Fiber Reinforced Epoxy Laminates Research Articles

Bi-stable hybrid composite laminates containing metallic strips: an experimental and numerical investigation

This study scrutinizes the static characteristics of a new category of bi-stable hybrid composite laminates (BHCLs) that contain multiple metallic strips (aluminum) distributed along the middle layer of a carbon fiber reinforced epoxy laminate. With this new class of BHCLs, the direction of curvature of the laminates does not change during the snap-through between the two stable states, unlike the conventional bi-stable cross-ply laminates. The laminates were modeled using finite element analysis and were experimentally validated. BHCLs with two to five metallic strips were fabricated for this purpose. The effect of the number, width, and thickness of the metallic strips on the static characteristics of the laminate were numerically investigated using ABAQUS. Further, the curvatures, out-of-plane displacement, and static snap-through load of the laminates were determined experimentally. The results showed a strong relationship between the residual curvature and the load-carrying capability of the laminate and the number, width, and thickness of the metallic strips, as well as the laminate geometry. Knowledge of this characteristic will allow designers to tune the parameters for a given application and to achieve the desired performance. Good qualitative and quantitative agreement was observed between the numerical and the experimental results.

Influence of Fiber Volume Content on Thermal Conductivity in Transverse and Fiber Direction of Carbon Fiber-Reinforced Epoxy Laminates.

Thermal conductivity is an important material property for thermo-mechanical calculations, as mechanical properties strongly depend on the temperature and heat distribution in the manufactured parts. Although several suggestions for approximation formulae have been made, existing experimental data are rare and are not comparable due to different measurement methods. In addition, scarcely has the thermal conductivity in both the fiber direction and transverse direction been studied. The aim of the current research is to show the influence of carbon fiber volume content on the thermal conductivity of laminates. The values are then used to verify the micromechanical models used in the literature. A strong influence on the thermal conductivity could be determined. For the transverse thermal conductivity, the correlation was exponential; for the conductivity in the fiber direction, a linear correlation was found.

New nonlinear regression modeling and multi-objective optimization of cutting parameters in drilling of GFRE composites to minimize delamination

This work focuses on optimization of the cutting parameters to minimize delamination resulting from drilling of woven roving Glass Fiber-Reinforced Epoxy (GFRE) laminates, using sequential quadratic programming algorithm based on new developed multiple nonlinear regression models. The influence of drilling parameters namely; speed, feed and drill pre-wear on drilling response variables namely; thrust force, torque, peel-up delamination and push-out delamination of GFRE composites has been analyzed through 3D plots. Analysis of variance (ANOVA) was employed to study the influence of drilling parameters on drilling response variables. From the experimental results and ANOVA, it was observed that drilling response variables are most influenced by feed and drill pre-wear, while the effect of speed is relatively insignificant. The conclusion of the multiple objective optimization revealed that, high rotational speed and low feed rate are the optimum drilling parameters for most of the drilling response variables.

Effect of Thermal Ageing on the Impact and Flexural Damage Behaviour of Carbon Fibre-Reinforced Epoxy Laminates.

Most of the composite materials that are used in aerospace structures have been manufactured using a thermostable matrix, as epoxy resin. The region of stability of these polymers is defined by the glass transition temperature (Tg). However, operating temperatures close and above the Tg can cause a variation in the properties of the polymer and consequently, modify the mechanical properties of the composite material. Therefore, it is necessary to understand the failure mechanisms that occur in the material in order to ensure stability and durability. The effect of temperature and time of exposure on the impact and flexural mechanical responses of carbon/epoxy composites are studied in this work. For that purpose, ageing treatments at temperatures below and above the Tg have been considered and then, impact and flexural tests have been performed. It was observed that thermal ageing cause two different effects: at temperatures below the Tg, there is an increase of the maximum strength because of a post-curing effect; however, the mechanical properties decrease at higher temperatures of thermal ageing due to the thermo-oxidation of the epoxy resin and the loss of adhesion in the matrix/fibre interface.

