Fiber Reinforced Polymer Composite Plate Research Articles

Predicting delamination in composite laminates through semi-analytical dynamic analysis and vibration-based quantitative assessment

Delamination is a frequent failure mode of laminated fiber-reinforced polymer (FRP) composites structure in aeronautical and other industries, leading to changes in vibration characteristics. Vibration-based techniques evaluate and compare the dynamic response between damaged and undamaged structures, and guarantee the non-destructive measurement with reliability and repeatability. Previous studies typically concentrate on using finite element method to obtain vibration characteristics and enhance the database for intelligent algorithms. This paper presents a semi-analytical result using the Chebyshev−Ritz method to expand delamination prediction. Vibration frequency serves as a global damage indicator, and multi-order frequency characteristics are utilized to identify the delamination length and location of FRP composite plates. A database of natural frequencies corresponding to damage parameters for FRP laminated plates is generated based on the established model using the region approach. An intelligent approach, known as a genetic algorithm optimization-based back-propagation (GA-BP) artificial neural network, is utilized for system identification. The network model is subjected to a sensitivity analysis, where artificial noise is added to vibration frequency to distinguish between the actual structure and the numerical model. The results indicate that the GA-BP algorithm shows good accuracy and stable performance against the standard neural networks for delamination analysis.

Modeling and analysis of acoustoelastic guided waves propagation in anisotropic fiber reinforced polymer composite plates under initial gradient stress

Process-induced initial gradient stress is inevitable during the fabrication of fiber reinforced polymer (FRP) composites. In this research, governing wave equations with variable coefficients are established for FRP plates under initial gradient stress, based on the acoustoelastic theories. The Legendre polynomial (LP) method is utilized to derive the solving algorithm. The dispersion curves are obtained without layer slicing, which provides a more realistic analysis model for gradient stress. The accuracy and convergence of the proposed method are discussed through numerical examples. The influences of initial gradient stress on dispersion slowness curves of Lamb and SH waves are analyzed, considering the parabolic initial gradient stress distribution, in which it’s common in the manufacturing process of FRP composites. The effect of initial gradient stress distribution on the phase velocity is investigated in detail. The influence of the anisotropic effect of FRP on guided wave propagation under initial gradient stress is discussed. The numerical analysis shows that the behavior of guided waves is influenced not only by the initial gradient stress but also dominated by propagation direction in anisotropic FRP composite plates. These results can provide a useful reference for the testing based on guided waves for FRP composite, especially when the initial gradient stress is encountered.

Dynamic properties of natural fiber-reinforced polymer composite plates and tubes

Thirty-six flax fibre-reinforced epoxy (FFRE) plates with two, three, and four fabric layers and lengths ranging from 160 mm to 270 mm and nine FFRE tubes with a diameter of 60 mm, a length of six times the tube diameter plus an overly of 50 mm with two, three, and four fabric layers were manufactured. One-hundred-eighty impulse excitation tests were conducted on FFRE plates to determine the dynamic properties of the plates in the bending mode, and 91 impulse excitation tests were conducted on the FFRE tubes to determine the dynamic properties of the tubes in the transverse, torsional, and longitudinal directions. FFRE plates showed up to six times larger specific energy capacities compared to counterpart glass fibre-reinforced polymer plates, showing significant potential for FFRE plates to replace the use of GFRP plates where considerable damping of energy is required. The results showed that the damping ratio of the FFRE plates decreased with the increase in layers and natural frequency. For the FFRE tubes, the highest damping ratio belonged to the transverse vibration mode, followed by the torsional or longitudinal vibration modes.

Resonant air coupled inspection of glass fiber reinforced polymer composite plate using single sided access of near and far side of low velocity impact damage

Resonance based nonlinear techniques works efficiently in detecting small size damages in the composite structures. Local defect resonance (LDR) is a resonance based nonlinear technique which enables to activate the damage directly. In this study, recently developed LDR based automated methodology is carried out from far side of the impact damage to detect the LDR frequency and mode shape of the impact damage. This methodology is implemented by carrying out experiments on glass fibre reinforced polymer (GFRP) plate using air coupled emission (ACE) technique. This plate contains three artificial delaminations and one low velocity impact damage. Initially, the LDR frequency and mode shape of each damage is accomplished using ACE testing, justified with Laser Doppler Vibrometry (LDV). Later, the Otsu’s algorithm is performed to get the accurate size of the impact damage. Subsequently, a broadband backward sweep is used to detect all delamination including the impact damage. Then, maximum amplitude of each frame has been found from output data of all spatial nodes. Later, the LDR frequency frame ( N L) has been identified in the time domain from the slope and curvature plots followed by Discrete Fourier Transform (DFT) to detect the LDR frequency and mode shape of the damage. So, it has been observed that less than defect size is obtained when inspected from the far side. Further, this method will be extended to find out the depth of individual damage.

