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With the increasing frequency of human space activities, the orbital space environment is deteriorating. It is of great practical significance to enhance the strength and toughness of spacecraft structures. High strength & toughness bio-inspired helicoidal composite metastructures with mid-plane symmetry characteristics were designed and a corresponding hot-pressing preparation process was developed. The carbon fibre reinforced polymer metastructures with cross-ply, quasi-isotropic and 5°, 10° and 20° helicoidal lay-ups were characterized by quasi-static indentation performance tests, and the damage modes and the failure mechanisms were analyzed. The load-displacement curves, peak forces, failure displacements, stiffnesses and energy absorptions, were used as the mechanical property measures, with the thicknesses of the structures including 37 and 73 layers. The results show that, compared with the traditional lay-up method, the symmetric helicoidal lay-up can effectively reduce the interlayer stress and significantly improve the quasi-static indentation performances of the metastructures. Especially with a helicoidal angle of 10°, the metastructures have excellent performance enhancement in terms of peak loads and energy absorptions. The research results not only provide a theoretical support for the design and fabrication of high-performance composite metastructures in the aerospace field, but also lay a practical foundation for their practical application. [ABSTRACT FROM AUTHOR]

Carbon fibre reinforced polymer (CFRP) plays an increasingly important role in many fields, and the non-destructive testing (NDT) for its defects is drawing more and more attention. In this paper, a finite element model is established and the surface temperature difference between the defective and non-defective areas is selected as the characteristic quantity to systematically study the impact of three parameters, such as scanning direction, laser power and scanning speed, on the detection effect in the line laser scanning thermography NDT system. Qualitatively, the scanning direction is consistent with the carbon fibre orientation, the higher the laser power, and the slower the scanning speed is, the more favourable the defect detection. Further, the data obtained from the simulation are fitted, and the results show that the scanning speed and laser power have exponential and linear relationships with the maximum temperature difference, respectively. A related experimental system was established, the laser power was set to 7-, 10-, 13- and 15 W as well as the scanning speed to 10-,20-, 40- and 50 mm/s, to investigate the temperature variation of CFRP specimens containing artificial defects. The experimental results show that a greater laser power or lower scanning speed can obtain better defect detection compared with a smaller power or higher scanning speed. [ABSTRACT FROM AUTHOR]

Carbon Fiber Reinforced Polymer (CFRP), a novel high-performance material, has found extensive use across various domains. Due to the intricate structure of CFRP and variability in its manufacturing process, such as differences in resin curing speeds or carbon fiber alignment, defects including voids and inclusions can inevitably occur. These defects can compromise the material's performance and reliability, making Non-Destructive Testing (NDT) essential for early defect detection and real-time monitoring. This paper reviews existing NDT technologies like visual inspection, computed tomography (CT), ultrasonic testing, acoustic emission testing, infrared thermal imaging, eddy current testing, and Raman spectroscopy. To facilitate performance comparison, we use spider charts to illustrate key aspects of each technique, including detection accuracy, damage localisation, interface details, and online monitoring capabilities. These charts specifically highlight the superior overall performance of CT. The principles, applications, and cutting-edge advancements in NDT techniques and Structural Health Monitoring systems (SHM) are systematically discussed. This review delves into the principles, strengths, and limitations of CFRP damage detection methods, includes detailed examples and provides a selection criterion for the work of NDT researchers. [ABSTRACT FROM AUTHOR]

Glass fibre-reinforced polymer (GFRP) wastes may be mechanically processed into small strips called "macro fibres," which were used as short reinforcement fibres to produce macro fibre reinforced concrete (MFRC). The addition of such macro fibres into concrete has proven to be effective in enhancing the flexural strength and toughness of concrete, but it also slightly reduces the compressive strength of concrete. This paper presents a study on the behaviour of CFRP-confined MFRC. A total of 84 CFRP-confined MFRC cylinders were prepared and tested in axial compression. The test parameters included the CFRP confinement stiffness, macro fibre content, and fibre length. The test results show that the compressive strength and ultimate axial strain can be significantly enhanced through the use of CFRP confinement. The ultimate axial strain of CFRP-confined concrete with macro fibres is slightly higher than that without macro fibres. The test results were compared with two well-known stress-strain models for FRP-confined concrete, including Teng et al.'s design-oriented model and Jiang and Teng's analysis-oriented model. A comparative analysis showed that both models slightly underestimate the compressive strength and slightly overestimate the ultimate axial strain for CFRP-confined MFRC. [ABSTRACT FROM AUTHOR]

