Fiber-reinforced Composite Plates Research Articles

Modeling of the nonlinear dynamic degradation characteristics of fiber-reinforced composite thin plates in thermal environment

In this research, the nonlinear dynamic degradation characteristics of fiber-reinforced composite plates in thermal environment are investigated through a novel dynamic degradation model, which is established by introducing the thermal and time fitting coefficients simultaneously to express dynamic elastic moduli of such composite materials. Based on the classical laminated plate theory, the improved exponential function method, the complex modulus approach and the Ritz method, the dynamic equations are derived to solve the dynamic parameters. Besides, a particle swarm optimization algorithm is employed to iteratively calculate dynamic elastic moduli, and the nonlinear least squares technique in MATLAB software is utilized to draw the three-dimensional fitted surfaces of dynamic elastic moduli, degradation time and temperature data, so that the concerned fitting coefficients in the model developed can be identified. In order to validate the dynamic degradation model, experimental measurements of E120 carbon fiber/ FRD-YG-03 resin composite thin plates are undertaken. The first three natural frequencies, resonant responses and modal damping ratios obtained from the model are compared with experimental results at different degradation time and stabilized thermal environment, which are shown to be in good agreement. Also, the specific influences with and without consideration of the degradation behavior on the dynamic characteristics are investigated and evaluated.

Design of fiber-reinforced variable-stiffness composites for different open-hole geometries with fiber continuity and curvature constraints

In this study, the optimum design of fiber-reinforced composite plates with different hole geometries for various load conditions is investigated. Strain energy/compliance is optimized using three different design methodologies: constant-stiffness (CS), variable-stiffness (VS), and variable-stiffness with least-squares & continuity constraints (LSC). In all the cases, variable-stiffness and LSC designs both reveal better structural performance with reduced compliance and less stress concentrations around the hole in comparison to the optimum constant-stiffness designs. The compliance significantly decreases after optimization especially for the bi-axial loading case. Most importantly, the LSC method allows manufacturable fiber angle distributions that satisfy the maximum curvature limit, making the proposed LSC method applicable to well-established variable-stiffness manufacturing techniques such as 3-D printing and automated fiber placement. The benefits obtained by using variable-stiffness becomes less pronounced as the hole size decreases with respect to the area of the plate. The use of variable-stiffness is found to be more advantageous over shape-optimization methods of constant-stiffness composites. The comparison to the literature findings (Huang et al., 2016) reveals that 13% further reduction in structural compliance with the proposed LSC design method is possible. The proposed design method provides manufacturable variable-stiffness composites with significant improvements in structural performance.

Geometrically nonlinear analysis of time-dependent composite plates using time function optimization

In this paper, a novel approximation method is presented for the large deformation analysis of moderately thick fiber-reinforced composite plates based on elasticity responses at asymptotic times. The displacement vector is approximated using separation of variables, by two functions of geometrical parameters and one function of time parameter with unknown coefficients. The unknown coefficients of the time function are determined employing the least squares optimization and the Lagrange multipliers methods. It is shown that the geometrically nonlinear responses of time-dependent composite plates can be obtained by finding the optimum coefficients of the time function with low computational cost and high precision.

A Local Sensitivity-Based Multiscale Stochastic Stress Analysis of a Unidirectional Fiber-Reinforced Composite Material Considering Random Location Variation of Multifibers

This paper describes an efficient computational method for estimating the probabilistic properties of the maximum microscopic stresses in a unidirectional fiber-reinforced composite material against microscopic random variations of fibers locations. Some microscopic geometrical random variations will cause a large variation of the microscopic stresses, even if the influence on the homogenized elastic properties is small. The random variation of the microscopic stresses will have a significant influence on the apparent strength of composites, and therefore, estimation of the random variation will be important for reliability-based design of a composite structure. Further, for more precise analysis, a unit cell containing many inclusions should be employed. When the number of random variables becomes large, a multipoint approximation-based approach will not be appropriate. Therefore, a computational approach with a local surrogate constructed by a successive sensitivity analysis is proposed in this paper. The realizations of the microscopic stresses are estimated with the successive sensitivity-based local surrogate, and the probabilistic properties of the stresses are estimated with using the approximated realizations in the Monte Carlo simulation. As an example, the multiscale stochastic stress analysis of a unidirectional fiber-reinforced composite plate under unidirectional tensile load along the transverse direction is performed with considering randomness in fibers locations. For this problem, probabilistic properties as the expectation and coefficient of variation of the maximum microscopic stresses in resin are estimated. From comparisons between the direct Monte Carlo simulation and the proposed method, validity and effectiveness of the proposed approach are discussed.

