This paper investigates the effect of atmospheric pressure plasma treatment speed on the surface properties of polyimide (PI) thin films and reflects the plasma modification mechanism through DFT calculations. Through experiments, the effects of treatment speed on surface chemical composition, morphology, wettability, and mechanical properties were analyzed in detail. The results show that as the treatment speed decreases, the content of oxygen elements and oxygen-containing functional groups on the film surface first increases and then decreases, reaching a peak at 6 mm/s. At the same time, the surface free energy increases significantly, and wettability is improved. Surface roughness increases as speed decreases, but excessive machining may result in a decline in mechanical properties. The tensile test results show that after being treated at a speed of 6 mm/s, the tensile strength of the film reached 259.2 MPa, and the elongation at break was 25.02 %. Based on Materials Studio (MS) software and density functional theory (DFT) calculations, the chemical bond dissociation energy of PI molecules was analyzed, and the reactivity order of polar functional groups (-C=O, -OH, -COOH) was determined, thereby revealing the reaction mechanism of the plasma treatment process.

In order to improve the lap shear strength (LSS) of carbon fiber/epoxy composite resistance welding joint, this study used atmospheric plasma to treat the CF/EP surface to improve its physical and chemical properties and enhance its resistance welding strength with thermoplastic resin (PA6). This study investigated the effects of atmospheric plasma treatment power (800 W, 900 W, 1000 W) and treatment time (30 s, 35 s, 40 s) on the LSS of CF/EP resistance welding joint. The results show that the enhancement mechanism of CF/EP resistance welding joint varies with changes in treatment power and treatment time. Extending the treatment time at low treatment power can improve the LSS value of CF/EP resistance welding joint to a limited extent, while extending the treatment time at high treatment power weakens the enhancement effect of atmospheric plasma treatment on the LSS value of CF/EP resistance welding joint. The LSS value of CF/EP resistance welding joint can only be maximized when atmospheric plasma treatment is performed at the appropriate treatment power and treatment time. The study results show that the optimal atmospheric plasma treatment parameter is 900W/35s (i.e. atmospheric plasma treatment of CF/EP at a treatment power of 900W for 35s). When the CF/EP surface is treated with the atmospheric plasma under the optimal treatment parameter, the LSS value of the CF/EP resistance welding joints can reach 21.35 +/- 1.17 MPa, which is an increase of approximately 161% compared to the untreated CF/EP welding joints. By observing the surface morphology of CF/EP after atmospheric plasma treatment and analyzing the wettability and chemical composition changes of the CF/EP surface, it can be seen that atmospheric plasma treatment not only effectively improves the roughness of the CF/EP surface, but also generates a variety of oxygen-containing polar groups on the CF/EP surface, improving the wettability of the CF/EP surface. This improves the interfacial bonding strength between the CF/EP surface and the thermoplastic resin, changes the failure mode of the CF/EP resistance welding joint, and significantly improves the LSS value of the CF/EP resistance welding joint.

This study establishes a systematic mechanistic framework for phthalonitrile resins containing polyimide skeletons (PIPN) to address their narrow processing window and unclear thermo-mechanical regulation. Six PIPN model compound with varied dianhydride structures PM (PMDA), BP(BPDA), F (6FDA), ABP(ABPDA), K(BTDA), E (BPADA) were designed and synthesized. Through integrated multiscale simulations and experimental characterization, a comprehensive "structure-weak interactions-packing order-molecular mobility-energetics-macroscopic properties" correlation model was constructed for the first time. Molecular backbone rigidity, symmetry and planarity govern the performance: fully rigid PM-PIPN exhibited strongest pi-pi stacking and electrostatic interactions, yielding the highest melting point (390 degrees C) and superior predicted modulus. Conversely, flexible segments (E-PIPN) or sterically hindered groups (F-PIPN) systematically weakened intermolecular interactions, reducing both melting point and modulus while increasing Poisson's ratio. Electrostatic potential analysis, weak interaction visualization (IRI), mean square displacement (MSD) and cohesive energy density calculations synergistically revealed the regulation mechanisms from electronic, spatial, dynamic and energetic perspectives. This mechanistic framework provides theoretical foundations for rational molecular design of high-performance PIPN resins.