APPLICATION OF HOOKE’S LAW TO ANGLE PLY LAMINA

Aerospace-grade carbon fiber reinforced polymer composite plates with four different fiber orientations 0º, 30º, 45ºand 60º is produced with the autoclave curing method and subjected to tensile testing. The stress-strain curves of the composite specimens are compared with Hooke’s law. It is observed that Hooke’s law coincides precisely with the experimental results for samples containing fibers parallel to the loading direction. However, it does not coincide with samples where the fibers make a certain angle with the applied load direction.. Moreover, it is reported that Hooke’s law converges the experimental results for small strain values but diverges significantly from the experimental results at higher strain values.

Free vibration analysis and prediction modeling of delaminated tapered FRP composite plates

Delamination (the separation between plies) is a common failure in Fiber Reinforced Polymer (FRP) laminated composites. The presence of delamination reduces the structural stiffness and changes in dynamic responses. The change in dynamic parameters can be successfully used for assessing structural health monitoring (SHM) for composite structures. SHM requires large amount of numerical/experimental data. This study focuses on the influence of the delamination parameters (size and in-plane location) on vibration behavior of a laminated tapered fiber reinforced polymer (FRP) composite plate with ply drop-off. Furthermore, developing a surrogate model as a fast-executing model to predict the shift in the natural frequency to reduce the computational effort for solving forward problems. The layerwise theory (LWT) has been used, and the delamination is modeled by “constrained mode” were solved using the finite element method (FEM). The numerical model was validated with an experimental modal analysis of tapered plates without delamination to make the model more robust. The effect of delamination was studied using surface plots produced using response surface methodology (RSM). The results show that the delamination size and location significantly affect the natural frequency shift. The RSM and ANN models were considered as surrogate models, and it was evaluated using an experimental modal analysis. The results shows that the single-output ANN model can predict the shift in the natural frequency with a minimum Root Mean Square Error (RMSE).

Identification of delamination severity in a tapered FRP composite plate

The typical failure in fibre-reinforced polymer (FRP) laminated composites is delamination. It reduces structural stiffness and changes in dynamic responses, which can be successfully used for assessing structural health monitoring (SHM) of composite structures. SHM often requires the solution of an inverse problem. This study focuses on solving the inverse problem with minimal computational time to predict delamination size, in-plane location, and interface. For the inverse model, two computational intelligence algorithms, the surrogate-assisted real-coded genetic algorithm (SARGA) and an artificial neural network (ANN) were used. A surrogate model is a fast-executing model for predicting the shift in the natural frequency using a forward ANN. For ANN training, the database size was optimized. The layerwise theory was solved using the finite element method for a laminated tapered FRP plate with ply drop-off, and ‘constrained mode’ is used to model the delamination. The experimental modal analysis was conducted on a glass-fibre reinforced polymer tapered composite plate with one intact plate and three artificially delaminated plates. The algorithms are validated using numerically simulated and experimentally measured frequencies. The numerical validation showed a better prediction of delamination size, in-plane location, and interface when compared with the experimental validation. Nevertheless, SARGA can reasonably predict the size, in-plane (x) location and interface of the delamination with an average overlapping ratio of 72.89%. The comparison of algorithms demonstrates the application of SARGA with the frequency-based approach for delamination detection and real-time condition monitoring in real-world applications.

