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The present study deals with fabricating and characterizing glass fiber reinforced epoxy composites with heavy mineral filler (magnetite particles) for potential low-energy radiation shielding applications. The composite materials were fabricated by the hand layup method. Glass/epoxy composite was used as control sample, and radiation shielding composites were manufactured by mixing 20 and 30% (by weight) magnetite particles with epoxy resin. It was revealed that the tensile properties of the magnetite-modified composites were increased, and the composites containing 30% filler exhibited maximum improvement than the control ones. Further assessment of the composite samples was performed by DMA (Dynamic Mechanical Analysis), TGA (Thermogravimetric Analysis), FTIR (Fourier-Transform Infrared) spectroscopy, water uptake (%), and SEM (Scanning Electron Microscopy) testing. The radiation shielding ability of the control and filler-modified composites was assessed by using a gamma (γ) radiation source (60Co). Then, the shielding efficiency was characterized by radiation-reduced intensity (%), LAC (Linear Attenuation Coefficient), MAC (Mass Attenuation Coefficient), HVL (Half Value Layer), TVL (Tenth Value Layer), and SVL (Sixteenth Value Layer). It was revealed that the 30% magnetite filler content composite experienced relatively good attenuation performance against γ-ray than other studied composites. [ABSTRACT FROM AUTHOR]

In recent years, fiber-reinforced plastics (FRPs) materials like glass fiber-reinforced plastic (GFRP) and carbon fiber-reinforced plastic (CFRP) are next-generation polymer-based composite materials tailored for lightweight engineering applications in aerospace, marine, chemical, and automotive industries. Applying inclined holes in GFRP material is essentially used in producing robotic parts, microelectronics components, wind turbine blades, etc. The bending actuators and microhinges of microrobots constructed from CFRP materials also require inclined holes. Laser percussion drilling techniques produce a high aspect ratio of high-resolution inclined holes. The geometrical deviation of the laser-drilled hole is usually evaluated in terms of hole circularity and hole taper. No literature is available for inclined hole drilling of the above two types of FRPs using infrared (IR) laser. In this paper, the thickness of each FRP is taken as 1, 3 and 5 mm, respectively. The one-parameter-at-a-time (OPAT) method was used to analyze the individual effects of laser input parameters, such as pulse current, pulse width, assist gas pressure, workpiece thickness, and incidence angle, on output performance characteristics of hole circularity at top (THC), bottom (BHC), and taper (TH) during laser percussion-inclined drilling with millisecond (ms) pulsed Nd: YAG. Pulse current of 200–225A or 275–300A does not affect THC at a zero-degree angle of incidence. A greater pulse current (300 A) is produced during inclined drilling at 100∘ and 200∘. SEM/EDX investigation reveals hole surface and material composition. [ABSTRACT FROM AUTHOR]

This research paper offers an in‐depth comparative analysis focused on the long‐term durability of shear connectors fabricated from composite materials within a composite and concrete beam structure, extending over a length of six meters. To carry out this evaluation, the experiment employs a four‐point bending test designed to rigorously assess the performance and efficacy of two distinct types of tie straps utilized within the structure. The central element of this investigation, a composite beam integrated within a concrete deck, serves as the primary test specimen, providing a realistic and applicable context for the assessment. The overarching goal of this study is to meticulously examine and compare the resilience and resistance of these shear connectors when subjected to realistic, practical loading conditions. By doing so, the research aims to shed light on the critical performance characteristics of composite shear connectors, especially their role and effectiveness in enhancing the structural integrity and durability of composite and concrete beams in various structural applications. The outcomes of this study are expected to offer significant insights and contribute valuable knowledge to the field of structural engineering, particularly in understanding and improving the performance of composite shear connectors in structural frameworks. [ABSTRACT FROM AUTHOR]

For hard-to-cut materials and composites abrasive water jet machine (AWJM) has been identified as a lucrative and competent material removal technique, in which a high-speed jet of abrasive and water strikes the workpiece surface to erode the desired material. In this paper, the influence of key input parameters (water pressure, standoff distance, traverse rate and abrasive mass flow rate) on responses such as surface roughness (Ra), kerf taper (Kt), and maximum delamination length (Max. DLL) of machined specimen during AWJM of glass fibre reinforced polymer (GFRP) composite is examined through experimental investigations. Response surface methodology (RSM) based central composite design (CCD) approach and Taguchi design based L16 orthogonal array is used for experimentation. Moreover, a hybrid approach of RSM-Desirability and Taguchi Methodology-Grey Relational Analysis (TM-GRA) are used for Multi-response optimization (MRO) and their results are compared for evaluation of process parameters of AWJM on GFRP. Confirmation tests are carried out to validate the experimental results, and they showed that using the RSM-Desirability approach, at the optimum level of parameters, the percentage errors for Ra, Kt, and Max. DLL have been less than 6.312%, 7.229%, and 6.78%, respectively. As per the results Ra, Kt and Max. DLL improves by 12.6%, 14.4% and 73.6% respectively by using RSM-Desirability approach as compared to TM-GRA. The microscopic features of optimally machined surfaces are investigated using the scanning electron microscope (SEM). [ABSTRACT FROM AUTHOR]

