Fiber Reinforced Polymer Laminates Research Articles

Shear Behavior of RC Beams with Corroded Stirrups Strengthened Using FRP Laminates: Effect of the Shear Span-to-Depth Ratio

Abstract Externally bonded reinforcement fiber-reinforced polymer (EBR FRP) laminates have been used around the world for the shear strengthening of reinforced concrete (RC) beams with corroded sti...

Thermal defect characterization and heat conduction modeling during fiber laser cutting carbon fiber reinforced polymer laminates

High-power fiber laser has been proven to be feasible for cutting carbon fiber reinforced polymers with several advantages including noncontact force, high efficiency and flexibility, while the characteristics of thermal damage and heat conduction in materials are not yet fully understood. Continuous-wave fiber laser was applied in this work to cut 2.0-mm-thick carbon fiber reinforced polymer laminates with different layup configurations. The influence of processing parameters including laser power and cutting speed on thermal damage was investigated. The characteristics of various thermal defects on different positions of machined surface were analyzed using high-resolution SEM and mathematical models. Interestingly, swollen fibers were observed and they connected together to form irregular swollen masses. According to further analysis on the initial heat distribution, it showed that cutting speed was the main factor affecting heat accumulation. In addition, modified heat conduction model was developed to analyze heat transfer within unidirectional carbon fiber reinforced polymer laminates in comparison with experimental results, which can be applied to predict heat affect zone during high-power fiber laser cutting composite materials.

Numerical simulation of delamination growth in fiber reinforced polymer laminates using cohesive zone modeling

In this study, the key parameters of cohesive zone modeling, which significantly affect the accuracy in delamination problems, are examined. The study is performed on various standard fracture toughness specimens subjected to mode I, mode II and mixed mode loading. The compressive buckling of a composite laminate is then modeled and the results are validated using virtual crack closure technique. It is shown that the bi-linear interface law with identified parameters provides the best match for the standard fracture toughness specimens while for buckling delamination the effect of interface law shape and interfacial strength is substantial and cannot be ignored.

Effects of resin pre-coating on interfacial bond strength and toughness of laminar CFRP with and without short aramid fibre toughening

The brittle adhesive layer in carbon fiber-reinforced polymer (CFRP) laminates was strengthened by using short aramid fibers in this study. To ensure the feasibility and effectiveness of short aramid fiber interfacial toughening at the interface between the carbon-fiber face sheets, the self-prepared short aramid fibre tissue and the wettability treatment technology with resin pre-coating were applied to enable short aramid fibres to be well embedded in the uneven regions in the CFRP fabrics with fibres oriented at 0° and 90° to form a strong pulling resistance. The ultimate load and the mode I interlaminar fracture toughness have been improved by 75% and 103.9% from the double cantilever beam mode I crack propagation tests, respectively. The reinforcing mechanisms within the “composite adhesive layer” as a result of short aramid fibres are discussed together with detailed scanning electron microscopy observations and comparison test results.

Numerical modeling of deteriorated concrete bridge bent caps with externally bonded CFRP retrofit

Deterioration of old concrete bridge bent caps due to spalling and rebar corrosion is a common occurrence. Carbon fiber-reinforced polymer (CFRP) laminate external retrofit is a viable option for regaining such bent cap capacity and serviceability. In this study, a three-dimensional numerical modeling of significantly deteriorated bent caps from a 78-year old cast-in-place bridge in Forney, Texas, was performed. The purpose was to determine the effectiveness of the repair and strengthening process. Numerical models of the bent caps in the original undamaged, damaged, epoxy mortar repaired and CFRP strengthened states were created and calibrated using strain data obtained from full-scale live load testing. The calibrated model strains showed good agreement with those from the load testing. With short span lengths and deep sections, the model strains were small and the effect of the repair/strengthening at modest levels. The neutral axes of the bent cap sections, found from numerical modeling, moved slightly downward after the repair/strengthening process. The model with no section loss showed the highest tensile capacity, and subsequent levels of concrete spalling resulted in progressively smaller capacity. After the first crack initiation, inelastic behavior set in along with crack opening, which explains the increased rate of strains. Truck live loads were adequately represented in the developed numerical models.

Impact and acoustic emission performance of polyvinylidene fluoride sensor embedded in glass fiber-reinforced polymer composite structure

Smart materials find vital applications in the aerospace industry due to their ability to adapt to surrounding conditions according to design requirements and applicability. Piezoelectric materials are commonly used under the category of smart materials for transducer applications. Among piezoelectric materials, piezo polymer polyvinylidene fluoride (PVDF) is widely used for structural health monitoring (SHM) applications of composite structures, acoustic emission (AE) sensor, accelerometer, strain gauge, pressure sensor, and so on because of its outstanding piezo stress constant ( g 33), piezo strain constant ( d 33), flexibility, and lightweight. In this article, glass fiber-reinforced polymer (GFRP) laminates have been prepared by embedding the PVDF sensor into GFRP for the first time. A detailed study has been done on the behavior and characterization of the PVDF sensor embedded in GFRP. The PVDF sensors embedded in laminates were subjected to impact test, where a constant weight of 5.5 kg was dropped from a height of 10–60 mm in the interval of 10 mm, and the voltage response of the PVDF sensor was recorded. Sensitivity analysis and AE test of the PVDF sensor in GFRP were also carried out. This is useful for various aerospace applications especially for SHM of aircraft.

