Fiber Reinforced Polymer Laminates Research Articles

A Constitutive Model for Circular and Square Cross-Section Concrete Confined with Aramid FRP Laminates

Fiber-reinforced polymer (FRP) has been used for seismic retrofitting and structural reinforcement over recent decades. Numerous researchers have created stress–strain models based on experimental data to predict the mechanical properties of FRP-confined concrete. In this study, circular and square cross-section specimens with different design concrete strength were prepared, and the compressive strength of the specimens confined with different layers of aramid FRP (AFRP) were measured in compressive tests. A constitutive model was proposed to simulate the uniaxial compressive stress–strain relationship of the AFRP-confined concrete, which was derived from the Mohr–Coulomb failure envelope theory, and the corresponding axial strain was determined from the regression analysis. The internal friction angle of the proposed constitutive model was determined for the cylindrical concrete specimens confined with one and two layers of AFRP. The compressive strength of one and two layers of AFRP-confined concrete specimens were used to obtain the parameters of the constitutive model; the absolute average error between experimental and predicted compressive strength was 7.01%. Then, the constitutive model was used to predict the strength of a three-layer AFRP-confined concrete specimen, and the absolute average error was 4.95%. The cross-sectional shape coefficient of the square concrete specimen was obtained analytically. Substituting the cross-sectional shape coefficient into the proposed constitutive model, the average absolute error of the square cross-section concrete specimen was about 3.84%. The results indicated that the proposed constitutive model can predict the compressive strength of circular and square cross-section concrete specimens confined with AFRP.

Cross-scale data-based damage identification of CFRP laminates using acoustic emission and deep learning

Damage characterization of laminated composites has undergone extensive research, leading to the development of several damage models that incorporate acoustic emission (AE). However, feature extraction from AE data will cause the loss of certain information in the construction of damage models, which manifestly falls short of feature analysis in the frequency domain. In this study, a novel cross-scale data-based damage identification methodology for carbon fiber-reinforced polymer (CFRP) laminates is proposed by combining the AE technique with deep learning approach. Elementary experiments involved with single damage mode are designed to avoid blind inference, and the cross-scale correlation of AE features between component materials and CFRP laminates is established by wavelet packet transform (WPT). The time–frequency spectrums of AE signals of CFRP laminates by continuous wavelet transform (CWT), which adequately preserve the frequency domain information, are adopted as inputs to the convolutional neural network (CNN) model. The proposed methodology achieves a high accuracy of 96.3% in detecting and classifying damage modes (i.e., matrix cracking, matrix/fiber debonding, and fiber breakage) in unidirectional CFRP laminates.

Experimental and theoretical study on the flexural behaviour of RC beams strengthened with externally bonded reinforcement on grooves CFRP laminates

This paper presents a study on the flexural capacity of Reinforced Concrete (RC) beams strengthened with Externally Bonded Reinforcement on Grooves (EBROG) Carbon Fibre Reinforced Polymer (CFRP) laminates. Thirteen single-shear tests and seven RC beams strengthened with CFRP are examined, comparing Externally Bonded Reinforcement (EBR) and EBROG techniques with different groove distributions. The results showed that EBROG improved the bond and flexural performance. Comparison with existing prediction models reveals that while the literature models accurately predict EBR results, they underestimated the bending capacity for EBROG due to calibration based on EBR bond parameters. Consequently, a numerical model is developed to simulate Intermediate Crack Debonding (ICD) for various bond-slip laws, applicable to the different strengthening techniques. The proposed model is validated using experimental flexural tests and calibrated bond-slip laws obtained from single-shear tests, demonstrating accurate prediction of ICD failure for both EBR and EBROG.