To meet the stringent demands for high thrust-to-weight ratios and extreme lightweighting in next-generation aero-engines, advanced polymer matrix composites (PMCs) have been extensively utilized in the design of primary load-bearing structures for bypass casings. However, inevitable characteristic cutouts—such as piping and assembly holes ranging from 30 to 100 mm in scale—within the cylindrical casing induce severe stress concentrations around the hole edges. This significantly disrupts structural continuity and leads to a drastic degradation in critical load-bearing capacity. To address this mechanical bottleneck, a multiaxial load decoupling analysis under complex service conditions was initially conducted, revealing the evolutionary mechanisms of the casing's structural mechanical responses induced by various dominant load components. Building upon this, leveraging the OptiStruct finite element solver, a synergistic optimization of the free size (ply thickness) and stacking sequence was performed on the composite laminates in the primary load-bearing zones, thereby establishing the optimal anisotropic material distribution to satisfy macroscopic stiffness requirements.To overcome the strength degradation inherent to cutout regions, this paper proposes a refined localized interleaved reinforcement strategy driven by a comprehensive parametric study. By innovatively introducing the dual equivalence criteria of "equal-ratio" and "equal-area," parameterized models for circular and square patches are constructed. The study first quantitatively evaluates the nonlinear mapping relationships among the patch geometric area, structural weight penalty, specific strength enhancement efficiency, and critical load-bearing capacity. This quantitative evaluation highlights a remarkable "efficacy reversal" phenomenon, wherein the performance of square patches surpasses that of circular configurations beyond a critical reinforcement ratio. Furthermore, to elucidate the underlying physical mechanisms driving this phenomenon, the mechanical response characteristics within the high-gradient stress regions surrounding the cutouts are systematically extracted. This approach qualitatively delineates the internal load-transfer pathways and reveals the distinct mechanical regulation mechanisms of the two patch configurations across multi-scale cutout diameters. Building upon these mechanistic insights, explicit size-dependent engineering guidelines are established, determining the optimal critical reinforcement ratios to be 2.1–2.2 for small cutouts and 2.3–2.4 for medium-to-large cutouts. Additionally, the sensitivity of the overall enhancement efficacy to the intra-ply proportions within the reinforcement layers is systematically clarified. To bridge the gap between theoretical mechanics and practical manufacturing, these mechanistic insights and quantitative criteria are translated into a comprehensive six-step engineering design workflow, explicitly embedding the size-dependent critical ratios and the 2.4 patch configuration transition threshold. Ultimately, a synergistic design methodology integrating global stacking sequence optimization with localized interleaved reinforcement is proposed, establishing a comprehensive structural design paradigm tailored for cutout structures in advanced composite bypass casings. These findings not only elucidate the damage tolerance enhancement mechanisms of composite casings but also furnish robust theoretical foundations and engineering references for the lightweight and highly reliable design of complex load-bearing structures in aero-engines.

The three-dimensional hollow structural design combined with component regulation has been recognized as an effective strategy for achieving lightweight, broadband microwave absorption. Herein, nitrogen-doped hollow carbon microcubes modified with in situ catalytic growth carbon nanotubes (Ni@CNTs/N-HCMs) were successfully fabricated using a salt-template technique followed by a subsequent chemical-catalyzed self-deposition (CCSD) process and a simple water-washing step for template removal. Benefiting from the unique structural features improving the impedance matching and the synergistic effect of multiple components enhancing loss capacity, the microwave absorption performance of the as-obtained Ni@CNTs/N-HCMs composites could be effectively regulated and optimized. Remarkably, with a filling loading of only 3.5 wt%, the optimal reflection loss can reach up to -46.7 dB at 3.7 mm and the maximum effective absorption bandwidth attains 6.1 GHz at 2.0 mm, respectively. Importantly, the salt templates are more economical and environmentally friendly, and the salt templates offer the potential for recycling, facilitating large-scale production of the material. This study provides an innovative path for constructing high-performance functional carbon-based microwave absorption materials.

