COMPOSITES SCIENCE AND ENGINEERING

Research on the compression properties of Kagome lattice sandwich structure

PEI Yongyong, YU Xiaochen, XU Haibing, LÜ Dongxi, ZHU Yingdan

2023, 0(5): 5-11. DOI: 10.19936/j.cnki.2096-8000.20220828.032

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The compression properties of composite Kagome lattice sandwich structure were studied by the combination of finite element numerical simulation and experimental verification. The effects of different structural parameters on the flattening properties and failure modes of Kagome lattice sandwich structure were analyzed. The results show that under the compression load, the diameter of the rod has great influence on the peak load amplitude of the Kagome lattice sandwich structure, while the height of the core and the angle of the rod have little influence on the peak load amplitude. The main failure modes of the sandwich structure include fracture at the maximum deformation of the rod, fracture at the connection between the rod and the panel and fracture at the cross connection. By comparing the finite element numerical simulation results of Kagome lattice sandwich structure with the flat compression testing results, the reliability of the finite element model is verified.

Preparation and performance study on ultra-thin nickel-plated carbon fiber tubular structure battery

WANG Yazhen, ZHANG Juntao, LI Hui, MA Xinqi, ZONG Wenbo, JI Tianqi, WU Haihong

2023, 0(5): 12-18. DOI: 10.19936/j.cnki.2096-8000.20221028.032

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Carbon fiber structure battery has both excellent mechanical properties of carbon fiber reinforced composite materials and good energy storage performance, which has broad application prospects in aerospace, new energy vehicles and other fields. In this article, ultra-thin nickel-plated carbon fiber battery (Ni-CFB) was prepared by coating process. Based on the design method of embedding integrated structure battery, the sandwich structure battery tube (SSBT) was prepared by resin vacuum transfer process, with the battery as the core and the carbon fiber braid as the skin. The electrochemical properties of Ni-CFB were tested, and the electrochemical performance attenuation behaviors of SSBT under different loading were evaluated. The results show that the specific capacity of Ni-CFB reaches 156 mAh/g at a charge-discharge rate of 0.1 C, which is 30% higher than the specific capacity of conventional batteries of lithium-iron phosphate-graphite system. When the compression loading ratio and flexure loading ratio reach 550 N/g and 89.1 N/g, the capacity of SSBT is remained at 80% and 60% or more, respectively. Results indicate that SSBT has good structural efficiency and energy storage efficiency, which has great potential in lightweight design and safety design on energy storage systems.

Hygrothermal resistance of modified methyl diphenylacetylene silane composites

BAI Xiaotao, JIA Yuxiang, HU Wenjie, ZHANG Xiaohui, JIANG Fengguang, LIU Min, ZHOU Quan*

2023, 0(5): 19-24. DOI: 10.19936/j.cnki.2096-8000.20230528.003

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GF/MDPES-GBMI composites were prepared using modified bismaleimide (GBMI) blended with methyl diphenylacetylene silane (MDPES) resin. The effects of water absorption, dehydration behavior and hygrothermal aging on the interface of GF/MDPES-GBMI composites were studied through water absorption/loss experiments and theoretical calculation. The results show that with the increase of GBMI content in MDPES-GBMI resin, the diffusion coefficient of the composite decreases from 0.019 3 mm²/s to 0.014 7 mm²/s, and the permeability coefficient decreases greatly from 9.94×10^-4 mm²/s to 1.84×10^-4 mm²/s. At the same time, the equilibrium water absorption rate and the equilibrium water loss rate also decreases. Although the flexural strength of the composite decreases after hygrothermal aging, this property recovers after dehydration. Water molecules exist in a quasi-free form in the pores of GF/MDPES-GBMI composites, and the law of water absorption and dehydration follows Fick’s second law.

