Unidirectional Carbon Fiber Epoxy Research Articles

Mode II Delamination under Static and Fatigue Loading of Adhesive Joints in Composite Materials Exposed to Saline Environment.

This study investigates the fatigue delamination behavior of adhesive joints in epoxy carbon composite materials under Mode II fracture loading. The joints were characterized using the End-Notched Flexure (ENF) test, comprising adhesive joints formed by bonding two unidirectional carbon fiber epoxy matrix laminates with epoxy adhesive. These joints were subjected to different exposure periods (1, 2, 4, and 12 weeks) in a saline environment. Prior to dynamic fatigue testing, critical Mode II energy release rate values were determined through quasi-static tests, serving as a reference for subsequent fatigue characterization. This study aimed to comprehend how exposure duration to a saline environment affected the initial stage of fatigue delamination growth and employed a probabilistic model based on the Weibull distribution to analyze the experimental data. The results, gathered over a two-year experimental program, revealed varying behaviors in adhesive joint resistance to delamination based on exposure duration. A noteworthy reduction in fatigue strength capacity was observed, with fracture energies for infinite fatigue life reaching approximately 20% of their static loading capacity. This study sheds light on the deterioration of adhesive joints when exposed to a saline environment.

The effect of X-ray computed tomography scan parameters on porosity assessment of carbon fibre reinfored plastics laminates

Combinations of X-ray Computed Tomography (XCT) scan times, from 30 s to 60 min, and voxel sizes, from 6 to 50 µm, were investigated for their effect on the porosity measurements of a unidirectional carbon fibre epoxy composite volume. The sample had a total void volume of around 2%, which is typical of the tolerance expected in the aerospace industry. The volume contained localised voids that create sub-volumes with representative high (5%) and low (1%) porosity regions. The ability to detect small-size voids in the lower porosity regions decreased as the voxel size increased. Scan resolutions above 25 µm resulted in a coarser segmentation and overestimation of the porosity due to the presence of partial volume effects. Scan times shorter than 2 min resulted in noisy images, requiring aggressive filtering that affected the segmentation of voids. Porosity segmentation was performed by thresholding and Deep Learning methods. Deep Learning segmentation was found to recognise noise better, providing more consistent and cleaner segmented data than thresholding. To capture micro-voids that contribute to porosity levels at the typical aerospace tolerance of 2%, scan parameters with a voxel size equal to or smaller than 25 µm, scan times of 2 to 8 min, and deep learning segmentation were found to be the most promising. These shorter scan times can be used to increase the productivity of CT scanning for porosity or observing time-resolved events. The data provided here contributes to the body of knowledge studying X-ray hardware settings and optimising image segmentation.

Finite element analysis on prosthetic leg under different loads and flexion angles for medical applications

Prosthetic legs (PL) are mainly used to perform leg amputations more easily. The design and performance of these legs mainly depend on the material selection and manufacturing methods. In the present study, alternative materials are considered for PL such as Al alloy, Ti alloy, Uni directional Carbon fiber epoxy (UDCFE), and combined composite material (CF, UDCFE and Ti alloy) to perform static and fatigue analysis . Static analysis was performed under four different load conditions 60 kg,70 kg, 80 Kg and 90 kg. Fatigue analysis was done under low cycle fatigue conditions. Theoretical calculations are evaluated at various inclinations of the foot 10°, 20°, and 30° with the ground. The results obtained theoretically are compared with Ansys results. The best material which gives the lesser value of deformation and lower damage factor is selected for the design. Further, experimental studies were suggested based on the results obtained from this work.

Radiation and lead nanoparticles effects on the mechanical properties of unidirectional carbon fiber/epoxy composites

This study investigates the effects of two different parameters on the mechanical properties of carbon fiber-epoxy composites. The two addressed parameters are the composite’s exposure to gamma radiation with different doses, and the incorporation of lead nanoparticles with different weight percentages in the epoxy matrix. Unidirectional carbon fiber-epoxy composites are manufactured using the hand layup vacuum bagging process, and they are characterized by tensile tests and scanning electron microscope. The first part of the study entails fabricating composite laminates with different weight percentages of lead nanoparticles, namely, 0wt%, 1wt%, 2wt%, 3wt%, 4wt% and 5wt%. The results show that composites incorporating lead nanoparticles up to 3wt% exhibit monotonically improved tensile strength and Young’s modulus without compromising their ductility. Whereas, degradation of these mechanical properties is observed with increasing lead content beyond 3wt%. For the second part of the study, composite specimens are exposed to different doses of gamma radiation, namely, 0, 25, 50, 75 and 100 kGy. It is observed that the tensile strength, the modulus of toughness and the ductility of the composites improve for radiation exposures up to 25 kGy. However, radiation exposures higher than 25 kGy lead to deterioration in the tensile strength, modulus of toughness and Young’s modulus with negligible effect on the ductility.

