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Carbon fiber reinforced polymer (CFRP) laminates are widely used to strengthen and retrofit deteriorated concrete structures, yet their long‐term performance and durability under varied environmental conditions remain critical areas of investigation. This study comprehensively examined the behavior of small concrete beams externally bonded with CFRP laminates under three distinct hygrothermal regimes: immersion in water at 23, 45, and 60°C for up to 112 days. The experimental program encompassed direct tension pull‐off testing of the CFRP–concrete assembly and four‐point bending tests on the beams. Pull‐off tests revealed complex failure modes, with bonding epoxy failure (43%) and concrete substrate cohesion failure (39%) being dominant. Notably, pull‐off strength exhibited nonmonotonic trends across all environments, suggesting that environmental degradation is not solely time‐dependent. Flexural capacity increased by 20%, 49%, and 11% for room temperature (RT), moderate temperature (MT), and high temperature (HT) conditions, respectively, after 112 days, highlighting the synergistic effect of CFRP strengthening and ongoing concrete curing. A calibrated three‐dimensional finite element model, developed using Abaqus, accurately replicated the experimental results and facilitated parametric studies on factors influencing CFRP‐strengthened beam performance. This included concrete compressive strength, number of CFRP layers, laminate thickness, and FRP type. The study elucidates the complex interplay between environmental exposure, material properties, and structural performance, contributing valuable insights for enhancing durability predictions and design guidelines for CFRP‐strengthened concrete structures in diverse climatic conditions. [ABSTRACT FROM AUTHOR]

Abstract\nHIGHLIGHTSOne of the remaining challenges for advancing the wide application of composite materials is to further improve the mechanical properties of composites. The fiber/matrix damage phenomenon produced by the composite model under axial loading has been observed through the establishment of a numerical model of composite damage. Axial crush tests have been performed on C-type carbon fiber reinforced polymers (CFRP) stanchions for the cargo floor structure of transport category airplanes using a finite element approach. The failure morphology and crashworthiness parameters of the specimens with different fiber layups have been recorded, and the effects of fiber orientation and angle of entrapment on the crashworthiness of the composites have been investigated. The present study demonstrates that the crashworthiness of composites can be effectively improved by fiber orientation design. Appropriate addition of 45° layer and 90° layer can effectively improve the crashworthiness of C-type CFRP laminates, and the performance of the two-angle and spiral laminates design is improved by 26% and 19%, respectively.The effect of stacking sequences on the crashworthiness of thin-walled C-type CFRP structures was investigated.The crashworthiness index and failure morphology of CFRP specimens with different fiber layup angles, layup sequences and pinch angles were analyzed.Several sets of fiber layup combinations with superior impact properties were derived from comparative analyses.A theoretical model is proposed to reveal the mechanism of the influence of different fiber layups on the crashworthiness and energy-absorbing properties of C-type CFRP. [ABSTRACT FROM AUTHOR]

