Laminate Plate Research Articles

In-situ structural health monitoring of glass fiber reinforced composites by tufted reinforcement

Through-the-thickness reinforcement (TTR) techniques have been increasingly applied to fiber-reinforced polymer composite laminates to reduce the issues caused by the weak out-of-plane properties which can reduce significantly their load-bearing capacity. The present work investigates the electrical response of carbon tuft threads as reinforcements of GFRP omega stiffened panel. Besides the mechanical contribution of the tuft reinforcements to the composites structures, this study focuses on the evaluation of the electrical response on the tufted yarns as a means of monitor the structural health. The first studies consisted of evaluating GFRP composite laminate plates reinforced with carbon tufts by means of the electrical response through tufts to damage generated by multiple low-velocity impacts. Once the tufts exhibited their ability to respond continuously while increasing damage, pull-off mechanical tests were performed in the omega stiffeners assisted by electrical resistance measurements as well as acoustic emission (AE) and Digital Image Correlation (DIC). The results showed that the measures of electric resistance on the yarns are capable to distinguish important events during the mechanical tests, as the delamination and tuft failure. Furthermore, they are in common agreement with the cumulative energy on AE and strain field response on DIC.

Composite repair patch evaluation using pulse-echo laser ultrasonic correlation mapping method

Composite patch bonding repair is widely applied to metal and composite aircraft repair owing to its light weight and high resistance to fatigue and corrosion. However, composite patch repairing is done by vacuum bag processing in general, and the process itself is susceptible to manufacturing defects. In addition, the composite repair patches require more frequent inspections owing to the difficulty of the damage prediction. In this paper, we propose pulse-echo laser ultrasonic correlation mapping for a rapid quality evaluation method of composite repair patching. This method uses a pulse-echo ultrasonic propagation imaging system as a tool for in-situ and full-field inspection, and an ultrasonic correlation mapping (UCM) method was developed for fast and straightforward defect visualization. Two composite patch repair specimens were tested, and then UCM results were compared with other results using existing visualization methods. We also tested a composite laminate plate to verify the applicability of UCM to general composite parts. The UCM results showed similar or better performance than current visualization methods in all cases. Test results showed that the proposed system is suitable for both in-process quality evaluation and in-service field inspection.

Flutter of delaminated three-phase nano-composite beam-plates

ABSTRACTIn this article the supersonic flutter instability of delaminated carbon nanotube reinforced three-phase composite plate is investigated. The classical laminate plate theory and piston aerodynamic theory are developed to construct the governing equation of delaminated three-phase nano-composite plates. The effective material properties are obtained using Halpin-Tsai relation and rule of mixture. The effects of different parameters including carbon nanotubes (CNTs) weight percentage, fiber volume fraction, CNTs aspect ratio and different fiber orientation on flutter pressure of delaminated reinforced composite plates are considered. According to the results, appending small amount of CNTs (4% wt) into the matrix epoxy can improve the flutter critical pressure by 33% in comparison to the neat matrix epoxy.

Specific Energy Absorption Evaluation on GFRP Laminate Plate by Optical, Thermographic and Tomographic Analysis

Over the years, a large number of studies have been carried out on glass fiber composite materials in order to analyze their impact behavior. This is very important for the automotive applications, for example for bumper or crash-box. This paper presents the analysis performed on GFRP (Glass Fiber Reinforced Polymer) laminated plate specimens (epoxy matrix reinforced with E-glass, twill woven, 200 g/m2) subjected to drop impact tests. The tests have been conducted at two different impact speeds in Low Impact Velocity LVI maintaining the same impact energy to estimate the strain-rate effect. All the tests were performed referring to ASTM 7136 at standard ambient temperature. Then the SEA (Specific Energy Absorption) of the specimens was calculated, using three different non-destructive measurement techniques (Optical Analysis, IRThermography and X-ray Computed) to analyze the surfaces of rupture and the specimen interlaminar damages. The chosen geometry of the specimens allowed to reduce the costs and to use a simplest test bench giving additional information to the material behavior.

Behaviour of plain-woven glass-fiber reinforced polymer laminate plates during symmetrical bending on a circular support – Part I: Experimental evaluation

Behaviour of plain-woven glass-fiber reinforced polymer laminate plates during symmetrical bending on a circular support – Part I: Experimental evaluation

Effect of fiber orientation on the compressive response of plain weave carbon fiber/epoxy composites submitted to high strain rates

Composite materials undergo intricate damage processes, which are accentuated when these materials are exposed to impact loading conditions. In this context, this work aims to study the behavior of fiber reinforced polymer composites submitted to high strain rate in compression. A composite laminate plate was obtained using a plain weave carbon fiber fabric and an epoxy resin as matrix. The Split Hopkinson Pressure Bar (SHPB) technique was used to apply compressive loads at three different strain rates and in six different directions (0°, 15°, 30°, 45°, 60° and 75°) relative to the warp. The compressive failure modes were studied using a high speed camera to record the SHPB test. With increasing strain rates, it was possible to identify a transition from longitudinal cracking failure to delamination buckling failures. Similarly, the off-axis loading conditions (mainly for 45°) resulted in extension-shear coupling effects, which promoted the delamination buckling failures.