The goal of this study was to determine the effect of cutting methods on the edges of selected materials applied in structural elements and floor sheathing of unmanned air vehicles. Three cutting methods for MGS L285 epoxy resin composites used for production of unmanned air vehicles manufactured in one of the European companies were presented. Composites reinforced by glass and aramid fibres are approved for certified production of air vehicle elements (AMC-20). Cutting was applied to each material using different technologies, such as: milling, laser cutting and abrasive water jet cutting. The authors focused on the edge quality of the tested specimens cut using various methods. Quality assessment was based on electronic microscopic scanning images and measurement of the specimen maximum damage. In summary, the choice of an appropriate composite cutting method depends on the type of material and its parameters, and it is crucial for the quality of the machined product. The authors focused on determining the selection of parameters for chosen cutting methods and materials used in the military unmanned aerial vehicle industry. Among the conducted tests, the results indicate that better cutting effects are obtained for milling methods in the case of GFRP + L285 (0.143 ± 0.073 µm) and CFRP + L285 (0.072 ± 0.027 µm), and the worst for AFRP + L285 (0.831 ± 0.269 µm). The water jet method gives the worst results in the cutting zone (results above 0.224 μm). [ABSTRACT FROM AUTHOR]

The work analyzes the fracture topography of composite specimens subjected to three-point bending - static and impact. Scanning electron microscopy was used for this purpose. The tests were performed for two different materials, namely polypropylene and polyamide PA6, each reinforced with unidirectional glass fibers. In one case, the fibers were distributed evenly, and in the other, there were areas more and less reinforced with fibers. It was observed that in all cases the tension and compression parts could be clearly distinguished. However, for different materials and with different methods of destruction, varying failure mechanisms were observed, noted based on the analysis of the fracture topography. It was observed that regardless of the loading method and material, in the tensile part there were visibly protruding fibers, and in the compressed part it was the matrix, rather than the fibers, that was destroyed. In the case of statically loaded samples, damage occurred at the macrostructural level, and in the case of dynamically loaded samples, at the microstructural level. Additionally, the samples with uneven fiber distribution were more susceptible to delamination. [ABSTRACT FROM AUTHOR]

The paper investigates the behavior of glass‐fiber reinforced polymer (GFRP) reinforced concrete columns with integrated steel spirals (hybrid reinforcement). Six concrete columns were tested under eccentric axial loading, resulting in failure due to bending. Columns with outer steel longitudinal bars experienced steel yielding at peak loads, while those with GFRP outer rebars failed due to concrete crushing. The results revealed that using GFRP as outer longitudinal bars led to peak loads 3–10% lower compared to columns with steel rebars. Inner confinement by steel spirals increased the load‐carrying capacity. Additionally, columns with inner tubular steel exhibited greater strength than those with steel spirals, indicating a slightly enhanced confinement effect. A finite element model was developed to analyze structural behavior, considering both material and geometric nonlinearity. The model's accuracy was validated by comparing predictions with test results. Parametric analysis from the nonlinear FE model showed that eccentricity significantly impacted column load‐carrying capacity. Increasing inner confinement area and the number of inner longitudinal bars improved structural stiffness and load‐carrying capacity. Furthermore, a simplified theoretical method was proposed. Comparison between experimental failure loads and theoretical predictions revealed differences within 20%, indicating satisfactory reliability of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of six full‐scale one‐way reinforced concrete slabs with variations in reinforcement detailing. Test specimens consisted of two reference concrete slabs reinforced fully with glass fiber reinforced polymer (GFRP) rebars or with steel rebars and four hybrid‐reinforced slabs. The variables included the arrangement of rebars, mechanical reinforcing ratio, and the ratio of steel rebar area to GFRP rebar area. The fabricated specimens were subjected to four‐point loading until failure in the strong floor laboratory. Experimental results indicated that hybrid reinforcement enhances stiffness compared to FRP reinforcement and provides a higher load‐bearing capacity than steel reinforcement. Also, it was observed that FRP bars placed as tensile reinforcement, similar in number and diameter size to steel bars placed as compressive reinforcement in a slab result in the highest ultimate capacity. Moreover, it was observed that while the mechanical reinforcing ratio contributes to the overall behavior of hybrid‐reinforced concrete slabs, the ratio of steel rebar area to GFRP rebar area is not considerably effective. Furthermore, image processing was employed to determine the exact crack widths of specimens after failure. Finally, finite element modeling results showed good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