Application of Edge Detection Based on Hexagonal Image Structure to Delamination Detection of Carbon Fiber Reinforced Polymer Material

Abstract Delamination is one of the most critical damage modes in carbon fiber reinforced polymer materials, and is invisible to the naked eye. Although delamination defect images of carbon fiber reinforced polymer materials can be obtained through ultrasonic tomography, it is still difficult to accurately identify the position and contours of defect images. In this study, four different delamination defect images of carbon fiber reinforced polymer composite plates were obtained through a finite element simulation and fan-beam ultrasonic tomography. A hexagon algorithm based on interpolation is proposed that transforms the reconstructed defect images from square pixels into hexagonal pixels. The interpolation algorithm is based on the overlap between the square and hexagonal pixels. As the experiment results verify, the use of the hexagonal structure-based morphological method for edge detection significantly reduces the recognition error from 7.74% to 0.148% in comparison with a traditional quadrilateral structure. The experimental results also showed that this method can effectively reduce the artifact interference and obtain complete and accurate target edge information more effectively than a square structure.

The wavenumber imaging of fiber waviness in hybrid glass–carbon fiber reinforced polymer composite plates

Out-of-plane waviness is one of the most common defects which degenerates the strength, stiffness, and fatigue life of hybrid glass–carbon fiber–reinforced polymer composites (FRPs). An accurate and high-speed non-destructive testing method is highly desired for large composite structures in industries. Ultrasonic phased array is a great candidate for such application. This paper applies the wavenumber algorithm to image the waviness in hybrid FRP plates which are a multi-layered medium. The central frequency of 5 MHZ is chosen in order to maximize the ply resonance. Transducers are migrated virtually to each interface between glass and carbon plies in order to overcome the difficulty of wave propagation analysis in such multi-layered system. The wavenumber algorithm demonstrates a better computational performance compared to that of the traditional total focusing method (TFM) in time domain up to 6 times. The glass ply depth and waviness angle can be more accurately presented with relative errors less than 1.5% and 14.8%, respectively. In addition, the resin-rich defect characterization is also achievable with a maximum error of 14.4%.

A micromechanical-based study on the tribological and creep-relaxation behavior of sand-FRP composite interfaces

Fiber-reinforced polymer (FRP) composites have a promising potential to be utilized to extend the lifespan of geostructures in harsh environments due to their high durability, satisfactory strength and cost-effectiveness. The FRP-soil interaction is critical to model soil-structure interaction problems and assess the performance of foundation systems where composites are used. In this paper, the contact behavior of sand-FRP interfaces at the fundamental level of the grain-scale was investigated with a custom-built micromechanical testing apparatus, with an emphasis on the normal contact response, the tangential load – displacement relationship as well as creep and relaxation behavior. Leighton Buzzard sand (LBS), a typical silica sand, and custom manufactured glass fiber reinforced laminated FRP plates were used in the study. It was shown that the surface texture, thickness, and fiber orientation of the FRP composite plates have important influences on the tribological behavior of the sand-FRP interfaces, and plowing damage was observed to be a dominant mechanism from the shearing tests, particularly at higher normal loads. The results also suggested that creep and relaxation had a significant influence on the interface behavior of sand-FRP and these phenomena should be considered in the long-term design of FRP included composite geostructures.

Impact localization for composite plate using the modified error-outlier algorithm with Pugh’s concept selection under various temperatures

The previous error outlier based impact localization algorithm has a weak point during the impact localization due to a reciprocity problem coupled with the symmetric boundary conditions of target structures. Thus, the modified error outlier based impact localization algorithm was proposed to overcome the improper impact localization due to this reciprocity problem. The previous impact localization method using fiber Bragg grating sensors did not consider the effect of the operating temperature of structures although they were operated under various temperatures. Thus, this study experimentally verified the error outlier impact localization algorithm by performing impact localization for a carbon fiber-reinforced polymer composite plate under various temperatures. It was found that the total average error of 2.0 mm was estimated under the given temperatures, being only 2.5% of the pre-assigned grid size of 80.0 mm on the plate. Therefore, we concluded that the modified algorithm can overcome the reciprocity problems and be sufficiently used for impact localization using fiber Bragg grating sensors under various temperatures.

Vibration suppression effect of porous graphene platelet coating on fiber reinforced polymer composite plate with viscoelastic damping boundary conditions resting on viscoelastic foundation

This work is devoted to the investigation of vibration suppression effects of the viscoelastic foundation, viscoelastic damping boundary condition and porous graphene platelet coating (PGPC) on the fiber reinforced polymer (FRP) composite plate. A dynamic model is built by combining the first-order shear deformation theory, the multi-segment partition technique, the virtual spring technology, the Rayleigh-Ritz approach, and the mode strain energy method. Afterwards, the structural natural frequencies, modal shapes and modal damping ratios are calculated, as well as the verification of the convergence and the correctness of the constructed model. Finally, the vibration suppression effect of the FRP-PGPC composite plate with different parameters, such as geometrical and material parameters, foundation and boundary condition types, are discussed in details.