Experimental and numerical dynamic analysis of laminate plates via Carrera Unified Formulation

This work consists on evaluating potentialities and limitations of finite element formulations developed via CUF to predict free vibration response of laminated composite plates by using real experiments. Therefore, finite elements were developed via Carrera’s Unified Formulation (CUF) for laminated plates, which were implemented as a FORTRAN subroutine (UEL – User Element subroutine) linked to commercial finite element software ABAQUS™, to simulate free vibration of composite laminates. In addition, laminated plates made of composite material, resin epoxy and carbon fibre, with two different layups, were submitted to experimental vibration tests. The experimental tests were carried out by using an impact hammer, which excited the structure with impulse signal, and accelerometers, which measured the output data. Dynamic characteristics, such as natural frequencies, mode shapes and Frequency Response Functions were presented for the specimens. Then numerical results were compared to real experiments, discussing different aspects of the formulated finite elements. In addition, there is a demonstration how to connect native finite elements from ABAQUS™ to elements formulated via CUF (using UEL subroutines) and how to solve this problem using numerical time integration algorithms implemented in ABAQUS™, including discussion about the influence of time integration parameters on the dynamic response.

Modeling creep behavior of carbon nanotube/fiber/polymer composite cylinders

In this research, the effects of multi-walled carbon nanotubes on the distribution of long-term creep strains in thick-walled multi-walled carbon nanotube/fiber/polymer three-phase laminated composites are studied. In the first step, micromechanical models are developed to calculate the elastic properties of multi-walled carbon nanotube/vinylester and multi-walled carbon nanotube/E-glass fiber/vinylester composites. Using classical lamination plate theory, equilibrium and compatibility equations and strain–displacement relations, the distribution of effective stresses is considered. Moreover, utilizing Schapery single-integral model for nonlinear viscoelastic materials, Prandtl–Reuss relations and Mendelson’s approximation method, not only the distribution of circumferential and radial strains is investigated but also the effects of fiber orientation and weight fraction (wt.%) of the multi-walled carbon nanotubes on the way of distribution are studied. The results demonstrated that the addition of the multi-walled carbon nanotube to the vinylester can reduce absolute values of the radial and circumferential creep strains and dimensionless effective stresses. Moreover, most reduction occurred in the inner wall of the cylindrical shell when fiber orientation was α = 90°.

Analytical solution and numerical validation of piezoelectric energy harvester patch for various thin multilayer composite plates

The study of vibrational energy harvesting using piezoelectric patch integrated on isotropic beam-like or plate-like thin structures has received significant attention over the past decade. Multilayer orthotropic composite plates are widely used in aerospace, automotive and marine applications, where they can be considered as host structures for vibration-based energy harvesting. In this paper, an exact analytical solution and numerical validation of a piezoelectric energy harvester structurally integrated to a thin multilayer orthotropic plate are presented. Electroelastic model of the thin multilayer composite plate with the piezoelectric patch harvester is developed based on a distributed parameter modeling approach with classical laminate plate theory assumptions for all-four-edge-clamped (CCCC) boundary condition. Closed-form steady-state expressions for coupled electrical outputs and structural vibration response are derived under harmonic transverse force excitation in the presence of a resistive load. Analytical electroelastic FRFs related to the voltage output as well as vibration response to force input are derived and generalized for different boundary conditions of host plate. The results of numerical and analytical models from multiple vibration modes are compared first for validating the analytical model with a case study employing a thin PZT-5A piezoceramic patch attached on the surface of a multilayer orthotropic composite CCCC plate. For this purpose, finite-element analysis is carried out by using ANSYS mechanical APDL software. Then, it is important to specify parameters in energy harvesting model, so positioning of piezoceramic patch harvester and excitation point force on the voltage output FRFs is discussed through an analysis of dynamic strain distribution on the overall plate surface. In addition, the effects of various composite laminate plates with different stacking sequences as host structures on generated power are discussed in details as well.

