Carbon Fiber Composite Structures Research Articles

Mechanical and Interfacial Properties Characterisation of Single Carbon Fibres for Composite Applications

The mechanical and interfacial properties of single carbon fibres have been experimentally investigated. Longitudinal tensile strengths were determined using single filament as well as impregnated yarn specimens at various gauge lengths ranging from 5 to 200 mm. The tensile behaviour of the fibre depends on gauge length due to the presence of flaws along the fibre. Axial compressive strength was obtained by the tensile recoil method. The transverse modulus was measured by nano-indentation technique. Shear modulus was obtained by a torsional pendulum test. The apparent shear strength of carbon fibre/epoxy interface was characterised by a microbond fibre pull-out test. Data obtained in this work constitute important materials’ data input for the design and simulation of carbon fibre composite structures.

Analysis of adhesively bonded CFRE composite scarf joints modified with MWCNTs

The main objective of the present work is to improve the performance of bonded joints in carbon fiber composite structures through introducing Multi-Walled Carbon Nanotubes (MWCNTs) into Epocast 50-A1/946 epoxy, which was primarily developed for joining and repairing of composite aircraft structures. Results from tension characterizations of structural adhesive joints (SAJs) with different scarf angles (5–45°) showed improvement up to 40% compared to neat epoxy (NE)–SAJs. Special attention was considered to investigate the performance of SAJs with 5° scarf angle under different environments. The tensile strength and stiffness of both NE-SAJs and MWCNT/E-SAJs were dramatically decreased at elevated temperature. Water absorption showed a marginal drop of about 2.0% in the tensile strength of the moist SAJs compared to the dry one. Cracks initiation and propagation were detected effectively using instrumented-SAJs with eight strain gauges. The experimental results agree well with the predicted using three-dimensional finite element analysis model.

Redesigning of a Canard Control Surface of an Advanced Fighter Aircraft: Effect on Buckling and Aerodynamic Behavior

Abstract A redesign of canard control-surface of an advanced all-metallic fighter aircraft was carried out by using carbon fibre composite (CFC) for ribs and panels. In this study ply-orientations of CFC structure are optimized using a Genetic-Algorithm (GA) with an objective function to have minimum failure index (FI) according to Tsai-Wu failure criterion. The redesigned CFC structure was sufficiently strong to withstand aerodynamic loads from stress and deflection points of view. Now, in the present work CFC canard structure has been studied for its buckling strength in comparison to existing metallic design. In this study, the existing metallic design was found to be weak in buckling. Upon a detailed investigation, it was revealed that there are reported failures in the vicinity of zones where initial buckling modes are excited as predicted by the finite element based buckling analysis. In view of buckling failures, the redesigned CFC structure is sufficiently reinforced with stringers at specific locations. After providing reinforcements against buckling, the twist and the camber variations of the airfoil are checked and compared with existing structure data. Finally, the modal analysis has been carried out to compare the variation in excitation frequency due to material change. The CFC structure thus redesigned is safe from buckling and aerodynamic aspects as well.

Design and Optimization of a Composite Canard Control Surface of an Advanced Fighter Aircraft under Static Loading

Abstract The minimization of weight and maximization of payload is an ever challenging design procedure for air vehicles. The present study has been carried out with an objective to redesign control surface of an advanced all-metallic fighter aircraft. In this study, the structure made up of high strength aluminum, titanium and ferrous alloys has been attempted to replace by carbon fiber composite (CFC) skin, ribs and stiffeners. This study presents an approach towards development of a methodology for optimization of first-ply failure index (FI) in unidirectional fibrous laminates using Genetic-Algorithms (GA) under quasi-static loading. The GAs, by the application of its operators like reproduction, cross-over, mutation and elitist strategy, optimize the ply-orientations in laminates so as to have minimum FI of Tsai-Wu first-ply failure criterion. The GA optimization procedure has been implemented in MATLAB and interfaced with commercial software ABAQUS using python scripting. FI calculations have been carried out in ABAQUS with user material subroutine (UMAT). The GA's application gave reasonably well-optimized ply-orientations combination at a faster convergence rate. However, the final optimized sequence of ply-orientations is obtained by tweaking the sequences given by GA's based on industrial practices and experience, whenever needed. The present study of conversion of an all metallic structure to partial CFC structure has led to 12% of weight reduction. Therefore, the approach proposed here motivates designer to use CFC with a confidence.

