COMPOSITES SCIENCE AND ENGINEERING

Optimization design of winding parameters of composite shell based on nonlinear finite element theory

ZU Lei, FAN Wen-jun, ZHANG Qian, MOU Xing, WU Shi-jun, ZHANG Gui-Ming, WU Qiao-guo, GENG Hong-bo

2022, 0(10): 5-12. DOI: 10.19936/j.cnki.2096-8000.20221028.001

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Based on nonlinear finite element theory, the winding parameters of composite shell under internal pressure was optimized. Based on the conical shell element and thin shell theory, the strength analysis model of composite shell was established. The results were in agreement with the hydraulic test results of solid rocket motor case, and the comparison results with the commercial finite element software ABAQUS show that the model has high computational efficiency and can be used in the stress analysis of the composite shell and the burst pressure prediction. The strength analysis model and genetic algorithm were used to optimize the slip coefficient of non-geodesic winding of composite shell. The results show that the bursting pressure is the highest when the slip coefficient is 0.19, which is 10.7% higher than that of geodesic winding. The results show that this platform can be used to optimize the sliding coefficient of the spiral layer to achieve the best mechanical properties of the composite shell.

Study on damage evolution and dynamic mechanical properties of chopped basalt fiber reinforced concrete under freeze-thaw

LIU Lu, HE Kang

2022, 0(10): 13-19. DOI: 10.19936/j.cnki.2096-8000.20221028.002

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The freeze-thaw environment will cause damage to concrete materials. Based on the experimental study, the damage evolution law and dynamic mechanical properties of chopped basalt fiber (6 mm) concrete under freeze-thaw cycle are studied. The non-metallic ultrasonic detector is used to measure the longitudinal wave velocity of basalt fiber concrete under different freeze-thaw cycles (0, 25, 50, 75, 100, 125) when the fiber content is 0%, 0.2%, 0.4% and 0.6%. Dynamic uniaxial compression test of chopped basalt fiber concrete with Hopkinson compression bar. The effects of fiber content and freeze-thaw cycles on the quality, longitudinal wave velocity and dynamic mechanical properties of basalt fiber concrete are analyzed. The microstructure of the specimen under freeze-thaw cycle was observed by SEM. Freezing and thawing will cause fatigue damage of concrete materials, peeling damage of material surface, mass reduction and longitudinal wave velocity reduction. The addition of basalt fiber will increase the integrity of the specimen and reduce the fatigue damage of concrete caused by freeze-thaw. The effect is the best when the content is 0.4%. The freeze-thaw cycle reduces the dynamic peak stress, elastic modulus and toughness of the specimen under dynamic load, and increases the peak strain. Under the same freeze-thaw times, the toughness of the specimen increases first and then decreases with the increase of fiber content. SEM test results show that the freeze-thaw cycle will expand the internal cracks of concrete and increase the damage degree, and the addition of fiber will reduce the freeze-thaw damage degree.

Parametric modeling and strength analysis of large-size wind turbine blades embedded root connection

WANG Zhen-gang, TANG Xue, JIANG Chuan-hong, LI Xiao, ZHANG Shi-qiang, XIE Lei

2022, 0(10): 20-24. DOI: 10.19936/j.cnki.2096-8000.20221028.003

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A finite element modeling script for wind turbine blade embedded root connection was developed based on Python, through the parameterized geometric model of the wind turbine blade embedded root connection, the material properties, contact settings, grid mesh and loads constraint were set automatically, and realized the parameterized finite element modeling of the wind turbine blade embedded root connection. The pretension is applied to the blade bolt and hub bolt by finite element analysis software. Under the pretension and the external loads, contact nonlinear calculation is performed according to the finite element calculation results. The static and fatigue strength of the embedded root connection bolt and insert connection in laminate is analyzed through GL 2010 and VDI 2230 standard, providing guidance for the wind turbine blade embedded root connection design optimization. Embedded root connection finite element modeling script developed on Python significantly shortened the detail design and structural strength verification cycle of the wind turbine blade embedded root connection.