A progressive damage model for carbon fiber-reinforced polymer laminates subjected to fastener pull-through failure

Most studies on composite joints focus on in-plane bearing mode, while little attention to fastener pull-through failure mode from out-of-plane loads. This paper presents a 3D continuum damage mechanics (CDM) model to investigate and assess the mechanical behaviors of carbon fiber-reinforced polymer (CFRP) laminates subjected to pull-through failure. The proposed model based on the use of intralaminar and interlaminar damage models is established and implemented by means of a user-defined subroutine VUMAT for Abaqus/Explicit. The novelty lies in the material model integrating the thresholds preset by the semianalytical approximation approach, which largely eliminates unnecessary fracture angle enumerations in Puck’s IFF theory, coupled with the simple parabolic interpolation search (SPIS) technique for optimal fracture angle search, considerably reducing the computational burden. Moreover, the numerical results compare well with experiments, effectively replicating the load–displacement response, damage modes, failure behaviors and damaged areas. This study provides an accurate and efficient computational methodology to analyze pull-through failures, enhancing the damage modeling and predictive capabilities for composite joints under out-of-plane loads.

Optimal Shear Strengthening of Severely Deficient RC Beam Using JFRP Laminate with Anchor

High-strength jute fibre-reinforced polymer (JFRP) laminates have recently been introduced to strengthen RC beams against shear. In contrast to synthetic-based composites, JFRP laminates would be more ductile, compatible with steel shear rebar and effective in reducing debonding due to their lower modulus of elasticity. The prime objective of this research was providing an optimal solution to strengthen a severely deficient RC beam against shear using an externally bonded JFRP laminate with anchor. Fabrication of the JFRP laminate was carried out with the maximum fibre content of 37.5% to obtain high tensile strength. Five full-scale RC beam specimens were cast. Shear strengthening was done by an externally bonded JFRP laminate with double connector, multiple connector and embedded-bar anchor systems. The dimensions of JFRP laminate were obtained based on proposed guidelines. Based on the experimental test, the average tensile strength of the fabricated JFRP laminate was found to be 162 MPa. Results also showed that the JFRP laminate with multiconnector anchor increased the maximum shear capacity of deficient RC beams by 89% and the beams had failed by the fracture of laminate. Beams strengthened with embedded-bar anchor had shown flexural ductile failure. Both beams failed after yielding of flexural bar. The proposed guidelines could be used for shear strengthening of severely deficient beams to enhance the maximum shear capacity using full strength of JFRP laminate with anchor. KEYWORDS: RC beam, Shear strengthening, JFRP laminate, Anchor, Optimal design

Numerical Analysis on the Propagation of Ultrasonic Guided Wave in Damaged Carbon Fiber Reinforced Polymer Laminate

AbstractIn recent years, the propagation of ultrasonic guided waves (UGW) along the structure to inspect has amply proven to be an excellent strategy for the health monitoring of isotropic and composite structures (SHM—structural health monitoring). For the proper development of the SHM system, the finite element method (FEM) must be mentioned, since the possibility to study the UGW in very complex structures, even characterized by different materials. Successfully locating any possible damage and identifying its severity are key factors in SHM, thus allowing to reduce the design costs. Numerically, the damage can be modeled with several approaches but it is still not clear which is the best solution to accurately reproduce the UGW mechanisms in a faulty structure. The objective of this paper is to study the various effects that different severities of damage can have on UGW propagation. For the scope, various numerical approaches are considered and the results are compared.

A comprehensive review on in-plane and through-the-thickness auxeticity in composite laminates for structural applications

Auxetic laminates are part of a fascinating branch of materials denominated as auxetics, which display a NPR (Negative Poisson’s Ratio), an uncommon property in the engineering world. Auxeticity is at the root of enhancements in shear and indentation resistance, fracture toughness and energy absorption, making the design of NPR a desirable feat in structural engineering. In composite laminates made of conventional, i.e. positive Poissons ratio, materials, auxeticity is a result of the combination between particular angular configurations and anisotropic materials. Such laminates can be used in a wide array of engineering applications, especially those which require high energy absorption capacity, including aerospace, personal defense and sports industries. This review focuses on particular property enhancements reported in the scientific world brought about by the design and application of IP (In-plane) and TTT (Through-the-thickness) NPR fibre-reinforced polymer laminates under QSI (Quasi-static indentation), LVI (Low-velocity impact) and fatigue solicitations. Furthermore, some insight is given on some possible future paths for further investigation of this topic.