The objective of this study is to evaluate the potential for enhancing the mechanical characteristics of carbon fiber reinforced polymer (CFRP) composites through the embedding of STF-impregnated woven carbon fabric within their structure, referred to as STFFC. The dynamic and static characteristics of the proposed STFFC were evaluated through a series of experimental tests including tensile, modal, dynamic mechanical analysis (DMA), low-velocity impact (LVI), and compression after impact (CAI) tests. The shear thickening fluid (STF), which was prepared by dispersing nano-silica particles in a solvent of polyethylene glycol (PEG), exhibited an abrupt increase in storage and loss modulus upon exceeding a critical shear strain. The result of the modal test revealed that the addition of STF-impregnated fabric into the CFRP composite led to greater damping ratios of 17.71–417.86%, despite the degradation of tensile strength by 10.81% and Young's modulus by 12.49%. DMA results show that the STFFC has a larger tan δ except for between intersections of 118 °C, and 161 °C. For impact responses, the STFFC resulted in a lower contact force, with a reduction of 2.41–3.30%, and an increase in absorbed energy of 2.87–5.00%. Meanwhile, the CAI strength of the STFFC was degraded by 3.62 to 6.20%. Despite the reduction of tensile, impact, and CAI characteristics of the STFFC, it is noteworthy that the CFRP composites exhibited relatively minor degradation even with the application of STF. The results of the study suggest that embedding STF-impregnated woven carbon fabric can enhance the potential of CFRP composites, making them even more promising solutions for various applications. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study delves into the efficacy of plasma jet array treatment in bolstering the interlaminar toughness of Carbon Fiber Reinforced Polymer (CFRP) prepregs, a crucial parameter for their deployment in high‐performance domains. Employing high‐frequency pulsed microsecond plasma jet arrays for surface modification, this research not only demonstrated a 19.49% upsurge in peak load capacity but also a remarkable 29.94% enhancement in Mode I interlaminar fracture toughness, as evident from Double Cantilever Beam (DCB) tests. Furthermore, the surface wettability improvements were underscored by a substantial decrease in water contact angle from 108.33° to 31.45° and a total surface energy augmentation from 12.20 to 64.16 mN/m, post a 1‐min plasma treatment. X‐ray Photoelectron Spectroscopy (XPS) results indicated an appreciable rise in oxygen functionalities, suggesting enhanced resin‐fiber bonding. Additionally, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) analyses revealed notable decreases in surface roughness and microscale defects, contributing to smoother surfaces conducive to better adhesive bonding and reduced manufacturing defects. These multifaceted improvements, stemming from alterations in surface chemistry and topography, underpin the significant potential of plasma treatment in advancing CFRP laminate applications requiring superior durability and mechanical resilience. Highlights: A plasma jet arrays method to enhance CFRP's interlaminar properties was studied.The influence mechanism of plasma modification was revealed in detail.The interlayer toughening mechanism of CFRP after plasma modification is proposed. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymer (CFRP) and aluminum alloys (Al) are widely used in the new generation of commercial aircraft due to their excellent mechanical/physical properties. CFRP/Al countersink bolted structures are important connection forms, where the radius of the countersink fillet affects the mechanical connection performance. The countersink fillet radius is an important factor affecting the mechanical performance of bolted joints. In this paper, the countersink fillet radius is controlled by specially-designed drill-countersink tools with different countersink fillet radii. Meanwhile, the finite element model based on the progressive damage method of composite material is established and utilized to simulate the mechanical performance of different composite/metal bolted joints. The failure mechanism of CFRP/Al bolted joints is analyzed. The results show that the countersink fillet radius can be effectively controlled by specially-designed drill-counterbore tools. The ultimate strength of bolted joints with dimple in the CFRP layer is higher than that in the aluminum alloy layer. In terms of the countersink fillet radius, both CFRP and aluminum alloy materials have the maximum strength when the countersink fillet radius is 1.0 mm. That is, the countersink fillet radius should be slightly larger than the bolt fillet radius, which is conducive to a better mechanical performance.

To achieve precise removal of different coatings from carbon fiber-reinforced polymer (CFRP), we propose real-time monitoring for laser-layered paint removal. Current methods for laser paint removal on CFRP surfaces primarily focus on temperature control to safeguard the CFRP against potential damage, yet encounter challenges in providing real-time monitoring capabilities. In this study, we present laser-induced breakdown spectroscopy (LIBS) combined with partial least-squares discriminant analysis (PLS-DA) models as a promising approach. Initially, in this study, we analyze the elemental composition of carbon fiber substrates, primer, and topcoat to identify key characteristic elements for evaluating the laser-layered paint removal effectiveness. Subsequently, we explore changes in the intensities of characteristic spectral lines associated with the characteristic elements in different layers. Lastly, we develop PLS-DA models to effectively identify and classify the carbon fiber substrates, primer, and topcoat, enabling real-time monitoring of laser-layered paint removal. Based on the measured LIBS characteristic intensities and PLS-DA models, we accurately identified materials using Al I (396.164 nm) and Cr I (428.984 nm), or exclusively Cr I (428.984 nm), with 100% accuracy. The results demonstrate the feasibility of integrating LIBS with PLS-DA for monitoring laser-layered paint removal and show its potential in high-quality surface cleaning and automation. [ABSTRACT FROM AUTHOR]

Corrosion may cause uniform or localized deterioration to steel bridges, which could gradually diminish carrying capacity as the damage worsens. Carbon fiber reinforced polymer (CFRP) has immense promise due to its low weight and excellent durability, elasticity, and strength. This paper investigates the effectiveness of CFRP as a repair for corroded steel I-girder ends in terms of shear and end-bearing capacities. First, this study presents finite element validation of corrosion and CFRP modeling; based on the result, the setting and analysis process can be implemented in the case study. Then, the simulation of five cases of uniform corrosion involves a range of corrosion damage situations, encompassing corrosion heights, widths, and thickness loss. The stiffener, end web, and inner web simulate the corroded part. Finite element analysis (FEA) uses nonlinearity buckling analysis and assigns the Shell S4R element type steel. The constitutive isotropic elastic model is applied to steel, while CFRP utilizes an orthotropic lamina. The CFRP failure pattern uses the Hashin Damage Criterion model constitutive. Three layers are applied to each side of the model. Analysis shows CFRP in stiffener corroded area significantly increases remaining shear capacity by 0-11.8% for one side and 0-19% for both sides, in bearing capacity by 0-8.4% and 0-17.3%, respectively. Its efficacy in end-bearing is 0-6.3% in the end web, inner web, and combination areas. End web shear capacity increased slightly, while inner and combination web capacity decreased by 0-2% from the health model. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Shanghai Jiao Tong University (1006-2467) is the property of Journal of Shanghai Jiao Tong University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study develops a double cantilever beam test by using a specific fixture for measuring the representative critical energy release rate of rigid composite rods. Carbon fiber reinforced epoxy composite rod was used for the evaluation. Finite element analysis applying Cohesive Zone Model was used to estimate the relationship between load and displacement. In addition, for verifying the effect of specimen width on the measurement, the representative critical energy release rate was estimated and compared with reference to the crack length measured from the center or outer tip of the crack. The numerical results showed close value to that of experiment. This suggests that an effective representative critical energy release rate can be measured by the proposed method. [ABSTRACT FROM AUTHOR]