Research on low speed flat head impact performance of Nomex honeycomb sandwich panel

HUANG Gui-bin, DUAN Yue-chen, XIE Xin

2022, 0(10): 25-32. DOI: 10.19936/j.cnki.2096-8000.20221028.004

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The anti-flat punch impact performance of Nomex honeycomb sandwich structure is studied on the ballistic characteristics under high-speed or high-energy impact, and it is mostly in the form of the punch perpendicular to the plate surface, rather than the common oblique impact. In order to study the low-speed flat-head impact resistance of the aluminum panel Nomex honeycomb structure, a detailed model of the Nomex honeycomb sandwich structure was established in ABAQUS. A hemispherical head low-velocity impact test platform was built for impact test. The accuracy of the simulation model was verified by comparing the impact force-time curve and punch velocity-time curve. The damage morphology, mechanical response and energy absorption of the structure under 0°, 15°, 30° and 45° flat head impact were discussed by simulation. The results show that as the impact angle increases during oblique impact, the maximum concave depth of the surface decreases, and the horizontal slip distance increases but the debonding area is the same. The impact angle increases from 0° to 45°, the contact time increases by 34.88%, and the peak contact force drops by 12.79%, and the honeycomb wicking can be reduced by 63.28%.

Field full-scale experimental study on the bonding performance of large diameter GFRP bars and concrete

WANG Feng-jiao, BAI Xiao-yu, CHEN Ji-guang, YU Long-tao, LI Ming, ZHU Lei

2022, 0(10): 33-37. DOI: 10.19936/j.cnki.2096-8000.20221028.005

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In order to study the adhesion performance of GFRP tendons and concrete, the field ultimate pullout test of GFRP tendons was carried out by using the test method of field trenching and grouting to clarify the adhesion performance of GFRP tendons and concrete, and to analyze the ultimate pullout bearing capacity of GFRP tendons and the factors affecting the slippage. The results show that the failure mode of GFRP anti-floating reinforcement is mainly shear slip failure. The ultimate pullout bearing capacity of GFRP bars increases with the increase of vertical anchorage length and anchor bar diameter. The bending treatment can effectively reduce the anchor bar slippage, and the longer the vertical anchorage length, the smaller the slippage of GFRP bars. The slippage of GFRP bars decreases with the increase of bending length. Bending the GFRP bar will weaken its ultimate bearing capacity, and the method of increasing its ultimate bearing capacity through the current bending process is less effective.

Experimental study on the influence of freeze-thaw cycles on the pore structure of hybrid fiber reinforced concrete

GUAN Xi-bin

2022, 0(10): 38-43. DOI: 10.19936/j.cnki.2096-8000.20221028.006

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In order to study the effect of freeze-thaw cycle on the performance of hybrid fiber concrete, the rapid freeze-thaw cycle tests of concrete with different fiber volumes were carried out, focusing on the variation law of mechanical behavior and pore structure characteristics of hybrid fiber concrete. The test results show that with the increase of freeze-thaw cycle, the compressive and splitting tensile strength of hybrid fiber concrete decreases, and the amount of freeze-thaw damage increases, while the addition of fiber reduces the amount of freeze-thaw damage and the strength reduction caused by freeze-thaw. This phenomenon becomes more and more significant with the increase of fiber volume. From the microscopic analysis, the pore parameters of fiber reinforced concrete, such as air content, bubble spacing coefficient and average chord length, are negatively correlated with the compressive and splitting tensile strength of the specimen, but positively correlated with the amount of freeze-thaw damage. When the volume content of fiber is constant, the more freeze-thaw cycles, the greater the air content, bubble spacing coefficient and average chord length of concrete, and the smaller the specific surface area of pores.

Study on bending properties of GFRP reinforced by carbon nanotubes at low temperature

MA Jia-he, WANG Gong-dong, YAO Song-yang, HAN Cheng-lin, LI Hua, GUO Feng, MA Qun-long

2022, 0(10): 44-49. DOI: 10.19936/j.cnki.2096-8000.20221028.007

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The GFRP laminates with interlayer pre-embedded carbon nanotube films (CNTF) and carbon black films were treated with low-temperature cycling (-58 ℃~room temperature), respectively, followed by cantilever beam bending tests. By observing microscopic images, analyzing load-displacement curves and comparing bending ultimate loads, the effects of both films on the bending properties of GFRP laminates and the enhancement mechanism of GFRP laminates after low-temperature cycling were investigated. The test results show that CNTF has the most obvious strengthening effect on the laminate and is least affected by the low-temperature cycling energy. The carbon black film also has certain strengthening effect, but it is slightly weaker than CNTF.

