Table of Content

28 June 2019, Volume 0 Issue 6

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AXIAL COMPRESSIVE BEHAVIOR OF CFRP-STIRRUP CONFINED ROUNDED RECTANGULAR CONCRETE COLUMNS

XU Yang, WEI Yang, CHENG Xun-yu, DUAN Mao-jun

2019, 0(6):  5-11. 

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Axial compression tests were carried out on 24 carbon fiber polymer-stirrup confined rectangular concrete columns with chamfering. The test shows that CFRP and stirrups form a dual constraint system for the core concrete, which complements each other. It effectively improves the bearing capacity and deformability of the concrete column in which stirrups ensure the residual bearing capacity and ductility after the fracture of FRP. The axial compression performance of FRP-stirrup rectangular concrete columns with chamfering is closely related to the number of FRP layers and the chamfering radius of specimens. Increasing the chamfering radius can improve the properties of the concrete column significantly. With the same layers of FRP, the bigger the chamfering radius is, the better the performance will be. Besides, increasing the number of FRP layers can effectively improve the bearing capacity and deformation capacity of the confined concrete column with identical chamfering radius. Combined with the test results, the bearing capacity calculation model of CFRP-stirrup confined rectangular concrete columns with chamfering is proposed by considering the effective constraint coefficient of the rectangular concrete column, and on the basis of the ultimate stress calculation model of confined circular concrete columns.

EXPERIMENTAL STUDY ON THE REINFORCEMENT OF THE SIDE AND BOTTOM OF CFRP PLATE

DENG Lang-ni, YE Xuan, LU Yun-peng, MA Jin-chao

2019, 0(6):  12-16. 

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Fiber composite materials are widely used in the field of building structural reinforcement. The traditional CFRP reinforcement method is usually externally sticking CFRP, which is prone to peeling damage, easy to wear and corrosion, etc., and the embedded reinforcement method can well avoid the external decoration method. The embedded CFRP reinforcement method mainly has two kinds of reinforcement methods, one is to slot the bottom surface and the other is to be grooved on the side for reinforcement. In this paper, the flexural behavior of the reinforced concrete beams embedded with CFRP panels and the bottom-mounted and bottom-mounted CFRP panels were tested. The bearing capacity and mid-span deflection of the specimens were compared between the two panels in the same reinforcement. The effect of crack development and comparative analysis of the side and bottom reinforcement were investigated. The test results show that both kinds of reinforcement methods can significantly improve the bearing capacity and rigidity of the reinforced beam. And, for the yield load, ultimate load and crack development, the side splicing reinforcement is close to the reinforcement effect of the bottom splicing reinforcement in all aspects. Although the bearing capacity is slightly inferior, the gap is small, the construction convenience, applicability and durability are better, and the bottom panel can be replaced under many conditions.

INFLUENCE OF CRACK PARAMETERS ON THE LAMB NONLINEAR INDEX OF ULTRASONIC IN COMPOSITE

ZHANG Qing-song, TIE Ying, YIN Zhen-hua, XIA Xiao-song

2019, 0(6):  17-23. 

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For detection of cracks in composite, a 3D finite element wave model of anisotropic composite plate considering the nonlinear crack contact was established to explore the interaction between nonlinear Lamb waves and different sizes of cracks in composite structure. The influence of the length and width of cracks on the nonlinear index of nonlinear Lamb waves was explored. The results show that the nonlinear index increases with the increase of the length of cracks within a certain range. As the width of cracks increases, the nonlinear index decreases. Using the SNAP nonlinear ultrasonic testing device in experiment, the feasibility of crack detection in composite materials by testing ultrasonic nonlinear index was verified. The experimental results show that the presence of cracks in the structure can be qualitatively evaluated by measuring the nonlinear index in the composite. This is of great significance to the follow-up nonlinear non-destructive testing of composite materials.

