Forced vibration analysis of delaminated bilayer beams considering interface contact is conducted based on the semi-smooth Newton method. Beam elements with only translational degrees of freedom are employed to model the upper and lower sub-beams. The contact complementarity conditions at the delamination interface are transformed into non-smooth equations using the Fischer-Burmeister complementarity function. By incorporating a generalized Jacobian matrix formulation and an adaptive regularization strategy, the Newmark-β time-domain stepwise integration method is utilized for the solution, enabling robust capture of the dynamic opening and closing states of the delamination interface. To validate the effectiveness and accuracy of the model, a delaminated bilayer beam with both ends clamped is taken as an example. The results indicate that, even with a relatively small number of elements, the natural frequencies and time-displacement curves obtained are in good agreement with the finite element solutions from ANSYS. Even without considering geometric nonlinear factors, changes in contact conditions can still induce complex nonlinear dynamic behaviors in bilayer beams with delamination. As the excitation frequency varies, the system may undergo nonlinear dynamic behaviors such as periodic motion, period-doubling motion, and chaotic motion.

In this study, a sizing agent containing hydroxylated poly(phthalazinone ether sulfone ketone) (HPPESK) grafted multi-walled carbon nanotubes was designed to address the issue of insufficient interfacial bonding strength between short carbon fiber and thermoplastic resin matrix, which can lead to fatigue wear. This sizing agent effectively enhanced the interfacial and tribological properties of SCF/PPESK composites, achieving a friction coefficient as low as 0.14 under dry friction conditions at room temperature and a wear rate as low as 3.7×10^-16 m³·N^-1·m^-1. Compared to untreated composites, the wear rate decreased by approximately 24%. Furthermore, microstructural analysis and elemental surface analysis revealed the friction and wear mechanism of the SCF/PPESK composites, confirming that enhancing the interface is an effective strategy for improving the wear resistance of composites.

Adhesive joints are among the most vulnerable regions in composite material structures, particularly susceptible to damage under lateral impacts, which significantly affects their connection strength. This study proposes a novel page-type adhesive joint (PTAJ) and investigates its transverse impact damage and residual strength through finite element simulation and experimental testing. The findings demonstrate that the post-impact residual strength coefficient of the PTAJ exhibits a decreasing trend with increasing impact energy. Notably, the residual strength coefficient significantly improves with an increase in lap length. Furthermore, the PTAJ achieves a residual strength exceeding four times that of a single-lap adhesive joint of comparable dimensions, thereby showcasing its superior impact resistance characteristics and engineering potential.

To investigate the degradation behavior of the anchorage performance of carbon fiber reinforced plastics (CFRP) under seawater erosion, tensile shear tests of the bond joints between anchor fan and CFRP sheets, as well as pull-out tests of the bond joints between anchor bolt and concrete, were conducted under seawater wet-dry cycles. The failure modes, ultimate loads, and ultimate displacements of the specimens were summarized with the variation of wet-dry cycles, and the influence of adding short-cut carbon fibers to the resin material on the bond performance was analyzed. The test results showed that with the increase of wet-dry cycles, the failure mode of the anchor fan-CFRP sheet specimens gradually shifted from partial delamination to complete delamination on the bond interface. The ultimate load of the anchor fan-CFRP sheet specimens increased by 17.6% after 240 wet-dry cycles, while the ultimate load of the anchor fan-CFRP plate specimens decreased by 42.79%. The ultimate displacement of the anchor fan-CFRP specimens initially increased and then decreased by 40% to 50%. The ultimate load of the anchor bolt-CFRP specimens increased after each wet-dry cycle, with an increase of 25.16% after 180 cycles. The failure mode of the anchor bolt-CFRP specimens gradually changed from conical concrete breakout to complete pull-out of anchor bolt. The bond performance of the specimens with additional short-cut carbon fibers was not significantly improved.

Integrated carbon fiber reinforced polymer (CFRP) drive shafts featuring a flange-membrane disk-tube structure have emerged as a significant development direction for lightweight, high-performance transmission components, owing to their excellent specific strength/stiffness ratio and weight reduction potential. Addressing the unresolved challenge that existing models struggle to accurately characterize the influence of non-uniform resin distribution on cure-induced deformation and residual stresses within integrated CFRP drive shafts, this study proposes a novel cure deformation prediction method that incorporates resin distribution heterogeneity. Representative volume element (RVE) models with varying resin contents are established to predict the composite mechanical properties, thermal expansion, and chemical shrinkage characteristics. These predicted properties are then mapped onto a macroscopic finite element (FE) model of the drive shaft to simulate deformation behavior and stress distribution during the curing process. The research results demonstrate that non-uniform resin distribution significantly impacts deformation and residual stresses in integrated CFRP drive shafts. Specifically, for every 1% increase in the difference in resin volume fraction between the upper and lower sides of the shaft, the maximum cure-induced deformation increases by 0.63 mm, and the maximum residual stress rises by 1.05 MPa. Notably, when the resin volume fraction difference between the upper and lower composite sections reaches 40%, the maximum bending deformation of the tube section can reach 23.67 mm (without membrane disks) and 22.45 mm (with membrane disks). Concurrently, residual stresses are concentrated predominantly in the fillet regions of the integrated flange and membrane disk, exhibiting a maximum stress increase of 102.4%. Based on these findings, the paper further discusses deformation suppression strategies suitable for implementation in engineering. This work provides a crucial theoretical foundation and pathways for process optimization in the manufacturing of high-precision integrated CFRP drive shafts.