Piezoresistive in-situ strain sensing of composite laminate structures

Various methods have been developed to monitor the health and strain state of carbon fiber reinforced polymers, each with a unique set of pros and cons. This research assesses the use of piezoresistive sensors for in situ strain measurement of carbon fiber and other composite structures in multidirectional laminates. The piezoresistive sensor material and the embedded circuitry are both evaluated. For the piezoresistive sensor, a conductive nickel nanocomposite sensor is compared with the piezoresistivity of the carbon fiber itself. For the circuit, the use of carbon fibers already present in the structure is compared with the use of nickel coated carbon fiber. Successful localized strain sensing is demonstrated for several sensor and circuitry configurations. Numerous engineering applications are possible in the ever-growing field of carbon-composites.

Hybrid carbon fiber composite lattice truss structures

Carbon fiber reinforced polymer (CFRP) composite sandwich panels with hybrid foam filled CFRP pyramidal lattice cores have been assembled from linear carbon fiber braids and Divinycell H250 polymer foam trapezoids. These have been stitched to 3D woven carbon fiber face sheets and infused with an epoxy resin using a vacuum assisted resin transfer molding process. Sandwich panels with carbon fiber composite truss volumes of 1.5–17.5% of the core volume have been fabricated, and the through-thickness compressive strength and modulus measured, and compared with micromechanical models that establish the relationships between the mechanical properties of the core, its topology and the mechanical properties of the truss and foam. The through thickness modulus and strength of the hybrid cores is found to increase with increasing truss core volume fraction. However, the lattice strength saturates at high CFRP truss volume fraction as the proportion of the truss material contained in the nodes increases. The use of linear carbon fiber braids is shown to facilitate the simpler fabrication of hybrid CFRP structures compared to previously described approaches. Their specific strength, moduli and energy absorption is found to be comparable to those made by alternative approaches.

Fibrous structures: An integrative approach to design computation, simulation and fabrication for lightweight, glass and carbon fibre composite structures in architecture based on biomimetic design principles

In this paper the authors present research into an integrative computational design methodology for the design and robotic implementation of fibre-composite systems. The proposed approach is based on the concurrent and reciprocal integration of biological analysis, material design, structural analysis, and the constraints of robotic filament winding within a coherent computational design process. A particular focus is set on the development of specific tools and solvers for the generation, simulation and optimization of the fibre layout and their feedback into the global morphology of the system. The methodology demonstrates how fibre reinforced composites can be arranged and processed in order to meet the specific requirements of architectural design and building construction. This was further tested through the design and fabrication of a full-scale architectural prototype.

Effect of Vibration Characteristics for Carbon Fiber Composite Materials on Musical Instruments Making

Carbon fiber and its composite materials have a series of excellent properties such as high specific strength, high specific modulus, high temperature resistance, corrosion resistance, fatigue resistance and small thermal expansion coefficient, which can be widely applied to musical instrument manufacturing field. This paper introduces the structure and performance of carbon fiber, and mainly introduces the latest application of carbon fiber composite material, and the effect of vibration characteristics on musical performance. This paper also puts forward that for instrument design material substitutes the use of carbon fiber composite material structure of 2 layers and 3 layers structure should be considered, and the single layer structure is not feasible.

Study on Preparation Method and Energy-Absorbing Characteristics of Carbon Fiber Composite Energy Absorber

By analyzing advantages and disadvantages of the existing energy absorbers, carbon fiber composite and regular hexagon honeycomb structure were chosen as material and topological structure respectively to make a big-bearing, lightweight energy absorber. Preparation method of carbon fiber composite honeycomb energy absorber was studied, which was applied to manufacture some specimens,and it is feasible because of the specimens good consistency and regularity. Quasi-static compression tests of the specimens were carried out, and then the related parameters of energy-absorbing characteristics were calculated. The results show that the carbon fiber composite honeycomb energy absorber has excellent energy-absorbing characteristics.

A slot spiral in carbon-fibre composite laminate as a conformal load-bearing antenna

Conformal load-bearing antenna structures, which afford load-bearing structures with radar capability, are a promising technology to reduce weight and drag of air vehicles. This article presents an investigation of the mechanical and electromagnetic performance of slot log-spiral antenna in carbon-fibre composite structures. Compared with traditional rectangular slots, equiangular slot spiral antenna is found to offer broader bandwidth and better mechanical strength. Through experimental testing and finite element analyses, a new tip design is proposed that can significantly reduce the stress concentration of the non-load-bearing log-spiral antenna. Results of mechanical tests also show that the compressive strength of a carbon-fibre composite plate featuring a spiral slot is comparable with that pertinent to a plate with a circular hole of the same size. Filling the slots with epoxy resin can further enhance the compressive strength.

