behavior of the quasi-isotropic CFRP deviated from the commonly observed electrical response of unidirectional or cross-ply CFRPs due to the presence of the 45° layers. During initial stages of loading the resistance drops and afterwards it follows a positive slope up to final fracture. This repeatable pattern was observed for both the neat and the CNT-doped specimens, with the latter having smoother electrical recordings. The effect of temperature was calculated to be limited for the specific material and test/measurement configuration. The electro-mechanical response was correlated to stiffness degradation and acoustic emission findings enabling the identification of the specific regions during the fatigue life referring to specific mechanisms of damage accumulation. More specifically the experimental results revealed that the occurrence of the initial drop of the electrical resistance is linked with the occurrence of the Characteristic Damage State (CDS), associated with a specific percentage of stiffness reduction. This finding was used in order to predict the remaining life independently from the applied stress level with a high degree of confidence, assuming a constant stress level throughout the whole lifetime. The remaining life prediction for the CNT-doped specimens had higher coefficient of confidence ( R 2).

OS1520 見掛けの横弾性係数を考慮した一方向CFRPの圧縮強度予測(OS15-4 複合材料の変形と強度,OS-15 微視構造を有する材料の変形と破壊)

Compressive strength of a unidirectional CFRP was estimated based on a model of column buckling on elastic foundation. It was shown that the compressive strength based on the column buckling model coincided with the compressive strength based on the fiber kinking model when high fiber volume fraction was supposed for the unidirectional CFRP. Apparent shear modulus of a carbon fiber in the in-phase buckling was calculated considering shear and bending deformation as an apparent shear deformation. Compressive strengths of unidirectional CFRPs were estimated by considering the apparent shear modulus. The estimation results on various types of unidirectional CFRP showed good agreement with the experimental results. Upper and lower limit of the compressive strengths of the unidirectional CFRPs were revealed theoretically.

Effect of thermal aging on the adhesive strength of joints of double-chain polymers with fibers and on the properties of unidirectional CFRPs based on them

The paper presents a study on the effect of thermal aging on the adhesive strength of joints of some double-chain polymers and fibers. It is shown that the initial shear strength of joints of a steel wire with double-chain polymers based on bisaminonitrile (R = −CH 2 −) is significantly higher than that in the case of polymers based on the “A-B” monomer. The type of thermal stabilizer affects the strength of the fiber/matrix interface only slightly. Prolonged heating (up to 100 hours) of the joints at 350 °C does not reduce the strength of joints based on the “A-B” monomer, while that of joints based on bisaminonitrile decreases by 20-30%. The thermal stability of carbon-fiber-reinforced plastics appeared to be higher, which was likely due to the effect of scale factor. The strength of a test specimen batch decreased only upon exposure to 400 °C for more than 100 hours.

804 一方向CFRPの材料端部における微視的応力分布の3次元解析(OS9-(2)オーガナイズドセッション《複合材料の変形と破壊およびマルチスケール計算技術》)

In this study, the distributions of microscopic stresses at a free edge of a unidirectional carbon fiber-reinforced plastic (unidirectional CFRP) are analyzed three-dimensionally based on a homogenization theory. For this, the mathematical homogenization theory for elastic materials is reconstructed for unidirectional CFRPs with free edges using a traction free boundary condition. This theory is then applied to the analysis of microscopic stress distributions at a free edge of a unidirectional CFRP subjected to in-plane uniaxial tension. It is shown that microscopic shear stress noticeably occurs at the free edge, especially at the interface region between a carbon fiber and epoxy matrix.

207 ユニットセル配置にずれを有する周期材料への均質化理論の適用(OS6-(2) 複合材料の変形と破壊およびマルチスケール計算技術,オーガナイズドセッション)

In this study, a time-dependent homogenization theory is rebuilt for periodic composite materials in which their unit cells are arranged with misalignment. As a numerical example, the transverse elastic-viscoplastic properties of unidirectional carbon fiber-reinforced plastics (unidirectional CFRPs) with misaligned cell arrangements are analyzed using the present theory. It is thus shown that the transverse elastic-viscoplastic anisotropy of the unidirectional CFRPs decreases with the increase of misalignment of the cell arrangement.

