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The use of sustainable natural fibers as reinforcement in polylactic acid (PLA) composites offers a promising approach to developing environmentally friendly and renewable composite materials. This research article explores the impact of weave designs on various mechanical properties of fiber‐reinforced polymeric composite (FRPC) laminates. Four different weave designs, including 1/1 plain, 2/2 matt, 4/1 satin, and 3/1 twill, were developed using flax yarn obtained from the Linum usitatissimum plant. These weave designs were incorporated into composites by wrapping the flax yarn with PLA filament as the matrix, followed by compression molding. The study examines the static and dynamic mechanical properties of the subsequent flax/PLA composites, including flexural strength, Charpy strength, tensile strength, and viscoelastic characteristics like damping factor, loss, and storage modulus. The plain 1/1–reinforced composite exhibits superior tensile strength (12 MPa), tensile modulus (9800 MPa), and flexural properties (29 MPa) due to the higher number of intersection points in the weave design, while in the case of impact strength (6.7 kJ/m2), satin structure‐reinforced composite showed superior properties due to higher float length of warp yarns and lower intersection points in the weave structure. [ABSTRACT FROM AUTHOR]

State‐of‐the‐art organosheets suffer from several shortcomings that limit their applicability in high‐performance materials, mainly due to the imperfect combination of glass fibers and polymer. To overcome these issues, a novel hybrid fiber is presented, in which every single filament consists of a glass core and an individual, thin, thermoplastic polymer coating. Those fibers can immediately be consolidated into organosheets, without the necessity of the critical combination step. Production is realized by an ultra‐rapid inline coating of the filaments, incorporated into a standard spinning system. This solvent‐free process is realized by coating of the fibers with a tailor‐made, monomeric precursor solution, which is radiation‐polymerized immediately after application. Within fractions of a second, the coating layer is thus solidified, before coiling of the hybrid fiber. Due to the very low thickness of the coating and specific formulation of the precursor, tackless layers can be achieved before the coiling, even at industrial spinning speeds. Highlights: Glass fibers are coated with a thermoplast via in situ polymerization.A precursor is developed which polymerizes in 100 ms.Glass fibers are coated completely with thermoplast by using a UV tunnel.Spinning velocities of about 600 m/min can be achieved.Hybrid fibers are consolidated into glass fiber‐reinforced plastics (GFRP). [ABSTRACT FROM AUTHOR]

The properties of unidirectional (UD) composites has been investigated by analyzing their elastic and strength characteristics under shear loading. The UD fiber‐reinforced polymer (FRP) composites usually consist of fibers randomly dispersed throughout the cross‐section in the transverse direction which is generally not accounted for. A micromechanical model based on finite element analysis (FEA) approach is utilized here to examine these properties. The study begins by identifying micro scale unit cells or repetitive unit cells (RUCs) at the micro scale, as well as representative volume elements (RVEs). The distribution of fiber volume fraction (Vf) varies among various micro scale unit cells positioned in the transverse cross‐section. The elastic properties and strength are estimated by considering the properties of the matrix and fibers, and the configuration of micro scale unit cells, which feature a fiber arrangement which is categorized as hexagonal and varying Vf at different locations (from 0.35 to 0.75). However, the overall Vf for the UD composite remains constant at 0.65. Studies are also carried out with the random distribution of fibers at micro scale unit cells. The findings reveal that the random distribution of fibers significantly impacts the shear behavior of the composite. This investigation provides valuable insights into how the mechanical properties of the UD composite are subjective by the distribution of fiber, thereby contributing to the design and development of this light weight high‐performance material. Highlights: Elastic and strength analysis of UD composites is presented.Emphasis is on fiber dispersion in transverse plane.Microscale unit cells, RUCs and RVE are identified.Studies are carried out based on micromechanical model.Influence of fiber distribution on shear behavior is investigated. [ABSTRACT FROM AUTHOR]

In this paper, a new type of foldcore sandwich panel (tentatively called X‐type foldcore sandwich panel) is proposed by combining the X‐type corrugated sandwich panel and the Miura‐ori sandwich panel. The experimental specimens are prepared by using a glass fiber‐reinforced polymer. To systematically reveal the low‐velocity response mechanism and impact resistance of sandwich panels, a hemispherical impactor is used to impact panels. The effects of impact energy, impact position, diameter of tup, and impact mass on low‐velocity impact performance of X‐type foldcore sandwich panels are considered. The damage morphology, response process, and failure mechanism are analyzed under different working conditions. The results show that under the impact of 75 and 125 J, the impact resistance of the node is better than that of the base. Under 200 J impact, the impact resistance of the base is better than that of the node. Compared with the traditional foldcore sandwich panel, the new configuration reduces the impact resistance difference between two positions (node and base). Highlights: A new foldcore sandwich panel is proposed.The impact effect of energy, mass, position, and tup diameter is investigated.Damage morphology, response process, and impact resistance are analyzed.The new structure reduces differences in impact resistance. [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]

Natural fiber‐reinforced polymer composites (NFRCs) are increasingly favored over synthetic fiber‐reinforced alternatives due to their beneficial properties and environmental sustainability. Mechanical properties of composites are critical to ensure optimized utilization of NFRCs. Here, this research explores the effects of different fiber parameters on the tensile strength of high‐density polymer composites reinforced with banana fiber and utilizes the Taguchi method for both experimental and statistical analysis of the outcomes. Three different parameters are considered here: weight fractions, fiber orientation angle, and plasma treatment to fabricate the composites using the compression molding process. Taguchi analysis revealed that fiber orientation angle has the greatest influence among the three variables, with plasma treatment and weight fraction following in impact on tensile strength. The composite that exhibited the highest tensile strength was determined to have a weight fraction of 10%, a fiber orientation angle of 90°, and a plasma treatment period of 5 min. This combination yielded a strength of 30.351 MPa. The analysis of the interaction between any two factors was done using contour plots. In order to compare the experimental tensile strength values with the anticipated values derived from the regression equation, regression analysis was carried out. Highlights: Composites were made up of recycled HDPE (rHDPE) from plastic bottles using a compression molding technique.The Taguchi method is applied to achieve an experimental design employing an L4 orthogonal array.Contour plot analysis is conducted to identify points of minimum and maximum responses, as anticipated from the results.Tensile strength was optimized to a maximum of 30.351 MPa. [ABSTRACT FROM AUTHOR]

Natural fiber‐reinforced composites are gaining significant popularity for their biodegradability and eco‐friendliness. Fiber modifications and hybridization have been used to address issues like hydrophilicity and fiber inhomogeneity. However, efficient manufacturing is still a challenge for natural fiber‐reinforced polymer composites. The present study explores the potential of microwave processing of hybrid laminates composed of sisal and jute fibers. The laminates, consisting of linear low‐density polyethylene (LLDPE) as matrix and sisal and jute as reinforcement materials were subjected to microwave processing at specific power, time, frequency, and loads. Four types of laminates with different stacking sequences: sisal‐sisal‐sisal (SSS), sisal‐jute‐sisal (SJS), jute‐sisal‐jute (JSJ), and jute‐jute‐jute (JJJ) were developed. The developed composites showed ~3% void content, with the SJS and JSJ composite having the least and highest void content, respectively. The SJS composite showed the highest tensile and flexural strength of 15.27 and 20.40 MPa, respectively, out of all the configurations and an improvement of 42% and 85% over pure LLDPE. Hybrid composites having high‐strength fibers in the skin layer exhibited superior mechanical properties. Microscopic examination of the fractured specimens revealed that fiber pull‐out and fiber breakage were the primary failure mechanisms of failure. Lateral failure due to delamination between matrix and fiber was predominant with grip and gauge regions as frequent failure points. The incorporation of sisal and jute fiber reinforcement into the polymers doesn't change the thermal stability of the fabricated composites significantly. The above results show that microwave‐assisted processing is a promising method for producing natural fiber‐reinforced hybrid polymer composites. Highlights: Development of hybrid laminates using microwave energy at 2.45 GHz.The mechanism of microwave‐based processing of polymer composites has been discussed.Effect of layering sequence on mechanical and thermal properties of the developed composite.Assessment of tensile strength with morphology, flexural strength and thermo‐gravimetric analysis. [ABSTRACT FROM AUTHOR]

