COMPOSITES SCIENCE AND ENGINEERING

MEASUREMENT AND ANALYSIS OF 3D DEFORMATION IN GLASS FIBER REINFORCEDCOMPOSITES BY USING COMPUTED TOMOGRAPHY

MAO Ling-tao, WEI Kai, ZHU Zi-yan, LIU Hai-zhou

2018, 0(9): 5-10.

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A glass fiber reinforced composite specimen was scanned by using industrial Computed Tomography (CT) in situ, and CT images of the specimen under different loading were obtained. The digital volume correlation (DVC) technique was applied to calculating the three-dimensional displacement fields and strain fields in the specimen, and the strain evolution and damage mechanism were revealed. The microstructure of the fiber reinforced composite can be used as the carrier of deformation. The accuracy of the experiment is 0.063 voxels (2.8 μm). The displacement field and strain field distribution obtained by DVC can reflect the internal structural characteristics of the specimen directly. With reference of the distribution of transverse shear strain, the shear band was formed before the specimen was broken, which eventually led to the interface delamination. In addition, the wrapping of the cross section due to the transverse shear was verified by the distribution of its displacement. These results show that the DVC method combined with CT can directly reflect the deformation characteristics of the internal structure of the composite, and provide a new method on studying the internal deformation and the failure of the material.

A CHECKING METHOD FOR DEFLECTION OF REINFORCED CONCRETEBEAMS BONDED WITH FRP DURING DESIGN STAGE

JIANG Shi-yong, CAI Tao, YAO Wei-lai, GONG Hong-wei

2018, 0(9): 11-16.

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At present, the reinforcement specification of China adopts the design method based on the ultimate state of the bearing capacity when externally sticking FRP to strength the concrete beam. In the design stage, only the bearing capacity of the strengthened beam is designed, and there is a lack of controlling checking for the deformation of the reinforced beam. The process cannot guarantee that the strengthened beam meets the requirements of the normal service limit state during long-term use. However, the methods used to calculate the long-term deflection of the strengthened beam in the existing studies mostly require complicated programming and cumbersome iterative calculation processes and are not applicable to the reinforcement design phase. Therefore, there is still a need of a simple, relatively accurate and safe analytical method to calculate the deflection of the reinforcement beam, so as to meet the requirements for a wide range of designs used in actual engineering for structural reinforcement. In this paper, creep tests of concrete beams (RC beams) reinforced with CFRP plates are carried out under sustaining-load. The short-term stiffness B_s of reinforcement beams and the deflection increase coefficient λ caused by concrete creep and shrinkage are deduced. A method for checking the deflection of strengthened beams at the design stage was proposed and compared with the test data. The results show that the method proposed in this paper can be used to check the deformation of the reinforced beam during the reinforcement design process, which can ensure the safe use of the strengthened beam.

ANALYSIS OF AFFECTING FACTORS OF ICE COATING LOAD ON WIND TURBINEBLADE BASED ON RESPONSE SURFACE METHOD

LI Jiang-chao, CHENG Bin, LI Xi-yang

2018, 0(9): 17-22.

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In this paper, the NACA4412 airfoil blade is taken as the research object. By constructing the wind turbine test bench, the four-factor and three-level test schemes are designed using the response surface analysis method by taking the wind speed, temperature, humidity and running time as the influencing factors. The overall deformation of the iced blade was used as the evaluation index to explore the influence of four factors on the ice load of the wind turbine blade. Using Design-Expert 8.0 mathematics statistics software, a multi-variable response model of blade deformation of ice-covered wind turbine was established. The response surface relationship between the factor and the response deformation was analyzed to predict the deformation of ice-covered blades. The accuracy and reliability of the regression model are verified by experiments, which provides a theoretical basis for the research on wind load of wind turbine blades. This research is of great significance to further improve the stability of wind turbine operation and reduce the operation and maintenance cost.