This study investigates the influence of fibre orientation and heat flux on the post‐fire (residual) load‐bearing properties of carbon fibre‐reinforced polymer (CFRP) laminates. As a result, a deep insight into the post‐fire load‐bearing response is gained, which is necessary to fully understand and assess the advantages of CFRP laminates containing different fibre orientations for use in load‐bearing structures. Specimens were produced from three CFRP laminates containing different fibre orientations, exposed to varying heat fluxes up to 40 kW/m2 and then loaded in either tension or three‐point bending at ambient room temperature. The study's results have shown that the post‐fire behaviour of CFRP specimens is sensitive to changes in fibre orientation and heat flux. For example, specimens with an anisotropic fibre orientation in tension had the highest tensile load‐bearing capacity, whereas those with bidirectional and multi‐directional fibre orientations demonstrated lower tensile load‐bearing capacities. In bending, however, specimens containing bidirectional and multidirectional fibre orientations had higher load‐bearing capacities than specimens with an anisotropic fibre orientation. Furthermore, the data also shows that exposure to a heat flux reduces the load‐bearing capacity in both the bending and tensile specimens. [ABSTRACT FROM AUTHOR]

The prerequisite to equip structures with in situ electrical health monitoring systems in a meaningful manner is to estimate potential damage locations. In this context, an analytical approach to model the spatial and temporal evolution of transverse inter-fibre fractures (IFF) is exemplified for [ 90 3 / 0 2 ] s cross-ply laminates under three-point bending. The model is based on the tensile load in the bottom 90°-layer. The effective stress is computed directly from the specimen displacement, whereas the strength is considered to be periodically distributed due to material inhomogeneities along the specimen. The continuous comparison between the sinusoidal strength function and the effective stress allows modelling progressive damage in form of IFF. A modified Hann window is used to consider their effect to the bottom 90°-layer. Experiments with the same configuration are performed and the observed IFF evolution is used to tune the model parameters in an optimisation procedure, e.g., the peak separation of the sinusoid and the length of the Hann window. The comparison between model and experiment shows a high level of agreement. The model is thus capable to reproduce experiments with minimal computational effort. This makes it highly suitable as input for electrical monitoring models that rely on the continuous damage evolution of the investigated structure. In its current form, the model is limited to the specified configuration. However, the simple analytical approach allows it to be easily adapted. It is furthermore shown that progressive composite damage in terms of spatial and temporal evolution can be accurately described using an analytical approach. [ABSTRACT FROM AUTHOR]

The thermal stability of carbon fibre-reinforced polymer (CFRP) and its constituents (neat epoxy resin and carbon fibre) are studied in terms of mass loss using a thermogravimetry technique at different heating rates and two atmospheric conditions (air and pure nitrogen). By interpreting the mass loss over a temperature range of 25–900 °C, it was possible to identify the specific mechanisms of polymer degradation. In an oxygen-free pure nitrogen atmosphere, the thermal degradation of epoxy resin used as the composite's matrix is strongly inhibited up to the temperature of 400 °C, after which it undergoes thermal decomposition, in contrast to the carbon fibre reinforcement that does not degrade in nitrogen. In an air atmosphere, however, the CFRP and its constituents degrade via a complex reaction pathway encompassing three endothermic reactions (pyrolysis of the epoxy resin, oxidation of the residue from the first pyrolysis reaction and carbon fibre oxidation) that overlap and one endothermic reaction in nitrogen (pyrolysis of the epoxy resin). A deconvolution technique based on fitting log-normal distributions to the first derivative of the mass loss data has also been undertaken to separate the thermal decomposition reactions for each CFRP to understand the effect of each reaction's contribution. It can be used to evaluate complex thermal degradation processes that can be characterised by finding the respective kinetic parameters of each reaction, e.g. by using combined kinetics analysis.

Renewed call for the replacement of conventional materials with carbon fibre reinforced plastics (CFRPs) in many high-performance applications is responsible for the current wave of research on minimum quantity lubrication (MQL) strategy in machining. Due to their competitive advantages over conventional materials, polymer matrix composites (PMCs) are now attracting the attention, of researchers, especially in the field of machining. Although most manufacturing methods require less machining, precision machining like milling and drilling call for more research inputs. For this purpose, this review article assesses various aspects of nanofluid preparation and its application in CFRPs. Recent scientific reports on nanofluids with a focus on properties, preparation, and application (including respective methodologies) were analyzed, to contribute to the growing database for future research in this field. This review article shows that cutting temperature and cutting force remain the key determinants of surface finish, while tool wear constitutes a major parameter that machining scientists would like to keep under full control by the use of appropriate cutting fluids. Uncertainties around the quality of nanofluids which is scarcely discussed in the literature is raised in this review, while advocating for more research to unravel it. Furthermore, this review article sheds more light on the machining operations of carbon fiber-reinforced plastics using nanoparticle-laden fluids for a safe and sustainable machining experience. Finally, this review assesses the possibility of achieving excellent CFRP processing using a sustainable approach to fill existing gaps identified in literature like wasted cutting liquids, environmental pollution, and exposure of operators to health hazards.