STUDY ON RHEOLOGICAL PROPERTIES AND CURING REACTION KINETICS OF PEK-C/EPOXY RESIN BLEND SYSTEM

ZHOU Shuai, CHENG Chao, SUN Ze-yu, ZHANG Huisup

2019, 0(6):  24-29. 

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The epoxy resin was toughened and modified by polyetherketone cardo (PEK-C) in the paper. The rheological properties of PEK-C/E51/E100 blends with different PEK-C contents were systematically studied. The effects of different PEK-C contents on the curing reaction of blends at different heating rates were analyzed by DSC, and the apparent activation energy and curing reaction order of the curing reaction of each blend system were calculated in detail. The results show that the introduction of PEK-C shortens the gelation time of the blend system, which may be related to the promotion of the curing of epoxy resin by the hydroxyl groups in PEK-C. Meanwhile, the addition of PEK-C does not affect the curing mechanism of the epoxy resin.

EXPERIMENTAL STUDY ON BENDING DEFORMATION AND FAILURE OF LAMINATED DAMAGE COMPOSITES

QIN Reng, LI Xiao-tong, SHANG Ya-jing, ZHOU Wei

2019, 0(6):  30-36. 

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In order to study the damage characteristic of composite with symmetric delamination, the buckling failure behavior and deformation field information of specimen containing symmetric multilayered unidirectional glass fiber reinforced composite specimens under three-point bending test were studied by using acoustic emission (AE) and digital image correlation (DIC) method. Then, the damage pattern of specimens was identified by k-means clustering analysis. The results showed that lamination damage led to the reduction of the bearing capacity of the material and the weakening of the resistance to deformation, and the layered damage under compression load was more obvious than that under tensile load. The layered damage composite material produced more AE damage signals during loading. The AE signals can be divided into three categories: low frequency, medium frequency and high frequency by cluster analysis, which were corresponding to matrix cracking and delamination, fiber debonding and fiber fracture of the symmetrical layered specimens. The displacement field of the specimen with stratified damage was unstable and the distribution of strain field was more dispersed than that of the blank control sample. AE technology can monitor internal damage information in real time, and DIC method can analyze the changes of specimen surface displacement field. Therefore, the combination of the two technologies is of great value for the structural health monitoring of composite materials.

EXPERIMENTAL STUDY AND FINITE ELEMENT ANALYSIS ON BEARING CAPACITY OF JOINT OF GFRP TUBES SCAFFOLDS

WU Wei-kai, LI Fei, CHEN Hui-guo, DENG An-zhong

2019, 0(6):  37-42. 

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To apply composite tubes to the scaffolding structure, the problem of connection between members should be settled. Seeing the low transverse strength of GFRP tubes, we need to study the mechanical properties of member nodes when applying traditional steel fasteners to GFRP tube connection. In this paper, the author first imposed preload torque on GFRP tubes with cushion-free fasteners and cushioned fasteners and obtained therefrom the rules of bearing of GFRP tubes with two different fasteners. After that, based on the pretension test, the author performed the anti-slide test and studied the influence of cushions on the anti-slide bearing capacity of the nodes. In the end, the author established a finite element model of the nodes and optimized the thickness of the middle-layer cushions with the model built. The research demonstrated that: the increase in semicircular steel cushions could noticeably enhance the preload torque bearable for GFRP tubes, improve the distribution of force in GFRP tubes and better the anti-slide bearing capacity by about 26.3%. In the meantime, the finite element model indicated the appropriate cushion thickness to be 3.5 mm.

EXPERIMENTAL STUDY ON MECHANICAL PROPERTIES OF BASALT-CELLULOSE HYBRID FIBER REINFORCED CONCRETE

ZHANG Zhen-lei

2019, 0(6):  43-48. 

