This study aims to the axial compression performance of GFRP pipe spiral reinforcement composite confined concrete columns. A total of 29 specimens were fabricated and subjected to axial compression tests, with variations in concrete strength, yield strength of spiral reinforcement, stirrup ratio of spiral reinforcement, and longitudinal reinforcement ratio as parameters. The failure process of the specimens was observed, and the failure modes of different specimens were summarized. The load-displacement and load-strain curves were obtained. The influence of various parameters on the axial compression performance of specimens was investigated. The test results indicate that specimens fail due to the fracture of the GFRP tube, the crushing of the core concrete, or the breakage of the spiral reinforcement. Ultimate load-bearing capacity of GFRP tube spiral reinforced concrete columns increases with rising concrete strength, while their deformability diminishes. With increasing yield strength and stirrup ratio of spiral reinforcement, both the ultimate load-bearing capacity and shape-shifting capability of GFRP-pipe spiral reinforced concrete columns enhance. The longitudinal reinforcement ratio has minimal influence on these columns. GFRP pipe can enhance the axial compression peak stress of reinforced concrete columns by over 30%, and increase the ductility coefficient by over 90%. The addition of spiral reinforcement can increase the axial compressive peak stress of GFRP-pipe concrete columns by over 10%, and enhance its ductility by over 20%. Finally, a formula for calculating the axial compression bearing capacity of GFRP-pipe spiral reinforced composite confined concrete columns is proposed, and the calculated results closely align with the experimental findings.

The study of photocuring kinetics is an important part of photocuring research. Using an external UV light source coupled with differential scanning calorimetry, the photocuring behavior was tested at different light intensities and temperatures. This investigation provided heat flow curves, curing degree curves, and curing rate curves for the resin during the curing process. The autocatalytic model was used to fit the curing rate curves. The parameters obtained were fitted using linear or nonlinear regression to establish the curve function relationship. Previous studies had limitations as they almost considered the effect of a single variable on the photocuring kinetics model. This paper proposed a hypothesis that simultaneously incorporated curing temperature and light intensity as variables within the derived photocuring kinetic equation. The reliability of the proposed photocuring kinetics model was verified by comparison between actual experiment and finite element curing simulation. The maximum error between simulation and actual experiment is calculated to be no more than 6.5%. This study extends the understanding of photocuring kinetics and provides new perspectives and methods for optimizing the photocuring process.

The bonding between carbon fiber reinforced polymers and titanium alloys is widely used in aircraft structures to achieve light weight and sufficient strength. In this study, the combination treatment of pickling, anodizing and a special resin pre-coating technology was used to improve the bonding strength of the adhesive layer/titanium alloy interface. At the same time, in order to compare the failure of the 2 joints(no reinforcement treatment and resin pre-coating treatment) after hygrothermal aging, 80 ℃/95%RH was selected as the aging environment, and the tensile test of single lap adhesive bonding was conducted after aging. The results show that the strength of the joint reinforced by resin pre-coating increases by about 52.54% without aging. After 30 days of aging, the tensile strength of the unstrengthened joints decreased by about 20.83%, while the tensile strength of the joint after the resin pre-coating treatment decreased by about 30.44%. Resin pre-coated treatment not only increased the interface bonding strength of titanium alloy plate/adhesive layer, but also played a positive role in the cohesion strength of the adhesive layer. However, compared with the initial joints, the pre-coated resin reinforced joints are more sensitive to the environment.

In order to solve the problem of insufficient detection accuracy caused by small target size and similar features in the detection of composite inclusion defects, an improved YOLOv8 algorithm was proposed. First, the SPD convolution module is introduced to reduce information loss, and the MCA attention mechanism is incorporated to enhance the three-dimensional channel feature extraction capability, thereby improving defect recognition accuracy. Subsequently, the BiFPN bidirectional pyramid network was used to improve the multi-scale feature fusion to improve the model’s ability to identify similar features and size difference defects. Finally, to tackle the bottleneck of small target detection, a Shape IoU loss function is added to optimize the shape and scale of bounding boxes, improving the detection performance for small-size defects. Experimental results show that the improved algorithm achieves a 10.1% increase in mAP@0.5 and a 7.4% increase in mAP@0.95, with an 8.1% improvement in recall rate. The test results in the composite material defect detection system validate the reliability and practicality of this method, providing an efficient and accurate technical solution for composite material inclusion defect detection.