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.

Nonlinear vibration study of fiber-reinforced composite thin plate with strain-dependent property based on strain energy density function method

The strain energy density function method is proposed to study the nonlinear vibration behavior of the fiber-reinforced composite thin plate with strain dependence. First, the material nonlinearity of the fiber-reinforced composite is extended to the vibration field. On the basis of Jones-Nelson nonlinear model, a theoretical model with the consideration of the strain-dependent nonlinearity is established to illustrate the theoretical principle of the strain energy density function method. In the model, the nonlinear elastic moduli in different fiber directions are expressed as a function of the strain energy density. The nonlinear natural frequencies are solved by Ritz method in conjunction with the classical laminated plate theory and Hamilton’s principle, and the nonlinear vibration responses are calculated by Newton–Raphson iteration method. Moreover, a TC300 carbon/epoxy composite plate is taken as a research object. In order to determine the corresponding parameters in the theoretical model, the composite beam specimens are cut off to conduct the stress-strain measurement. The nonlinear natural frequencies and vibration responses of the composite plate under different excitation levels are obtained. The comparisons between the theoretical calculation and experimental test show that the maximum calculation error of the first six natural frequencies with considering the strain-dependent nonlinearity is less than 4.3%, and the maximum calculation error of the resonant responses is less than 12.0% for the third mode and the sixth mode, thus the practicability and reliability of the proposed method have been verified.

Experimental study of film cooling over a fiber-reinforced composite plate with anisotropic thermal conductivity

An experimental investigation was carried out to analyze the film cooling performance over a fiber-reinforced composite plate with anisotropic thermal conductivity (ATC). The influence of the ATC and its spatial variations on the cooling effect under different blowing ratios was studied. It was found that the heat transfer in the plate was enhanced in the direction with higher thermal conductivity. The average value and the uniformity of the cooling efficiency changed with different inclined angles between the directions of the ATC and the mainstream. The highest average cooling efficiency was achieved with different values of the stream-wise angle α and the span-wise angle β when different regions downstream of the film cooling were considered. For example, when the blowing ratio was equal to 0.5, the corresponding α and β for the highest average cooling efficiency in the downstream region (1D ≤ X ≤ 5D) were 60° and 0°, respectively. For the downstream region (0D ≤ X ≤ 10D), the corresponding α and β were 35° and 60°, respectively. When the blowing ratio was different, the affected laws of α and β also exhibited variations.

Crack detection of a HPCFRCC thin plate using electrical resistivity method

Electrical resistivity measurement has been used as a test for studying the durability-related properties of cement composites for decades. Applications of electrical resistivity measurement namely health monitoring and crack detection are of great importance for increasing the service life of structures. The former is the capability of cement composite to sense its own strain (piezoresistivity) and the latter is based on the irreversible change of resistivity in the presence of crack. In this study, at first the effect of different fractions of silica fume and carbon fiber on piezoresistivity of cement composites were evaluated by monitoring the variations of resistivity under compression. Secondly, a high performance carbon fiber-reinforced cement composite (HPCFRCC) thin plate specimen was subjected to four-point bending while the variations of resistivity were recorded so that the zone at which the initiation of crack occurs can be detected. Results showed that both compressive strength and water absorption are highly affected by silica fume content while flexural strength slightly changed by increasing silica fume. While the addition of carbon fiber increased water absorption, it marginally affected mechanical strengths. Piezoresistivity test showed the ability of carbon fiber as a functional filler and the facilitated dispersion of fibers in high concentration of silica fume particles. It was confirmed that when carbon fiber content increases to more than 0.4 volumetric percentage, conductivity of specimen substantially increases and required sensitivity from piezoresistivity test is obtained. Crack detection test showed that when cracks are formed the planar surface resistivity of thin plate significantly changes. Thus, the formation and propagation of cracks can be monitored using electrical resistivity measurement in self-sensing cement composites.