On the relationship between moisture uptake and mechanical property changes in a carbon fibre/epoxy composite

Polymer composite materials are widely used in marine applications where an understanding of the long-term performance is essential for economic, safety and durability requirements. Although moisture absorption in composites has been studied for many years, the relationship between the mechanisms of moisture absorption and consequent changes in material behaviour has received much less attention. Understanding degradation is necessary for developing lifetime assessments. In this work, long-term exposure of a unidirectional carbon fibre epoxy composite material in water has been investigated in relation to mechanical property changes and moisture uptake. Using diffusion modelling and microscopy of the fracture surfaces, it is possible to correlate water absorption to experimental data showing how the position of water in the material causes changes to flexural properties (modulus decreased by 14% and strength by 20%) and in the glass transition temperature, Tg reduced by 18%. Flexural modulus has been shown to be most affected by water interaction with the fibre interface; Tg by water interaction within the resin; and flexural strength equally by water interaction with both fibre interface and resin.

DETERMINATION OF MECHANICAL PROPERTIES OF COMPOSITE MATERIALS WITH DIFFERENT FILLERS POLYMER MATRIX

In this study, the preparation and characterization of carbon fiber reinforced epoxy composites are aimed at today's increasing use of composite materials. In this study, composite materials consisting of unidirectional carbon fiber-epoxy resin were prepared and the effects of fiber inclination angle on layered epoxy composite materials were investigated using various characterization techniques. Composite materials were prepared by autoclave method. At the stage of characterization of prepared composite materials Scanning electron microscopy (SEM) has been applied for tensile, compression tests and characterization of fracture surfaces to determine the mechanical properties. Keywords: Carbon fiber,epoxy resin,polymer composite,mechanical properties.

Role of calcium carbonate on hardness and fracture toughness of carbon fiber reinforced epoxy composites

The present study seeks the role of nano-calcium carbonate (n-CC) on physical properties and fracture toughness of unidirectional carbon fiber/epoxy (UDCF/Ep) composites. The loading of n-CC is 1.5 wt. %, 3 wt. % and 5 wt. % in UDCF/Ep composite. Unfilled and n-CC filled UDCF/Ep composites were probed for the density, hardness, and single edge notched bending (SENB) test in accordance with governing ASTM standards. The measured density and hardness of the composites augmented with n-CC loading. However, n-CC was found to enhance the fracture toughness until 3 wt. % filler. Post-test, specimens were examined under a scanning electron microscope to analyze the involved fracture features. The SENB specimen was modeled and analyzed in the ANSYS for the peak load condition which affirmed the region of maximum stress intensity.

Multifunctional Carbon Fiber Composite with Improved Electromagnetic Interference Shielding and Interlaminar Fracture Toughness Characteristics

In this study, multifunctional carbon fiber-epoxy composites with improved electromagnetic interference shielding and interlaminar fracture toughness were manufactured. The interest in manufacturing multifunctional composites has been driven by the need for materials that simultaneously perform structural and non-structural functions. Unidirectional carbon fiber-epoxy composite laminates stitched with Dyneema13, Copper, and Kevlar13 were prepared using resin infusion process. Representative specimens from the unstitched and the stitched composites were tested using rectangular waveguide and Mode I interlaminar fracture tests. The electromagnetic shielding effectiveness experimental results showed that stitched composites exhibited improved shielding effectiveness compared to unstitched composites. For example, composite stitched with copper showed the highest increase of 102.2% in shielding effectiveness whereas composite stitched with Dyneema13 showed the smallest increase of 75.4% in shielding effectiveness compared to the unstitched. Results revealed that the dominant effect of shielding in these composites is absorption. The Mode I experimental results showed that composite stitched with Kevlar13 exhibited the highest crack initiation interlaminar fracture toughness (GIC-initiation), whereas composite stitched with Dyneema13 exhibited the highest maximum crack propagation interlaminar fracture toughness (GIC-maximum). The experimental results comply with the goal of the study to produce multifunctional composite with improvement in the mechanical and electromagnetic properties.

