Graphene oxide (GO) films have excellent selective permeability, but their low preparation efficiency and poor water resistance seriously affect their development and application. In order to improve the water resistance of GO films, a rapid preparation method of self-supporting hydrophobic polymer (PMMA)/GO composite films was proposed. Hydrophobic PMMA and hydrophilic GO were dispersed together by adjusting the proportion of ternary solvent (acetone-ethanol-water), and the dispersion mechanism was explained. In this method, the self-supporting composite film is formed rapidly by self-assembly at the gas-liquid interface by means of a volatile solvent system and a negative pressure assisted film forming method, and the shortest film forming time is only 6 s. The FTIR, XRD and SEM results of the composite films show that PMMA and GO are successfully combined and a dense lamination structure is formed. With the increase of PMMA content, the degree of interlayer regularity of the composite films first increases and then decreases. As the film-forming pressure increases, there is a corresponding decline in the film’s uniformity. The composite film exhibited a 44.39% increase in tensile strength due to the addition of PMMA and the exploitation of its structural uniqueness. The water resistance of the film is obviously enhanced, and the volume swelling rate is reduced by 98.11% compared with GO film. In this paper, a ternary solvent system is used to greatly improve the film formation property and film formation speed of GO, and the prepared composite film has good water resistance, which can greatly expand the application scenario of GO film.

Studied the influence of various factors on the interfacial bonding performance between nickel-titanium shape memory alloy (NiTi-SMA) wire/epoxy resin. Firstly, the bonding strength of the SMA wire/epoxy resin interface was determined by SMA wire pull-out tests, focusing on the effects of adhesive type, SMA wire bonding length, and prestrain level on the interfacial failure mode and bonding strength. Then, based on the cohesive zone model, numerical simulation of the interfacial mechanical behavior were conducted to further analyze the shear stress distribution during the SMA wire pull-out process. Finally, a load-slip constitutive model was established based on the experimental results. The results show that the failure modes of Sikadur-330 CN and Lica-102 are both interfacial bonding failures between SMA wire and epoxy resin, with effective bonding lengths ranging from 2.0 cm to 3.0 cm. The epoxy resin Sikadur-330 CN exhibits the best bonding performance, with a bonding strength approximately 1.20~1.42 times that of the other adhesive. The bonding strength at the prestrain level of 12% is 1.37~3.16 times that of other pre-strain levels. The established load-slip constitutive model can effectively simulate the mechanical behavior of the SMA wire/epoxy resin interface. This study provides theoretical support for the preparation and practical engineering applications of FRP/SMA composite materials.

Based on experimental verification of the feasibility of the simulation model, this paper investigates the influence of sleeve material, bolt aperture size and bolt preload on the tensile properties of composite-titanium alloy bolted joints with sleeve, using numerical simulation methods. This research provides some theoretical guidance for the design of the structure. The results indicate that the influence of sleeve material on the bearing capacity of bolted joints with sleeve is negligible. When the bolt aperture is between 5 mm and 7 mm, increasing the bolt hole size can enhance the bearing capacity of the joint. With the 7 mm bolt aperture, the tensile failure load of the joint with sleeve increases by 32.21% compared to the joint without sleeve. However, when the hole diameter exceeds 7 mm, the bearing capacity of the joint will decrease. When the tightening torque ranges from 0.5 N·m to 3.5 N·m, increasing the bolt tightening torque can enhance the bearing capacity of the joint. But exceeding 3.5 N·m results in a decline in the bearing capacity of the joint.

The properties of carbon fiber composites depend largely on the environment in which they are used. The effects of three aging environments (distilled water, 10% sulfuric acid solution and sodium hydroxide solution) at the same temperature (70 ℃) on the secondary impact damage and residual compressive strength of T700 carbon fiber/epoxy resin matrix composites were studied. Fourier transform infrared spectroscopy (FTIR), the surface morphology before and after aging and the C-scan damage morphology were studied and analyzed. The results show that only physical damage occurs in the samples in distilled water and acid solution, and the changes of surface topography, C-scan damage morphology and residual compressive strength are related to the infiltration of water molecules. In alkali solution, the sample is seriously damaged, and the resin also has a chemical reaction. The properties of the material and the C-scan damage morphology have both effects on hygroscopicity and chemical damage of the resin. The research results are of great practical significance for improving the continuous service life and maintenance economy of these composite materials in complex environment.