A convenient and practical method for predicting the ultimate strength of structures was developed for accelerating the progress of structural design scheme demonstration in the early stage of projects. Firstly, an analytical expression for the equivalent modulus of laminate was derived based on the laminate theory. Secondly, according to the assumption that the failure occurred layer by layer and stiffness degradation, the first layer failure strength and ultimate strength of laminate are obtained by numerical algorithm. Then, by comparing the predicted values and the tested values of equivalent mechanical parameters of laminate, it was found that the predicted values of equivalent modulus are completely consistent with the tested values, the predicted values of ultimate tensile strength are also completely consistent with the tested values, only the predicted values of ultimate compressive strength were 10% lower than the tested values. Finally, the ultimate strength of typical end frame flange structures was predicted by the traditional structural finite element method, based on equivalent mechanical properties of laminate. Through comparison with test, it was found that the predicted ultimate load was 15% lower than the experimental failure load. The method has a fast calculation speed and enough precision for structural design scheme demonstration in the early stage of projects.

The strength of the resin itself and the interface strength between the resin and carbon fiber are important factors affecting the mechanical properties of continuous carbon fiber reinforced thermoplastic composites. In order to improve the mechanical properties of continuous carbon fiber reinforced polypropylene (CF/PP) thermoplastic resin based composites, this paper modified high melt index PP by adding maleic anhydride grafted polypropylene (PP-g-MAH) and aminated nano silica (SiO₂-NH₂). Continuous carbon fiber reinforced polypropylene thermoplastic resin based composites were prepared by melt impregnation and hot pressing. The results showed that the addition of PP-g-MAH and SiO₂-NH₂ increased the crystallinity of PP by 2.5%, the tensile strength by 4.8%, and the bending strength by 5.3%; the bending strength and interlayer shear strength of CF/PP composite materials were increased by 112.2% and 66.0%, respectively, to 543.7 MPa and 17.2 MPa.

High performance fiber woven fabric can be utilized as blast-resistant structural material for improvised explosive devices (IEDs) in the cabin of civil aviation aircraft. In some cases, explosive devices are enhanced with fragments to increase their destructive effect. To evaluate the protective performance of fiber woven fabrics under blast loads with fragments, this research conducted free-field blast experiments with secondary fragments on aramid (Aramid) and ultra-high molecular weight polyethylene (UHMWPE) plain weave fabrics. Additionally, overpressure sensors and high-speed cameras were employed to record the experimental process. The failure behavior of the fabrics was analyzed through theoretical analysis of shockwave and fragment propagation and experimental results. It was observed that the high-velocity fragments accelerated by the blast shockwave altered the blast loading characteristics, and resulted in changes to the fabric’s failure modes. At close stand-off distance (SOD), the shockwave impacts the fabric before the fragments, and the preloading of the shockwave deteriorates the fragment-resistance of the fabric. The results indicate that: under the same charge, thicker fabrics are required to provide complete protection against blast shockwave and fragments. Therefore, enhancing the fragment-resistant properties of fiber fabrics will be a focal point for improving protective performance in subsequent research.

Based on the experiment, the application mode of carbon fiber and the effect of impact load on the mechanical properties of freeze-thaw damaged concrete were investigated. The impact compression tests of four kinds of concrete (plain concrete, carbon fiber concrete, carbon fiber cloth concrete, carbon fiber and fiber cloth concrete) under different loading rates were carried out by using Hopkinson pressure rod (SHPB) after different freeze-thaw cycles (0, 25, 50, 75, 100). The influences of the number of freeze-thaw cycles, carbon fiber reinforcement mode and loading rate on the dynamic stress-strain curve, peak stress, toughness and energy consumption of concrete materials were analyzed. The results show that: ①the peak stress of carbon fiber concrete, carbon fiber cloth concrete and carbon fiber and fiber cloth concrete is 1.30, 1.63, 1.95 times of plain concrete under 0 freeze-thaw cycles and 0.3 MPa impact pressure, both carbon fiber and carbon fiber cloth can effectively improve the dynamic compressive strength of concrete materials, and the lifting effect of carbon fiber cloth is more significant; ②compared with non-freezing-thawing specimens, the peak stress of plain concrete specimens with freezing-thawing cycles of 25, 50, 75 and 100 times decreased by 3.93%, 19.01%, 28.52% and 41.95%, and the peak stress of four kinds of concrete specimens was linearly and negatively correlated with the number of freezing-thawing cycles; ③when the impact pressure was 0.3 MPa and the freeze-thaw cycle was 100 times, the toughness of the samples of carbon fiber and fiber cloth concrete, carbon fiber cloth concrete and carbon fiber concrete was 3.78, 2.44 and 1.81 times that of plain concrete, respectively, carbon fiber and carbon fiber cloth can not only enhance the toughness of the specimen, but also enhance the freezing resistance of the specimen; ④during freeze-thaw cycles of 25, 50, 75 and 100 times, the unit volume dissipative energy of carbon fiber and fiber cloth concrete specimens decreased by 1.70%, 3.64%, 6.07% and 12.14%, respectively, and the unit volume dissipative energy of raw concrete specimens decreased by 21.43%, 35.71%, 53.57% and 73.21%, the presence of carbon fiber has a certain enhancement effect on the freeze-thaw damage resistance of concrete.

