Carbon Fiber Composite Laminates Research Articles

Influence of resin content on mechanical properties of composite laminates

The resin content has an important effect on the mechanical properties of composite laminates. In order to study the influence of different resin content on the mechanical properties of composite laminates, the mechanical properties of the standard samples of carbon fiber composite laminates with resin content of 30, 35, 40, 45, and 50% have tested, and the fracture regions of the samples have scanned by scanning electron microscope. The test results show that the tensile strength of the carbon fiber composite laminates increases first and then decreases with the change of resin content. When the resin content is 35%, the tensile strength reaches the maximum. Moreover, the elastic modulus decreases with resin content.

Effect of fibre orientation on mechanical properties of carbon fibre composites

The research aims to investigate the carbon fibre composite laminate for effect of their layer configuration including their number and relative orientation of fibre angles on their mechanical properties and its consistency with the results obtained from simulated data using finite element analysis (FEA) on mechanical properties. The laminate composite with four types of fiber layer orientations were prepared using total eight layers including unidirectional and cross ply layers with different orientations. The flexural properties of the samples were evaluated. The results of experiments found consistent with the simulated data and it indicates that the fibre orientations and its layer sequence influence the characteristics of laminate composites. The composite with 0 orientated unidirectional fibre layers shows maximum flexural strength. The flexural strain is higher for laminate composite having layers with cross plies (45° fibre orientations). The different position of cross ply in the sequence shows variations in flexural properties because the typical nature of the three point bending flexural test of laminate composite where top side layers are under compression and bottom side layers are under tension.

Comparison between honeycomb and composite corrugated cores in sandwich panels under compression loading

The study is to evaluate the compression properties of the polymeric composite corrugated-core sandwich structure against the honeycomb-core structure. The skin facings are from the prepreg carbon fibre composite laminate, while the core is made of different materials. Four core types are suggested; carbon fibre corrugated-core, fibreglass corrugated-core, Nomex honeycomb-core, and Kevlar honeycomb-core. The study is based on an experimental work of edgewise compression testing, and the comparison between alternatives are based on the specific properties-to-weight ratio. The analysed results prove there is superior compression capacity of the polymeric composite corrugated-core sandwich members to the honeycomb-core members, in particular in the nonlinear stage of compression test. The bonded surface between the honeycomb structure and the skins is often less than that of the corrugated profile for the same sandwich panel sizes. This contact area between the core and skin facings plays an important role in carrying load mechanism.

Damage model based on gradient property method for simulating the tensile behavior of composite laminates with Variable Angle Tow reinforcement

In this work Tailored Variable Angle Tow (VAT) patches with various layup directions are employed to reinforce open-hole carbon fiber composite laminates and the tensile behaviour of the reinforced laminates is investigated. The relationship between the tensile behaviour of the reinforced laminate and the fiber orientation of the VAT reinforcement is revealed by experiments. Moreover, this paper proposes a multi-scale finite element model to simulate the reinforced laminate under tensile load. The multi-scale model, consisting of a unit cell model and a gradient property model, is designed to characterize the constitutive response of VAT composites with various fiber fractions and gradient properties. The comparison of the simulation and experimental results indicates that the model not only provides accurate computed tensile strength with the deviation less than 6%, but also presents failure mode predictions that in accordance with the experimental results.

A Lamb Wave Wavenumber-Searching Method for a Linear PZT Sensor Array.

In this paper, a wavenumber–searching method based on time-domain compensation is proposed to obtain the wavenumber of the Lamb wave array received signal. In the proposed method, the time-domain sampling signal of the linear piezoelectric transducer (PZT) sensor array is converted into a spatial sampling signal using the searching wavenumber. The two–dimensional time-spatial-domain Lamb wave received signal of the linear PZT sensor array is then converted into a one-dimensional synthesized spatial sampling signal. Further, the sum of squared errors between the synthesized spatial sampling signal and its Morlet wavelet fitting signal is calculated at each searching wavenumber. Finally, the wavenumber of the Lamb wave array received signal is obtained as the searching wavenumber corresponding to the minimum error. This method was validated on a 2024-T3 aluminum alloy. The validation results showed that the proposed method can successfully obtain the wavenumber of the Lamb wave array received signal, whose spatial sampling rate does not satisfy the Nyquist sampling theorem; the wavenumber error does not exceed 2.2 rad/m. Damage localization based on the proposed method was also validated on a carbon fiber composite laminate plate, and the maximum damage localization error was no more than 2.11 cm.

