Fiber Reinforced Plastic Plates Research Articles

Enhancing damping estimation accuracy of exponential windowed responses of a GFRP plate through Finite Element Model Updating approach

Fibre reinforced polymer (FRP) panels are widely employed in ship and marine structures due to their better specific stiffness and strength when compared to metals. Therefore, an accurate estimation of the dynamic behaviour of such panels is necessary from its operational and serviceability point of view. In this study, the influence of exponential window functions and the associated decay rates on the damped dynamic responses of a Glass Fibre Reinforced Plastic (GFRP) plate has been investigated experimentally, using impact hammer testing. In a standard experimental modal testing of a structure, exponential window functions are commonly employed to prevent spectral leakage of the signal and achieve a good signal-to-noise ratio. However, this exercise modifies the Frequency Response Functions (FRFs) and introduces numerical damping into the measurements. A novel technique involving a Finite Element Model Updating using Inverse Eigen-Sensitivity algorithm is employed to estimate the unbiased FRFs and identify the induced numerical damping. The model updating is carried out in two stages: updating stiffness parameters first, followed by updating damping parameters in the second stage. The updating algorithm and the two-stage strategy adopted therein is found to be effective in identifying the induced numerical damping along with the unbiased FRF expressions.

Damage Propagation and Residual Strength of Simple Block-Loaded CFRP Plates with Circular Holes under Tension–Tension Fatigue Conditions

Holes and their effects on the fatigue behavior and damage propagation of thin-walled structural components remain objects of research. In this paper, the previously untreated effect of round holes in thin plain-woven carbon fiber-reinforced plastic plates subjected to simple block loading is examined, and the implication on both damage propagation and residual tensile strength is investigated. Using three-dimensional digital image correlation, the damage propagation in the performed experimental tests is acquired, and the damage size is quantified. The evaluations reveal a relationship between the damage propagation and applied load level, for which an empirical model has been previously established by the authors. As the number of cycles increases, a saturation behavior is found. Once the increased load is imposed on the plate, damage propagation resumes, leading to further damage propagation that can be described with the same empirical model as the initial damage propagation, including renewed saturation behavior. The subsequent experimental tests to determine the residual tensile strength reveal a positive effect of the existing damage size, as the ultimate load significantly exceeds the ultimate load of the non-damaged plate.

Experimental Investigation on Bonded and Screwed Carbon Fiber-Reinforced Plastic Plates on Timber Column–Sill Joints

In this study, timber column–sill joints strengthened with carbon fiber-reinforced plastic (CFRP) plates using bonds and screws were subjected to loading tests. Twelve joint specifications were considered depending on different combinations of the CFRP plate surface finish and thickness and the type of bond, and the corresponding effects on the load–displacement behavior of the joints were investigated. Three failure modes were observed in addition to the peeling of the CFRP plate. The specimens that failed owing to screw tear out and screw head pull-through in the CFRP plate or splitting of the sill showed load–displacement curves of a similar shape. Those that failed owing to buckling of the CFRP plate showed a rapid and substantial load decrease due to failure. This failure mode was only observed in 0.50 mm thick CFRP plate specimens. When a peel-ply CFRP plate was installed in the column–sill joint specimens, similar secant stiffnesses were observed in the silicon and epoxy resin-bonded specimens, both with high shear strength. Although the specimens with bonds with a high shear strength showed lower deformation performance, the specimens' maximum load increased with the bond's shear strength. The maximum load improved for a 0.75 mm thick peel-ply silicon- or epoxy-bonded CFRP plate. The load's maximum value after peeling the CFRP plate was 0.79–1.23 times as large as the maximum load of the no-bond specimens and did not change significantly.

Experimental study of a composite beam externally bonded with a carbon fiber-reinforced plastic plate

According to the characteristics of steel fiber reinforced concrete (SFRC) with high tensile strength and carbon fiber reinforced plastic (CFRP) with high strength and light weight, a composite beam composed of CFRP plate, SFRC and ordinary concrete (OC) is developed in the paper. Eight specimens, including four CSOCBs with different heights of the SFRC and four SFRC–OC composited beams with varying heights of the SFRC, were tested to analyze the flexural behavior. The results show that the composite beam composed of OC, SFRC and CFRP improves the ultimate load capacity of the beam under unidirectional load, enhances the cracking and deformation resistance of the beam, and solves the defects of the weak tensile capacity of ordinary concrete beams. Applying them to the building structure can improve the stability of the structure and prolong the service life of the building. A prediction model for the bending capacity of the CSOCB was proposed and validated. Based on the limit state design method, the design formula for the bending capacity of the composite beam is described in detail herein.

