Fiber Reinforced Polymer Plates Research Articles

A novel variable curvature clamping anchor for the multilayer CFRP plate cable: Concept, numerical investigation, and design proposals

This paper proposed a novel variable curvature clamping anchor (VCCA) for the multilayer carbon fiber-reinforced polymer (CFRP) plate cable and systematically evaluated the anchor performance using the finite element (FE) method. The design concept of the anchor, function of variable curvature waveform, anchor configuration and components design were first presented, then the stress distribution of the CFRP plate with different layers and failure mode of the anchor system were investigated. The six parameters affecting the anchor performance were also studied, including the number of waveforms, bolt preload, anchor length, thickness of ear plate, thickness of clamping plate, and thickness of clip. Finally, the design proposals of the anchor were given. The results indicate that the peak compressive stress has been successfully transferred from the loading end to the back of the anchor, and the interfacial shear stress of the CFRP plate was small and less than one-sixth of the shear strength. In addition, the failure of the anchor system occurred in the cable body part and not inside the anchor. The number of waveforms and the thickness of the clip slightly affected the peak transverse compressive stress, whereas the bolt preload, anchor length, ear plate thickness, and clamping plate thickness had an important influence on the axial stress distribution and peak transverse compressive stress. The novel VCCA proposed in this paper has essential engineering value and significance, filling the gap of the anchor for the multilayer CFRP plate cable, contributing to promoting the application of large-tonnage CFRP plate cable in bridges and space structures, and landing a solid foundation for subsequent experiments.

A Fuzzy Similarity-Based Approach to Classify Numerically Simulated and Experimentally Detected Carbon Fiber-Reinforced Polymer Plate Defects

This paper presents an eddy current approach for testing, estimating, and classifying CFRP plate sub-surface defects, mainly due to delamination, through specific 2D magnetic induction field amplitude maps. These maps, showing marked fuzziness content, require the development of a procedure based on a fuzzy approach being efficiently classified. Since similar defects produce similar maps, we propose a method based on innovative fuzzy similarity formulations. This procedure can collect maps similar to each other in particular defect classes. In addition, a low-cost analysis system, including the probe, has been implemented in hardware. The developed tool can detect and evaluate the extent of surface defects with the same performance as a hardware tool of higher specifications, and it could be fruitfully employed by airline companies to maintain aircraft in compliance with safety standards.

Effect of temperature variation on the plate-end debonding of FRP-strengthened steel beams: Coupled mixed-mode cohesive zone modeling

Fiber-reinforced polymer (FRP) strengthened steel beams may experience significant temperature variation during their service life. Because of the different coefficients of thermal expansion (CTEs) of FRP and steel materials, thermal stresses can be generated by temperature variation at the FRP-to-steel interface and consequently influence the plate-end debonding mechanism. Therefore, an accurate prediction of the debonding failure of FRP-strengthened steel beams under combined mechanical and thermal loading is of great importance for the strengthening design. This paper proposes a closed-form analytical solution based on a coupled mixed-mode cohesive zone model (CZM) (i.e., with the consideration of Mode-I and Mode-II mixity), to analyze the effect of thermal stress on the debonding failure of FRP-strengthened steel beams. An excellent agreement has been achieved between the analytical solution and the finite element (FE) modeling in terms of interfacial full-range debonding behavior. Further parametric studies were conducted and indicated that the thermal stresses induced by elevated temperatures tend to reduce the plate-end debonding load and such effect becomes more significant when a thicker FRP plate is adopted.

Structural performance evaluation of UHPC/conventional concrete cast on new Y-shape FRP stay-in-place formwork for concrete bridge decks

Overthe pastfewyears, there has been a rise in the use of Stay-In-Place (SIP) structural formworks made of fibre reinforced polymer (FRP). This study investigates the performance of decks made of FRP SIP structural formworks with an improved configuration using conventional and ultra-high performance concrete under static loadings. The proposed new composite deck consisted of a glass fibre reinforced polymer plate stiffened with Y-shape ribs for resisting tensile and shear stresses while reinforcements was placed on the compressive side of the deck. The new composite deck was compared with conventional reinforced concrete solid decks and a composite deck consisting of square hollow section (SHS) stiffeners. Results showed that the deck made of Y-shape stiffeners failed in punching shear, and the use of Y-shape stiffeners significantly enhanced the ultimate strength and shear capacity of the proposed deck. It was also concluded that the voids in the concrete deck with SHS stiffeners resulted in lightweight structures but had a negative influence on the ultimate strength of the deck cast on FRP SIP formwork. Increasing the concrete strength from 34 MPa to 140 MPa resulted in a 71% enhancement in the maximum load-carrying capacity but did not considerably influence their stiffness.