Compression modulus is one of the key mechanical properties of epoxy resin composites filled with hollow glass microspheres, the prediction of compression modulus has certain engineering research significance. In this paper, the compression modulus of epoxy resin composites filled with different volume fraction of hollow glass microspheres were experimentally investigated, followed by the comparison with the predicted values using Nielsen model and the linear model as well as the square law summation model. The results show that the theoretically predicted values using linear model exhibit the lowest error for samples with volume fraction of hollow glass microspheres exceeding 30%. However, for samples with lower volume fractions, the predicted values deviate significantly due to the obvious misattribution of glass microspheres. In contrast, the Nielsen model provides relatively accurate predictions for samples with lower volume fraction of hollow glass microspheres. Among the three models, the square law summation model exhibits the largest deviation in estimating the compression modulus of epoxy resin composites filled with hollow glass microspheres.

The comprehensive mechanical properties and failure modes of SiC/SiC composites are closely related to the mesostructure of the fiber preform. This article is based on the multi-scale analysis method of composite, conducting multi-scale unit cell modeling, combined with progressive damage analysis, to analyze and predict the mechanical properties of fiber bundles and woven composites, and comparing them with bending test results to verify the correctness of the multi-scale analysis method and component constitutive model. Further analysis was conducted on the influence of fiber weaving structure and layup angle on the macroscopic comprehensive mechanical properties of two-dimensional SiC/SiC composites. The calculation results showed that under the same fiber volume fraction conditions, fiber mesostructures had little effect on the elastic modulus of the composite, but had a significant impact on the failure strength. The fiber weaving structure mainly affected the in-plane direction tensile strength, and the twill structure was about 30% higher than the plain structure; the angle of fabric layering has a significant impact on the tensile and shear strength in the in-plane direction. The in-plane tensile strength of the 0° layering structure is about 85% higher than that of the 45° layering structure, while the in-plane shear strength is about 30% lower; in addition, the weaving structure and ply angle have almost no effect on the interlayer shear strength, which is mainly determined by the interlayer reinforcing fibers and the interlayer matrix porosity. The results of this article can provide support for the design of fiber preform structures in the development of SiC/SiC composite components.

This article proposes a new structural joint integration configuration scheme and establishes a nonlinear analytical model for the bending process of C-shaped composite material tape springs. By utilizing the buckling and subsequent buckling phenomena of plates and shells, the basic configuration of composite material structure joint integration is designed. Through the principle of minimum potential energy, the recovery bending moment of the composite material structure joint integration configuration during the bending process is derived, a mapping relationship has been established between the geometric parameters of the integrated joint, material mechanical performance parameters, and the assistance effect (recovery torque). Using a non-contact full field deformation measurement system, an experimental platform was established to verify the theoretical results of the assistance effect. Combined with the finite element progressive damage failure analysis method, the mechanical behavior and material damage evolution mode of the composite structure integrated joint under quasi-static folding were studied. Further research was conducted on the impact of different geometric parameters on the stability support and assistance effects of integrated joints. This exploratory study can significantly reduce the number of parts, reduce the weight of the structure, and reduce the processing cost of the product while meeting the basic functional requirements of the unpowered backpack exoskeleton structure joint system in the early stage.