Preparation and properties study of B₄C/PI composite for neutron radiation protection

LONG Xin-xi-ming, PAN Lei, ZHANG Hao-ran, GAO Li-xin, WANG Ruo-fan

2022, 0(10): 50-55. DOI: 10.19936/j.cnki.2096-8000.20221028.008

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With the rapid development of nuclear technology application industry, higher requirements are put forward for the types, service environments and structural properties of neutron radiation protection materials. B₄C/PI composite material was prepared for the development of functional/structural integrated neutron radiation protection materials. Boron carbide is an important neutron radiation shielding material with high shielding efficiency. B₄C particles were selected as additive particles, and silane coupling agent KH550 was used to functionalize B₄C particles to improve the dispersion of particles in polyimide matrix, and B₄C/PI composites were successfully prepared. The results show that B₄C/PI composite has good neutron radiation shielding performance, mechanical properties and thermal stability. When the content of B₄C is 10%, the composite exhibits excellent properties. At 680 ℃, the residual mass of the composite is 70.674%, thermal neutron shielding rate is 62.36%, and tensile strength is 57.27 MPa. It shows great application potential for materials requiring high thermal stability and neutron radiation shielding, such as fusion reactor systems and nuclear waste disposal.

Preparation and performance study of carbonized silk/PDMS/Fe₃O₄ composite flexible strain/magnetic dual-mode sensors

GONG Yong-qing, LIU Yu-hui, YAN Lei, ZHAO Xue, WU Qi-lin

2022, 0(10): 56-62. DOI: 10.19936/j.cnki.2096-8000.20221028.009

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The high electrical conductivity carbonized silk fabrics were prepared by using crepe de chine silk as raw materials under high temperature heat treatment, and were combined with polydimethylsiloxane (PDMS) elastomer and Fe₃O₄ nanoparticles to prepare a flexible magnetic/strain dual-mode sensor. The sensors exhibited stretchability in a strain range of 0%~60%, with a maximum strain sensitivity (GF) of 9.49, and good stability over 200 stretching/recovery process. The addition of Fe₃O₄endowed the sensor with a response to a small magnetic field below 50 mT. When the addition of Fe₃O₄was 25wt%, its magnetic field sensitivity (GF_m) could reach to 39.73%/T. The sensor could accurately monitor finger bending and magnetic field, realizing dual-mode sensing. Finally, a non-contact magneto-electrical switch was successfully prepared, making the visual magnetic field detection possible.

Study on characterization of pore structure of basalt fiber concrete and split tensile test

JIA Jing-en, ZHANG Bin

2022, 0(10): 63-69. DOI: 10.19936/j.cnki.2096-8000.20221028.010

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Based on the experimental study of the internal pore structure characterization of basalt fiber concrete with different lengths (0 mm, 6 mm, 12 mm, 18 mm) and the mechanical properties of splitting tension under different strain rates, the techniques of nuclear magnetic resonance and scanning electron microscope were used to analyze the T₂ spectrum distribution, pore size distribution, porosity and the bond between fiber and concrete. Dynamic splitting tests were carried out on basalt fiber concrete specimens of different lengths at different strain rates by using universal testing machine and split Hopkinson pressure bar, and the effects of fiber length and strain rate on the splitting tensile properties of concrete were analyzed. The results show that the T₂ spectrum curve of basalt fiber concrete is bimodal. The T₂ spectrum peak value and porosity of plain concrete specimen are the largest. The incorporation of fiber can effectively reduce the porosity of the specimen, and the effect is best when the length is 6 mm. The internal pores of the specimen are mainly micropores and small holes. The incorporation of fiber increases the proportion of micropores in the specimen, while the proportion of small holes decreases. As the strain rate increases, the specimen exhibits a strain rate strengthening effect, and the dynamic increase factor has a good logarithmic correlation with strain rate. The incorporation of fiber can effectively enhance the tensile strength of the specimen and reduce its ultimate strain. The effect is best when the fiber length is 18 mm. SEM result shows that the bond between basalt fiber and concrete material can effectively bear the load, reduce the crack expansion and enhance the resistance of the specimen to deformation.