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In order to study the effect of basalt fiber and cellulose fiber mixing on the mechanical properties of concrete, the different basalt fiber lengths (6 mm, 12 mm, 30 mm) and different fiber contents (2.7 kg/m³, 4.0 kg/m³, 5.4 kg/m³) were analyzed by cube compression, splitting tensile and flexural strength test. The results indicate that compressive strength, splitting tensile strength and flexural strength were increased after adding a reasonable content of hybrid fiber. When the content of basalt fiber and cellulose fiber is 4 kg/m³ and 1.6 kg/m³, respectively, the cube compression, splitting tensile and flexural strength are increased by 13.94%, 35.46% and 18.75%, respectively, than that of the ordinary concrete. When the basalt fiber length is 12 mm and the content is 4 kg/m³, the fiber reinforced concrete shows a good enhancement effect. And with the increase of the content, the strength of fiber concrete increases first and then decreases. When the content of cellulose is 1.6 kg/m³, the effect of concrete is the best.

STUDY AND DESIGN OF AUTOMATIC PAVING SYSTEM OF GLASS FIBER CLOTH FOR M-W CLASS WIND TURBINE BLADE

CHEN Chuan-xun, ZHANG Hua-qiang, LIU Wei-sheng, YANG Xian-hai

2019, 0(6):  49-52. 

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In order to resolve the problems as high labor intensity, low efficiency and being harmful to health of artificial laying of glass fiber cloth on wind turbine blades, this paper designed a set of automatic laying system of glass fiber cloth on wind turbine blades, based on principle and working procedure of artificial laying of glass fiber cloth on wind turbine blades. Adopting the advanced sensing information acquisition technology, the control principle and technology and the information fusion technology, this system can optimize the path planning and adjust the roll posture and placement speed, according to the profile of the blade. The motion trajectory of the system is precisely controllable, and the cloth roller posture and rotation speed are adjusted adaptive. The results show that the designed paving system has better stability, high paving efficiency, and a strong engineering application value, and it can also greatly reduced labor intensity.

STUDY ON BENDING STIFFNESS OF CFRP BOX BEAM CROSS-SECTION PARAMETERS

YANG Hai-ru, YUAN Wei, CHEN Guo-zhi, FANG Jian

2019, 0(6):  53-57. 

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In this paper, the finite element software Abaqus is used to simulate and analyze the influence of cross-section parameters of box beam on its bending stiffness, including the beam section height, the upper and lower flange wall thickness, the upper flange wall thickness and the lower flange wall thickness, so as to improve its bending stiffness when the weight of the beam was unchanged, and compare with the same size of metal materials. The results show that the bending stiffness of CFRP box girder can be improved effectively by increasing the section height of the beam, thickening the upper and lower flange and thickening the upper flange. The bending stiffness of the lower flange thickening is the most effective, and thickening of the upper flange is the worst, which provides a reference for the design optimization of composite material box beam and has a certain practical value.

STUDY ON ABSORBING BOUNDARY PARAMETERS OF COMPOSITE FOR ULTRASONIC GUIDED WAVE

XIA Xiao-song, ZHENG Yan-ping, XIONG Yong-jian, ZHANG Qing-song

2019, 0(6):  58-63. 

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In the ultrasonic nondestructive testing research, the finite element simulation of the lamb wave propagation process is helpful to understand its propagation characteristics and improve the test accuracy. Due to the structural size limitation and anisotropy of the composite material, the appearance of the boundary reflection wave in the simulation process will cover the damage waveform, and the test result is to suppress the reflected wave. The setting of the absorption boundary is particularly important. In order to effectively absorb the boundary reflection, a multi-layered Rayleigh damped incremental absorption layer is added at the model boundary. By changing the parameters such as absorption length and damping maximum, it is found that the multi-layer damping absorption layer with increasing Rayleigh damping can effectively reduce the boundary reflection wave, and the absorption boundary length has the greatest influence on the absorption effect. In order to effectively absorb the reflected wave, the absorption boundary length should be larger than the wavelength of 2 times.

