COMPOSITES SCIENCE AND ENGINEERING

STUDY ON THE PERFORMANCE OF EMBEDDED BOLT CONNECTION OF WIND TURBINE BLADE

GONG Min, NI Ai-qing, WANG Ji-hui, QIN Zhi-wen

2020, 0(9): 5-10.

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The model of embedded bolt sleeve bolt connection of wind turbine blade is established. Using finite element software ANSYS to study the stress form of embedded bolt sleeve connection bolt under conditions such as tension, compression, and different preload and its influence on load factor and fatigue life. The results show that when the external load is tensile force, when the external load is less than the critical load, the bolt load increases linearly with the external load, and the bolt factor is a fixed value. When the external load is greater than the critical load, the bolt load coefficient increases rapidly, which greatly affects the fatigue life of the bolt. When the external load is pressure force, the bolt load factor is a fixed value. When the bolt service standard is met, the greater the preload is, the smaller the bolt load factor is, the longer the bolt fatigue life is.

FLUID-SOILD COUPLING ANALYSIS OF COMPOSITE FLOATING STRUCTURAL SYSTEM FOR PHOTOVOLTAIC POWER STATION

YANG Chen, FANG Hai, HAN Juan, LIU Wei-qing

2020, 0(9): 11-16.

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In view of the defects and shortcomings of the traditional plastic floating system, such as low strength, poor durability, and easy to sink, etc, this paper presented a new type of composite floating system for photovoltaic power station. A new type of UPVC-FRP composite tube floating system was designed and manufactured by using glass fiber reinforced composite material and UPVC plastic tube combined with hand paste forming process. At the same time, the process of manufacturing and installation was produced, and the buoyancy of static load was analyzed. By adopting fluid-solid coupling FEM, the hydrodynamic characteristics of UPVC-FRP composite tube floating system caused by wind, wave and current were studied. The reliability of the FEM in this paper was verified. The results showed that the maximum draft depth was 0.346 m, which meet the buoyancy requirements of floating body under static load combination. In addition, the composite tube floating system square array can greatly improve the effect of the floating system against wind, wave and flow damage.

STUDY ON THICKNESS OF LINING LAYER OF FLEXIBLE PIPE BONDED BY GLASS FIBER REINFORCED COMPOSITES FOR OIL AND GAS TRANSMISSION

LI Ping, YAN Ting-jun, LI Peng, CONG Ri-feng

2020, 0(9): 17-24.

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The inner liner plays a supporting role in the manufacturing process of glass fiber reinforced composite bonded flexible pipe. To ensure the strength of the lining layer, the method of increasing wall thickness is usually adopted, which will not only increase the manufacturing cost of the pipe, but also reduce the flexibility of the pipe. In order to ensure the accuracy of the finite element simulation results, the mechanical properties of the material used in the lining layer were measured by mechanical properties experiments. According to the mechanical characteristics of the lining layer, the effects of winding mode, number of winding layers and hot melt temperature on the thickness of the lining layer were studied. ABAQUS finite element analysis software was used to calculate the minimum thickness of the lining layer of glass fiber reinforced composite bonded flexible pipe with a diameter of 65 mm, which provides a theoretical reference for the reasonable selection of the inner liner thickness.

STUDY ON DYNAMIC STRESS RESPONSE FOR CERAMIC MISSILE RADOME IMPACT ON COMPOSITE PETAL-TYPE FRAGILE COVER

WANG Min, LI Xing-de

2020, 0(9): 25-28.

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This paper takes the missile radome as the subject of study. The missile radome is made of ceramic matrix composites. The finite element models of both ceramic missile radome and composite petal-type fragile cover are built by FEM. Transient dynamic mechanical analysis for the radome-cover impact process is computed using Abaqus software. In combination with the Fortran programming, the transient responses and the failure modes are obtained after the calculation. Calculation results show that, after the radome-cover impact, the integrity of radome remains unchanged and the protection cover breaks into pieces from the designated stress trough. The impact tests are carried out. The velocity of ceramic missile radome impact on fragile coveris 7.1 m/s. Results from radome to fragile cover impact test show good coincidence with the FEM simulation results. The process and parameters obtained in this paper provide a good guide for similar design.