Use of Experimentally Determined Parameters of the Cohesive Zone in the Numerical Evaluation of the Resistance to Delamination of Polymer Composites Materials

The technique of cohesive zones makes it possible to evaluate the stability of the material, both at the beginning of the crack propagation and to the appearance and development of defects in the places of stress concentration. The ability to reliably determine the parameters of fracture of polymer composite materials and to predict the behavior of structural elements from them under loading is an urgent task for the aerospace industry. It is proposed to use the length of the cohesive zone in the finite-element 3D model for mode I of interfacial delamination of the carbon fiber composite laminates in the form of a double cantilever beam (DCB). The length of the cohesive zone is calculated from the experimentally determined parameters such as the local interlayer cohesive strength of the material and the critical strain energy release rate. The determined length of the cohesive zone is used in the model to select the minimum number of finite elements at their optimum size, which ensures a higher accuracy of calculations of the main parameters of fracture toughness of carbon fiber composite laminates. As a result of the research, the main parameters of crack resistance are determined and the optimal length of the interface elements is chosen. The obtained model accurately describes the process of crack growth along the entire length of the cohesive zone, and the results of its application correlate well with the results of the experiments.

Dynamic characterisation of interlaminar fracture toughness in carbon fibre epoxy composite laminates

In this work, the rate dependence of mode I interlaminar fracture toughness for two different materials systems, IM7/8552 and IM7/M91, both unidirectional UD carbon-fibre epoxy composite laminates have been examined over a wide range of loading rates from 0.5 mm/min up to 2000 mm/s at room temperature. Quasi-static fracture tests were performed using a DCB (double-cantilever beam) method with a screw-driven testing machine, while the dynamic tests were carried out using a WIF (wedge-insert fracture) specimen loaded dynamically in a hydraulic system. For performing the tests at high displacement rates, a special setup was designed and manufactured which allowed the insertion of the wedge within the DCB specimens at different cross-head displacement rates. The experimental technique used a pair of strain gauges attached to the bending surface of one of the arms of the cantilever beams and far from the initial crack tip. The peak values of the recorded strain were used to determine the fracture toughness under dynamic conditions through use of the compliance calibration method. A finite element model was developed to check the consistency of the measurements and validate the data reduction method used. The results exhibited rate insensitive behaviour in the case of the IM7/8552 laminates while IM7/M91 showed the contrary behaviour with maximum peak at 500 mm/s of displacement rate, with a toughness increase of ≈95% with respect to the quasi-static conditions.

Transient response predication of nickel coated carbon fiber composite subjected to high altitude electromagnetic pulse

Metal materials are gradually replaced by fiber reinforced composite and the electromagnetic shielding capacity needs to be quantitatively evaluated, especially for intense electromagnetic pulse. Equivalent permittivity and permeability of fiber composite are calculated by multi-scale model based on finite element method, which results are close to theoretical values. Transverse electrical conductivity is obtained by contact network model and numerical results are in agreement with experimental data. The propagation characteristics of high altitude electromagnetic pulse penetration through fiber reinforced composite is investigated by numerical method based on electromagnetic wave theory in time domain. It is found that fiber orientation and stacking sequence can affect the shielding capacity of fiber composite. Composite laminates stacked alternately at 45 degrees satisfy the shielding requirement when high altitude electromagnetic pulse incidence at any angle. Nickel-coated carbon fiber composite laminate show better shielding than that of carbon fiber composite laminate.

Transverse failure of carbon fiber composites: Analytical sensitivity to the distribution of fiber/matrix interface properties

SummaryAn analytic differentiation method is presented to calculate the sensitivity of the transverse failure response of carbon fiber composite laminates to the distribution parameters of the fiber/matrix interface properties. The method starts with the evaluation of the sensitivities of the transverse failure response with respect to the interface properties of each fiber, ie, the cohesive failure strength and the critical displacement jump. These individual sensitivities are then used to calculate the sensitivities with respect to the mean and standard deviation of the interface properties. The derived sensitivities are implemented in a nonlinear interface‐enriched generalized finite element method solver specially developed for this application. The interface‐enriched generalized finite element method solver combines a cohesive modeling of the fiber/matrix interface failure with finite element meshes that do not conform to the composite microstructure. The approach is first demonstrated on a model material involving a one‐dimensional domain containing N cohesive interfaces described by randomly selected cohesive failure properties. The method is then applied to the more complex problem of a composite laminate involving a large number of fibers.