Reconstruction of cracks in a carbon fiber-reinforced polymer laminate plate from signals of eddy current testing

This article aims to study the quantitative eddy current testing of structures of carbon fiber reinforced polymer (CFRP) material; numerical schemes for forward and inverse analysis of eddy current testing signals are proposed and validated for eddy current testing of the CFRP material. At first, an efficient forward solver based on the database approach is updated to treat anisotropic eddy current problem for efficient simulation of the eddy current testing signals due to crack in CFRP material, and an inversion scheme based on the conjugate gradient method is developed using the updated fast forward solver for sizing defect in a CFRP plate. Second, a hybrid inverse analysis scheme is proposed and implemented to improve the sizing accuracy of crack in a CFRP plate using eddy current testing signals of high frequency. Third, eddy current testing signals due to artificial cracks in a CFRP plate are measured and adopted to reconstruct the profile of the cracks. A good agreement between the true and the reconstructed defect sizes demonstrated the validity of both the fast forward solver and the new inversion scheme for sizing defects in the CFRP plate from eddy current testing signals.

A novel damage characterization approach for laminated composites in the absence of material and structural information

Laminated composites have been increasingly used in structural components. However, transverse impact to a composite laminate can cause initial damage such as notches and delamination, jeopardizing the integrity and safety of composite laminated structures. With this concern, this study proposes a novel damage characterization approach for the identification of initial damage in composite laminates, even in the absence of material and structural information. In particular, starting from the vibration equation of composite laminates, a novel concept of damage-caused force is formulated to characterize damage, and strategies of isotropization and normalization are further integrated to deal with the absence of material and structural information. Thereby, a baseline-free damage index is established using the damage-caused force, by which the presence, location, and size of initial damage in cross-ply composite laminates can be characterized without knowledge of material and structural parameters. The capability of the approach is numerically verified on carbon fiber-reinforced polymer (CFRP) laminates with a notch and a delamination, respectively. The applicability of the approach is experimentally validated by identifying a notch and a delamination in CFRP laminates, respectively. The CFRP laminates are excited by lead-zirconate-titanate (PZT) actuators and scanned by a scanning laser vibrometer (SLV) to acquire high-resolution mode shapes. Numerical and experimental results show that the proposed approach features high robustness to environmental noise and is capable of identifying initial damage in cross-ply composite laminates without prior material and structural information.

Experimental assessment of the performance of reinforced concrete beams strengthened with carbon fiber reinforced polymer laminates

In this study, experimental research is carried out to assess the flexural performance of RC beams strengthened with different amount of CFRP laminates at the tension face. Twelve rectangular RC beams were fabricated and three are un-strengthened and used as reference beams and the remaining nine are strengthened with different amount of CFRP varying from single to triple layers and all are tested to failure under three points bending test. The increase of ultimate strength provided by the bonded CFRP laminates is assessed and failure modes is identified and compared to the un-strengthened RC beams. The results indicated that the flexural capacity of the beams was significantly improved as the amount of the laminates increases that ranged from 20% to 52% increased for single to triple layers laminates. It is concluded that the attachment of CFRP laminates has substantial influence on the performance of CFRP strengthened RC beams. Based on the observed results, recommendations are made that externally application of CFRP laminates can be used for a significant enhancement of the strength deficient RC beams in increasing the ultimate load carrying capacity.
 Keywords: CPRP laminate, Reinforced concrete, ductility, index, epoxy resin, flexural strengthening

Analysis of interfacial stresses in concrete beams strengthened by externally bonded FRP laminates using composite beam theory

Applications of externally bonded fiber reinforced polymer (FRP) laminates retrofitting of existing concrete structures play a key role in ensuring the strength and rigidity of modern buildings design. The determination of interfacial stresses between the FRP laminate and the concrete substrate is important in the design phase in order to predict FRP end debonding failures. In this paper, governing equations that define the mechanics behavior of concrete beams with externally bonded FRP laminates considering the bond-slip relationship between FRP laminates and concrete are derived using composite beam theory and closed-form solutions are presented. Comparisons of the developed model with the published FE model and existing analytical solutions in the literature confirm the feasibility and accuracy of this novel approach. In addition, a parametric study using the developed methodology investigates the effect of various factors on the interfacial behavior of externally bonded FRP for strengthening concrete beams.