Computational micromechanical modelling of the material removal process in a carbon fibre composite under single-erodent particle impact

A multiscale model is developed to understand the material removal process in a unidirectional carbon fibre epoxy composite impacted by a single-erodent particle. The embedded cell approach is used to model the carbon fibre and epoxy at a microscale. The micromodel is embedded centrally in the macroscale lamina of the composite plate. The carbon fibre is considered to be elastic with orthotropic strain limits as the failure criteria. The epoxy matrix is modelled as an elastic--plastic material with multilinear isotropic hardening. The maximum equivalent plastic strain limit is used as the matrix material failure limit. Using this embedded micromechanics model, the role of matrix and the fibre in developing the composite material erosion behaviour has been clearly elucidated. The results from the simulation indicate the change in the matrix erosion behaviour as a function of the fibre volume fraction. For the current thermoset matrix, material erosion response changes from brittle behaviour to ductile behaviour with an increase in fibre volume fraction. The current study has been able to highlight the individual role of matrix and the fibre in developing the semi-ductile erosion response peculiar to a fibre-reinforced composite material.

Multifunctional Carbon Nanotubes Enhanced Structural Composites with Improved Toughness and Damage Monitoring

The potential of carbon nanotubes (CNT) as multifunctional filler in poly(epoxy)-based structural composites has been investigated. In a first step the reinforcement effect of CNT has been studied by tensile and three points bending tests, which evidenced significant improvements of stress and strain at break (respectively +17% and +30% for tensile tests on unidirectional carbon fibre-epoxy composites). Moreover, fracture experiments have also revealed a positive effect of CNT on the toughness (G1c) of carbon fibres-epoxy composites (+105% of improvement at the initial stage). In a second step, the health monitoring capability quantum resistive strain sensors (sQRS) made of CNT filled epoxy nanocomposite, incorporated in the core of glass fibres-epoxy composites has been studied. It was shown that during cyclic tensile tests, following the evolution of the relative resistance amplitude (Ar) of sQRS with strain gives a pertinent information on non-reversible phenomena such as plastic deformation and cracks’ development within the composite. In particular, the evolution of the sQRS sensitivity (gauge factor GF) under and over the elastic limit, allows to track damage accumulation throughout the composite. These results suggest a possible use of sQRS for the structural health monitoring (SHM) of composites in fields such as boating, wind energy, aeronautics and automotive.

The effect of GNP addition on mechanical and residual stress properties of 2024-T3 aluminum and carbon fiber reinforced FML

In this study, fiber metal laminated (FML) composites were produced according to the order of 3/2 stacking by using 0.8 mm thickness 2024 T3 quality aluminum sheets, unidirectional carbon fiber fabric and epoxy resin. In the first production epoxy resin was used without additive. In the second production, graphene nano powder was added to the epoxy resin at a rate of 1%. As a result of the experiments, it was found that addition of graphene nano powder to the epoxy resin provided an increase of 9% in tensile strength and an increase of 24% in the interlaminar shear strength. The amount of permanent compressive stress in the composite increased by about 50%.

Validating a micromechanical modelling scheme for predicting the five independent viscoelastic constants of unidirectional carbon fibre composites

In this paper we experimentally validate a new micromechanical modelling scheme for predicting the five independent viscoelastic constants of a unidirectional carbon fibre epoxy resin composite. This study has built on a number of previous papers by these authors, where extensive finite element calculations were used to validate a much more easily implemented, classical analytical micromechanical approach for predicting the viscoelastic properties of composite materials. For formulating the viscoelastic predictions, the elastic-viscoelastic correspondence principle is used to convert the static elastic solutions to their complex steady state viscoelastic forms simply by replacing static elastic moduli of the matrix and the fibers by their complex viscoelastic moduli.To formulate accurate micromechanical predictions for comparison and validation by experimental measurements, appropriate values for the five independent elastic constants of the reinforcing carbon fibres in the experimental materials are required. To obtain them, we have used the ultrasonic immersion method (UIM) and an inverse modelling scheme as previously described by Smith. The UIM allows the full stiffness tensor to be determined for both the carbon fibre composite and the epoxy resin matrix at a frequency of 2.25 MHz. The validated Hashin–Rosen composite cylinders micromechanical model was then used to determine the best fit elastic constants of the carbon fibres. Once these were determined, the ‘viscoelastic properties’ of both the pure epoxy matrix and the carbon fibre composite were studied using low frequency measurements (1 Hz). The results showed that for the two viscoelastic constants that can be routinely measured experimentally, namely the in-plane longitudinal and transverse Young's moduli, these are very well predicted by the same micromechanical model. Most importantly, following this validation, the micromechanical model can then easily provide all of the five independent viscoelastic composite stiffness constants. These values are critical for accurate vibration damping and noise cutting design of advanced engineering composite parts exposed to oscillatory loading such as aircraft wings and tails or wind turbine blades.