Fibre waviness is frequently observed manufacturing defect which leads to a reduction of mechanical performance of the fibre reinforced polymer (FRP) composites. The current study investigates the effect of out-of-plane fibre waviness as a manufacturing defect on the flexural performance of carbon fibre reinforced polymer (CFRP) composites. Specimens with the non-uniform hump and non-uniform indentation waviness were fabricated using the transverse strip method. Experimental tests were conducted in the three-point flexural configuration using specimens with and without fibre waviness to investigate the flexural behaviour. Each of the above type of non-uniform waviness was investigated to evaluate the effect of the extent of the wave for three severity levels. Load-displacement response and digital optical microscopy were used to identify typical failure modes and damage initiation and progression in flexural specimens under test. Fibre kinking leading to delamination and fibre fracture were observed as prominent failure modes in hump as well as indentation waviness. Experimental investigation revels 12–30% reduction in flexural strength with increase in wave severity for the range considered in this study. [ABSTRACT FROM AUTHOR]

This study focuses on investigating the fatigue and wear behaviour of carbon fibre reinforced polymer (CFRP) gears, which have shown promising potential as lightweight and high-performance alternatives to conventional gears. The gears were fabricated via an autoclave process using an 8-layer composite made of T300 plain weave carbon fabric and ET445 resin and were tested in pair with a 42CrMo4 steel pinion and under nominal tooth bending stress ranging from 60 to 150 MPa. In-situ temperature monitoring was performed, using an infrared camera, and wear rates were regularly assessed. The result of the wear test indicates adhesive wear and three-body abrasion wear mechanisms between the CFRP gears and the steel counterpart. A finite element analysis was performed to examine the in-mesh contact and root stress behaviour of both new and worn gears at various loads and a specified running time. The results point to a substantial divergence from ideal meshing and stress conditions as the wear level is increased. The fatigue results indicated that the CFRP gears exhibited superior performance compared to conventional plastic and composite short-fibrous polymer gears. The described composite gear material was additionally compared with two other composite configurations, including an autoclave-cured T700S plain weave prepreg with DT120 toughened resin and a vacuum-impregnated T300 spread plain weave carbon fabric with LG 900 UV resin. The study found that the use of the T700S-DT120 resulted in additional improvements. [ABSTRACT FROM AUTHOR]

Laser surface pretreatment is an effective approach for improving the mechanical properties of adhesive joints. In the case of laser surface treatment of carbon fibre reinforced polymer (CFRP), ultraviolet (UV) lasers and lower pulse fluence infrared (IR) lasers are usually used to ensure the surface pretreatment quality. With respect to improving the surface treatment efficiency as much as possible, the influence of higher pulse fluence (12.7 J/cm2) IR laser pretreatment parameters on the mechanical properties of CFRP/aluminium alloy hybrid joints were investigated in this study. Scanning electron microscopy (SEM), contact angle measurements, confocal laser scanning microscope (CLSM), and X-ray photoelectron spectroscopy (XPS) were used to analyse the surface modification and failure modes of the adhesive surface. Additionally, the influence of the IR laser pretreatment parameters on the failure mode of CFRP/aluminium alloy adhesive joints under tension loading was discussed. The results showed that in addition to surface free energy, subsurface damage and mechanical interlocking were important factors affecting the shear strength of CFRP/aluminium alloy adhesive joints when a higher pulse fluence IR laser was applied for surface pretreatment. Finally, the optimized laser surface pretreatment parameters considering both the treatment efficiency and quality were obtained for the CFRP/aluminium alloy adhesive joint. [ABSTRACT FROM AUTHOR]

Residual strains affect the properties and performance of composite components, therefore measuring and predicting them are important. The prediction of residual strains from a model can be achieved by two steps: the generation of a geometric ply map and the modelling based on that to predict 3D residual strains. A novel method for identifying the most effective algorithm for characterising fibre orientation for the geometric ply map using ultrasound C-scan data has been developed. Finite element models were generated based on the fibre-orientation data from three different algorithms: the Radon transform, 2D fast Fourier transform, and Sobel filter. The models were used to predict residual strains due to three different severities of in-plane fibre waviness induced in a set of 18 specimens. Stratified leave-one-out cross validation was applied to obtain optimum parameters for the three characterisation algorithms and to update the values of the coefficient of thermal expansion for the material. Residual strains on the surface of the specimens were obtained from calculations based on the out-of-plane displacements measured using a digital image correlation system. The predicted and measured residual strain maps were decomposed into feature vectors using orthogonal polynomials to reduce data dimensionality and make quantitative comparisons. The measured residual strains and the predictions based on models using optimised parameters showed good agreement. The differences in performance were quantified based on the accuracy of the predicted residual strains, which showed that the Radon transform performed best. [ABSTRACT FROM AUTHOR]