Development and verification of a cure-dependent visco-thermo-elastic simulation model for predicting the process-induced surface waviness of continuous fiber reinforced thermosets

Process-induced surface waviness effects represent a major concern for series production of high-quality lightweight structures based on fiber reinforced plastics (FRP). This paper suggests a method for the numerical prediction of these effects by using the example of processing glass fiber reinforced plastics (GFRP) in a resin transfer molding (RTM) process. The influence of reaction kinetics, chemical shrinkage and cure-dependent viscoelastic properties of the resin are taken into account. Furthermore, the dependence of surface quality on curing cycle, consolidation pressure, textile architecture and thickness of neat resin layer (NRL) at the part surface are investigated. The work is based on published material data and a visco-thermo-elastic simulation approach which has been previously presented and validated. All numerical results are compared to the surfaces of FRP plates that were manufactured with the corresponding parameter variations. Based on a literature survey, different surface waviness values have been identified for comparison of experimental and numerical results. Satisfactory agreement between experiments and simulations is found. Furthermore, it is shown that the analyzed NRL thickness has no relevant influence on the surface waviness while the curing temperature significantly affects the surface waviness. The role of relaxation-induced change of the surface waviness is highlighted by performing long-term measurements and corresponding time-dependent simulations. It is concluded that relaxation plays a decisive role in the appropriate selection of the subsequent surface finishing process. The suggested simulation approach provides a basis for optimization strategies to improve surface quality and reduce post-processing effort.

An experimental investigation on the effectiveness of damping changes for damage detection in a Fibre Reinforced Plastic Plate

Fibre reinforced plastics (FRP) are extensively used because of their high specific strength and stiffness. However, throughout their service life, such materials are susceptible to damages, which when accumulated may result in catastrophic failure. Studies on effects of stiffness loss due to damage has been exercised by quite a large number of researchers but very less investigators have involved the variations in dissipative behaviour in combination with such stiffness loss. However, damage in these structures not only causes local reduction of stiffness but is also observed with increased dissipation behaviour. One of the most convenient ways to carry out health monitoring exercise to detect damages is to conduct systematic vibration testing. The present study investigates the likely changes in natural frequencies and mode shapes of a rectangular FRP composite plate along with damping factors due to the induced damage. The FRP plate considered has been modal tested and dynamic responses i.e., natural frequencies, mode shapes and modal damping factors are derived through curve-fitting technique from the frequency response function measurements. In this study, changes in dynamic responses due to a locally induced damage in the FRP plate is studied. For this, in order to maximize the effects of local reduction in the stiffness on the modal parameters, a partial-cut is provided in a localised region of the plate in the first damage case. In the second damage scenario, the partially-cut area has been filled with epoxy resin matrix to create a region with localised change in material properties and with limited stiffness loss. Damping changes has been observed to be significant and more sensitive than variations in natural frequencies and mode shapes. The study suggests that damping parameters along with stiffness changes together can be put into practice to develop an effective vibration-based health monitoring scheme

Thermal buckling of thin injection-molded FRP plates with fiber orientation varying over the thickness

The different thermo-elastic properties of glass fibers and polymer matrices can generate residual thermal stresses in injection-molded fiber-reinforced plastic (FRP) objects. During cooling from mold to room temperature, these stresses can be relaxed by large deformations resulting from an instability of the unwarped configuration (i.e., buckling). This article investigates the thermal buckling of thin FRP disks via an analytical formulation based on the Föppl-von Kármán theory. A novel extension of our previous work is the assumption of cylindrical orthotropy with material parameters varying over the disk thickness in order to account for thickness dependency of the glass fiber orientation distribution. A disk parameter generalizing the thermal anisotropy ratio for homogeneous orthotropic disks is introduced and its relation with the occurrence and periodicity of buckling is discussed. This is done for a skin-core-skin model, for which the core-to-total thickness ratio is defined. For fiber orientation distributions typical of injection-molded disks, it is found that there exists a value of the thickness ratio for which no buckling occurs. It is also demonstrated that the periodicity of the first buckling mode is described by the generalized thermal anisotropy ratio, thus extending the results obtained for a homogeneous fiber orientation distribution. Improvements in the accuracy of the predictions for experimental data available in the literature when using the skin-core-skin model are shown. Finally, we study the relation between buckling temperature and disk thickness and propose an expression for the dependence of the normalized buckling temperature on the thermal anisotropy ratio. Results of FEM simulations are used to validate the proposed expression, proving its applicability and accuracy.