Accurate modelling of instabilities caused by multi-site interface-crack onset and propagation in composites using the sequentially linear analysis and Abaqus

Even well-established non-linear FEM codes may present convergence issues when solving highly unstable problems, e.g. fracture mechanics problems, especially in the presence of a pronounced snap-back behaviour. In composites, at lamina level, the debonds occurring between the fibres and matrix, lead to multiple-crack configurations. Each individual debond growth is an unstable process. Then, when multiple debonds occur the problem becomes highly unstable. Moreover, experimental evidence shows that a sequence of multiple debonds originates a macro-crack that extends over the whole lamina thickness. In this article a new Python based numerical tool implementing a Sequentially Linear Analysis (SLA) procedure, which is able to call the FEM software Abaqus, is described and tested. The Linear Elastic Brittle Interface Model (LEBIM) is also included in Abaqus by means of a UMAT subroutine. Numerical results for a representative 100-fibre model show that the tool is able to adequately model simultaneous onset and propagation of multiple debonds resulting in a completely unstable process composed by a series of instability events. Eventually, these numerical results together with some previous experimental results for transverse failure loads for unidirectional carbon fibre-epoxy matrix plies allow us to estimate the tensile strength and critical fracture energy of the fibre-matrix interface by a simple inverse analysis.

Evolution of kink bands in a notched unidirectional carbon fibre-epoxy composite under four-point bending

Kink-band nucleation and propagation has been monitored over time in three dimensions (3D) by time-lapse X-ray computed tomography (CT) in the compressive zone of a blunt notched unidirectional (UD) T800 carbon fibre/epoxy composite under in situ four-point bending (FPB). The kink bands that develop from micro-buckling are classified into two types, namely type 1 and type 2 by analogy with Euler buckling. Type 1 (shear) kink bands accommodate a lateral displacement of the fibres either side of the kink band; whereas type 2 kinks comprise conjugate pairs forming chevrons (accompanied by a tilt if the bands are wedge-shaped). In the central plane of the sample the kink bands lie in the plane of bending, whereas near the side surfaces the lack of lateral constraint means that type 2 kink band pairs protrude out of the surface (normal to the bending plane) from the notch corners down the sides of the sample. Moreover, a comparison of CT scans during loading and after unloading shows that geometries measured post-mortem on cross-sections may not be wholly representative, with the angle of the broken fibre segments within the kink bands reduced by 10–20° and the curvature of buckled fibres almost halved. The novelty of this work relates to the observation of the nucleation and propagation of fibre kink bands in three dimensions and the definition and quantification of kink band variables that could lead to more accurate modelling and simulation of compressive behaviour.

An experimental study into aging unidirectional carbon fiber epoxy composite under thermal cycling and moisture absorption

An experimental study into aging unidirectional carbon fiber epoxy composite under thermal cycling and moisture absorption

Interlaminar fracture toughness and electromagnetic interference shielding of hybrid-stitched carbon fiber composites

In the current study, the production of multifunctional hybrid-stitched composites with improved interlaminar fracture toughness and electromagnetic interference shielding effectiveness is reported. Unidirectional carbon fiber-epoxy composite laminates stitched with Kevlar, nylon, hybrid stitched with both Kevlar and nylon and unstitched were prepared using resin infusion process. Representative specimens from unstitched and stitched composites were tested using rectangular waveguide and Mode I double cantilever beam tests. The Mode I experimental results showed that composite stitched with Kevlar exhibited the highest crack initiation interlaminar fracture toughness (GIC-initiation), whereas composite stitched with nylon exhibited the highest maximum crack propagation interlaminar fracture toughness (GIC-maximum). The four-hybrid stitching patterns exhibited higher GIC-initiation than the unstitched and stitched with nylon composites and lower than stitched with Kevlar composite, whereas they had higher GIC-maximum than the unstitched and stitched with Kevlar composites, although lower than stitched with nylon composite. The electromagnetic shielding effectiveness experimental results showed that stitched composites exhibited improved shielding effectiveness compared to unstitched composites. For example, composite stitched with nylon had highest shielding effectiveness value of 52.17 dB compared by the composite stitched with Kevlar which had 40.6 dB. The four hybrid-stitched composites exhibited similar shielding effectiveness with an average value of 32.75 dB compared to the unstitched composite shielding effectiveness of 22.84 dB. The experimental results comply with the initial goal of this study to manufacture multifunctional hybrid stitching composites with combined properties between Kevlar and nylon-stitched composites.