PREDICTION OF ELASTIC PROPERTIES OF 2D WOVEN COMPOSITES BASED ON RVE METHOD

LAI Wei-qing, WANG Xiu-mei, XIN Liang-liang, GENG Shu-dong

2019, 0(6):  64-72. 

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In order to predict the elastic properties of 2D woven composites, based on the representative volume element (RVE) method, the mesostructured theoretical calculation model and the finite element analysis model of the 2D woven composites were established. Firstly, considering the extrusion deformation between the warp and weft fiber yarns and the gap thickness at the interlacing point, the deformation factor k is introduced to establish a modified mesoscopic geometric model of the two-dimensional woven composite material. Based on the corrected geometric model, the calculation method of macroscopic elastic constant under two models is given. The results show that the maximum errors of macroscopic elastic constants between experimental values and values calculated by the theoretical calculation model was 3.89%, while the maximum errors of macroscopic elastic constants between experimental values and values calculated by finite element analysis model was 9.18%, respectively. The rationality of the corrected model and the correctness of the theoretical calculation model and the finite element analysis model were proved, which laid the foundation for exploring the meso-mechanical properties of 2D woven composites.

COMPARATIVE TESTS OF MECHANICAL PROPERTIES AND FAILURE MECHANISM OF DIFFERENT FIBER-REINFORCED CONCRETE

ZHANG Pei-hui, FANG Sheng-en, HONG Hua-shan

2019, 0(6):  73-79. 

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In order to investigate mechanical properties and failure features of different fiber-reinforced concrete, specimen tests were carried out to compare the effects of different fiber volume fractions on compressive strengths, splitting tensile strengths and modulus of elasticity. Five different types of fiber-reinforced concrete were evaluated involving basalt fibers, carbon fibers, steel fibers, polypropylene fibers and the hybrid of basalt and polypropylene fibers. More attentions were focused on the basalt fiber-reinforced concrete. The effects of superplasticizer and silica fume on the mechanical properties of basalt fiber-reinforced concrete were further discussed. The test results demonstrate that the 0.05%~0.2% volume fraction addition of basalt fibers improved the splitting tensile strengths, as well as the integrity of the damaged specimens. However, the cubic and axial compressive strengths of basalt fiber-reinforced concrete decreased with the increase of the volume fraction. On the other hand, under the precondition of an identical volume fraction, polypropylene fibers mostly contributed to the splitting tensile strengths of concrete since all the fibers presented a satisfactory anti-cracking effect. However, all the 5 types of fibers show little effects on modulus of elasticity and caused adverse effects the compressive strengths. With respect to the basalt fiber-reinforced concrete, superplasticizer commonly used in engineering could weaken the bonding interfaces between fibers and concrete, resulting in worse mechanical properties. Fortunately, this influence could be improved by adding silica fume.

RESEARCH ON CARBON FIBER REINFORCED POLYMER STAY-CABLE AND ITS MECHANICAL PROPERTY

ZHU Yuan-lin, LIU Li-hua, ZHOU Jia-qi, HUANG Sheng-bin

2019, 0(6):  80-84. 

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This paper studied a new kind of CFRP stay-cable and its mechanical property. A new structure of CFRP stay-cable was proposed and manufactured. Instead of parallel arrangement of the CFRP tendons, CFRP tendons in new structure of CFRP stay-cable is twisted together in cable and diverge in the anchor end. The tensile strength and tension-tension fatigue behaviour of the new structure of CFRP stay-cable were tested. Experimental results show that the new structure of stay-cable and its manufacturing process are feasible. The twist angle of 2.5°~3.5° and the divergence angle of 2.5° are suitable for CFRP tendons, and the slight twist and bending of tendons will not lead to premature failure. The static load tensile anchorage efficiency of the new CFRP stay-cable is more than 95%. After 2.5 million fatigue loading tests, the anchorage part is not damaged and the broken tendon rate of the cable is less than 5%. With the increase of fatigue loading cycles, the elastic modulus of the CFRP cables basically remains unchanged. The cable extension at the anchorage end and the retractions of the tendons and anchor plates at the back end of the anchorage are less than 1 mm.