EFFECTS OF THICK COMPOSITE CURING TEMPERATURENON-UNIFORMITY ON MECHANICAL PROPERTIES

LIU Gui-ming, ZHAN Li-hua, CHEN Xiao-ping, CHANG Teng-fei

2018, 0(9): 23-29.

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Temperature gradient distribution of thick composite along the thickness direction in curing process was measured using a method of setting Teflon film and thermocouple monitor in different position. The relationship between temperature non-uniformity and mechanical performance was studied by means of tensile test and shear test. And, laminate micro-structural fracture surface was analyzed by SEM. The results show that there are obvious temperature gradient along the thickness direction in the curing process of thick composite, and the mechanical properties of tensile strength and inter-layer shear strength show a downward trend with the increase of temperature difference. Employing the top laminate as reference, when there is 20.6 degree inner temperature difference in composite laminate tensile, the strength difference is 7.4%, and the shear strength difference is 6.8%. Likewise, when there is 10.2 degree inner temperature difference, the tensile strength difference is 3.8%, and the shear strength difference is 3.4%. This is due to the high curing temperature, and inter-facial strength between resin and carbon fiber reduces. This study provides significant experimental evidence and theoretical reference for the necessity of controlling the composite temperature distribution uniformty for the thick section parts of the composite materials during the autoclave curing.

COMPOSITE MOMENT GYROSCOPES BRACKET STRUCTURE OPTIMIZATION AND SIMULATION

DONG Xiao-yang, SHI Wen-feng, GUO Jin-hai, ZHANG Yu-jie

2018, 0(9): 30-35.

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To increase the structure efficiency of moment gyroscopes bracket, based on modal and mass ratio optimization, the dynamics model of moment gyroscopes bracket was analyzed. By calculating with FEM, the weight of composite moment gyroscopes bracket is 7.32 kg, the base frequency is 255.06 Hz, and the ω/m is 34.83 Hz/kg. To increase the efficiency of composite, the geometry structure was optimized, the research shows that the ω/m is improved by 4.2% when the thick of the base structure is increased by 1 mm. The ω/m is improved by 39.21% with the T strength stiff addition. Based on the T strength stiff structure, the composite lay designing was conducted, the research shows the efficiency of gyroscopes bracket structure is higher with quasi-isotropy lay design, which is 48.49 Hz/kg. Considering the processing of integral cure, the ω/m is 47.79 Hz/kg with _ns lay design.

EXPERIMENTAL STUDY ON SHEAR RESISTANCE OF BFRP REBAR BASALT FIBERREINFORCED CONCRETE DEEP BEAMS WITHOUT STIRRUPS

ZHANG Zhi-jin, LIU Hua-xin, LI Qing-wen, WANG Xue-zhi

2018, 0(9): 36-40.

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For studying the influence of basalt fiber on crack development, failure mode, mid-span deflection, diagonal cracking strength and ultimate shear strength of basalt fiber reinforced polymer (BFRP) reinforced concrete deep beams without stirrups, 5 test beams were designed and prepared with the parameters of volume ratio and length of basalt fiber, and the four points concentrated force load tests were carried out. The results showed that with the increase of fiber characteristic parameters, the diagonal compression failure transforms to shear compression failure. In contrast with the common concrete beam, the mid-span deflection and crack width of the basalt fiber reinforced concrete deep beams decrease with the growing of fiber characteristic parameters, and the diagonal cracking strength and ultimate shear strength of specimens increase with the growing of fiber characteristic parameters. Based on taking account of the influence of basalt fiber, the ultimate shear capacity of the basalt fiber reinforced concrete deep beams was calculated with reference to the code of GB 50010—2015, and the experimental values basically coincide with the calculated values.

CHARACTERIZATION OF FAILURE AT THE COMPOSITE ADHESIVE LAYER WITH DEFECTS

TANG Zhe-tao, ZHAO Shuai, LIU Yong, XU Yang-jian

2018, 0(9): 41-45.