Internal damage evaluation of composite structures using phased array ultrasonic technique: Impact damage assessment in CFRP and 3D printed reinforced composites

The application of non-destructive techniques for the evaluation of internal damage in composite materials is a challenge due to their complexity. The aim of this study is to analyse the ability of ultrasonic technique to identify and evaluate manufacturing defects and internal damage in composite laminates. Artificial object inclusions of different shapes, sizes and materials were embedded in carbon fibre reinforced epoxy (CFRP) laminates. Comprehensive investigation of non-destructive evaluation using phased array ultrasonic testing to trace and characterize the embedded defects is presented. Phased array ultrasonic technique was able to precisely locate most of the artificial inclusion in the composite laminates. Nerveless, the shape and size of the inclusions were not accurately determined due to the high signal attenuation and distortion characteristics of the carbon fibre epoxy composite.Furthermore, a major concern affecting the efficient use of composite laminates is their vulnerability to low velocity impact damage. The dynamic behaviour of composite laminates is very complex as there are many concurrent phenomena during composite laminate failure under impact loading. Thus, the practicality of the previous results is demonstrated by the evaluation of impacted carbon fibre reinforced epoxy laminates using ultrasonic testing. The influence of laminate thickness and impact energy on impact damage is also investigated. The performance of phased array ultrasonic testing for the inspection of composite laminates with barely visible impact damage is evaluated. In addition, fibre-reinforced thermoplastic composites are becoming more significant in industrial applications due to their excellent mechanical performance and potential recycling. In this study, impact damage in 3D printed continuous glass fibre reinforced thermoplastic laminates is also analysed. Phased array ultrasonic testing is performed and the amount of damage is quantified in terms of delaminated area.

Influence of basalt fiber hybridization on the vibration-damping properties of glass fiber reinforced epoxy laminates

Glass fiber-reinforced composites are one of the oldest and the most widely used composite types in fiber reinforced polymeric composite industry for commercial and industrial applications. The tailorability for specific material applications to provide several design advantages associated with strength, chemical resistance, impact damage tolerance, thermal insulating and low cost are the primary advantages of glass fiber reinforced composites. The goal of this work is to study the significance of basalt fiber hybridization as a diagnosis of improvement of vibration damping properties of glass fiber reinforced composites, and as a means of preliminary examination to ensure the feasibility for potential applications. The hybrid composite laminates with different ratios of basalt and glass fibers were prepared using vacuum assisted resin transfer molding (VARTM) process. Free vibration tests were conducted to identify the vibration damping properties of hybrid composites, depending on basalt fiber loading rate. Free vibration tests evidenced a monotonic increase in damping ratio and loss modulus as basalt fiber content increased, but the natural frequency and storage modulus decreased together with the basalt fiber loading. Uniaxial tensile tests were also performed in order to compare the influence of hybridization on storage modulus and tensile modulus. The results of tensile tests showed that tensile modulus almost exhibited similar trend with storage modulus and incorporation of basalt fiber caused deteriorations in tensile strength and tensile modulus of glass fiber reinforced composite.

In-plane shear strength analysis of Basalt Fiber-Reinforced Epoxy Laminates with Biowaste Catalyst Free Carbon

This study aims to analyse the effects of carbon nanospheres (CNSs) on the in-plane shear properties of basalt fiber-reinforced epoxy composite laminate (BFR). The CNSs were obtained from an economical fibrous residue attained from the sago palm tree, which is known as biowaste sago bark. Hand lay-up method was used to fabricate the unidirectional basalt fiber-reinforced epoxy composite laminates. The epoxy resin was mixed with carbon nanosphere particles (i.e., 0.6 wt% - 1 wt%). In-plane shear tests have been conducted as per ASTM standards. In addition, emphasis on the microstructural investigation using Scanning Electron Microscopy (SEM) is given, in order to study the fracture surfaces of the composite laminates. The results demonstrated significant improvement in in-plane shear strength when carbon nanosphere particles were included in the basalt fiber-reinforced epoxy composite laminate. The best result was obtained at 1.0 wt% CNSs. It displayed an increment of 37.1% in in-plane shear strength, and 36.4% increment in modulus of rigidity, respectively, in comparison to neat basalt fiber-reinforced epoxy composite laminate. The improved accomplishment of CNSs/basalt fiber-reinforced epoxy composite laminate is due to good distribution of CNSs particles in the epoxy matrix.