The purpose of this research is to investigate the influence of CFRP strips wrapping scheme (partial wrapping) in strengthening of CFST column subjected to axial compression. To complete the experimental investigation in an economical way, the central composite design (CCD) of the response surface methodology (RSM) was used to design the experiments. Based on the CCD experimental model, 9 unique tests were performed and the failure mode of the specimens, load–deformation behaviour, ultimate strength and ductility behaviour were studied. The test results showed that externally bonding CFRP strips is an effective approach to restraining axial deformation and enhancing the ultimate capacity of the column under compression. By bonding three layers of CFRP strips, the deformation of the columns was restricted to a maximum of 55.78% and 50.27% compared to the column bonded with one layer, when set at spacings of 20 mm and 30 mm, respectively. The ANOVA, Pareto chart and contour plot of RSM revealed that the layers of the CFRP wrapping scheme was more significant than the strips spacing in increasing the strength capacity of the CFST column. The suitability of design models proposed in various literatures for predicting the strength capacities of CFST columns strengthened with CFRP wrapping scheme was also examined. A simple design model, derived considering the column geometry and material strength of column and CFRP composites, was proposed to predict the axial strength capacities of CFST short columns confined by CFRP strips by using regression analysis. The proposed design model provides a more accurate and reasonably stable prediction compared with other existing design models. [ABSTRACT FROM AUTHOR]

The demand for higher fuel efficiency and low fuel pollution rates leads to the development of lightweight hybrid structures. The predominant aim is to develop innovative light products with extreme versatility with bionomic and economic balance. Lightweight materials in the structures have successfully solved these problems in many industries, especially automobiles and aerospace. There is an emerging scope in producing automotive components by joining Al and Mg-based alloys with materials such as thermoplastics, ceramics and fibre-reinforced composites. Developing hybrid structures by employing metal–polymer joining is still a significant challenge. There are as many joining techniques available for joining metal with a polymer. Owing to certain drawbacks, some methods are ineffective, such as high processing time for adhesive bonding and mechanical fastening due to increased weight. The friction-based welding technique benefits hybrid joining due to its low heat-affected zone with less metallurgical damages. The study provides an overview of many emerging technologies for joining aluminium to thermoplastic/carbon fibre-reinforced polymer for lightweight structures. The paper compares different joint configurations and the effect of process variables on the microstructural and mechanical properties of hybrid joints. In addition, attempts are made to comprehend contemporary developments in the finite element simulation studies of hybrid structures. The paper also highlights recently developed strategies and gaps in areas where future studies might be focussed. Thus, the paper gives an overview of the advancements and relevance of the emerging joining technique for aluminium to polymers/carbon fibre-reinforced polymer hybrid structures. [ABSTRACT FROM AUTHOR]

In the present era of architecture, different cross-sectional shapes of structural concrete elements have been utilized. However, this change in shape has a significant effect on load-carrying capacity. To restore this, the use of column confinements with elliptical sections has gained attention. This paper aim to investigate the effect of elliptical shape sections of confined concrete reinforced with Carbon Fiber Reinforced Polymer (CFRP) and steel tube on axial load-carrying capacity. This study is achieved using following tools Finite Element (FE) in Abaqus and Artificial Neural Networks (ANN) modeling. The study involved a 500-mm-high column with three sets of aspect ratios: 1.0, 1.5, and 2.0. In each aspect ratio, three different layers of CFRP were used, i.e., .167, .334, and .501-mm. Analytical results showed that with the increase in aspect ratio from 1 to 2, there is a decrease in ultimate axial load of about 23.2% on average. In addition, the combined confining pressure of steel tube and CFRP increases with a decrease in dilation angle as the number of CFRP layers increases. The failure mode for the column with a large aspect ratio is local buckling at its mid-height along the minor axis. The result showed a good correlation between FE and experimental results of ultimate stress and strains, with a mean squared error of 2.27 and .001, respectively. Moreover, ANN and analytical models showed a delightful correlation of R2 of .97 for stress models and .88 for strain models, respectively. The elliptical concrete section of the column confined with steel tubes can be adopted for a new architectural type of construction; however, with more than three aspect ratios, the wrapping of the section with CFRP jackets is highly recommended.

Fibre reinforced polymer (FRP) strengthening is a possible option when the load carrying capacity of a structure needs to be increased for various reasons. On the other hand, the focus nowadays aims to save the environment by reducing the waste material. A suggestion was made to use waste concrete as an aggregate. If this new material was used more, it would be possible to use recycled concrete aggregate (RCA) and carbon fibre reinforced polymer (CFRP) to strengthen reinforced concrete (RC) structures and make them more environmentally friendly. An experimental investigation study on the shear behaviour of RC beams strengthened with CFRP strips was carried out. Tests were conducted on six reinforced concrete beams, with variations in the replacement ratio of RCA and strengthened by different configurations of CFRP under four-point loading. The results indicated that the load carrying capacity was increased, on average, by 18.09 and 35.04% for beams strengthened with CFRP with an inclined strip (IS) and continuous strip (CS) configurations respectively. The results also indicated that the increases in the stiffness were 21.08 and 37.31 for beams strengthened with CFRP in the IS and CS configurations, respectively. In addition the ductility of the beams increased after strengthening.