This study successfully prepared high-performance polyimide/polyetherketone ketone (PI/PEKK) composite films through atmospheric pressure plasma modification combined with solution coating technology, with the aim of improving the thermal stability and mechanical properties of aviation cable insulation materials. Firstly, a PEKK multi-scale water-based dispersion scraping process was developed, and 380 degrees C was determined to be the optimal sintering temperature. Composite film performance tests show that a PEKK coating with a concentration of 10 wt% can form a uniform and continuous coating on the PI film surface, and the PI/PEKK composite film exhibits excellent comprehensive performance. In terms of thermal stability, the glass transition temperature reaches 292 degrees C, which is a significant improvement over the pristine PI film (272.5 degrees C). The initial decomposition temperature (T5%) exceeds 520 degrees C, and the carbon residue at 800 degrees C remains above 57%. In terms of dielectric properties, the dielectric constant in the 40 Hz low frequency range has been increased to 3.49, while maintaining low dielectric loss. In terms of mechanical properties, the tensile strength reached 293.28 MPa, and the peel strength was as high as 5.12 N/cm.

The effects of different welding parameters and water absorption on the properties of ultrasonic welded carbon fiber reinforced polyetheretherketone (CF/PEEK) composite joints were studied. The results show that the lap shear strength (LSS) reaches a maximum of 40 MPa when the welding pressure is 0.35 MPa, the welding time is 3.0 s, and the welding amplitude is 24 um (80%). The mechanical strength and fracture morphology of the welded joints were characterized by a universal testing machine and scanning electron microscope (SEM). The results show that the influence of welding parameters on the LSS of the joint increases first and then decreases. Too low or too high welding parameters will deteriorate the mechanical properties of the joint. In addition, the failure modes of four types of joints were analyzed and summarized. The study found that the boiling time was negatively correlated with the combined LSS value. With SEM observations post-hygrothermal aging, interfacial morphologies before/after aging were compared; water molecules induced resin swelling, reducing joint strength.

Recognized as a critical environmental hazard in modern industry, electromagnetic radiation poses substantial risks to human health and the ecosystem, necessitating lightweight and broadband microwave absorption materials as essential components of electromagnetic safety strategies. This work demonstrates a hollow engineering strategy for magnetic graphene composites, wherein centrifugal spray drying combined with subsequent high-temperature pyrolysis yields graphene hollow microspheres with magnetic nanoparticles uniformly anchored onto their inner and outer walls. The influence of pyrolysis temperature on the microwave absorption properties of the resulting composites is systematically investigated. Experimental results reveal that the pyrolysis temperature critically governs the phase crystallinity, graphitization degree and magnetic characteristics, thereby determining both their dielectric loss and magnetic loss capacities as well as the impedance matching behavior. An optimal pyrolysis temperature (800 ℃) yields superior broadband microwave absorption, achieving a minimum reflection loss (RLmin) of -45.3 dB and an effective absorption bandwidth (EAB, RL<-10 dB) exceeding 5.8 GHz at a thin thickness of 1.82 mm. The exceptional performance is attributed to the synergistic interplay of multiple attenuation mechanisms, including dielectric loss from the defective rGO and hollow cavity-induced multiple reflections, magnetic loss from the embedded nanoparticles, and enhanced impedance matching enabled by the hollow architecture. These findings advance the understanding of pyrolysis-temperature effects on microwave absorption and establish a promising platform for hollow-structure engineering.

As the issue of electromagnetic pollution continues to intensify, the design of high-performance microwave absorption materials featuring lightweight, broad bandwidth and strong absorption has become a key research focus. In this work, we propose a strategic integration of electrospinning technology and melamine-assisted chemical vapor deposition (CVD) to construct carbon nanotube (CNT)-bridged polymer-derived carbon nano-fiber (PCNF) composites (denoted as CNTs/M@PCNFs). In this architecture, CNTs effectively bridge adjacent PCNFs, forming an interconnected conductive network. The resulting composites exhibit significantly enhanced dielectric loss capability due to the improved conductivity, interfacial polarization, and multiple scattering. Furthermore, nitrogen doping derived from melamine introduces additional dipole polarization and optimizes impedance matching. Consequently, the composites achieve excellent microwave absorption performance, with a low filler loading of only 10 wt%, a strong minimum reflection loss of-39.8 dB, and a broad effective absorption bandwidth of 7.85 GHz. This work offers a new avenue for developing high-performance microwave absorption materials.