Marine propellers are frequently exposed to the corrosive effects of seawater, which can significantly reduce their performance and durability. As a result, high corrosion-resistant materials are used in the fabrication of the propellers. Fiber-reinforced polymers (FRPs) have recently taken over as the material of choice when it comes to creating corrosion-resistant structure. To get the desired mechanical properties and performance, it is necessary to combine FRP composites with other materials, such as steel or aluminum. The present work deals with evaluating the bond strength between Aluminum hub and carbon fiber reinforced polymer (CFRP) propeller blade profile. Araldite 2011 adhesive was used to establish the bond between the aluminum hub and CFRP propeller blade profile. A universal testing machine(UTM) was used to evaluate the bond strength of CFRP propeller blade profile-Al hub bonded joint specimens. The Al hub and CFRP propeller blade profile were subjected to axial thrust conditions. The surface interaction values obtained from the experiments were given as input data in Finite Element (FE)-model for complex geometry. The von-Mises stress criterion was used to assess the bond strength between Al hub and CFRP blade profile. In addition, bonded joint specimens were also subjected to cyclic aging at intervals of 0, 30, 60, and 90 days, respectively. The cyclic aged specimens were mechanically characterized using UTM. The Fourier transform infrared (FTIR)spectrum was used to analyze the aging behavior of adhesive (Araldite 2011), and the surface of the fractured specimens was analyzed using scanning electron microscopy (SEM). The extended aging period affects the Al hub/adhesive interface in bonded joints, leading to lower load joint failure. [ABSTRACT FROM AUTHOR]

The present work deals with validating the bond strength between Aluminum hub and carbon fiber reinforced polymer (CFRP) propeller blade profile. Araldite 2011 adhesive was used to establish the bond between aluminum hub and CFRP propeller blade profile. A universal testing machine (UTM) was used to evaluate the bond strength of CFRP propeller blade profile—Al hub bonded joint specimens. The Al hub and CFRP propeller blade profile were subjected to axial thrust conditions. The surface interaction values obtained from the experiments were given as input data in Finite Element-model for complex geometry. The von-Mises stress criterion was used to assess the bond strength between Al hub and CFRP blade profile. In addition, bonded joint specimens were also subjected to cyclic aging at intervals of 0, 30, 45, 60, and 90 days respectively. The cyclic aged specimens were mechanically characterized using UTM. The surface of the fractured specimens was analyzed using scanning electron microscopy. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Defense Sciences / Savunma Bilmleri Dergisi is the property of Turkish Military Academy Defense Sciences Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Geopolymer concrete (GPC) has been the subject of ongoing research as a suitable substitute for conventional concrete production because of its benefits for the environment. However, there is little research regarding retrofitting the structural part if a GPC member fails. The current study thus concentrates on the damaged GPC structural members/columns. For this purpose, twelve columns which include four CC columns, four GPC Columns, and four FRGPC columns, were retrofitted with CFRP sheets and tested in the electrohydraulic testing apparatus (5000 kN). The results showed significant improvement in the ultimate load value of all 12 columns. Axial strain in all 12 columns also increased significantly. The ductility index of the columns was also calculated using axial strain values. The axial load--displacement behavior, ductility, and loading capacity of the evaluated columns are all significantly improved by the addition of steel fibers. [ABSTRACT FROM AUTHOR]