Experimental Investigation of the Influence of Stacking Sequence and Delamination Size on the Natural Frequencies of Delaminated Composite Plate

The vibration properties of the composite structures is critical to the reliability and durability of the structures. Vibration becomes worst in case the delamination is present within laminates. In this research work, experimental, finite element and analytical techniques have been applied in order to analyze the influence of stacking sequence and delamination sizes on the natural frequencies of carbon fiber reinforced polymer composite (CFRP) plate with and without delamination. The boundary conditions in this research work was (SSSS) (all sides simply supported. Experiments were performed to study the vibration characteristics of (CFRP) delaminated composite plate. Software package ABQUS was used to model and analyze the vibration response of carbon fiber reinforced polymer composite plate for (SSSS) boundary condition and the effect of stacking sequence and delamination size was calculated. Rayleigh- Ritz Method was used to find the natural frequencies for different delamination sizes and stacking sequences. The results was concluded that natural frequencies were significantly affected by the delamination sizes and stacking sequences. Stacking sequence of (0/90/45/90) showed higher values of natural frequencies in lower mode subjected to all-sides simply supported boundary conditions. It was interesting to see that there were small differences in values of natural frequencies among the stacking sequences for lower modes but the difference gradually increased in case of higher modes.
 

Characterization of multilayer delaminations in composites using wavenumber analysis: numerical and experimental studies

Delamination is one of the most common and dangerous failure modes for composites because it takes place and grows in the absence of any visible surface damage. The successful implementation of delamination detection in aerospace composite structures is always challenging due to the general anisotropic behavior of composites and multilayer delamination scenarios. This article presents a numerical and experimental investigation to detect and characterize the multilayer delaminations in carbon fiber–reinforced polymer composite plates using guided waves and wavenumber analysis. Multiphysics three-dimensional finite element simulations of the composite plate with five different delamination scenarios are conducted to provide the out-of-plane wave motion for wavenumber analysis. The out-of-plane results from finite element simulations of one delamination and two delaminations are validated by the scanning laser Doppler vibrometer measurements. It is found that the wavenumber analysis can identify the plies between which the delamination occurs and evaluate the delamination severity by comparing the new wavenumbers due to the trapped waves in the delamination regions, which is potentially related to delamination severity. Both numerical and experimental results demonstrate a good capability for the detection and characterization of multilayer delaminations in composite structures.

Application of artificial neural networks for quantitative damage detection in unidirectional composite structures based on Lamb waves

This article provides a quantitative nondestructive damage detection method through a Lamb wave technique assisted by an artificial neural network model for fiber-reinforced composite structures. For simulating damages with a variety of sizes, rectangular Teflon tapes with different lengths and widths are applied on a unidirectional carbon fiber–reinforced polymer composite plate. Two characteristic parameters, amplitude damage index and phase damage index, are defined to evaluate effects by the shape of the rectangular damage in the carbon fiber–reinforced polymer composite plate. The relationships between the amplitude damage index and phase damage index parameters and the damage sizes in the carbon fiber–reinforced polymer composite plate are quantitatively addressed using a three-layer artificial neural network model. It can be seen that a reasonable agreement is achieved between the pre-assigned damage lengths and widths and the corresponding predictions provided by the artificial neural network model. This shows the great potential of using the proposed artificial neural network model for quantitatively detecting the damage size in fiber-reinforced composite structures.

An Investigation on Cutting of the MWCNTs-Doped Composite Plates by AWJ

In this study, cutting of multi-walled carbon nanotubes (MWCNTs)-doped composite sheets by abrasive water jet machining (AWJM) and the effects of the water jet on cut composite materials were analyzed. The influence of MWCNTs doping to glass fiber-reinforced polymer composite plates was investigated. In addition, mechanical properties of doped composite and the effects of cutting by AWJM method were determined. It has been found that the addition of nanoparticles to layered glass fiber composite materials plays an effective role in the strength of the material and affects the abrasive water jet (AWJ) cutting quality. Additionally, composite materials were drilled using different water jet cutting parameters such as cutting speed, fixed nozzle diameter, cutting pressure and abrasive garnet. The entry–exit hole diameter, kerf, delamination, splintering, burring, thickness and hardness change were investigated. As the cutting speed increased, rotational slip, cutting start point, circularity and circular error increased. The thickness of the composites cut by water jet method increased and surface hardness decreased due to delamination. As the cutting speed increased, the hole inlet and outlet dimensions increased, which leads to an increased in size of the kerf.