Fiber Reinforced Polymer Laminates for Strengthening of RC Slabs against Punching Shear: A Review.

Reinforced concrete flat slabs or flat plates continue to be among the most popular floor systems due to speed of construction and inherent flexibility it offers in relation to locations of partitions. However, flat slab/plate floor systems that are deficient in two-way shear strength are susceptible to brittle failure at a slab–column junction that may propagate and lead to progressive collapse of a larger segment of the structural system. Deficiency in two-way shear strength may be due to design/construction errors, material under-strength, or overload. Fiber reinforced polymer (FRP) composite laminates in the form of sheets and/or strips are used in structurally deficient flat slab systems to enhance the two-way shear capacity, flexural strength, stiffness, and ductility. Glass FRP (GFRP) has been used successfully but carbon FRP (CFRP) sheets/strips/laminates are more commonly used as a practical alternative to other expensive and/or challenging methods such column enlargement. This article reviews the literature on the methodology and effectiveness of utilizing FRP sheets/strips and laminates at the column/slab intersection to enhance punching shear strength of flat slabs.

Study on the Growth and Properties of Electrolessly Deposited Thin Copper Coatings on Epoxy-Based CFRP

In this study, copper coatings smaller than 3 µm were created by electroless deposition on epoxy-based carbon fiber-reinforced polymer (CFRP) laminates for enhancing their electrical properties. This well-known method of metallization was employed with a self-designed combination of reagents, and the coatings were studied to evaluate their physical and chemical properties. A five-stage plating strategy was applied to 40 mm × 40 mm samples, and three different coatings were produced during the work. The metal layers created were studied and characterized to evaluate their, electrical conductivity, thickness, and adhesion to substrates, among other properties. In addition, the growth mechanisms of the microstructure were analyzed in detail for a better understanding of the process. The results showed that the proposed metallization strategy presents good characteristics and is a strong candidate for enhancing the electrical performance of CFRP.

Anchorage systems for reinforced concrete structures strengthened with fiber-reinforced polymer composites: State-of-the-art review

Fiber-reinforced polymer (FRP) composites have been widely used to strengthen the deteriorated reinforced concrete structures due to their outstanding characteristics of light weight, high strength, as well as noncorrosion. A successful strengthening with the FRP composites would equip the existing structures with the prominent improvement in terms of the durability, ductility, and bearing capacity. Current studies indicate that a simple and reliable anchorage system for the FRP composites will help improve the performance of the strengthened structures both efficiently and economically. Up till now, various anchorage systems have been developed for the FRP composites. Therefore, it is necessary to select appropriate anchorage systems according to different needs and establish relevant design specifications. In view of the aforementioned objectives, this paper systematically summarizes the anchoring mechanism of anchorage systems for two commonly used FRP products (FRP laminates and FRP bars) in different strengthened systems. Additionally, a state-of-the-art review as well as the advantages and disadvantages of each anchorage system are presented. Finally, shortcomings in the current state of knowledge and recommendations beneficial to further study are put forward.

A Proposed Soft Computing Model for Ultimate Strength Estimation of FRP-Confined Concrete Cylinders

In this paper, the feed-forward backpropagation neural network (FFBPNN) is used to propose a new formulation for predicting the compressive strength of fiber-reinforced polymer (FRP)-confined concrete cylinders. A set of experimental data has been considered in the analysis. The data include information about the dimensions of the concrete cylinders (diameter, length) and the total thickness of FRP layers, unconfined ultimate concrete strength, ultimate confinement pressure, ultimate tensile strength of the FRP laminates and the ultimate concrete strength of the concrete cylinders. The confined ultimate concrete strength is considered as the output data, while other parameters are considered as the input data. These parameters are mostly used in existing FRP-confined concrete models. Soft computing techniques are used to estimate the compressive strength of FRP-confined concrete cylinders. Finally, a new formulation is proposed. The results of the proposed formula are compared to the existing methods. To verify the proposed method, results are compared with other methods. The results show that the described method can forecast the compressive strength of FRP-confined concrete cylinders with high precision in comparison with the existing formulas. Moreover, the mean percentage of error for the proposed method is very low (3.49%). Furthermore, the proposed formula can estimate the ultimate compressive capacity of FRP-confined concrete cylinders with a different type of FRP and arbitrary thickness in the initial design of practical projects.