Laminated plates with holes are often used in industrial applications such as aeronautics, automobiles, and marine. It is necessary to present a study of the combined effect of deformation theories and thickness variation for the laminated plate with a hole. This manuscript considers analysis theories named: Kirchhoff, layer-wise, and Reissner-Mindlin, to study their validity for different thickness aspect ratios under transverse compression loading. Studies are conducted on CFRP laminate (symmetric cross-ply and quasi-isotropic), and the performed numerical (FEM) analysis processes are validated through existing literature. Transverse shear, circumferential, radial, and radial-hoop stress variations with stress concentration factors are presented along the thickness and around the hole configurations (18 cases are covered) of the plate. Also, the resultant effects are discussed on in-plane, and out-of-plane stresses for laminates to specify the selection of design conditions (theory, thickness, model, and laminates). This research may provide engineers and researchers with various assessments and design insight for laminate structures with a hole. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of Nanjing University of Aeronautics & Astronautics is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study investigates the shear behavior of the reinforced recycled aggregate concrete (RAC) strengthened with near-surface mounted-carbon fiber reinforced polymer (NSM-CFRP). Different percentages of the coarse RAC were used. A total of 15 reinforced concrete beams having the same cross section of (150×200×1,150 mm3) were used and strengthened with different spacing, length, and inclination of NSM-CFRP strips. Results indicated that strengthened beams showed comparable behavior with those made with conventional concrete. On the other hand, the behavior of the recycled aggregate concrete beam shows a reduction in the load capacity with 16.5% as the recycled aggregate replacement percentage increased to 75%. The stiffnesses of the strengthened beams were significantly affected by the RAC incorporation ratio because of the weak bond between the epoxy adhesive and the surrounding concrete as the replacement ratio increased more than 25% by volume. Concrete with a higher replacement ratio has lower bond strength and shear strength than concrete made with natural aggregate. As the replacement percentage increased, the cost of the concrete decreased; for instance, a 34% reduction in the cost of aggregate is noted when the replacement ratio increased to 75%. [ABSTRACT FROM AUTHOR]

Concrete has a high degree of fire resistance at moderate temperatures. High temperatures, however, cause concrete to lose its stiffness and strength. The effects of cooling techniques and retrofitting on the strength of concrete exposed to high temperatures have not been synchronized in previous studies. This experimental research aims to evaluate the effect of cooling conditions and the effectiveness of retrofitting concrete subjected to elevated temperatures. Four types of concrete: M 20 normal concrete (NC); M 20 metakaolin concrete (MC); M 40 standard concrete (SC); and M 40 self-compacting concrete (SCC) are considered in this study. A total of 864 samples consisting of cube, beam, and cylinder specimens are subjected to sustained elevated temperatures of 400°C, 600°C, and 800°C for 2 hours rating. The weight and strength of half of the heat-damaged samples are assessed following natural air cooling (NAC) and water jet cooling (WJC). The remaining 50% of samples retrofitted with carbon fiber reinforced polymer (CFRP) are tested to evaluate the upgraded strength. The experimental findings demonstrate that water jet cooling (WJC) causes more strength degradation, and CFRP proves to be effective in restoring the strength of heat-deteriorated specimens. Overall, self-compacting concrete (SCC) has shown high resistance to elevated temperatures. [ABSTRACT FROM AUTHOR]

This study employed novel joint treatments to strengthen the carbon fiber reinforced polymer (CFRP) composites. Vertically aligned carbon nanotubes (VACNTs) were prepared in situ on the catalyst-treated CF surface via the chemical vapor deposition (CVD) method, intertwining into three-dimensional fiber-nets and fully surrounding CF to form an integrated structure. The resin pre-coating (RPC) technique was further used to guide diluted epoxy resin (without hardener) to flow into nanoscale and submicron spaces to eliminate void defects at the root of VACNTs. Three-point bending testing results showed the "growing CNTs and RPC"-treated CFRP composites yielded the best flexural strength, a 27.1% improvement over the specimens without treatment, while the failure modes indicated that the original delamination failure was changed into "flexural failure" with through-the-thickness crack propagation. In brief, growing VACNTs and RPC on the CF surface enabled toughening of the epoxy adhesive layer, reducing potential void defects and constructing the integrated quasi-Z-directional fiber bridging at the CF/epoxy interface for stronger CFRP composites. Therefore, the joint treatments of growing VACNTs in situ via the CVD method and RPC technique are very effective and have great potential in manufacturing high-strength CFRP composites for aerospace applications. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Fuzhou University is the property of Journal of Fuzhou University, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Carbon-fiber-reinforced polymers (CFRPs) enable lightweight, strong, and durable structures for many engineering applications including aerospace, automotive, biomedical, and others. High-modulus (HM) CFRPs enable the most significant improvement in mechanical stiffness at a lower weight, allowing for extremely lightweight aircraft structures. However, low fiber-direction compressive strength has been a major weakness of HM CFRPs, prohibiting their implementation in the primary structures. Microstructural tailoring may provide an innovative means for breaking through the fiber-direction compressive strength barrier. This has been implemented by hybridizing intermediate-modulus (IM) and HM carbon fibers in HM CFRP toughened with nanosilica particles. The new material solution almost doubles the compressive strength of the HM CFRPs, achieving that of the advanced IM CFRPs currently used in airframes and rotor components, but with a much higher axial modulus. The major focus of this work has been understanding the fiber–matrix interface properties governing the fiber-direction compressive strength improvement of the hybrid HM CFRPs. In particular, differences in the surface topology may cause much higher interface friction for IM carbon fibers compared to the HM fibers, which is responsible for the interface strength improvement. In situ Scanning Electron Microscopy (SEM)-based experiments were developed to measure interface friction. Such experiments reveal an approximately 48% higher maximum shear traction due to interface friction for IM carbon fibers compared to the HM fibers. [ABSTRACT FROM AUTHOR]