A growing variety of composites utilize natural plant fibers with naturally occurring veins structured hierarchically in an effort to reduce dependence on petroleum‐based materials. In this article, ramie fibers were extracted by alkaline delignification. Then, ramie fibers and PP matrix, were prepared in filament form and an amino‐silane coupling agent KH550, and maleic anhydride grafted polypropylene were added to improve interfacial compatibility. Ramie fiber/polypropylene fiber‐reinforced polymer composites (FRC) were prepared by hot pressing after using a carding machine. This method preserves the structure and length of ramie fibers to a large extent, thus greatly improving the mechanical properties of the material. After optimization, the FRC prepared from plant fibers of 2 cm length and 60% content had a density of 0.95 g/cm3, showed an increase in tensile and flexural strength of 276% and 339%, respectively, compared to the pure PP matrix. The specific strength of the FRC in the work was higher than galore FRC prepared from talc, carbon fiber, other plant fibers, and so forth. The FRC has a wide range of potential applications due to its own low‐cost, lightweight, and high‐performance, and is highly feasible in replacing the current polymers in the preparation of numerous everyday items. Highlights: The preparation method of FRC resulted in a more complete fiber length and structure.The mechanism to improve the interfacial compatibility of RF and PP is discussed.The effect of varying fiber length on the FRC mechanical properties was investigated. [ABSTRACT FROM AUTHOR]

Ensuring the stability of composite structures in the marine environment is crucial. The harsh and corrosive nature of marine conditions presents unique challenges, making maintenance a top priority. In this study, the impact of seawater aging on the mechanical, buckling, structural, and thermal properties of glass fiber‐reinforced polymer nanocomposites was investigated. Composites were produced using the VARTM method with 2% nano Al2O3 and 2% nano TiO2. Aging was conducted in a seawater environment at room temperature for 120, 240, and 360 days. Mechanical properties, including tensile, compressive, flexural, impact, and buckling tests, were performed, and water absorption was determined. Structural analysis was carried out using SEM images. The experimental results indicated that the presence of nanoparticles minimized the effect of seawater. TiO2 preserved tensile strength by 10.33%, impact energy by 6.8%, and critical buckling load by 3.06% compared to the pure composite. Al2O3 reduced water absorption to 0.594% and preserved tensile strength by 6.67%, impact energy by 4.02%, and critical buckling load by 2%. Thermal test revealed an increase in thermal conductivity with aging, with the TiO2‐doped composite exhibiting the smallest increase (14.66%). The significance of the obtained results was confirmed through ANOVA analysis. Highlights: Glass fiber‐reinforced nanocomposite was produced with nano Al2O3 and TiO2.The effect of seawater aging was investigated.It showed that TiO2 nanoparticles are a good candidate against seawater aging.The experimental results showed statistical significance. [ABSTRACT FROM AUTHOR]

In the past decade, polymer‐based glass fiber‐reinforced laminate composites have gained significant popularity in various mass transit applications, including marine, aircraft, and automotive industries. However, it is crucial to consider the degradation and potential failure of these materials, especially in mass transit networks. To address this concern, fractographic analysis has emerged as a valuable approach for investigating fracture surfaces, extracting vital information, and facilitating the development of new materials. Furthermore, it sheds light on the underlying physical mechanisms that contribute to composite failure. This paper primarily focuses on examining flaws, failure modes, and performing fractography analysis on fiber‐reinforced polymer (FRP) laminate composites subjected to various loading conditions such as tension, compression, flexure, impact, shear, and fracture. Fractography, as an indispensable method, plays a pivotal role in the comprehensive development of composite structures and has become a reliable tool for composite engineers. The outcomes of this study are expected to serve as a foundation for identifying areas that require further investigation in terms of fracture analysis and failure modes specific to FRP composite materials, particularly those used in marine applications. Highlights: Introduction to FRP laminate composites in marine structures.Concise analysis of failure modes in FRP laminate composites.SEM fractography review of FRP laminate composites under varied loading conditions.Comprehensive study on tensile, flexural, impact, compression, shear, and fracture toughness failure modes.Summarization of identified defects in FRP composites. [ABSTRACT FROM AUTHOR]

For fiber‐reinforced polymer structures, the out‐of‐plane stiffness is much lower than the in‐plane stiffness and is extremely prone to damage and instability. The potential of variable stiffness (VS) laminates was explored to enhance the stiffness in the thickness direction. Based on the finite strip method (FSM), a semi‐analytical solution for bending problems of laminates was derived, which is called the variable‐stiffness discrete strip (VSDS) method. By comparing with traditional constant stiffness (CS) laminates, the influence of design parameters of VS laminates on the bending shape and stress distribution of laminates under two load cases were studied. Combining the results of FE models, the accuracy of VSDS has been verified, and the strategy of VS layout configuration design to improve the bending resistance was proved. Highlights: Variable stiffness discrete strips (VSDS) method was presented based on FSM.Bending performances of VS laminates under two load conditions were studied.The method has the ability to reduce the computation cost of bending problems.The solutions of VSDS agree well with the results of FE models.The improvement mechanism of VS laminates on bending resistance was explored. [ABSTRACT FROM AUTHOR]

The study proposed using twisted rope made of flexible fiber‐reinforced polymers (FRPs) instead of wire and synthetic ropes in high load‐bearing and corrosive environments. Finite element model verification and parameter analysis were conducted for the rope, along with deriving theoretical equations for its tensile properties. Increasing the lay length improved model accuracy, with a maximum bearing capacity within a 10% margin of error compared to experimental results. The model length had minimal impact on calculation results, while changes in radial mesh size (0.13 and 0.2 mm) and friction coefficient (0–0.2) greatly affected maximum contact stress. The tensile strength and elastic modulus of the strand remained almost constant (approximately 1142 MPa and 44 GPa) when the friction coefficient was altered. Increasing lay length (6D–20D) enhanced the tensile properties of the strand, whereas tendon diameter (1–3 mm) had negligible impact. Arranging inner and outer strands with the same lay length was better for circular ropes than those with the same lay angle. Inverse lay direction reduced rope torque and increased strand contact stress. Rectangular ropes had higher strength and modulus conversion efficiency, with lower contact stress compared to circular ones. The accuracy of rope equations improved with longer lay lengths, and adding a correction factor for lay length can modify the equation. Highlights: A flexible FRP rope with high strength and twisted form was proposed.The effect of construction factors on the tensile behaviors of ropes was clarified.Equations for calculating the tensile properties of ropes were derived. [ABSTRACT FROM AUTHOR]

The innovative combination of additive manufacturing (AM) and continuous fiber‐reinforced polymer composites (CFRPCs) confers products with the dual advantages of integrated manufacturing and designability of properties, but lack an efficient and reliable method for property prediction. This study presents a materials informatics framework using reduced‐order models and machine learning (ML) to extract the structure–property (SP) linkages between microstructures and macroscopic elastic properties of AM‐CFRPCs. The initial step involves generating microstructural 2D cross‐sections and representative volume elements (RVEs) with random fiber and pore distributions based on the minimum potential method. Then, finite element (FE) calculations are performed on RVEs to obtain nine macroscopic elastic properties. Following that, the quantification and dimensionality reduction of the 2D cross‐sectional dataset are conducted separately using two‐point spatial correlations and principal component analysis (PCA). Finally, a Bayesian optimized composite kernel support vector regression (CK‐SVR) algorithm is used to effectively establish complex mapping relationships between the reduced‐order representations of the microstructures and the mechanical properties. Despite the reduced‐order dataset containing only 3–6 variables, the framework generates an interpretable model exhibiting excellent accuracy with all predicted R2 values surpassing 0.91. Therefore, this framework presents a prospective solution for expediting the design and optimization of AM‐CFRPCs. Highlights: A materials informatics scheme is proposed to predict the 9 elastic properties of AM‐CFRPCs.Microstructures are quantified and dimensionally reduced by two‐point statistics and PCA.SP linkages are established between 2D cross‐sections and 3D macromechanical properties.Modified CK‐SVR exhibits higher prediction accuracy compared to conventional models. [ABSTRACT FROM AUTHOR]