Fabrication and Characterization of Basalt Fiber Reinforced Epoxy Laminate for Low Frequency Passive Noise Reduction: Transfer Matrix Approach

Fabrication and Characterization of Basalt Fiber Reinforced Epoxy Laminate for Low Frequency Passive Noise Reduction: Transfer Matrix Approach

Evaluation of stiffness in a cellulose fiber reinforced epoxy laminates for structural applications: Experimental and finite element analysis

Abstract Natural fiber composites have been proved to have the ability to replace the synthetic fiber composites in many structural applications. Unprecedented growth in the field of computational techniques has opened the doors of analysis and simulation of composite materials under various environment. Modelling and simulation using various available softwares saves a lot of time and resources. In the present work, an attempt has been made to analyze the tensile behavior of jute fiber reinforced epoxy based polymer composite materials using the student version of commercially available finite element code Siemens PLM NX 10.0. In most of the structural applications, materials are required to have enough stiffness to resist the shape deformation under normal loading conditions. Therefore, emphasis is given to the load-deformation behavior of the developed composites. A 3-dimensional model of the test specimen was developed using ply-stacking method and the strain-stress values were verified by the available literature. The model showed a good agreement between the experimental and software results. Effect of ply angle, fiber percentage, fiber type, number of layers and weft fiber angle on the stiffness of laminate have been studied.

Experimental study of the influence of thickness and ply-stacking sequence on the compression after impact strength of carbon fibre reinforced epoxy laminates

Composite structures are particularly vulnerable to impact which drastically reduces their residual strength [1–3]. In this work, the influence of laminate thickness, ply-stacking sequence and scaling technique on the impact damage tolerance of CFRP laminates is investigated by means of compression after impact (CAI) tests. Drop-weight impact tests were carried out to determine impact response of the different composite laminates. CAI tests were performed in a non-standard CAI device in order to obtain the compression residual strength. In addition, open-hole compression (OHC) tests were performed for comparative purposes. Ultrasonic C-scanning and cross-sections of CAI samples were examined to assess failure mechanisms of the different configurations.It was observed that damage tolerance decreases as impact energy increases. In addition, thicker laminates show higher CAI strength due to higher bending stiffness. Furthermore, angle-ply laminates depict better performance in terms of damage tolerance. Finally, the results obtained demonstrate that introducing ply blocking had a negative effect on the damage resistance but, conversely, an improvement of the CAI strength.

Ilss improvement of quasi-isotropic glass fiber reinforced epoxy laminate enhanced with arc discharged multi-walled carbon nanotubes

Multi-Walled Carbon Nanotubes produced by arc discharging of pure graphite rods was mixed in complete matrix system in order to fabricate eight-layer quasi-isotropic glass fiber/ MWCNTs/ epoxy hybrid laminate. The effect of nano-reinforcement on interlaminar shear strength (ILSS) of GFRP composite was assessed by varying the amount of nanoparticles in the epoxy i.e. 0, 0.5, 1.0, 1.5 and 2 wt.% respectively and conducting 3-point bend tests on short beams extracted from the laminates manufactured by vacuum assisted hand layup method. It was observed that when compared to neat epoxy laminate, laminates with MWCNTs showed enhanced interlaminar strength of 14 to 41%. As nanotubes produced from arc discharge are stiffer and straighter, their presence in the matrix system can be credited with such results. Also, in-depth property improvement can be attributed to the formation of the matrix-MWCNTs rich region in between the plies.