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Delamination is the main form of failure of composite materials. The bonding strength of the adhesive layers in composite materials has a direct impact on the overall strength of materials or structures, while it will inevitably produce holes or defects in the actual adhesive layer during manufacture of composite materials. In our work, fracture test of double-cantilever beam (DCB) specimen, its finite element simulation by using cohesive zone model and inverse identification of cohesive parameters were carried out. In addition, the bilinear cohesive zone model was compared with the multi-segment interpolation cohesive zone model in terms of the fracture simulation of adhesive layer. The simulation results show that the multi-segment interpolation cohesive zone model has achieved a better result, which is more suitable for predicting the delamination of composite materials.

ANALYSIS ON EDGEWISE COMPRESSIVE FAILURE LOAD AND MODE OF COMPOSITESANDWICH STRUCTURES WITH CIRCULAR DEBOND DEFECTS

ZHANG Wei, LUO Li-long, ZHANG Guo-fan, WU Cun-li

2018, 0(9): 46-51.

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In order to analyze the edgewise compressive failure load and mode of composite sandwich structures with debond defects, damage initiation criteria and damage evolution laws are employed to simulate the damage and failure process of the panels and adhesives. Three dimensional progressive damage analysis models are established which can take into account the material failure. Failure load and mode are analyzed for two typical sandwich structures based on the three dimensional model, and the analysis results are validated by the test results. The results show that the edgewise compressive failure mode of sandwich structures with central circular debond defect is material failure when the panel is weak. As the load increases, damage occurs around the debond zone and extends along the width direction, and finally failure occurs when the material is totally damaged. Failure mode is overall buckling when the panel has strong rigidity, and the structure loses load-carrying capacity and collapses rapidly when buckling happens. The analysis failure load matches well with the test value, and failure mode is also consistent well with the test results.

ULTRASONIC TESTING METHOD OF HIGH SONIC ATTENUATION RESIN MATRIX COMPOSITE

GAO Xiao-jin, ZHOU Jin-shuai, GONG Wen-hua

2018, 0(9): 52-57.

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According to the characteristics of the resin matrix composites with high sonic attenuation, the high energy ultrasonic excitation technology and the signal enhancement technology of the receiving end are used to test the material. The excitation voltage, damping resistance and waveform of the excitation signal are analyzed, the excitation mode of bipolar square wave pulse string is put forward, the amplifier circuit of the receiving end is designed, and the testing parameters are determined. The results show that the excitation voltage is proportional to the ultrasonic amplitude when less than the breakdown voltage. When other conditions are unchanged, the ultrasonic signal with the largest amplitude can be excited when the damping resistance of the ultrasonic instrument is adjusted to the maximum. Under the same condition, the amplitude of ultrasonic wave excited by different waveform sequence from high to low is bipolar square pulse string, single square wave, sharp pulse. The proposed method can test the resin matrix composites with high sonic attenuation, as well as the defects not bigger than 5 mm.

EFFECTS OF INTERFACE POLLUTION ON COMPOSITEINTERLAMINAR FRACTURE TOUGHNESS

LI Zhan-ying, LI Jin-hua, LU Xiao-feng

2018, 0(9): 58-62.

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In order to analyze the effect of interface pollution on the composite inter-laminar performance of fiber glass reinforced composites (FRP), the double cantilever beam (DCB) specimens with interface pollution were tested. The crack propagation process of the DCBs was simulated using the finite element method with the virtual crack closure technique (VCCT). It is found that the mode Ⅰ inter-laminar fracture toughness of the specimens with interface pollution is lower than that of the specimens without interface pollution. The variance of the specimens with interface pollution is higher than that of the specimens without interface pollution. The simulation results are in good agreement with the experimental results. The prediction of delamination load using VCCT is feasible.

IMPROVED DESIGN AND EXPERIMENTAL STUDY OF PRESTRESSEDCFRP TENDON CLIP ANCHORAGE

ZHANG Jun, CAI Wen-hua, XUN Yong, HU Xia-min

2018, 0(9): 63-69.