Concrete in coastal areas is susceptible to structural damage caused by corrosion and expansion of reinforcement. Near‐surface mounted (NSM) fiber‐reinforced polymer (FRP) bars have become effective for strengthening damaged reinforced concrete structures. The bonding performance of NSM FRP bars in concrete is a key factor limiting their application and promotion in civil engineering. In this study, the influences of the conditioned environment, such as the chloride salt concentration, immersion time, and bond length of the FRP bar, on the bonding performance were investigated experimentally. First, material properties in a conditioned environment were studied. Subsequently, the failure mode, bond stress–slip curve, and bond strength of the NSM FRP bar in concrete were investigated. Finally, the microstructure and chemical composition of the materials were revealed using scanning electron microscopy and energy‐dispersive spectroscopy (EDS) images of the materials under environmental conditions. The transfer mechanism of NSM FRP bars in concrete with epoxy was revealed. The results showed that the failure modes of the pullout specimens can be divided into epoxy splitting failure and basalt fiber‐reinforced polymer (BFRP) pulling failure. The chloride‐salt concentration was a critical factor affecting the bond properties, and the longer the bond length, the lower the bond strength. The microstructure clearly shows that the degradation of the bonding behavior at the interface of the NSM FRP bar in concrete in a conditioned environment is attributable primarily to the resin damage of the epoxy, resulting in pit corrosion. There was no significant damage to the fibers in the FRP bar, and the degradation was primarily due to resin matrix damage and interfacial debonding. The EDS results showed that the degradation of the epoxy resin and BFRP bars was caused by CO bond and SiO bond fractures, respectively. [ABSTRACT FROM AUTHOR]

In this study, a data‐driven model was developed to predict compressive strength of concrete columns after confining with Fiber‐Reinforced Polymer (FRP). Through application of Response Surface Method (RSM), interactions of input parameters are investigated in addition to their individual influence. Moreover, RSM is utilized in conjunction with unification to enhance model's accuracy. Furthermore, sensitivity analysis is employed together with RSM, to determine the effect size of statistically significant parameters. It is revealed that the real behavior of FRP confined concrete cannot be predicted by single‐parameter studies. Therefore, interaction terms should be included in the model to yield a more accurate prediction. Moreover, the model shows the highest sensitivity to FRP failure strength which this sensitivity decreases as corner radius increases. Therefore, regarding rounded‐corner sections, high improvements are achievable even by utilizing low strength FRPs. It is also shown that higher improvement may be limited due to premature debonding which elastic modulus mismatch between different phases is supposed to be responsible for it. [ABSTRACT FROM AUTHOR]

Strengthening of reinforced concrete (RC) members in bridges and buildings is often required to improve flexural performance. Strengthening using fiber‐reinforced polymer (FRP) composites has become popular as FRPs offer multiple advantages compared with conventional strengthening practices like steel jacketing and concrete enlargement. External bonding (EB) using carbon FRP (CFRP) laminates/fabric has become a common strengthening practice. The effectiveness of the EB strengthened system is reduced due to possible debonding of FRP from concrete substrate. The near‐surface mounting (NSM) of FRP laminates is efficient in reducing the debonding failure, but it is not effective under dominant compression loading. Hybrid FRP (HYB) strengthening combines the advantages of both the NSM and EB techniques. HYB strengthening can enhance the performance of RC members under all loading combinations. The main objective of this study is to understand the flexural crack opening behavior of control and hybrid FRP strengthened RC column members under pure bending. The digital image correlation (DIC) analysis shows that the crack width and its propagation are significantly reduced due to hybrid FRP strengthening. The crack widths measured using the DIC are compared with the analytical predictions based on Eurocode 2 and fib bulletin 90. HYB FRP strengthening increased the strength and post‐cracking stiffness of RC elements under flexure without compromising the ductility. In addition, the HYB strengthening distributed the damage under flexural loading, unlike localized damage observed in control RC elements. [ABSTRACT FROM AUTHOR]

In an era flooded with a multitude of studies investigating the performance of concrete structures retrofitted using fiber‐reinforced polymer (FRP) materials, this review addresses the critical need for a comprehensive overview of the retrofitting of concrete members using near‐surface mounted (NSM)‐FRP composites, aiming to save time and effort while providing engineers and research community with valuable resources relevant to the field. This review focuses on the key factors influencing both the flexural and shear retrofitting processes of reinforced concrete (RC) beams, such as the percentage, type, size and geometry of NSM‐FRP reinforcement, as well as groove design, groove‐filling materials and beam depth. Moreover, the paper explores the failure modes associated with each retrofitting type, for example, debonding failures, shear/flexural failure and rupture of steel or NSM‐FRP reinforcement, to name a few. The review also delves into the bond behavior of NSM‐FRP‐bonded joints, examining factors, such as the bonded length, surface texture of NSM‐FRP reinforcement and type of bonding agent, which would affect the bond behavior and strength of the joints. The failure mechanisms associated with the bonded joints, such as interfacial bond failure, FRP rupture and splitting of the adhesive cover, are also highlighted. Finally, this compilation aims to guide engineers and researchers by offering a critical and comprehensive database for optimal designs, further development and suggesting future research directions. [ABSTRACT FROM AUTHOR]

Nowadays, building structures in corrosive environments requires some considerations. Being lightweight, high tensile strength, and corrosion resistance are the features that make fiber-reinforced plastic (FRP) bars an alternative component for longitudinal steel reinforcement of concrete. On the other hand, the linear elastic behavior of FRP bars, alongside the brittle behavior of concrete, makes brittle members without considerable ductility. In this paper, the effect of compression region confinement with CFRP sheets on the FRP-reinforced concrete beams was experimentally investigated. Eight GFRP reinforced beams with 2 m length, including one reference beam and seven confined beams, were constructed and tested under a four-point bending test. Based on the type of confinement, specimens are categorized into four groups. Flexural behavior improvements, including load carry capacity, energy dissipation capacity, and ductility, were observed in at least one specimen of each confined group. According to the results, the specimen that was spirally confined with a 30 mm ribbon width and angle of 10° had the best total energy absorption up to about 110% improvement in comparison to the unconfined specimen. On the other hand, vertically confined specimens with 50 mm ribbon width showed the highest improvement in ductility indices and load carrying capacity up to 60% and 11% in comparison to unconfined specimens, respectively. Due to concrete compression zone fractures in flexural failure mode, the over-reinforce method is considered the design philosophy. Results indicate that regardless of the confinement type (discrete vertical, discrete spiral, or continuous spiral confinement), there is an optimal amount for width, blank space between ribbons, and depth of confinement to achieve the best flexural behavior. [ABSTRACT FROM AUTHOR]

This review provides an in‐depth analysis of the electrical responses and relaxation behaviors of various polymeric materials including fiber‐reinforced polymer composites, polymer nanocomposites (PNC), and nanofiller‐reinforced polymeric films and coatings using dielectric spectroscopy (DS). The underlying theory of DS, corresponding instrumentation, various dielectric parameters, relevant equations, interpretations, and polarization mechanisms are thoroughly explored. The impact of synthetic and natural fibers and a diverse range of nanofillers on the dielectric responses and relaxation mechanisms of fiber‐reinforced composites, and PNC and films, respectively, are also examined. For each summarized article, we provide an overview of the composite or film preparation, followed by concise explanations of the dielectric behaviors under diverse conditions, including variations in temperature, frequency, moisture levels, fiber/filler ratios, and chemical treatment. In essence, this review contributes to a nuanced understanding of the intricate relationship between material structure, properties, and performance via DS data interpretation across a spectrum of scenarios. [ABSTRACT FROM AUTHOR]

As the weakest link in the shield segment, the reinforcement and repair technology of shield segment joint has received widespread attention. In this study, an finite element model utilizing a cohesive zone model (CZM) was constructed to simulate the mechanical behavior of the shield segment joint during the whole fracture process. The proposed modeling method of joint allows multiple layers of steel bars to be stacked without interference by applying cohesive elements. Cohesive elements were employed to represent the mechanical response of potential fracture surfaces in concrete, as well as the interfaces between steel–concrete and fiber-reinforced polymer (FRP)–concrete, by utilizing various constitutive models tailored for mixed-mode loading conditions. A group of experiments was chosen to assess the precision of the proposed model by comparing the mechanical response and the fracture patterns. Finally, parameter analyses were conducted to study the reinforcement effect of the FRP bonding length and width on the shield segment joint. The results indicate that external bonding of FRP can effectively enhance the bearing capacity and stiffness of shield segment joints. However, insufficient bonding length or width may significantly reduce the strengthening effect and potentially decrease the ductility of the joint. [ABSTRACT FROM AUTHOR]