Laser cutting of basalt fibre reinforced polymers by QCW fiber laser: Interaction mechanisms and effect of laser parameters

In the paper, laser cutting of basalt fibre reinforced polymer laminate using a 450 W QCW fiber laser, working in a pulsed regime is presented. Preliminary tests were performed on a basalt laminate, 1.3 mm in thickness, changing the pulse power (Pp) and pulse duration (D) to find the maximum cutting speed. Then a 33 experimental plan was carried out changing the pulse power, the pulse duration, and the cutting speed. The kerf width and the heat-affected zone were measured in the section and on the external surfaces. ANOVA analysis was adopted to assess the process parameters’ influence. The interaction mechanisms were found and discussed. From the results, the BFRP laminate appears easy to cut at maximum cutting speeds up to 3500 mm/min. However, thermal damages occur. Kerf geometry and HAZ are mainly affected by the cutting speed, while the Pp and D seem to have a minor role.

Damage mechanisms and analytical model of CFRP laminate under low-velocity normal and oblique impacts

The present work investigates the energy absorption performance of carbon fibre-reinforced polymer (CFRP) laminates subjected to low-velocity normal and oblique impacts. Experimental tests are conducted on laminates exposed to varying impact energies at both normal and oblique angles. The numerical model is developed to simulate the dynamic response of the CFRP. The research employs a combination of experimental and numerical methods to reveal the underlying damage mechanisms. The changes observed in the oblique impact response are explained through an analysis of the damage mechanisms. Analytical models for each energy absorption mechanism are proposed based on the principles of energy conservation and the theory of large bending deformation of anisotropic materials. The energy absorption performance of the laminates under oblique impacts, considering rebound and penetration conditions, is discussed. It is found that the delamination is the primary energy absorption mechanism of CFRP laminate under rebound conditions, while elastic deformation of fibres is the primary energy absorption mechanism under penetration conditions. Furthermore, the energy absorption performance of the laminate is found to be affected by the peak force and effective thickness of the plate, which change with the oblique angle. This paper makes a significant contribution by utilising experimental, numerical, and theoretical approaches to gain insights into the damage mechanisms of laminates subjected to oblique impacts.

Performance of FRP-Upgraded RC One-Way Ribbed Slabs with an Opening in Flexure Zone

Reinforced concrete (RC) one-way ribbed slabs serve as a prevalent flooring solution in the Middle East. In this region, the occurrence of openings within these slabs is frequent, particularly when making modifications to existing buildings. However, these openings compromise the stiffness and load-bearing capacity of the slabs, necessitating strengthening measures. All of the available investigations were carried out on strengthening RC one- and two-way solid slabs with openings. However, a noticeable research gap exists, as none of these studies have delved into the strengthening of RC one-way ribbed slabs with openings. This gap was bridged in this study by conducting a comprehensive experimental inquiry into the effectiveness of utilizing fiber-reinforced polymer (FRP) laminates to restore the flexural capacity of RC one-way ribbed slabs featuring flexure openings. The experimental program comprised four half-scale one-way ribbed slabs (having three ribs) divided into one unstrengthened specimen without openings to act as a reference, one unstrengthened specimen with a single opening located in the peak-moment region, and two FRP-strengthened slabs each having a single opening located in the peak-moment region. The dimensions of each slab were 2600 mm (length) × 825 mm (width) × 175 mm (thickness). The openings were square (side length = 400 mm), which included cutting the middle rib. The slabs were tested under four-point flexure until failure. It was revealed that strengthening slabs using FRP sheets fully restored the flexural capacity, which was even exceeded by up to 8%. However, the secant stiffness and dissipated energy were partially restored compared with the unstrengthened slab without opening, and these response parameters were reduced by up to 19% and 32%, respectively. Moreover, the displacement ductility for strengthened specimens was moderately reduced compared with the unstrengthened specimen without opening. Furthermore, an analytical procedure was suggested based on section analysis for quick and reasonable assessment of the peak load for both unstrengthened and strengthened one-way ribbed slabs with and without flexure openings.

