Carbon Fabric Epoxy Composites Research Articles

Improving the damage tolerance of composite T-joints using shape memory alloy tufts

This paper presents a novel approach to improve the structural properties and damage tolerance of fibre-reinforced polymer composite joints via tufting using shape memory alloy (SMA) filaments. T-shaped joints made of carbon-epoxy composite material were reinforced with thin SMA (Ni-Ti nitinol) tufts. Experimental testing and finite element (FE) modelling reveal that the ultimate load, ultimate displacement and absorbed energy capacity of the T-joint increase with the areal density of SMA tufts. Improvements of over 110% in strength and 450% in absorbed energy capacity were achieved by SMA tufting. Under certain conditions, the shape memory effect of the tufts can be activated via electrical resistance heating to partially or completely close cracks in the T-joint caused by over-loading. The novel use of SMA tufts both to improve the resistance against cracking and to close cracks when they occur is a unique approach to improving the damage tolerance of composite structural joints.

Structural response validation of composite cylindrical pressure vessels using FEA

Cylindrical pressure vessels constructed using filament winding technique are a good example of the advantages that fibre-reinforced composite materials offer over common structural materials on a specific/unit weight basis. The high specific properties of composite materials over metals can reduce the weight of pressure vessels with a high potential for applications in submarines and ROV/AUV. An innovative method for the optimisation of composite cylindrical structures is through simulation of the pressure vessel response using as parameterised finite element model. In this paper the effect of boundary conditions has been analysed for a cylindrical pressure vessel of carbon-epoxy composite material subjected to internal pressure. For the said study, a parametric Finite Element model using an 8 noded layered solid brick element has been created in the finite element analysis software ANSYS using its Parametric Design Language features. The elasticity solution for a single layer circular tube has also been presented in reference to the works of Herakovich and Pindera towards validation of the numerical model. Pressure vessel finite element models, with different boundary conditions have been used to study convergence in comparison to the exact solution. A comparison of the through thickness distribution of stresses from different finite element cylindrical models in ANSYS against the exact solution for a composite tube under internal pressure have been presented for the validation of the numerical model and proposed boundary conditions. It has been demonstrated that only one element in circumferential direction using displacement coupling conditions at the boundary is sufficient, which would significantly enhance the computational efficiency of a structural analysis and make these models computationally efficient even for a non-linear analysis with axi-symmetric loads for both static and dynamic cases.

Structural and modal analysis of gas insulated switchgear structure made up of glass-epoxy and carbon-epoxy composite materials for seismic application

Earthquakes cause significant loss of life and infrastructure damage. As a result, there has been a huge increase in the development of technologies and materials to mitigate the effects of earthquakes in the infrastructure sector. Along with the infrastructure industry, the electrical sector is working to design structures that can withstand the effect of an earthquake. The purpose of this study is to develop lightweight frame structure for Gas Insulated Switchgear (GIS) for seismic applications. In the proposed study, GIS frame structure incorporates composite materials such as carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) in addition to traditional materials such as steel. These composite materials are subjected to experimental testing in order to determine their mechanical properties. To select optimal material for the frame structure, the structural and modal performance of these materials is evaluated using finite element simulations for the GIS frame structure under seismic loading as per California Building Code (CBC) and International Building Code (IBC) code.

Identification of diffusion properties of composites materials for aircraft applications

The paper deals with the identification of planar anisotropic diffusion properties of carbon-epoxy composite materials for aircraft applications, based on the exploitation of short-time gravimetric tests. The method consists in performing short time gravimetric tests on composites samples and measuring the initial slope of their mass uptake curve with respect to t. The identification is performed by minimizing the sum of squared residuals, the residual being the difference between the measured slope and the analytical slope. The identification protocol allows determining the 2 coefficients of diffusion along the principal directions of orthotropy and the orientation of the orthotropic frame reference with respect to the sample frame. Analysis and discussion of results allow to propose a robust identification protocol.

On the Identification of Orthotropic Elastic Stiffness Using 3D Guided Wavefield Data.