RESEARCH OF THE MIXED-WEAVING GRADIENT FABRIC REINFORCED PHENOLIC RESIN OBLIQUE MATERIALS FOR HEAT-RESISTANCE

LI Pan-pan, LIU Yi-tao, QIN Rong-rong, WANG Meng

2019, 0(6):  85-89. 

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This article addresses the demand for the heat-resistant materials of aerocraft, the structural of mixed-weaving gradient fabric reinforced phenolic resin oblique materials were introduced. The heat-resistant material is a gradient functional material, and the function of the material gradually transform from the outer layer to the inner layer from ablation to heat insulation, achieving integration of heat insulation. The two functional layers use the same high temperature resin matrix with thereby no obvious interface. The anti-ablative layer reinforcing fiber is mainly composed of ablation resistant fiber, and the heat insulating layer reinforcing fiber is mainly composed of high temperature resistant fiber. The functional layer and gradient effects are achieved by ablative fiber-heat insulation fiber of woven faber, shaping by oblique winding. To improve the materials anti-scour performance, the ply direction of woven faber presents a certain angle with the aerocraft′s heading. The obtained materials (mounted on the tooling bottom plate) is evaluated on a high-temperature supersonic gas flow engine, which can withstand the heat flow density of 1750 ℃, 2000 kW/m² , scouring up to 40 s. The result shows that the rate is less than 40 g/100 cm² and the back temperature is below 270 ℃.

STUDY ON DEFORMATION OF COMPOSITES OF ARAMID FIBER/CARBON FIBER COMPOUND STRUCTURE

WU si-bao, LI song-ming, LU hai-jun

2019, 0(6):  90-94. 

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Resin matrix composites possess the advantages of high specific strength, high specific modulus, high designability, strong corrosion resistance and integration molding, which have been widely used in the fields of aerospace, vehicles, ships, electronics, etc. In some practical application fields, different resin matrix composites need to be compound to obtain functional composites with excellent comprehensive properties that single resin matrix composites don′t possess. When different kinds of resin matrix composites are combined, their respective degree of size change with the change of temperature is different during the compound thermal process because of the difference of their thermal expansion coefficient, which creates the internal stress of the compound structure and eventually lead to a certain deformation. In this paper, the influence of compound process (compound temperature and compound pressure), compound methods (secondary bonding and co-bonding), the pre-deformation of aramid fiber composite on the deformation of the composite of aramid fiber/carbon fiber compound structure were studied. The results show that the deformation of the compound structure can be decreased obviously with the decrease of compound temperature. When the compound temperature drops from 180 ℃ to 120 ℃, the deformation of the compound structure decreases by 80%. Appropriate increase of compound pressure contributes to decrease the deformation of the compound structure, whereas the deformation is no longer decreased when compound pressure reaches 0.3 MPa. Aramid fiber-carbon fiber secondary bonding (aramid fiber composite and carbon fiber composite both have been cured completely before they are combined) and carbon fiber-aramid fiber dry-wet co-bonding (carbon fiber composite have been cured completely, while aramid fiber is not cured before they are combined) are beneficial to decrease the deformation of compound structure compared by aramid fiber-carbon fiber dry-wet co-bonding (aramid fiber composite have been cured completely, while carbon fiber is not cured before they are combined). The pre-deformation of aramid fiber composite is an effective way of the deformation control of compound structure.

RESEARCH OF AN UNDERWATER COMPOSITE SHELL FOR LIFE RAFT OF LARGE DEPTH

KONG Dong-ming, HOU Xin, SUN Chao-ming, HUANG Qi-zhong

2019, 0(6):  95-99. 