GEP Tree-Based Prediction Model for Interfacial Bond Strength of Externally Bonded FRP Laminates on Grooves with Concrete Prism.

Reinforced concrete structures are subjected to frequent maintenance and repairs due to steel reinforcement corrosion. Fiber-reinforced polymer (FRP) laminates are widely used for retrofitting beams, columns, joints, and slabs. This study investigated the non-linear capability of artificial intelligence (AI)-based gene expression programming (GEP) modelling to develop a mathematical relationship for estimating the interfacial bond strength (IBS) of FRP laminates on a concrete prism with grooves. The model was based on five input parameters, namely axial stiffness (Eftf), width of FRP plate (bf), concrete compressive strength (fc′), width of groove (bg), and depth of the groove (hg), and IBS was considered the target variable. Ten trials were conducted based on varying genetic parameters, namely the number of chromosomes, head size, and number of genes. The performance of the models was evaluated using the correlation coefficient (R), mean absolute error (MAE), and root mean square error (RMSE). The genetic variation revealed that optimum performance was obtained for 30 chromosomes, 11 head sizes, and 4 genes. The values of R, MAE, and RMSE were observed as 0.967, 0.782 kN, and 1.049 kN for training and 0.961, 1.027 kN, and 1.354 kN. The developed model reflected close agreement between experimental and predicted results. This implies that the developed mathematical equation was reliable in estimating IBS based on the available properties of FRPs. The sensitivity and parametric analysis showed that the axial stiffness and width of FRP are the most influential parameters in contributing to IBS.

Strengthening of Reinforced Concrete Beams with Circular Opening at Flexure Zone by Various Types of Fiber Reinforced Polymer

This paper aims to investigate the flexural behaviour of reinforced concrete (RC) beams containing circular opening at mid-beam span and strengthened using externally bonded Textile Reinforced Concrete (TRC) sheets, Carbon Fibre Reinforced Polymer (CFRP) sheets and Carbon Fibre Reinforced Polymer (CFRP) plates. The flexural behaviour including ultimate load, deflection, crack pattern as well as failure mode was investigated. Five RC beams with the dimensions of 1700 mm length and cross section of 200 mm x 250 mm with design concrete strength of 64 N/mm2 were tested under 4-points loading. The tested RC beams consists of solid beam as a control beam, unstrengthened RC beam with circular opening and strengthened RC beams with circular opening. The circular opening with ratio of 0.32 is classified as small opening with diameter of 80 mm was kept constant for all beam specimens. The inclusions of circular opening at the middle of beam span slightly decreased the ultimate load of beam about 6.2% compared to control beam. The reduction of stiffness was also experienced in RC beam with opening. The application of strengthening in beams with circular openings manages to regain the beam capacity about 17.5 to 22.6% higher than the unstrengthened RC beams with opening.

A transfer learning approach for damage diagnosis in composite laminated plate using Lamb waves

Lamb wave-based damage diagnosis systems are widely regarded as a likely candidate for real-time structural health monitoring (SHM), although analysing the Lamb wave response is still a challenging task due to its complex physics. Recently, deep learning (DL) models such as convolutional neural network (CNN) have shown robust classification performance in various structures using Lamb wave-based diagnostic strategies. However, these DL models are often designed to address isolated tasks, which means that the model needs to be re-trained from scratch to accommodate any small change to the setup. Thus, such data-dependency of the DL model designed for the SHM system can restrict its full usage. This paper presents a study on a version of the transfer learning framework (TLF) based on 1D-CNN autoencoder (AE) and a classifier as a possible way to address this problem. In the transfer learning approach, the knowledge learned by a network represented as source model, while performing one or more tasks is utilized to improve the damage diagnosing ability of another network represented as target model operating under other conditions. In TLF, a ResNet AE model will selectively outsource its pre-trained layers to a separate 1D-CNN model, which is a supervised learning model aimed to perform tasks, such as classification. In order to train both the source model and the target model, two separate databases are constructed using the Open Guided Waves diagnostic data repository containing scanned Lamb wave signals generated from a 2 mm thin carbon fibre-reinforced polymer plate structure, in which a range of frequencies and artificial defects are used. A TLF variant which includes transferred layers of pre-trained ResNet AE and 1D CNN classifier, have been developed, trained and tested with an unseen database containing 144 samples. Based on the test performance, the adopted version of TLF achieved an impressive 82.64% accuracy and emerged as the most robust, balanced and computationally more economical classification model.

