COMPOSITES SCIENCE AND ENGINEERING

Prestress loss of RC columns reinforced with prestressed carbon-fiber reinforced polymer fabric using self-locking/wedge-cutting anchorages

LU Chun-ling, YUAN Guo-hua, HUANG Dong-fa, WANG Qiang

2022, 0(8): 5-14. DOI: 10.19936/j.cnki.2096-8000.20220828.001

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To solve the problem of large prestress loss of carbon-fiber reinforced polymer fabric during load-holding process using self-locking anchorage. We developed a wedge-type tensioning and anchoring device for carbon-fiber reinforced polymer fabric based on the "wedge-cutting effect". Under constant temperature and humidity conditions, 12 sets of prestressed carbon-fiber reinforced polymer fabric reinforced RC column specimens were tested. The effects of self-locking/wedge-cut anchorage, column surface roughness, prestress level and one-off/repeated tensioning on prestressing loss were considered, and the friction loss caused by the relative sliding of carbon-fiber reinforced polymer fabric and column surface during tensioning and the prestress losses of carbon-fiber reinforced polymer fabric during load holding were analyzed. The test results show that compared with the self-locking anchorage, the use of wedge-cut anchorage to tension carbon-fiber reinforced polymer fabric can effectively reduce the prestress losses ratio during the carbon-fiber reinforced polymer fabric load-holding process, which in turn can reduce the total prestress losses of carbon-fiber reinforced polymer fabric by up to 41.4%, and the glue coating can reduce the friction loss and prestress losses caused by elastic retraction of carbon-fiber reinforced polymer fabric, and the secondary tensioning can reduce the prestress losses caused by retraction of carbon-fiber reinforced polymer fabric. Based on the test results, the calculation formula of prestress losses is established, which provides a reference for the calculation of prestress losses of carbon-fiber reinforced polymer fabric.

Mechanical properties of graphene functionally graded cantilever plate based on nonlinear gradient element

ZHANG Peng-cheng, YU Yin-xin, LI En-guo, ZHAO Tian-yu, FU Tao

2022, 0(8): 15-22. DOI: 10.19936/j.cnki.2096-8000.20220828.002

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Aiming at the complex gradient changes of graphene-reinforced composite materials, a finite element method based on 20-node nonlinear gradient element is proposed to satisfy the analysis of the mechanical properties of complex gradient materials. In this paper, the finite element models of U-shaped, X-shaped and O-shaped gradient distribution cantilever plates are established, and the static displacement, stress and mode of the cantilever plates under the three gradient distribution forms are compared and analyzed. The method in this paper is compared and verified with the finite element layered method. The results show that compared with the nonlinear gradient element method, the traditional layered method model will cause the bending stiffness of the X-shaped cantilever plate and the corresponding natural frequencies of each order to be larger than the actual values, while the bending stiffness of the O-shaped cantilever plate and the corresponding natural frequencies of each order are smaller than the actual values. Compared with the U-shaped distribution, the X-shaped gradient distribution can improve the bending stiffness of the cantilever plate, mentioning the natural frequencies of each order of the cantilever plate, while the O-shaped distribution can reduce the bending stiffness of the cantilever plate and reduce the natural frequencies of each order. The nonlinear gradient element method can solve the stress in the thickness direction of the functionally graded plate, which provides a theoretical basis for the fatigue life analysis of the functionally graded plate.

Edgewise fatigue dynamic simulation method and application of wind turbine blade

TANG Xue, WANG Zhen-gang, YUAN De-xuan, WANG Jian, XIE Lei

2022, 0(8): 23-27. DOI: 10.19936/j.cnki.2096-8000.20220828.003

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On the one hand, the fatigue damage of wind turbine blade is caused by the insufficient fatigue strength of the blade itself. On the other hand, it is caused by the gradual cracking of trailing edge which caused by excessive breath effect. Aimed at a large megawatt wind turbine blade, this paper simulated one of the cycles which against 2 million times edgewise fatigue cyclic load, got the dynamic response of the blade under the edgewise fatigue cycle load. At the same time, this paper extracts the blade strain time history curves and partial node displacement time history curves, and studies the fatigue strength and breathing effect. The results show that the blade structure is safe under 2 million times edgewise fatigue cyclic load. The accuracy of the calculated results was verified by the edgewise fatigue test.