Time-temperature-transformation (TTT) diagram of a domestic T800 carbon fiber epoxy prepreg

HE Liang, XU Xiaowei, HU Dabao, LEI Yang, LI Yao

2023, 0(5): 25-31. DOI: 10.19936/j.cnki.2096-8000.20230528.004

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The curing kinetics and the time-temperature-transformation (TTT) diagram of prepreg system play an important role in designing and optimizing the curing cycle in order to obtain the ultimate properties of related products. In the present study, the curing kinetics of the domestic prepreg system with T800 carbon fiber and highly toughened epoxy resin were characterized by differential scanning calorimetry (DSC), and fitted using the autocatalytic model; in the aspect of phase transition behavior, the relationship between glass transition temperature and degree of cure was tested and fitted, and the relationship between gelation time and temperature was also obtained. Based on the obtained results, TTT diagram of the prepreg system was developed, providing the theoretical guidance for determining the curing cycle for composite parts.

Preparation and characterization of epoxy resin-modified polydicyclopentadiene
and its carbon fiber composites

YANG Qing, CHENG Chao, DIAO Chunxia, LÜ Yueen, ZHOU Fei, DING Xiaoma, CHEN Zhengguo

2023, 0(5): 32-36. DOI: 10.19936/j.cnki.2096-8000.20220928.031

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In this paper, bisphenol A epoxy resin with methyl nadic acid anhydride curing agent was added to DCPD monomer/Grubbs 2nd catalyst, blend polymer was obtained by step reaction polymerization. Contact angle meter, differential scanning calorimeter (DSC), infrared spectrometer (FT-IR), mechanical testing machine and scanning electron microscope (SEM) were used to characterize the epoxy resin-modified PDCPD. The results show that the wettability between modified DCPD monomer and the carbon fiber fabric is significantly improved as the contact angle decreased from 83.2° to 22.6°, and the glass transition temperature of 10 phr epoxy-modified PDCPD is increased from 124.7 ℃ to 133.2 ℃. No epoxy functional group (913 cm^-1) is found in the infrared spectrum of the modified PDCPD, indicating that the epoxy resin in the mixed system reacts completely. The mechanical test shows that the flexural strength of PDCPD after modification is increased by 13.3%, and the fracture toughness is decreased by 11.0%. The microstructure shows that the cured epoxy resin is uniformly distributed inside the PDCPD as microspheres with a diameter of less than 2 μm. The interlaminar shear strength of the carbon fiber composite based on PDCPD after modification is increased from 8.2 MPa to 15.1 MPa, the cross-sectional structure shows that the addition of epoxy resin can effectively improve the adhesion of PDCPD to carbon fibers.

Study on stiffness regulation method of thermosetting/thermoplastic hybrid composite structure

MA Qingyuan, YANG Rui, MENG Xiangpeng

2023, 0(5): 37-44. DOI: 10.19936/j.cnki.2096-8000.20220928.032

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This paper proposes a thermosetting/thermoplastic hybrid composite structure with variable stiffness characteristics. The hybrid composite structure is based on the continuous fiber reinforced thermoplastic composite CF/PEEK as the basic structural layer and the continuous fiber reinforced thermosetting composite GF/EP as the variable stiffness functional layer. By applying a temperature field to the hybrid composite structure, the elastic modulus of the functional layer material in the structure can be changed, thereby changing the structural stiffness. In this paper, a stiffness regulation method is proposed based on the thermosetting/thermoplastic hybrid composite structure. The method takes the stiffness distribution function of the structure as the optimization goal, the layer distribution of the hybrid composite structure and the temperature vector composed of different heating film temperatures on the structure surface are the optimization variables, and the optimization results are calculated and obtained. According to the optimization results, a customized temperature gradient field is applied to the hybrid composite structure, and the stiffness distribution of the structure can be approximated to show the change of the objective function.