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Now there is a 10 mm diameter monolithic CFRP tendon anchor without sleeve and it′s conical degree is 1∶10 in research group, the failure mode of the anchorage is the inner CFRP tendon cut off. This paper improved and redesigned the clamp anchorage for diameter 10 mm and 12 mm CFRP tendon. The improved anchorage set three conical degree and we cancel the cone angle difference between the anchor ring and the clip. The clip has two pieces, and the redesigned gap makes the clamp looked on the transverse section from the big diameter end to the small diameter end are six, eight and four pieces respectively. The influences of anchorage conical degree, pretightening force and thickness of aluminum sleeve on anchorage are analyzed through experiments. The results show that when the conic degree is 1∶15, the anchorage achieves the ideal failure of the external rupture on CFRP tendon, and the reduction of the conical degree can reduce the stress concentration on the inner CFRP tendon. The inner wall of the clamp handled as tooth pattern and the experiments adopt patterned aluminum sleeve can reduce the slippage of the anchorage. The experiment results show that large diameter anchorage is suitable for large thickness aluminum sleeve, and the smaller thickness sleeve is suitable for small diameter anchorage. The increase of pretightening force will reduce the slippage of each component of the anchorage, but it will not affect the ultimate tensile force of the anchorage.

RESEARCH ON VIBRATION OF CARBON FIBER COMPOSITE WIND TURBINE BLADES

YANG Hai-ru, MA Xiang-yu, YU Guo-ming, XU Shi-wei

2018, 0(9): 70-74.

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Carbon fiber composites are of high strength, high modulus, light weight, fatigue resistance. According to the characteristics of wind turbine blade vibration and deformation form, the carbon fiber composite wind turbine blades were designed. The finite element analysis software ANSYS was used to simulate the blade, and the natural frequency of the carbon fiber composite wind turbine blades was obtained. Compared with the resin blade for comparison, the natural frequency of the carbon fiber composite blade is higher than the blades′. Carbon fiber blades modal experiment was performed, and the experiment results and simulation results are similar.

EFFECT OF INORGANIC COMPONENTS ON PROPERTIES OFCERAMIZABLE POLYURETHANE FOAM COMPOSITES

SHI Min-xian, HE Dong-pei, SHEN Yi-feng, YAO Ya-lin

2018, 0(9): 75-81.

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Ceramizable polyurethane foam composites were prepared by using polyether polyols, polyisocyanates, foaming agents, and ceratable inorganic fillers. The effects of inorganic components such as glass frit, vermiculite powder, expandable graphite and ammonium polyphosphate on the properties of ceramizable polyurethane foam composites were studied. The results show that with the increase of the amount of glass frit, the density and the thermal conductivity of foam composites increase, but the compressive strength. When the amount of vermiculite powder is less than 6, the shrinkage of the composites after high temperature treatment decreases with the increase of the amount of vermiculite powder. When the total amount of expandable graphite and ammonium polyphosphate with the rate of 1∶1 is 9 phr, the limited oxygen index is 33. Finally, the optimized proportion of all components was determined by experiment study.

RESEARCH ON A NEW KIND OF HONEYCOMB SANDWICH STRUCTUREIN ANTIBACTERIAL ANTIMILDEW AND FLAME RETARDANCY

CHEN Ping, ZHU Xiu-di, SUN Chao-ming, SONG Zhi-qian

2018, 0(9): 82-86.

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Honeycomb sandwich structure is consisted of a thin panel and a thick honeycomb, it has the advantage of light weight, high strength, high stability and so on. It has been widely used in internal structures of aerospace, aviation, subway and passenger car. The study of the traditional honeycomb sandwich structure was mainly focused on the mechanic properties. With the development of the aerospace, a higher safe requirements was proposed forward by engineers. Based on the traditional processing technique, with the method of adding a certain proportion of auxiliaries, this paper introduces a new kind of material, which has the safe properties combined with anti-bacterial, mold proof, flame retardancy, low smoke and so on. The antibacterial and antimildew properties were investigated by antifungal and antibacterial experiments, flame retardancy was studied by combusting experiment, and the concentration of toxic gases after burning was studied by toxicity experiment. These experiments show that the materials have excellent safety performance, and excellent mechanical property, The aim of the work in this paper is to lay the foundation for our aerospace development.