Analysis of interfacial failure in omega stiffened composite panel with embedded defect

CHENG Li-nan, XU Si-wen, CHEN Xiang-ming, LI Xin-xiang, QU Tian-jiao

2022, 0(8): 28-34. DOI: 10.19936/j.cnki.2096-8000.20220828.004

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This article aimed at the interface de-bonding between stringer and skin as the structure under post-buckling loads. A four-point bending test that includes non-defect and embedded defect was firstly set up to characterize post-buckling failure in typical regions of stiffened panels and the cohesive zone model (CZM) considering the effects of through-thickness compression on the inter-laminar shear failure of composite laminates was employed. The numerical result is in good agreement with experimental one. The results indicate that: embedded defect at flange/skin interface has slight influence on the load capacity of the structure, but embedded defect at flange/radius-filler interface has significant influence on the load capacity of the structure, and delamination always initiated at the flange/radius-filler interface area.

Research on burst strength and fatigue performance of carbon fiber wound composite cylinder with aluminum alloy liner

KANG Kai, ZU Lei, WU Qiao-guo, ZHANG Qian, ZHANG Gui-ming

2022, 0(8): 35-43. DOI: 10.19936/j.cnki.2096-8000.20220828.005

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In this paper, the relationship between burst pressure and fatigue life of carbon fiber wound composite cylinders with aluminum alloy liner is studied by means of experimental tests and numerical simulations. The design and manufacture of carbon fiber wound composite cylinders with aluminum alloy liner were carried out, and the hydrostatic burst and fatigue performance tests were carried out. The burst pressure, fatigue life and failure morphology of the cylinders were obtained. The burst pressure prediction method based on progressive damage analysis model and the fatigue life prediction method based on Morrow mean stress correction and Manson-Coffin equivalent strain are proposed, and the prediction results agree with the tests. The influence of cylinder design parameters on burst pressure and fatigue life is analyzed. It reveals that under the condition of higher nominal pressure or larger diameter of the cylinder, it is difficult for the cylinder with 2.25 times burst safety factor to meet the requirements of minimum burst pressure and minimum fatigue life at the same time only by autofrettage, and it is necessary to appropriately increase the burst safety factor or the thickness of the cylinder.

Effect of EMAA content on interlaminar fracture self-healing properties of plain woven carbon fiber composites

HU Ming-hao, GUO Pan-deng, TIE Ying, PI Xiao-fan, ZHANG Zhen-zhen

2022, 0(8): 44-51. DOI: 10.19936/j.cnki.2096-8000.20220828.006

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The effects of poly [ethylene-comethacrylic acid] (EMAA) content on the interlaminar fracture performance and repair effect of plain weave carbon fiber composites were investigated based on experimental and numerical methods. The EMAA self-healing unidirectional laminated carbon fiber composites were prepared using a three-dimensional suture toughening and staged curing process. The crack extension behavior and fracture toughness properties of the composites were investigated under loading and repair conditions based on type I interlaminar fracture toughness tests. The nonlinear spring model was used to study the discrete bridging mechanism. At the same time, numerical modeling and simulation calculation before and after repair were realized by using the double-zoned cohesive zone model and modified spring parameters. The results of the experimental and simulation studies show that the developed numerical models can predict the type I crack extension resistance curves and fracture toughness of the original and repaired composites with 3D self-repair networks more accurately. The incorporation of EMAA improves the actual toughness of interlaminar cracks. The interlayer toughness and repair efficiency are positively correlated with the content of EMAA.

Experimental study on the mechanical properties of ultra-high strength concrete with polyformaldehyde crude fiber

XIA Yang-hao, YANG Ding-yi, ZHAO Lin, Qian Yun-feng, Gao Han

2022, 0(8): 52-57. DOI: 10.19936/j.cnki.2096-8000.20220828.007

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In order to explore the influence of polyformaldehyde (POM) crude fiber on the mechanical properties of ultra-high strength concrete (UHSC) to promote its popularization and application, the working performance, compressive strength, flexural strength, bending toughness and fracture toughness of ultra-high strength concrete (UHSC) with the volume content of POM fiber from 0% to 2.0% were studied. The experimental results show that the addition of POM fiber reduces the performance of UHSC, but it can improve the compressive strength, flexural strength, bending toughness and fracture toughness of UHSC. When the fiber content is 1.0%, its flexural strength increases obviously. The specimen with fiber content of 1.5% has the largest compressive strength, and the improvement effect on bending toughness is the most significant. And the fracture toughness is also significantly improved.