Scanning laser Doppler vibrometry is a widely adopted method to measure the full-field out-of-plane vibrational response of materials in view of detecting defects or estimating stiffness parameters. Recent technological developments have led to performant 3D scanning laser Doppler vibrometers, which give access to both out-of-plane and in-plane vibrational velocity components. In the present study, the effect of using (i) the in-plane component; (ii) the out-of-plane component; and (iii) both the in-plane and out-of-plane components of the recorded vibration velocity on the inverse determination of the stiffness parameters is studied. Input data were gathered from a series of numerical simulations using a finite element model (COMSOL), as well as from broadband experimental measurements by means of a 3D infrared scanning laser Doppler vibrometer. Various materials were studied, including carbon epoxy composite and wood materials. The full-field vibrational velocity response is converted to the frequency-wavenumber domain by means of Fourier transform, from which complex wavenumbers are extracted using the matrix pencil decomposition method. To infer the orthotropic elastic stiffness tensor, an inversion procedure is developed by coupling the semi-analytical finite element (SAFE) as a forward method to the particle swarm optimizer. It is shown that accounting for the in-plane velocity component leads to a more accurate and robust determination of the orthotropic elastic stiffness parameters.

A Study on Design of S-Duct Structures and Air Intake for Small Aircraft Applied to High Strength Carbon-Epoxy Composite Materials.

Recently, many structural parts using composite materials are being applied to small aircraft and UAV in the world. The aim of this work is to design the engine intake structure of a small aircraft. For structural safety evaluation, a finite element analysis method was applied. In this work, structural design and numerical analysis of air intake and s-duct structures for small aircraft were performed. The target structure is composed of an s-duct and a cylindrical intake structure. Firstly, an investigation of the mechanical properties of carbon/epoxy material was conducted. The distributed pressure load and acceleration condition was applied to the structural design. The structural design load was investigated considering safety factors. The structural analysis was performed to analyze the validity of the design results. Through the structural analysis using the finite element analysis method, it was confirmed that the designed air intake structure is safe. The manufacturing of the prototype structure will be carried out based on the designed result.

Vol4 num4-7 Delamination behavior under mode I and mode II of adhesive bonded joints for different surface treatments

The automotive, aerospace and renewable energy generation industries have replaced significantly the use of traditional materials, such as steel and aluminum, by reinforced fiber composites. It has recognized that joints drilling and screwing joints damage the fibers introducing a higher concentration of stresses. That is why the application of structural adhesives, as a method of joining in reinforced composites, has increased in recent years. Delamination is the most critical failure mode of composite materials resulting in stiffness and structural strength losses. This works studies the behavior against delamination under mode I and mode II interlaminar fracture of adhesive bonded joints in carbon-epoxy composite materials, using structural adhesives of epoxy and acrylic bases. For the execution of the joints, different surface treatments have been employed: sanding, grit blasting and peel ply technique, allowing to make a fracture resistance comparision study. The double cantilever beam (DCB) and end notched flexure (ENF) tests configuration were used to determine stress-strain behavior and fracture toughness for mode I (GIC) and mode II (GIIC), respectively. Surface modifications have been evaluated by  contact angle measurements and scanning electron microscopy (SEM). The experimental results are shown in the same situation. The experimental results obtained show that, even if not showing the same delamination tendency for both fracture modes, the strain energy release rate are higher for an improved of wetting properties and an increase of surface roughness.

Stability and failure analysis of compressed thin-walled composite structures with central cut-out, using three advanced independent damage models

In this paper, the phenomenon of stability and failure of axially compressed thin-walled structures with central cut-out, made of composite materials, were investigated. The tested structures were made of carbon-epoxy composite material, using autoclave technique. Within the framework of the studies, experimental tests on actual constructions were carried out, as well as advanced numerical simulations using the finite element method in the ABAQUS® software. The process of axial compression of thin-walled composite structures was carried out in the full range of load, up to total failure. During the experimental tests, post-critical equilibrium paths were recorded, using the universal testing machine - Instron 4485. Additionally, acoustic emission signals were recorded using the AMSY-5 device, and the level of deformation was tested, using the non-contact three-dimensional measurement technique offered by the ARAMIS system. Simultaneously to the experimental tests, numerical calculations were carried out using progressive failure analysis (PFA), based on the damage initiation Hashin's criterion of as well as damage evolution based on the energy criterion. In the numerical analyses, the cohesive zone model (CZM) and the model allowing for the simulation of damage due to material cracking (xFEM) were also used. A significant effect of conducted numerical calculations was the simulation of the failure phenomenon of thin-walled composite structures, in terms of loss of load-carrying capacity, using three independent damage models (model PFA, CZM and xFEM). The above constitutes a novelty, with respect to current papers from the subject literature. The use of the above-mentioned techniques of experimental research and numerical simulations made it possible to conduct a comprehensive analysis of the damage state of the composite material. The obtained results of the numerical tests demonstrated very high agreement with the results of the experimental studies.