A nonlinear dynamic model of fiber-reinforced composite thin plate with temperature dependence in thermal environment

In this paper, the material nonlinearity induced by the high temperature is introduced in the modeling of fiber-reinforced composite thin plate structure, and a nonlinear dynamic model in thermal environment is established using Hamilton's principle in conjunction with the classical laminated plate theory, complex modulus method and strain energy method. The nonlinear relationships between the elastic moduli, Poisson's ratios and loss factors and temperature change are expressed by the polynomial method. Then, the dynamic equations in the high temperature environment are derived to solve the inherent characteristics, dynamic responses and damping parameters with considering temperature dependent property. Also, the identification principle of concerned fitting coefficients in the theoretical model is illustrated. As an example to demonstrate the feasibility of the developed model, the experimental test of a TC500 carbon/epoxy composite thin plate is implemented. The results of the developed model and experimental test show a good consistency, and both indicate that the high temperature has complicated influence on its dynamic characteristics, especially on damping property.

Experimental and numerical investigation on the dynamic characteristics of thick laminated plant fiber-reinforced polymer composite plates

Although considerable attention has been devoted to the experimental research works of plant fiber-reinforced composites, theoretical determination of their structural characteristics is also much needed one in their evolution. But it is still considered as a difficult process due to the several factors such as short and discontinuous fiber form, plant fiber’s intrinsic characteristics, fiber anisotropy and porosity. In this study, vibration characteristics of woven jute/epoxy and woven aloe/epoxy laminated composite plate structures are investigated theoretically and experimentally. The elastic constants of the woven jute/epoxy and woven aloe/epoxy laminated composites are obtained through experimental testing. The governing differential equations of motion for the uniform woven jute/epoxy and woven aloe/epoxy laminated thick composite plates are carried out using the p-version finite element method based on higher-order shear deformation theory. The effectiveness of the developed finite element formulations is demonstrated by comparing the natural frequencies obtained using the present finite element method with those obtained from the experimental measurements. Also a comparative study is carried out between the results of h-version FEM and p-version FEM to check their accuracies and efficiencies. The effects of aspect ratio and angle of fiber orientation under various end conditions on the free vibration responses of the woven jute/epoxy laminated composite plate are also investigated. The forced vibration response of the woven jute/epoxy laminated composite plate under the harmonic force excitation is carried out under various end conditions.

Modal shape measurement of fiber-reinforced composite plate with high efficiency and precision based on laser linear scanning method

The laser linear scanning method is proposed to measure the modal shape of fiber-reinforced composite thin plate with high efficiency and precision. First, by establishing the laser scanning frame model of the composite plate, the corresponding extraction principle of modal shape data and laser scanning rate selection criterion are explained in detail to clarify the theoretical principle of laser linear scanning method. The corresponding test procedure of modal shape, drawing method from the shape scanning data, and control method of the constant laser scanning rate are also proposed based on the developed laser linear scanning system. Then, a TC300 carbon fiber/resin composite thin plate is taken as a research object to verify the effectiveness and reliability of such a method, through comparing the results obtained by the traditional experimental modal method and finite element method. Moreover, the influences of constraint boundary condition, excitation level, laser scanning rate, scanning spacing, scanning path mode, the fiber angles, and fiber material damage on modal shape results are also discussed. It has been found that laser linear scanning method can improve test efficiency of modal shape of the composite plate with high preciseness. Except for scanning path mode, the other parameters have a major impact on each shape morphology, and their effects can be quantitatively analyzed by identifying the positions and clarity of nodal lines of each modal shape. Especially, the high-density modal shape results and their equal amplitude lines in different projection views can be used to determine whether or not the composite plate is damaged as well as its damaged degrees.

A new nonlinear vibration model of fiber-reinforced composite thin plate with amplitude-dependent property

In this paper, the material nonlinearity is introduced in the dynamic modeling of fiber-reinforced composite thin plates, and a new nonlinear vibration model of such composite plate structures with amplitude-dependent property is established with the consideration of the nonlinear stiffness and damping characteristics, which is observed and confirmed in the nonlinear vibration characterization experiment. In this new model, the elastic moduli and loss factors are expressed as the function of strain energy density on the basis of Jones–Nelson material nonlinear model. By using the identified parameters under different excitation amplitudes, these elastic moduli and loss factors are characterized as the function of the maximum dimensionless strain energy density. Then, the power function fitting technique is used to determine the nonlinear stiffness and damping parameters in the model, and the nonlinear natural frequencies, vibration responses and damping ratios of a TC300 carbon/epoxy composite thin plate are calculated and measured in a case study. The comparisons between the theoretical and experimental results show that the maximum calculation error of natural frequencies with consideration of amplitude-dependent property is less than 4.3%, and the maximum calculation errors of resonant response and damping results are no more than 12.5 and 9.6% in the 3rd mode and the 6th mode, respectively. Therefore, the practicability and reliability of the proposed model have been verified.