Study on internal pore structure and dynamic mechanical properties of carbon fiber reinforced concrete under high temperature

ZHANG Jing-li, JIU Yong-zhi

2022, 0(8): 58-63. DOI: 10.19936/j.cnki.2096-8000.20220828.008

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In order to study the changes of internal pore structure and dynamic mechanical properties of carbon fiber reinforced concrete with different lengths (0 mm, 3 mm, 6 mm and 12 mm) under high temperature (25 ℃, 100 ℃, 200 ℃ and 400 ℃),the T₂ spectrum distribution, pore diameter and porosity of the specimen were analyzed by nuclear magnetic resonance (NMR), the dynamic uniaxial impact compression tests of concrete specimens under different high temperatures are carried out by using Hopkinson compression bar, and the effects of carbon fiber length and temperature on the dynamic mechanical properties of concrete are analyzed. The results show that when the fiber length is 6 mm, the reinforcement effect of concrete is the best, and the increase of temperature will reduce the strength and quality of specimens. The T₂ spectrum curve of carbon fiber reinforced concrete is bimodal. When the fiber length is 0 mm, the T₂ spectrum peak value of the specimen is the largest, the number of pores is the largest, and the peak value is the lowest when the fiber length is 6 mm. The addition of fiber can effectively reduce the number of pores. With the increase of temperature, the peak value of T₂ spectrum increases, the number of pores in the specimen increases, the porosity increases, and the temperature effect causes the deterioration of the specimen. The addition of carbon fiber can enhance the dynamic compressive strength of specimens and reduce the ultimate strain. The rise of temperature will cause damage to carbon fiber reinforced concrete, reduce its dynamic compressive strength and strain rate effect, and DIF will decrease.

Influence factors on compressive properties of thermoplastic GF/PP bistable rod composites

SUN Yu-qing, ZHAO Fang, SHAO Hui-qi, JIANG Jin-hua, CHEN Nan-liang

2022, 0(8): 64-69. DOI: 10.19936/j.cnki.2096-8000.20220828.009

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Thermoplastic bistable composites have promising applications in the field of space deployable structures due to their advantages of light weight, superior mechanical properties and high space utilization. The objective of the paper is to discuss the mechanical properties of GF/PP bistable composite material used for supporting rod. The basic mechanical properties of the glass fiber fabric, the tensile and bending properties of the composite material under the condition of flat plate, and the axial compression property of bistable composites under the first steady state are investigated in this paper by designing the area weight of glass fiber fabric, laying angle and curvature radius. The results show that the area weight of glass fiber fabric and laying angle have a certain effect on the tensile and bending properties of bistable composites. The composites with fabric weighing of 200 g·m^-2 or 300 g·m^-2 and laying angle of ±30° have better tensile and bending properties in axial and transverse direction. The influence factors of the compression properties of bistable composites include the area weight of glass fiber fabric, laying angle and curvature radius from strong to weak. The axial compression properties of bistable composites are superior when with fabric weighing of 300 g·m^-2, laying angle of [±30°/0°/90°/±30°] and curvature radius of 2.5 inch.

Study on the influence of winding tension on the strength of filament winding composite materials

DU You-yao, DENG Chun-zhi, CHANG Xin, XU Zi-li, ZHANG Ying-ming, GAO Yue

2022, 0(8): 70-74. DOI: 10.19936/j.cnki.2096-8000.20220828.010

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The composite sleeve made by tension winding is an effective way to prevent the damage of permanent magnet of rotor for high-speed permanent magnet motor. In this paper, the strength of NOL ring made by different winding tensions and the curing residual stress of winding composite structure were experimentally studied, in order to study on the influence of winding tension on the strength of composite material. The effects of winding tension on the material strength of composites and the residual stress of winding structure were found. The theoretical estimation method of tensile strength for filament winding materials considering the influence of winding tension and the variation law of fiber volume fraction was established. The mechanism of the influence of winding tension on the strength of composite material was found. A reference for choosing appropriate winding tension for winding composite structures was provided.