Analyzing the Sample Geometry Effect on Mechanical Performance of Drilled GFRP Connections.

A considerable effort to understand the bolted joints’ mechanical behavior in pultruded profiles has existed in the literature over the past decades. However, most investigations focused on the single-bolt connections, and only a few works considered single-lap joints. This paper investigates the mechanical performance of a single-lap connection of pultruded glass fiber-reinforced polymer (GFRP) plates owning to the experimental data deficit in the literature. Tensile tests of specimens with different geometries generate a database comprising 80 single-bolt joints. The shear-out failure was predominant for the considered GFRP pultruded plates, with the end length mainly affecting the load-bearing capacity. Hart-Smith’s theoretical model overestimated the ultimate resistance of all considered joints—the exceptionally low efficiency of the GFRP composite points out the necessity of additional means for strengthening the drilled connections. Additionally, finite element (FE) software Abaqus simulated the bolted joints; this study employs the user-defined subroutine experimentally verified in the literature. In the considered examples, the ultimate resistance prediction error decreased from 25.7% to 2.9% with increasing the plate thickness (from 4 mm to 8 mm) and width (from 25 mm to 35 mm), which proves the reasonable adequacy of the simplified FE model and makes it a valuable reference for further bolted joints’ development.

Debonding analysis of FRP-to-concrete interfaces between two adjacent cracks in plated beams under temperature variations

Externally bonded fiber-reinforced polymer (FRP) composites have been widely used for the strengthening and repairing of reinforced concrete (RC) beams. Existing studies have denstrated that the full-range behavior and the associated debonding mechanism of the FRP-to-concrete interface between two adjacent cracks in the FRP-plated RC beam are different from those of the pull-off bonded joint. Moreover, the bond behavior between the FRP and the concrete may be affected by interfacial thermal stresses induced by the service temperature variations (i.e., the thermal loadings). Based on a fully reversible bilinear bond-slip model, this paper presents an analytical study to investigate the full-range deformation behavior of the FRP-to-concrete interface between two adjacent cracks under combined mechanical and thermal loadings. The analytical results have indicated that the thermal loadings may significantly influence the full-range deformation behavior and the axial stress distribution of the FRP plate, although the material properties of concrete, adhesive, and FRP are assumed to be not affected by the service temperature variations. A temperature increase leads to an increase in the ultimate load of the bond interface and vice versa. A finite element (FE) model with different considerations of the bondline damage is developed to verify the proposed analytical solution. The reliability of the proposed analytical solution is then validated by the comparisons between the analytical results and the corresponding predictions provided by the FE model.

Mechanical properties of carbon/glass fiber reinforced polymer plates with sandwich structure exposed to freezing-thawing environment: Effects of water immersion, bending loading and fiber hybrid mode

