Fiber-reinforced Composite Plates Research Articles

Progressive failure analysis of U-notched thin composite plates repaired with a double-sided composite patch

In this study, carbon fiber-reinforced U-notched composite plates were repaired with composite patches made of the same material using adhesive bonding and their mechanical performance was investigated experimentally and numerically. Repairs were made by applying a double-sided composite patch to the notched thin composite plates. The repaired composite plates were tested under tensile load. The effect of the variation in notch width and depth on the repaired plate failure load and type was investigated. At the end of the experiments, load–displacement graphs of each specimen were obtained. The effect of variation in notch depth and width in the repaired specimens was not as dominant as in the non-repaired specimens. While the variation in notch dimensions changed the failure load between 34% and 37% in the non-repaired specimens, this rate was between 18% and 21% in the repaired specimens. In the numerical analysis, progressive failure analysis was performed using the Hashin Failure Criteria. Subroutine codes were written in the program Ansys, which uses the finite element method for numerical analysis. In the results, numerical and experimental load–displacement graphs and failure types of the specimens are presented comparatively. The convergence rate of the experimental and numerical data was between 92% and 99.8%.

Experiments and modelling of ultrasonic waves in composite plates under varying temperature

Guided wave (GW) structural health monitoring (SHM) systems offer an attractive solution as an in-situ quasi real-time assessment of structural damage, but their sensitivity and efficiency may be impaired under varied environmental and operational conditions. Thus, virtual tests, such as that based on the Finite Element (FE) method, represent a valid approach for simulating and investigating SHM systems, enabling a substantial reduction in experimental campaigns. In this work, GW propagation characteristics in a carbon fibre-reinforced composite plate are studied under a varying temperature condition, representative of the aeronautics application. At first, GW SHM system was physically tested at room temperature (20°C), and the results were used to calibrate and assess the proposed FE modelling approaches, characterised by different element types and mesh sizes. A temperature independent averaged time compensation factor is proposed to mitigate the numerical data dependency on excitation frequency and propagation angle. Two temperature variations (from 20°C to -50°C, and 20°C to 65°C) were experimentally and numerically considered to investigate the effect of varying temperature on the GW. For all test cases, the compensated numerical data was compared to the experimental results, and discussed in terms of dispersion curves, focusing on the zero-order symmetric, S0, and antisymmetric, A0, modes. Results show that both 2D and 3D FE approaches can accurately predict the changes in GW due to varying temperature, with the group velocity of the A0 mode being less sensitive to temperature variations.

Effect of orientation of CNTs and piezoelectric fibers on the damping performance of multiscale composite plate

The present work deals with the study of active constrained layer damping treatment of multiscale carbon nanotube-based hybrid carbon fiber-reinforced composite plates. The distinctive feature of novel multiscale hybrid carbon fiber-reinforced composites is that the wavy/straight carbon nanotubes are distributed uniformly in the matrix phase of hybrid carbon fiber-reinforced composites, and the waviness of carbon nanotubes is considered to be coplanar with two mutually orthogonal planes. Firstly, the effective elastic properties of hybrid carbon fiber-reinforced composites are estimated using the Mori-Tanaka method. The outcomes of the Mori-Tanaka method suggest that the transverse effective elastic properties of hybrid carbon fiber-reinforced composites containing wavy carbon nanotubes are better than those of hybrid carbon fiber-reinforced composites with straight carbon nanotubes. Secondly, a finite element model using the layer-wise first-order shear deformation theory is developed to study the damping performance of hybrid carbon fiber-reinforced composite plates integrated with the active constrained layer damping treatment. The constraining layer of active constrained layer damping treatment is a 1–3 piezoelectric composite layer with vertically/obliquely-oriented piezo-fibers. The piezo-fibers make an angle [Formula: see text] with the vertical plane of a layer coplanar with the xz- or yz-plane. The effect of the orientation of piezo-fibers angle on the control authority of active constrained layer damping treatment patches is investigated. Our results reveal that the performance of multiscale hybrid carbon fiber-reinforced composite plates has improved due to the incorporation of wavy carbon nanotubes, and the orientation angle of piezo-fibers has a major impact on the control authority of active constrained layer damping patches. The proposed multiscale composite with the combination of wavy carbon nanotubes and active constrained layer damping patches can be actively used in the aerospace and transport industries to control the mechanical vibrations of structures.