Carbon fiber-reinforced poly(ether ether ketone) (CF/PEEK) composites exhibit broad application prospects. However, due to the inert surface and low wettability of CF, the weak interfacial bonding between CF and PEEK limits the performance enhancement of CF/PEEK composites. To address this issue, in this study a flexible polymer sizing agent-sulfonated poly(aryl ether ketone) (SPEKC) is employed to modify the surface of CF. The surface morphology and structure of CF, as well as the interfacial and mechanical properties of the composites are investigated. Also, the interfacial reinforcement mechanism is analyzed. The results indicate that the sulfonic acid groups enhance the hydrophilicity and stability of the SPEKC sizing agent. The CF/PEEK composite modified with SPEKC-3 exhibits the best mechanical properties, with flexural strength and interlaminar shear strength reaching 1 232.61 MPa and 73.57 MPa, respectively, representing improvements of 14.8% and 6.2% compared to unmodified CF/PEEK composites.

To address the poor interfacial adhesion between high-modulus carbon fibers and resin matrices caused by the fibers' high chemical inertness and low surface energy, this paper proposes a novel method for modifying carbon fibers via the cathodic electrochemical grafting of imidazole-based ionic liquids. This study systematically investigated the effects of IL concentration and current density on the physicochemical structure of polyacrylonitrile-based HMCF surfaces and the interfacial properties of the resulting composites. The results indicate that the ILs were successfully grafted onto the acidified carbon fiber surfaces via electrochemical action, establishing a “chemical bridge” between the fiber and the matrix. Specifically, the amino terminals bonded with the oxygen-containing functional groups on the fiber surfaces, while the other ends participated in the curing reaction of the epoxy resin. This dual mechanism significantly improved both the surface wettability and the interfacial bonding strength ofthe carbon fibers. Notably, the optimal modification effect was achieved at an IL concentration of 5wt% and a current density of 25 A·m^-2, where the interfacial shear strength increased from 42.27 MPa (untreated) to 95.52 MPa, representing a remarkable enhancement of 125.9%. This study elucidates the interfacial reinforcement mechanism of electrochemically grafted ILs and provides a novel technical approach for optimizing the interfaces of HMCF com-posites.

In this paper, two kinds of composite materials reinforced with different fabric structures were designed and developed. Based on this new multi-layered multi-directional angle-knitted structure, the damage evolution mechanism of the warp and weft loaded specimens and its correlation with the fabric structure were systematically characterized through multiaxial mechanical testing (tension, compression and in-plane shear), combined with digital image correlation (DIC) technology and failure interface micro-topography analysis. Experimental data show that three-dimensional multi-directional woven composites made from different fabric structures have different effects on their mechanical properties due to different volume content and aggregation state of internal load-bearing fibers. Composites with a higher volume content of load-bearing fibers and a concentrated distribution structure exhibited significantly improved mechanical performance.

Existing composite repair technologies face limitations in complex process and timeliness, which require heating/pressurization equipment for curing and prove unsuitable for in-situ, low-energy, rapid field repairs. Frontal polymerization (FP) polymers, typified by dicyclopentadiene (DCPD), present compelling potential for emergency equipment maintenance. These resins achieve rapid curing under minimal thermal initiation, featuring simple processing, ultra-fast kinetics, low energy consumption, and exceptional mechanical properties. Consequently, this work investigates FP-based rapid repair of perforated composite laminates, systematically evaluating the impact of patch ply count, adhesive interlayer, and patch geometry on restoration efficacy. Results demonstrate optimal repair performance with 4 patch plies. However, the lack of adequate bonding between the FP patch and damaged parent plate initially limits the strength recovery ratio to 40.74%. The application of a rapidly curing epoxy adhesive (DP100 glue) at the repair interface increased the strength recovery ratio to 71.94%. Further geometric optimization of a trapezoidal patch configuration increased this ratio to 84.48%. Compared to conventional external patch repair, the FP-based technique delivers substantial advances: energy consumption decreases by 1~4 orders of magnitude, repair time shortens from hours to minutes, and the process eliminates auxiliary heating/pressurization equipment.