The detection of impact and depth defects in Glass Fiber Reinforced Polymer (GFRP) composites has been extensively studied to develop effective, reliable, and cost-efficient assessment methods through various Non-Destructive Testing (NDT) techniques. Challenges in detecting these defects arise from varying responses based on the geometrical shape, thickness, and defect types. Long Pulse Thermography (LPT), utilizing an uncooled microbolometer and a low-resolution infrared (IR) camera, presents a promising solution for detecting both depth and impact defects in GFRP materials with a single setup and minimal tools at an economical cost. Despite its potential, the application of LPT has been limited due to susceptibility to noise from environmental radiation and reflections, leading to blurry images. This study focuses on optimizing LPT parameters to achieve accurate defect detection. Specifically, we investigated 11 flat-bottom hole (FBH) depth defects and impact defects ranging from 8 J to 15 J in GFRP materials. The key parameters examined include the environmental temperature, background reflection, background color reflection, and surface emissivity. Additionally, we employed image processing techniques to classify composite defects and automatically highlight defective areas. The Tanimoto Criterion (TC) was used to evaluate the accuracy of LPT both for raw images and post-processed images. The results demonstrate that through parameter optimization, the depth defects in GFRP materials were successfully detected. The TC success rate reached 0.91 for detecting FBH depth defects in raw images, which improved significantly after post-processing using Canny edge detection and Hough circle detection algorithms. This study underscores the potential of optimized LPT as a cost-effective and reliable method for detecting defects in GFRP composites. [ABSTRACT FROM AUTHOR]

This article investigates the behavior of hybrid FRP Concrete-Steel columns with an elliptical cross section. The investigation was carried out by gathering information through literature and conducting a parametric study, which resulted in 116 data points. Moreover, multiple machine learning predictive models were developed to accurately estimate the confined ultimate strain and the ultimate load of confined concrete at the rupture of FRP tube. Decision Tree (DT), Random Forest (RF), Adaptive Boosting (ADAB), Categorical Boosting (CATB), and eXtreme Gradient Boosting (XGB) machine learning techniques were utilized for the proposed models. Finally, these models were visually and quantitatively verified and evaluated. It was concluded that the CATB and XGB are standout models, offering high accuracy and strong generalization capabilities. The CATB model is slightly superior due to its consistently lower error rates during testing, indicating it is the best model for this dataset when considering both accuracy and robustness against overfitting. [ABSTRACT FROM AUTHOR]

Over the course of many years of use, impingement wear from dust, sand, and other materials can damage wind turbine blades, necessitating repairs and other maintenance work. Recently, wind turbine operators are turning to protective films, which allow such work to be completed more efficiently, as an alternative to the conventional approach of using paint to repair wind turbine blades. However, the erosion resistance characteristics of repaired blades remain unclear. In this study, we create paint- and protective film-coated samples to reproduce repairs, measure their erosion resistance, and study underlying factors in an effort to verify the erosion resistance of repaired materials and associated mechanisms. The low erosion resistance of GFRP can be significantly improved by applying a protective film made of a ductile material. Such material effectively protects the surface of the GFRP. Moreover, the erosion resistance of protective films made from polyurethane material is superior to that of paint. We recommend use of protective film with wind turbine blades when manufacturing blades and regular maintenance. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the nonlinear structural behavior of concrete deep beams internally reinforced with glass fiber-reinforced polymer (GFRP) reinforcing bars and containing a web opening of various sizes and locations within the shear span. Three-dimensional (3D) numerical simulation models were developed for large-scale GFRP-reinforced concrete deep beams (300 mm × 1200 mm × 5000 mm) with a shear span-to-depth ratio (a/h) of 1.04. Predictions of the numerical models were validated against published experimental data. A parametric study was conducted to examine the effect of varying the opening size and location on the shear response. Results of the numerical analysis indicated that the strength of the deep beam models with an opening in the middle of the shear span decreased with an increase in either the opening width or height. The rate of the strength reduction caused by increasing the opening height was, however, more significant than that produced by increasing the opening width. Placing a web opening in the compression zone close to the load plate was very detrimental to the beam strength. Conversely, a negligible strength reduction was recorded when the web opening was placed in the tension side above the flexural reinforcement and away from the natural load path. Data of the parametric study were utilized to introduce simplified analytical formulas capable of predicting the shear capacity of GFRP-reinforced concrete deep beams with a web opening in the shear span. [ABSTRACT FROM AUTHOR]

This paper proposes a technique for detecting impact-induced surface and subsurface fractures in Glass Fibre Reinforced Composites (GFRPs) and hybrid composite materials. Various categories of composite samples, namely Unidirectional GFRP, Bidirectional GFRP, Woven mat GFRP and Carbon-flax hybrid composites are fabricated by the hand-layup process, and cracks are induced in the samples by three-point flexural bending test using a Universal Testing Machine. Near-field microwave Non-Destructive Testing (NDT) is employed in detecting the above cracks by recording the S11 parameter from the microwave transceiver probe throughout the sample. For image rendering the resulting outputs are passed as a 2-dimensional array to the image-rendering algorithms, namely Iterative Curve-Based Interpolation (ICBI), Improved New Edge-Directed Interpolation (INEDI) and the Lanczos algorithm. The most suitable algorithm to identify the clear picture and size of crack is identified, and the effectiveness of Microwave NDT for these composites is analysed. [ABSTRACT FROM AUTHOR]

