Composite laminate structures are widely used, and damage identification is of great significance to ensure the safety of structures and prolong their service life. In this paper, the element-level damage indicator is introduced to describe the change of the in-plane and out-plane upward stiffness of laminates. Aiming at the damage index, a two-step damage identification method was established, that is, the damage element was screened by the damage location index, and then the damage degree was identified by the optimization method. The regularization method was used for quantitative damage recognition. Since the traditional regularization method adopts uniform regularization parameters for each damage parameter, which is not conducive to the convergence and stability of the identification results. In this paper, an adaptive regularization damage identification (ARDI) method based on weighting coefficient is proposed, which can improve the identification efficiency while considering the stability of identification results. The effectiveness of the proposed method is verified by numerical examples, and the influence of the number of measurement points and noise level on recognition results is analyzed. The results of the proposed method are compared with the direct method and the traditional regularization method, and it is found that the dispersion of calculation results and the efficiency of the proposed method have obvious advantages. Finally, an experimental work was conducted to verify the effectiveness of the proposed method.

With the wide application of composite materials in aerospace and automotive fields, it has become more and more important to accurately predict their mechanical properties. In this study, a transfer learning-based stress-strain curve prediction method for short fiber reinforced polymers was proposed. Firstly, the database was constructed by DIGIMAT and the Latin hypercube sampling technique was used to select samples to improve the efficiency of model training. Then, using artificial neural network (ANN) as a surrogate model, and through the transfer learning method, the stress-strain prediction model of the new material can be quickly obtained. The results show that the transfer learning model can effectively capture the key features of the stress-strain behavior of materials, especially in predicting the fifth-order polynomial coefficients. The effects of fiber volume fraction and aspect ratio on the mechanical properties of materials were further analyzed, and it was found that the fibers with larger length-diameter ratios could transmit stress more effectively. This study provides an effective tool for the performance prediction of short fiber reinforced polymers, especially when data acquisition is difficult or the cost is high, the potential and application prospects of transfer learning in the performance prediction of composite materials are demonstrated.

Ultrasonic guided wave-based damage detection and localization methods are widely applied in various engineering structures. However, the anisotropy of composite materials increases the complexity of guided wave propagation, often resulting in oversized imaging areas and false artifacts, which compromise localization accuracy. In this study, a novel damage localization method for delaminations in composite plates is proposed, integrating delay-and-sum (DAS) principles with the sparrow search algorithm (SSA). By designing a fitness function based on the time of flight (ToF) of scattered signals, the damage imaging problem is transformed into a scattering source search problem. The fitness function evaluates the sparrow population distribution, iteratively refining the search process to approximate the most probable scattering source locations. The damage region is ultimately represented by the areas of sparrow aggregation. Experimental results demonstrate that, compared to traditional imaging methods, the proposed approach significantly reduces the localization area and enhances accuracy.

Mechanical tests and simulation methods were utilized to study the failure behavior and attributes of [±45]_3S wrapped composite round pipes under various compression circumstances. Quasi-static axial and radial compression failure tests were performed on the composite wound cylindrical pipes, followed by an investigation of the wound round pipe’s energy absorption characteristics. LS-DYNA was used to create a finite element model of the Hashin and Chang-Chang failure criterion for simulation, and the failure reaction and energy absorption damage process of the circular tube were investigated. The efficiency of the established simulation model was thoroughly validated using comparative tests and numerical analysis. The results demonstrate that the wound tube mostly absorbs crushing energy via matrix fracture and fiber buckling. The Chang-Chang failure criterion simulates deformation more accurately, which is consistent with test results in which the initial peak value, total energy absorption, and specific energy absorption of axial and radial compression are all less than 10%.