EXPERIMENTAL STUDY ON TORSIONAL BEHAVIOR OF RC BOX BEAM STRENGTHENED BY CFRP UNDER DIFFERENT TORQUE-TO-SHEAR RATIOS

MA Sheng-qiang, SUN Jian-feng

2020, 0(9): 29-36.

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In this paper, the torsional behavior of CFRP reinforced concrete box beams under different torque-to-shear ratios were investigated in the experimental study. According to different torque-to-shear ratios (ie, 0.958, 1.597, and 2.556), 12 reinforced concrete box beams were divided into 3 groups, and 3 beams in each group were strengthened by CFRP with different configurations, such as U-shaped strips and U-shaped strips with longitudinal strips. The test results showed that at the ultimate load the cracking angles of all beams were proportional to the torque-to-shear ratios. But, when the torque-to-shear ratio was 0.958, the angle of cracks was close to the 45° angle of the crack angle under pure shear failure. Besides, two failure modes appeared in the experiment: U-shaped strips peeled off and the longitudinal strips ruptured, which shows the longitudinal strips compressed the U-shaped stripes to contribute the torsional strength for the "CBSL" series strengthened beams. Moreover, the improvements of torque of the beams presenting 76.2% for 3CBSL2, 55.2% for 1CBSL2, and 46.9% for 2CBSL which shows increase in torsional resistance was inversely proportional to the torque-to-shear ratio. For beams strengthened with only U-shaped strips, however, the torsional capacity was increased moderately, due to the U-shaped strips which have not significantly enhanced the reinforcement effect of the box girder. Therefore, the torsional behavior and strengthening effectiveness of the strengthened beams is affected by the CFRP configuration and the torque-to-shear ratio.

STUDY ON BEARING CHARACTERISTICS OF LAMINATED PLATE WITH SINGLE JOINT BASED ON PARAMETRIC METHOD

WANG Shuai-pei, NI Kai-qiang

2020, 0(9): 37-41.

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Three dimensional cumulative damage theory and Yamada-Sun failure criterion are used to simulate the failure process and load-bearing characteristics of laminated plate with single joint based on ABAQUS in this paper, and the simulation results are in good agreement with the test results. A parameterized method of 3D finite element modeling of laminated plate with single joint is proposed with the help of Python language and self programming. This method can realize the automatic completion of the whole process from modeling to analysis to post-processing, which greatly reduces the time cost of early modeling. At last, the influence of geometric parameters, fastener parameters and load factors on the load-bearing characteristics of the laminated plate with single joint is studied. The results show that the load-carrying capacity of laminated plate with single joint can be effectively improved by choosing appropriate plate length, end distance to hole ratio, width to hole ratio, increasing hole diameter, hole roughness and bolt preload.

STUDY ON PREPARATION AND MECHANICAL BEHAVIOR OF HIGH-DENSITY WARP KNITTED AEROSTAT ENVELOPE MATERIAL

ZHANG Cheng-long, CHEN Nan-liang, GENG Yi, SHAO Hui-qi

2020, 0(9): 42-47.

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The localization of the aerostat envelope has important strategic significance for the engineering application of the stratospheric airship. Because of its harsh service environment, high-performance special fibers are generally used to weave plain cloth as the bearing layer. However, special fibers such as polyarylate and PBO are currently monopolized by foreign countries, with higher prices and the risk of domestic bans. In order to realize the localization of aerostat envelope, this paper uses domestic polyester high-density biaxial warp knitted fabric and polyester film to laminate by TPU to prepare a new type of high-performance low-cost aerostat envelope material. The mechanical properties and failure mechanisms such as tensile, tearing and crack response were experimentally analyzed. The test results show that the polyester-based high-density biaxial warp-knitted skin has excellent mechanical properties (tensile strength> 950 N/cm, tear strength> 600 N), which can meet the requirements of aerostat envelope mechanical properties and can improve the isotropic problem of the envelope material. At the same time, it was found that the high-density warp-knitted skin material has better weft tearing performance than the warp direction, and the existence of cracks causes stress concentration effects in the crack zone, which will aggravate the failure of the envelope. And the loss of strength is determined by the projected length of the crack in the transverse direction.