Study on axial compression failure characteristics of composite
longitudinal circular corrugated cylindrical shell

LIANG Zeqian, WEI Gang, LI Xiang

2023, 0(5): 45-52. DOI: 10.19936/j.cnki.2096-8000.20230528.007

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Lightweight structure and high-efficiency materials are the pursuit of aerospace and other industrial fields, such as automobiles, buildings, infrastructure, etc. The use of fiber-reinforced composites can effectively reduce the weight of the structure and improve the load-bearing capacity. The longitudinal circular corrugated structure of composite materials can greatly improve the load/mass efficiency of structural axial compression, thereby meeting the strength requirements of new composite materials and structures in the aerospace field. Based on the self-designed mould, the composite circular corrugated cylindrical shell was fabricated by vacuum bag hot-pressing method. On this basis, the axial compression performance of the structure is studied. The results show that compared with ordinary cylindrical shells with equal thickness and cross-sectional area, the ability of longitudinal circular corrugated cylindrical shells to bear axial load is significantly enhanced. For longitudinal circular corrugated cylindrical shells with the same structure and different thickness, the failure mode changes from overall buckling deformation to local crushing failure of the end face due to the increase of thickness. The numerical model was established and verified, and the influence of typical design parameters on axial compression performance of longitudinal circular corrugated cylindrical shell was simulated. The results show that when the preparation conditions are allowed, decreasing the size of single cell is beneficial to improving the axial compression resistance of longitudinal circular corrugated cylindrical shell, while decreasing the height has no obvious effect. The research results can provide reference for the application of longitudinal corrugated cylindrical shells in energy absorption of structures.

Study on preparation and properties of solid buoyancy materials by vacuum vibration casting

JI Youping, ZHANG Zuochao, YANG Wentao

2023, 0(5): 53-58. DOI: 10.19936/j.cnki.2096-8000.20230528.008

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A novel process by combination of vacuum and vibration was developed for the preparation of solid buoyancy materials (SBM). Epoxy resin is used as the matrix and two kinds of hollow glass microspheres with different sizes were mixed as the lightweight fillers. The influence of the vibration time on the curing temperature of the hollow glass microspheres/epoxy system, as well as on the bubble defects, density, water absorption and mechanical properties of SBM were studied at a certain vibration frequency. The results show that the vibration time is an important factor affecting the quality and performances of the SBM. If the vibration time is too long, the center temperature of the hollow glass microspheres/epoxy system increases too fast, and the accumulation of curing and vibration heat leads to the resin exploding. If the vibration time is too short, the hollow glass microspheres/epoxy system will not uniformly mixed, leading to the unevenly distributed density of SBM, and the resultant SBM will have to many pores defect. The optimal vibration time is 90 min, the SBM sample prepared under this condition has a low density (0.51 g/cm³), low water absorption rate (0.37wt%), and excellent mechanical properties (e.g. the compressive strength of 31.6 MPa and the impact strength of 5.29 kJ/m²) as well as a uniform distribution. This newly developed process is suitable for the preparation of large-sized SBMs, and it can meet the requirements for the application of SBMs for the infrastructure construction of both marine equipment and offshore platforms within 1 000 meters of water.

Analysis of the effect of temperature on the deterioration of the pore structure of
concrete with different fibre contents

ZHAO Suzheng, ZHANG Wen

2023, 0(5): 59-64. DOI: 10.19936/j.cnki.2096-8000.20230528.009

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To reveal the influence of temperature on the pore structure of fiber concrete, a series of NMR tests on basalt fiber concrete at different temperatures was carried out, focusing on the analysis of pore structure parameters, including porosity, T₂ spectrum distribution, pore size distribution, etc., and the fine morphological changes caused by high temperature were observed by scanning electron microscopy. The test results showed that the T₂ spectra of fiber concrete specimens at different temperatures showed a "ripple-like" fluctuation pattern, which indicated that the internal pore structure characteristics of the specimens changed significantly after experiencing high temperature; under high temperature, the number of large pore size pores of plain concrete, low-fiber-doped concrete and high-fiber-doped concrete increased in order, and the degree of pore structure deterioration increased in order. The pore structure degradation degree is aggravated; and with the increasing temperature, the pore number ratio of basalt fiber concrete and plain concrete is close to each other; the microscopic morphology of concrete analyzed by electron microscope scan intuitively shows that with the increasing temperature, the basalt fiber concrete experiences the evolution process of surface compacting, new pore constantly sprouting, pore width continuously enlarging, and series penetration, and finally developing into macroscopic fissures.