Design of a Z-pin transitional implantation mechanism with high reliability and efficiency

DUAN Xue-jun, WU Qing-tang, ZOU Yang, WEI Wei, YING Yu-xiang, XIU Dong, WU Huan

2022, 0(10): 70-75. DOI: 10.19936/j.cnki.2096-8000.20221028.011

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In order to solve the technical problems of poor reliability, poor precision and low efficiency of the current Z-pin transitional implantation, a novel method of Z-pin transitional implantation is proposed. The Z-pin was implanted into the basic foam board in two steps, and the allocation principle of the two implantation depths, how action models work, and the enhancement principle of implant effect were analyzed, and finally a completed Z-pin transitional implantation process was got. According to the process flow, a set of high-performance Z-pin transitional implantation mechanism integrating the functions of conveying, pressing and cutting is designed, using this mechanism and the implantation process method. The process experiment of Z-pin transitional implantation that used typical matrix was carried out, and the data were recorded. The test results show that the implantation mechanism runs smoothly, the automatic action is smooth, and it is reliable and efficient, the length, implantation depth, angle and other technical indicators of the Z-pin meet the expected requirements,the correctness and rationality of the institutional structure scheme and the implantation method are proved.

The effect of moisture absorption-drying on the microstructure of the bonding interface of composite materials

ZHANG Wei-rui, QIN Meng-lan, CHEN Chen, GU Ling-cong, YAO Dong-dong, ZHENG Ya-ping

2022, 0(10): 76-84. DOI: 10.19936/j.cnki.2096-8000.20221028.012

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In order to study the effect of moisture absorption-drying on the microstructure of the bonding interface of composite materials, three various approaches including grinding, dry peel ply and wet peel ply are firstly used to treat the surface of the composite material, and then moisture absorption-drying treatment at 26 ℃, 65%RH and 70 ℃, 85%RH are conducted. OM, SEM, FTIR, XPS are used to study the effect of moisture absorption-drying on the morphology and composition of the bonding interface of composite materials. The physical morphology analysis shows that the composite material treated with dry peel ply will be residual fiber tows on the surface after it absorbs moisture at 26 ℃, 65%RH, which will affect the single-lap shear strength. The composite materials treated with grinding and wet peel ply do not show significant change after moisture absorption-drying at 26 ℃, 65%RH. After the composite materials are placed at 70 ℃, 85%RH to absorb moisture, there is a phenomenon of matrix cracking, and the polyester fiber tow remains on the surface of the composite material treated with dry peel ply. The above phenomenon will reduce single-lap shear strength, and cannot be recovered after drying. The chemical composition analysis indicates that the O element percentage of the composite material surface treated with wet peel ply decreases after absorbing moisture in these two systems, and can not be recovered after drying. In addition, polyester fiber tow remains on the surface of the material treated with dry peel ply, which changes the O element content.

The influence of room temperature tackifier on the properties of vinyle ester resin composites

YU Meng-hai, WANG Ya-ting, LI Guo, LI Xiang

2022, 0(10): 85-90. DOI: 10.19936/j.cnki.2096-8000.20221028.013

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A room temperature liquid tackifier for vinyl ester resin was developed for the preparation of preforms, and the composite material was prepared by VARI molding process. The effects of tackifier content on fiber fabric setting effect, VARI molding processability and mechanical properties of composites were studied. The setting effect of the tackifier was evaluated by the experimental methods of thickness rebound and U-shaped rebound; the VARI molding processability of the setting fabric was evaluated by the permeability test of the preform; and the mechanical properties of the composites were characterized by bending and interlaminar shear tests. The results show that when the content of the tackifier is 6wt% of the fiber fabric, the presetting of the fabric is the best, and it can maintain a good permeability; the amount of the tackifier has little effect on the bending properties and interlaminar shear properties of the composites, which can improve the manufacturability and achieve no significant decrease in the mechanical properties of the composite material.