Adhesive ability of a heat-resistant double-chain polymer and the strength of CFRP based on it

The adhesive ability of a heat-resistant polyiminoquinazolindione (PIQD) binder, based on a double-chain polymer, and the physicomechanical characteristics of unidirectional CFRPs made with it are investigated. It is shown that, at room temperature, the strength of model adhesive joints (PIQD-steel wire) and of the CFRPs in shear and bending is rather low — about half of that of similar specimens based on an epoxy binder. At the same time, all their mechanical characteristics, to a large measure (50%), are retained at temperatures up to 450°C, which considerably exceeds the heat resistance of all polymer matrices used at the present time. The elastic modulus of the CFRPs in bending practically remains the same up to 450°C.

A Modified Kinematic-Hardening Viscoplasticity Model for Off-Axis Creep Behavior of Unidirectional CFRPs at High Temperature

A macromechanics constitutive model to describe the anisotropic creep behavior of unidirectional composites under off-axis loading conditions is developed with a particular emphasis on accurate prediction of temporal creep softening due to stress variation. A viscoplasticity model that takes account of a combined isotropic and kinematic hardening is adopted as a base for this formulation, and the evolution equation of the kinematic hardening variable is elaborated to enhance the accuracy of prediction of the transient creep softening due to stress variation. Validity of the modified kinematic-hardening viscoplasticity model is evaluated by comparing with the experimental results on unidirectional T800H/3631 carbon/epoxy composites. It is demonstrated that the proposed model can adequately describe the off-axis creep behavior of the unidirectional CFRP laminate under constant and variable stress conditions.

541 一方向CFRPのひずみ速度に依存する非線形挙動の引張・圧縮非対称性とその力学的モデル化(OS7-2 微視構造を有する材料の変形と破壊,OS7 微視構造を有する材料の変形と破壊)

541 一方向CFRPのひずみ速度に依存する非線形挙動の引張・圧縮非対称性とその力学的モデル化(OS7-2 微視構造を有する材料の変形と破壊,OS7 微視構造を有する材料の変形と破壊)

Thermal and geometrically non-linear stress analyses of an adhesively bonded composite tee joint

Adhesive bonding technique is used successfully for joining the carbon fibre reinforced plastics to metals or composite structures. A good design of adhesive joint with either simple or more complex geometry requires its stress and deformation states to be known for different boundary conditions. In case the adhesive joint is subjected to thermal loads, the thermal and mechanical mismatches of the adhesive and adherends cause thermal stresses. The plate-end conditions may also result in the adhesive joint to undergo large displacements and rotations whereas the adhesive and adherends deform elastically (small strain). In this study, the thermal and geometrically non-linear stress analyses of an adhesively bonded composite tee joint with single support plus an angled reinforcement made of unidirectional CFRPs were carried out using the non-linear finite element method. In the stress analysis, the effects of the large displacements were considered using the small displacement–large displacement theory. The stress states in the plates and the adhesive layer of the tee joint configurations bonded to a rigid base and a composite plate were investigated. An initial uniform temperature distribution was attributed to the adhesive joint for a stress free state, and then variable thermal boundary conditions, i.e. air flows with different velocity and temperature were specified along the outer surfaces of the tee joints. The thermal analysis showed that a non-uniform temperature distribution occurred in the tee joints, and high heat fluxes took place along the free surfaces of the adhesive fillets at the adhesive free ends. Later, the geometrical non-linear thermal-stress analysis of the tee joint was carried out for the final temperature distribution and two edge conditions applied to the edges of the vertical and horizontal plates (HP). High stress concentrations occurred around the rounded adherend corners inside the adhesive fillets at the adhesive free ends, and along the adhesive–composite adherend interfaces due to their thermal–mechanical mismatches. The most critical joint regions were adhesive fillets subjected to high thermal gradients, the middle region of HP, the region of the vertical plate corresponding to the free end of the vertical adhesive layer–left support interface. In addition, the support length had a small effect of reducing the peak stresses at the critical adherend and adhesive locations.