The Self-Healing Capability of Carbon Fibre Composite Structures Subjected to Hypervelocity Impacts Simulating Orbital Space Debris

The presence in the space of micrometeoroids and orbital debris, particularly in the lower earth orbit, presents a continuous hazard to orbiting satellites, spacecrafts, and the international space station. Space debris includes all nonfunctional, man-made objects and fragments. As the population of debris continues to grow, the probability of collisions that could lead to potential damage will consequently increase. This work addresses a short review of the space debris “challenge” and reports on our recent results obtained on the application of self-healing composite materials on impacted composite structures used in space. Self healing materials were blends of microcapsules containing mainly various combinations of a 5-ethylidene-2-norbornene (5E2N) and dicyclopentadiene (DCPD) monomers, reacted with ruthenium Grubbs' catalyst. The self healing materials were then mixed with a resin epoxy and single-walled carbon nanotubes (SWNTs) using vacuum centrifuging technique. The obtained nanocomposites were infused into the layers of woven carbon fibers reinforced polymer (CFRP). The CFRP specimens were then subjected to hypervelocity impact conditions—prevailing in the space environment—using a home-made implosion-driven hypervelocity launcher. The different self-healing capabilities were determined and the SWNT contribution was discussed with respect to the experimental parameters.

Shear response of carbon fiber composite pyramidal truss structures after high-temperature exposure

Shear behavior and residual strength at room temperature of carbon fiber composite sandwich panel with pyramidal truss cores exposed to different temperatures for different time were studied experimentally and analytically. Experimental results showed that the residual shear modulus and strength of composite sandwich panels decreased with increasing exposure temperature and time. The decreasing of shear modulus and strength after thermal exposure was mainly attributed to the degradation of the matrix property and fiber-matrix interface property. The effect of high-temperature exposure on failure mode was revealed as well. The failure was characterized by node rupture when sandwich panels were exposed to temperature in a range of 20–250°C, while node rupture and face sheet delamination were observed when specimens were exposed to 280°C. The analytical formulae were also presented to describe residual shear modulus and strength after thermal exposure.

A practical structural health monitoring system for carbon fibre reinforced composite based on electrical resistance

Abstract A practical structural health monitoring system based on measuring changes in the electrical resistance of a carbon fibre composite structure is presented. Electrical contact with the fibres is provided by flexible printed circuit boards which are interleaved with the carbon fibre plies during the lamination of the composite. The resistance between opposite pairs of contacts was measured before and after an impact load which caused barely visible impact damage (BVID) in the panel. It was found that even low levels of impact damage produced measurable changes in resistance in the vicinity of the damage. Therefore was demonstrated that electrical resistance measurements are a practical means of locating BVID. Various parameters were studied in order to better understand the mechanisms involved and optimise the system for improved sensitivity and accuracy. The location of the contacts in the through thickness direction, the spacing and orientation of the contacts and the residual thermal stress of the laminate were all investigated and recommendations made. A structural health monitoring system for composites based on electrical resistance has several important potential benefits over acoustic, ultrasonic or optical methods; it adds little parasitic mass, causes no reduction in mechanical integrity, can be carried out on structures either in or out of service conditions and is very simple in concept, implementation and data interpretation.

Hybrid truss concepts for carbon fiber composite pyramidal lattice structures

A novel hybrid truss construction concept is presented that incorporates a second-phase core material into trusses of carbon fiber (CF) composite pyramidal lattice (CPL) structures. Embedded core materials of wood and silicone rubber are selected for trial structures. Hybrid CPL structures were fabricated using a hot press molding approach and out-of-plane compression tests were performed to investigate properties. For prototype wood–core truss CPL, structural efficiencies increased comparing with solid truss CPL, while energy absorption capability was enhanced for rubber–core truss CPL. Employing the hybrid truss construction, the density-specific performance space of CF composite lattice structures can be expanded, and desired functional potential can be realized by judicious selection of core materials while simultaneously retaining structural properties.

A phase synthesis time reversal impact imaging method for on-line composite structure monitoring

Comparing to active damage monitoring, impact localization on composite by using time reversal focusing method has several difficulties. First, the transfer function of the actuator-sensor path is difficult to be obtained because of the limitation that no impact experiment is permitted to perform on the real structure and the difficulty to model it because the performance of real aircraft composite is much more complicated comparing to metal structure. Second, the position of impact is unknown and can not be controlled as the excitation signal used in the active monitoring. This makes it not applicable to compare the difference between the excitation and the focused signal. Another difficulty is that impact signal is frequency broadband, giving rise to the difficulty to process virtual synthesis because of the highly dispersion nature of frequency broadband Lamb wave in plate-like structure. Aiming at developing a practical method for on-line localization of impact on aircraft composite structure which can take advantage of time reversal focusing and does not rely on the transfer function, a PZT sensor array based phase synthesis time reversal impact imaging method is proposed. The complex Shannon wavelet transform is presented to extract the frequency narrow-band signals from the impact responded signals of PZT sensors. A phase synthesis process of the frequency narrow-band signals is implemented to search the time reversal focusing position on the structure which represents the impact position. Evaluation experiments on a carbon fiber composite structure show that the proposed method realizes the impact imaging and localization with an error less than 1.5 cm. Discussion of the influence of velocity errors and measurement noise is also given in detail.