In this article, two kinds of carbon/glass fiber hybrid rod with the sandwich structures were designed and developed through the pultrusion technology, including the fiber random hybrid (RH) mode with multi-layer sandwich structure and fiber core-shell hybrid (CH) mode with single-layer sandwich structure. The hybrid sandwich-structure plates were prepared from the rod and immersed in bending loading, temperature alternating and sustained water immersion as long as 360 days. The effect of fiber hybrid mode/sandwich structure on the degradation mechanism of mechanical properties was revealed through the digital image correlation and thermogravimetric analysis. Through the fiber hybrid design, the strength improvement percentages of RH plates with multi-layer sandwich structure were up to ∼50% (tensile strength), 30 ∼ 40% (flexural strength) and 18% (in-plane shear strength) compared to CH plates with single-layer sandwich structure. Higher bending loading level brought about the decrease of flexural strength and in-plane shear strength close to 18% and 19%, respectively. During the immersion, microcracks or microvoids formed and expanded in the resin tensile area under the bending loading and water diffusion, leading to the uncoordinated stress concentration for single-layer sandwich-structure CH plate. By uniformly dispersing carbon fibers into glass fibers, the uneven interface stress concentration can be effectively alleviated for multi-layer sandwich-structure RH plates. The comparison of mechanical properties with the others’ work showed the interface shear strength was more sensitive to the bending loading and immersion temperature. The long-term life prediction showed the maximum increase percentages of mechanical properties of multi-layer sandwich structure were 435.4% (tensile strength) and 149.2% (flexural strength) and 110.7–114.2% (shear strength) compared to the single-layer sandwich structure.

NONLINEAR FINITE ELEMENT ANALYSIS OF MECHANICALLY ANCHORED REINFORCED STEEL I BEAMS

Aim: Steel structural elements can lose their strength in vehicle crashes, fire, fatigue, decay, humidity, etc. Consequently, their load-bearing capacities reduce considerably. A widely used strengthening method for steel beams is fiber-reinforced polymer strips or plates. One of the most important problems for this practice is sudden end-strip debonding due to the high normal and shear stress concentration. In this study, the structural behavior of deformed steel I-beams strengthened by carbon composites under bending was studied numerically. Using a commercial nonlinear finite element program (ABAQUS), a finite element model verified with the formerly executed experimental study was presented. To examine the effect of Mechanical Anchorage on large samples, a parametric study was carried out with the verified finite element model. In the parametric study, mainly three parameters were considered. Flange slenderness ratio (Bf/tf), web slenderness ratio (H/tw), and length to cross-sectional depth ratio (L/bf). Results derived from the nonlinear analysis revealed that the employment of the bolt anchorage increases the load capacity of the deformed elements and sustains the elements to resist more loads. However, the behavior and strengthening capacity of this practice is accordingly dependent on the flange slenderness ratio and web slenderness ratio of the proposed beam. Obtained results also indicate that the efficiency of mechanical anchorage in short-span beams is higher compared to the long-span beams.

Semi-Analytical Finite Element Method for calculating dispersion curves of a CFRP plate

Composite Materials are widely used thanks to their mechanical characteristics. Non destructive evaluation requires knowing the exact dispersion curves to determine the propagative waves and to resolve the phase velocity of symmetrical and antisymmetrical modes. The aim of this paper is to plot the dispersion curves of a Carbon Fibre Reinforced Polymer plate using Semi Analytical Finite Element Method algorithm. This method combines the analytical expression of the displacement and the finite element method procedure. The resultant advantage is both simplicity and rapidity. The obtained results showed that the method accuracy depends on the elements number of meshing. To ensure good precision and fast computation of the method, the elements number and the order of the interpolation functions must be optimized.

Dynamic analysis of RC beams externally bonded with FRP plates using state space method

The state space method is used to investigate the in-plane linear dynamic behavior of reinforced concrete (RC) beams externally bonded with fiber-reinforced polymer (FRP) plates. The state space formulae are properly set up by selecting the appropriate generalized displacements and their conjugated forces as state variables. By adopting the numerically stable method to solve the homogeneous state equations with respect to the mode function vectors, the frequencies and corresponding modal shapes for the free vibration of the FRP-strengthened RC beams under generalized boundary conditions are subsequently obtained. The orthogonality of the vibration modes is established based on the concept of symplectic inner product. By utilizing the modal superposition method, the analytical solutions of the inhomogeneous governing equations for forced vibration and the dynamic responses of the FRP-strengthened RC beams subjected to a uniformly distributed step load, concentrated triangular impulse load at the mid-span, moving concentrated load, and vertical seismic load are obtained. Finally, several numerical examples are presented to validate the results against those obtained by the general-purpose finite element software ABAQUS. Good agreement between the results is observed. Moreover, parametric studies are conducted to investigate the effects of the cross-sectional geometric and material properties of the FRP plate and adhesive layer on the peak interfacial shear stress at the plate end when the strengthened beam is subjected to a uniformly distributed step load or a moving concentrated load.