EXPERIMENTAL AND NUMERICAL ANALYSIS OF THE EFFECT OF STACKINGSEQUENCE ON AXIAL CRUSH PERFORMANCE OF FOAM-FILLED GFRPRECTANGULAR TUBES MANUFACTURED USING VARI PROCESS

TAPA Arnauld Robert, WANG Ji-hui, WANG Chang-zeng, YUNUSA Mujaheed

2018, 0(9): 87-97.

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Known as a critical design parameter for energy absorbers, the laminate stacking sequence can affect the overall property of laminated composite structures during crush. However, a proper investigation of the effect of stacking sequence still needs to be addressed given the influence of other design parameters such as the manufacturing process. Many analyses have been done so far to understand this effect on axial crush performance of foam-filled GFRP tubes, but most of the tubes used were manufactured using pultrusion, winding or hand layup processes. In this paper, we investigate the effect of stacking sequences on a recently developed kind of foam-filled GFRP tubes manufactured using vacuum assisted resin infusion (VARI) process. Under axial crush loading, we experimentally and numerically investigate the foam-filled GFRP rectangular tubes. The fiber stacking sequence which can achieve the best energy absorption performance were obtained.

A MEASUREMENT METHOD RESEARCH ON DEFORMATION PROPERTY OF PREPREG

LI Yan, YUAN Chong-xin, LI Yong-hang, CAI Zhi-qiang

2018, 0(9): 98-101.

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Software is very popular in composite design and manufacturing field, which could increase efficiency and reduce costs. During design and layup process, software needs a lot of material property parameters. Most of them can be obtained from suppliers, but warning angle and limit angle are not provided by suppliers. They are usually set according to engineering experience, which are not accurate. The two values are important to predict producibility with software during the design and manufacturing process. This paper is aimed to find an approach to measure the values of warning angle and limit angle of composite lamina. A novel approach of flat model was developed to measure the warning angle and limit angle as the initial values, and then the values were corrected by spare model. After several iterations, warning angle is 9.8° and limit angle is 19.6°, which are the best results for the material. A practical layup on pylon model was conducted to verify the warning angle and limit angle values. The results show that the practical deformation is close to the simulation, which indicates that the measurement method of the warning angle and the limit angle is reliable. In conclusion, the method could solve the layup problems during composite processing, and can be a guidance for layup simulation and laminate design.

STATUS OF INTERNAL INSULATING MANDREL FORINSULATORS OF UHV COMPOSITE STRUTS

ZHANG Qiang, ZHAO Wei-sheng, LI An-rui

2018, 0(9): 102-105.

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The application status of composite pillar insulators in UHV power station is introduced in this paper. The composite pillar insulators are mainly composed of three parts: the internal insulating mandrel, the silica gel coating and the umbrella skirt, and the fittings at both ends. The core rod which plays the key bearing role in the composite pillar insulators is emphatically introduced. The classification of internal insulating mandrel, its advantages and disadvantages, forming mechanism and manufacturing process method are reviewed, which provides reference for the material selection of the UHV composite post insulators in the future.

RESEARCH OVERVIEW OF FIBER REINFORCED PMR POLYIMIDE MATRIX COMPOSITES

GAO Long-fei, LI Song, XIAO Yuan-yu, ZHANG Xue-mei

2018, 0(9): 106-110.

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Since the 1970s, research work on PMR thermosetting polyimide resins and their composites has been carried out domestic and abroad. Up to now, the maximum temperature of fiber-reinforced PMR polyimide composites can reach 450 ℃. In this paper, the modification methods of polyimide resin and the molding process of fiber reinforced PMR polyimide composites and their research situation are introduced, and the future development trend of fiber reinforced PMR polyimide composites is also discussed.

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