BEHAVIOR OF FRP TUBE STRENGTHENED STEEL MEMBERS UNDER ECCENTRIC COMPRESSION LOAD

WEI Shao-jie, FENG Peng, YANG Jia-qi, LIU Tian-qiao

2020, 0(9): 48-60.

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In this paper, the steel columns were strengthened by pultruded GFRP tube, GFRP sheet and grouting, and their behavior was investigated through eccentrically compression tests. Through tests on 20 steel columns, the influences of different sections, slenderness ratios and eccentricity ratios on the strengthening effect were addressed. Ultimate strength after strengthening, failure mode, load-displacement curve,and strains at key positions were investigated. The test results showed that the ultimate strength of strengthened steel members increased by up to 169%. In addition, the failure mode of the eccentrically compressed members were transitioned from global lateral buckling to local deformation in the unstrengthened area. In addition, the finite element model of steel column was constructed, and the simulation results are in good agreement with the test results. Finally, the finite element modeling is used to analyze six parameters including the length ratio of the strengthened section, the bending stiffness ratio, the ultimate strength and yield strength of the steel, the initial deflection of the core steel members and the slenderness ratio of the core steel members, and the influence law of each parameter on the test was revealed.

ONE-SIDED STITCHING DEVICE AND EXPERIMENTAL RESEARCH FOR GLASS FABRIC

TIAN Hui-fang, SU Xiao-wei, WU Ying-feng, ZHANG Yang

2020, 0(9): 61-67.

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Stitching technology was widely used because it can effectively reduce delamination failure and improve impact damage tolerance of composites such as glass fiber. Comparing and analyzing the current stitching technology, a new one-side stitching device which has the features of double-thread reinforcing and stitching with variable angle is designed in this paper. Theoretical analysis on the double-needle cooperation was performed to verify that it meets the principle of stitching work. And then, the kinematic cooperative movements of the various mechanisms were analyzed to provide theoretical guidance for the debugging and use of the device. In the experimental part, the effects of the angle of the double needle on the success rate of the stitching was firstly studied. It shows that the larger the angle is, the higher the success rate is and the stitching device can basically meet the demand of stitching work. And then, the effects of other stitching parameters on stitching were investigated. It shows that the increase in the thread diameter is not conducive to stitch and the increase in the needle diameter is conducive to stitch, and it needs to reasonably select stitching parameters. Supporting with slotted is more effective than supporting with foam when stitching, but the success rate of support with foam can reach 94.3%, which still has research and application value.

SIMULATION ANALYSIS AND APPLICATION RESEARCH ON SHEAR PERFORMANCE OF PVC CORE MATERIAL BASED ON ANSYS

ZHANG Zhen-cong, HUANG Hui-xiu, CHEN Li-gui, LIU Wei-sheng

2020, 0(9): 68-73.

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According to the current general surface treatment method of composite core materials, the core material simulation model based on ANSYS is used to predict its out of plane shear modulus, and the theoretical calculation results of the classical sheet model of composite material mechanics are checked with it, and the two results coincide with each other. Based on the results of the simulation model, the influence of different factors on the shear modulus of the core material is further discussed. The results show that the core material has higher shear modulus when the hole diameter is 2 mm, the width of the deep groove is 1.2 mm, the height of the deep groove bottom is 2 mm and the height of the shallow groove is 3 mm. The test results show that the error value between the two is 1.74%, which is within the acceptable range. The design concept of "simulation first, then verification though experiment" is efficient, time-saving and labor-saving. At the same time, comparing the simulation results with Wang Yaoxian′s semi-empirical formula, it is found that when p=2.047, the error value between the two is no more than 0.97%, and the coincidence is good. The empirical formula can be used to predict the simple form of core shear modulus.

STUDY ON MULTI-LAYER HONEYCOMB SANDWICH STRUCTURE OF AERONAUTICAL COMPOSITE BY AIR-COUPLED ULTRASONIC INSPECTION TECHNIQUE

ZHANG Ji-min, ZHOU Hui, LIU Kui

2020, 0(9): 74-78.