An investigation and comparison of tensile strength in Fiber Sandwiched Wood Composite (FSWC) materials subjected to axial loading

The demand of composite materials like Fiber Reinforce Polymer (FRP), Carbon Fiber Reinforce Polymer (CFRP) and Glass Fiber Reinforce Polymer (GFRP) are increasing rapidly in industrial use because the characteristics of these materials involving higher strength to weight ratio and least cost incorporates the researchers to make interest. Composite materials are helping the industries in combination with different materials to achieve the desired material properties. Now a days, these materials had taken a part of sheet metal in many aerospace industries. Carbon fabric or epoxy composite materials are used in various industries for manufacturing special purpose applications. To evaluate the material performance, it is necessary to understand their mechanical properties like tensile strength. The tensile strength is usually used to determine the tensile testing data for the quality assurance of materials. Fiber Sandwiched Wood Composite (FSWC) materials are prepared by sandwiching the layers of wood and fibers. The composite materials with wood lead to variation in tensile strength. In that event, some specimen was prepared using teak wood and fibers involving Carbon, Aramid, Jute, and Banana. The specimens were evaluated for tensile strength using Universal Testing Machine (UTM) as per the ASTM 3039 standards. The comparison had been made with plain teak wood having known properties. The hybrid layers of Carbon and Aramid Fibers with teak wood presented the higher value. A comparison had made of FSCM and plain Materials like teak wood and aluminium. The results shows that the Carbon Aramid hybrid composites have 2.65% more strength as compare to Teak Wood and 1.79% more than the Aluminium.

Experimental Investigation of Open-Hole Compression Strength of Carbon Epoxy Composite Material and Determination of Localized Strains Using Digital Image Correlation Technique

The biggest application of the fiber-reinforced composites are in the field of military and commercial aircrafts. Carbon fibers either alone or with the Kevlar 49 fibers, are widely used as main material in many aero plane wing, fuselage and empennage components. Composites materials have wide applications in different industries because of it has very different properties from the metals and polymers. In the drilling of Carbon/Epoxy Composites the cut surface quality is very much dependent on the drilling parameters set during drilling which further effect the strength of the hole during extension/compression loading. In this research, Carbon Fiber Epoxy Composite material is drilled with the standard carbide drill bit and Open Hole Compression (OHC) tests are performed on the Universal Testing Machine. The Digital Image Correlation (DIC) technique is used to find out the strain distribution around the hole during compression loading. From the experimental method and DIC, maximum strength of carbon epoxy composite is achieved by drilling at 1600-2400 mm/min in presence of notch. It was also observed that failure of the structure is dependent on the drilling feed rate and 1600-2400 mm/min was the optimized drilling range.

Effects of solid lubricant fillers on the flexural and shear strength response of carbon fabric-epoxy composites

Multi-layered carbon fabric-epoxy composites (CFEC) encounter certain challenges in expanding their usage mainly due to their low interlaminar shear strength (ILSS) and sensitivity to delamination damage. The present article focuses on evaluating the effectiveness of the fillers molybdenum disulfide (MoS2) and hexagonal boron nitride (h-BN) (2–8 wt%) on the flexural and the shear properties of the CFEC. The filler dispersion in epoxy resin is achieved by ultrasonication and composite fabrication through vacuum-assisted hand lay-up process. The filler surface area, evaluated as per nitrogen adsorption principles, reveals characteristics of hysteresis isotherm and mesoporous structure in both the fillers. Fourier transform infrared analyses on MoS2 reveal the stretch vibration due to molybdenum-sulfur and disulfide bonds whereas, in the h-BN, the transverse stretching and the out-of-plane bending happen due to boron-nitrogen and the boron-nitrogen-boron molecular group, respectively. Further analysis in the atomic force microscope shows more regular filler distribution at the outer surface for 4 and 6 wt% filler loaded CFEC whereas, 8 wt% filler loading results in an uneven particle distribution and attains the minimum surface roughness. The study exhibits the maximum ILSS (43.46 MPa) which is 43% enhancement compared to the neat CFEC for 6 wt% h-BN loaded CFEC. The maximum flexural strength (532 MPa) was noticed in 4 wt% MoS2 loaded CFEC signifying 62% improvement compared to the neat CFEC. The structural property improvements were witnessed because of the regularly distributed filler that strengthens the fiber-matrix interaction zone and reduces the matrix crack. The findings reveal that the proposed enhanced scheme by solid lubricant fillers proves to be more favorable for improving the matrix-dominated properties and the bending stiffness compared to the other particle-reinforced approaches.