In view of the multiple damages in a small range of composite structures, how to determine the reasonable repair size boundary under the hygrothermal environment has an important engineering application value for the design of the repair scheme of the super manual and the formulation of the composite repair standard for civil aircraft. Through ABAQUS software simulation and experimental verification, the influence of the repair size boundary on the vibration characteristics of carbon fiber/epoxy plywood with double-hole damage under the hygrothermal effect is investigated. Based on the first-order shear deformation theory (FSDT) and Hamilton’s principle, the intrinsic equations and the free vibration control equations of the laminate under moist heat effect were derived. A double-sided merged/separate step-repair plywood model was established by using ABAQUS software, and the vibration characteristics of double-sided gouge-repair plywood with different damage hole spacing and intact boards were analysed under different temperatures, humidities and hygrothermal coupling effects. The results show that the intrinsic frequency of the combined repair decreases with the increase of hole spacing, the intrinsic frequency of the separate repair increases with the increase of hole spacing, and this trend does not change with the change of temperature and humidity. When the damage hole distance is less than 20 mm, i.e., when the damage hole distance is less than 5 times the damage hole diameters, the combined repair is more effective; when the damage hole distance is 20 mm and 22 mm, the combined repair or separate repair has little effect on the recovery effect of the performance of the plywood; when the damage hole distance is greater than 22 mm, i.e., when the damage hole distance is greater than 5.5 times the damage hole diameters, the separate repair is more effective, and this kind of repair boundary can be well resisted by the temperature and humidity. Repair boundary can well resist the influence of temperature and humidity.

In order to improve the bonding performance of composite-steel interface, epoxy adhesive was modified by surface functionalized nano-montmorillonite (MMT) and silica (SiO₂). The effects of nano-particle content, adhesive layer thickness and lap length on the interfacial bonding performance of composite-steel double lap joint were studied. The test results show that when the mass ratio of nano-MMT/SiO₂ is 7∶3 and the total addition content is 1%, the tensile strength (46.13 MPa) and shear strength (12.79 MPa) of the specimens reach the highest, which are 53.2% and 44.85% higher than those of the pure epoxy adhesive specimens. The increase of the thickness of the adhesive layer can improve the bearing capacity and the maximum strain value of the specimen. The increase of lap length has obvious effect on improving the distribution gradient of strain and increasing the maximum shear stress and ultimate slip. As the overlap length increases, the bearing capacity of the specimen first increases rapidly and then slowly increases, which can be attributed to the existence of an effective bond length. Compared with pure epoxy adhesive, the epoxy adhesive modified by surface functionalized nano-MMT/SiO₂ has uniform distribution of internal particles and obvious cross-section roughness. This can reduce stress concentration and promote composite-steel interface interaction, thereby improving its bonding performance.

Due to the lack of systematic research on mechanical properties and damage behavior of the single lap bonded structures made of carbon fiber reinforced polymer composite (CFRP) and aluminum alloy (Al) under tensile and bending loads, the further improvement of the bonding properties and reliability is limited. In this study, the finite element model of CFRP-Al single lap bonded structure was established, and the mechanical response and damage distribution of the bonded structure under tensile load and three-point bending load were analyzed. Three-dimensional Hashin failure criterion and cohesive zone model were used to simulate the evolution process of intra-layer damage, interlayer damage and adhesive damage of CFRP, and the validity of the damage model was verified by comparison and analysis with experiments. Then, based on the bonding parameters, a multi-objective optimization proxy model with tensile strength, shear strength and bending strength as optimization objectives was constructed. The maximum relative error between the results of the proxy model and the simulation results was 2.57%, which verified the accuracy of the proxy model. On this basis, NSGA-Ⅱ algorithm was used to iteratively optimize the proxy model, and the three-dimensional distributed Pareto optimal solution set was obtained. Compared with the initial model, the optimized tensile strength, shear strength and bending strength of the bonded structure were increased by 7.34%, 24.12% and 9.51%, respectively, and the comprehensive connection performance of the bonded structure was effectively improved. This study provides a reference for reliability optimization design of bonded structures.