A stretchable and large-scale guided wave sensor network for aircraft smart skin of structural health monitoring

Aircraft smart skin technology requires the integration of large-scale, lightweight, and integrative sensor networks with aircraft structural skin, but it is difficult to directly manufacture such sensor networks in a large-scale, low-cost, reliable, and simple way. To study this issue, a design and manufacturing method of a stretchable and large-scale guided wave sensor network is proposed in this article. The key principle of the method is to design and manufacture the guided wave sensor network in a limited scale and expand it in a large-scale for aircraft smart skin of structural health monitoring. To ensure the excellent stretchability of the network, the design method of a serpentine-based fractal island-interconnect structure combined with the flexible printed circuit manufacturing process is proposed. The whole manufacturing process of the guided wave sensor network is realized by the mature flexible printed circuit process and the piezoelectric transducers (referred to as PZTs) are integrated with the network by reflow soldering which is compatible with the flexible printed circuit process, which greatly reduce manufacturing costs, simplify manufacturing process, and improve the yield and stability of the network. The guided wave sensor network can be uniaxially stretched to 500% of its original size and work well when fully expanded to cover 2500% of its original area. The test results of guided wave response show that the PZTs on the network can excite and receive guided wave signal normally. In addition, the network is placed on the surface of a carbon fiber composite laminate with stiffeners and the validation results show that the network can be applied to both active and passive guided wave–based structural health monitoring of composite structures, including damage imaging and impact imaging.

Experimental and numerical investigation of open hole carbon fiber composite laminates under compression with three different stacking sequences

The open hole composite laminates with different stacking sequence were tested and the failure modes and strength were recorded. A progressive damage model of the open-hole composite laminate under compression was developed and in-plane damage is modeled by using the three-dimensional continuum shell elements and cohesive element was adopted for delamination failure simulation. Based on the ABAQUS user subroutine UMAT, this model simulates damage initiation, propagation and final failure. With different failure criteria, the strength and failure modes of open-hole laminates under compression were predicted in this model. Compared with the experiment results, the effects of different stacking sequences on the strength and final failure modes of composite laminates are analyzed.

Low-velocity impact behaviour of woven laminate plates with fire retardant resin

The understanding of the damage mechanisms for woven laminate plates under low-velocity impact is challenging as the damage mechanisms at the interface of adjacent layers are dominated by the fibre architecture. This work presents an experimental investigation of the behaviour of woven glass and carbon fibre composite laminates in a matrix of fire retardant resin under low-velocity impact. The performance is evaluated in terms of damage mechanisms and force time history curves. Six impact energy levels were used to test standard plates to identify the type of damage observed at various energy levels. Scanning electron microscopy (SEM) along with C-scans were used to characterise the damage. It has been observed that in woven composites, the damage occurs mostly between the fibre bundles and matrix. As the impact energy increases, the failure involves extended matrix cracking and fibre fracture. Moreover, due to the fibre architecture, both the contact forces between bundles of fibres and stretching of the bundles are responsible for the dominant matrix cracking damage mode observed at the low-impact energy level. As the impact energy increases, the damage also increases resulting in fibre fracture. The experimental evidence collected during this investigation shows that for both the carbon fibre and the glass fibre woven laminates the low-velocity impact behaviour is characterised by extended fibre fracture without a noticeable sudden load drop.