Preparation and study of non-Newtonian fluid reinforced Aramid matrix composites

YUAN Shi-qing, XU Da-tian, HU Biao, HUANG Jia-jun, TANG Li-yuan, LI Lu-yao, TIAN Mei-qin, HE Yu-fei

2022, 0(8): 75-81. DOI: 10.19936/j.cnki.2096-8000.20220828.011

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In view of the deficiency of the existing materials with impact resistance, this paper adopts the method of shear pressure of double-roll mill to impregnate the aramid fiber cloth with non-Newtonian fluid, and binds it closely with polyurethane matrix through curing reaction to prepare a new type of aramid fiber cloth reinforced non-Newtonian fluid matrix composite. The dispersion effect of particles in the medium was characterized by nano-particle size analyzer and potential analysis, and the viscosity of non-Newtonian fluid with shear frequency was measured by rheometer. When the amount of dispersed particles reaches 30wt%, an obvious shear thickening process can be observed, and the viscosity can reach three times of the initial viscosity. It is found that the initial viscosity of shear thickening fluid is positively correlated with the maximum viscosity after thickening. The results of impregnation rate test and scanning electron microscope (SEM) showed that the fiber and shear thickening fluid could be effectively bonded at a mass ratio of 1∶1 under the process of impregnation roller. To assess aramid fiber cloth reinforced non-Newtonian fluid shock resistance of composite materials, the scene simulation working condition of power cable laying, use commonly used in the construction process of cutting equipment for the preparation of polypropylene-shear thickening fluid impact test in situ impregnated aramid sandwich plate, the results show that the new type of non Newtonian fluid matrix composites have excellent shock resistance, it can meet the requirements of impact resistance of materials under complex working conditions.

Research on the aging properties of epoxy vinyl resin and its composite materials under high temperature and high pressure mineralized water conditions

LI Feng, WANG Ting-yi, ZHANG Jin, FAN Lu, YANG Cheng-rui, SHI Xian

2022, 0(8): 82-88. DOI: 10.19936/j.cnki.2096-8000.20220828.012

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In this study, the epoxy vinyl ester resin and its glass fiber reinforced composite materials have been successfully prepared, and the mineralized water aging test under high temperature and high pressure (70 ℃+5 MPa) has been conducted to investigate the performance of the degradation as well as the aging mechanism under high temperature and high pressure conditions. It has been found that the mechanical properties of as-prepared resin and composite materials are greatly influenced due to the aging. For instance, after 49 days of aging, the stretching of the composite material dropped to 56.79%. Meanwhile, the residual tensile strength of epoxy vinyl ester was only 27.30%. The characteristic functional groups of the ester within the resin significantly changed during the aging, due to hydrolysis of the ester groups as well as the formation of hydrogen bonds leading to the reduction of the mechanical properties of the materials. According to FTIR and XPS results, the degree of aging gradually decreased from the surface into the interior of the materials. From SEM, it was shown that the fracture failure mode of epoxy vinyl ester gradually changed from ductile fracture to brittle fracture as the aging was processed. In addition, the interfacial debonding occurred within the composite material matrix. In the end, the DMA results indicated that the rupture of the resin molecular chain after aging, as well as the plasticizing effect of water molecules, led to the decreasing of the glass transition temperature and the storage modulus of the composite materials.

Properties of low temperature curing vinyl ester resin prepreg thickened by organic bentonite

LIU Xiao-fan, WU Shu-guang, XU Ren-xin

2022, 0(8): 89-92. DOI: 10.19936/j.cnki.2096-8000.20220828.013

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In order to prepare a low-temperature curing vinyl ester resin prepreg and study the effect of thickener content on the properties of prepreg and composite materials, organic bentonite was used as thickener and alkali-free glass fiber cloth was used as reinforcement material to prepare fiber prepreg by one-step impregnation method. The composite was formed by vacuum bag pressing, preheated at 60 ℃ for 30 min, and cured at 90 ℃ for 1 h. The technological properties of different organic bentonite prepreg materials and mechanical properties of the composites were investigated. The results show that the resin content of each prepreg material is slightly different, and the viscosity level is grade 1, so the technological properties are good. When the mass content of bentonite is 10%, the tensile strength is 395 MPa, the bending strength is 382 MPa and the compressive strength is 201 MPa, and the comprehensive mechanical properties are the best.