This paper proposes an approach of stacking prepreg periodically for carbon fiber-reinforced polymer composites (CFRP) laminate. This paper will discuss the natural frequency, modal damping, and vibration characteristics of CFRP laminate with one-dimensional periodic structures. The damping ratio of CFRP laminate is calculated using the semi-analytical method which combines modal strain energy with the finite element method. The finite element method is used to calculate the natural frequency and bending stiffness which are verified with experiments. The numerical results of the damping ratio, natural frequency, and bending stiffness are in good agreement with the experiment results. Finally, the bending vibration characteristics of CFRP laminate with one-dimensional periodic structures and traditional CFRP laminate are investigated with experiments. The finding confirmed that the CFRP laminate with one-dimensional periodic structures exists band gaps. This study provides theoretical support for the promotion and application of CFRP laminate in the field of vibration and noise. [ABSTRACT FROM AUTHOR]

This paper presents a procedure for rehabilitating plastic hinges with damaged/fractured weldable longitudinal rebars in severely damaged reinforced concrete (RC) bridge columns and possible improvements regarding connection protection and plastic hinge development. Damaged/fractured longitudinal rebars are replaced with new rebar segments, and the basis of this approach involves connecting intermediate machined parts to the original longitudinal rebars by welding with an off-the-shelf steel equal angle. The proposed rehabilitation design procedure is based on capacity design principles, with equations that define the new geometries and required ductility, and it is validated experimentally on three 1∶6 -scale RC circular column specimens. Compared with the original columns, the ductility capacity of the rehabilitated columns increased from 39% to 58%, and the energy dissipation (equivalent viscous damping ratio) increased from approximately 50% to 250%. The base shears of the rehabilitated columns were smaller than those of the original columns owing to the reduction in the rebar area; thus, shear failure was avoided, and the demand on the foundation was reduced. The rehabilitation procedure, by adopting a welding connection that is easily performed on site and concentrates the damage in the new rebar segments, promises to be a quick, simple, reliable, and effective means to improve the ductility and shear capacity of RC bridge columns without using mechanical couplers or changing the column dimensions. [ABSTRACT FROM AUTHOR]

Carbon fiber composite adhesives joints provide higher specific strength and fatigue life than traditional joints. However, carbon fiber composites and adhesives are polymeric materials that may lose their integrity in hygrothermal environment. Predicting the environmental degradation behavior of composite joints is challenging because of limited understanding of the complex failure behavior. Moreover, the experiments are time-consuming and therefore it is essential to use accelerated aging methods such as the open faced method. However, the challenge is how to incorporate the accelerated fracture test data into the fracture prediction of real joints. To address this, a methodology is presented for predicting mode II cohesive law parameters of degraded CFRP epoxy adhesive joints using a direct method, and an accelerated aging test. End notched flexure (ENF) specimens made with CFRP laminate and epoxy adhesive were used to study the mode II fracture. Accelerated and uniform aging was achieved using open-faced specimens aged at 40 °C and 82% relative humidity (RH). Fracture testing of aged open-faced specimens along with crack-tip images were used to determine the degradation in trapezoidal traction-separation law (TSL) with aging. These variations in trapezoidal TSL with aging were used to develop a 3D finite element (FE) model of a closed ENF specimen that captures the non-uniform degradation across the specimen width. The TSL parameters degraded significantly at the specimen edges compared to width center for the closed ENF specimens. Validation of the FE model with aged closed ENF joint showed good agreement.

Carbon fiber reinforced polymer (CFRP) has been in high demand over the last few decades, especially in the aircraft manufacturing industry, due to their superior properties. However, drilling of CFRP materials is more complicated than common metal due to their exceptional anisotropic and non-homogenous features. This unique microstructure often leads to drilling-induced defects such as delamination, thermal damage and burr formation which compromises the structural integrity. Therefore, a good understanding of this composite material is required to realize its full potential. This review paper summarizes the knowledge available in literature on drilling of CFRP and their outcomes are compared comprehensively in a simple way. It covers key aspects such as drilling mechanism, cutting parameters and tool geometries for conventional drilling. Also, drilling-induced damages and potential solutions for those problems are addressed and covered in this paper