Behavior of fiber‐reinforced polymer reinforcing bars – Experimental investigation of the stress distribution along the bond length Due to the non‐rusting properties of fiber‐reinforced polymer reinforcement (FRP), it is possible to position this reinforcement close to the surface in components without restricting its durability. In this case, the proportion of the concrete cover remains to ensure the bond. The normative minimum concrete cover is adapted to the bond behavior of reinforcing steel. As the geometry and material properties of FKB vary, their bond behavior is bar‐specific and cannot be equated with that of reinforcing steel. For this reason, the transferability of the minimum concrete cover defined for reinforcing steel to ensure the bond for FRCs must be questioned. To derive a minimum concrete cover, it is necessary to investigate the stress distribution along the bond length. The ring test was developed in the 1990s to experimentally determine the bond stress τ acting along the reinforcing bar and the radially acting internal pressure pi. This article aims at experimentally determining the stress distribution along the bond length for three different FKBs. For this purpose, the ring test is modified so that a (quasi‐)continuous measurement of the bond stress and the internal pressure along the bond length as a function of the pull‐out force is possible. As a result, the different stress distributions are compared and a minimum concrete cover to ensure the bond is derived from the internal pressure. [ABSTRACT FROM AUTHOR]

Very high cycle fatigue (VHCF) experiments are limited in practice due to their long testing times. In ultrasonic fatigue test (UFT) systems, the cyclic oscillation is applied using resonance at 20 kHz with a pulse and pause sequence. However, determining optimal pulse durations to achieve minimal testing time and avoid thermal‐induced fatigue damage in fiber‐reinforced polymer composites remains a challenge. In this work, several fatigue experiments, temperature analyses, and digital light optical microscopy were carried out to evaluate the influence of pulse duration on the fatigue behavior of a carbon‐fiber fabric reinforced in polyether‐ketone‐ketone (CF‐PEKK) composite. A shorter pulse duration with the same pulse–pause ratio as the longer pulse duration is proposed for higher stress amplitudes to avoid any thermal influence during mechanical fatigue without altering the underlying fatigue damage mechanisms. Highlights: The current pulse–pause ratio = 1:6 leads to effective test frequency of ∼3000 Hz.Fatigue strength of the composite is independent of ultrasonic pulse duration.Short pulse duration leads to mechanical fatigue across all cyclic amplitudes. [ABSTRACT FROM AUTHOR]

High specific impact strength and stiffness are demanded in various applications, leading to the widespread utilization of fiber‐reinforced polymers. Synthetic fiber‐reinforced polymers have been used to meet these engineering requirements. However, the current popularity of biocomposites arises from their environmental friendliness, ease of availability, and affordability, making them a favored alternative to synthetic‐based fiber‐reinforced polymers. An assessment must be conducted to determine whether biocomposites can replace their synthetic fiber counterparts, necessitating a thorough investigation into their impact behavior. This study aims to unveil the impact performance of hybrid biocomposites made from unidirectional prepregs comprising flax/polypropylene fibers and nonwoven mats composed of hemp/polypropylene fibers. The impact performance of hybrid biocomposites has also been studied concerning the number of layers and stacking sequence. Eight different designs of biocomposite plates are manufactured through compression molding and subsequently subjected to high‐velocity impact tests. Additionally, numerical simulation using the FEM is utilized to model and analyze the impact behavior of one specimen. The test results indicate that each design possesses unique characteristics and impact behaviors differ. Highlights: Adding prepreg significantly improved mechanical performance in the biocomposites.Performance enhancement varies depending on the stacking sequence.Adding multiple layers of UD prepregs enhances mat impact performance.Numerical simulations validate the Tsai‐Wu criterion for impact testing. [ABSTRACT FROM AUTHOR]

To reveal the durability of fiber‐reinforced polymer (FRP) profiles, which differ from FRP bars due to the clear variations in the internal structure of the fibers. This study experimentally investigated the tensile properties of FRP profiles in the seawater sea sand concrete (SSC) environment at 25, 45, and 60°C. Unidirectional basalt FRP profiles, multidirectional basalt FRP profiles, and basalt and carbon hybrid FRP profiles were considered. SEM analysis was performed to evaluate the corrosion mechanism. Results show that the strength degradation of FRP profiles accelerated with rising ambient temperature due to resin corrosion in hyperthermia. After 63 days of immersion in the SSC environment solution, multidirectional basalt FRP (BFRP) profiles exhibited more severe corrosion than unidirectional BFRP profiles (82.5% and 88.2%, respectively). The hybrid FRP profiles exhibited a strength retention of 86.4%, which was higher than that of multidirectional BFRP profiles due to the superior alkali resistance of carbon fibers compared to basalt fibers. In addition, prediction models of FRP profiles based on the Arrhenius relation were proposed with a high correlation coefficient of R2. Highlights: Durability of FRP profiles in SSC environment was studied.Basalt and carbon fibers hybrid reinforced multidirectional polymer profiles.Corrosion mechanism of FRP profiles was revealed.Tensile property prediction model of FRPs in SSC environment was proposed. [ABSTRACT FROM AUTHOR]

This study examines the influence of weathering aging on the mechanical properties and durability of flax fiber‐reinforced polymer composites (FFRP) intended for outdoor applications. Employing an accelerated weathering environment replicating natural outdoor conditions, encompassing UV radiation, condensation, and water spray, the FFRP samples with 2 and 4 mm thicknesses underwent exposure durations of 0, 500, 1000, and 1500 h. Mechanical tests characterized tensile, flexural, and inner‐plane shear properties, while a custom‐made apparatus measured the long‐term tensile creep behavior. Additionally, scanning electron microscopy allowed for the observation of microscopic changes in fiber and matrix. The findings illustrate a consistent decline in tensile and flexural properties with increased weathering exposure, resulting in reductions of 17% and 38% in the tensile strength and modulus, and 24% and 52% in the flexural strength and modulus after 1500 h. Intriguingly, inner‐plane shear strength exhibited a slight increase after 500 h before a subsequent decrease. Furthermore, samples with the same thickness demonstrated an increased creep development with longer weathering durations. Despite this, the mechanical degradation rate induced by weathering was comparatively slower for thicker samples. Overall, the diminished mechanical properties of FFRP post‐weathering can be attributed not only to the polymer but also to the substantial role played by flax fibers in this process. Highlights: UV weathering degrades the mechanical properties of flax/polyester composites.Both the instantaneous elastic properties and the long‐term creep behavior are affected by weathering.Thickness influences the mechanical degradation of the composites caused by UV weathering.SEM confirmed UV‐water weathering resulted in the degradation of both natural fiber and polymer matrices. [ABSTRACT FROM AUTHOR]