Use of the FRP plates instead of steel sheets in the joints of wooden structures

The use of steel plates in the joints of wooden structures is a common practice. However, because of the presence of natural moisture in the wood, steel sheets are easily corroded, and for this reason, the wood near the joints decays over time and thus, shortens the life of wooden structures. This study examines the feasibility of using noncorrosive fibre reinforced plastics (FRP) instead of steel plates applied in different joint areas of wooden structures, in terms of mechanical strength. In the study, six samples were tested with five different joint types, four different materials and two different experiments. As a result, it was found that besides many physical advantages of FRP, the strength of the carbon fibre reinforced plastic samples exceeded that of the samples reinforced with steel sheets by 50%, and the strength of the glass fibre reinforced plastic samples reached 70% of the strength of samples reinforced with steel sheets.

Effects of electron beam irradiation on hypervelocity impact behavior of carbon fiber reinforced plastic plates

The effects of electron beam irradiation were examined on perforation holes and fragments from quasi-isotropic carbon fiber reinforced plastic plates (CFRP plates). CFRP plates with a total dose up to 60 MGy of electron beam irradiation were prepared for hypervelocity impact experiments. The perforation holes of CFRP plates in the hypervelocity impact experiments were decreased with electron beam irradiation when aluminum alloy spherical projectiles (2017-T4) of diameter of 1 mm struck at an impact velocity of 5 km/s. However, a slight reduction in the size of the perforation hole was observed at 2 km/s. Fragments ejected from CFRP plates were examined after collection from the impact side and rear side of the targets. The cumulative number distributions of fragment length and aspect ratio were compared among specimens with different total doses.

Center Clamp Forming of a Rectangular Cup with Bottom Edge Trimming Using a Continuous Carbon-Fiber-Reinforced Thermoplastic Sheet

Center clamp forming method has been applied to avoid wrinkles in the press forming of a rectangular cup with bottom edge trimming using a continuous woven carbon fiber-reinforced plastic plate. Trimming of a bottom edge during forming is a convenient method to obtain smooth bottom without any other successive process. But it closes the die profile that may cause fiber wrinkle. By the center clamp forming compared with free forming, it is confirmed that this is one of the methods to achieve smooth top flat surface of the cup without wrinkles. Monitoring pressure using pressure sensors elucidated pressure application process during the press forming and cooling process. Difference of the pressure holding time in the cooling process was observed between the pressure on the side plate and that on the top flat plate. Sliding descent during the cooling under constant load indicated the solidification finishing time of the thermoplastic resin.

Comparison between segmentation performances of a tool based on wavelet decomposition and multithreshold and of a U-net convolutional neural network applied to shearography images of carbon fiber reinforced plastic plates with low-velocity impact damages

Carbon fiber reinforced plastics (CFRPs) have been used to replace metallic alloys in many industries because of their high strength-to-weight ratio. Due to their anisotropic behavior, low-velocity impacts can produce defects whose effects on material performance are hard to foresee. Nondestructive testing (NDT) methods are a convenient alternative to evaluate their integrity. Shearography, an image-based optical interferometric technique for measuring deformation, is one of these NDT possibilities. The segmentation of defects in the resulting images provided by such a method is essential to correctly locate and indicate the severity of impact damage. This task is especially intricate for shearography images with barely visible impact damage because of their usual low signal-to-noise ratio. We compare a combination of wavelet decomposition with multithresholds introduced in a previous publication with a U-net convolutional neural network for analyzing impact damage in CFRP plates. Both tools are detailed and then evaluated using the Matthews correlation coefficient and the equivalent diameter criterion. The results showed that U-net provided a better impact damage characterization in both evaluation metrics, allowing a safer defect detection that is less dependent on the inspector’s ability to interpret them.

Metrological Performance of Hybrid Measurement Technique Applied for the Lamb Waves Phase Velocity Dispersion Evaluation

The work presents the metrological evaluation of the modified hybrid spectrum decomposition and zero-crossing technique. The presented technique enables to reconstruct the phase velocity dispersion curve part of Lamb wave modes using only two signals. This is set to consequently simplify the of complex guided wave signals analysis. Experimentally measured asymmetric A0 mode Lamb wave signals propagating in 4 mm thickness non-homogeneous Glass Fibre Reinforced Plastic (GFRP) plate are used for assessment of the proposed technique. The phase velocity dispersion curve (DC) segments are obtained using three different filter bandwidths as reference using the DC obtained by the semi-analytical finite element method SAFE. The proposed technique quantitative and qualitative characteristics are presented. Using this technique and employing various band-pass filters it is shown that the DC segments are reconstructed in approximately 50% - 88% bandwidth of the incident signal frequency spectrum. The average of the calculated expanded uncertainties for all filter bandwidths is equal to approximately 2%. The narrower filter bandwidth has produced smaller systematic errors equal to 1.8%, yielding to wider reconstructed dispersion curve segments.

