The study involves monitoring residual strains and investigating failure behavior in thick L-shaped composite laminates. It aims to explore how the stacking sequence under high thickness conditions affects the structural load-bearing capacity and failure modes. Utilizing embedded fiber bragg grating (FBG), the study monitors the evolution and distribution characteristics of the temperature field and strain field within the curved region of the L-shaped composite laminate during the curing process. It aims to investigate how thickness and ply orientation angle influence the thermal residual strain and spring-in angle in L-shaped composite laminates. Conducting bending tests, utilizing DIC(digital image correlation) to observe the strain field and failure modes in the lateral cross-section. And comparing the results with empirical formulas, exploring the influence of thermal residual stress under different ply orientations on the load-carrying capacity and failure modes. The results indicate that the large-thickness L-shaped laminates exhibit a certain temperature gradient, but the temperature difference between the upper and lower layers and the middle layer is relatively small. Due to the mold effect, L-shaped laminates with angles are more likely to generate pre-loaded regions on the inner side of the corner compared to pure 0° ply. The results of the bending test indicate that the ultimate load obtained for pure 0° ply is essentially consistent with the theoretical prediction. However, for quasi-isotropic ply, the ultimate load is 25% smaller than the theoretical prediction. The pre-load region has a certain influence on the subsequent load-carrying capacity and failure mode.

In order to investigate the structure and mechanical properties of stitched composite materials, aramid fibers were utilized as stitch threads and a modified lock stitching technique was employed to prepare unidirectional carbon fiber fabric preforms with different stitch densities and numbers of stitch layers. Composite materials were prepared by vacuum-assisted resin transfer molding (VARTM) process, and their internal structure as well as type Ⅰ interlaminar fracture toughness, impact performance, bending and compression properties were systematically investigated. The results show that the composite material exhibits the best comprehensive mechanical properties when stitched 9 layers at a density of 4 mm×4 mm. Compared with the unstitched composite material, the type Ⅰ fracture toughness increases by 50.8%, the maximum impact load increases by 46.2%, the energy absorption rate increases by 27.0%, the bending strength increases by 15.4%, the compressive strength increases by 4.1%, and the compressive modulus does not decrease. Conversely, for composite materials stitched with 3 layers at once, the bending and compression properties decrease with different stitch densities both decrease. After analysis, it is found that increasing the stitch density effectively enhance the interlayer performance of composite materials, while increasing the number of stitch layers help to reduce the impact of stitching on in-plane performance, providing important references for selecting stitching process parameters.

Needled-punched ceramic matrix composites are promising for a wide range of applications in hot-end structures in aerospace field. However, the manufacturing defects causing in the process of pre-fabrication and deposition lead to a high degree of dispersion in their properties. It is difficult to accurately predict their mechanical behavior. A sub-regional parametric characterization method for pore defects in needle-punched ceramic matrix composites was proposed based on X-ray microscopy and 3D image reconstruction techniques. Combined with the idea of probabilistic fitting, the size and structural characteristics of the material pore defects were parametrically characterized, and it was found that the equivalent diameter of the pores in the fiber-web layer was larger than that in the unidirectional layer, but the aspect ratio was smaller than that in the unidirectional layer. The elastic properties of the materials were predicted and analyzed using ellipsoid fitting and multiscale modelling methods, and the predictions differed from the experimental results by about 3.1% with good accuracy. The discussion of pore parameters revealed that: the unidirectional layer porosity has better uniformity in the distribution direction, and the reduction of the elastic properties in the direction of the fiber bundle length is lower than that in the other directions; in comparison, the fiber-web layer has higher porosity, and it is beneficial to reduce the porosity of the fiber-web layer to further improve the overall elastic properties of the material by improving the process parameters.

Permeability is a key parameter in the molding process of fiber composites, which is determined by the fiber structure. For the component with curvature, the fiber shear deformation is hard to avoid, which changes the fiber structure and affects the permeability. In order to study the changing trend of fiber in-plane permeability under shear deformation and to establish the prediction model of permeability main value and direction, two-dimensional radial flow experiments were used to test the permeability of woven fiber and non-crimp fiber. By ellipse tensor superposition and Kozeny-Carman equation, fiber redirection and fiber volume fraction were extracted as the main influencing factors of permeability. The factors were quantified to establish a permeability prediction model. By combining the theoretical model with the experimental data and several sets of literature data, the model parameters are further simplified, and the in-plane permeability prediction model is obtained which is widely applicable to orthotropic woven fiber fabric and non-crimp fiber fabric.