Delamination migration in CFRP laminates under mode I loading

This paper focuses on the effect of interfacial fibre orientation and interleaved veil on the delamination migration of carbon fibre reinforced polymer laminates under Mode I loading. Double cantilever beam specimens with midplane interfacial fibre orientations of 0/0, 90/90, 0/90, 0/45 and 90/45 were tested under two conditions: one with interleaved thermoplastic polyphenylene sulfide veil at the midplane and one without. Results show that, except for the 0/0 configuration, all other orientations exhibit varying levels of migration associated with the interfacial fibre orientation and veil interleaving. The apparent fracture toughness determined with the modified compliance calibration method is closely related to the delamination migration and hence a structural energy dissipation measure dependent on interfacial fibre orientation and the interleaved veil. Distributions of the fibre and matrix materials around the delamination front are found to be closely related to the delamination migration behaviour along its path. The experimental observation and rationalisation presented in this paper provide further knowledge regarding delamination migration and its correlation to the apparent fracture toughness, which is of direct relevance to the damage tolerance design of laminated composite components.

Effect of microcapsules addition on impact properties of carbon fiber reinforced polymer and glass fiber reinforced polymer composites

Fiber reinforced composites are ubiquitous in the aerospace and automobile industries due to their significant superior characteristics such as strength to weight ratio, corrosion resistance, fatigue resistance, specific strength and specific modulus. Impact is common kind of damage found in aircraft and automobile structures. The cause of damage may be sudden strike from a bird, falling of tool during servicing or striking of debris during transportation. Hence, predicting the behavior of composites under impact is necessary and also some mechanism to repair these damages should be found. So, this work aims at determining the effect of inclusion of microcapsules containing healing agents on impact behavior of Fiber Reinforced Polymer (FRP) composite. The resin stuffed and hardener stuffed microcapsules were prepared by in-situ polymerization. These capsules of diameter ranging from 0.19 µm to 0.30 µm were mixed in epoxy resin system during the manufacturing of FRP laminates. Experimental investigation was performed under ambient conditions to observe the variation in impact properties of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) composites. It was observed that value of peak load was boosted with addition of capsules and more energy was absorbed during elastic deformation and less during plastic deformation. Also, partial healing was observed due to addition of capsules at 2.5 wt. %.

Alternative Approaches to Predict Shear Strength of Slender RC Beams Strengthened with Externally Bonded Fiber-Reinforced Polymer Laminates

AbstractThe method provided in ACI 440.2R for predicting the shear strength of reinforced concrete (RC) beams strengthened with externally bonded reinforcement (EBR) gives conservative estimates of...

Combined Fuzzy and Genetic Algorithm for the Optimisation of Hybrid Composite-Polymer Joints Obtained by Two-Step Laser Joining Process.

In the present work, genetic algorithms and fuzzy logic were combined to model and optimise the shear strength of hybrid composite-polymer joints obtained by two step laser joining process. The first step of the process consists of a surface treatment (cleaning) of the carbon fibre-reinforced polymer (CFRP) laminate, by way of a 30 W nanosecond laser. This phase allows removing the first matrix layer from the CFRP and was performed under fixed process parameters condition. In the second step, a diode laser was adopted to join the CFRP to polycarbonate (PC) sheet by laser-assisted direct joining (LADJ). The experimentation was performed adopting an experimental plan developed according to the design of experiment (DOE) methodology, changing the laser power and the laser energy. In order to verify the cleaning effect, untreated laminated were also joined and tested adopting the same process conditions. Analysis of variance (ANOVA) was adopted to detect the statistical influence of the process parameters. Results showed that both the laser treatment and the process parameters strongly influence the joint performances. Then, an uncertain model based on the combination of fuzzy logic and genetic algorithms was developed and adopted to find the best process parameters’ set able to give the maximum joint strength against the lowest uncertainty level. This type of approach is especially useful to provide information about how much the precision of the model and the process varies by changing the process parameters.

Расчет усилия обжатия при проектировании усиления железобетонных конструкций внешним армированием с предварительным напряжением

The article provides general information on external reinforcement systems with the use of fiber reinforced polymers (FRP) with prestressing for strengthening of reinforced concrete structures. A classification of existing systems is submitted. The author has performed calculation of the prestressing force taking into account all prestress losses for an externally strengthened reinforced concrete element. Herewith, there were applied steel plates, FRP laminates, based on the methodology set out in SP 63.13330, taking into account the properties of each of the prestressed materials and different levels of initial prestressing.

A Comparative Analytical study of Standard Composite Double Cantilever Beam using Virtual Crack Closure Technique and Cohesive Zone Modelling method

Double cantilever beam specimens made up of Carbon Fibre-Reinforced Polymer laminate (CFRP) and Glass Fibre-Reinforced Polymer (GFRP) laminate were modelled, analysed and their fracture parameters were evaluated using Abaqus-Standard. For the quasi-isotropic specimens, load-displacement responses were computed by varying tensile loads using Virtual Crack Closure Technique (VCCT) and Cohesive Zone Modelling (CZM) method. From the results, it was seenthat modelling effort and computational-time required were quite higher in CZM method. Onset of delamination for both specimens were studied using VCCT after computing energy release rates. Also, the delamination pattern onset was found comparable in both the materials with delay of initiation in GFRP laminate specimen