The current research study centers on exploring natural fibers due to the increasing need for sustainable and eco‐friendly alternatives in various industries. In India, where coconut trees are widely grown for their tender coconuts and by‐products, the leftover fruit leaf stalks become agricultural waste once the coconut is harvested from the trees. So this research work involves the development of composite materials with natural fiber components by using unsaturated polyester resin (UPR) as the matrix material along with alkali‐treated coconut tree secondary flower stalk fiber (ACSF) for reinforcing. The composite materials were formed using the compression molding technique with different weight compositions of 20%, 30%, and 40% of ACSF and 80%, 70%, and 60% of UPR, respectively. From the results, the 30ACSFC reveals a maximum value of 42 N/mm2, 58 N/mm2, 10 kJ/m2, and 48 HD in flexural, tensile impact, and hardness tests, respectively. In the water absorption analysis, 20ACSFC had observed a lower moisture content, which explains the low weight percentage of ACSF in the composite. From the TGA analysis, 30ACSFC had a residual mass of 18% due to the significant change in the cellulose because of alkali, leading to strong adhesion in the composition matrix. The SAC analysis reveals that at the peak and trough levels of frequency, varying the composition of composite materials leads to improved sound absorption coefficients that surpass the performance of the 30ACSFC composite. The SEM study was carried out to identify the mechanism of failure in the elongated specimens of the tensile test, which was based on the phenomena of matrix crack, fiber pull‐out, fiber shearing, void and interfacial bonding, and de‐bonding. These results indicate the possibility of creating lightweight composites with improved strength and stiffness, making them suitable for use in roof panels, door panels, insulation, and other related applications. The incorporation of ACSF as a reinforcing material introduces new prospects for sustainable and environmentally friendly composite materials, showcasing promising mechanical and thermal properties. Highlights: Enhanced mechanical strength: Evaluation of tensile strength, flexural strength, and impact resistance showcases how ACSF reinforcement improves the composite's load‐bearing capacity and durability.Effective acoustic dampening: A study of sound absorption and transmission properties reveals the composite's potential in noise reduction applications, such as architectural acoustics and automotive soundproofing.Thermal insulation potential: An assessment of thermal conductivity and expansion helps identify whether the composite is suitable for applications requiring enhanced insulation or efficient heat transfer.Moisture resistance and stability: An analysis of moisture absorption and dimensional changes informs the composite's suitability for humid environments, ensuring its resistance to degradation and maintaining the dimensional stability. [ABSTRACT FROM AUTHOR]

The objective of this study is to establish a conceptual framework for fiber-reinforced polymer composite (FRPC) panels designed for structural purposes through the incorporation of a third phase (fillers). The present investigation was aimed to design and fabricate 3-phase polymer composite panels that offer enhanced thermal insulation and strength while maintaining low material and labor expenses. Two types of fibrous reinforcements (jute fabric and glass fabric) of different origins were used as reinforcement; polypropylene (PP) was used as the matrix, and microcrystalline cellulose (MCC) was used as particle reinforcement material. The composite materials were fabricated with different MCC concentrations (0, 2 wt%, and 4 wt%), using a hot compression molding technique. It was found that MCC helped to enhance the mechanical performance of the composite panels, while the thermal conductivity showed a slight reduction due to lower concentrations of MCC used. For polypropylene/glass (PPG) composites, thermal conductivity was reduced from 0.214 to 0.193 W/m·K by the addition of 4% MCC fillers. Similarly, for polypropylene/jute (PPJ) composites, it was reduced from 0.14 to 0.126 W/m·K by 4% MCC fillers. The Charpy impact strength of both PPG and PPJ composites was enhanced by the addition of fillers, and the effect was more significant in the case of PPG (increased from 24.83 to 43.98 kJ/m2 for 4% fillers). Cost analysis of the composite panels was also done, showing PPJ panels to be slightly cheaper as compared to PPG. The findings indicate that the developed composite panels have the potential to serve as partitioning as well as the outer shield of the building due to their effective thermal and mechanical properties. [ABSTRACT FROM AUTHOR]

This paper presents the findings of a large‐scale experimental study that focus on assessing structural behavior of reinforced concrete (RC) cantilever slabs with carbon/epoxy fiber‐reinforced polymer (CFRP) composite strips using a near‐surface‐mounted (NSM) approach. The NSM/CFRP system evaluated in this study was implemented in strengthening the shoulders of the Slide Canyon Bridge in California, USA. The experimental phase is divided into two main parts: (i) determining the design parameters for NSM, including the bondline strength through pull‐out tests, and (ii) conducting a practical evaluation of the bending behavior of original and retrofitted RC cantilever slabs, each with varying NSM reinforcement and three different development lengths. Results of this study indicated that the use of NSM‐CFRP has a considerable benefit in that it significantly improves ductility and changes the failure mode of the unstrengthened RC slab from the typical brittle shear‐based failure mode to a more ductile flexural‐based failure mode. The large‐scale slab specimens' performances, which had different development lengths, showed little variance, except for the slab specimen with a development length of 457.0 mm that exhibited an appreciable flexural stiffness as compared to other specimens evaluated in this study. In order to simulate the serviceability and ultimate behavior of the RC slab specimens, linear and nonlinear finite element analyses were performed. A satisfactory agreement between numerical and experimental results was achieved especially at load level prior the initiation of large‐size cracks. [ABSTRACT FROM AUTHOR]

This study presents new neural‐network (NN)‐based models to predict the axial load‐carrying capacities of fiber‐reinforced polymer (FRP) bar reinforced‐concrete (RC) circular columns. A database of FRP‐reinforced concrete (RC) circular columns having outside diameter and height ranged between 160–305 and 640–2500 mm, respectively was established from the literature. The axial load‐carrying capacities of FRP‐RC columns were first predicted using the empirical models developed in the literature and then predicted using deep neural‐network (DNN) and convolutional neural‐network (CNN)‐based models. The developed DNN and CNN models were calibrated using various neurons integrated in the hidden layers for the accurate predictions. Based on the results, the proposed DNN and CNN models accurately predicted the axial load‐carrying capacities of FRP‐RC circular columns with R2 = 0.943 and R2 = 0.936, respectively. Further, a comparative analysis showed that the proposed DNN and CNN models are more accurate than the empirical models with 52% and 42% reduction in mean absolute percentage error (MAPE) and root mean square error (RMSE), respectively involved in the empirical models. Moreover, within NN‐based prediction models, the prediction accuracy of DNN model is comparatively higher than the CNN model due to the integration of neurons in each layer (9‐64‐64‐64‐64‐1) and embedded rectified linear unit (ReLu) activation function. Overall, the proposed DNN and CNN models can be utilized as paramount in the future studies. [ABSTRACT FROM AUTHOR]

Digital image correlation (DIC) and finite element analysis (FEA) are used to assess the cylindrical spool-shaped ASTM D7291 and I-beam-shaped specimens for through-thickness (TT) mechanical characterization of thick (25 mm) fiber reinforced polymer matrix composites. The composites are made of E-glass woven fabrics reinforcing a vinyl ester matrix. DIC full-field measurements and FEA showed a rather uniform strain distribution within the gage section of the ASTM D7291 specimen. However, strain concentrations are revealed at the bondlines between the end-tabs and the test specimen, in addition to strain gradients at the curved section of the specimen. DICmeasured and FEA-predicted strain fields of the I-beam specimens exhibited a region of uniform strain distribution within the gage section larger than that of the ASTM D7291 specimen. Nevertheless, high stress concentrations at the fillet (curved flange-to-web transition) regions and some amount of web bending occur in the I-beam specimen. Beyond providing the TT mechanical properties of the E-glass woven/vinyl ester composites, the current work discusses advantages and caveats of both promising specimens, providing quantifications of stress concentration factors and length of zones were strains and stresses may be considered uniform. Highlights • Stress/strain distributions of through-thickness tensile specimens are evaluated. • The main drawback of the spool-shaped specimen is adhesive failure. • The modified I-beam specimen shows acceptable stress concentration factors. • The modified I-beam is adequate for strength and Poisson ratio characterization. • I-beam specimens are easier to manufacture and do not require adhesive joints. [ABSTRACT FROM AUTHOR]

Optimizing the high‐temperature energy storage characteristics of energy storage dielectrics is of great significance for the development of pulsed power devices and power control systems. Selecting a polymer with a higher glass transition temperature (Tg) as the matrix is one of the effective ways to increase the upper limit of the polymer operating temperature. However, current high‐Tg polymers have limitations, and it is difficult to meet the demand for high‐temperature energy storage dielectrics with only one polymer. For example, polyetherimide has high‐energy storage efficiency, but low breakdown strength at high temperatures. Polyimide has high corona resistance, but low high‐temperature energy storage efficiency. In this work, combining the advantages of two polymer, a novel high‐Tg polymer fiber‐reinforced microstructure is designed. Polyimide is designed as extremely fine fibers distributed in the composite dielectric, which will facilitate the reduction of high‐temperature conductivity loss for polyimide. At the same time, due to the high‐temperature resistance and corona resistance of polyimide, the high‐temperature breakdown strength of the composite dielectric is enhanced. After the polyimide content with the best high‐temperature energy storage characteristics is determined, molecular semiconductors (ITIC) are blended into the polyimide fibers to further improve the high‐temperature efficiency. Ultimately, excellent high‐temperature energy storage properties are obtained. The 0.25 vol% ITIC‐polyimide/polyetherimide composite exhibits high‐energy density and high discharge efficiency at 150 °C (2.9 J cm−3, 90%) and 180 °C (2.16 J cm−3, 90%). This work provides a scalable design idea for high‐performance all‐organic high‐temperature energy storage dielectrics. [ABSTRACT FROM AUTHOR]