Carbon fiber reinforced plastics have high strength and stiffness, and are widely used in industrial applications. The bonding form between steel and carbon fiber reinforced plastics is crucial for enhancing the strength at the bonding interface. In this study, a novel bonding structure was proposed: steel plates with equidistant holes, and carbon fiber fabric woven in an S-shape and bonded between the steel plates and carbon fibers to form a hybrid adhesive-woven bonding. The destructive tests were performed on both the hybrid adhesive-woven bonding joints and the adhesive bonding joints, comparative results indicate that the introduction of weaving process alters the stress state at the adhesive interface, transforming the failure mode from complete delamination at the steel-adhesive interface to a coupled failure mode that includes complete delamination at the steel-adhesive interface, partial delamination at the steel-adhesive interface, carbon fiber (damage) fracture, weaving slip, and steel plate distortion. Moreover, the unit thickness peak strength of the hybrid adhesive-woven bonding joints was found to be 25% higher on average than that of the adhesive bonding joints. Furthermore, the influences of the number of holes and the weaving width on the strength of the hybrid adhesive-woven bonding joints were investigated. It was observed that the strength of the bonding joints initially increased and then decreased with an increase in the number of holes. As for the weaving width, the strength of the bonding joints increased, but the rate of increase gradually slowed down. The bonding joints with a weaving width of 25 mm and a double-hole structure exhibited the highest strength, while those with a weaving width of 10 mm and a four-hole structure had the lowest strength, with an improvement of 106.38% compared to the lowest strength.

Compared to the traditional mixed variational principles, the superiority of generalized mixed variational principles with splitting factors is very obvious. At present, the selection of splitting factor values in generalized mixed models is an open problem. Based on the theory of strain energy equal to complementary energy and strain energy and complementary energy equal to half of the mixed energy in the linear elastic problem, an error analysis method for selecting splitting factors is proposed. This method provides a new approach for obtaining appropriate splitting factors for the compatible generalized mixed elements. Numerical example analyses show that the splitting factor value of the compatible mixed element obtained by the method in this paper can adapt to the 3D composite laminated plate problem, and more accurate numerical results can be obtained under the same mesh model.

In order to analyze the strain development law of the PVC-CFRP confined concrete column-RC beam exterior joints with core steel tube, through low cyclic tests of ten exterior joints with core steel tube(CST) and one typical joint. The effects of the steel ratio of the CST, stirrup ratio of the joint, axial compression ratio, longitudinal reinforcement ratio of the beam, and CFRP strips spacing were analyzed. The test results show that shear failure occurred at the joints, while no damage occurred at the PVC-CFRP confined concrete columns and beams. In the early stage, the shear force of the joint is mainly borne by the concrete; when the specimen bearing capacity reaches the peak bearing capacity, the diagonal pressure of the joint is still borne by the concrete, while the joint’s ring stirrups and the column’s longitudinal reinforcement jointly bear the diagonal tension. The CST can directly participate in the shear resistance. The calculating formula of the joint shear bearing capacity is proposed by considering the influence of the steel ratio of the CST, stirrup ratio of the joint, and axial compression ratio are considered, and introducing the comprehensive influence coefficient of joint shear resistance. The calculated results agree well with the experimental data.

In order to study the lightning damage characteristics of carbon fiber composite laminates under different protection methods, the lightning damage of three kinds of carbon fiber composite laminates, which are unprotected, aluminum-coated and copper-mesh-protected, is studied by the way of simulation and test. Three kinds of laminated plate models are established in the finite element simulation software, and A+B+C^* combined waveform lightning current is uniformly applied to analyze the damage characteristics of the laminated plate under different protective methods, at the same time, the protective effect of copper mesh with different characteristic parameters is evaluated. The simulation results show that the damage shape is determined by the conductivity laminates. The damage shape of unprotected laminates is related to the laminates, the damage area and depth of the laminate are reduced effectively with protection of spraying aluminum or copper mesh, the damage area and damage depth decrease with the increase of the width of copper mesh. The validity of the finite element model is verified by experiments.

Carbon fiber reinforced plastics (CFRP) laminates are prone to damage and instability when subjected to out of plane loads due to their significantly lower normal stiffness compared to in-plane stiffness. In order to toughen the thickness direction, the effect of modified nano ZnO toughened films on the mechanical properties of CFRP laminates was studied. Nano-ZnO is first modified by coupling agent to obtain modified nano-ZnO, which was added into epoxy resin as nano-filler. By blending modified nano-ZnO particles at different mass ratios from 0 to 4wt% in the presence of a curing agent, some cohesive films with different interlaminar properties were formed between the two interfacial surfaces in a composite specimen, which have been applied in end-notched flexure (ENF) tests and double cantilever beam (DCB) tests. A series of finite element (FE) models, together with the predetermined model parameters, were built to assess the influence of modified nano-ZnO and curing agent. The results show that, for the toughened beam (with 4wt% modified nano-ZnO and 2wt% GEL2-BS), the critical loads of ENF tests and DCB tests increases by 30.25% and 68.40%, respectively.