A multiple particle impact model for prediction of erosion in carbon-fiber reinforced composites

Material loss and degradation due to erosion remains a major concern in engineering applications for composite materials. A finite element based model has been developed to predict the erosion behavior of unidirectional carbon fiber-epoxy (CFRP) composites subjected to solid particle impacts. In this model, the CFRP plate is subjected to multiple particle impacts at a velocity of 45 m/s, with steel balls as the erodent particles. The Influence of impact angle, erodent particle stream orientation (parallel and transverse to the fiber direction) and erodent particle size has been studied by varying the impact angle from 15⁰–90⁰ and particle sizes considered are of radii 150 µm, 200 µm and 250 µm. The model captures the influence of the erodent particle to particle impacts and the target surface properties by defining two new ratios, kinetic energy ratio, “ηk” and substrate surface property ratio, “ηs”. The cumulative eroded mass predictions are higher for transverse to fiber impact as compared to parallel to fiber impacts. It is also observed that as the erodent size increases the total eroded mass loss increases at all impact angles. The eroded mass predictions obtained from the numerical model compare favorably with the eroded mass results obtained from experimental data reported in the literature.

Parametric study of composite bolted joint under compressive loading

Use of composite structures in various sectors is rapidly increasing. The composite materials are becoming very popular due to high strength to weight ratio, high stiffness to weight ratio, low coefficient of friction, improved appearance etc. Extensive literature is available for the behavior of composite bolted joints subjected to tensile loading for the aerospace structures. The work reported in this paper is an attempt to extend the analytical model for studying the behaviour of composite bolted joint under compressive loading. The model is capable of conducting the parametric study on the joint stiffness variation with respect to parameters such as plate width, bolt diameter and stacking sequence for compressive loading. The model is verified experimentally. The experiments were designed to study the effect of variation in the parameters on the joint stiffness. Unidirectional and bidirectional carbon fibre epoxy composite laminates were tested as per ASTM D5961. The parameters viz. stacking sequence, bolt diameter, plate width of the joint stiffness are identified as significant.

The effect of silicon carbide whiskers on the Mode I interlaminar fracture of carbon fiber composites

This paper reports on the Mode I interlaminar fracture toughness improvement of carbon fiber-epoxy composites as a result of incorporating SiC whiskers in the epoxy matrix. Five laminates of unidirectional carbon fiber-epoxy composites at different weight fractions of SiC whiskers were manufactured using hand layup vacuum bagging process. Optical and scanning electron microscopic analysis were conducted to give an insight into the fracture morphogoloy, failure mechanisms, and the energy dissipation mechanisms created by the presence of the whiskers in the composite. Experimental results showed that composites containing 5wt% whiskers exhibited 67% increase in the crack initiation interlaminar fracture toughness GIC, whereas it exhibited 55% increase in the maximum GIC compared to pristine composite. The optical and SEM fractographs revealed a strong relation between the microstructure of the fractured surfaces and the energy release rate trend of the composites.

X-ray computed tomography study of kink bands in unidirectional composites

An experimental study on the axial compressive failure of cylindrical unidirectional (UD) carbon fibre-epoxy rods has been performed to better understand kink bands and the relevant damage mechanisms in three dimensions (3D). Post-mortem X-ray micro-computed tomography (micro-CT) imaging has shown that fibre kink bands predominantly all lie within the same plane in a cylindrical rod sample uniaxially compressed without lateral constraint. Kink bands at different stages of development are contained in the damage volume and the geometric parameters of fully developed kink bands are consistent through the damage zone, with a kink-band width ω≈20–320 μm, kink-band angle β≈11–40° and fibre rotation angle Φ (φ+φo)≈18–52°. Fibre failure, longitudinal splitting and matrix micro-cracks within the fibre kink zone are identified by scanning electron microscopy (SEM) and X-ray micro-CT observations. The smallest radius of curvature that corresponds to maximum amount of bending of the unbroken buckled fibres was ∼280μm (40 fibre diameters). Kink-band boundary planes and longitudinal splitting have been extracted and visualised in 3D for the first time.