A combination of fiber reinforced polymer (FRP) and concrete subjected to seawater or crude oil is a desirable solution to reduce resource shortage and environmental issues. In current decades, numerous investigations have considered the utilization of FRP composites as a way for concrete confinement. Such composites have been typically limited to wrapping concrete columns at ambient temperatures. This raises the question of whether such composites can be utilized in some other applications. For that reason, the effectiveness of carbon fiber reinforced polymer (CFRP) wrapped concrete under seawater or crude oil exposure for 90 days and 720 days long-term impacts at ambient temperature concentrations have been tested experimentally. To accomplish this objective, 16 column specimens were prepared and tested. The impacts of exposure conditions, exposure time, loading type, and CFRP thickness were examined. Although it is evident that control columns' load-bearing capacities are reduced when immersed in seawater or crude oil, there is a noticeable improvement in load-bearing capability for columns immersed in seawater for a prolonged period of time for 720 days compared to those immersed in crude oil for the same amount of exposure. The strength of the confined control column and the columns submerged in seawater or crude oil significantly improved as compared to the unwrapped column without soaking in seawater or crude oil under monotonic or cyclic loading. The results of the experiment and the available design-oriented strength models can encourage the widespread use of FRP confined seawater or crude oil concrete in artificial islands and offshore structures. It was determined that these models are insufficient for predicting the strength of RC columns that had been submerged in seawater or crude oil and then encased in CFRP confinement.

In the last few decades, several contributions have used the Fiber Reinforced Polymer (FRP) for reinforcing slabs. However, previous studies disregarded the effect of spacing between the bands of the Carbon Fiber Reinforced Polymer (CFRP), which appears scientifically to be of great importance for enriching the literature. The principal objective of this paper is to ascertain the experimental data and results on the strengthened concrete slabs’ behavior when changing the spacing between the CFRP bands. To meet this objective, six slabs with 600 mm length, 500 mm width, and 50 mm thickness have been utilized. To begin with, we have put to test one reference slab without strengthening while the other slabs were strengthened with CFRP strips. Secondly, the strengthened slabs have been reinforced with three CFRP bands of 50 mm wide by varying either the spacing between them among 50 mm, 100 mm, and 150 mm, or the number of the CFRP layers. This research paper casts light on several points describing the strengthened concrete slabs’ behavior. It is worth mentioning that the slab breaking load increased when the spacing between the CFRP strips was small; and the bands were distributed close to the center.

Atmospheric pressure plasma with dielectric barrier discharge is used to improve the adhesion of novel composite carbon fiber reinforced low melting poly (aryl ether ketone) (CF/LMPAEK) to aerospace coatings under ambient and gas flow (Ar‐O2). The surface activation is evaluated by contact angle measurement and X‐ray photoelectron spectroscopy (XPS). Different atmospheres are used to prevent aging of the treated surface. The water contact angle is considerably reduced after plasma treatment, and the formation of oxygen and nitrogen polar groups is confirmed by XPS analysis. Plasma treatment improves the adhesion of CF/LMPAEK to the topcoat on the primer coating system to the traditional abrasion treatment level. This effect even is intensified with Ar‐O2 plasma. The topcoat alone presents a higher adherence, which provides a reduced coating usage option. [ABSTRACT FROM AUTHOR]

Reinforced concrete deep beams are a vital member of infrastructures such as bridges, shear walls, and foundation pile caps. Thousands of dollars and human lives are seriously threatened due to shear failure, which have developed in deep beams containing web openings. This paper investigates numerically the overall behavior of simply supported concrete deep beams reinforced with carbon fiber-reinforced polymer (CFRP) sheets through forty specimens grouped in four groups. The numerical analysis results agreed well with the experimental results in the literature, particularly the visual failure initiation with a failure load difference of nearly 7%. Finite element analyses indicated that the presence of an opening with considerable width reduced the failure load by about 71% compared to the corresponding solid specimens. In addition, the reinforced concrete deep beam samples started to behave differently when the (b/h) ratio increased more than (2.0). The findings showed that the compression stress strut pathway had been disrupted by the web opening leading to stress redistribution, and the structure will behave as two separate members. Thus, the upper web-opening part sustained the most stress, while the part under the web-opening did not show any stress concentration. The numerical stress distribution results showed that the attributed reason is that rebars and openings helped redirect the stresses to the compression strut. Using CFRP sheets with a width of more than 160 mm significantly improved the reinforced concrete deep beam with web-opening due to the increasing confinement to the upper part of the reinforced concrete deep beams with the opening. [ABSTRACT FROM AUTHOR]