Two-dimensional continuous fiber reinforced ceramic matrix composites are important application materials in the aerospace field. However, the application of such materials is severely constrained by interlaminar fracture. In order to monitor and evaluate the interlaminar mode Ⅰ fracture toughness of materials, the direct current potential drop test (DCPD) of interlaminar mode Ⅰ fracture was carried out. The loading data during the initiation and propagation of interlaminar mode Ⅰ crack and the potential drop data of corresponding measuring points were obtained. The cause of the change of related characteristics was quantitatively analyzed by establishing a force-electric model. The test results show that at the initial stage of the crack, that is, the inflection point of the linear to nonlinear loading curve, the potential drop at the prefabricated crack tip has a smooth-lifting change. With the further expansion of the crack, the debonding and fracture of the fiber are caused, and the uplift curvature is increased on the potential drop curve. When the crack propagation is subjected to resistance, such as Z-pin pull-out and secondary cracks initiation, the uplift of the potential drop curve will be significantly slowed down. Finally, the validity of the proposed force-electric model to explain the above curve changes is proved by the experimental data. The research results have certain guidance and reference value for the application of electrical properties of materials to monitor and evaluate the interlaminar mode Ⅰ fracture toughness.

In the process of composite winding, the frictional behavior between the fiber and mandrel can lead to slip. The condition of stable winding is that the maximum slippage coefficient of the designed fiber trajectory is less than or equal to the friction coefficient between the fiber and the mandrel, so the friction coefficient between the carbon fiber and the mandrel is an important basis in the design of the fiber trajectories. Friction experiments using a sled based on principle of plane friction are performed in order to characterization the friction coefficient. The influence patterns of normal force, velocity, roughness, resin viscosity, contact material, the angle of fiber and the direction of motion and the type of fibers on the coefficient of friction were obtained. The results show with the increase of normal force or the decrease in velocity and roughness will lead to the decrease in the coefficient of friction. A change of viscosity and fiber orientation have a double effect on the coefficient of friction, which shows different effects with the change in normal force and velocity, and different contact materials and fiber types will lead to different coefficients of friction due to the differences in the surface conditions.

In this paper, the failure modes of the bonded-bolted lap joint of carbon-glass hybrid composite under bending loads were investigated through numerical simulations and experimental validation. The influence of the thickness ratio of the upper lap plate on the strength and stiffness of the hybrid joint was then examined, and the optimization design is presented based on the numerical and experimental results. The results show that the numerical and experimental load-displacement curves are in good agreement, with the initial damage occurring due to adhesive layer failure at the right end of the joint area, at which point the first peak load is achieved. With the increase of displacement, cracks continue to propagate until complete failure of the adhesive layer occurs, after which the bolt continues to bear load independently until the composite material undergoes compression failure, leading to the overall structural failure eventually. The optimization results indicate that increasing the thickness ratio of the upper lap plate can effectively enhance the ultimate load capacity of the joint. Specifically, the ultimate load capacity of the joint structure with a upper thickness of 65% of the total FRP skin is increased by 98.6% compared to the original design (with the upper thickness of 50% of the total). The final failure mode shifts from the compression at the right-side of the bolt hole in the upper lap plate to both the upper and lower plates with similar degrees of failure, and the optimal structural efficiency achieved.

Both of heat distortion temperature (T_HD) and glass transition temperature (T_g) are commonly used to characterize heat resistance of glass fiber reinforced unsaturated polyester resin matrix composites (GFRP) in lots of engineering design and applications. In this study, the suitable method of testing T_HD of GFRP were established by selecting experimental approaches. The effects of curing systems and curing conditions of resins, different fabric pattern of reinforcement and fiber content of GFRP on their T_HD and T_g are studied. The correlation between T_HD and T_g of GFRP and its matrix resin was investigated. The initial temperature of glass transition T_g,G′i and the final temperature of the glass transition T_g,G′f by the curve of storage modulus vs. temperature are defined to be applied in manufacturing, inspecting and engineering application of GFRP.