A general solution for stress resultants around a circular cutout in laminate plates under different in-plane loadings: analytical and experimental investigations

The current work focuses on extending the analytical solution given by Greszczuk to determine the stress distribution in multilayered composite plates subjected to arbitrary in-plane loadings. This is achieved by introducing an arbitrary oriented uniaxial, biaxial, and shear loading conditions into Greszczuk solution. The present solution has exactly reproduced most of the results of the analytical solution existing in the literature. The varying parameters, such as fiber orientation angle, type and load orientation, stacking sequence, and anisotropic modulus ratio $$E_{1}/E_{2}$$ , are examined. In the second part of this study, digital image correlation (DIC) technique is used to obtain full-field surface strain measurements in unidirectional E-glass/epoxy specimens with different fiber orientation angles, in order to show its effect on stress concentration and failure modes. The analytical results obtained by the present solution compare favorably with those obtained using DIC technique. Compared to the experimental data, the accuracy of the present approach is within 10%. The simplicity of the present solution gives the design engineer a useful tool for optimizing laminate plates in the presence of a circular cutout.

Detecting Changes in Fiber Orientation in a Simulated Chopped Fiber Plate Using Curvature Mode Shapes

The use of chopped fibers in the manufacturing of carbon fiber composite parts is becoming more popular in order to reduce production costs, especially in the automotive, wind, and gas storage industries. The orientation of the fibers in a chopped fiber part is important because the material properties of the part depend upon it. Phenomena such as shear alignment can result in undesired material properties, and therefore, a method for detecting the presence of undesired fiber orientations is needed. In this paper, a metric based on a part's curvature mode shapes is developed to identify the presence and location of fibers whose orientation is different from that of a desired alignment. A proof-of-concept experimental analysis shows the effectiveness of the metric at locating a region in a carbon fiber laminate plate that has been modified by rotating the fibers 90 deg. A finite element model is also developed to validate the experimental results and explore other modification scenarios. In each case, the metric is effective in identifying areas in which fiber alignment changed relative to a baseline model. In one case, a change as small as 3 deg was identified.

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.

A multi-state model updating method for structures in high-temperature environments

A multi-state model updating method is studied to solve the problem of updating finite element model of structures in high-temperature environments. The key to the problem is to update temperature dependent parameters like elastic modulus and temperature independent parameters like density properties simultaneously in different states. Traditional multi-model updating method only deals with problems with constant parameters in different boundary conditions. To develop the method, specific constraint matrix was designed and an improved Sequential Quadratic Programming method was used to solve the problem. The vibration test of a carbon fibre reinforced bismaleimide composite laminate plate in the high-temperature environments was used to verify the method. The finite element model of the plate in different temperature boundary conditions was updated simultaneously utilizing the presented method. Compared with the traditional method, the multi-state model updating method got a similar updating result. In the meanwhile, it remains the physical meaning of parameter-temperature relations and was proved to be computational efficient with the introduction of additional constraints.

Dynamic response of circular composite laminates subjected to underwater impulsive loading

The dynamic response and failures of carbon/epoxy composite laminates subjected to underwater impulsive loading are investigated experimentally. The effect of impulsive intensity and thickness of laminates on dynamic deformation, failure modes, and associated mechanisms is identified and quantified respectively. The plates are subjected to underwater impulsive loads of different intensities with a lab-scaled underwater explosive simulator. 3D DIC is employed to capture the dynamic response in terms of response rate, mid-span deflection, and deflection-profile history during the elastic response process, followed by a series of postmortem non-destructive investigation and microscopic examinations to examine the failure modes and its distributions, and analyse the associated mechanisms. The results show that the intensity of impulse, thickness and failure of panels affect the dynamic response of laminate plates significantly. The non-surface failure has very limited influences on the tendency of the deflection-impulse relationship, and the local failure on the surface occurring later than the delamination and fiber fracture through the thickness of laminates. The blast resistance of composite laminates is not enhanced continuously with the increasing thickness due to the inconsistent changes of failure modes. With similar areal mass, meanwhile, composite laminates perform better blast-resistant performance than that of the metallic structures.

Remote acoustic detection of localized delamination in vibrating composite layered plates

Adhesively bonded, layered composite materials are ubiquitous in naval, aerospace, and automotive applications. One common challenge with such materials is the presence of delamination discontinuities at the interlaminar bonds which can have severe adverse effects to structural health and system performance. Worse yet, delamination is often visually indiscernible as it occurs below visually-obstructing surface layers, making non-visual defect detection techniques attractive in comparison. In this presentation, remote acoustic detection of localized delamination in a 0.3-m-square composite laminate plate subject to 100-6000 Hz noisy broadband forcing will be investigated. Remote measurements of the radiated acoustic field from composite plates with and without known localized delamination are collected with a 15-element microphone array. Here, statistical comparisons of spectral amplitudes between plates with and without damage are then used to evaluate remote acoustic detection performance. Additional sig...