A rigorous analytical solution of interfacial stresses and overall stiffness of beam structures bonded with partially covered plates

Beam structures with partially covered plates have been widely used in macro members and micro devices, such as concrete beams with fiber-reinforced plastic (FRP) plates, aircraft structures with FRP patches and smart beams with actuators/sensors. Based on the two-parameter elastic foundation model and the classical Euler–Bernoulli beam model, a rigorous analytical solution of interfacial stresses and overall stiffness of plated beams is obtained, and influences of the interface and plate properties are presented. The limitation of the assumption of the same curvature of host beam and plate, which was widely adopted in previous studies, has been clarified. And the present solution is applicable to a wider range of interface and plate properties, especially for large values of plate thickness, plate modulus and interfacial stiffness, as well as small values of plate length. The saturation phenomenon of overall stiffness is observed in some cases, and critical values of the interface and plate parameters corresponding to the saturation limit of overall stiffness can be referred for design. The results can provide guidance for the optimal design of widely-used plated beams to prevent premature interfacial debonding and acquire better overall performance, such as higher stiffness with FRP plates or shape control with actuators, by manipulating the interface and plate properties.

Probabilistic dynamic analysis of composite plates due to low velocity impact

The low velocity impact (LVI) analysis of fiber-reinforced plastic (FRP) plates is a significant study to evaluate the reliability of lightweight structures. This study has wide applications in offshore and naval industries. Safety and reliability assessment as per the international standards is one of the basic objectives of the study. LVI on FRP plates are studied taking the material parameters and loading as random variables. FRP plates are subjected to failure under impact by in-plane loading. To evaluate the safe load carrying capacity and the reliability under impact, dynamic analysis of composite plate subjected to LVI is carried out. Reliability analysis is performed to calculate the stochastic behavior of FRP plates. During impact, the in-plane damage modes such as matrix cracking, fiber failure, and shear cracking are modeled using a failure criterion. The out of plane delamination is modeled using cohesive surfaces. The variability related with the system properties due to the inherent scatter in the geometric and material properties and input loads are modeled in a stochastic fashion. The stochastic finite element analysis (SFEA) is performed to determine the stochastic response of system using Gaussian process response surface method (GPRSM). The safety level qualification is achieved in terms of reliability level targeted.

Damping of carbon fibre-reinforced plastics plates with holes

ABSTRACTThis paper mainly deals with the specific damping capacity (SDC) of carbon fibre-reinforced plastics (CFRP) plates with holes of different sizes, positions and quantity control. Through establishing a three-dimensional damping matrix and using the finite element analysis (FEA) and Matlab, numerical calculations were conducted on the SDC of CFRP plates with same layering scheme, and a vibration test as well as a damping analysis was implemented on the CFRP test pieces with middle holes. By comparing the calculation and experimental results, good accuracy was found in predicting the modal frequency as well as SDC of the CFRP vibrations through the three-dimensional damping matrix analysis model. By comparing the modal damping of plates with different hole sizes, it could be found that as the hole size increases, the frequency showed a slowly changing tendency. The SDC of the plates with holes could reach 170% of that of the plates without holes.

Guided wave time-reversal imaging of macroscopic localized inhomogeneities in anisotropic composites

Estimation of damage position and extent in the inspected structure is among the emerging problems of active structural health monitoring (SHM) with elastic guided waves. Unlike conventional non-destructive testing (NDT) techniques, which assume continuous surface scanning, SHM systems operate only with data from a limited number of sensors. Nevertheless, in the case of isotropic (metal) plate-like structures, computational time-reversal techniques have proved to be effective for estimating in situ the location and size of wave sources and/or local scatterers within the SHM concept. With composite plates, the reconstruction procedure faces additional difficulties associated with the complexity of wave phenomena caused by their lamination and anisotropy. In this article, we present an extension of the time reversal technique for the case of composite laminate plate-like structures. This technique relies on the simulation of the reversed guided waves generated by reciprocal surface loads applied at a sparse set of measurement points of a real sensor network. The proposed implementation is based on the far-field asymptotics for guided waves generated in arbitrarily anisotropic laminate waveguides by a prescribed source, which have been derived from the path integral representations in terms of Green’s matrix for the structures considered. The performance of this approach has been experimentally tested on cross-ply carbon fiber-reinforced plastic plates showing reliable and adequate results for both active (piezoactuators) and passive (artificial defects) source characterization.