Spectral Representation of Uncertainty in Experimental Vibration Modal Data

It is well known that structures exhibit uncertainty due to various sources, such as manufacturing tolerances and variations in physical properties of individual components. Modeling and accurate representation of these uncertainties are desirable in many practical applications. In this paper, spectral-based method is employed to represent uncertainty in the natural frequencies of fiber-reinforced composite plates. For that, experimental modal analysis using noncontact method employing Laser-Vibrometer is conducted on 100 samples of plates having identical nominal topology. The random frequencies then are represented employing generalized Polynomial Chaos (gPC) expansions having unknown deterministic coefficients. This provides us with major advantage to approximate the random experimental data using closed form functions combining deterministic coefficients and random orthogonal basis. Knowing the orthogonal basis, the statistical moments of the data are used to estimate the unknown coefficients.

Nanoclay enhancement of flexural properties and water uptake resistance of glass fiber-reinforced epoxy composites at different temperatures

In this study, glass fiber-reinforced epoxy-nanoclay composite plates, with I.30E clay contents ranging between 0 and 5 wt.%, were manufactured by hand layup with hot pressing. Flexural strength of unexposed fiber-reinforced epoxy-nanoclay reached an optimum improvement of 11% for 1.5 wt.%. Scanning electron microscope analysis showed that at this clay loading, better interfacial adhesion of clay with glass fibers was achieved. At higher clay loadings, clay agglomeration and presence micro-voids led to less strength improvement. The maximum water uptake was found to decrease with increasing clay loading and moisture diffusion at 80℃ was about 80% higher than that at room temperature. Post exposure flexural tests revealed a behavior similar to that of unexposed samples with nanoclay loading of 1.5 wt.% leading to optimal flexural properties. Exposure to moisture resulted in degradation of fiber-reinforced epoxy-nanoclay flexural properties with about 36% reduction in strength for 80℃ and 8% for room temperature.

Dynamic characterization of the thickness-tapered laminated plant fiber-reinforced polymer composite plates

Evolution of the laminated woven natural fiber fabric-reinforced polymer composite structures makes a way to the development of the non-uniform laminated composite structures in order to achieve the stiffness variation throughout the structure. An attempt is made in this work to carry out the experimental and numerical investigations on the dynamic characteristics of the thickness-tapered laminated woven jute/epoxy and woven aloe/epoxy composite plates. The governing differential equations of motion for the thickness-tapered laminated composite plate are developed using the h-p version FEM based on higher order shear deformation theory. The validation of the present finite element formulation is carried out by comparing the natural frequencies obtained using the finite element formulation with those natural frequencies determined experimentally. The developed model is further validated with the available literature works on tapered composite plate to confirm the efficiency of h-p version FEM. This work also explores the study of the vibrational characteristics of composite plates under the influence of plant fiber’s transverse isotropic material characteristics and porosity associated with plant fiber composites through the elastic constants evaluated in the author’s previous work. Also the influences of aspect ratios, ply orientations, and taper angles under various end conditions on the natural frequencies of the woven jute/epoxy composite plate are studied using the present finite element formulation. The forced vibration response of the thickness-tapered laminated woven jute/epoxy composite plate under the harmonic force excitation is carried out considering CFCF and CFFF end conditions.

Identification of damage in composite structures using Gaussian mixture model-processed Lamb waves

Composite materials have comprehensively better properties than traditional materials, and therefore have been more and more widely used, especially because of its higher strength–weight ratio. However, the damage of composite structures is usually varied and complicated. In order to ensure the security of these structures, it is necessary to monitor and distinguish the structural damage in a timely manner. Lamb wave-based structural health monitoring (SHM) has been proved to be effective in online structural damage detection and evaluation; furthermore, the characteristic parameters of the multi-mode Lamb wave varies in response to different types of damage in the composite material. This paper studies the damage identification approach for composite structures using the Lamb wave and the Gaussian mixture model (GMM). The algorithm and principle of the GMM, and the parameter estimation, is introduced. Multi-statistical characteristic parameters of the excited Lamb waves are extracted, and the parameter space with reduced dimensions is adopted by principal component analysis (PCA). The damage identification system using the GMM is then established through training. Experiments on a glass fiber-reinforced epoxy composite laminate plate are conducted to verify the feasibility of the proposed approach in terms of damage classification. The experimental results show that different types of damage can be identified according to the value of the likelihood function of the GMM.