Optimal design of vibro-impact resistant fiber reinforced composite plates with polyurea coating

This paper studies on optimal design of vibro-impact resistant fiber reinforced composite plates (FRCPs) with polyurea coating. Initially, a theoretical model for the coated FRCP structures under elastic boundary conditions is proposed, through which dynamic stiffness and impact damage area are predicted. Here, based on the first-order shear deformation theory and the Rayleigh-Ritz method, the dynamic stiffness of coated FRCP structures is calculated, which is taken as an index of vibration suppression performance. Regarded as an index of anti-vibration performance, the impact damage area is identified by employing the Hertz contact law and the predefined delamination threshold load. After validation of the proposed model against a series of experiments on coated and uncoated FRCP specimens, optimization analysis is then conducted based on the Non-dominated Sorting Genetic Algorithm, where the maximum dynamic stiffness, the minimum impact damage area and structural mass are defined as objective functions, and thickness ratio, elastic modulus ratio and ply orientation angle are taken as design variables. It has been found that to possess the desired vibration and impact resistant capabilities together with maintaining lightweight property, it is recommended to choose design variables associated with the turning point of Pareto-optimal solutions as the final optimal results.

Modeling and free vibration analysis for bolted composite plate under inconsistent pre-tightening condition

During the service process of bolted composite structures, the local bolt pre-tightening force may decrease, that is, the bolts are inconsistently pre-tightening, which will affect the integrity of the whole system. Here, a semi-analytical modeling method for bolted composite plates with inconsistent pre-tightening conditions is studied. To simulate the uneven pressure distribution on the bolted joint surface, a variable stiffness spring surface model is proposed and a method to obtain the parameters of the model is also described. For a specific connection structure, each joint is simplified into a spring surface model and modeling of inconsistent bolt preload in the connection structure could be realized by assigning different parameters to each spring surface model. Based on the classical laminate plate theory, the strain and kinetic energy of the composite plate are calculated and the motion equation of the structures is deduced by the Rayleigh-Ritz method. Finally, a modal test is applied for a multi-bolted fiber-reinforced composite plate. The accuracy of the model is verified by both test and 3D finite element analysis results. The influence of loosening degree, position and quantity of loosening bolts on natural frequencies of bolted composite plates is further analyzed.

Effect of graphene nanoplatelets on mechanical and impact properties of an aramid/glass-reinforced epoxy composite

Abstract This study aims to characterize and evaluate the effects of graphene nanoplatelets (GnPs) added to the epoxy matrix and the fiber stacking sequence on the mechanical and impact responses of carbon/aramid hybrid composites. For this purpose, Aramid/Glass/Aramid and Glass/Aramid/Glass stacking sequences as well as full Aramid and Glass fiber configurations were used in an epoxy matrix with various contents (0.1, 0.25, 0.5 wt%) of GnPs. Tensile and flexural tests were conducted per mechanical characterization and low-velocity impact (LVI) tests with 30 J impact energy were performed by a drop-weight impact test. According to results, aramid fiber location has a significant effect on the peak load values, absorbed energy, and displacement of the hybrid composites. In addition, the inclusion of 0.25 wt% GnPs into the epoxy matrix increased the LVI properties of pure glass and hybrid fiber-reinforced composites. However, the incorporation of GnPs into the epoxy matrix caused a deterioration in the LVI properties of the aramid fiber-reinforced composite plates. Moreover, the best increase in the mechanical properties of pure and hybrid fiber-reinforced composites was obtained by adding 0.1 and 0.25% wt% GnPs into the epoxy matrix.

Dynamic Buckling of Composite Structures Subjected to Impulse Loads Using the Lyapunov Exponent

This paper focuses on dynamic buckling of composite structures subjected to impulse loads. Using the Lyapunov exponent, the Budiansky–Hutchinson criterion is improved and its algorithm is constructed. Based on it, the nonlinear dynamic buckling loads are evaluated for typical composite structures such as a fiber-reinforced composite plate, composite laminated cylindrical shells and a laminated plate with delaminations and matrix cracks that are all subjected to impulse loads. The improved criterion of dynamic buckling is validated through comparisons with the results in the published literatures.