Study on tensile damage of composites based on nonlinear mixing Lamb wave

WANG Lele, ZHENG Guoyan, LI Haiyin, YIN Zhenhua, ZHENG Yanping

2023, 0(5): 65-70. DOI: 10.19936/j.cnki.2096-8000.20230528.010

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The invisible damage of composite plates under tensile stress was detected by nonlinear mixing Lamb wave. A finite element model based on the propagation characteristics of nonlinear mixing Lamb wave is established. The relationship between the composite plate and the nonlinear response of nonlinear mixing Lamb wave under different tensile displacement and the influence of different tensile damage degree in the composite plate on the nonlinear coefficient of nonlinear mixing Lamb wave are studied. The simulation results are verified by snap nonlinear ultrasonic testing device. The research results show that the existence of strain can be detected by using nonlinear mixed Lamb waves; in a certain region, with the increase of tensile displacement, the sum-frequency amplitude of the mixed Lamb wave and the nonlinear coefficient of the sum-frequency gradually increase. The mixed Lamb wave detection method can effectively evaluate the tensile damage of composite plates.

Experimental study on behavior of the MCSCFC tunnel lining segment

BI Jinglong, CHENG Shi

2023, 0(5): 71-79. DOI: 10.19936/j.cnki.2096-8000.20230528.011

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A novel tunnel lining and segment i.e. the multi-cell steel tube-sandwich concrete-fibre reinforced polymer (FRP) tube-core concrete (MCSCFC) segment was proposed. The MCSCFC segment comprised the following four parts: multi-cell square steel tube; concrete between FRP tubes and square steel tube walls; FRP tubes placed in cells; core concrete confined by FRP tubes. To understand mechanical behaviors of the MCSCFC and conventional reinforced concrete (RC) segments under the lateral uniform compression, the 4 segment model specimens (3 MCSCFC and 1 RC) with different thicknesses of FRP tubes were tested under the lateral uniform compression. The failure modes, load-displacement and load-strain curves of segment model specimens were analysed and discussed. Experimental investigation-based conclusions were drawn: ①The MCSCFC segments exhibit distinctive post-yield hardening behaviour under the lateral uniform compression; ②compared to that of the RC segment, the bearing capacity of MCSCFC segment increased up to 41.8% when the segment thickness was reduced by 39.4%.

Study on quality defects of wind turbine blades caused by thick light wood core

LIU Jingyu, YUAN Wei, SONG Houli, MEI Tongrui

2023, 0(5): 80-85. DOI: 10.19936/j.cnki.2096-8000.20230528.012

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Light wood, also known as Balsa, is a tropical fast-growing tree of kapok family native to South America and the West Indian Ocean Islands. It has the characteristics of small density, stable volume and structure and not easy to deform. Through years of application verification, its performance has been fully recognized by the wind power blade industry. In recent years, with the continuous decline of the cost of wind turbine generator, the price of wind power continues to decline. As a key component accounting for 25%~30% of the cost of the whole machine, it provides support for reducing industry cost by cooperating with the development of large blades of high-power wind turbine. To meet the needs of structural design, light wood with a thickness of more than 30 mm, which was rarely used in the past, has become a common choice in the structure of large wind turbine blades. In the actual manufacturing process of wind power blades, there are many defects such as bubbles, delamination caused by this kind of light wood, which seriously affect the manufacturing quality of wind power blades. In order to improve this problem, the defect occurrence mechanism, light wood material characteristics and influence are analyzed, and the solution of destroying the adhesion of bound water and reducing the total content of residual water is locked.