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Magnesium potassium phosphate cement (MKPC) with rapid hardening and early high strength can be used as inorganic adhesive for externally bonded carbon fiber reinforced polymer (CFRP). This study aims to tailor MKPC as inorganic adhesive with good infiltration and bonding strength for CFRP-reinforced concrete. The influences of water-to-binder (w/b) ratios and particle sizes of potassium dihydrogen phosphate (PDP) on the fresh properties, hydration kinetics, pore structure, and strength development of MKPC were studied. The bonding strength of CFRP/concrete with MKPC-based adhesive was evaluated by double-shear tests. Results showed that a lower w/b ratio and a finer PDP enhanced the strength of MKPC due to a refined microstructure. The bonding strength of CFRP/concrete was dependent on the rheological characteristics and strength of MKPC. The use of a coarse PDP in MKPC was beneficial to enhance the bonding strength of CFRP/concrete. MKPC with coarse PDP and a w/b ratio of 0.2 resulted in the greatest bonding strength, corresponding to a 20 % enhancement compared to epoxy resin. The superior bonding performance of MKPC was ascribed to its higher strength, a better infiltration for CFRP, and a larger MPC/concrete interfacial transition zone (ITZ). • A high-peformance magnesium potassium phosphate cement was prepared by a composite retarder. • The rheological behavior and the workability of the MKPC slurry are the factors influence the adhesive property. • The smaller particle size of KH 2 PO 4 improved the mechanical performance of MKPC. • The infiltration of MKPC into CFRP and the ITZ between MKPC and concrete can reflect the adhesive property. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymers (CFRP) alone cannot meet the increasing requirements of the aerospace industry. Therefore, graphene nanoplatelets (GNPs) dispersed homogeneously in the matrix offer unique advantages. This study aimed to increase the thermal and electrical properties by adding functionalized GNPs (f -GNP) to the aviation epoxy matrix (Araldite LY5052) in CFRP at different rates (neat - 0.5–1–1.5 wt%) for the first time and to provide homogeneous dispersion with surfactant. The results showed that FGNP as an additive achieved significant homogeneity. While the glass transition temperature (T g) in the neat composite is 121 °C, it is 123 °C, 127 °C and 133 °C in nanocomposites with 0.5–1–1.5 wt% additives, respectively. In addition, the melting point is 366 °C in the neat composite and 368.6 °C, 370 °C, and 370.3 °C in the nanocomposites with 0.5–1–1.5 wt% additives, respectively. The oxygen groups in the additive increased the energy barrier, thus increasing the percolation threshold. There was a 50 % increase in electrical conductivity in the sample with 0.5 wt% doping with bulk current density and an 18 % increase with 1 wt% doping with surface current density. Meanwhile, the π-π bonds formed by the surfactant with GNPs and the hydrogen bonds formed with the matrix served as a bridge by filling the gaps in the interphase, significantly increasing the flow of heat and electricity. [Display omitted] [ABSTRACT FROM AUTHOR]

• A CFRP subsurface defects collection and detection platform was designed. • A CFRP subsurface defects dataset was created specifically for practical production purposes. • A novel network was designed to effectively address the challenges associated with intrinsic similarly and edge disruption in CFRP infrared images. • Our model demonstrates state-of-the-art performance on the CFRP dataset and is suitable for COD detection tasks. Infrared thermography, due to its fast detection speed, low cost, and intuitive results, is widely used in carbon fiber reinforced plastics (CFRP) materials detection. However, CFRP infrared image noise and lower resolution lead to intrinsic similarly and edge disruption, making it impossible to obtain satisfactory results. Additionally, the current methods require a lot of preprocessing and post-processing operations. Since camouflaged object detection has achieved good results in solving intrinsic similarly and edge disruption. Therefore, this paper proposes an edge and high-level semantic guided network (EHSGNet) based on camouflaged object detection for infrared thermography CFRP subsurface defect detection, achieving end-to-end detection of CFRP. This paper also constructed a dataset containing CFRP samples with both natural defects and artificially simulated internal defects to validate our method. Since the temperature change is achieved in the temperature-controlled chamber by means of hot air heating, it can heat the sample uniformly and improve the quality of CFRP infrared images, so our experiments will be carried out in the temperature-controlled chamber. The experiments were conducted on CFRP specimens with different sizes, shapes and depths of artificial defects. The experimental results demonstrate that the proposed EHSGNet outperforms current approaches significantly on our dataset, with precision (PRC) and recall (RCL) reaching 94.3% and 93.1%, respectively. [ABSTRACT FROM AUTHOR]