Effect of locally deposited nanosilica particles on interlaminar fracture toughness of high glass-transition temperature epoxy carbon fiber-reinforced composites

This study explores the toughening of fiber-reinforced composite laminates to prevent against mode 1 delamination by using a selective placement of nanosilica particles in only the out-of-tow interlaminar regions of the laminate. In place of a conventional homogenous particle distribution throughout the laminate, “selective toughening” through controlled particle deposition is examined with the objective to increase the nanosilica toughening efficiency. Using a laboratory-scale manufacturing route conceptually similar to a combined prepreg and resin-film process, uni-directional carbon fiber composite laminates containing high glass-transition temperature amine-cured Dow D.E.R. 330 epoxy are produced from both particle distribution configurations. Comparisons are made by double cantilever beam testing for mode 1 delamination fracture energy G1C and by examination of the fracture surfaces. The results show that further nanosilica toughening efficiency is possible with local deposition and toughening compared to the conventional homogenous particle distribution throughout the laminate. For the same total nanosilica particle content in the laminate, the delamination toughening effects are maintained or improved when locally toughened in only the out-of-tow interlaminar regions. For mode 1 delamination initiation and propagation, fracture energy increases in the range of 60% over the untoughened laminates are found for the laminates with a local particle distribution. By comparison, those laminates with a conventional homogeneous particle distribution saw increase of 20–35% over the untoughened laminates. The implications of the localized toughening approach are discussed to provide further guidance in optimizing the use of nanosilica particles and particle toughening in general in composite laminates.

Vibration energy harvesting of multifunctional carbon fibre composite laminate structures

A sustainable power supply for a wide range of applications, such as powering sensors for structural health monitoring and wireless sensoring nodes for data transmission and communication used in unmanned air vehicles, automobiles, renewable energy sectors, and smart city technologies, is targeted. This paper presents an experimental and numerical study that describes an innovative technique to harvest energy resulted from environmental vibrations. A piezoelectric energy harvester was integrated onto a carbon fibre reinforced polymer (CFRP) laminate structure using the co-curing method. The integrated composite with the energy harvester was lightweight, flexible and provided robust and reliable energy outcomes, which can be used to power different low-powered wireless sensing nodes. A normalised power density of 97 μW cm−3m−2s4 was obtained from resonance frequency of 46 Hz sinusoidal waves at amplitude of 0.2 g; while the representative environmental vibration waves in various applications (aerospace, automotive, machine and bridge infrastructure) were experimentally and numerically investigated to find out the energy that can be harvested by such a multifunctional composite structure. The results showed the energy harvested at different vibration input from various industrial sectors could be sufficient to power an autonomous structural health monitoring system and wireless communications by the designed composite structure.

Through-thickness thermal conductivity enhancement of carbon fiber composite laminate by filler network

This paper successfully introduces highly conductive filler network in composite laminate to enhance its through-thickness thermal conductivity (TC). The effects of filler type, filler content, filler dimension, and ply scheme on through-thickness TC are investigated. The results show that one-dimensional carbon fiber fillers occupy both interlaminar and inter-tow regions forming the river-pattern conductive network inside the modified composite. Hence, the through-thickness TC is enhanced effectively up to 2.21 W·m−1 K−1 for the carbon fiber filler modified composite, which increases with increasing filler content. The composites modified by shorter fiber fillers show higher through-thickness TCs than those modified by long fillers, due to relatively higher content of shorter fillers in inter-tow gap, easy orientation along through-thickness direction and higher filler volume faction in conductive path. These results prove the superiority of continuous conductive network with concentrated fillers, and guide the structural design of composite laminate to manage its through-thickness TC.

Damage detection and location in woven fabric CFRP laminate panels

The need for multifunctional carbon fibre composite laminates has emerged to improve the reliability and safety of carbon fibre composite components and decrease costs. The development of an electrical selfsensing system for woven fabric carbon fibre composite laminate panels which can detect and locate damage due to impact events is presented. The electrical sensing system uses a four probe electrical resistance method. Two different sensing mats are investigated, the main difference between them are the surface area of the electrodes and the distance between the electrodes. To investigate the damage sensitivity of the sensing system for woven fabric carbon fibre composite laminate panels, panels are produced with various thicknesses from 0.84 to 3.5 mm and are impacted at energies from 1 to 10 J to generate barely visible impact damage. Damage is detected using global electrical resistance changes, the changes in electrical resistance vary depending on carbon fibre volume fraction, spacing distance between the sensing electrodes in the sensing mats, the surface area of the electrodes, damage size, and damage type; it is found that the thicker the panel, the less sensitive the electrical resistance system is. The effect of the surface area of the sensing electrodes is high on the electrical resistance baseline, where the baseline increases by up to 55% when the surface area of the sensing electrodes increases from 100 mm2 to 400 mm2; while spacing distance between electrodes has a greater effect on damage sensitivity of the electrical resistance sensing system than the surface area of the sensing electrodes.