Al7Si0.3Mg alloy is a typical representative of hypoeutectic Al-Si alloys. Owing to its low density, high specific strength and excellent castability, it is extensively applied in the manufacture of lightweight components in the aerospace and automotive industries. However, iron impurity in the alloy tends to form needle-shaped β-Al5FeSi iron-rich phases, which cut through the aluminum matrix and deteriorate the microstructure and mechanical properties of the Al7Si0.3Mg alloy. This work takes Al7Si0.3Mg alloys with Fe content in the range of 0.2 wt.% to 1.2 wt.% as the research object, and systematically investigates the influence of Fe content on the microstructure and properties of the alloy. In industrial production, a certain proportion of Fe is commonly introduced into the alloy to improve demolding performance and prevent aluminum melt from adhering to mold steel. Although Fe is generally regarded as an impurity element in aluminum alloys, appropriate Fe content can induce the formation of stable iron-rich phases such as α-Al(Fe,Mn)Si and β-AlFeSi. These phases can pin grain boundaries to a certain extent, enhance the high-temperature stability of the alloy and reduce its thermal cracking tendency. Nevertheless, once the Fe content exceeds the critical threshold, a large number of coarse, acicular and plate-like β-AlFeSi phases will precipitate along grain boundaries in a network distribution, which severely damages the continuity of the alloy matrix and becomes the initiation site of cracks, ultimately leading to a significant reduction in the ductility, impact toughness and fatigue life of the alloy. To resolve the above-mentioned scientific and engineering problems, this paper adopts scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and room-temperature tensile testing to systematically investigate the effect of Fe content variation on the evolution behavior of iron-rich phases, as well as the microstructure and properties of commercial cast Al7Si0.3Mg alloys in Al-Si-Mg system.

The room-temperature curing system, comprising epoxy resin L285 and H287 curing agent, has a wide range of applications in general aviation. The mass ratio of epoxy resin to curing agent significantly influences its performance. In this study, the effects of deviation from theoretical mass ratios (10:3, 10:4, 10:5, and 10:6) on the rheological, cross-link density, and performance were systematically investigated using viscosity tests, mechanical tests, scanning electron microscopy analysis, dynamic mechanical analysis, thermogravimetric analysis, and moisture absorption analysis. The results showed that a 10:4 ratio yielded optimal performance in the cured epoxy material, with a tensile strength of 73.03 MPa, bending strength of 131.16 MPa, thermal stability (Ti=295 degrees C), heat resistance (Tg=95.01 degrees C), and moisture absorption of 0.57%. The 10:3 ratio exhibited a slower viscosity increase, extending the processing window to 300 min. However, its lower cross-link density (1.19x10-2 mol/cm3) resulted in reductions of 17.8% in tensile strength and 29.7% in flexural strength compared to the 10:4 benchmark. While the 10:5 and 10:6 ratios also showed declines in mechanical performance (15.1% and 19.2% for tensile strength and 14.5% and 29.1% for flexural strength, respectively), the 10:5 formulation achieved the highest Tg peak temperature of 103.7 degrees C. The backpropagation neural network accurately predicted performance parameters, aligning with experimental data. This study provides scientific guidance for aerospace composite design and application.

This study employs argon plasma treatment on Aramid fiber III and investigates the changes in various properties under different aging times. Surface analysis techniques including x-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy, combined with interfacial shear strength and dynamic contact angle measurements, were employed to systematically characterize the chemical composition, microstructure, roughness, wettability, and interfacial bond strength of the fiber surface. The fracture morphology at the interface before and after fiber pull-out was also analyzed. Results indicate: After 3 days of aging, the (O + N)/C ratio increased by 2.28%, and interfacial shear strength reached 42.34 MPa, an increase of 8.90%. After 7 and 30 days, the (O + N)/C ratio decreased by 11.72% and 6.78%, respectively, while interfacial strength remained stable with no significant fluctuations. Surface energy and roughness showed minimal change throughout aging, with only a 2.1% decrease after 30 days, indicating well-preserved interfacial bonding. Molecular dynamics simulations reveal that the quantity, position, and orientation of active functional groups modulate the interfacial bonding energy, clarifying the mechanism by which aging duration influences interface performance.