The performance of natural fiber‐reinforced polymer composites (NFRPCs) can be markedly affected by fiber length, to the extent that a sole mean value and standard deviation fail to accurately represent its overall dispersion. Hence, measuring the variability of fiber length is crucial to comprehend its influence on the properties of the resulting composites. Unfortunately, few studies have been conducted on this topic. This work consisted of two research stages: the first related to the effect of both fiber length distribution and processing temperature on the properties of oil palm empty fruit bunch (OPEFB) fiber‐reinforced vinyl acrylic composites, while the second stage analyzed the influence of the fiber length distribution on the material performance under accelerated weathering tests. Broadly, composites were characterized by tensile mechanical testing, optical microscopy and SEM, FTIR spectroscopy, TGA, and microbiological analysis. The key results showed that processing the material at temperatures surpassing 75°C did not lead to a homogenous phase between the components, rendering it unworthy of consideration. Furthermore, composites containing the longest OPEFB fibers exhibited the lowest elongation‐at‐break values. Regarding the incidence of aging treatments, pronounced effects were observed in those composites exposed to UV radiation and salt fog. In detail, the elongation at break decreased by up to 34%, while the tensile strength increased by up to 1 MPa, and Young's modulus rose by up to 17%. Finally, two fungal genera, Fusarium sp. and Rhizophydium sp., were identified on the OPEFB fibers; nevertheless, no fungal growth was observed on the composites. Highlights: Natural reinforcement/filler size measured as fiber length distribution.Effect of fiber length distribution on composite performance.Composite performance after accelerated weathering tests. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the hysteretic performance of prestressed concrete beams with aramid fiber‐reinforced polymer (AFRP) tendons. Eight beams were constructed and tested under cyclic loading, with test variables covering the type of prestressing tendons (AFRP and steel), the ratio of internal tendons to external tendons (3:0 and 1:2) and the bond condition of internal tendons (fully bonded, partially bonded, and unbonded). Results showed that the failure of all the beams was dominated by concrete crushing and nonprestressed rebars rupturing at pure bending sections. AFRP prestressed beams exhibited commensurate bearing capacity, displacement ductility, energy dissipation and residual deformation with steel prestressed beams. The combination of internal and external tendons, and using unbonded or partially bonded tendons could improve the ductility of AFRP prestressed beams. Additionally, the finite element (FE) models of AFRP prestressed beams were developed using ABAQUS based on the coupling method under the local coordinate system. The simulated results closely matched the experimental results in terms of the failure mode and load–displacement curve. Parametric predictions, including the unbonded length of AFRP tendon, partial prestressing ratio, jacking stress and concrete strength were presented to extend the experimental works. [ABSTRACT FROM AUTHOR]

Interfacial stress concentrations at fiber‐reinforced polymer (FRP) ends can easily cause premature debonding failure of FRP‐strengthened beams. To solve this problem in narrow beams, a hybrid strengthening method was proposed in our previous study, but the theoretical stress analysis was lacking due to the complexity at the anchorage zone. In this study, the interfacial stresses of the hybrid strengthened beam were initially analyzed by decomposing it into a purely bonded beam under three different effects, including the load on the beam, the tensile force at the end of the FRP strap released from anchor plates and a pair of eccentric forces induced by the side anchorage system towards the midspan. By summing the special solutions of the three cases, the expressions for the total interfacial stresses of a hybrid strengthened beam were determined. Moreover, a formula for the shear stiffness of the side anchorage system was proposed, in which the side plate and the bolt were compared to a deep cantilever beam and an elastic foundation beam, respectively. Finally, a finite element model was developed to verify the applicability of the proposed theoretical model. The theoretical and simulated results were in satisfactory agreement for a hybrid strengthened beam. [ABSTRACT FROM AUTHOR]

With the advancement in the concrete technology, the application of precast concrete elements in the buildings and road infrastructures is increasing very rapidly. One of such applications is the use of precast hollow concrete elements in the bridge construction. As the conventional steel reinforcement is highly susceptible to corrosion, the use of non‐corrosive reinforcement in precast hollow concrete piers and piles of bridges could be a good option for the durability of bridge structures., In this regard, hollow concrete columns reinforced with fiber‐reinforced polymer (FRP) have been considered as a potential solution to overcome the structural deterioration due to corrosion. In the past, limited studies have been carried out on hollow concrete columns reinforced with FRP, consequently, the behavior of such columns is not fully understood. Therefore, to comprehensively evaluate the behavior of hollow concrete columns for various design parameters, a finite element model (FEM) was developed in this study using the commercial tool "Abaqus". The model was developed and verified based on the experimental results of studies conducted by two independent research groups on circular concrete columns. The proposed model well predicted the peak loads with an error less than 10% and the failure modes of the tested columns. The verified constitutive relation and establishing method were further employed to conduct parametric evaluations to observe the influence of different parameters, such as inner‐to‐outer diameter ratio, longitudinal reinforcement ratio, lateral reinforcement ratio, and concrete strength, on the behavior of hollow concrete columns. Parametric analyses show that reduced inner‐to‐outer diameter ratio and larger longitudinal or lateral reinforcement may lead to higher peak load and confined concrete strength. Finally, based on the experimental and FEM evaluations, the strength prediction equations were developed for the analysis and design of hollow concrete columns reinforced with GFRP bars. [ABSTRACT FROM AUTHOR]

Employing the laser ultrasonic system, information on fatigue evolution can be captured and explicitly stored in the frequency‐wavenumber wavefield of the guided wave. This paper presents a deep‐learning architecture for processing the frequency‐wavenumber wavefield, which comprises two distinct steps: fatigue characterization and evolution prediction. Firstly, the fatigue characterization step employs a convolutional autoencoder (CAE) for compressing the frequency‐wavenumber wavefield and a fully connected network (FCN) for obtaining the fusion fatigue characteristic. Due to the high cost of experimental samples, extensive simulation‐generated wavefields are used to pre‐train the network. Subsequently, the fatigue evolution prediction model based on the latent ordinary differential equation (Latent‐ODE) is trained for the step‐by‐step prediction of fatigue evolution with a small amount of composite fatigue test data. The results validate the effectiveness of the deep‐learning architecture in characterizing fatigue and predicting its evolution, as well as the feasibility of the frequency‐wavenumber wavefield compression of guided wave. Highlights: The deep‐learning architecture for fatigue evaluation and prediction is proposed.The frequency‐wavenumber wavefield of guided wave is fused for fatigue evaluation.The fatigue evolution prediction is achieved using the Latent‐ODE model.The fatigue life of the composite specimen is predicted. [ABSTRACT FROM AUTHOR]

The injection molding market is expected to grow with the increasing demand from various industries, such as automotive and furniture. However, weld lines in the injection molded part reduce the structural strength and affects its appearance. This study evaluates the effect of the weld line on the structure by shifting the position of the weld line outside the area where the load is applied by manipulating the opening time of the injection gates. We examined the effect of weld lines on the strength of a chair through coupled resin flow and structural analyses. The analysis revealed that the position of the weld lines is crucial for structural strength if the knockdown factor (KDF) is low. Additionally, controlling the opening time of the gate and shifting the position of the weld line improved the structure's appearance, number of weld line and avoid the lower meeting angle. However, depending on the material, the effect may be weak. For example, when the weld line location did not change much despite changing the gate timing, little change was observed in the number of weld lines. Hence, the improvement strategy of weld line should be considered for material types and strength. Highlights: Injection molding growth driven by automotive, packaging, furniture demand.Weld lines impact structural strength and appearance.Shifting weld line position outside load area improves the structural appearance and strength.Effects of shifting weld line position depended on the material types.Weld line position is crucial for low knockdown factor and affects strength. [ABSTRACT FROM AUTHOR]