High-Temperature Effect on the Tensile Mechanical Properties of Unidirectional Carbon Fiber-Reinforced Polymer Plates.

Carbon fiber-reinforced polymer (CFRP) has the advantages of a high strength-weight ratio and excellent fatigue resistance and has been widely used in aerospace, automotive, civil infrastructure, and other fields. The properties of CFRP materials under high temperatures are a key design issue. This paper presents the quasi-static tensile mechanical properties of unidirectional CFRP plates at temperatures ranging from 20 to 600 °C experimentally. The laser displacement transducer was adopted to capture the in situ displacement of the tested specimen. The results showed that the tensile strength of the CFRP specimen was affected by the high-temperature effect significantly, which dropped 68% and 16% for the 200 and 600 °C, respectively, compared with that of the room temperature. The degradation measured by the laser transducer system was more intensive compared with previous studies. The elastic modulus decreased to about 29% of the room temperature value at 200 °C. With the evaporation of the resin, the failure modes of the CFRP experienced brittle fracture to pullout of the fiber tow. The study provides accurate tensile performance of the CFRP plate under high-temperature exposure, which is helpful for the engineering application.

The curve cluster analyses for the characterizations of material defects by long-pulsed laser thermography

Laser thermography is a novel non-destructive testing method enabling the detections of defects on vertical surfaces (e.g., cracks) and those on parallel surfaces (e.g., delaminations). The thermal response of defects near the surface of the specimen in the temperature field is the basis for defect detection work; however, the thermal response characteristics of defects under direct laser irradiation have not been systematically investigated. In this paper, we investigated the thermal response characteristics of five materials under long-pulsed laser excitations: copper, 45 steel, aluminum alloy, carbon fiber reinforced polymer plate, and ceramic resin composite coating. These specimens exhibited significantly different thermal conductivities. An important characterization parameter, characteristic temperature, was found, which can characterize the difference in thermal conductivity of different specimens. The surface of the 45 steel was coated with 3Cr13 coating, and cracks on the coating surfaces generated significantly different thermal response characteristics. The findings of this study illustrated the feasibility of long-pulsed laser thermography for demonstrating the heat entrapment effect due to cracks and provide a method for defect detection.

Weighted adaptive Kalman filtering-based diverse information fusion for hole edge crack monitoring

The information fusion of different sensors is an effective means of improving the damage quantification of aircraft structures operating in a complex environment. A weighted adaptive Kalman filtering-based information fusion method (WAKFIFM) is proposed to achieve the feature-level fusion of diverse signals of the hybrid piezoelectric-fiber optic sensor network. The damage identification results obtained from guided wave signals and strain signals are described by the quantification curves of damage index (DI) and crack length. A new fusion curve is obtained by fitting the above two quantification curves using the quadratic polynomial method. The mean square error and the root mean square error of the fusion curve and the actual curve are used as the error and the covariance of the proposed WAKFIFM, respectively. The weighted value in WAKFIFM is the reciprocal of the square of the actual measured maximum DI. The hole edge crack propagation experiments are conducted on both an aluminum plate and a carbon fiber reinforced polymer plate in a load-temperature changing environment.A new damage location method integrated with DI information is developed to obtain a more accurate result. The feature-level fusion results show that the proposed WAKFIFM can improve the accuracy of damage quantification, compared against that obtained from the single guided wave signals or fiber optic sensor signals.

Effects of temperature variation on intermediate crack-induced debonding and stress intensity factor in FRP-retrofitted cracked steel beams: An analytical study

Fiber-reinforced polymer (FRP)-retrofitted steel structures in service are likely to experience significant temperature variations due to seasonal and diurnal service temperature changes. Even without the material system degradation, such temperature variations may influence the intermediate crack-induced (IC) debonding mechanism in FRP-retrofitted steel structures, mainly due to the interfacial thermal stress induced by the different thermal expansion coefficients of the FRP plate and the substrate steel. This paper presents a closed-form analytical solution for the full-range debonding process of an FRP-retrofitted notched steel beam under combined thermal and mechanical loading. A bilinear bond-slip relationship is used for describing the non-linear property of the bonding layer. The effects of thermal stress on the interfacial stress distribution, the IC debonding load and the stress intensity factor (SIF) at the notch are examined for the FRP-retrofitted steel beam at various service temperatures. The analytical solution is verified through the comparison between analytical and finite element (FE) results. Parametric investigations have indicated that a temperature decrease may lead to a reduced IC debonding load while an increased SIF, and vice versa. Such effect is more significant when a thicker and stiffener FRP plate is applied to retrofit the steel beam.