The effect of different curing conditions on hardness, thickness, and residual stress of carbon fiber reinforced epoxy composites

In this study, an attempt has been made to optimize the curing process of carbon fiber reinforced epoxy laminates. The effect of four factors: curing temperature, cooling method, wetting method, and resin-to-hardener ratio was studied. Custom non-regular fractional factorial design was utilized to choose the combination of these factors levels. Vickers micro-hardness test was conducted to study hardness in all the specimens. Thickness measurements were taken. The residual stresses along fiber direction were measured using Timoshenko bending beam method. Box plots were drawn to understand data variability. ANOVA was used to analyze results. It was shown that curing at 180℃ or lower, applying furnace cooling, raising resin-to-hardener ratio, and avoiding wetting the bottom side have reduced data variability, lowered thickness, and residual stress.

Damage resistance of carbon fibre reinforced epoxy laminates subjected to low velocity impact: Effects of laminate thickness and ply-stacking sequence

A major concern affecting the efficient use of composite laminates is the effect of low velocity impact damage on the structural integrity [1–3]. The aim of this study is to characterize and assess the effect of laminate thickness, ply-stacking sequence and scaling technique on the damage resistance of CFRP laminates subjected to low velocity impact. Drop-weight impact tests are carried out to determine impact response. Ultrasonic C-scanning and cross-sectional micrographs are examined to assess failure mechanisms of the different configurations.It is observed that damage resistance decreases as impact energy increases. In addition, thicker laminates show lower absorbed energy but, conversely, a more extensive delamination due to higher bending stiffness. Thinner laminates show higher failure depth. Furthermore, quasi-isotropic laminates show better performance in terms of damage resistance. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the damage resistance and on the delamination area.

Low-cost, environmentally friendly route for producing CFRP laminates with microfibrillated cellulose interphase

In this paper, a cost-effective and eco-friendly method to improve mechanical performance in continuous carbon fiber-reinforced polymer (CFRP) matrix composites is presented. Unsized fiber fabric preforms are coated with self-assem- bling sugarcane bagasse microfibrillated cellulose, and undergo vacuum-assisted liquid epoxy resin infusion to produce solid laminates after curing at ambient temperature. Quasi-static tensile, flexural and short beam testing at room temperature indicated that the stiffness, ultimate strength and toughness at ultimate load of the brand-new two-level hierarchical composite are substantially higher than in baseline, unsized fiber-reinforced epoxy laminate. Atomic force microscopy for height and phase imaging, along with scanning electron microscopy for the fracture surface survey, revealed a 400 nm-thick fiber/matrix interphase wherein microfibrillated cellulose exerts strengthening and toughening roles in the hybrid laminate. Market ex- pansion of this class of continuous fiber-reinforced-polymer matrix composites exhibiting remarkable mechanical perform- ance/cost ratios is thus conceivable.

Determination of ply level residual stresses in a laminated carbon fibre-reinforced epoxy composite using constant, linear and quadratic variations of the incremental slitting method

Measurement of residual stresses in FRP composites is by no means a trivial task and there are no commonly applied or standardised methods currently available. As a result, characterisation of residual stresses is often avoided, resulting in the use of conservative safety margins, which has consequently resulted in structures being overdesigned. In the work described here, the incremental slitting method has been demonstrated to be a technique suitable for measuring residual stress in thin (∼0.3mm) plies of a [0°2/90°2]4s carbon fibre-reinforced epoxy laminate. The stresses measured using a constant stress approximation approach provided the best agreement with measurements obtained using the layer removal technique and stresses predicted using a semi-coupled transient-thermal and structural model.

Influence of moisture uptake on the static, cyclic and dynamic behaviour of unidirectional flax fibre-reinforced epoxy laminates

This papers aims to characterize the influence of moisture uptake on the mechanical behaviour of unidirectional flax fibre-reinforced epoxy laminates. Monotonic and cyclic tensile tests and free vibration characterization are carried out. Results show that UD flax-epoxy composites, when exposed to hygrothermal conditioning at 70°C and 85% RH, exhibit a diffusion kinetic which follows a one dimensional Fickian behaviour. The mass uptake at equilibrium is approximately 3.3% and the diffusion coefficient 6.5×10−6m2s−1. Water vapour sorption is shown to induce a significant change in the shape of the tensile stress-strain curve, a decrease in the dynamic elastic modulus of about 20% and a 50% increase in the damping ratio. Contrary to all expectations, water saturation does not degrade the monotonic tensile strength of such a flax-epoxy composites and leads to an increase in the fatigue strength for a high number of cycles.