Experimental and simulation study of eigen frequency responses of Luffa cylindrica sponge fibre polymer composite

The vibration frequencies of plant fibre (Luffa cylindrical sponge) reinforced composite structure has been studied in this article Initially, a simulation model of Luffa fibre reinforced polymer composite plate has been developed through the commercial finite element analysis package. Further, the finite element frequency solutions are compared with own experimental frequency data (recorded using the in-house fabricated Luffa fiber composite) for the validation purpose. The current analysis mainly performed on two composite plate fabricated using the different weight of fibre (no fibre and 6.4%). Moreover, the simulation frequencies are computed using the experimental elastic properties of Luffa fibre polymer composite plate. After the necessary verification, the simulation model has been extended to explore the influence of various structural parameters on the free vibration frequency.

Vibration Characteristics of Carbon Fiber Reinforced Polymer Composites under Varying Fiber Orientation Composition

Many engineering applications today are increasingly made of laminated composite plates. The properties of laminated composite plates can change as the laminate and fiber composition change, enabling the engineering structure and components to be customized according to the desired static or dynamic properties. Therefore, it is of interest to investigate variation in dynamic properties of composites under different fiber orientation composition to forecast their vibration response. In this study, the natural frequency and mode shape of carbon fiber-reinforced polymer composite plates were obtained numerically under varying composition of the 0°, ±45° and 90° fiber orientations. Sixteen different cases were simulated using finite element method, showing changes in the natural frequency and mode shape of carbon fiber-reinforced polymer composite plates with changes in the composition of the fiber orientation. The first five values of natural frequency and mode shape of the composite laminate were reported and analyzed using a surface regression method. In addition, the effect of the stacking sequence on the natural frequency of the composite plate having the same orientation composition was also analyzed. Comparison with previous studies showed good agreement of the present numerical modeling. Numerical results indicate potential to develop relationships to estimate modal properties based on composition of fiber orientation.

Experimental, Numerical and Finite Element Vibration Analysis of Delaminated Composite Plate

The vibration of the delaminated composites concerns the structure safety and dynamic behavior of the composite structures as it can be vital in the presence of delamination. In this research paper, the finite element simulations, numerical simulations and the experimental work are combined to analyze the vibration behavior at different delamination size, different stacking sequences and different boundary conditions. The finite element analysis software packages like Ansy and Abqus are used to fetch the vibration response of carbon fiber reinforced polymer composite plate for different boundary conditions, stacking sequences and delamination sizes. Experiments are carried out to study the vibration behavior. Numerical results were obtained using the first order shear deformation theory. Rayleigh-Ritz method was used to derive the governing equations to find the natural frequencies and the results were computed using Matlab tool. The results from finite element, numerical and experimental analysis were then compared and verified that the maximum percentage of error is ignorable. It is seen that the natural frequencies of carbon fiber reinforced polymer decreased with an increase in delamination size subjected to all boundary conditions. The higher values of natural frequencies found for all sides clamped boundary conditions.

An experimental study on milling of natural fiber (jute)- reinforced polymer composites

The interest in materials having natural, environmentally friendly, renewable and low density/cost is increasing day by day due to sanctions imposed to reduce the emission rates, especially the Kyoto Protocol. In recent years, the use of environmentally friendly composites by using natural fibers such as flax, jute and sisal has increased in engineering applications. Milling operation has frequently been an important method of machining which can achieve the desired dimensions and tolerances for the plate-shaped parts. In this study, the effects of cutting parameters such as cutting speed and feed rate on cutting force, delamination factor and surface roughness in end milling of jute fiber-reinforced polymer composite plates with different orientation angle (0°/90°, 30°/−60° and ±45°) were examined by using the cemented carbide (WC) end mills (two, three and four number of flutes). Cutting force, deformation factor and surface roughness were found to be influenced by the feed rate and cutting speeds. In addition, increasing the number of the flutes of the cutting tools reduced the cutting force, delamination factor and surface roughness.