When the composite parts with corner are manufactured by autoclave process, due to structural reasons, there is a pressure difference in the corner area of composite parts, resulting in a thicker concave corner and a thinner convex corner after curing. The hat stringer was taken as the research object to analyze the causes and key influencing factors of the thickness deviation of the corner of the composite parts manufactured by the autoclave process, and the experimental verification was carried out. According to the results of theoretical analysis and experimental verification, the thickness deviation of the corner is directly related to the ratio of the radius and the thickness of the corner (R/t). The smaller the R/t value, the greater the thickness deviation of the corner. When the R/t value is determined, the thickness deviation and forming quality of the corner can be significantly improved by reducing the thickness and bridging risk of the auxiliary materials in the corner zone during the curing package of the test parts, such as using the cut glass fabrics instead of the whole breather as the gas-conducting material during the curing of the parts.

Aramid fiber has good electrothermal insulation and flame retardant properties. In this paper, aramid fiber fabric was used as the isolation layer between metal copper mesh and carbon fiber composite laminates and three kinds of composite laminates with structure of non-aramid fiber, a layer of aramid fiber and two layers of aramid fiber were prepared. The lightning protection efficiency of composite laminates containing aramid fiber under the action of lightning current C and D waves and the influence of aramid fiber thickness on the lightning protection efficiency of composite laminates were analyzed. At the meantime, the lightning protection mechanism of aramid fiber fabric as isolation layer was discussed. The results show that under the action of lightning current C-wave and D-wave, the area damage of the first layer of carbon fiber with a layer of aramid fiber is reduced by 69.1% and 78.9% respectively and the depth damage is reduced by 72.2% and 68.8% respectively. The carbon fiber laminates containing two layers of aramid fiber have no lightning damage. It is proved that the aramid fiber can effectively resist the current flowing in the direction of thickness, reducing the current density and the lightning ablation damage of the CFRP laminates greatly. This study provides a strong support for the later design of aircraft lightning protection structure.

Continuous fiber 3D-printed composites balance the mechanical properties of composites and the printing process of extremely complex structures, which has a promising development prospect. To investigate the damage evolution behavior and failure mechanism of fiber-reinforced 3D printed composites, 5% and 15% continuous Kevlar fiber-reinforced 3D printed composite specimens were prepared, and three-point bending and acoustic emission monitoring tests were conducted. A damage mode identification method for Kevlar fiber 3D printed composites combining wavelet packet transform and k-means clustering algorithm is proposed to investigate the damage mechanism of 3D printed composites with different Kevlar fiber contents. The results showed that the maximum load of specimen B (15% fiber content) was increased by 29% compared with that of specimen A (5% fiber content). Due to the low fiber content of specimen A, the internal triangular filler structure was the first to undergo severe matrix cracking and delamination, which ultimately caused Kevlar fiber breakage, whereas the damage of specimen B was mainly concentrated in the late stage of bending loading. The method provides ideas for failure analysis of fiber-reinforced 3D printed composites.

In order to obtain the interfacial properties parameters of carbon fiber reinforced plastic(CFRP)/ethylene propylene diene monomer (EPDM) adhesive for engines, this paper obtained the interfacial fracture energy and experimental curves based on DCB specimens and bilinear cohesive force models. Combined with the DCB simulation platform built using ABAQUS, the simulation curves were output. Based on the difference between the simulation curve and the experimental curve, establish a formula for the overlap between the simulation curve and the test curve as the optimization objective function. Use optimization algorithms such as response surface to solve for the minimum value of the function and its corresponding variable values, and obtain the accurate values of the interface properties parameters. This article uses a combination of properties testing, numerical simulation, and optimization calculation to obtain the properties parameters of the CFRP/EPDM adhesive interface, and verifies the parameters based on testing and simulation. The results are in good agreement, providing a criterion for interface failure and failure of engines in service engineering.

The lightweight design of the wheel hub was carried out, and the original aluminum alloy rim was replaced by carbon fiber composite material, and the optimization method using neural network as the surrogate model was adopted. Based on the isostiffness theory, the initial thickness of the carbon fiber composite rim was determined. Considering the influence of aluminum alloy spokes and carbon fiber rim thickness on their performance, Latin hypercube sampling was used to generate multiple groups of test samples. Based on the experimental samples, the neural network was used as a surrogate model to optimize the thickness of the spokes and the thickness of the carbon fiber layup at various angles of the rim. In order to obtain the best carbon fiber layup sequence, the carbon fiber rim layup sequence was further optimized in Optistruct. The resulting CFRP/aluminum hub is 18.43% lighter in weight and meets the requirements for stiffness and strength.