Influence of distributed out-of-plane waviness defects on the mechanical behavior of CFRP laminates

One of the most common defects induced during manufacturing of laminates is out-of-plane fibre waviness. This defect significantly affects the mechanical behavior of the laminate and reduces fatigue life and the load capacity of the material. Therefore, it is important to understand the impact of fibre waviness on the performance of composite laminates. In this work, multiple out-of-plane waves have been introduced throughout a Carbon Fibre Reinforced Polymer (CFRP) laminate at different thickness positions. The specimens were tested under tensile loading and an analysis of the surface of the laminate has been carried out by means of Digital Image Correlation (DIC). The results obtained by DIC were able to predict the apparent strain of the laminate quite accurately, as well as locate up to seven undulations at different depths. It was proved that a laminate with multiple wrinkles has 16% less tensile load strength. The results were used to validate different Finite Element (FE) models of the laminate showing a good agreement. These simple models were able to predict the initiation and propagation of failure in both the matrix and the fibre.

Hysteretic performance of foam-infilled corrugated FRP-steel sandwich shear wall

A new foam-infilled corrugated carbon fiber reinforced polymer (FRP)-steel sandwich shear wall (CFSSW) is proposed for steel frame structures subjected to severe wind or seismic loadings. To reduce the excessive out-of-plane buckling deformation of conventional steel plate shear wall (SPSW), corrugated FRP laminates are fixed on both sides of the steel plate (SP). Moreover, to further improve the hysteretic behavior of the shear wall, PET foam is chosen as filler between the corrugated FRP laminates and the steel plate. Three, 1/3 scaled, single-storey shear wall specimens were built by using, as wallboard, the flat steel plate, the steel plate with corrugated FRP laminates (VCP) and the foam-infilled corrugated FRP-steel sandwich plate (VCSP). Experimental tests were carried out under low-cycle horizontal loading to study their shear performance. The results show that the CFSSW structure exhibited clear stress development pattern and stable energy dissipation capacity. Only using FRP corrugated plates as buckling-restraining components, the initial stiffness, ultimate bearing capacity and cumulative energy dissipation of conventional steel plate shear wall can be improved by 22.01%, 13.93% and 49.07%, respectively. The contribution of the infilled PET foam allowed to increase the initial stiffness, bearing capacity and energy dissipation of 28.17%, 36.39% and 105.93%, respectively. Besides, with the restraining effect of only FRP corrugated laminates or both FRP and infilled PET foam, the maximum out-of-plane displacements of the steel plate under shear force were reduced by 67.9% and 92.1%, respectively. Moreover, PET foam can help FRP laminates to effectively bear the shear forces and increased the ultimate shear capacity to 5.9% higher than nominal ultimate shear capacity of the steel plate.

Full-field deformation and failure analysis for compression after impact of carbon fibre reinforced polymer laminates

Residual compressive strength after impact is a critical design factor in assessing damage tolerance of carbon fibre-reinforced polymers (CFRP) for structural applications in aircraft. This study investigated compression after impact (CAI) performance of quasi-isotropic CFRP laminates by measuring 3D deformation and strain using three-dimensional digital image correlation (3D DIC). Before the CAI, these test panels were subjected to drop-weight impact testing with energy levels representing visible impact damage (VID). During the CAI testing, deformation behaviours throughout the full loading sequence were captured by twin-camera imaging systems at the front and back faces of panels at standard speed. A single-camera high-speed imaging system captured ultimate failure behaviours at the sample front face. The single-camera high-speed system used four planar mirrors to achieve 3D DIC measurements. This study investigated the effect of boundary conditions on the compressive behaviours of the test panels, where the effect of additional support plates at the front and back surfaces to reduce the unsupported area was compared with the boundary condition of standard anti-buckling guides. The panels with added supports were found to experience deformations dominated by local buckling and final out-of-plane displacements in an S-shaped profile. These panels also exhibited residual strength reductions correlating to impact damage levels and ultimate failure initiating at the damaged region and propagating rapidly along the transverse axis. In comparison, the panels without added supports exhibited failure dominated by global buckling as manifested by large out-of-plane displacements, which had an arc-shaped profile. The DIC measurements were compared against those of mounted biaxial strain gauges. The single-camera high-speed system was shown not only to be feasible for high strain rate testing applications; it also offered a significant cost saving compared to an equivalent twin-camera high-speed system.