Composite foam sandwich structures are subject to delamination defects within their panels during manufacture and use, which can seriously affect the load-bearing properties of the structure. In this paper, the bearing performance of carbon fiber/polyurethane foam sandwich structures containing initial delamination defects within the panel under bending load is investigated using a combination of three-point bending test and finite element simulation, and the effects of the length and width of the initial delamination defects, as well as the location of delamination defect thicknesses, on the bending performance of the composite foam sandwich structures are analyzed. Based on the cohesive zone model (CZM), the extension evolution of initial delamination defects were analyzed, and the extension mechanism of initial delamination defects under bending load was discussed. The results show that the ultimate load decreases with the increase of the defect length and width, where the width has a greater influence; the expansion path of delamination defects is less affected by the size and shape, and the delamination defects expand transversely along the panel from the middle boundary of the defects; the location of the delamination defects is moved from the surface layer to the middle layer, and the ultimate load of the sandwich structure is then increased.

Carbon fiber epoxy composites have been widely used in aerospace and other fields, and with the development of laser technology, the study of the interaction between laser and materials is of great value. In this paper, the carbon fiber epoxy composite was irradiated with high energy continuous laser, and the new coatings were prepared on the surface of the carbon fiber epoxy composite with silicone resin as the base material, boron nitride as the filler, and polytetrafluoroethylene (PTFE) emulsion with different contents. At a power density of 17.1 W/cm², the damage degree of carbon fiber epoxy composite increases with the extension of irradiation time. The reflectance of the modified resin-based protective coating can reach to 83.7%. With the increase of PTFE content, the holes of the coating are reduced, the F—C—F bond is gradually strengthened, and the contact angle is increased, which improves the surface hydrophobic property of the coating.

To improve the high temperature resistance of joints in cable roof structures made of carbon fiber reinforced polymer (CFRP), the CFRP tendon wedge-type anchorage system was studied. Firstly, the glass transition temperature test of CFRP tendons was carried out to obtain the starting and ending temperatures of the glass transition of CFRP tendons (126 ℃, 192 ℃). Based on this, the target test temperature for the transverse compressive mechanical test at elevated temperature was further worked out. Then, the same two aluminum plates with semicircular grooving were made of A6061-T6 aluminum alloy to simulate the wedge in the anchoring system. By conducting experiments, the transverse compressive mechanical properties and deformation characteristics of CFRP tendons with the influence of aluminum plate are obtained under high temperature. The results can provide data support for the construction of the constitutive model of CFRP tendons under high temperature. By establishing the finite element model corresponding to the test, the average error between the calculated strain value and the strain value obtained by the test is less than 5%, the validity of thermal and mechanical parameters in the finite element model is demonstrated, and the anchorage system model can be further constructed for high-temperature analysis.

In this paper, 3-isocyanatopropyl triethoxysilane (KH-907) was employed as a modifier, while phenol and formaldehyde served as monomer raw materials. The intermediate of N-(3-triethoxysilylpropyl) phenyl carbamate was synthesized by controlling the conditions of the addition reaction. Subsequently, this intermediate reacted with formaldehyde under the catalysis of an alkaline catalyst, successfully synthesizing the organosilicon-modified phenolic resin liquid (IPTES-PF). The chemical structure and curing behavior of the modified phenol-formaldehyde (PF) were investigated via fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The effects of the addition amount of organosilicon and the material ratio on the mechanical properties and thermal stability of the modified PF were studied through mechanical property tests and thermogravimetric (TG) analysis. The results indicated that the introduction of KH-907 enhanced the heat resistance of PF. Moreover, as the content of the modifier KH-907 and the molar ratio of formaldehyde increased, the mechanical properties of the organosilicon-modified PF initially rose and then declined. When the content of KH-907 was 15% and the molar ratio of phenol to formaldehyde was 1∶1.8, the mechanical properties of the organosilicon-modified PF resin liquid were optimal, with a tensile shear strength of 7.06 MPa and a peel strength of 328 N/5 cm. The impact strength of the silicone modified PF composite and the grinding ratio of the consolidated abrasive tool reach the maximum when the content of KH-907 is 15%, which are 2.87 kJ/m² and 20.913, respectively.