The application of carbon/glass hybrid fiber composites significantly enhances the design flexibility of wings. When meeting the strength requirements, incorporating a certain proportion of glass fibers into the matrix can effectively improve the thermal stability, insulation, and dielectric properties of the wings. Using the finite element software Nastran, we investigated the structural characteristics of high aspect ratio wings made from hybrid fiber composites. The study discusses the effects of different hybridization methods and ratios on the modal characteristics, maximum deformation, stress, strain, and buckling properties of the high aspect ratio wings. The results show that both the hybridization method and ratio significantly affect the structural characteristics of the high aspect ratio wings. As the volume fraction of carbon fiber plies increases, the structural performance of the wings improves. Buckling tends to occur in the skin near the trailing edge at the wing root. Optimizing the ply design of the main load-bearing spar or only the regions prone to buckling can increase the critical buckling load of the wing. However, optimizing the ply design of the spar significantly enhances the overall load-bearing capacity of the wing and reduces the maximum deformation.

In order to investigate the effect coefficient of CFRP-confined concrete columns in marine environment, five groups of 27 specimens were subjected to axial compression tests in both normal and marine environments. The failure mode, axial deformation, and ultimate failure load of each group were compared and analyzed, and validity coefficient of the CFRP-confined concrete columns theoretical model in the marine environment was calculated. The results showed that in the marine environment, the bonding effect between the CFRP sheet and concrete column is enhanced, leading to a change in the failure mode of the concrete column. Importantly, the substantial enhancement in the ultimate bearing capacity of concrete columns achieved by increasing the number of CFRP sheets remains unaffected by seawater corrosion conditions. Furthermore, the effectiveness coefficient of the constraint in the marine environment remains applicable to the theoretical model.

In this paper, water-soluble phenolic resin is used as the sizing agent and precursor of carbon paper, and graphene oxide (GO) is used as a functional filler to prepare carbon paper for high-performance proton exchange membrane fuel cells. Differential scanning calorimeter and thermos-gravimetric analyzer were used to characterize the water-soluble phenolic resin and GO. It was found that as the GO content increased, the carbon residual rate of the resin increased significantly, from 57.36%to 66.23%. The micromorphology of the modified carbon paper was observed with a scanning electron microscope and it was found that as the GO content increased, the interface bonding between the resin carbon and the carbon fiber was significantly improved. In addition, a universal testing machine, a four-probe tester and a mercury injection tester were used to explore the effects of resin concentration and graphene oxide on the mechanical properties, electrical properties and porosity of carbon fiber paper. The results show that with the increase of resin concentration and GO content, the conductivity and mechanical properties of carbon paper are significantly enhanced. In order to ensure that the fuel cell has good water vapor transmission capacity, electrical conductivity and mechanical properties, the carbon paper needs to have appropriate pore and pore size distribution, high electrical conductivity and good mechanical strength. When the resin concentration is 30wt%, the carbon paper modified with 0.6wt% GO has the best performance, with a tensile strength of 25.56 MPa, a porosity of 65.27%, and a surface resistivity of 1.365 Ω·sq^-1.

Bismaleimide (BMI) resin has been used in a wide range of fields because of its excellent mechanical properties and thermal stability. However, BMI resin has the disadvantages of high melting point, poor processing ability, high curing temperature and great brittleness. The most commonly used modification method is the addition of allyl compounds and BMI copolymerization. In this paper, literature on the modification of BMI by allyl compounds in recent years was reviewed. It includes allyl bisphenol A, allyl phenolic resin, allyl ether compounds, allyl phenoloxy resin and boron-containing compounds, aiming to provide reference and guidance for the modification of BMI resin.

Honeycomb core materials have attracted wide attention due to their low density, lightweight, high specific strength, high specific stiffness, excellent compressive performance, and good thermal insulation properties. Currently, they have been widely used in various fields such as aerospace, vehicles, ships, construction, and mechanical engineering. In recent years, continuous fiber reinforced composite honeycomb cores with lightweight and excellent mechanical properties have gained attention as replacements for traditional aluminum honeycombs and aramid paper honeycombs. This article provides a comprehensive review of the latest research progress on carbon fiber and glass fiber reinforced composite honeycomb cores. In terms of carbon fiber composite honeycomb cores, different preparation methods such as hot press molding method, vacuum-assisted resin transfer molding method, inter-locking method, 3D printing method, and tailor-folding method are introduced. Regarding glass fiber composite honeycomb cores, the focus is on the research progress in preparation methods. This article reviews the recent advances in the field of continuous fiber reinforced composite honeycomb cores, aiming to provide an indepth overview for beginners in this field.