Failure characterisation of sandwich beams using integrated acoustic emission and digital image correlation techniques

The paper presents the experimental study of the failure behaviour of sandwich beams subjected to bending. The samples examined are sandwich beams made of polyethylene terephthalate foam core and glass fibre-reinforced polymer laminate face sheets. In a series of experiments, it has been proposed to integrate diagnostic techniques with acoustic emission and digital image correlation to accurately track the cracking process on the surface as well as in the entire volume of the beam. The research programme carried out allowed observing various modes of failure in composite specimens. The results obtained showed that the integration of acoustic and optical diagnostic techniques provided complementary results and can be used successfully for failure monitoring in sandwich beams.

Flexural Strength of Damaged RC Beams Repaired with Carbon Fiber-Reinforced Polymer (CFRP) Using Different Techniques

In this study, an experimental program was developed to investigate the flexural behavior of pre-damaged reinforced concrete (RC) beams that had been repaired and strengthened using carbon fiber-reinforced polymer (CFRP) laminates under a monotonic load. Two techniques were used: externally bonded reinforcement (EBR) and near-surface-mounted (NSM) reinforcement, to repair and strengthen the tested beams. The experimental program involved casting and testing nine simply supported RC rectangular beams; one beam was considered as the reference beam and did not undergo additional strengthening, and the remaining beams were strengthened using CFRP laminates. These eight beams were divided into two main groups for the purposes of strengthening: beams for which the EBR technique was used, and beams for which the NSM technique was used. The primary variables observed in the EBR and NSM groups included four damage percentages obtained according to the preload (20, 40, 60, and 80%) from the ultimate load carried by the reference beam. The experimental results show that decreasing the damage percentage leads to an increase in ultimate strength from about 3.6% to 17.2% for the beams repaired using the EBR technique and from 27.6% to 57% for the beams repaired using the NSM technique; additionally, the NSM method was more effective than the EBR method in terms of the flexural strength and mode of failure. However, using CFRP laminates enhances the flexure capacity of strengthened RC beams.

Influences of nano-SiO2 on the tensile, flexural, and compressive characteristics of the open-hole carbon fiber-reinforced polymer laminated composites: experimental study

Carbon fiber are of great importance materials exploited in various industrial applications in the recent years. Because of its strong flexural and compressive properties, these fibers have been commonly utilized as a reinforcement for producing polymer composite laminates. Carbon fiber-reinforced polymer (CFRP) laminates are subjected to extreme forces and damaged. In the component assembly of the structures, one of the conventional damages that still occurs on the CFRP laminates is holes that is created on the specimen by drilling tools, which causes a reduction in the laminates’ mechanical strength. One of the suggested ways to strengthen the mechanical properties of composites is to add nanoparticles. Therefore, the impact of silica nanoparticles (nano-SiO2) on the tensile, flexural, and compressive characteristics of the open-hole CFRP laminated composites is experimentally determined in this research. Nano-SiO2 with various weight percentage of 0, 1, 2, 3, and 4 is added into the CFRP. A scanning electron microscope images are used to observe the microscopic structure of the composites. The results showed that adding 1–3 wt.% of nano-SiO2 into the CFRP enhances the tensile, flexural, and compressive strength of the specimens and reduces the fiber pull out and delamination.

A novel bio-inspired microstructure for improved compressive performance of multidirectional CFRP laminates

In this work, we design, manufacture, test and discuss the first bio-inspired microstructural concept to enhance longitudinal compressive performance of multidirectional (MD) Carbon Fibre Reinforced Polymer (CFRP) laminates. To do so, we take inspiration from biologically occurring layered materials; one remarkable example being the anchoring spicula of the deep-sea glass sponge Monoraphis chuni. We designed numerically various concepts and then devised a strategy to reproduce, in a MD CFRP laminate, the characteristic alternation of stiff and soft regions observed in this material, followed by a bespoke procedure to manufacture the laminate. We evaluated their performances by means of small-scale notched compression tests and direct comparison with an industrially relevant baseline laminate. Our results show that the proposed concept led to a statistically significant increase in the failure load and in the average ligament specific stress at failure. Furthermore, the designed microstructure showed potential to delay damage initiation from a stress concentration and to arrest damage propagation. We conclude that the presented microstructural concept is potentially of great value for the design of lightweight structures undergoing compression loading.

Experimental and Numerical Comparative Study on RC Beam Flexurally Strengthened with CFRP Laminate.