Riveted structures are often subjected to tensile loads at different loading rates, and the tensile rate has a significant impact on the strength of carbon fiber reinforced composites (CFRP)-metal riveted structures. To investigate the effect of loading rate on the single and double lap riveted joints strength of CFRP/Al, a numerical model of CFRP/Al single and double lap riveted joints was established using the VUMAT subroutine function in ABAQUS. This model is based on continuum damage mechanics, the 3D Hashin failure criterion, and strain rate effects. The study examined the impact of four tensile rates-1 mm/s, 100 mm/s, 200 mm/s, and 300 mm/s—on the strength of single and double lap riveted joints, and tensile tests were conducted to validate the accuracy of the numerical model. The results indicate that as the tensile rate increases, the strength of both single and double lap riveted joints also increases, with a more significant increase observed in double lap riveted joints. Additionally, as the tensile rate increases, the degree of damage to CFRP decreases, indicating that higher tensile rates have a noticeable suppressive effect on CFRP damage.

In this paper, quartz fiber paper was prepared by wet forming method with different ratio of micro and nano quartz fibers. After dipping in PTFE emulsion and pre-burning to remove small organic molecules, the composite substrate was prepared by hot pressing and sintering, and the dielectric, mechanical and thermal properties of the substrate were characterized and analyzed. The results show that the density and water absorption decrease with the increase of the content of quartz fiber while the proportion of total fiber remains unchanged. In terms of dielectric properties, the dielectric constant decreases with the increase of quartz fiber content. When the quartz fiber proportion reaches 80%, the dielectric constant is at its lowest to 2.21, and the dielectric loss presents a nonlinear relationship, and the lowest is 0.000 96 when the proportion of quartz fiber is 40%. In terms of thermal conductivity, the increase in quartz fiber content results in an enhancement of the composite’s thermal conductivity, and reaches a maximum of 0.232 W/(m·K) when the proportion of quartz fiber is 80%. In terms of mechanical properties, the tensile strength and elastic modulus decreased with the increase of quartz fiber content, and decreased to 17.85 MPa and 1538.76 MPa when the proportion of quartz fiber was 80%.

Based on the issue of stitching thread pullout in carbon fiber three-dimensional preforms prepared using tufting processes after high-temperature treatment, a novel unilateral stitching technique-“riveting”-has been developed, with the stitching line referred to as a full-line rivet (FLR). In this study, a two-dimensional braiding technique was used to fabricate the FLR, and a three-dimensional fabric preform was created using the unilateral riveting technique. The research primarily focuses on the effects of FLR parameters and high-temperature treatment on the pullout performance of FLR. The results show that the pullout strength of FLR increases initially and then decreases as FLR weaving pitch increases. The pullout strength of FLR exhibits an exponential growth pattern with the increase in the number of woven strands. After the riveted preform undergoes high temperature treatment at 300~600 ℃ for 1 h, the pullout strength of FLR decreases from 25.79 N to 2.96 N, and the rate of performance degradation slows down as the temperature increases. Under the 600 ℃ treatment condition, the pullout strength of FLR is approximately 7 times higher than that of tufting.

This article analyzes the electromagnetic performance of functional composite material structures with different curved profiles. The variation patterns of horizontal polarization electromagnetic performance in relation to different bending extents of functional composite structures are studied. The influence of core material electromagnetic properties on the horizontal polarization electromagnetic performance of the structures is also explored. Based on both the core material and structural form, an integrated optimization design is proposed to enhance the low-frequency electromagnetic performance of the functional composite structures. The results show that the average RCS for both metallic curved structures and functional composite material structures with horizontal polarization decreases gradually with increasing bending extent. The functional composite material structures exhibit an RCS reduction effect across various bending extents, but the RCS reduction effect weakens as bending extent increases. Merely altering the electromagnetic properties of the core material does not fundamentally address the issue of efficient low-frequency electromagnetic wave absorption in curved structures. A comprehensive approach, leveraging both the electromagnetic properties of the material and the structural advantages of the composite, is essential. By introducing gradient electromagnetic core materials and optimizing the core material filling structure, the low-frequency dual-polarization electromagnetic performance of the functional composite structures is enhanced. In particular, the RCS reduction effect in horizontal polarization in the L-band exceeds 8 dB compared to using a single type of electromagnetic core material. This article achieves functional composite material structures with highly efficient low-frequency reduction performance in the 1~4 GHz range, while also maintaining good broadband electromagnetic performance in the 4~12 GHz mid-to-high-frequency range.