In coastal regions, the deterioration of structures and bridges due to environmental conditions and corrosion is a significant concern. To combat these issues, the use of corrosion-resistant materials like fiber-reinforced polymers (FRPs) materials, engineered cementitious composites (ECCs), and rubberized ECCs (RECC) shows promise as normal concrete (NC) alternatives by providing increased ductility and energy absorption properties. The effectiveness of confining concrete columns using GFRP tubes with ECC/RECC was assessed in this research by evaluating their performance through compression and push-out tests. The study explored key parameters such as GFRP tube thickness and the presence of shear connectors along the tube height, as well as examining various types of concrete. Additionally, a comprehensive parametric investigation utilizing finite element analysis (FEA) was conducted to analyze how different factors influence the behavior of confined concrete columns. These factors included the effect of GFRP tube thickness and diameter on the overall behavior of different types of confined concretes. The results demonstrate that GFRP tubes significantly enhance column capacity, while the presence of ECC/RECC exhibits even greater improvements in capacity, stiffness, and toughness compared to NC. This approach shows promise in reinforcing coastal infrastructure and addressing corrosion-related concerns effectively. [ABSTRACT FROM AUTHOR]

Highlights Glass fiber reinforced polymer (GFRP) composite tubes have become increasingly popular in crashworthiness applications. On the other hand, square section GFRP tubes are prone to damage in a catastrophic failure mode in the early stages of the crushing process. At this point, triggering mechanisms have great potential to ensure deformation in progressive mode and improve the compression performance of GFRP tubes. Motivated by these facts, this paper aims to optimize the compression performance of square GFRP tubes by implementing notch‐type triggering mechanisms. The effects of notch width, number and length on the axial compression response of tubes were investigated to determine the optimal trigger configurations that would maximize specific energy absorption (SEA) and minimize peak crushing force (PCF). Experiments were conducted based on Taguchi L9 orthogonal array design, and Taguchi coupled Weighted Aggregated Sum Product Assessment (WASPAS) method was employed for optimizing multiple responses. The optimization results revealed that the proposed trigger mechanisms induced progressive crushing by preventing catastrophic failure, thereby significantly improving the compression performance of GFRP tubes. In particular, the results showed that the PCF of intact GFRP tube decreased by up to 38%, while SEA increased by up to 130% with the help of proposed trigger mechanism. The compression performance of square GFRP tubes improved by notch‐type triggering. The notch width, length and number were chosen as design parameters. Taguchi experimental design was used to find the best configuration of design parameters. The optimum configurations were examined through the entropy‐WASPAS approach. The results revealed that significant improvements can be achieved using trigger mechanism. [ABSTRACT FROM AUTHOR]

AbstractDue to its superior performance, the foldcore structure has the potential to replace traditional honeycomb materials. Single-ridgeline V-shaped, double-ridgeline M-shaped, and curved S-shaped foldcore structures were designed based on the principle of origami by controlling areal density. Three foldcore sandwich structures were fabricated from GFRP by hot compression molding method, and PU foam-filled foldcore sandwich structures were also prepared by in-situ foaming. The strength analysis models of the three types of foldcore under out-of-plane compression load were established through differentiation and integration. Subsequently, the quasi-static compression performance and failure modes of the foldcore were investigated through experiments. The analysis model has a certain degree of accuracy in predicting the strength of the structure. It was found that the primary failure mode of V-shaped foldcore under out-of-plane compressive loading was wall buckling. In contrast, the M-shaped foldcore had higher buckling resistance and the failure mode changes from buckling to crushing. S-shaped foldcore had a higher compression strength, and its failure mode changed to wall shear fracture. In addition, lightweight foam filling improved the failure stress of the foldcore. [ABSTRACT FROM AUTHOR]

The current code provisions in ACI 440.11 are based on the flexural theory that applies to slender members and may not represent the actual structural behavior when the shear span-to-reinforcement depth ratio is less than 2.5 (i.e., deep members). The Strut-and-tie method (STM) can be a better approach to design deep members; however, this chapter is not included in the code. Research has shown that STM models used for steel-reinforced concrete (RC) give satisfactory results when applied to glass fiber-reinforced polymer-reinforced (GFRP)-RC members with a/d less than 2.5. Therefore, this study is carried out to provide insights into the use of STM for GFRP-RC deep members based on the available literature and to highlight the necessity for the inclusion of a new chapter addressing the use of STM in the ACI 440.11 Code. It includes a design example to show the implications of ACI 440.11 code provisions when applied to GFRP-RC deep members (i.e., isolated footings) and compares it when designed as per STM provided in ACI 318-19. It was observed that current code provisions in ACI 440.11 required more concrete thickness (i.e., h = 1.12 m) leading to implementation challenges. However, the required dimensions decreased (i.e., h = 0.91 m) when the design was carried out as per STM. Due to the novelty of GFRP reinforcement, current code provisions may limit its extensive use in RC buildings, particularly in footings given the water table issues and excavation costs. Therefore, it is necessary to adopt innovative methods such as STM to design GFRP-RC deep members if allowed by the code. [ABSTRACT FROM AUTHOR]