Aiming at the strength problem of the fiber-reinforced composite material transmission shaft structure applied in the new generation of aero engines, the research on the strength optimization design method of the composite material transmission shaft structure and the calculation and experimental verification of the strength parameters were carried out. By comparing the strength parameter calculation results of the RVE finiteelement model with the experimental results, all errors were within the reasonable range, which proved the correctness of the finite element simulation method. The overall model example of the unidirectional winding layer structure of the fiber-reinforced metal matrix composite material shaft structure was selected for optimization design application, and the composite material shaft laminated composite structure model was established to design the optimal layering scheme of the composite material shaft structure. Under the condition that the layer thickness remains unchanged, the optimallayering angle of 47.8° was obtained through calculation; under the condition that the layering angle remains unchanged, theoptimal layering thickness of 8 layers was obtained through calculation. The response surface method was used to optimize the strength design of the fiber-reinforced composite material low-pressure turbine shaft, and the optimization parameters were selected, with the maximum von Mises stress and the maximum Tsai-Wu index as the response values. The response surface model was obtained, and the second-order response surface approximated equation was obtained, thereby obtaining the optimal solution of the response values and the corresponding optimization parameters. These parameters were applied to the composite material low-pressure turbine shaft, and the results showed that the weight reduction rate of the optimized composite material shaft structure was 35.21%.

To address the issue of excessively high computational costs associated with 3D refined modeling in the ultimate strength analysis of large and medium-sized marine sandwich composite structures, an efficient “shell-solid coupling” simplified finite element model was proposed and validated. The 3D progressive damage failure criteria were dimensionally reduced and adapted to 2D shell elements. Taking a typical L-shaped stiffener connection structure as the research object, two simplified modeling strategies were comparatively evaluated: the coupling of solid elements for the core and shell elements for the skin (Method 1), and the equivalent overall shell element modeling for the entire sandwich panel (Method 2). The results indicated that Method 2 yielded significant deviations in predicting the basic structural stiffness. In contrast, Method 1, combined with a meshing strategy that allocates no less than 6 elements in critical regions (such as hat-shaped stiffeners), achieved a nearly hundredfold increase in computational efficiency while accurately reproducing nonlinear failure modes and keeping the ultimate load prediction error within 7%.

Aiming at the problem of low automation of the auxiliary system of fiber winding equipment, a robot automatic fiber hanging and cutting mechanism is designed, and the yarn breaking effect of key picking and cutting modules is emphasized and experimentally studied. Glass fiber and epoxy resin, which are widely used in the industrial field, are selected as the materials for this study. The influence of the number of fibers, the distance between the blades and the applied tension on the rotation angle of the robot end axis at the moment of fiber cutting is studied under both dry and impregnated states. At the same time, the morphology of the fiber bundle fracture is compared and analyzed to evaluate the cutting effect. The experimental results show that the rotation angle of the robot end axis increases with the increase of the number of fibers, and decreases with the increase of the distance between the blades or the applied tension. Under the condition of high tension, the impregnation treatment has no significant effect on the cutting effect. Under the same experimental conditions, the minimum cutting force required for the glass fiber bundle in the impregnated state is lower, and the morphology of the fracture is more uniform.

To address the resonance problem induced by the coupling between the structural modes of the tri-blade propeller quadrotor UAV and excitations at the propeller frequency (43-55 Hz) and its third harmonic (129-165 Hz), a resonance suppression method based on laminate parameter optimization is proposed. First, modal analysis was conducted to identify the roll mode of the entire UAV within the propeller frequency band and the bending-torsion mode of the middle frame within the third harmonic band, clarifying the resonance risk under multi-mode coupling. Subsequently, a sensitivity analysis of laminate parameters was performed to reveal that a higher proportion of 0° plies at the neutral surface results in a more significant enhancement of structural stiffness, and that the laminate parameters of the arms exert a coupled influence on multiple modes of different orders of the UAV. Therefore, with the constraints that the target modes (roll mode of the entire UAV and middle frame mode) are shifted out of the operating frequency band and no new resonance is induced in non-target modes, an optimization scheme was screened out, which adopts 45° plies at the neutral surface of the arms and reinforced 0° plies for the middle frame. Verification results from frequency response curves show that after optimization, the roll mode of the entire UAV is shifted to 59 Hz and the high-frequency mode of the middle frame is shifted to 188 Hz, both of which are moved away from the bandwidths of the propeller frequency and its third harmonic. In addition, the multi-directional frequency response curves at each measuring point exhibit no significant resonance peaks within the operating frequency band, no abrupt phase change of -90°, and the peak acceleration response of the arms is reduced by 20%, indicating that the resonance risk of the structure is effectively suppressed.