In order to reduce delamination and other damages during milling of carbon fiber reinforced composite (CFRP), improve its service life and production efficiency, the experiment of milling CFRP unidirectional laminates along various fiber angles (θ) was carried out by MV80 three-axis CNC machining centers. Based on the single factor experimental method, the influence of fiber angle and milling parameters on milling force and milling surface quality was studied. The results show that the main milling force is positively correlated with fiber angle at<90°, and negatively correlated with fiber angle at>90°; as the spindle speed increases, the main milling force decreases, and the main milling force increases with the increase of milling depth and feed rate per tooth; in different fiber directions, the surface roughness of CFRP decreases with the increase of spindle speed, but increases with the increase of milling depth and feed rate per tooth. When the fiber angle is 90°, the surface quality is optimal. The weight of milling force affected by different parameters is analyzed by orthogonal experiment. The results show that the fiber angle is the most important factor, followed by milling depth. And a mathematical model for milling force processing was constructed through linear regression of experimental data, aiming to provide a certain reference basis for optimizing processing parameters and digital processing of carbon fiber epoxy resin based composite.

Chemorheological analysis has been widely applied in the processing of thermoset matrix composites. However, traditional chemorheological models for predicting processing viscosity, such as the Dual-Arrhenius (DA) rheological model, exhibit limited accuracy in thermoset resin systems with multi-field coupling effects. To address this limitation, an artificial intelligence (AI)-based approach was introduced. The reactivity of the hydantoin epoxy resin/maleic anhydride (HY/MAD) system was investigated using differential scanning calorimetry (DSC), and viscosity data were collected under isothermal curing conditions at 65~85 ℃. A backpropagation artificial neural network (BP-ANN) model was developed and systematically compared with the DA model to analyze the rheological behavior of the HY/MAD system. The results demonstrate that the BP-ANN model significantly outperforms the DA model in predictive accuracy: the mean square error is reduced by 26.0%, the mean absolute percentage error decreases sharply by 65.0%, the root mean square error is lowered by 13.0%, and the coefficient of determination improves by 0.25%. This marked enhancement in prediction precision provides critical support for optimizing process parameters and material design in thermoset matrix composite manufacturing, particularly in scenarios involving complex multi-physics coupling.

This article focuses on the roller impregnation method and studied the influence of five process parameters on the quality of impregnated fabrics and the physical and mechanical properties of composite materials through the design of a five factor and three level orthogonal experiment. The research results indicate that the number of cycles in the impregnation process has the greatest impact on the resin content, followed by the resin preheating temperature. Rolling impregnation is suitable for low resin preheating temperature (30 ℃) and multiple rolling cycles (≥5 cycles) to ensure that the prepreg fabric has a high resin content, resulting in ideal resin content, density, and thickness of the composite material. The size of the mesh has a significant impact on the uniformity of fabric impregnation. A smaller mesh size (0.8 mm) is more conducive to uniform rolling impregnation, and the resulting composite material has higher mechanical properties.

A multi-role, long-endurance, vertical takeoff and landing tiltrotor composite fixed-wing UAV is designed. Maximum takeoff weight is 30 kg, and extended duration of flight is over 24 hours. Conceptual design, aerodynamic analysis and structure design of the UAV are completed. Static loading test of middle wing section is carried out, which is compared with numerical analysis data. Based on finite element analysis, the strength, stiffness and stability of the airframe are checked. Hashin failure criterion is used to determine the damage of carbon fiber panel and balsa wood core of composite sandwich structure, carbon fiber skin is also checked. Wing skin laminate design is optimized, and structure performance is assessed. It is showed that climbing by 2.5g load with pay load below the fuselage is the severest load case. High stress state is found in the center aera of the middle wing. Buckling tends to occur firstly at the upper skin of the middle wing. Initial structure damage mode is compression damage of balsa core. Performance requirements with excessive load margin is satisfied by initial composite laminate layup. Wing skin laminate layup is optimized by sub-region semi equi-strength design. Weight of the wing is reduced by 1.51 kg, about 17% decrease. Wing load margin is reduced to 0.13 which shows outstanding improvement of structure loading efficiency. The endurance of the UAV is estimatedby energy consumption relationship.