AbstractStudying the mechanical responses of GFRP and aluminum samples under varying loads is crucial for developing methods to enhance their mechanical properties. This research investigates the impact of z-pinning on single-lap adhesive joints through low-velocity shear impact tests. The study involves testing two types of joints: single-lap adhesive joints and single-lap hybrid pin-adhesive joints with six reinforcing pins, subjected to drop weight tests at load levels of 22.5, 27.5, and 32.4 J. The findings demonstrate that z-pinning can increase the joints’ load-bearing capacity by up to 18.87% and energy absorption by 20.58%. This enhancement is attributed to the additional composite substrate layers in the hybrid joint, which help absorb impact loads. In contrast, in the single-lap adhesive joint, only the layer adjacent to the adhesive bears the impact load. Observations from the tests indicate that in the single-lap adhesive joint, the first composite layer next to the adhesive undergoes complete delamination, whereas in the hybrid joint, all laminates fracture at the steel pins. In summary, this study underscores the significant potential of z-pinning to improve single-lap adhesive joints, providing an innovative approach to enhance their load-bearing capacity and energy absorption. [ABSTRACT FROM AUTHOR]

The main, well-known scientific results were obtained by outstanding scientist Yu. N. Rabotnov in the field of creep theory, hereditary elasticity, damage mechanics, technical theory of shells. However, in the last years of his life, the academician Yu. N. Rabotnov was keen on some problems in the field of mechanics of fiber-reinforced composite materials. He proposed new, original strength criteria, simplified methods for ply-by-ply calculation of composite laminates. One of Yu. N. Rabotnov's scientific passions were connected with description of specific fracture modes of layered fibrous composites having the types of delamination and splitting. On the base of energy fracture criterion, it's possible to estimate the scale effect of strength – the dependence of critical stresses on the absolute sizes of composite members. Such models of specific fracture modes make it possible to estimate the danger of such technological defects as thin polymeric film between composite layers. [ABSTRACT FROM AUTHOR]

The drilling of composite structure leads to its damage, near the peripheral areas of the drilled hole, due to the laminar structure of the composites. The goodness of a drilling process can be evaluated by measuring the extent of the damage caused by it. In the present study, lock-in thermography non-destructive inspection method is proposed to characterise the drilling damages in glass fiber–reinforced polymer panel. A semi-automated image processing methodology is proposed to calculate damage parameters, namely delamination area and size, and delamination factor. The effect of excitation frequency on the damage characterisation is studied to decide the optimum frequency range to measure the damage parameters through signal-to-noise ratio and damage visibility. The damage parameters are measured at optimum frequency. The study showed that the lock-in thermography technique has the potential to characterise drilling damage. [ABSTRACT FROM AUTHOR]

Fiber composite materials are key components of numerous future technologies. This results in a strongly increased demand and also in increasing amounts of waste in the upcoming years. Thus, recycling of fiber composite materials has become an intensively researched topic. At 95 wt %, glass fiber‐reinforced plastics make up the largest part. This review article will provide an overview of the state of the art of common recycling strategies and technologies, with particular focus on the advantages and challenges of glass fiber‐reinforced polymer recycling. [ABSTRACT FROM AUTHOR]

In this research, the effects of imbedding steel wires into the polyurethane foam of GFRP/Foam sandwich panel under three-point bending has been investigated. For this reason, three samples of non-reinforced, reinforced with two wires above and below and reinforced with three wires above and below the foam inside the GFRP sandwich panel were manufactured by vacuum bagging and tested under three-point bending in order to measure the specific strength of each sample. Moreover, a finite element model (FEM) was utilized using the Abaqus/Explicit package to further observe and analyze the stresses inside the samples. The results showed that imbedding steel wire inside the foam of the GFRP sandwich panel increased the bending strength by 25.2% in the two wire and 56.75% in the three-wire sample and bending modulus by 51.8% in two and 86% in three wire sample respectively. Since the weight of the wires with respect to the whole structure in negligible, the specific bending modulus of the sandwich panel was also improved by 21% in two and 44.8% in the three-wire sample. Finally, the results obtained from the experiments showed to have a decent agreement with the simulated model. [ABSTRACT FROM AUTHOR]