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The air-coupled ultrasonic C scan technique based on the penetrative opposite side detection mode was utilized to study the inspection of composite multi-layer honeycomb sandwich structure. The result of air-coupled ultrasonic inspection on the triple-layer honeycomb structure was study under the exposed state of honeycomb surface. Meanwhile, the result of air-coupled ultrasonic inspection on the triple-layer honeycomb structure was studied when the honeycomb surface was skinned and compared with the conventional water jet TTU result. The adaptation and reliability of the air-coupled ultrasonic C scan results were proved through the analysis of ultrasonic path and the detection of traditional rays and CR. It was shown that not all bonding interface defects could be detected by the air-coupled ultrasonic technique under the exposed state of honeycomb surface. However, when the honeycomb surface was skinned, compared with conventional water jet TTU, the air-coupled ultrasonic result was not affected by the honeycomb cell being not aligned. And the fast and effective inspection was realized.

STUDY ON THE MECHANICAL PROPERTIES OF NOMEX-HONEYCOMB SANDWICH COMPOSITES

HE Jing, YANG Xiao-lin, ZHU Xiu-di, SUN Chao-ming

2020, 0(9): 79-84.

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Honeycomb sandwich composites were prepared by using three brands of unidirectional prepreg, one type of multi-surface density adhesive film and a type of Nomex honeycomb core, through a hot-pressing process. The paper studies the effect of the surface density of adhesive film on climb drum peeling of honeycomb sandwich panel, and the factors which affect the long beam bending, panel shearing (three-point bending) and insert shearing. When using the same Nomex honeycomb core material, the results are as follows. The surface density of the adhesive film has obvious influence on the climb drum peeling performance of the honeycomb sandwich panel. The long beam bending load of the honeycomb sandwich panel is mainly affected by the performance of the prepreg. The deflection under 450 N load is controlled by the modulus of prepreg after curing. The effect of prepreg and adhesive film on the performance of panel shearing of sandwich panel is small. The performance of insert shearing has nothing to do with the surface density of the adhesive film.

AUTOMATIC DEFECT DETECTION OF WIND BLADE SURFACE VIA UAV

MAO Xi-wei, XU Ying-ying

2020, 0(9): 85-89.

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With the rapid development of industrialization for wind power electricity generation, the continuous expansion of wind turbine capacity, the length of wind turbine blades is increasing, and the probability of blade damages is also increasing. Therefore, it is very urgent and important to monitor the condition of the wind turbine blade and detect the defect. As the traditional methods used for detecting the wind turbine blades are time-consuming, laborious and costly, this study proposed a new method based on Unmanned Aerial Vehicle (UAV) and image processing technologies to achieve the wind blade inspection rapidly, automatically and low-costly. An experiment is carried out to test the defect detection performance of the proposed method by using the wind turbine blade images collected in real situations. Furthermore, the experimental results show that the presented algorithm is effectiveness, reliability and accuracy, which can basically meet the requirements of blade defect detection, and is of great significance in practical engineering.

MECHANICAL STUDY ON Y-TYPE COMPOSITE MATERIAL-STEEL JOINT OF SHIP

XU Lu-jie, PAN Bin, ZHANG Gui-ming, WANG Ji-hui

2020, 0(9): 90-94.

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In this paper, the Y-type composite-steel plate joint of warship was studied. The finite element method was used to calculate the Y-type composite joint. The three-dimensional Hashin failure criterion was used for fiber failure, the maximum stress criterion was used for sandwich layer. And the UMAT failure subroutine is compiled to analyze material failure. The reinforced joint and the unreinforced joint were analyzed, and finally verified by experimental method. The results show that the reinforcement can significantly increase the load of Y-type embedded steel plate joints, and change the failure mode of joints from skin damage to delamination damage of adhesive layer and PVC shear failure at the embedded steel plate. With the increase of the distance between steel plate and PVC, the mechanical properties of joints decreases. When the force decreases, the damage will occur ahead of time.

RESEARCH ON GAS-TIGHT DETECTION TECHNOLOGY OF COMPOSITE FORMING MOLD

ZHENG Wei-tao, ZHANG Yong-bing, ZHANG Xiao-bo, ZOU Zhen-yu

2020, 0(9): 95-99.