Self-prestressing bonded patches employing iron-based shape memory alloy (Fe-SMA) and carbon fiber reinforced polymer (CFRP) for lifetime extension of cracked steel structures are investigated. The repair patches, applicable in confined spaces, are bonded over cracks, with prestress generated within Fe-SMA via activation (heating and cooling) to induce compression on cracks. Experimental tests involve cracked steel plates repaired with Fe-SMA and Fe-SMA/CFRP bonded patches, with a patch width of 50 mm and varied patch lengths of 100 500 mm. Fe-SMA strips are activated to 180 ℃ using electric heating, generating prestresses of 154 254 MPa. Fatigue tests (∆ σ =90 MPa, R =0.2) show fatigue life extensions of ≥ 4.2 and ≥ 5.5 times for Fe-SMA and Fe-SMA/CFRP repairs. The 100 mm long Fe-SMA/CFRP patch exhibits optimal performance in lifetime extension, achieving complete crack arrest. As patch lengths decrease, failure modes shift from Fe-SMA (and CFRP) fracture to patch debonding while all patches remain effective in fatigue life extension. Finite element analysis with experimental validation quantifies the effects of prestress and load-sharing on reducing stress intensity factors at crack tips, thus retarding crack propagation. Design recommendations are proposed for the application of self-prestressing patches. • Bonded repair patches using iron-based shape memory alloy (Fe-SMA) and carbon fiber reinforced polymer (CFRP). • Fe-SMA activation and prestress estimation. • Effective fatigue life extension even complete crack arrest by self-prestressing bonded patch repair. • Patch length optimization and design recommendations. • Numerical analysis on repair mechanism through stress intensity factors. [ABSTRACT FROM AUTHOR]

The cracking of screw connections at the corners of wallboards is a typical failure mode for cold-formed steel (CFS) shear walls, resulting in premature performance degradation of CFS structures. A toughening method with carbon fiber reinforced polymer (CFRP) sheets at screw connection locations is proposed for strengthening the CFS shear walls. Totally 6 full-scale CFS shear walls with or without CFRP-toughened connections were tested, and the parameters of the lamination scheme, wallboard type and screw distance were investigated. A numerical model is developed for simulating the seismic behaviour of the tested specimens, and a theoretical model for predicting their shear strength is proposed. Results showed that the shear strength and lateral stiffness of the CFS walls with CFRP-toughened screw connections increased by more than 30 %, and the continuous lamination scheme provided greater strength. The fastener-based numerical model could effectively be used for predicting the hysteretic performance of toughened CFS shear walls well; both the pinch behaviour and ultimate strength are predicted well, and it can be used as an effective tool for the seismic design of toughened CFS shear walls with a theoretical model. • Novel CFS composite shear wall with CFRP-toughened screw connections was proposed. • Influence of the lamination scheme, wallboard types and distance of screws were considered. • Experimental investigation, numerical simulation and theoretical calculation of the toughened wall were performed. • The generation and expansion of cracking at the corners of wallboards were inhibited. • The shear wall with CFRP-toughened had good seismic behavior. [ABSTRACT FROM AUTHOR]

Due to a filament-by-filament and layer-by-layer structure produced by an additive manufacturing (or namely 3D printing) technique, mechanical properties of 3D printed materials diverge considerably from those of carbon fiber reinforced polymer (CFRP) composites made by traditional processes. This study aims to experimentally characterize their mechanical properties through the off-axis tensile, compressive and V-notch shear tests. Advanced imaging techniques, such as digital image correlation (DIC), scanning electron microscopy (SEM) and computed tomography (CT), are used to investigate anisotropic nature of materials and failure mechanisms of the 3D printed CFRP composites. The applicability of conventional failure criteria to the 3D printed CFRP composites, including Tsai-Wu, Tsai-Hill, Hoffman, Maximum Stress, Hashin, Puck and LaRC05, is assessed systematically. The experimental results divulge that the filament-by-filament and layer-by-layer features intrinsic to 3D printed CFRP composites lead to an uneven yet organized distribution of voids. This characteristic contributes on the development of claw mark strain patterns, parallel track inter-fiber failure patterns, and distinct compression failure modes such as delamination and interlayer crack under loading perpendicular to the fiber direction. The voids in the 3D printed CFRP materials are partially responsible for the significant asymmetry when off-axis angle increases. Notably, the conventional failure criteria exhibit limited capability for predicting the off-axis tensile strength accurately. This phenomenon can be attributed to the redistribution of inherent fiber waviness as the fiber encounters tensile loads. Based on the experimental results, the inter-fiber failure as per the LaRC05 is modified to obtain an enhanced failure criterion for predicting the off-axis tensile strength. This study is expected to provide fundamental understanding of structural characteristics and mechanical properties for 3D printed CFRP composites. [Display omitted] • Asymmetric elasticity and multiscale failure behaviour of 3D printed C-CFRP. • The voids contributes to the distinctive deformation and failure modes. • The conventional failure criteria can't predict the off-axis tensile strength accurately. • A refined LaRC05 failure criteria considering the redistribution of fiber waviness. [ABSTRACT FROM AUTHOR]