Impact localisation with FBG for a self-healing carbon fibre composite structure

We demonstrated the localisation of impacts in orthotropic carbon fibre reinforced polymer (CFRP) composite materials to within a few centimetres, using a sparse array of fibre Bragg grating (FBG) sensors. This type of sensor is easily embedded in composites permitting the development of structures with integrated sensing capability. Impact location was determined by measuring the differences in time-of-flight of ultrasonic Lamb waves at three surface-mounted sensors. An algorithm was developed taking into account the angle dependence of the optical fibre sensor sensitivity and the variation of Lamb waves propagation velocity with direction and wave mode. The performance of FBG sensors for impact localisation was compared to that of standard piezoelectric transducers (PZTs), which are already widely used for that purpose. The FBG-based system showed promising potential for a non-intrusive impact detection system applied to self-healing composite structures.

The Study of Low-Velocity Impact Characteristics and Residual Tensile Strength of Carbon Fiber Composite Lattice Core Sandwich Structures

In this paper, low-velocity impact characteristics and residual tensile strength of carbon fiber composite lattice core sandwich structures are investigated experimentally and numerically. Low-velocity impact tests and residual tensile strength tests are simulated by the FE (finite element) software, ABAQUS/Explicit and its subroutine (VUMAT). In order to give more detailed description about the impact damage of the structure and improve modeling accuracy, multi-steps analysis method is employed to simulate impact process and residual tensile strength test in one analysis model. The calculation results computed by the FE model have been compared to the value of experiments, the difference of impact process simulation is about 3.3% and that of tensile strength test simulation is about 12.9%. The calculation error of computation model is acceptable, since unavoidable damage could be introduced in the courses of manufacture, processing and transportation of composite materials, and these damages are determinated difficultly in the computation programs. Next, the degradation tendency chart of residual tensile strength and impact energy threshold Uo of carbon fiber composite lattice core sandwich structures are obtained by the computation value of residual tensile strength after impacted with different impact energy. Previously, this threshold can only be obtained by experiment tests. After the contact force which is bigger than the threshold Uo impact on the sandwich structures, the residual tensile strength of structures are degraded greatly. This conclusion is significant for the design and application of carbon fiber composite lattice core sandwich structures.

Application of Carbon Fiber Composite on Space Camera Frame

General materials can satisfy the structure strength requirement of space effective payload easily. But it can hardly satisfy the structure stiffness requirement of space payload. Carbon fiber composite has many excellent properties, such as high relative strength, high relative stiffness, small expansion coefficient, good fatigue resistance and excellent vibration resistance. It can be used to make space products. Firstly, this paper discussed the properties of carbon fiber composite material. Compared with common materials, such as aluminum alloy and titanium alloy, carbon fiber composite material is more suitable for applications of space instruments. Secondly, the metal part embedded technique of carbon fiber composite structure was studied. According to the carbon fiber composite structure of a space camera frame, a few structure forms of embedded part ware studied. A space camera frame of carbon fiber composite was designed and manufactured. Finally, finite element analysis and mechanical tests on the space camera frame was carried out. The results reveal that the characteristic frequency of carbon fiber composite frame is up to 104Hz.The space camera frame is of high stiffness and dimensional stability.

Low-velocity impact characteristics and residual tensile strength of carbon fiber composite lattice core sandwich structures

In this paper, low-velocity impact characteristics and residual tensile strength of carbon fiber composite lattice core sandwich structures are investigated by experimentally and numerically. Low-velocity impact tests and residual tensile strength tests are performed using an instrumented drop-weight machine (Instron 9250HV) and static test machine (Instron 5569), respectively. The FE (finite element) software, ABAQUS/Explicit is employed to simulate low-velocity impact characteristics and predict residual tensile strength of carbon fiber composite lattice core sandwich structures. These numerical investigations create a user-defined material subroutine (VUMAT) to enhance the damage simulation which includes Hashin and Yeh failure criteria. The impact contact force and the tensile strength are accurately estimated using the present method. From results of this paper, the degradation of residual tensile strength can be divided to three stages for different impact energies, and amplitudes of degradation are affected by stacking sequences.

Carbon fiber composite lattice structure filled with silicon rubber

In the present study, the highly efficient composite lattice structures were filled with silicon rubber in their enormous space, to enhance their mechanical property and energy absorption capacity. Out-of-plane compression tests were carried out to evaluate the enhancement. The initial response and failure mode of the newly developed structure kept the same as that before filling. However, a higher stress level region was appeared which benefited to its energy absorption.