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E‐glass fibers are widely preferred due to ease of processing and its low cost, which has substantial scope in the fields of electronics and electrical insulation applications. Because of its low strength and corrosion resistance, use of E‐glass fibers is limited in aerospace and automotive applications. There is a need for enhancing the properties of the composite to overcome such limitations. Therefore, an attempt is made to introduce multi‐walled carbon nanotubes (MWCNT) as fillers into E‐glass fibers to meet the industry needs. In the current study, woven glass fiber of 5 layers and multi‐walled nano carbon fillers of 2, 4 and 6 by wt%, LY556 epoxy resin, and HY951 hardener were used to prepare 4 different type of composites along with the neat epoxy glass fiber reinforced polymer composites (GFRP). The hand‐layup route was used in the composite preparation due to its low cost, technological feasibility, and simple process setup. The developed samples were characterized for mechanical properties via tensile, flexural and impact tests. Tribological characteristics were performed by air jet erosion test. Chauvenet's criterion is applied for identifying the outliers (if any) from the data of repeated test properties. Taguchi's L9OA (orthogonal array) is selected for obtaining optimal hybrid composite, which yield better mechanical properties. Empirical relations are developed for the material properties in terms of process variables. The sample (4 wt% MWCNT) exhibited enhancement of 17.27% in tensile strength, 6% of impact strength and 7.3% of flexural strength when compared with neat epoxy GFRP. This hybrid composite is considered for thermal aging and observed at 60°C, 8% increase in tensile, 7% increase of impact and 15% in flexural strength due to the precipitation on carbon nano tubes along the gain boundaries. The present study recommends 4% MWCNT fillers in developing hybrid glass epoxy polymer composites for use in aerospace, automotive and civil construction industries due to economic and technological feasibility. Highlights: Utilize low‐cost E‐glass fibers in electronics and electrical insulation applications.Improve composite properties for aerospace and automotive industries.Develop hybrid glass epoxy composites with 2 to 6 wt% MWCNT fillers.Examine wear characteristics under air jet erosion and study the impact of thermal aging on mechanical properties.Apply Chauvenet's criterion for outlier identification in measured properties datasets. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive study focused on evaluating the strain generated within short concrete columns reinforced with glass-fiber-reinforced polymer (GFRP) bars and spirals under concentric compressive axial loads. This research was motivated by the lack of sufficient data in the literature regarding strain in such columns. Five full-scale RC columns were cast and tested, comprising four strengthened with GFRP reinforcement and one reference column reinforced with steel bars and spirals. This study thoroughly examined the influence of various test parameters, such as the reinforcement type, longitudinal reinforcement ratio, and spacing of spiral reinforcement, on the strain in concrete, GFRP bars, and spirals. The experimental results showed that GFRP–RC columns exhibited similar strain behavior to steel–RC columns up to 85% of their peak loads. The study also highlighted that the bearing capacity of the columns increased by up to 25% with optimized reinforcement ratios and spiral spacing, while the failure mode transitioned from a ductile to a more brittle nature as the reinforcement ratio increased. Additionally, it is preferable to limit the compressive strain in GFRP bars to less than 20% of their ultimate tensile strain and the strain in GFRP spirals to less than 12% of their ultimate strain to ensure the safe and reliable use of these materials in RC columns. This research also considers the prediction of the axial load capacities using established design standards permitting the use of FRP bars in compressive members, namely ACI 440.11-22, CSA-S806-12, and JSCE-97, and underscores their limitations in accurately predicting GFRP–RC columns' failure capacities. This study proposes an equation to enhance the prediction accuracy for GFRP–RC columns, considering the contributions of concrete, spiral confinement, and the axial stiffness of longitudinal GFRP bars. This equation addresses the shortcomings of existing design standards and provides a more accurate assessment of the axial load capacities for GFRP–RC columns. The proposed equation outperformed numerous other equations suggested by various researchers when employed to estimate the strength of 42 columns gathered from the literature. [ABSTRACT FROM AUTHOR]

The rotor blades of wind turbines are becoming increasingly longer, which increases the diameter at the blade connection. Transport problems are the result, as the rotor blades no longer fit under highway bridges, for example. The increase in diameter can be prevented by increasing the bearing strength of the laminate using fiber metal laminates (FMLs). Individual layers of fiber material are replaced by metal foils in FMLs. This work is focused on the infusion of thick-walled FMLs, with infiltration experiments being carried out in-plane and out-of-plane. For the out-of-plane infusion tests, the metal foils are perforated and it is investigated whether the holes should be arranged alternately or aligned in the metal foils. It has been shown that greater laminate thicknesses can be realized with aligned holes. For the determination of voids and dry-spots, the metal foils are treated with a release agent before infusion and after curing the laminate can be demolded ply by ply. The samples made of glass fiber-reinforced plastic (GFRP) and steel/aluminum measure 500 mm by 800 mm by 20 mm. [ABSTRACT FROM AUTHOR]

Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) offer an alternative to traditional reinforced concrete columns for new construction applications due to their high strength, ductility, and corrosion resistance properties. Despite their popularity, there is a lack of accurate analytical models for the cyclic/seismic performance of CFFT columns. This is due to the absence of precise stress–strain models for FRP tubes and confined concrete under cyclic loading. Previous experiments on CFFT columns suggest that even minimal reinforcement (≤1%) provides essential energy dissipation for extreme events. However, existing stress–strain models for FRP-confined concrete often neglect the contribution of longitudinal and transverse steel reinforcement. While some researchers have proposed material models to address this issue, the analytical modeling of confinement effects from both steel reinforcement and FRP tubes, especially under lateral cyclic loading, continues to pose a significant challenge. This study aims to use previously collected experimental data to evaluate current analytical modeling approaches in OpenSeesPy3.5.1.12 to simulate the lateral cyclic behavior of CFFT columns with ±55° glass fiber-reinforced polymer (GFRP) fiber orientation. Both the lumped inelasticity and the distributed inelasticity modeling approaches are applied. The performance of various FRP confinement models is compared. The effect of plastic hinge length is also considered in the lumped plasticity approach. The findings suggest that integrating a fiber element section into the plastic hinge zone enhances the efficiency of the distributed inelasticity approach. This method accurately captures the non-linear behavior in the critical region and precisely predicts the shape of the hysteretic curve, all while reducing computational costs. Conversely, the lumped inelasticity modeling approach effectively forecasts energy dissipation and peak load values across the entire cyclic hysteresis curve, offering significant computational savings. Finally, a generalized modeling methodology for predicting the response of CFFTs under cyclic lateral load is proposed and subsequently validated using experimental results found in the existing literature. [ABSTRACT FROM AUTHOR]

The goal of this study is to determine the effect of cutting methods on the edges of selected materials applied in structural elements and floor sheathing of unmanned air vehicles. Three cutting methods for MGS L285 epoxy resin composites used for production of unmanned air vehicles manufactured in one of the European companies have been presented. Composites reinforced by glass and aramid fibers are approved for certified production of air vehicle elements (AMC-20). Cutting was applied to each material using a different technology such as: milling, laser cutting and abrasive water jet cutting. The authors focus on the edge quality of the tested specimens cut by various methods. Quality assessment was based on electronic microscopic scanning images and measurement of the specimen maximum damage. In summary, the choice of an appropriate composite cutting method depends on the type of material and its parameters, and it is crucial for the quality of the machined product. The authors focus on determining the selection of parameters for chosen cutting methods and materials used in the military unmanned aerial vehicle industry. Among the conducted tests, the results indicate that better cutting effects are obtained for milling methods in the case of GFRP+L285 (0.143±0.073 µm) and CFRP+L285 (0.072±0.027 µm), and the worst for AFRP+L285 (0.831±0.269 µm). The water jet method gives the worst results in the cutting zone (results above 0.224 µm).

The work analyzes the fracture topography of composite specimens subjected to three-point bending - static and impact. Scanning electron microscopy was used for this purpose. The tests were performed for two different materials - polypropylene and polyamide PA6, each reinforced with unidirectional glass fibers. In one case, the fibers were distributed evenly, and in the other, there were areas more and less reinforced with fibers. It was observed that in all cases the tension and compression parts could be clearly distinguished. However, for different materials and with different methods of destruction, different failure mechanisms were observed, noted based on the analysis of the fracture topography. It was observed that regardless of the loading method and material, in the tensile part there were visibly protruding fibers, and in the compressed part it was the matrix, not the fibers, that was destroyed. In the case of statically loaded samples, damage occurred at the macrostructural level, and in the case of dynamically loaded samples, at the microstructural level. Additionally, samples with uneven fiber distribution were more susceptible to delamination.

Abstract This article investigates the behavior of hybrid FRP Concrete-Steel columns with an elliptical cross section. The investigation was carried out by gathering information through literature and conducting a parametric study, which resulted in 116 data points. Moreover, multiple machine learning predictive models were developed to accurately estimate the confined ultimate strain and the ultimate load of confined concrete at the rupture of FRP tube. Decision Tree (DT), Random Forest (RF), Adaptive Boosting (ADAB), Categorical Boosting (CATB), and eXtreme Gradient Boosting (XGB) machine learning techniques were utilized for the proposed models. Finally, these models were visually and quantitatively verified and evaluated. It was concluded that the CATB and XGB are standout models, offering high accuracy and strong generalization capabilities. The CATB model is slightly superior due to its consistently lower error rates during testing, indicating it is the best model for this dataset when considering both accuracy and robustness against overfitting.