The limit state model of fiber-reinforced polymer (FRP) concrete under axial compressive load can be divided into design and analytical models. The axial compressive stress and strain included in the limit state form the basis of the model parameters. Accurately calculating these parameters can provide a decision-making basis for evaluating the performance of FRP-reinforced concrete structures. Through a comprehensive evaluation of the limit state model performance of FRP-partially confined concrete with a design-oriented approach, it is shown that existing models generally exhibit poor generalizability, low prediction accuracy, and high dispersion. In response to the limitations of existing design models, the compressive strength and ultimate compressive strain of 112 FRP partially confined concrete cylinders were predicted using the XGboost (extreme gradient boosting) machine learning method. The research results indicate that the XGboost model not only overcomes the shortcomings of existing empirical models, such as poor generalizability, low prediction accuracy, and high dispersion but also reflects the importance of various parameters on axial compressive stress and strain. Moreover, compared to existing design models, the computational values based on the machine learning model align better with the experimental values, with significantly reduced deviation and randomness, ensuring the accuracy and stability of the prediction results.

In order to analyze the influence effect of the reinforced span and the adjacent span and the longitudinal prestress loss effect of the CFRP plate reinforcement of the continuous T-beam bridge with different spans, so as to improve the utilization efficiency of the CFRP plate and the reinforcement effect of the T-beam. Firstly, the reinforcement and loading tests of the single-piece reinforced concrete T-beam reinforced by CFRP plate are carried out, and the test results are compared with the finite element analysis results to verify the rationality and accuracy of the finite element model. Then, a numerical model of CFRP plate reinforcement of 5 m×30 m continuous T-beam was established, and the influence of reinforcement effect and longitudinal prestress loss effect of reinforced span and adjacent span were analyzed. Finally, the tensile stress value of CFRP plate is optimized based on the influence matrix method and applied to the 5-span continuous T-beam solid bridge, and the prestress compensation of the 5-span T-beam of the bridge is verified by the load test after reinforcement to meet the design requirements. The results show that the influence law of reinforcement and longitudinal prestress loss of continuous T-beam bridge reinforcement span and temporary span are obvious, and the tensile stress value of CFRP plate can be significantly improved by optimizing the tensile stress value of CFRP plate based on the influence matrix method, and the optimization effect of side span and secondary side span can reach 38.16% and 24.64%, respectively.

The material used for the domestic radar cover is glass fiber/epoxy prepreg prepared by solution impregnation method currently, the prepreg prepared by solution impregnation method has problems such as difficulty in accurately controlling resin and volatile content, as well as environmental pollution caused by solvent volatilization. The glass fiber/epoxy prepreg (ES78/E40) were prepared by hot-melt film method using domestic raw materials, and the physical properties of the ES78/E40 prepreg were systematically researched as well as the mechanical and flame retardant properties of the composite material. The relevant properties of prepreg prepared by solution impregnation method were compared. The results show that the physical, mechanical, and flame retardant properties of ES78/E40 prepregs meet the requirements. The room temperature tensile strength and compressive strength of domestically produced prepregs were 517 MPa and 443 MPa, respectively, and the tensile and compressive strength retention of composites was about 80% at 71 ℃; compared with the performance of prepreg prepared by solution impregnation method, the tensile and compressive properties have been improved by 11.8% and 9.9%, respectively. ES78/E40 prepreg can be applied to secondary load-bearing structural components such as domestic radar covers.

As a practical and effective tool for surface deformation measurement, digital image correlation (DIC) technology has been widely accepted and increasingly used to measure the deformation and damage behavior of composite materials. Composite materials have the properties of non-uniformity and anisotropy, which lead to complex deformation behaviors after being loaded. Traditional measurement techniques cannot accurately capture these behaviors due to various factors. As an advanced optical measurement technology and means, DIC has significant advantages in measuring the deformation behavior of composite materials. The principle of DIC and the factors that affect measurement accuracy are described in detail. Then, the application of DIC in deformation measurement and damage characterization of composite materials is mainly introduced. Finally, the possible development direction of DIC in the future is prospected.