Rubber buffers are one of the most important components for structural vibration damping in light aircraft. This study presents a finite element model developed using ABAQUS, which has been experimentally validated. The stiffness of rubber buffers with varying geometric parameters under different loading conditions was analyzed using ABAQUS. The stiffness of rubber buffers is predicted via a BP neural network model. A novel approach integrating the finite element method with neural network analysis is proposed. This method initially derives buffer stiffness data through the finite element model, which is subsequently utilized to train the neural network model for predicting rubber buffer stiffness. The results indicate that both geometric parameters and loading conditions significantly affect the stiffness of rubber buffers. The proposed integration of the finite element method and neural network analysis not only reduces time and economic costs but also enhances calculation accuracy, rendering it more suitable for engineering applications. Comparative analyses reveal that the prediction accuracy of the BP neural network ranges from 67.59% to 88.5%, which is higher than that of traditional formulas. Furthermore, the model demonstrates superior capability in addressing multivariate linear coupling relationships.

The rational structural design and precise compositional regulation of lightweight and broadband carbon-based absorbing materials is an urgent task at present to deal with the complex electromagnetic environment. The soluble salt template assisted preparation technology holds good feasibility for constructing unique hollow carbon-based microwave absorbents due to their reusability and economy of salt templates. Nevertheless, magnetic modified nitrogen doping hollow carbon microcapsules fabricated by employing salt-template technique have not been explored. Herein, we adopt a green and low cost NaCl soluble salt template assisted synthesis strategy to universally fabricate 3D unique hollow carbon-based microwave materials loaded with precursors of magnetic particles. Following the high-temperature pyrolysis and wash desalting template, we have successfully achieved mass preparation of magnetic modified nitrogen doping hollow carbon microcapsules. Benefiting from the unique chemical component dominance and distinctive structural merits, the optimized Ni magnetic modified nitrogen doping hollow carbon microcapsules (Ni@N-HCNs) delivered extremely outstanding microwave absorption performance (MAP), including an optimal minimum reflection loss value (RLmin) of -37.7 dB and an effective absorption bandwidth of 5.5 GHz under a filling level of only 5 wt%. More excitingly, the widest effective absorption bandwidth could cover up to 7.87 GHz (10.03-18.0 GHz) at a thin matching thickness of 2.6 mm. Due to the large-scale production and simple preparation process, Ni@N-HCNs composites might be considered as one of the most competitive candidates for the design of lightweight and high performance microwave absorbents.

Polyimide (PI) films are widely utilized in electronic and aerospace applications due to their exceptional thermal stability, mechanical strength, chemical and radiation resistance, and dielectric properties. However, their poor surface wettability, adhesion, and printability significantly limit their industrial applicability. This study employs atmospheric pressure air plasma to modify the surface of PI films, aiming to enhance their etchability and wettability while investigating the mechanical properties under various treatment conditions. The physical alterations induced by plasma treatment are thoroughly analyzed. Results indicate that plasma treatment increases the concentration of oxygen-containing functional groups on the PI surface, introducing new O=C-O- groups, which elevate surface free energy and improve wettability. As the treatment speed decreases, surface etching intensifies, leading to increased roughness. Tensile strength tests and a three-dimensional dynamic optical strain testing system were employed to assess the impact of plasma modification on mechanical properties, revealing the stress-strain evolution mechanisms of PI films before and after treatment. This work provides insights into optimizing plasma treatment parameters for improved PI film performance.