Carbon fiber-reinforced polymer (CFRP) laminates can significantly improve the flexural performance of the bamboo scrimber. This study evaluated the effects of three fabrication methods (one-time hot pressing, secondary hot pressing, and secondary cold pressing) on the flexural performance of CFRP-bamboo scrimber composites. Four-point bending experiments and theoretical analysis were conducted to study the failure modes, flexural performance, load-displacement relationships and strain curves over time of CFRP-bamboo scrimber composites. Besides a theoretical model was proposed to describe the flexural stiffness of CFRP-bamboo scrimber composites. The results indicated that the CFRP-bamboo scrimber composite specimens demonstrated four failure modes depending on the treatment methods. Overall, the static flexural modulus of the one-time hot pressed specimens was superior (up to 1.93 times that of the untreated bamboo scrimber specimen), and the static flexural strength of the secondary cold pressing specimens was superior (up to 3.58 times greater than that of the untreated bamboo scrimber specimen), although neither the static flexural modulus nor the static flexural strength of the secondary hot pressing specimens was satisfactory. Finally, it was illustrated that the theoretical models, established to describe the load-displacement, could accurately predict the experimental results. [ABSTRACT FROM AUTHOR]

Fibre reinforced polymer (FRP) strengthening is a possible option when the load carrying capacity of a structure needs to be increased for various reasons. On the other hand, the focus nowadays aims to save the environment by reducing the waste material. A suggestion was made to use waste concrete as an aggregate. If this new material was used more, it would be possible to use recycled concrete aggregate (RCA) and carbon fibre reinforced polymer (CFRP) to strengthen reinforced concrete (RC) structures and make them more environmentally friendly. An experimental investigation study on the shear behaviour of RC beams strengthened with CFRP strips was carried out. Tests were conducted on six reinforced concrete beams, with variations in the replacement ratio of RCA and strengthened by different configurations of CFRP under four-point loading. The results indicated that the load carrying capacity was increased, on average, by 18.09% and 35.04% for beams strengthened with CFRP with an inclined strip (IS) and continuous strip (CS) configurations respectively. The results also indicated that the increases in the stiffness were 21.08 and 37.31 for beams strengthened with CFRP in the IS and CS configurations, respectively. In addition the ductility of the beams increased after strengthening. [ABSTRACT FROM AUTHOR]

Composite materials specifically carbon fibre reinforced polymers (CFRP) are finding an increased usage in industries like aerospace, marine, automobile, and sport owing to high strength and stiffness properties compared to traditional metals and their alloys. The setup preparation cost and curing time of materials are very high in the autoclave process, different out-of-autoclave (OoA) processes are being developed. The heat transfer fluid (HTF) method for curing is quite possibly the most encouraging technique which is ideal for small-sized components, quick, compact, energy-efficient, and achieves a great reduction in cost and time. This research paper describes the design and development of a novel HTF curing setup for CFRP prepreg. The specimens have been manufactured using the HTF curing process according to ASTM standards. The mechanical properties like tensile and flexural strength have been measured for fabricated test coupons. The results obtained for mechanical properties in the HTF curing process have been compared with samples prepared with autoclave and microwave curing processes. It has been observed that mechanical properties obtained in the HTF curing process are 48% higher than other curing processes because of the presence of less void content and high bonding developed in fibre-matrix during the process. [ABSTRACT FROM AUTHOR]

In recent years, carbon fibre reinforced polymer (CFRP) laminates have conquered the structural rehabilitation market due to their ease and quick installation, high strength, anticorrosion properties, and other properties often repeated in the literature. The full potential of these high-strength elements can only be exploited by prestressing. However, the glued laminate joint is partially rigid, resulting in slippage that leads to premature debonding and failure. Therefore, anchoring of the laminate ends is required to stop or delay premature failure and/or perform prestressing. This article discusses the anchoring issues of CFRP laminates and guidelines for the development of anchoring systems. To achieve this goal, the laminate strip was bent, the required clamping forces were determined, possible cases of damage were identified, and individual stress concentrations were modelled. The methodology for calculating the anchor length and the pull-off force is also presented. [ABSTRACT FROM AUTHOR]

• FE models are developed and validated for CFRP-reinforced CHS KT-joints. • The contact is optimised between CFRP and KT-joints. • A load-bearing capacity improvement coefficient k is proposed. • The effects of 20 parameters on k are investigated numerically. • Parametric formulae are established for k. This study numerically analyses the load-bearing capacity of Carbon Fibre Reinforced Polymer (CFRP) strengthened circular hollow section (CHS) multiplanar KT-joints based on experiments. Compared to unreinforced joints, the load-bearing capacity improvement coefficient k was proposed and investigated. First, the experiments on bare and CFRP-reinforced CHS KT-joints were briefly described. Three-dimensional numerical models were then established for bare and CFRP-strengthened CHS KT-joints. Refined and simplified CFRP models were established. The effectiveness of the simplified CFRP model was validated by comparing it with experimental results. To improve computational efficiency, the contact between CFRP and steel tubes was optimised by the combination of surface-based cohesive behaviour and tie. A parametric study was carried out to analyse the effect of 20 independent parameters on k. We found that k is primarily influenced by non-dimensional geometric parameters, load of brace-T, number of CFRP layers, and CFRP properties. Parametric formulae for k were established through nonlinear regression analysis. The proposed parametric formulae agree well with numerical analysis and experimental results. [ABSTRACT FROM AUTHOR]