As aerospace technology advances towardlightweight and low-cost solutions,the performancerequirements forcomposite materials have become increasingly demanding. In this paper, a certain type of low-speed fixed-wing UAV airfoil NACA2415 was selected as the research object, and three different forms of wings were designed, including pure carbon fiber material structure, PMI foam sandwich structure and lightweight prepreg sandwich structure, and then the static loading test was carried out, and the finite element analysis was used to check the wing, and the stress, deformation and Tsai-Wu index results of the wing were given, and the optimal composite structure design form was compared. Finally, the accuracy of the finite element analysis results is verified by a static test. The results show that the lightweight prepreg sandwich structure meets the mechanical bearing requirements of the wing, and reduces the overall weight of the wing by 36.9%, achieving the purpose of light weight and low cost.

Aiming at the engineering problems such as large dimensional deviation, numerous internal defects and poor quality consistency that may occur in the RTM batch production for aircraft radome, studies were carried out on runner design, mold thermal compensation, process parameter optimization and optimization of non-destructive testing methods. Taking the wedge-shaped thin-walled cylinder component with a large opening (outer diameter Φ_A, height H, wall thickness 1.6 mm) as the research object, the resin flow, thermal stress deformation and defect assessment mechanism were systematically analyzed by means of ESI Group numerical simulation, GOM 3D scanning and rotary through-transmission water ultrasonic testing. The results show that the triggered linear one-inlet-one-outlet runner can significantly improve the filling uniformity and control the injection time within the process window. After mold thermal compensation and profile dimension compensation, the maximum outline deviation is reduced from 4 mm to less than 1.5 mm. The rotary through-transmission water ultrasonic method enables efficient non-destructive testing of thin-walled components embedded with copper mesh, and the products meet the Class C requirements of GJB 2895-97. This research can provide engineering references for the quality consistency control of RTM molded complex curved components of aviation composite materials.

Silica (SiO₂) aerogels exhibit excellent thermal insulation properties owing to their unique nanostructure, and have been widely used in the field of unmanned aerial vehicles (UAVs). However, their practical applications in high-temperature parts of engines are severely restricted by the limitation that their long-term service temperature cannot exceed 650 ℃. The type and reaction characteristics of silicon precursors determine the particle size and crystal phase of SiO₂ aerogel nanoparticles. At elevated temperatures, the shrinkage and collapse of nanoporous structures, as well as crystal phase transitions, significantly affect their thermal stability. This paper reviews the research progress on the high-temperature resistance of SiO₂ aerogels prepared from organosilicates, doped precursors, inorganic precursors and crystalline precursors. Research has shown that the high-temperature resistance of SiO₂ aerogels can be improved to above 1 200 ℃ through modification strategies such as element doping, increasing the particle size of SiO₂ sol particles, and regulating the crystal form of precursor particles. Combined with the current research status, the future development directions of high-temperature-resistant SiO₂ aerogels are discussed.

Pre-oxidation is an important step in the production process of polyacrylonitrile (PAN) based carbon fibers. During the pre-oxidation process, PAN fibers are transformed into a non-melting and non-combustible state at 200-300 ℃ in an air atmosphere, providing structural support for the carbonization reaction and directly determining the mechanical properties of carbon fibers. The existing pre-oxidation methods with heating forms have problems such as long processing time, high energy consumption, and uneven oxygen diffusion causing skin-core structure. Therefore, finding new pre-oxidation methods with different reaction forms has always been one of the key research directions in carbon fiber research. This paper reports the current research status of microwave, ultraviolet, electron beam, gamma ray and plasma irradiation treatment of PAN fibers, and finds that the energy field-assisted pre-oxidation method can effectively reduce the pre-oxidation temperature and shorten the pre-oxidation time, solving the shortcomings of long processing time and high energy consumption in traditional pre-oxidation.

As a core primary load-bearing structural component of aircraft, the fuselage frame is characterized by a special structure, large quantities demanded, and stringent requirements for quality consistency. Its manufacturing technology level directly determines the aircraft's lightweight degree, structural safety, and production efficiency, making it a key focus and difficulty in aviation composite manufacturing field. This paper systematically analyzes the common structure and manufacturing technologies of composite fuselage frames, focusing on analyzing 9 kinds of manufacturing technologies, including thermoset composite automated preforming/3D braiding + autoclave curing/liquid composite molding, and thermoplastic composite fuselage frame manufacturing, from the aspects of equipment and technology control maturity, product consistency, applicable scenarios, and application cases. In addition, the future development trends of allthe abovetechnologies are evaluated and discussed.