Determination of layerwise material properties of composite plates using mixed numerical–experimental technique

ABSTRACTThe global material properties and boundary conditions of Fibre Reinforced Plastics (FRP) plates can change substantially from their initial values after prolonged use. Since composite plates use different materials in different layers, a method for determination of layerwise material parameters can be useful for structural health monitoring. Vibration responses being sensitive to material properties, an inverse material identification methodology using experimental modal testing and finite element model updating can be a reasonable option. Most of the existing inverse techniques are limited to the determination of average homogenized material constants only. The current two-staged technique, supplemented by information from specially fabricated ‘Characteristic plates’ having material properties same as those of the ‘Actual plate’ but different stacking sequences, is proposed as an effective solution. Modal testing has been conducted on a rectangular FRP plate under various boundary conditions and the difficulties associated with the implementation of such technique have been critically judged.

Effect of laminated angle of carbon fiber on interior noise on an enclosure under center point excitation

This paper presents a novel method to control passively the interior noise of an enclosure such as car cabin by using the movement of the peak level and peak frequency according to the laminated angle of carbon fiber reinforced plastic composite plate. Recently, the use of carbon fiber reinforced plastic laminated plates in a car has been increased in order to reduce the weight of a car. For example, the metal plate roof has been replaced by the carbon fiber reinforced plastic plate roof for weight reduction of an electric vehicle. The characteristics of the interior noise inside of a car made of carbon fiber reinforced plastic plate roof can be changed according to the laminated angle of carbon fiber. In this paper, how this characteristic is changed was studied based on the effect of laminated angle of carbon fiber. In order to perform this study, a closed box with one flexible side wall and five acoustically rigid side walls was modelled as the interior compartment of a car. The flexible side wall of the closed box regards as the roof plate of a car. For the flexible side wall of the closed box, three carbon fiber reinforced plastic plates with different angle-ply (± θ) laminates each other were used. Therefore, three carbon fiber reinforced plastic plates with the fiber lamination angles of [−15/15/15/–15]s, [–30/30/30/–30]s, and [–75/75/75/–75]s were fabricated and used as the flexible side wall of the closed box. How the interior noise inside of the closed box was changed according to the laminated angle was studied by theoretical and numerical methods. For the validation of theoretical and numerical methods, the experimental work was performed. Finally, the carbon fiber reinforced plastic plate roof for a passenger car was numerically simulated, and the effect of the laminated angle on the interior noise was studied.

Stress performance of embedded carbon fiber reinforced plastics plate consolidated reinforced concrete structure

With the development of the building industry, various novel building materials have emerged. Modern buildings requires higher on performance of building materials, and the performance of old buildings has not been able to keep up the pace of the times. Extending the service time of old buildings by repairing and reinforcing is inevitable. In this study, 10 reinforced concrete beams including 2 ordinary reinforced concrete beams and 8 carbon fiber reinforced plastics (CFRP) plate reinforced test beams were manufactured. Three-dimensional finite element model was established using finite element software to simulate and compare the stress performance of the strengthening beams with different number of CFRP plate, size, number of groove and shear span ratio. The results demonstrated that the ultimate carrying capacity of the embedded CFRP plate reinforced beams was obviously superior to that of the ordinary reinforced concrete beams; two plates and two grooves were appropriate; the larger the shear span ratio, the better the bearing performance and the smaller the deformation. CFRP plate consolidated reinforced concrete can effectively stabilize buildings which need repairing and reinforcement.

Analysis of Harmonic Vibration Characteristics for a Composite Honeycomb Panel of the Spacecraft Scanner

The coordinate and frequency distributions of the values of displacement and acceleration amplitudes, the vibration acceleration amplification factors, and the equivalent von Mises stresses are obtained from the data on the simulation modeling of harmonic vibration of the composite honeycomb panel for spacecraft scanner and its related operational equipment (a scanner, magnetometer, optical devices, etc.) mounted on it. A dynamic simulation model of the composite honeycomb panel was developed using modern finite element analysis tools, such as ANSYS APDL. Carbon fiber reinforced plastic plates with an aluminum foil honeycomb core in the form of regularly shaped hexagonal cells that make up the honeycomb panel are approximated by multilayer plate finite elements. The related operational equipment, such as optical devices, a scanner and magnetometer, are represented in the model by lumped masses rigidly attached to the panel. The spectrum of natural frequencies and vibration modes of the spacecraft scanner honeycomb panel is determined using the developed simulation model. The resonant displacement and acceleration amplitudes, the vibration acceleration amplification factors as well as the distributions of the amplitudes of the equivalent von Mises stresses are obtained in the operating frequency range of the investigated harmonic vibration mode of the spacecraft scanner honeycomb panel.