Study on influence of hydrothermal environment on runout of composite reinforced stiffened panels

SHANG Hai-jiang, LI Xing, GAO Li-min, WEN Shun-da

2022, 0(8): 93-98. DOI: 10.19936/j.cnki.2096-8000.20220828.014

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This paper takes the runout of the composite reinforced stiffened panel as the object, and analyzes its mechanical properties in hydrothermal and normal environment through experiments. This paper describes the configuration, test plan, test process and test results. The results show that the hydrothermal environment has little effect on the stiffness of the structure, but has a certain influence on the strength. Therefore, the influence of the hydrothermal environment should be considered in the structural design.

Research on thrust cutting force and hole quality of typical drilling bit in woven CFRP drilling

ZOU Cai-yong, SHI Guang-xing, LI Jie, LIU Si-nan

2022, 0(8): 99-104. DOI: 10.19936/j.cnki.2096-8000.20220828.015

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Woven carbon fiber reinforced polymer (CFRP) has been widely used in aerospace, national defense and military industry due to its excellent properties such as high specific strength and specific modulus. However, due to the special fiber wovening mode of woven CFRP, its cutting and material properties are quite different from those of unidirectional CFRP. In order to improve the drilling quality of woven CFRP, three kinds of typical structure drills, such as twist drill, the three point drill and octahedral drill, are used to systematically study the variation of axial cutting force and drilling quality under different drilling conditions. The experimental results show that the three point drill can effectively reduce the axial cutting force and improve the drilling quality, which is more suitable for woven CFRP drilling.

Study on influencing factors of R-area porosity of composite C purlin

YUAN Chao, LI Feng, CHEN Jing, QIU Qi-yan

2022, 0(8): 105-109. DOI: 10.19936/j.cnki.2096-8000.20220828.016

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According to the structure of composite C purlin, the influencing factors of R-area porosity of C purlin are studied through the process soft mold, pre-compaction operation and change of process parameters. The results show that the porosity in the R-area of C purlin can be significantly reduced by using the process soft mold in the curing process. To a certain extent, the stiffness of the soft mold can be improved and the porosity can be reduced, but when the stiffness of the soft mold reaches a certain degree, increasing the stiffness of the soft mold can not further reduce the porosity. Pre-compaction before curing can reduce the porosity of R-area of C purlin, and increasing the pressure and vacuum pumping operation can also reduce the porosity in the R-area.

Research and development status of recycled carbon fiber composites for strengthening cement-based materials

LIU Yao, WU Zhen-hua, ZHANG Zhi-fang, OUYANG Xiao-wei

2022, 0(8): 110-116. DOI: 10.19936/j.cnki.2096-8000.20220828.017

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The waste generated by Carbon Fiber Reinforced Polymer (CFRP) in the process of production, application and scrap is increasing year by year. How to dispose of this kind of waste has become a global problem. This paper firstly introduces the main recycling forms and methods of FRP, and then focuses on the up-to-date research of adding recycled FRP to cement-based materials. Existing studies show that the addition of CFRP has an obvious effect on mechanical properties of cement-based materials, as well as the temperature resistance and conductivity. This proves the possibility of using recycled CFRP to develop multifunctional cement materials, which opens a new window for recycling FRP materials, and is of great significance for waste recycling and environmental protection.

Research progress on reinforcement technology of silica aerogel materials

LI Yan-hua, WU Yi-fan, HAN Qi

2022, 0(8): 117-128. DOI: 10.19936/j.cnki.2096-8000.20220828.018

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Silica aerogel has a unique nano-network framework structure, which endows it with extremely high porosity and extremely low density. The complex micro-nano structure of silica aerogel can effectively block thermal convection, making it with extremely low thermal conductivity. Si—O—Si with excellent heat resistance constitutes the main structure of silica aerogel. Silica aerogel has a wide range of applications in building thermal insulation, aerospace thermal protection, sound absorption and noise reduction, weapon equipment manufacturing and other fields. Silica aerogel is one of the main research and development directions of thermal protection materials at home and abroad. However, silica aerogel has the disadvantages of low strength and poor continuity of nano-network skeleton structure, poor physical and chemical combination of nano-pore structure, and high brittleness of related products, which makes it difficult to combine thermal protection and load-bearing. In this paper, from the three perspectives of skeleton reinforcement, polymer reinforcement and second phase reinforcement, the research status and existing problems of silica aerogel reinforcement technology are discussed. This paper summarizes the research status of silica aerogel reinforcement technology at home and abroad, and provides ideas for the future development of silica aerogel framework reinforcement technology.

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