The narrow effective absorption band of manganese dioxide (MnO2) as dielectric loss material seriously limits their application in the field of electromagnetic functional materials. Morphology control engineering is one of the key strategies to modulate the electric structure and improve the electromagnetic loss ability. Herein, onedimensional manganese dioxide nanowires (alpha-MnO2 NW) were prepared by a controllable hydrothermal synthesis method. Interestingly, the morphology and crystal structure of manganese dioxide can be easily controlled by adjusting the proportion of manganese ions Mn2+/Mn7+. The results showed that with the increase of Mn7+, the surface morphology of MnO2 changed from nanowires to nanoflowers and the crystal structure also changed. When the molar ratio of Mn2+ to Mn7+ was 1:3, the manganese dioxide nanowires (alpha-MnO2 NW) possed notable microwave absorption performance, simultaneously achieving strong absorption characteristics at a thickness of 2.8 mm (-55.76 dB at 10.8 GHz) and ultrabroad absorption bandwidth (5.6 GHz) at a thin thickness of 2.1 mm with the filling content of 17.5 wt%, respectively. The research results can not only help to understand the relationship among the morphology, structure and microwave absorption of MnO2, but also help to realize the controllable synthesis of multi-morphology and multifunctional MnO2.

The performance of ceramic seams in spliced ceramic composite armors primarily depends on the properties of the adhesive layer. This study presents a sophisticated 3D finite element (FE) model developed to simulate the ballistic impact process. The primary objective was to enhance the penetration resistance of ceramic composite armor in vulnerable regions by modifying the bonding parameters between the ceramic chips. The results demonstrated that with an adhesive density of 2.0 g/cm3, the absorbed energy of the armor and the ballistic limit velocity were 3553.6 J and 391.2 m/s, respectively, reflecting increases of 48.1 and 22.1

In high temperature conditions, this can cause considerable changes in the mechanical properties of the composite. In order to determine the structural and mechanical property changes that occur in composite materials at elevated temperatures, to elucidate the damage mechanisms at elevated temperatures, and to improve the stability and durability of the materials. This paper studies how plasma treatment time affects the surface polarity, roughness, wettability and mechanical properties of carbon fibers. The results showed that the best wettability was attained after 10 min of plasma treatment, and new oxygen-containing functional groups (COO- and -C=O) developed on the fiber surface. The fundamental explanation is that during plasma surface treatment, the C-H group in the bisphenol A part chain segment present in the epoxy resin sizing agent's composition is oxidized, forming an organic oxide layer. In this paper, the plasma modification technology was utilized to improve the interfacial compatibility of carbon fiber and Polyimide (PI) resin, and the interlaminar shear strength reached 103.98 MPa, up 10.49 %, and the strength retention rate was 84.3 % at 300 degrees C. In this paper, the plasma modification technique was employed to increase the interfacial compatibility of carbon fiber and PI resin. It was found that the Inductively Coupled Plasma (ICP) treated carbon fiber surfaces underwent physical and chemical changes that effectively enhanced the interfacial compatibility with the resin. However, the chemical groups and physically etched regions on the surface of the plasma-modified fibers are able to impede the relative motion of the resin to a certain extent, thus improving the interfacial strength.

In order to meet the requirements for the use of high-temperature-resistant electromagnetic wires, the surface hydrophilicity and surface energy of PI films were improved by plasma modification, and polyether ether ketone (PEEK) emulsion was coated on the surface of PI films. High-performance PI/PEEK composite films were successfully prepared, and the interfacial strength between the PI film and Cu foil was significantly improved. The effects of sintering temperature on the melt swelling effect of PEEK on the surface of PI films were systematically studied and the optimal sintering process parameters were determined to be 334 degrees C and 20 min. The thermal stability, durability, and interfacial bonding strength of the composite films were thoroughly investigated through thermogravimetric analysis, aging experiments, and interfacial property tests. The results show that the modified composite films have excellent thermal stability at 400 degrees C and remain structurally stable after aging at 350 degrees C for 12 h. Especially after aging treatment at 300 degrees C, the grooves on the surface of the composite film completely disappeared, and the coating showed good swelling characteristics and a significant increase in tensile strength. By optimizing the plasma treatment parameters (800 W, 6 mm/s), the room temperature peel strength of the PI/PEEK composite film reached 9.55 N/cm, which was 77.84% higher than that of the untreated composite film. At the same time, the plasma treatment significantly enhanced the interfacial bond strength between the composite film@Cu up to 5.61 N/cm.