Simulation and Analysis of the Damage of Carbon Fiber Composite Laminates under Three Point Bending Load

Simulation and Analysis of the Damage of Carbon Fiber Composite Laminates under Three Point Bending Load

Strain-deformation Reconstruction of Carbon Fiber Composite Laminates Based on BP Neural Network

The Carbon Fiber Reinforced Polymer (CFRP) laminate structural components used in the aerospace and military domains require high precision and strong stability. Usually the deformation of these structural components is difficult to be measured directly during operation, but the deformation of the CFRP laminate structure can be reconstructed with strain information. The CFRP laminate structure can be designed to adapt to the requirements of different applications through layering of variable thickness. In this paper, aiming at the discontinuous stiffness and strength of the variable laminations within the CFRP laminate structure, the BP neural network is proposed to be applied to the deformation reconstruction of CFRP laminates. With strain as input and deformation as output, based on a large amount of experimental data, the BP neural network model between strain and deformation is obtained through training. In this paper, CFRP test piecs with equal thickness and variable thickness were designed, and the corresponding strain-deformation reconstruction experimental system was constructed. The strain on the surface of CFRP test piece was measured by the fiber grating sensor, and the deformation of the test piece was measured by the laser displacement sensor. The comparative analysis between the predicted deflection obtained by neural network reconstruction and the actual measured deflection shows that BP neural network can reconstruct the structural deformation of CFRP laminates within certain error range.

Hygrothermal effects on mode II interlaminar fracture toughness of co‐bonded and secondary bonded composites joints

Adhesive joints are being more extensively applied in the aeronautical industry, allowing for better integration between the structural parts and overall lower weight if compared with joints made with fasteners and rivets. However, a further evaluation of these new technologies is needed, once their critical fracture toughness under different environmental conditions is still unknown and this value is essential for design and certification of aircraft manufactured with these materials. Thus, this work focuses on the mode II fracture toughness characterization of carbon fiber composite laminates joined by co‐bonded (CB) and secondarily bonded (SB) techniques, using EA 9695 epoxy adhesive aged at different environmental conditions (room temperature ambient—RTA and elevated temperature wet—ETW). Dynamic mechanical analysis (DMA) was used to understand the effect of moisture absorption on the glass transition of materials and on the decreasing of Mode II fracture toughness after aging. The DMA results showed a reduction of 11% in Tg values for the GIIc values of ETW samples in comparison with specimens tested at RTA condition. Reductions about 92 and 94% in Mode II fracture toughnesses were obtained for CB and SB aged specimens, respectively when compared with the toughness values obtained for specimens tested at RTA. Further inspection of the fracture surfaces using scanning electron microscope proved that light fiber‐tear fracture occurred at both RTA and ETW conditions for CB joints, while fracture was mainly light‐fiber‐tear at RTA condition, becoming mostly cohesive after aging for SB joints. POLYM. COMPOS., 40:3220–3232, 2019. © 2018 Society of Plastics Engineers

Interfacially reinforced carbon fiber/epoxy composite laminates via in-situ synthesized graphitic carbon nitride (g-C3N4)

Carbon fiber composite laminates were interfacially reinforced through in-situ synthesis of g-C3N4 on the carbon fibers. The introduced g-C3N4 greatly improved the roughness, functional groups and wettability on the carbon fiber surface and markedly enhanced the interfacial properties of composite laminates. The surface free energy of carbon fibers was increased by 67.81%. Interlaminar shear strength and interfacial shear strength of composite laminates were increased from 51.84 to 72.09 MPa and 44.62–73.41 MPa, respectively. The significantly enhanced interfacial properties enabled the mechanical performance of composite laminates to reach a superior state. Tensile strength and bending strength were increased by 19.54 and 10.51%, respectively. The total absorbed energy of impact experiment was also enhanced from 1.14 to 1.78 J. Meanwhile, dynamic mechanical properties and hydrothermal aging resistance were also ameliorated significantly. The improved interfacial properties and mechanical properties were ascribed to the increased mechanical interlocking, enhanced chemical bonding and ameliorated wettability created by g-C3N4.