In this article finite element model is prepared for reinforced concrete beam which is flexurally held together by means of carbon fiber reinforced polymer laminate. The 3D analysis is conducted using ABAQUS software and the results are investigated, where maximum load, deflection at mid span and strain characteristics of both reinforcement and concrete are analyzed numerically. Later these parameters are investigated experimentally in a similar way by keeping all the important conditions such as loading, reinforcement detailing, boundary condition etc. identical. This comparative assessment illustrates that, the using of CFRP has a significant advantage to improve flexure behavior of RC beams. Various types of failure mode such as deflection and stress for whole cross section and for only reinforcement are achieved from finite element analysis. In addition, typical deflection, stress and strain contours of a specified node are found for unstrengthen and CFRP strengthened beam. This article also represents both the reinforcement strain values and concrete strain values for strengthened and unstrengthen RC beams and found a precise similarity while comparing with finite element modelling results. Furthermore, in terms of ultimate load, the deviation in result is as narrow as 4% for flexurally strengthened reinforced concrete beam by CFRP laminate. IUBAT Review—A Multidisciplinary Academic Journal, 6 (1): 13-24

Research on Energy Absorption Characteristics of Bouligand Biomimetic Structure Based on CFRP Composite Materials

Enhancing the impact resistance performance of carbon fiber-reinforced polymer (CFRP) laminates stands as a prominent research focus among various nations. Existing studies have shown a tendency towards arbitrary selection of the inter-ply helix angle values in CFRP laminates, which is accompanied by a limited number of samples representing the chosen helix angles. However, existing studies have shown a relatively random selection of spiral angle values between CFRP laminates, and the sample size of selected spiral angles is limited, posing certain limitations. In order to tackle this problem, we have employed a systematic arrangement of combinations to select the optimal helix angle for CFRP laminates. Inspired by the biological structures of Bouligand, we have sequentially chosen 19 distinct sets of helix angles, aiming to overcome the inherent limitations and enhance the research outcomes in this field. In this study, we established 19 finite element models to investigate the behavior of Bouligand-inspired CFRP composite panels under high-velocity bullet impact. The models were created by selecting 19 sets of helix angles within the range of 0 to 90° with a 5° interval. The results show that the energy absorption of the Bouligand layer-stacking composite plate is better than that of the conventional plate. The optimal spiral angles of the CFRP laminate are 25° and 30°, and the energy absorption characteristics of the laminate are the best at these angles. The impact resistance is also the best at these angles. The energy absorption of the Bouligand layer-stacking composite plate is 396% higher in absorbed internal energy and 361% higher in absorbed kinetic energy compared to the conventional layer-stacking composite plate, significantly improving the ballistic performance of the CFRP bulletproof material and providing a reference for the design of individual protection equipment.

On the ultrasonic characterization of the stacking sequence of CFRP laminates

Ultrasound in pulse-echo scan mode has already been demonstrated for the extraction of local fiber angle distribution in composite laminates. Depending on the ultrasonic (scan) parameters employed, different sensitivity, spatial resolution, and dynamic depth range can be reached.This study investigates the use of pulse-echo ultrasound testing in different frequency ranges to characterize the in-plane fiber angle distribution and ply stacking sequence in a multi-layer composite laminate. Minimization of the Mumford-Shah functional is performed as an edge-preserving smoothing procedure for the recorded ultrasonic dataset, followed by the application of a Gabor Filter-based Information Diagram approach to extract a 3D tomographic image of the fiber angles. The performance of the method is experimentally studied on ultrasonic datasets, recorded at various center frequencies, of a 5.5 mm thick 24-layer quasi-isotropic carbon fiber reinforced polymer laminate with stacking sequence [+45/0/−45/90]3s. For quantitative analysis, statistical metrics are employed to evaluate the accuracy and precision of the extracted angles over depth, and to better understand the interfering influence of adjacent plies. For the given case study, a 15 MHz ultrasound frequency is recommended as it provides a good balance between precision, accuracy, and depth range. To understand the influence of scan parameters on the fiber angle characterization, the 15 MHz ultrasonic dataset is analyzed for various noise conditions as well as different spatial step size of the scan.