To improve the tensile strength of welded hollow spherical joints (WHSJs) while maintaining their original structural configuration, a carbon fibre reinforced polymer (CFRP) is proposed in an innovative layered strengthening method. To assess the effect of varying the number of axial and circumferential CFRP layers on tensile properties, axial tensile tests were performed on 12 full-size Q235B WHSJs reinforced with CFRP. The experimental findings revealed that bonding the CFRP layers to the surfaces of the joints substantially increased their tensile strengths. Furthermore, with an increase in the number of layers, the resistance of the reinforced joints improved significantly, showing a proportional increase of 19.85%. The number of layers in the circumferential CFRP at the end anchorage was crucial for enhancing the axial tensile strength. By integrating the resistance equations for welded hollow spheres with those applicable to CFRP, new equations were derived for the resistance of CFRP-reinforced WHSJs. Additionally, the force analysis of circumferential CFRP led to the development of a simplified design formula to determine the optimal number of circumferential CFRP layers. • The tensile properties of 12 welded hollow spherical joint specimens with different reinforcement forms were studied. • The innovative reinforced node has a good load carrying capacity. • Different joint configurations lead to different final failure modes of specimens. • The strain of the member is analysed, and the bearing capacity of the welded hollow spherical joint reinforced by CFRP is deduced. • Some assumptions about the circumferential CFRP are made, the force characteristics of the circumferential CFRP are defined, and the bearing capacity formula is derived. • The relationship between layers of axial and circumferential CFRP with different tube and ball diameter ratios is designed. [ABSTRACT FROM AUTHOR]

Today, the use of a non-destructive technique to assess the integrity of reinforced concrete structures strengthened with carbon fibre-reinforced polymer (CFRP) is becoming increasingly important. It is highly important to assess the behaviour of the structure under load. This paper presents the evaluation of a reinforced concrete beam laminated with CFRP at the soffit using the acoustic emission technique. Two types of beams were made, a normal reinforced concrete beam and a reinforced concrete beam laminated with CFRP. CFRP was used to reinforce the bottom part of the beam. The beams were subjected to three-point loading and loaded to failure. During the loading tests, the integrity of the beams was monitored using the acoustic emission technique, and the crack patterns were observed visually. The intensity analysis was carried out on two sensors, designated as CH6 and CH7. CH6 and CH7 were located on top of the beam. Based on the intensity analysis of the acoustic emissions, five intensity crack zones were identified, namely zone A-no crack, zone B-minor, zone C-intermediate, zone D-follow up and zone E-major. With increasing load, which tended to progress the crack modes in the beam, the plots in the intensity zones developed for each crack mode from zone A to zone E. The crack progression matched well with the plots in the intensity zones. Using the intensity zones enables the early detection and prediction of damage.

The use of reinforced fibre polymers to strengthen and repair structural elements is widely spreading. However, there is lack of knowledge of the actual behavior of strengthened structures with FRP sheets. This paper discusses the experimental results of the flexural strengthening of reinforced concrete (RC) beams by carbon fibre-reinforced polymer (CFRP) sheets bonded by epoxy adhesive to the tensile surface of the beams. Using a four-point bending load system over an effective span of 1800 mm, a total of ten beams with an overall dimension of 150 mm * 200 mm * 2000 mm with different degrees of strengthening schemes were tested. The number of layers, strengthening scheme (side and U-shape bonding) and reinforcement ratio are the major parameters of the experimental study. The research indicates that the flexural strength of the beams was substantially improved as the layers of laminate increased (between 31.80 and 71.50 %) and using U shape in ends that delay or prevent debonding failure. The experimental results compared to that analytically obtained by using ANSYS model showing acceptable agreement with deviations varying no more than 10 % for all specimens.

This study uses a small-scale apparatus to investigate the influence of carbon fibre orientation and heat flux on the thermomechanical response of carbon fibre reinforced polymer (CFRP). The proposed test apparatus allows the thermomechanical behaviour, relating to the mechanical performance degradation with particular surface temperature and temperature gradient of a CFRP, to be investigated. The motivation of this study is to understand the mechanical response of load-bearing CFRP materials during heating using a cone heater. Experiments were performed on CFRP specimens produced in four unique lay-ups to study their thermomechanical bending behaviour in terms of failure times, displacement, temperature distribution and failure modes. The results from this study show that different fibre orientations respond differently to thermomechanical loads. For example, it is observed that CFRP containing uni-directional [90°] fibres demonstrate the worst overall load-bearing response to thermomechanical loading conditions. In contrast, woven bi-directional [0°, 90°] fibres demonstrate the best. Uni-directional [0°] fibres and unwoven multi-directional [0°, ±45°, 90°] fibres present a modest overall load-bearing response to thermomechanical loading conditions. These results demonstrate that it is possible to systematically evaluate the performance of different fibre lay-ups and relate the failures to heating of the solid to the glass transition temperature and decomposition temperature of the polymer matrix. • An approach for quantifying a CFRP thermomechanical behaviour is presented. • Four different CFRPs are exposed to a fire and load combination. • The influence of fibre orientation and heat flux on CFRP behaviour is complex. • Carbon fibre orientation influences the thermomechanical behaviour of CFRP. [ABSTRACT FROM AUTHOR]