Damage characteristics of basalt fiber recycled concrete under freeze-thaw cycle based on energy dissipation

LUO Hengyong, JIANG Junsong, ZHAO Kang

2023, 0(5): 86-93. DOI: 10.19936/j.cnki.2096-8000.20230528.013

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Based on the principle of energy dissipation, the damage characteristics of basalt fiber recycled concrete under freeze-thaw cycle are studied. The longitudinal wave velocity of freeze-thaw recycled concrete and basalt fiber recycled concrete is measured by non-metallic ultrasonic measuring instrument. The electro-hydraulic servo press and Hopkinson pressure bar device are used to carry out uniaxial compression tests on the specimens under static and dynamic loads. The changes of longitudinal wave velocity, relative dynamic elastic modulus and mechanical properties of the specimen are analyzed, with emphasis on the change law of energy dissipation. The results show that the freeze-thaw cycle will reduce the longitudinal wave velocity of the specimen, and the later freeze-thaw effect has a more obvious effect on the specimen. The addition of basalt fiber increases the integrity of recycled concrete and reduces the damage degree of freeze-thaw to the specimen. The strength and toughness of the specimen under dynamic load are higher than those under static load. The addition of basalt fiber increases the strength and ductility of recycled concrete. The peak stress and ductility of the specimen are continuously reduced by freezing and thawing, and the stress reduction degree is more obvious in the later stage of freezing and thawing. In the early stage of loading, the specimen will undergo elastic deformation, and the external input energy is stored in the form of elastic properties. The addition of basalt fiber can greatly improve the energy absorption effect of recycled concrete. The increase of freeze-thaw cycles reduces the energy consumption effect of the specimen and increases its mechanical damage. The freeze-thaw effect makes the specimen more prone to damage.

Study on nonlinear ultrasonic detection of low-speed impact damage of carbon fiber woven composite

CHENG Zhenfeng, JIA Kangkang, LI Cheng

2023, 0(5): 94-101. DOI: 10.19936/j.cnki.2096-8000.20230528.014

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In order to study the low-speed impact damage of carbon fiber epoxy matrix plain weave woven composites, an integrated finite element model of low-speed impact and ultrasonic detection was established. Based on the asymptotic homogenization method, the real meso-cell model of plain weave composites was constructed. Based on the three-dimensional Hashin failure criterion, the low-velocity impact damage of the extended macro composite plate model at different impact energies was numerically simulated. The nonlinear response of ultrasonic Lamb wave to the damaged area is used to evaluate the damage inside the material. Ram-5000 SNAP nonlinear ultrasonic testing system was used to test the test samples with different impact energies. The simulation results were compared, and the results showed that the integrated model was effective and feasible. Ultrasonic Lamb wave can be used to detect the impact damage of woven materials. The amplitude of second harmonic and relative quadratic nonlinear coefficient increase with the increase of impact energy.

Micromorphology studies of carbon fiber reinforced polymer surface cleaned by ultraviolet laser

WANG Hongen, LI Yun, XIA Ling, YANG Yang, LIU Weiping, ZHAN Xiaohong

2023, 0(5): 102-107. DOI: 10.19936/j.cnki.2096-8000.20230528.015

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The adhesive bonding pretreatment is an important process in the aerospace composites bonding. The bonding strength of the material is affected by surface morphology of the pretreated composite material directly. Based on ultraviolet (UV) pulsed laser cleaning technique of composite material, the effects of UV laser power and scanning speed on carbon fiber reinforced polymer (CFRP) surface morphology were studied by analyzing the laser cleaning microstructure of material surface under different process parameters, and also, comparison were made between single lap shear strength of bonded coupons pretreated by laser with those by other methods. The results show that when the laser frequency is 60 kHz and the scanning speed is 300 mm/s, the CFRP surface resin and interstitial resin are removed with the increase of laser power. The resin in the interstices of fibers is cleaned completely by the UV laser with the power of 8.5 W. The resins on the surface and in the interstices of fibers are cleaned completely by the UV laser with the power of 13.6 W. When the laser frequency is 30 kHz and the laser power is 13.6 W, the surface residual resin increases with the rise of the laser scanning speed. When the laser scanning speed is 500 mm/s, the carbon fibers have good integrity, the surface resin distributes uniformly and the resin in the interstices of fibers is completely removed. Mechanical test results show that when the laser frequency is 30 kHz, the laser power is 13.6 W, and the scanning speed is 500 mm/s, single shear strength of bonded coupons treated by laser could reach a equal level of that treated by peel ply, with significantly optimized discrete values (CV values).