Investigation on Residual Strength and Failure Mechanism of the Ceramic/UHMWPE Armors after Ballistic Tests

In this paper, the ballistic damage mechanism and residual bearing capacity of ceramic/backing plate armor were investigated. First, a series of lightweight armors were prepared, consisting of ceramic and ultra-high molecular weight polyethylene fiber-reinforced resin matrix composite (UHMWPE) plates, and were wrapped in a high-strength fabric. Then, the ceramic/UHMWPE armors were hit by one or two bullets, and finally subjected to compression testing. The results showed that the main failure mode of integral ceramic/UHMWPE armors was ceramic brittle fracture. Many zigzag patterns on the compression curve indicated that the specimens had undergone the stages of crack propagation, ceramic fragment reorganization, plastic deformation of UHMWPE backing plate, interlaminar tearing, and overall fracture. The failure of spliced ceramic/UHMWPE armors was mainly due to the dislocation between ceramic sheets; the smooth compression curves indicated that there was no recombination of ceramic fragments and obvious interlayer debonding during the compression. Under the maximum load, each ceramic/UHMWPE armor with ballistic damage did not suddenly break and fail. The structure and thickness of ceramic plates all had an impact on residual strength: under the same structure, the greater the thickness, the greater the residual strength, but the relationship between them was not linear; under the same thickness, the residual strength of the spliced ceramic/UHMWPE armor was higher. The residual strength was also related to the number of shots: after two bullets hit, its value was only one-third of that after one bullet hit.

Wave dispersion relations in laminated fiber-reinforced composite plates with surface-mounted piezoelectric materials

Wave dispersion relations in laminated fiber-reinforced composite plates with surface-mounted piezoelectric materials

Smart damping of a simply supported laminated CNT-based hybrid composite plate using FE approach

We present the finite element (FE) model using the first-order shear deformation theory (FSDT) to investigate the damping performance of laminated hybrid fiber-reinforced composite (HFRC) smart plates via the active constrained layer damping (ACLD) treatment. A unique feature of the HFRC is that the nanoscale carbon nanotubes (CNTs) are embedded in the matrix phase of carbon fiber composite to improve the overall properties, especially the damping characteristics of the resulting HFRC. Two- and three-phase micromechanical models are employed to determine the effective elastic properties of the base composite and HFRC respectively. The constraining layer of the ACLD treatment is considered to be made of vertically reinforced 1–3 piezoelectric composite (PZC) material. The system consists of a laminated HFRC plate integrated with the two patches of ACLD treatment and the numerical results are computed for three cases: symmetric and anti-symmetric cross-ply, and anti-symmetric angle-ply. The damping performance of the laminated HFRC square plate is significantly enhanced over the laminated base composite plate due to the incorporation of a small amount of CNTs. In particular, the anti-symmetric angle-ply case provides better damping than symmetric/anti-symmetric cross-ply cases. Analysis of the HFRC plate showed that its vibration amplitudes can be attenuated from ∼8 to ∼16% by adding a small amount CNTs. The effect of in-plane and transverse actuation of 1–3 PZC on the damping characteristics of the overall plate was also studied. We found that the transverse actuation significantly influences the damping performance of the overall plate. The outcomes of our study provide substantial evidence that the addition of a small amount of CNTs in the conventional composite structure can improve its damping performance significantly. This is practically possible in view of the recent research activities in the field of fabrication of large-scale CNT-based hybrid composite structures.

Research on vibration and impact-resistant performances of fiber reinforced resin matrix composite plates with polyurea coating

<p indent=0mm>In this paper, two types of dynamic models for vibration and impact analyses of the fiber-reinforced resin matrix composite plates with polyurea coating are established, respectively. Also, the vibration and impact resistant performances of the coating-composite plate structures are evaluated quantitatively. For one thing, the first-order shear deformation theory is adopted to represent the displacement field of the structural system, and the natural frequency is solved by the Rayleigh-Ritz method. Meanwhile, the vibration response subjected to impulse excitation is achieved by the mode superposition method, and the key index “dynamic stiffness” for evaluating the vibration resistant performance is obtained by the Fourier transform and convolution calculation operations. For another thing, with consideration of the structural deformation affected by the low velocity impact, an equivalent two-degree-of-freedom spring-mass model is established to describe the dynamic impact process and the change of contact force. Meanwhile, the linearized Hertz contact theory is utilized to obtain the impact contact force. After the impact response is solved by the Runge-Kutta method, the key data “load-displacement curve” for evaluating impact resistant property is further obtained. Finally, by taking T300 carbon fiber/epoxy-based composite plate specimens with and without polyurea coating materials as the research objects, an integrated vibration and impact test system is set up. Several dynamic parameters of those specimens with and without coating are obtained, which validate the theoretical analysis models as well as their prediction results. The research results indicate that after the polyurea coating is applied, the first four dynamic stiffness values of the composite plate specimens are increased with the maximum rising degree of 74.7%, and the impact contact forces and displacement peak values of the load-displacement curves are reduced by 13.9% and 13.3%, respectively. Hence, the contribution of polyurea coating to the effects of vibration suppression and impact resistance of the structure system has been effectively verified.

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.