In response to the application requirements of thermal protection materials for hypersonic aircraft engines, this paper investigates the performance of three-dimensional reinforced quartz fiber/phenolic resin gradient thermal insulation materials. The preform is prepared using a 2.5D weaving/needle combined process, and the molding is carried out using a resin vacuum infusion process. Various tests and analyses were conducted on the mechanical properties, thermophysical properties, and ablation performance of the material. The results showed that when the total thickness was constant, the intermittent distribution of the weaving layer and the web layer along the thickness direction had a significant impact on the overall performance of the material. When the number of layers was small, its ablation performance was better, and when the number of layers was large, its thermophysical properties were better. The tensile and compressive mechanical properties were mainly affected by the distribution of the web layer and its interface with the weaving layer. The gradient thermal insulation material proposed in this article has the advantages of light weight, good anti-ablation performance, strong mechanical properties, and excellent resistance to airflow erosion, providing more material references for aerospace thermal protection engineering.

In this paper, the hot-melt method was used to prepare aramid/epoxy prepreg 023F/DBE-125 and fiberglass/epoxy prepreg SW280F/DBE-125. Composite material test plates were made using the autoclave process, and their mechanical properties and ballistic impact resistance were characterized. To address the deformation issues encountered during the winding, curing, and processing of the thin-walled engine casing, the mold and the assembly gap of the casing, along with the material’s thermal expansion differences, were used as the design basis for the winding mold of the engine casing retaining ring. Through simulation technology and process trials, suitable winding and processing parameters were determined. Using the parameters obtained from the trial pieces, composite retaining rings were wound onto thin-walled engine casings, and the formed retaining rings were subjected to dimensional and internal quality inspection. The test results show that the performance indicators of the developed engine casing retaining ring meet the required standards. This study provides an important reference for the lightweight design and manufacturing of engine casings and has significant implications for the development of key components in aircraft engines.

3D-printed continuous carbon fiber reinforced composites (CCFRCs), with their exceptional properties such as high strength, high modulus, and lightweight, have extensive application potential in the aerospace and aviation sectors. However, the weak interfacial bonding between fibers and resin, especially the inadequate interlaminar performance, has become a critical factor limiting their further development. The effects of heat treatment on the interface properties and microstructure of 3D-printed CCFRCs were investigated. Through double cantilever beam (DCB) tests, the influences of process parameters such as ply angle, heat treatment temperature and heat treatment time on the interlaminar fracture toughness of CCFRCs were systematically investigated. Combined with scanning electron microscopy (SEM) analysis of fracture surface morphology, the mechanisms by which heat treatment affects the interlaminar performance of composites were revealed. The results show that the interlaminar fracture toughness of [0/45]₃ and [0/90]₃ specimens is higher than that of [0/0]₃ specimens. After heat treatment, the fiber bundles of [0/90]₃ specimens exhibit more matrix adhesion and rougher surfaces, leading to significantly improved interfacial bonding property. Among them, the interlaminar fracture toughness of [0/0]₃ specimens treated at 60 ℃ for 2 h reaches 1.570 kJ/m², representing a 50.67% increase compared to untreated specimens. In addition, longer heat treatment time results in more pronounced improvements in fracture toughness. Heat treatment enhances the interfacial bonding performance of CCFRCs and modifies their interlaminar failure mode by increasing resin fluidity, filling voids between deposition lines, and optimizing fiber alignment.