Inverse characterization of vegetable fibre-reinforced composites exposed to environmental degradation

The characterization of composite materials, particularly those reinforced with vegetable fibres, presents additional challenges, like the influence of the manufacturing process, fibre-matrix adhesion problems, progressive stiffness reduction or material degradation due to environmental elements (moisture, heat and UV) exposure.The present work studies the suitability of inverse characterization, based on modal properties, to determine the mechanical properties of jute fibre-reinforced composite plates, subjected to environmental exposure to simulate outdoors application conditions. With this method both the elastic and the damping properties of composite specimens are found, which highlights its great usefulness in the prediction of mechanical properties.It was found that this non-destructive method can better estimate material properties than the rule of mixtures, reflecting manufacturing, processing conditions and also the influence of moisture absorption and UV degradation on the mechanical properties of these natural fibre composites. This method is an important tool since it can be performed in the final parts where the results account for all external influences.

Experimental Analysis for the Effect of Impactor Geometry on Carbon Reinforced Composite Materials

For the last three decades, composites have become very preferable materials to be used in the automotive industry, structural parts of aircraft and military systems and spacecraft, due to their high strength and modulus. Composite materials are sometimes exposed to invisible or visible damage due to impact loading during their service life. In this study, the effect of impactor geometry with four different contact surfaces on woven carbon fibre-reinforced composite plates having three different thicknesses are investigated. In the first stage, composite plates were manufactured with the ply orientations of [45/-45/0/90/45/-45]2s, [45/-45/0/90/45/-45]3s, [45/-45/0/90/45/-45]4s based on conventional usage. In the second stage, carbon fibre-reinforced composite test panels were exposed to low velocity impact tests to obtain force-time, energy-time and force-displacement curves. Finally, semi and full penetration of composite panels and damage magnitude were determined. It was found that the impactor geometries with lower contact surfaces such as conical and ogive types were much more penetrative on composite plates than the other geometries, but they caused larger damage area in the vicinity of the impact point.

Stochastic finite element on vibration analysis of composite plates having random damping parameters

Damping parameters of composite structures possess significant uncertainty due to the structural complexity of such materials. Considering the parameters as random variables, this work uses the generalized polynomial chaos (gPC) expansion to capture the uncertainty in the damping and in the vibration responses of structures. A non-sampling based stochastic finite element formulation for damped vibration analysis is developed in which the gPC expansion is used to represent damping uncertainty and stochastic responses with unknown deterministic functions. The constructed gPC expansions for the parameters are used as random inputs to the FEM model to realize the responses on a few number of collocation points generated in random space. The realizations then are employed to estimate the unknown deterministic functions of the gPC expansion approximating the responses. The application of the proposed method is practiced on sample fiber-reinforced composite plates having random modal damping parameters. Utilizing a few random collocation points, the method indicates a very good agreement compared to the sampling-based Monte Carlo simulations with large number of realizations.

Biaxial behavior of high-performance fiber-reinforced cementitious composite plates

A total of 127 plate specimens were fabricated and tested, of various mixture proportions, fiber types, and casting methods, in order to investigate the behavior of both plain concrete and high-performance fiber-reinforced cementitious composite (HPFRCC) specimens under multi-axial loading. The majority of the test specimens were initially fabricated as larger loaf specimens, to achieve proper fiber directionality in the out-of-plane direction, and then cut and trimmed, with steel brush platens used for loading to minimize friction between the testing machine and the plate specimens. The test results indicate that HPFRCC materials can exhibit enhanced biaxial compression performance, compared to plain concrete specimens, due to passive confinement provided by fibers in the out-of-plane direction. The multi-axial behavior of HPFRCC materials obtained from the tests was further used to construct biaxial failure curves, and several modeling parameters have then been derived for nonlinear finite element analysis of HPFRCC planar members subjected to biaxial stresses.