A machine learning model for predicting the ballistic impact resistance of unidirectional fiber-reinforced composite plate

It has been a vital issue to ensure both the accuracy and efficiency of computational models for analyzing the ballistic impact response of fiber-reinforced composite plates (FRCP). In this paper, a machine learning (ML) model is established in an effort to bridge the ballistic impact protective performance and the characteristics of microstructure for unidirectional FRCP (UD-FRCP), where the microstructure of the UD-FRCP is characterized by the two-point correlation function. The results showed that the ML model, after trained by 175 cases, could reasonably predict the ballistic impact energy absorption of the UD-FRCP with a maximum error of 13%, indicating that the model can ensure both computational accuracy and efficiency. Besides, the model’s critical parameter sensitivities are investigated, and three typical ML algorithms are analyzed, showing that the gradient boosting regression algorithm has the highest accuracy among these algorithms for the ballistic impact problem of UD-FRCP. The study proposes an effective solution for the traditional difficulty of the ballistic impact simulation of composites with both high efficiency and accuracy.

Non-linear vibration and instability of multi-phase composite plate subjected to non-uniform in-plane parametric excitation: Semi-analytical investigation

Non-linear vibration and instability of a randomly distributed carbon nanotube fiber-reinforced composite (CNTFRC) plate under the action of different types of non-uniform in-plane periodic loadings are presented in this study. The composite plates are modeled considering von Kàrmàn non-linearity and Higher-order shear deformation theory (HSDT). The analytical expression for stresses (σxx,σyy,andτxy) distribution within the CNTFRC plate due to non-uniform loads is developed by solving the in-plane elasticity problem using Airy’s stress approach. Using these stresses, Hamilton’s principle is applied to derive the non-linear partial differential equations for dynamic instability and non-linear vibration of CNTFRC plates. Employing the Galerkin method, the non-linear partial differential equations are transformed into a set of non-linear ordinary differential (Mathieu type) equations. After dropping the nonlinearity terms, the linear ordinary differential equations are solved by using Bolotin’s method to trace the boundaries of the dynamic instability region corresponding to periods 2T and T. In the end, the non-linear ordinary differential equations are solved by using the Incremental Harmonic Balance method (IHB) for analyzing the non-linear vibration behavior of the CNTFRC plate. The result obtained from the current work will help in the appropriate design of the CNTFRC plate against stability and vibration in presence of non-uniform in-plane loadings.

Research on flexural performance of damaged RC beams strengthened by FPR plates

Combining two technologies of pasting fiber reinforced composite board (FRP) and externally reinforced steel plate concrete structure, fiber-reinforced composite material and steel plate composite reinforced concrete structure technology can effectively improve the stress performance of concrete reinforced structure. To explore the effect of the new technology steel plate anchoring FRP slab concrete beams and the effect of different damage levels on the reinforcement effect, in this paper, the author made 3 FRP reinforced beams with damage rates of 20%, 40%, and 60%, 1 RC beam with FRP plate only and an ordinary RC beam to analyze the reinforcement effect of the new process steel plate anchored FRP plate and the bearing capacity and plastic performance of the reinforced beam with different damage rates. The results show that the new technology steel plate anchoring FRP plate reinforcement technology can effectively prevent the occurrence of early peeling failure, improve the ductility and bearing capacity of the reinforced beam, and significantly increase the utilization rate of the FRP plate; as the damage rate increases, the ultimate bearing capacity of the reinforced beam increases, but the ductility is significantly reduced.

Full wavefield processing by using FCN for delamination detection

A novel full wavefield processing method by using fully convolutional neural networks is presented. The full wavefield of propagating Lamb waves in the fibre-reinforced composite plate was simulated by the parallel spectral element method. It resembles a full wavefield measurements acquired on a surface of the plate by the scanning laser Doppler vibrometer. The aim of the proposed technique is an identification of delamination location, size and shape. It is achieved by pixel-wise image segmentation by using the end-to-end approach. It is possible because of the large dataset of Lamb wave propagation patterns resulting from interaction with delaminations of random location, size and shape. It is demonstrated that the proposed method, tested on numerical data, is performing better than conventional adaptive wavenumber filtering method which was developed in previous work. Moreover, it enables better automation of delamination identification so that the damage map can be created without user intervention. The method was also tested on experimental data acquired on the surface of the specimen in which delamination was artificially created by a Teflon insert. The obtained results with the deep learning approach show its capability to predict the delamination in the numerically generated dataset with high accuracy compared to the conventional damage detection approach. Furthermore, the deep learning model shows the ability to generalize to a further experiential set.