In order to achieve the integrated molding of large-sized 3D composite material frames, this study developed a process-structure integrated design and optimization plan. The molding process was reasonably selected and the water-soluble mold preparation process was optimized. Performance standards for water-soluble molds that meet the molding process of large-sized 3D frame structures were formulated. The feasibility of the structural design scheme and process was experimentally verified through the production of test specimens. A 3D integrated framework configuration that balances process feasibility and structural mechanical properties was formulated and applied in the development of actual products. The product has been validated through experiments, proving the feasibility of the technical solution, which provides reference for the integrated design of support structures of space camera.

Plastic lined composite hydrogen storage cylinders (type Ⅳ hydrogen storage cylinders) have attracted widespread attention due to their advantages of lightweight, high strength, and good fatigue performance. However, the impact performance of foreign objects during transportation and use is unknown, which poses potential risks. This article combines experimental and numerical simulation methods to analyze the impact damage of type Ⅳ hydrogen storage cylinders. Firstly, impact tests were conducted on type Ⅳ hydrogen storage cylinders, and the depth and area of damage were measured and characterized. Then, a 3D finite element model of gas cylinder impact process considering intra layer and inter layer damage was established. Among them, the 3D Hashin criterion and Camanho empirical model are used to predict intra layer damage, and the cohesive zone model is used to predict inter layer damage. The simulation results have good consistency with the measurement results. Finally, based on the established model, the effects of impact angle, impact energy, and internal pressure on impact damage were studied. The results show that under different impact energies, the results of the model with cohesive elements are closer to the experimental values than those without cohesive elements. The impact energy dissipates within and between layers resulting in damage. The greater the depth of the pit, the greater the impact on the internal damage, resulting in more energy dissipated and less energy dissipated between layers. The smaller the damage impact angle, the larger the contact area between the impact object and the winding layer, and the larger the compressive area of the substrate, resulting in an increase in the damage area. Under pressure impact, the tensile damage to the substrate is more severe than without pressure impact, and the impact displacement is smaller. The research results of this article provide supplementary information for the study of delamination damage within and between the impact damage layers of composite material type Ⅳ gas cylinders.

With the development of three-dimensional braided technology, three-dimensional braided structures have developed from the initial three-dimensional four-directional structure to three-dimensional five-directional, six- directional and seven-directional structures. At present, the high-temperature off-axial loading performance of three-dimensional six-directional and seven-directional braided composites remains to be further studied. This article is based on the development of a certain three-dimensional six-directional braided composite component, braids three-dimensional six-directional braided preform by using T800HB-12K carbon fiber. The composite part was prepared by RTM process with TDE-85 resin system as matrix. The internal quality of the composite part was detected by industrial CT, and the study on sixoff-axis loading tests of three-dimensional six-directional braided composite components at room temperature and high temperature were carried out. The results show that the three-dimensional six-directional braided composite part still have excellent in-plane properties at a high temperature of 105 ℃, but the off-axis loading performance declined comparing to room temperature conditions. The ultimate load under AY working condition can reach at least 150% design load due to the high integrity of its own structure.

Bolted connections have been widely used in the field of aerospace due to their efficient and reliable connection performance. However, some issues, including delamination defects, perpendicularity errors, inevitably occur during the processing of holes in fiber-reinforced composite plates. Besides, the systematic and manual errors can also lead to the inappropriate preload or the existence of assembly gaps during the assembly process. Such will significantly affect the mechanical properties of bolted joint structure. In this work, we summarized four general influential factors on the properties of fiber-reinforced resin matrix composite bolted joints in machining and assembly processes: delamination defect, perpendicularity error, preload force and assembly gap. Meanwhile, their effects on mechanical properties and the corresponding reactional mechanisms have been systemically discussed. Moreover, we also proposed the future tendency of the factors affecting the mechanical properties of fiber-reinforced composite bolted joints.