Study on the Mechanical Characterization of Composite Materials forAutomotive Wheel Application

Nowadays the development of using fiber-reinforced polymer composites in the field of aviation, defense, automotive, and marine industry is growing due to their lower density as compared with conventional materials. In the automotive industry, the requirements of reduction of weight and fuel consumption have become an essential study without losing any mechanical strength. Fiber-reinforced polymer composite materials are an alternative automotive wheel materials having outstanding mechanical properties via lower density, high fatigue resistance, flexibility of design, stability of dimension, better resistance of corrosion, the resistance of high temperature, high mechanical strength and light in weight, etc. To determine the mechanical properties of fiber-reinforced carbon epoxy composite material using quasi-isotropic orientation having [45/0/0/0/0/-45/90/90/90/90/-45/0/0/0/0/45]s stacking sequences with a total number of 32 plies was prepared and mechanical characterization was performed. To quantify this analysis tensile and compression tests were performed by fabricating the samples through hand layup as per ASTM standards. From the result, fiberreinforced carbon epoxy composite material has excellent tensile strength in the longitudinal direction and moderate compressive strength in the transversal direction.

Experimental study on abrasive water jet machining of carbon epoxy composite

ABSTRACTCarbon epoxy composite material is widely used in various technological applications. Traditional machining of this material is difficult. This paper presents research work involved in abrasive water jet machining of carbon epoxy composite material. Four process parameters, namely pressure, traverse rate, stand-off distance and abrasive mass flow rate, are considered for this study. Response surface methodology is used to design the experiments. Effect of process parameters on surface roughness is investigated on the basis of analysis of variance. Surface roughness decreases with an increase in pressure and abrasive mass flow rate and a decrease in stand-off distance and traverse rate. A mathematical model is developed to predict surface roughness on the basis of analysis. Defects including delamination, fibre pull-out and abrasive embedment are examined in machined samples. Further, optimisation of process parameters is performed in order to minimise surface roughness. Confirmation experiments are performed to verify the predictive model and optimise set of process parameters.

Influence of the Test Method on the Characterization of the Fatigue Delamination Behavior of a Composite Material under Mixed Mode I/II Fracture.

Composite materials manufactured by overlapping plies with certain specific geometries are likely to lose part of their strength due to the presence of internally delaminated regions. The aim of this paper is to experimentally evaluate the generation and propagation of these interlaminar cracks in a carbon-epoxy composite material subjected to fatigue loading under mixed mode I/II fracture. Two different test methods were used for this purpose: The standardized mixed-mode bending (MMB) test and the asymmetric double cantilever beam (ADCB) test, with the goal of exploring the viability of the ADCB test as a simpler alternative to perform than the MMB test, especially in fatigue testing. With this aim in mind and after prior static characterization of the material in which the critical values of the energy release rate were determined under both test methods, the levels of the energy release rate to be applied in fatigue tests were defined for two mode mixity ratios, GII/Gc = 0.2 and 0.4 (0.34 ADCB), and a fatigue loading ratio, R = Gmin/Gmax = 0.1. The G-N fatigue onset curves were subsequently obtained from these experimental data. The most relevant result of the study is that the fatigue limits obtained using the MMB method are generally more conservative than those obtained via the ADCB method.

Study on carbon epoxy composite surfaces machined by abrasive water jet machining

Traditional machining of carbon epoxy composite material is difficult due to excessive tool wear, excessive stresses and heat generation, delamination, high surface waviness, etc. In the present paper, research work involved in the experimental study of abrasive water jet machining of carbon epoxy composite material is described. The aim of present work is to improve surface finish and studying defects in machined samples. Taguchi's orthogonal array approach is used to design experiments. Process parameters namely hydraulic pressure, traverse rate, stand-off distance and abrasive mass flow rate are considered for this study. Analysis of machined surfaces and kerf quality is carried out using scanning electron microscope to evaluate microscopic features. Further, the effect of machining parameters on surface roughness is investigated using analysis of variance approach. It is found that traverse rate and pressure are most significant parameters to control surface roughness. Optimization of process parameters is performed using grey relational analysis. Thereafter, confirmation tests are carried out to verify the improvement in the surface quality with optimum set of process parameters. It is found that surface finish of machined samples is improved by 10.75% with optimum levels of process parameters. Defects like delamination, fiber pull-out and abrasive embedment are also studied using SEM. It is observed that delamination and fiber pull-out are prominent in samples machined at low pressure and high traverse rate.