This study focuses on investigating the fatigue and wear behaviour of carbon fibre reinforced polymer (CFRP) gears, which have shown promising potential as lightweight and high-performance alternatives to conventional gears. The gears were fabricated via an autoclave process using an 8-layer composite made of T300 plain weave carbon fabric and ET445 resin and were tested in pair with a 42CrMo4 steel pinion and under nominal tooth bending stress ranging from 60 to 150 MPa. In-situ temperature monitoring was performed, using an infrared camera, and wear rates were regularly assessed. The result of the wear test indicates adhesive wear and three-body abrasion wear mechanisms between the CFRP gears and the steel counterpart. A finite element analysis was performed to examine the in-mesh contact and root stress behaviour of both new and worn gears at various loads and a specified running time. The results point to a substantial divergence from ideal meshing and stress conditions as the wear level is increased. The fatigue results indicated that the CFRP gears exhibited superior performance compared to conventional plastic and composite short-fibrous polymer gears. The described composite gear material was additionally compared with two other composite configurations, including an autoclave-cured T700S plain weave prepreg with DT120 toughened resin and a vacuum-impregnated T300 spread plain weave carbon fabric with LG 900 UV resin. The study found that the use of the T700S-DT120 resulted in additional improvements.

Tension-compression (T-C) fatigue response is one of the important design criteria for carbon-fibre-reinforced polymer (CFRP) material, as well as stress concentration. Hence, the objective of the current study is to investigate and quantify the stress concentration in CFRP dog-bone specimens due to T-C quasi-static and fatigue loadings (with anti-buckling fixtures). Dog-bone specimens with a [(0/90), (45/-45)4]s layup were fabricated using woven CFRP prepregs and their low-cycle fatigue behaviour was studied at two stress ratios (-0.1 & -0.5) and two frequencies (3 Hz & 5 Hz). During testing, strain gauges were mounted at the centre and edge regions of the dog-bone specimens to obtain accurate, real-time strain measurements. The corresponding stresses were calculated using Young's moduli. The stress concentration at the specimen edges, due to quasi-static tension, was significant compared to quasi-static compression loads. Furthermore, the stress concentration increased with the quasi-static loading within the elastic limit. Similarly, the stress concentration at the specimen edges, due to tensile fatigue loads, was more significant and consistent than due to compressive fatigue loads. Finally, the effects of the stress ratio and loading frequency on the stress concentration were noted to be negligible. [ABSTRACT FROM AUTHOR]

This study aims to experimentally and analytically investigate the effectiveness of non-uniform wrapping on circularised reinforced concrete (RC) columns under axial and flexural loads. Sixteen specimens including four square and twelve circularised RC specimens were prepared and tested. Specimens of the first group were square RC specimens. Specimens of the second and third groups were circularised RC specimens fully wrapped with two and three plies of carbon fibre reinforced polymer (CFRP), respectively. Specimens of the fourth group were circularised RC specimens non-uniformly wrapped with CFRP. The experimental results showed that, for an equivalent amount of CFRP, the performance of circularised RC specimens fully wrapped with CFRP was better than the performance of circularised RC specimens non-uniformly wrapped with CFRP. An analytical method was developed for the failure envelopes of the tested specimens. A good correlation between the experimental and analytical failure envelopes was obtained for the tested specimens. [ABSTRACT FROM AUTHOR]

In recent years, for the reinforcement of concrete structures, fibre-reinforced polymers have been extensively employed, thus enhancing the structural properties of the reinforced materials. This paper presents a pre-stressing strengthening method for the confinement of large-scale circular concrete columns. The axial compressive behaviour of confined columns was tested and analysed. The experimental and analytical results indicated that the stiffness, ductility, and bearing capacity of reinforced concrete (RC) columns strengthened with pre-stressed carbon fibre-reinforced polymer (CFRP) composites were significantly higher than those of non-prestressed columns. A theoretical relationship between the peak strength and bearing capacity of large-scale RC columns actively confined by pre-stressed CFRP composites was proposed. A tri-linear stress-strain model for the actively confined large-scale concrete columns was presented and compared with the experimental results. Moreover, the model is sufficiently simple for use in design. The results of the proposed model were compared with the experimental results of small-scale columns, and the influence of size was found to be critical to the analysis of RC columns confined by pre-stressed CFRP composites. [ABSTRACT FROM AUTHOR]