Axial compressive behavior of triaxial woven fabric confined concrete cylinder

ZHOU Yi, ZHANG Hong-hua, LI Wei

2022, 0(10): 91-98. DOI: 10.19936/j.cnki.2096-8000.20221028.014

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This paper adopts carbon fiber triaxial woven fabric, glass fiber triaxial woven fabric and carbon glass hybrid triaxial woven fabric respectively to confine concrete cylinder, and test the axial compression properties of constrained cylinder. The process of compression, failure mode of samples and the stress of yarns were analyzed by digital image correlation (DIC) technology and acoustic emission technology. The results showed that the concrete column confined by triaxial woven fabric had an obviously improved compressive strength and deformation quantity, for which the confined concrete cylinder by carbon fiber improved 92.1% in compressive strength and confined concrete cylinder by glass fiber improved 202% in deformation quantity. Through the comparative analysis of the results, it is found that the strength and deformation of carbon glass hybrid triaxial woven fabric confined concrete have been greatly improved. It is worth noting that the restraint effect of glass fiber as warp and carbon fiber as weft is obviously better than that of carbon fiber as warp and glass fiber as weft. The results provide a theoretical basis for analyzing the axial compression properties of the triaxial woven fabric confined concrete cylinder, and have a certain reference value for the application of triaxial woven fabric confined concrete.

Failure experiment and strength prediction of CF/PEEK single lap welded structure

LUO Feng, CHEN Xiu-hua, ZHANG Lei, ZHOU Yin-hua

2022, 0(10): 99-106. DOI: 10.19936/j.cnki.2096-8000.20221028.015

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In order to study the failure mode of carbon fiber/poly-ether-ether-ketone (CF/PEEK) single lap welded structure in elevated temperature wet condition and the influence of elevated temperature wet condition on its performance, the shear tests were carried out in the room temperature dry condition and the elevated temperature wet condition, respectively. At the same time, three different cohesive force models were used to predict the shear failure load of the structure. The test results show that CF/PEEK single-lap welded specimens in the elevated temperature wet condition show the same three failure modes as those in the room temperature dry condition, namely interface failure, mixed failure and laminate tearing failure. In the range of test error, compared with the room temperature dry condition, the single lap shear strength of welded joints with the same failure mode in elevated temperature wet condition has no obvious change, but the resin at the end of the lap plate has obvious plastic deformation in the elevated temperature wet condition, the average structural stiffness decreases by about 22%, and the average failure displacement increases by about 88%. The numerical results show that the strength prediction results of the exponential cohesive model in the three cohesive models are more consistent with the experimental results for the welded joints with only delamination failure in the room temperature dry condition.

Research progress on ultra-high temperature composites for thermal protection of hypersonic vehicles

LIU Yong-sheng, CAO Li-yang, ZHANG Yun-hai, CAO Ye-jie, WANG Jing, DONG Ning

2022, 0(10): 107-118. DOI: 10.19936/j.cnki.2096-8000.20221028.016

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Thermal protection system (TPS) is one of the key technologies of hypersonic vehicles, determining the success of its development. And the high-temperature thermal protection materials directly determine the performance of the TPS. In this paper, the research status of ultra-high temperature composites for thermal protection application such as C/C, C/SiC and C/UHTC composites was introduced. Then, the research progress on thermal conduction and ablation performances of the C/C, C/SiC and C/UHTC composites were mainly discussed, and the future directions were proposed. This paper is expected to provide a reference for the development of ultra-high temperature composites for thermal protection.

Research progress and prospect of continuous carbon fiber reinforced metal matrix composites

CHENG Xiao-le, PENG Yao, YANG Lei-peng, LÜ Shu-ting, ZHANG Dong, LI Yu, XIE Wang

2022, 0(10): 119-128. DOI: 10.19936/j.cnki.2096-8000.20221028.017

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Continuous carbon fiber reinforced metal matrix composites have excellent comprehensive properties such as light weight, high specific strength,high specific modulus, corrosion resistance, tensile resistance, etc., and are developing rapidly in the field of new materials. In this paper, the research progress of continuous carbon fiber reinforced magnesium-based, aluminum-based, nickel-based and copper-based composites is summarized, and it is pointed out that the interface problem is the main problem at present, and corresponding research ideas are given for key technical difficulties, such as starting with the research of fiber coating, the interface reaction between fiber and matrix, and strengthening the research of damage mechanism of composites in this field. Finally, a new technological idea of manufacturing continuous carbon fiber reinforced metal matrix composites by laser reinforcement is put forward, and the present technological research status and preliminary experimental exploration are discussed. Finally, it is pointed out that the advanced manufacturing technology has advantages in reducing the preparation cost of composite materials, improving the interface strength and increasing the structural complexity of parts.

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