Fiber‐reinforced polymer (FRP) composites are widely used in the aerospace and automotive industries due to their high strength‐to‐weight ratio. However, the manufacturing process of FRP composites is intricate, requiring precise control over multiple parameters, which can be challenging. To ensure top‐notch product quality and bolster confidence in the durability of composite materials, it requires a uniform curing evaluation technique and a predictive strength model. This study presents a rapid nondestructive quality inspection technique for composites, involving three distinct studies that employ machine learning techniques in combination with the frequency‐dependent dielectric response of materials. The first study introduces a nondestructive method for swiftly inspecting the cure state (degree of cure) of composite samples. This technique combines broadband dielectric spectroscopy with supervised machine learning algorithms, particularly support vector machines. The second study employs advanced artificial neural networks like multi‐layer perceptron to predict the tensile strength, a measure of mechanical performance, of composite materials. The results demonstrate an accurate classification of the curing state with 96.7% accuracy and a prediction of tensile strength with 87.5% accuracy. The final study explores the application of machine learning in quality monitoring of prepreg (raw materials for FRP) aging at room temperature. Highlights: Integration of machine learning with frequency‐dependent dielectric measurement offers efficient method for inspecting and monitoring the curing state and mechanical performance of composite materials.Machine learning and frequency‐dependent dielectric response used to accurately assess the curing state of fiber‐reinforced polymer composites with 96.7% accuracy, which saves the time and effort and also reduces the need for destructive testing.Advanced artificial neural networks, specifically multi‐layer perceptron, employed to predict mechanical performance of composite materials with 87.5% accuracy, enhancing confidence in product reliability.Novel dielectric measurement technique integrated with machine learning algorithms enables prepreg age monitoring at room temperature. [ABSTRACT FROM AUTHOR]

Void fraction and fiber volume fraction (FVF) are among the most important parameters determining the quality of fiber‐reinforced plastic products. Most of the voids in liquid composite molding–manufactured composites are directly related to the viscous matrix (resin) flow through the porous medium (fiber) during impregnation. In this investigation, a different method, resin spray rather than injection was used to reduce the resin's flow path, which resulted in low void content and higher FVF. The resin was sprayed on the surface of the preform, and compaction was applied to infiltrate the resin towards the thickness. Sample laminates were manufactured, and computer tomography scanning was applied to diagnose void content and laminae quality. The images collected from the scanner were analyzed using ImageJ software. Effects of compaction pressure and compaction speed were characterized. According to the investigation, compaction speed was the key factor in determining a laminate's void content. Only 1.5% void fraction was integrated with a compaction speed of 1 mm/min and a compaction pressure of 100 KPa. On the other hand, compaction speed has less of an impact on a laminate's FVF. Highlights: The void fraction of a composite is reduced via the spray and compaction method.Fiber volume fraction is not much affected by compaction speed.Slow compaction speeds minimize void content.Spray compaction is a low‐cost manufacturing method. [ABSTRACT FROM AUTHOR]

The application of fiber‐reinforced polymer (FRP) composite materials and structures in various industrial sectors is expanding significantly to meet the rising demand for efficient, reliable, and functional building materials. Using FRPs can be an excellent strategy for enhancing railway structures and equipment because of their high strength‐to‐weight ratio, tailorable mechanical properties, and suitable long‐term characteristics. However, the railway industry appears to be hesitant to adopt composite materials compared to other transportation sectors like aerospace. It seems that there is still a long way to go before FRPs reach their full potential in railway applications. The goal of the current study is to explore the current uses of FRPs in the railway industry and the significant challenges, obstacles and difficulties that must be overcome to put FRP‐based concepts into practice for structural and rail vehicle applications. Highlights: Applications of FRPs in railway vehicles and rail lines are reviewed.Main challenges for utilization of FRP in railway industry are studied.Future trends and applications of FRPs in the railway sector are introduced. [ABSTRACT FROM AUTHOR]

Dried leaves are the outstanding origin of cellulosic plant matter, and it is securing reputation as a renewable resource. Dried leaves fiber is suggested to possess the capability to substitute synthetic fibers in polymer laminates as a reinforcing component. The novelty of the present study reveals the effect of dried leaves fiber, cobalt, nickel, and ferrous reinforcement on the physical, mechanical, and thermal characteristics of epoxy, vinyl‐ester, and polyester polymers using artificial neural network (ANN) technique. These composites were fabricated using ultrasonication bath‐assisted wet layup method under ambient condition. The outcomes of this research exhibit that the dried leaves‐cobalt fillers reinforced in all three polymers possess higher mechanical and thermal stability characteristics when compared with other samples. The reason may be assigned to producing novel hydroxyl functional groups and strong interfacial bonding of fillers within the matrix as observed from Fourier‐transform infrared (FTIR) spectra and scanning electron microscope (SEM) micrographs, respectively. Moreover, as observed from the thermogravimetric analysis, the dried leaves‐ferrous filler‐reinforced polymer hybrid composites provided higher thermal stability. Statistical analysis was performed using the one‐way ANOVA technique and found that outcomes were significant statistically under the confidence level of 95%. Hence, this investigation not only emphasize the significance of investigating new polymer composites but also highlight the benefits of engaging advanced modeling to forecast the material characteristics precisely. Highlights: Dried leaves and cobalt/nickel/ferrous are applied reinforcement to polymers.Composites fabricated using ultrasonication bath‐assisted wet layup technique.LM Algorithm‐based ANN selected for predicting the best composite.Higher mechanical and thermal stability with dried leaves‐cobalt filler.One‐way ANOVA proved statistically significant within the material properties. [ABSTRACT FROM AUTHOR]

Natural fibers are one of the most attractive materials in biocomposites due to their potential for sustainability. This study aims to prepare sustainable composite materials using fibers from Sansevieria trifasciata (snake plant) and to investigate their mechanical, morphological, and water absorption properties. The composite was prepared with epoxy resin through a manual hand lay‐up process, maintaining standard parameters with changeable reinforcement (10%, 20%, and 30%). The mechanical properties (tensile, impact, and flexural strength), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and water absorbency of the composites were evaluated. The result showed that the tensile strength, flexural strength, and impact resistance of the composites are 6.99 MPa, 10.77 MPa, and 14 J, respectively, for 30% fiber components, which are significantly higher than other composite materials. The SEM analysis showed a strong interfacial bond between the snake plant fiber and the epoxy resin. The FTIR analysis revealed a reduction in hemicellulose and lignin and an improvement in the interfacial adhesion between snake plant fiber and epoxy resin. The composites also demonstrated time‐dependent increases in water absorption, with the sample containing 30% fiber components showing the best absorbency performance at 0.88%. Highlights: A study is being conducted on the effective and sustainable use of biowaste.The composite materials loaded with 30% fibers had significantly high tensile strength, flexural strength, and impact resistance.The SEM analysis of snake plant fiber‐reinforced polymer composite showed a strong interfacial bond between fiber and epoxy resin.The FTIR analysis of the composite revealed the reduction of hemicellulose and lignin.The use of non‐renewable materials is reduced, and eco‐friendliness is promoted. [ABSTRACT FROM AUTHOR]

Understanding the stress distribution within fiber‐reinforced polymers (FRPs) is critical to extending their operational lifespan. The integration of mechanoresponsive molecular force probes, referred to as mechanophores, presents a potential solution by enabling direct monitoring of stress concentrations. In this study, spiropyran (SP) mechanophores (MPs) are embedded within a polydimethylsiloxane (PDMS) matrix to visualize stress localization during loading within a single fiber‐reinforced framework. The SP mechanophore undergoes a transition from a non‐fluorescent state to an active state (merocyanine) through isomerization in response to mechanical forces. Using a single fiber mounted axially within the matrix, the fundamental failure modes observed in conventional fiber‐reinforced composites are replicated. Samples are strained under uniaxial tensile loading along the fiber direction and the localization of stresses is observed via MP activation. Stresses are concentrated in the matrix near the fiber region that gradually decreases away from the fiber surface. Confocal microscopy is used to visualize mechanophore activation and quantitatively assess fluorescence intensity. Finite element modeling is used to develop a calibration to quantify the stresses based on the observed fluorescence intensity. These outcomes underscore the viability of employing these mechanoresponsive molecules as a potential means to visualize real‐time stress distribution, thereby facilitating the design of high‐performance composites. [ABSTRACT FROM AUTHOR]