The foaming agent B-AEP was synthesized using N-aminethylpiperazine (AEP) and carbon dioxide as raw materials, and subsequently loaded onto the surface of graphene oxide (GO). This resulted in the successful preparation of functional graphene oxide particles with integrated nucleus, foam and reinforcement, known as GO@B-AEP. Furthermore, functional graphene oxide modified phenolic (GO/PF) microfoamed composites were prepared through a one-step limited foaming method. The structure of GO@B-AEP was characterized using infrared spectroscopy and scanning electron microscopy (SEM). The effects of varying amounts of GO addition, apparent density, and foaming agent content on the mechanical properties of GO/PF microfoamable composites were investigated using a multipurpose testing machine and Shore hardness tester. Additionally, SEM analysis was conducted to analyze the micropore structure and pore size distribution. The results demonstrate that optimal mechanical properties and thermal stability are achieved when the dosage of GO is 0.4wt%. Similarly, superior pore quality is observed at an apparent density of 1.0 g/cm³. Moreover, when the content of foaming agent is set at 1.5wt%, improved shape and size characteristics are observed in the pores along with significantly enhanced mechanical properties in GO/PF microfoamed composites.

This paper used chopped glass fibers as the skeleton structure and TEOS-modified phenolic resin as the binder to prepare a low-cost, medium- and low-temperature-resistant insulation glass fiber insulation tiles (GIT) by vacuum filtration method, and the influence laws of the hybrid resin binder on the microscopic morphology, mechanical properties and thermal insulation performance of the insulation tiles were specifically investigated. The results indicate that TEOS has good compatibility with phenolic resin and the rigid and flexible dual network interpenetrating structure can be successfully constructed. The prepared fiber glass tiles all have typical quasi-laminar distribution with densities range from 0.20 to 0.26 g/cm³. Among them, GIT-100 has the best comprehensive performance. The compressive strength in Z direction and X/Y direction shows maximum value of 0.695 MPa and 3.546 MPa at the strain of 5.1% and 4.2%, respectively, the rebound resilience ratio is as high as 90% at the compressive deformation of 15%, the thermal conductivity at room temperature is 0.047 5 W/(m·K), and the compressive strength decreases by 12.5% after heat treatment at 400 ℃.

In order to solve the problem of excessive weight of the mining helmet, carbon fiber reinforced composite (CFRP) material was devised to substitute for the conventional ABS plastic to realize the lightweight design of the mining helmet. The finite element model of steel ball-helmet for collision simulation was established. The mechanical properties of ABS and CFRP helmet shell were compared and analyzed in simulation. The strength and stiffness of CFRP helmet shell are superior to ABS casings, and have better protective properties. The input-output relationship between CFRP lamination parameters and helmet mechanical properties was simulated by BP neural network. And the global optimization of helmet mechanical properties was realized by particle swarm optimization algorithm. The optimization results indicate that the optimal lamination parameters consist ofa total number of 6 layers of CFRP, with each layer having a thickness of 0.2 mm and arranged in the following angle sequence . The collision simulation results show that the optimized CFRP helmet’s top experiences a maximum deformation of 19.601 mm, while the headform endures a maximum force of 4.891 kN. The optimization configuration can meet the requirements of relevant national standards and achieve a lightweight design with 49.3% weight reduction compared with the ABS helmet shell.

The suspended composite power equipment pedestal is a new type of vibration-damping pedestal, which mainly reduces vibration by extending the vibration transmission path and using composites. Aiming at the main load-bearing structure of the pedestal, a glass fiber reinforced plastic (GFRP) composite column is designed and prepared, and the effects of the fine parameters of the composite and the macroscopic parameters of the column on the dynamics of the GFRP column are analyzed by experimental and numerical calculation methods. The results show that the layup angle and fiber volume fraction have a large influence on the dynamic characteristics of GFRP columns, and the performance is not consistent with changing odd and even layups, and the macro parameters of the column structure also have an influence on the dynamic characteristics of the columns. The results of the study can provide a reference for the design and application of suspended composite power plant pedestals.

To reduce the weight of the vehicle body, a lightweight design was applied to the metal battery pack lid using glass fiber composite materials. The process involved utilizing black flame-retardant glass fiber grid cloth prepreg and DP590 steel plate integrated molding technology. Through experiments and microscopic analysis, acid-base cleaning, sandblasting, and electrophoretic coating were identified as the optimal modifications for the steel plate. Nine orthogonal experiments were designed for glass fiber-steel plate reinforced composite materials with a total thickness of 1.5 mm. Simulation analysis and experimental testing were conducted for the nine different combinations, focusing on bending and tensile simulations as well as testing experiments. The mechanical properties of the composite materials were obtained, with a maximum relative deviation of 1.49% between simulation and testing results, indicating the reliability of the simulation. Through extreme difference analysis of the orthogonal experiment results, the optimal process parameter combination was determined to achieve the best bonding strength. The recommended parameters include a mold temperature of 150 ℃, molding pressure of 12 MPa, steel plate thickness of 0.8 mm, and a 1+1 steel plate composite structure. The tested samples met design requirements for peel strength, water absorption, flame resistance, heat deformation temperature, and voltage resistance. The weight reduction achieved was 39.4%, meeting the requirements for lightweight design.