Purpose – This paper comprehensively addresses the influence of chopped strand mat glass fiber-reinforced polymer (GFRP) patch configurations such as geometry, dimensions, position and the number of layers of patches, whether a single or double patch is used and how well debonding the area under the patch improves the strength of the cracked aluminum plates with different crack lengths. Design/methodology/approach – Single-edge cracked aluminum specimens of 150 mm in length and 50 mm in width were tested using the tensile test. The cracked aluminum specimens were then repaired using GFRP patches with various configurations. A three-dimensional (3D) finite element method (FEM) was adopted to simulate the repaired cracked aluminum plates using composite patches to obtain the stress intensity factor (SIF). The numerical modeling and validation of ABAQUS software and the contour integral method for SIF calculations provide a valuable tool for further investigation and design optimization. Findings – The width of the GFRP patches affected the efficiency of the rehabilitated cracked aluminum plate. Increasing patch width WP from 5 mm to 15 mm increases the peak load by 9.7 and 17.5%, respectively, if compared with the specimen without the patch. The efficiency of the GFRP patch in reducing the SIF increased as the number of layers increased, i.e. the maximum load was enhanced by 5%. Originality/value – This study assessed repairing metallic structures using the chopped strand mat GFRP. Furthermore, it demonstrated the superiority of rectangular patches over semicircular ones, along with the benefit of using double patches for out-of-plane bending prevention and it emphasizes the detrimental effect of defects in the bonding area between the patch and the cracked component. This underlines the importance of proper surface preparation and bonding techniques for successful repair. Graphical abstract –

Abstract The current code provisions in ACI 440.11 are based on the flexural theory that applies to slender members and may not represent the actual structural behavior when the shear span-to-reinforcement depth ratio is less than 2.5 (i.e., deep members). The Strut-and-tie method (STM) can be a better approach to design deep members; however, this chapter is not included in the code. Research has shown that STM models used for steel-reinforced concrete (RC) give satisfactory results when applied to glass fiber-reinforced polymer-reinforced (GFRP)-RC members with a/d less than 2.5. Therefore, this study is carried out to provide insights into the use of STM for GFRP-RC deep members based on the available literature and to highlight the necessity for the inclusion of a new chapter addressing the use of STM in the ACI 440.11 Code. It includes a design example to show the implications of ACI 440.11 code provisions when applied to GFRP-RC deep members (i.e., isolated footings) and compares it when designed as per STM provided in ACI 318-19. It was observed that current code provisions in ACI 440.11 required more concrete thickness (i.e., h = 1.12 m) leading to implementation challenges. However, the required dimensions decreased (i.e., h = 0.91 m) when the design was carried out as per STM. Due to the novelty of GFRP reinforcement, current code provisions may limit its extensive use in RC buildings, particularly in footings given the water table issues and excavation costs. Therefore, it is necessary to adopt innovative methods such as STM to design GFRP-RC deep members if allowed by the code.

Abstract E‐glass fibers are widely preferred due to ease of processing and its low cost, which has substantial scope in the fields of electronics and electrical insulation applications. Because of its low strength and corrosion resistance, use of E‐glass fibers is limited in aerospace and automotive applications. There is a need for enhancing the properties of the composite to overcome such limitations. Therefore, an attempt is made to introduce multi‐walled carbon nanotubes (MWCNT) as fillers into E‐glass fibers to meet the industry needs. In the current study, woven glass fiber of 5 layers and multi‐walled nano carbon fillers of 2, 4 and 6 by wt%, LY556 epoxy resin, and HY951 hardener were used to prepare 4 different type of composites along with the neat epoxy glass fiber reinforced polymer composites (GFRP). The hand‐layup route was used in the composite preparation due to its low cost, technological feasibility, and simple process setup. The developed samples were characterized for mechanical properties via tensile, flexural and impact tests. Tribological characteristics were performed by air jet erosion test. Chauvenet's criterion is applied for identifying the outliers (if any) from the data of repeated test properties. Taguchi's L9OA (orthogonal array) is selected for obtaining optimal hybrid composite, which yield better mechanical properties. Empirical relations are developed for the material properties in terms of process variables. The sample (4 wt% MWCNT) exhibited enhancement of 17.27% in tensile strength, 6% of impact strength and 7.3% of flexural strength when compared with neat epoxy GFRP. This hybrid composite is considered for thermal aging and observed at 60°C, 8% increase in tensile, 7% increase of impact and 15% in flexural strength due to the precipitation on carbon nano tubes along the gain boundaries. The present study recommends 4% MWCNT fillers in developing hybrid glass epoxy polymer composites for use in aerospace, automotive and civil construction industries due to economic and technological feasibility. Highlights Utilize low‐cost E‐glass fibers in electronics and electrical insulation applications. Improve composite properties for aerospace and automotive industries. Develop hybrid glass epoxy composites with 2 to 6 wt% MWCNT fillers. Examine wear characteristics under air jet erosion and study the impact of thermal aging on mechanical properties. Apply Chauvenet's criterion for outlier identification in measured properties datasets.