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In this paper, several researches on the airtightness test of composite forming molds are conducted in the autoclave by static pressure method. Focusing on the unstable airtight test results for composite forming molds, the key factors affecting the airtightness of composite forming molds are analyzed based on the principle of the vacuum static boosting method. The airtightness test system of composite forming molds are optimized. Finally, the optimized systems are proved to be very stable through airtightness tests which based on the air tightness test standard of composite forming molds.

APPLICATION OF ONE-DIMENSIONAL DIFFERENCE METHOD IN COMPOSITE PROCESS MECHANICS

ZHANG Wei, ZHANG Xue-mei, MA Jun-yi

2020, 0(9): 100-105.

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As the deepening of the knowledge, a numerical method such as finite element, boundary element and etc. applying in composite process mechanics has been paid more and more attention. However, the tedious analysis process is discouraged and cannot be popularized to engineers. According to the characteristics of composite fabrication process, a one-dimensional difference algorithm is derived, which focuses on the variation of physical field distribution in the thickness direction of composite material. The simulation results show that the one-dimensional difference method has the characteristics of simple analysis, rapid calculation and enough precision. The variation of temperature field, curing field, material properties and other parameters in the composite are revealed, base on which the effects of curing cycle and thickness alteration of the laminate could be evaluated quickly.

RESEARCH ON COOLING SYSTEM OF WIND TURBINE BLADE MOULD

LI Rui-ying, WU Jian-dan , FAN Hu, LI Yi-quan

2020, 0(9): 106-110.

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Combined with the requirements of wind turbine blade manufacturing parameters and blade mould operation performance, referring to the performance comparison of various aspects of medium and considering the pressure of hydraulic turnover equipment, the cooling medium is selected in this article. Based on the principle of heat balance, the heat dissipation design and analysis of mould cooling are carried out to study the heat consumption of each part of the mould, so as to maximize the rational energy distribution. In addition, considering the original structure and function, the cooling channel is designed, and the model of cooling system is established. The mould cooling cycle monitoring and regulation system based on PLC control was established, and the parameter performance was optimized according to the test results to form a complete cooling system process. Finally, by using ANSYS to check the strength of the mold structure, an electric heating composite mould for wind turbine blade with rapid cooling function was successfully developed.

RESEARCH PROGRESS IN SELF-DIAGNOSIS COMPOSITES

WEI Jun, YAN Chun, ZHAO Yue, ZHAO De-gang

2020, 0(9): 111-117.

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Self-diagnosis composites are one kind of functional materials that can dynamically monitor the health of their structures and have been widely applied in many fields, such as aerospace, automobile industry, civil engineering, and so on. In this paper, the self-diagnosis principle of composites is introduced in detail, including self-diagnosis of piezoresistive effect, self-diagnosis of piezoelectric effect and self-diagnosis of optical fiber. The research progress of self-diagnosis resin-based composites and self-diagnosis concrete-based composites is also discussed. Finally, the shortcomings of the current self-diagnostic composites are summarized, and its prospect of application in the future is analyzed.

RESEARCH PROGRESS ON THE MECHANICAL PROPERTIES OF STITCHED FOAM-CORE SANDWICH COMPOSITES

XU Xue-hong, ZHENG Yi-zhu, CHEN Chen, CHEN Ji-ping

2020, 0(9): 118-122.

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The stitched foam-core sandwich composite is an advanced lightweight structural material with low manufacturing cost, good delamination resistance and high structural efficiency. It has attracted the attention from aviation, aerospace and other industrial field. Stitching technology for foam-core sandwich structures is introduced. Research progress on basic mechanical properties and impact resistance of stitched foam-core sandwich composites is reviewed. The application prospect of stitched foam-core sandwich composites is also presented.

THE STRUCTURE AND APPLICATION SCOPE OF COMPOSITE LAYING EQUIPMENT

FU Zhong-kui, ZHANG Hao-tian

2020, 0(9): 123-128.

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The automatic laying equipment is widely used in the automatic forming of composite materials with the characteristics of high efficiency, high speed and low waste rate. Starting from the basic framework, this paper introduces the existing automatic tape laying machine and fiber laying machine, analyzes the advantages and disadvantages of various laying equipment, and summarizes the scope of laying parts for each laying equipment. At last, the possibility and efficiency of automatic laying equipment in future are prospected from two aspects of improving production efficiency and reducing cost.

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