Fire resistance testing of components made of carbon fibre reinforced polymers (CFRP) usually demands intermediate-scale or full-scale testing. A bench-scale test is presented as a practicable and efficient method to assess how different fire protective systems improve the structural integrity of CFRPs during fire. The direct flame of a fully developed fire was applied to one side of the CFRP specimen, which was simultaneously loaded with compressive force. Three different approaches (film, non-woven, and coatings) were applied: paper with a thickness in the range of μm consisting of cellulose nanofibre (CNF)/clay nanocomposite, nonwoven mats with thickness in the range of cm and intumescent coatings with a thickness in the range of mm. The uncoated specimen failed after just 17 s. Protection by these systems provides fire stability, as they multiply the time to failure by as much as up to 43 times. The reduced heating rates of the protected specimens demonstrate the reduced heat penetration, indicating the coatings’ excellent heat shielding properties. Bench-scale fire stability testing is shown to be suitable tool to identify, compare and assess different approaches to fire protection.

• A water jet guided laser can cut through 6 mm thick carbon fibre reinforced polymer. • The material removal mechanism utilises thermal and fracture processes. • Water ingress occurs into the carbon fibre reinforced polymer during cutting. • Water jet pressure and average power are key parameters. Over the last decade, there has been an increased interest in exploiting carbon fibre reinforced polymer (CFRP) across the engineering sector due to its lightweight and high-strength characteristics. Laser cutting is the state-of-the-art (SOTA) method for cutting metals and alloys. However, the SOTA laser cutting process cannot be used for CFRP due to differences in the thermal and physical properties of the resin matrix and carbon fibre reinforcement. Water jet guided laser (WJGL) processing is becoming the technology of choice for challenging materials that cannot be processed with conventional laser technology. This paper uses a high-power nanosecond laser with an average power of 400 W to investigate the basic characteristics of WJGL cutting of CFRP. Experimental trials were performed to improve the understanding of the material removal mechanism, machining efficiency, and the effect of different process parameters on the process throughput and quality. The study shows that the material removal mechanism of WJGL cutting of CFRP is a combination of thermal-based (melting, vaporisation, and melt-ejection) and fibre fracture due to the action of the water jet and thermal stress. [ABSTRACT FROM AUTHOR]

In recent years, carbon fibre reinforced polymer (CFRP) laminates have conquered the structural rehabilitation market due to their ease and quick installation, high strength, anticorrosion properties, and other properties often repeated in the literature. The full potential of these high-strength elements can only be exploited by prestressing. However, the glued laminate joint is partially rigid, resulting in slippage that leads to premature debonding and failure. Therefore, anchoring of the laminate ends is required to stop or delay premature failure and/or perform prestressing. This article discusses the anchoring issues of CFRP laminates and guidelines for the development of anchoring systems. To achieve this goal, the laminate strip was bent, the required clamping forces were determined, possible cases of damage were identified, and individual stress concentrations were modelled. The methodology for calculating the anchor length and the pull-off force is also presented.

The use of reinforced fibre polymers to strengthen and repair structural elements is widely spreading. However, there is lack of knowledge of the actual behavior of strengthened structures with FRP sheets. This paper discusses the experimental results of the flexural strengthening of reinforced concrete (RC) beams by carbon fibre-reinforced polymer (CFRP) sheets bonded by epoxy adhesive to the tensile surface of the beams. Using a four-point bending load system over an effective span of 1800 mm, a total of ten beams with an overall dimension of 150 mm * 200 mm * 2000 mm with different degrees of strengthening schemes were tested. The number of layers, strengthening scheme (side and U-shape bonding) and reinforcement ratio are the major parameters of the experimental study. The research indicates that the flexural strength of the beams was substantially improved as the layers of laminate increased (between 31.80 and 71.50 %) and using U shape in ends that delay or prevent debonding failure. The experimental results compared to that analytically obtained by using ANSYS model showing acceptable agreement with deviations varying no more than 10 % for all specimens. [ABSTRACT FROM AUTHOR]

Tension-compression (T-C) fatigue response is one of the important design criteria for carbon-fibre-reinforced polymer (CFRP) material, as well as stress concentration. Hence, the objective of the current study is to investigate and quantify the stress concentration in CFRP dog-bone specimens due to T-C quasi-static and fatigue loadings (with anti-buckling fixtures). Dog-bone specimens with a [(0/90),(45/−45)4]s layup were fabricated using woven CFRP prepregs and their low-cycle fatigue behaviour was studied at two stress ratios (−0.1 & −0.5) and two frequencies (3 Hz & 5 Hz). During testing, strain gauges were mounted at the centre and edge regions of the dog-bone specimens to obtain accurate, real-time strain measurements. The corresponding stresses were calculated using Young’s moduli. The stress concentration at the specimen edges, due to quasi-static tension, was significant compared to quasi-static compression loads. Furthermore, the stress concentration increased with the quasi-static loading within the elastic limit. Similarly, the stress concentration at the specimen edges, due to tensile fatigue loads, was more significant and consistent than due to compressive fatigue loads. Finally, the effects of the stress ratio and loading frequency on the stress concentration were noted to be negligible.