Non-linear stability and load-carrying capacity of thin-walled laminated columns in aspects of coupled buckling and coupled stiffness submatrix

To assess a load-carrying capacity of compressed thin-walled plate structures in the paper the coupling buckling phenomenon of compressed columns was analyzed. The columns were of open cross-sections and made of coupled laminate. Selected configuration of laminate layers enables different types of coupling between membrane and bending states which describes the coupling stiffness submatrix B. Element values of stiffness matrix ABD were determined with application of classical laminate plate theory CLPT.The main aim of the work is to estimate an influence of chosen submatrix B elements on buckling, postbuckling and load-carrying capacity of analyzed thin-walled structures. The problem was solved with the Koiter’s theory application. The detailed computations were performed for uniformly compressed lip channel and top hat channel. The dimensions of both columns were chosen in a way which allowed to observe the strong coupling effect among different buckling modes. It were two laminate configurations considered which differed in value of stiffness reduction coefficients.

Adaptive analysis of plates and laminates using natural neighbor Galerkin meshless method

In this paper, natural neighbor Galerkin meshless method is employed for adaptive analysis of plates and laminates. The displacement field and strain field of plate are based on Reissner–Mindlin plate theory. The interpolation functions employed here were developed by Sibson and based on natural neighbor coordinates. An adaptive refinement strategy based on recovery energy norm which is in turn based on natural neighbors is employed for analysis of plates. The present adaptive procedure is applied to classical plate problems subjected to in-plane loads. In addition to that the laminated composite plates with cutouts subjected to transverse loads are investigated. Influence of the location of the cutout and the boundary conditions of the plate on the results have been studied. The results obtained with present adaptive analysis are accurate at lower computational effort when compare to that of no adaptivity. Further, the adaptive analysis provided accurate magnitude of maximum stresses and their locations in the laminate plates with and without cutout subjected to transverse loads. Additionally, failure prone areas in the geometry of the plates subjected to loads are revealed with the adaptive analysis.

An insight into the low-velocity impact behavior of patch-repaired CFRP laminates using numerical and experimental approaches

In this paper, the low-velocity impact response of patch-repaired CFRP laminates is investigated experimentally and numerically. This study considers various patches of different shapes and sizes placed on the single side of the parent laminate plates. In the low-velocity impact simulation, damage development and the failure process of the repaired laminate plates are analyzed based on continuum damage mechanics (CDM) theory which is derived from 3D Hashin failure criteria, and a cohesive zone model (CZM). In order to validate the proposed numerical approach, impact response such as impact force and energy are predicted from simulation. Moreover, the corresponding drop weight impact tests have been performed, and the numerical prediction is in a good agreement with the experimental measurements. Finally, the influence of patch parameters on repair performance has been analyzed according to the delamination surface area and absorbed energy of the repaired laminates from the low-velocity impact simulation. And, an optimal impact-resistance design of the patch repair is obtained based on the finding results.

The Effect of Metal on Composites Fatigue Damage in Mixed Structure

This paper investigated the fatigue damage coupling of composite laminate and metallic plate in multi-bolt joint. A progressive fatigue damage model for composite laminates and a modified Lemaitre damage model for metal material were developed. A phenomenological elastoplastic constitutive model was used to describe the in-plane shear nonlinearity of composite lamina. A formula for calculating the energy release rate of the low cycle fatigue was derived based on spherical tensor and shear tensor decomposition of the stress. The developed models were validated by the experimental results of a double-lap single-bolt metal-composite joint and were employed to simulate the fatigue damage of a double-lap, multi-bolt metal-composite joint. The result indicates that fatigue damage will harden the materials nearby the bolt region of the metallic plate for a multi-bolt joint structure when suffering to cyclic loads. This hardening behavior results to a transfer of bolt loads towards the harden region, which intensifies bearing damage and reduces tensile stress in the composite laminate, and improves the fatigue life of composite laminates fail in tensile mode.

Factors influencing the effect of attached mass on dynamic behavior of laminate composite plates using Taguchi technique

The present study addresses the effect of attached mass on dynamic properties of composite laminate plates, under flexural vibration, for clamped-free-free-free boundary conditions. Furthermore, factors influencing the effect of attached mass on natural frequencies of laminate composite are studied using the Taguchi method. The considered factor parameters are: attached mass weight, attached mass locations from the clamped edge, staking sequences, and number of layers. The results of this study indicate that the dynamic characteristics of the laminate composite plates are sensitive to the attached mass, where the natural frequencies are found to be inversely proportional to the mass weight. The results was found that the locations of the attached mass and number of layers were the most important factors affecting the natural frequencies, where the location of the masses fell into the antinodes and into the nodal area of vibration, respectively. In addition, the paper presents a good correlation between the numerical results obtained by the ANSYS software and those obtained experimentally.