Determination of the crack resistance curve for intralaminar fiber tensile failure mode in polymer composites under high rate loading

This paper presents the determination of the crack resistance curve of the unidirectional carbon-epoxy composite material IM7-8552 for intralaminar fiber tensile failure under dynamic loading. The methodology, proposed by Catalanotti et al. (2014) for quasi-static loading conditions, was enhanced to high rate loading in the order of about 60 s−1. Dynamic tests were performed using a split-Hopkinson tension bar, while quasi-static reference tests were conducted on a standard electromechanical testing machine. Double-edge notched tension specimens of different sizes were tested to obtain the size effect law, which in combination with the concepts of the energy release rate is used to measure the entire crack resistance curve for the fiber tensile failure mode. Digital image correlation is applied to further verify the validity of the experiments performed at both static and dynamic loading. The data reduction methodology applied in this paper is suitable for intralaminar fiber failure modes without significant delamination. Sufficient proof is given that quasi-static fracture mechanics theory can also be used for the data reduction of the dynamic tests. It is shown, that the intralaminar fracture toughness for fiber tensile failure of UD IM7-8552 increases with increasing rate of loading.

Study of the phenomenon of fatigue delamination in a carbon-epoxy composite under mixed mode I/II fracture employing an asymmetric specimen

The onset and growth of interlaminar cracks (delamination) were experimentally studied in an IM7/MTM45 carbon-epoxy composite material under mixed mode I/II dynamic loading, with a mixity grade GII/G of 0.24, employing for this purpose an asymmetric specimen.Static tests were previously carried out to obtain the critical fracture properties of the material. The dynamic test strategy was defined using these data. This consisted in the application of different fixed percentages of the critical ERR, Gcr. The results enabled the determination of crack onset fatigue curves, ΔG -N (number of cycles before crack onset, for a given ERR). A fatigue limit value of 38% Gcr has been obtained, understanding as such the ERR necessary for the onset of delamination. Delamination growth rates were shown to fit a Paris law trend with average crack growth rates of 10−4 mm/cycle. The fractographic analysis carried out on the tested specimens confirmed the presence of mode I and II fracture typologies, as well as evidencing the progression of micro-cracks due to fatigue.

Characterization and Investigation of Mechanical Properties of Composite Materials used for Leaf Spring

This paper deals with the characterization and mechanical properties of composite materials that can be used for the leaf spring. Aluminum based metal matrix and carbon epoxy composite materials have been used in various industries including automobile industry because of their light weight and good strength. In this present study rear leaf spring of Tata Ace (mini truck) made of EN45A spring steel has been considered. Metal Matrix Composite (MMC) leaf spring with Aluminum and 25% boron carbide manufactured by stir casting technique and carbon epoxy based leaf spring manufactured by hand layup fabrication technique were investigated for use in leaf spring. Both composite based leaf spring were examined under tensile stress and hardness test as per the standards - IS 1135: 1995 (Laminated Springs Assembly for Automobiles) and SAE (HS - J788 - Manual on Design and Application of Laminated Springs). The evaluation of EN45 steel and both composite based leaf spring shows that the composite spring has the low density, low weight and high strength. From the experimental results the strength of both composite materials matched with the properties of EN45 steel leaf spring and also it was found that by increasing the weight fraction and dimension will increase the strength and hardness of the specimen.

Micromechanical analysis of unidirectional polymeric composites material with triangular fibers

The purpose of this study is to investigate the mechanism of load transfer in unidirectional polymeric composites material with triangular fibers in the presence of broken fibers. It is assumed that all fibers with triangle-cross section lie in a same direction while loaded by a load at infinity. In previous studies, the behavior of polymeric matrix is assumed elastic, while the behavior of most polymeric matrix is elastic-perfect plastic. For this purpose, equilibrium equations by use of shear-lag theory have been derived and by proper using boundary and boundness conditions, displacement field and stress distribution were computed. Finally, the results of stress concentrations and di shear stress, at neighbor of broken fibers for carbon-epoxy composite material were extracted and compared with composite materials with circular fibers. The analytical results are compared to the detailed finite element values. A close match is observed between the two methods.

Fracture toughness and crack resistance curves for fiber compressive failure mode in polymer composites under high rate loading

This work presents an experimental method to measure the compressive crack resistance curve of fiber-reinforced polymer composites when subjected to dynamic loading. The data reduction couples the concepts of energy release rate, size effect law and R-curve. Double-edge notched specimens of four different sizes are used. Both split-Hopkinson pressure bar and quasi-static reference tests are performed. The full crack resistance curves at both investigated strain rate regimes are obtained on the basis of quasi-static fracture analysis theory. The results show that the steady state fracture toughness of the fiber compressive failure mode of the unidirectional carbon-epoxy composite material IM7-8552 is 165.6kJ/m2 and 101.6kJ/m2 under dynamic and quasi-static loading, respectively. Therefore the intralaminar fracture toughness in compression is found to increase with increasing strain rate.