Research on compensation of curing deformation of large size composite hat truss

LU Zhengbin, SUN Wei, LIU Lu, LÜ Xiulei, WEI Ning

2023, 0(5): 108-113. DOI: 10.19936/j.cnki.2096-8000.20230528.016

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The springback deformation problem widely exists in complex composite parts manufactured by autoclave, taking a large size cap shaped truss structure test piece as an example, a multi section profile compensation method is used to compensate the decomposed curing deformation, and the key technical issues involved in the compensation process, such as the selection of thermal expansion compensation base point, the consistency of section measurement, the section deformation compensation method, and the axial distortion compensation, are discussed and analyzed. Finally, a curing deformation compensation method for composite parts with high precision profile requirements is proposed, which realized the high-precision control of composite parts with large aspect ratio, and the profile deviation can be controlled below ± 0.30 mm, which is of guiding significance for the research on the profile compensation of composite part.

Trajectory planning for winding molding of variable curvature rubber heat insulation

XU Minghao, HOU Zengxuan, YAN Wencong, ZHANG Weichao, WANG Haodong, LUO Yangyang

2023, 0(5): 114-119. DOI: 10.19936/j.cnki.2096-8000.20230528.017

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In this paper, according to the requirements of winding molding of heat insulation of the solid rocket motor, the geometric features of variable curvature mandrel and the characteristics of winding molding were analyzed, the winding angle calculation method of variable curvature mandrel and the adaptive control method for rubber tape gaps based on geodesic method were studied to control the winding direction and satisfy the tape gaps requirement. The causes of tearing and wrinkle of the rubber tape were analyzed, and the determination conditions of tearing and wrinkle were established. The distribution of the contact pressure between the heat insulation and the elliptical concave roller was studied, and the winding pressure control method was proposed based on the Winkler model. Based on the above method and geodesic algorithm, the trajectory planning for winding molding of variable curvature rubber heat insulation was fulfilled. Finally, the feasibility of the algorithm was verified by the winding molding simulation of rubber heat insulation. The results show that the algorithm proposed is feasible and can satisfy the requirements of the winding molding of variable curvature rubber heat insulation with excellent effect.

Internal pressure prediction method of pyrolysis gas under fire
conditions for glass fiber/vinyl ester composites

XIE Jiang, YUAN Haoran, HAN Xuefei, LI Han, FENG Zhenyu

2023, 0(5): 120-128. DOI: 10.19936/j.cnki.2096-8000.20230528.018

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The pyrolysis reaction of polymer matrix composites will occur at high temperature. With the production of pyrolysis gas, the gas pressure will be formed in the material. In this paper, through the secondary development of UMATHT subroutine, the numerical simulation of matrix pyrolysis and pyrolysis product diffusion of composites in high temperature environment is carried out, the prediction model of internal pressure of composites is established, the coupling calculation of heat transfer equation, Arrhenius equation, Darcy’s law and ideal gas state equation is realized, and the change of internal pressure of glass fiber/vinyl ester composites under 75 kW/ m² heat flow is simulated. The results show that the pressure prediction value obtained by this method is in good agreement with the experimental value, and the maximum pressure peak error is about 4.68%, which can effectively predict the internal pressure change trend of glass fiber/vinyl ester. The pressure at each location begins to decrease after reaching its peak, and the influencing factors are different. The pressure decreasing at the 3 mm position is affected by the decomposition rate, permeability and porosity; the 6 mm position is caused by the increase of the porosity and the initial permeability; the 9 mm position is only affected by the initial permeability.

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