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The life raft shell is the key equipment for seafarers′ life-saving. In this paper, a kind of composite inflatable life raft shell for underwater is developed, which has the characteristics of high pressure resistance, reliable sealing and high-low temperature alternation resistance. Through the structural design and verification, moulding process research and performance verification of the life raft shell, the results show that the performance of the prepared life raft shell is reliable and can meet the requirements of product performance indicators.

TENSILE FRACTURE STRENGTH ANALYSIS OF SPLICED LAMINATE

GUO Hao-chang, LUO Wen, LUO Qi, WANG Wen-long

2019, 0(6):  100-104. 

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In the low cost manufacturing process of large structural parts, the splicing seam of fabric system is unavoidable. The staggered processing scheme of splicing seam directly affects the structural performance of fabric products. In this paper, three kinds of splicing schemes of different structure forms are put forward, and the orthogonal test of the thickness, splicing seam scheme and splicing seam distance of S-glass satin fabric is carried out by vacuum-assisted forming technology. The tensile properties of corresponding samples are tested, and the effects of different splicing parameters on the mechanical properties of the laminates are summarized. The finite element models of single-layer structure and interlaminar elastic structure are established by finite element simulation, and the tensile properties are calculated, which can provide reference for the lamination design of composite components.

DESIGN OF A COMPOSITE TIDAL CURRENT TURBINE BLADE

ZHU Fu-wei, REN Ming-fa, XU Di

2019, 0(6):  105-110. 

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There is great progress on research and development for tidal power equipment in the worldwide, and some of the power equipment has gradually applied on the commercial demonstration. Tidal turbine blade is the basis of energy conversion from tidal current to power energy, and is also the key component for power generation. Due to the advantages of composites such as light weight, high strength, corrosion resistance and easy forming, it has been the preferred material for the tidal current turbine blade. Based on the theory of blade element momentum and the composite mechanics, a composite tidal current turbine blade, which would be applied in a tidal with 2 m/s velocity, was developed. The finite element analysis results show that the blade can fulfill the serving requirements and has a high safety margin.

RESEARCH ON DESIGN TECHNOLOGY OF MOLDING MOLD FOR COMPOSITE PROPELLER

ZHANG Xin-yu, GAO Ting, ZHU Kun, YI Wei

2019, 0(6):  111-114. 

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The propeller is one of the most important components of the ship and its material requirements are extremely high. Composite material has become the first choice for propeller material due to its high strength, small specific gravity, corrosion resistance and low underwater noise. In addition, as a key procedure in the composite propeller forming process, mold design process also has high requirements. This paper mainly analyzes the research background of current composite propellers on the basis of the existing mold design,and sums up the inadequacies. And then, according to the molding principle of molding process, an integrated molded composite propeller mold was studied and designed. By introducing five main modules consisting of the analysis of the overall structure of the propeller, the comparative analysis of the existing mold structure, the overall design of the mold and the cavity design, the manufacture and molding of the propeller mold, and the analysis of the precision, and by combining with relevant calculations, the design result of the integral molding die was obtained. The technical problems of assembly deviation and low bonding strength had been effectively solved.

PROGRESS AND PROSPECTS OF DAMPING PROPERTIES OF COMPOSITE MATERIALS

SUN Cheng, SONG Chun-sheng, LIU Xing-yu, HUANG Yu-xiang

2019, 0(6):  115-121. 

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The present review aims at gathering the available literature on damping in composite materials. Further, damping properties of composite materials were reviewed and discussed in detail based on existing experimental and simulation efforts on such flows by experimental characterization, parameters affecting damping properties, mathematical and numerical model in view of damping properties. Although fibre reinforced composite materials have not been sufficiently developed so far, they have the potential to tailor damping by acting on constituents, geometry and boundary conditions. Finally, based on the development tendency of investigation into damping properties of composite materials and important problems potentially encountered in such a research, specific development directions were debated and prospected.