Crack propagation modeling of strengthening reinforced concrete deep beams with CFRP plates

Fracture analysis of reinforced concrete deep beam strengthened with carbon fiber-reinforced polymer (CFRP) plates was carried out. The present research aimed to discover whether crack propagation in a strengthened deep beam follows linear elastic fracture mechanics (LEFM) theory or nonlinear fracture mechanics theory. To do so, a new energy release rate based on nonlinear fracture mechanics theory was formulated on the finite element method and the discrete cohesive zone model (DCZM) was developed in deep beams. To validate and compare with numerical models, three deep beams with rectangular cross-sections were tested. The code results based on nonlinear fracture mechanics models were compared with the experimental results and the ABAQUS results carried out based on LEFM. The predicted values of initial stiffness, yielding point and failure load, energy absorption, and compressive strain in the concrete obtained by the proposed model were very close to the experimental results. However, the ABAQUS software results displayed greater differences from the experimental results. For instance, the predicted failure load for the shear-strengthened deep beam using the proposed model only had a 6.3% difference from the experimental result. However, the predicted failure load using ABAQUS software based on LEFM indicated greater differences (25.1%) compared to the experimental result.

Numerical study on the dynamic progressive failure due to low-velocity repeated impacts in thin CFRP laminated composite plates

In this paper, the mechanical response of Carbon Fibre Reinforced Polymer (CFRP) plates subjected to repeated low-velocity impacts is numerically investigated. 3D models of composite plates subjected to repeated low-velocity impacts were developed in Abaqus/Explicit software. The numerical models were validated using experimental data obtained from impact tests on CFRP plates using drop weight tower methodology through the comparison of commonly used parameters (i.e., maximum contact force, maximum impactor displacement, and energy absorption). Damage is intended as several modes for intralaminar failure such us fibre or matrix breakage and interlaminar failure (i.e., delamination). Puck failure criterion with linear strain softening was employed for acknowledging intralaminar failure. Additionally, the bi-linear traction–separation cohesive zone model was employed to account for interlaminar damage by defining zero thickness cohesive elements at the interfaces. A sequence of impacts was applied to the composite plate at three different energy levels. It was found that the impact time and the peak force increase in the sequential impacts which indicates a change in the stiffness of the laminate in sequential impacts. The analyses of the results of the damage accumulation and delamination in CFRP plates showed that most of the intra-laminar and interlaminar damage is limited to a few initial impacts in a repeated impact scenario.

Investigation of vibro-acoustic characteristics of FRP plates with porous foam core

Both theoretical and experimental investigations are performed on vibro-acoustic characteristics of composite plate comprising fiber-reinforced polymer (FRP) laminates with a porous foam core (PFC) subjected to planar acoustic wave (PAW) excitation in present work. Firstly, a theoretical model of the PFC-FRP plates is established through a combination of the advantages of analytical and finite element methods. The equivalent Young's and shear moduli and density of porous foam core with different porosity distributions is considered. The free and forced vibration equations subjected to PAW load are derived to solve natural frequencies, modal shapes and vibration responses of the PFC-FRP plates on the basis of the first-order shear deformation theory and the four-node quadrilateral isoperimetric finite element method. To solve the acoustic radiation powers (ARP), the Rayleigh integral approach is used to determine the quantitative relationships between the vibration velocity responses and acoustic radiation pressures. The sound transmission loss is further determined with the pre-defined proportional expression involving the ARP and the incident acoustic power (IRP). After the theoretical model is validated coarsely based on the separated literature results, a TC300 carbon/ GEL2 epoxy resin plate specimen is fabricated and an integrated vibro-acoustic experiment system is set up to give further validation of the proposed model, of which vibration and acoustic results are measured simultaneously without changing boundary conditions of the specimen. Finally, a detailed parametric study is conducted to obtain the optimum suppression performance of vibration and noise of this kind of composite plate.