The aerospace industry has been benefiting from the utilization of polymer materials since fiber‐reinforced polymer composites (FRPC) offer high performances at low densities compared to metals. FRPC facilitated the design of lightweight materials, which is extensively used in aviation today. Since their first integration into structural parts, FRPC has experienced exponential growth over the years and has received a special interest from manufacturing engineering. While FRPC today is a major focus in engineering, the design of polymer matrix relies on polymer chemistry. However, aircraft materials are facing a pressing issue related to sustainability, since their environmental footprint is at an alarming level. In this review, commercial thermosetting polymer composites employed in aircraft structures are exhibited from a chemistry perspective by depicting starting products and curing reactions. The potential of chemistry to help design next‐generation sustainable FRPC for structural parts by means of utilization of sustainable feedstock, energy‐efficient processing, and recycling, is disseminated. [ABSTRACT FROM AUTHOR]

The reinforced concrete (RC) beams could be upgraded in shear using steel and fiber‐reinforced polymer (FRP) having several shapes (bars, strips, or sheets). Using near‐surface mounted (NSM) Glass FRP (GFRP) bars is still limited compared to carbon FRP (CFRP) elements as shear reinforcement. Moreover, using reinforced high‐strength concrete layers (HSCL) as NSM shear strengthening for the RC beams is still limited. Herein, three RC beams internally reinforced in shear using different shear areas (without, 100 mm stirrups apart, and 200 mm stirrups apart) were experimentally tested as reference beams (CB). Other eight beams strengthened in shear using NSM HSCL, and bars were experimentally tested. Moreover, an extended finite element (FE) simulation was implemented through a verified FE model to study the effect of other NSM aspects on shear‐strengthened beam response. The results explained that, regardless of the internal stirrups area and external NSM characteristics, the shear‐strengthened beams showed higher load efficiency than the corresponding CB. The NSM upgraded shear beam had slightly higher load efficiency than the un‐strengthened beam having the same steel area as internally shear stirrups. Moreover, increasing the internal shear stirrups decreased the total efficiency of the NSM shear strengthening and the internal stirrups regardless of the NSM characteristics. Furthermore, the NSM HSCL was more efficient than the corresponding NSM bars in increasing the load capacity and stiffness of the shear‐strengthened beams. The reported analytical model predicted well the shear capacity of the tested beams. [ABSTRACT FROM AUTHOR]

Geopolymers, as a promising substitute for ordinary cement, exhibit different coating effects with regard to the durability of basalt fiber‐reinforced polymer (BFRP) bars. In this study, a comparative investigation was carried out on the shear performance of prestressed BFRP bars coated with seawater sea‐sand geopolymer mortar (SSGM). The alkaline content of the SSGM was 4% or 6%. The prestress level was 20% of the ultimate tensile strength at room temperature. The immersion temperatures were room temperature (RT), 40, or 60°C. Interlaminar shear tests and transverse shear tests were conducted at each period (30, 60, 120, and 240 days). The results showed that BFRP bar coated with 6% alkaline content exhibited a slightly higher degradation of shear strength. Furthermore, the prestress developed microcracks in the bars and weakened the interface between the fiber and resin matrix, particular at the elevated temperature. This led to further degradation of the BFRP bars. Additionally, a comparison was made between the shear strength results of BFRP bars coated with SSGM and those coated with ordinary portland concrete or seawater sea‐sand concrete, revealing that the long‐term shear performance of BFRP bars was less negatively impacted by the SSGM coating. Highlights: Coupled effects of SSGM coatings and sustained loading on the degradation of BFRP bars are investigated.SSGM provides better protection for BFRP bars than cement‐base concrete.Alkaline content of activator in SSGM has insignificant impact on the BFRP degradation. [ABSTRACT FROM AUTHOR]

In order to study the effect of different loading rates on the fracture behavior of fiber‐reinforced polymer (FRP) reinforced concrete, the fracture experiments of FRP‐reinforced concrete beams under different loading rates were carried out. The calculation method of fracture toughness was given by analytic deduction, and the effects of different loading rates on the fracture parameters were analyzed. The experimental results show that there are three critical points in the fracture process of FRP‐reinforced concrete beam, which are the crack initiation load, crack resistance load, and ultimate load points. The effective crack length at the crack resistance load point increases with the increase of loading rate, and the effective crack length at the ultimate load point does not vary as the loading rate. With the increase of loading rate, the elastic modulus and fracture toughness increase gradually, and there is a logarithmic relationship with the loading rate, which has obvious rate correlation. The fracture process zone (FPZ) length of FRP‐reinforced concrete beams gradually decreases with the increase of loading rate. Highlights: There are three critical points in the fracture process of FRP‐reinforced concrete.The calculation of fracture toughness can be given by analytical derivation.Fracture toughness is logarithmically related to the loading rate.Crack length at the ultimate load point does not vary as the loading rate. [ABSTRACT FROM AUTHOR]

The fiber‐reinforced polymer (FRP) has attracted much attention in civil engineering due to its durability and cost‐effectiveness. The soil–FRP structure interface plays an essential role when the FRP is adopted in geotechnical engineering, but its fundamental interfacial behavior remains unclear. In the present study, the atomistic models of silica representing sand, water film representing the lubricated condition, and cross‐linked epoxy representing FRP are constructed to investigate the FRP–sand interfacial properties at the nano‐scale through molecular dynamics (MD) simulations. The epoxy model geometry and forcefield are first validated by comparing the thermodynamic and mechanical parameters with experimental and simulation measurements. The silica–epoxy interfacial tribological and rheological behavior is then explored by conducting friction and creep simulations under dry and lubricated conditions. The friction force has been found linearly dependent on the normal load and increases with the sliding velocity while decreasing against water content. The modified Amontons law for the adhering surface could describe the silica–epoxy interfacial friction well. The shear stress level influences the creep characteristics with primary, secondary, and tertiary (or rupture) creep modes. The results of this study at the nano‐scale can be further developed to enhance the current contact laws of sand–FRP structure in micromechanics‐based modeling approaches. [ABSTRACT FROM AUTHOR]

Bast fibers such as flax, hemp, and jute‐reinforced polymer composites due to their exceptional properties are gaining significant demand as a sustainable and cost‐effective alternative to conventional synthetic fiber‐reinforced composites. This comprehensive study aims to shed light on the potential of bast fiber reinforced composites (BFRCs) as innovative materials for various industrial applications. The manuscript presents a comprehensive discussion on bast fibers, polymer matrices, and the fabrication techniques employed to produce BFPCs, highlighting the effects of different modification techniques on the resulting mechanical properties. Industrial and structural applications of BFPCs are explored, with a specific focus on their use in the automotive and aerospace industries, construction materials, and sporting goods. Finally, the manuscript concludes with a discussion of the challenges and future prospects of BFPCs. This manuscript can serve as a valuable resource for researchers, engineers, and professionals interested in the emerging field of bast fiber‐reinforced polymer composites. It opens new frontiers in material design and highlights the enormous potential of BFPCs to revolutionize industrial applications through their exceptional mechanical properties. Highlights: Materials and processing of fiber‐reinforced polymer nanocomposites.Exploration of various fiber and matrix modification techniques.Recent advances in the mechanical properties of bast fiber‐reinforced composites.Ashby charts to illustrate the comparative analysis. [ABSTRACT FROM AUTHOR]

Strengthening and repairing infrastructure with fiber‐reinforced polymers while achieving low‐cost, real‐time monitoring of cracks in engineering structures is highly challenging. Herein, a piezoelectric glass‐fiber‐reinforced polymer (piezo‐GFRP) sensor is used to monitor the mechanical behavior of cement beams with cracks under cyclic bending. The output voltage and frequency of the sensor are shown to be effective feedback signals for determining the mechanical behavior. The thin piezo‐GFRP sensor shows sufficient piezoelectric sensitivity to monitor the slight variations in the mechanical behavior of the cement beams during the early stages of cracking. It is indicated in this result that such sensors have the potential for the multifunctional structural health monitoring of engineering structures. [ABSTRACT FROM AUTHOR]