Global bending response of composite sandwich plates with corrugated core. Part II: Effect of laminate construction

Global bending response of simply supported composite sandwich plates with corrugated core was studied using carbon fiber reinforced epoxy laminates in both face plates and inclined webs in the corrugated core. Two different laminate constructions were considered, namely [0/α]S and [±α]S and the fiber orientation angle was varied from 0° to 90°. Sandwich plate geometric parameters, such as face thickness, pitch and face center distance were maintained constant, but the web inclination was varied from a triangular configuration to a square configuration. The web thickness was varied with web inclination angle so that the sandwich plates had the same cross-sectional area and, therefore the same mass. This allowed a direct comparison between different laminate constructions for each web inclination angle. It was shown that for the same mass, the maximum deflection under a distributed load depends on both the web inclination angle and the laminate construction. It is significantly higher with the [±α]S construction than with the [0/α]S construction. For both laminate constructions, the largest maximum deflection occurs at a web inclination angle of 48°, which can be attributed to the combined effect of the transverse shear stiffness components.

Influence of nanoparticle fillers content on the bearing strength behavior of glass fiber-reinforced epoxy composites pin joints

The objective of the present study is to investigate and compare the strength of single pin joints made with glass fiber-reinforced epoxy laminates containing two different nanoparticles, i.e. nanoclay and nano TiO2, with bare composites. The analysis has been done both experimentally and numerically. Single-hole pin-loaded specimens were tested for their tensile strength and the distance from the free edge of the specimen to the diameter of the first hole (E/D) ratio, width of the specimen to the diameter of the holes (W/D) ratio were evaluated. The influence of these geometry parameters on the strength of the pin-loaded composites was investigated. It was found that the bearing strength of pin joints increased with the addition of nanoclay as compared to that of nano TiO2.

Residual flexural strength after impact for textile carbon fiber reinforced polycarbonate laminates

This study prepared textile carbon fiber reinforced polycarbonate laminates of three kinds molded with different conditions and carbon fiber reinforced epoxy laminates consisting of the same carbon fiber textile. Drop-weight impact tests were conducted for these four laminates with three levels of impact energies. The residual flexural strengths were measured after impact. Results show that the residual flexural strengths for all laminates decrease clearly with increasing impact energy. The flexural strengths of these laminates without impact damage have mutually different values. Furthermore, the laminates exhibit a decreasing ratio of residual flexural strength by impact damage with mutually differing values. The reasons were examined through observations conducted using ultrasonic flaw detection and digital microscope.

A study of composite laminates failure using an anisotropic gradient-enhanced damage mean-field homogenization model

The failure of carbon fiber reinforced epoxy laminates is studied using an anisotropic gradient-enhanced continuum damage model embedded in a mean-field homogenization scheme.In each ply, a homogenized material law is used to capture the intra-laminar failure. The anisotropy of the homogenized material model results from the homogenization method and from the reformulation of the non-local continuum damage theory to account for the material anisotropy. As a result the damage propagation direction in each ply is predicted with accuracy as compared to the experimental results, while the problems of losing uniqueness and strain localization, which occur in classical finite element simulations when strain softening of materials is involved, can be avoided.To model the delamination process, the hybrid discontinuous Galerkin/extrinsic cohesive law method is introduced at the ply interfaces. This hybrid method avoids the need to propagate topological changes in the mesh with the propagation of the delamination while it preserves the consistency and stability in the un-cracked interfaces.As a demonstration, open-hole coupons with different stacking sequences are studied numerically and experimentally. Both the intra- and inter-laminar failure patterns are shown to be well captured by the computational framework.