Characterization test on nonlinear vibration of the fibre-reinforced composite thin plate

In this research, the characterization test on nonlinear vibration of a fibre-reinforced composite thin plate is studied. First, in order to improve the efficiency and precision of the test, a laser scanning vibration system is designed and developed. Then, test methods and procedures of the harmonic distortion and nonlinear time-varying damping of such thin plates are proposed from the time-domain perspective. Corresponding test methods and procedures of nonlinear vibration properties such as the hard/soft stiffness and amplitude-dependent damping are also presented from the frequency-domain perspective. Finally, the TC500 carbon fibre/resin composite plate is selected as an example for the research to carry out a case study. Potential nonlinear vibration phenomena of such plates are characterized by the proposed test methods. It has been proved that the related test system and techniques adopted in this paper can provide an important reference for the establishment of the nonlinear vibration test methodology of fibre-reinforced composite structures.

A Lumped Parameter Model of a Fibre-Reinforced Composite Plate with Temperature Dependence Based on Thermal Vibration Measurements

Background: Experimental modelling techniques are still rare for composite structures under complex thermal environments. Objective: In this paper, by taking a fibre-reinforced composite plate (FRCP) as an example, a lumped parameter model of the FRCP with temperature dependence is developed from an experimental perspective. Methods: Initially, a series of thermal vibration measurements are performed under different temperatures to characterize the temperature-dependent vibration behaviours of the FRCP, in which the natural frequencies and modal damping ratios are identified via the variational mode decomposition method. Then, according to the degree of freedom division criterion of the half-wave number, a mass-spring-damper lumped parameter model of this type of composite plate considering additional thermal stiffness is established. Finally, a novel method of determining the lumped stiffness and damping parameters in this model is proposed based on the above experimental data. Results: The developed model is verified by comparing the theoretical natural frequencies, modal shapes and resonant responses with the test results at 40, 120, 220 and 300 °C, for which the calculation errors are within an acceptable range. Conclusions: It has been found that the accuracy of this lumped parameter model can be further improved by applying a larger number of modes to inversely calculate the lumped stiffness and damping parameters. Meanwhile, the efficiency can also be increased by adopting an appropriate step size in the iterative calculation of the additional thermal stiffness.

An Amplitude- and Temperature-Dependent Vibration Model of Fiber-Reinforced Composite Thin Plates in a Thermal Environment.

A thermal environment has a complex influence on the dynamic characteristics of fiber-reinforced composite materials and structures. It is challenging to consider the effects of high temperature and external vibration energy simultaneously on their nonlinear vibration response. In this research, the material nonlinearities, due to both the excitation amplitudes and the high temperatures, are studied for the first time, and a new nonlinear vibration model of fiber-reinforced composite thin plates in a thermal environment is proposed by introducing the nonlinear thermal and amplitude fitting coefficients simultaneously. Then, based on the classical laminated plate theory, the complex modulus approach, and the power function and the Ritz methods, dynamic governing equations in high-temperature environments are derived to solve the nonlinear natural frequencies and vibration responses and damping parameters. Moreover, the three-dimensional fitting curves of the elastic moduli and loss factors, excitation amplitudes, and temperature values are obtained so that the key nonlinear fitting coefficients in the amplitude- and temperature-dependent model can be identified. To validate this model, the experimental tests on CF130 carbon/epoxy composite thin plates are undertaken. It is found that the 3rd and 5th natural frequencies, vibration responses, and damping results obtained from the nonlinear model are consistent with the experimental measurements, and the mechanism of nonlinear thermal vibration behaviour is revealed.

An effective microscale approach for determining the anisotropy of polymer composites reinforced with randomly distributed short fibers

In this paper, an effective microscopic modeling scheme is presented to analyze mechanical properties of composites with random short fibers. To this end, the displacement-load tests of the standard samples, which are acquired by cutting a short fiber-reinforced composite plate of 650 mm × 650 mm × 2.5 mm, are firstly executed under the quasi-static tensile loads. To identify the geometric sizes of the short fibers and their distributions at microscopic scale, the advanced micro-computed tomography (micro-CT) is employed by testing a small sample of 1 cm × 2.5 mm × 2.5 mm. On this basis, a simplified microscopic model is reconstructed by the 3D parametric finite-volume direct averaging micromechanics (FVDAM) theory according to the statistic results of the micro-CT images. The proposed method is further validated by comparing the effective modulus obtained from tensile tests. The scanning electron microscopy (SEM) is also used to visualize the fracture morphology of the fibers. It is found that brittle fracture occurs in the short-fibers paralleled to the external loading.