COMPOSITES SCIENCE AND ENGINEERING

PERFORMANCE OF CONCRETE CONFINED WITH STEEL SPIRALSAND BFRP UNDER AXIAL COMPRESSION

WEI Yang, ZHOU Yong-feng, ZHANG Xi, DUAN Mao-jun

2016, 0(4): 5-11.

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A total of 21 specimens was tested under axial compression to investigate the performance of the concrete columns externally confined with the fiber-reinforced polymer (FRP) and internally confined with steel spirals. The main experimental parameters of the experiment were the number of FRP layers and the spacing of the steel spirals. The test results show that performance of the FRP-steel-confined concrete columns is superior to that with only one confining material (FRP or steel). With the increase in the number of BFRP layers or the confinement ratio of steel spirals, the bearing capacity and deformation ability of the specimens increase accordingly. Longitudinal stress-strain curves of FRP-steel-confined concrete specimens consist of four stages of elastic stage, transition stage, hardening stage and residual stage. Based on the test results in this study and previous literature, the bearing capacity calculation model was proposed. The comparisons show that the predicted results are in good agreement with the experimental values.

STUDY ON THE FRP CONFINING EFFECT ON REINFORCED CONCRETE BRIDGEPIERS WITH RECTANGULAR HOLLOW SECTION

LIU Ke, DONG Zhen-hua

2016, 0(4): 12-20.

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High-piers of hollow section have been constructed in numerous spectacular reinforced concrete (RC) bridges, which can be an effective solution to maximize strength-mass and stiffness-mass ratios, and to reduce the weight contribution to the foundations and the mass contribution to the seismic response. Because of the wall thickness, ties or spirals reinforcements ratio, shear-span ratio, axial compression ratio et. al, the hollow RC piers designed in accordance with the old and existing codes were damaged in recent earthquakes due to insufficient flexural strength, shear strength or ductility. So in order to improve the seismic performance of the hollow bridge piers, the confinement effect on the behavior of RC bridge piers with fiber-reinforced polymer sheets (FRP) should be accurately estimated based on the seismic confinement theory of columns. According to this achievements, the confined performance of columns is obviously improved, and it is influenced by factors of the types of FRP sheets, FRP sheets thickness, the width and the space of FRP strips. In this paper, the finite element numerical simulation method was applied firstly. It is to study the behavior of FRP confined RC hollow bridge piers, such as the development laws of axial compression force, confined concrete compressive strain, stirrup and FRP tension strain. Based on the above simulated results, a new formula of lateral pressure with the complex confinement effect of FRP strips and stirrups was proposed, and then it is used to the compressive stress-strain model of FRP confined concrete. The formed compressive stress-strain model was further used to estimate the behaviors of FRP confined RC bridge piers with rectangular hollow cross section. The simulated results show that the curvature ductility, displacement ductility, ultimate deformation, ultimate strength are improved significantly. Then the calculation results was compared with experimental results, and it shows that the simulated results have good agreement with experimental results.

THE EFFECTS OF ELECTRIC-THERMAL LOAD ON THE SHEAR PROPERTYOF THE CFRP SINGLE-LAP JOINT AFTER REPAIR

ZHU Chen, ZHANG Jun, LU Peng-cheng, WANG Tao

2016, 0(4): 21-25.

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Carbon fiber resin matrix composite material is widely applied in the field of aviation. It has become the norm of the aircraft structural repair. The electric-thermal load was studied in the paper and was performed on the CFRP single-lap joint after wet lay up repair. The surface temperature field of single-lap joint and the resistance of sample were measured by the self-devised damage test device. The change rules of temperature and resistance under different current applications have been investigated. The scanning electron microscope was used to analyze the changes of surface morphology after shear failure. It demonstrated that shear strength slight increases under low electric current since post curing of resin. Higher current application has a detrimental effect on the properties of the joint. Shear strength decreases under higher electric currents since high temperature can induce interfacial damage of joint.

MICROWAVE ABSORPTION PROPERTY OF GF/CF/ACFFS MULTILAYER COMPOSITIES

YAO Bin, XIA Shao-xu, OU Xiang-hui, CHENG Chao-ge

2016, 0(4): 26-30.

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On the basis of the complex effect and design principle of structural composites, applying activated carbon fiber felts screen/epoxy (ACFFS/EP) as wave-absorption layers, carbon fibers (CF) as enhanced wave-absorption agents and glass fiber (GF) as impedance matching layer respectively, GF/CF/ACFSS was prepared by layer-by-layer assembly technique with the help of tailor-made mold. The effect of chopped CF mass fraction and of arrangements between the layers on microwave absorbing performance of GF/CF/ACFFS was investigated. Experimental results show that the maximum reflection loss(RL) to electromagnetic wave was up to -38.54 dB at the frequency of 14.2 GHz for three-layers GF/CF/ACFFS composites with ACFFS/EP at bottom when the mass fraction of CF is 0.7% within the frequency range of 2~18 GHz. In addition, the effective absorbing bandwidth (RL<-10 dB) was acquired at 11.33 GHz (6.17~17.5 GHz). Optimum microwave absorbing property of composites can be acquired with the suitable mass fraction of chopped CF, and absorbing materials with excellent property will be obtained when keeping reasonable combination of CF and ACFFS.

LAYOUT OPTIMIZATION OF COMPOSITE UAV WING STRUCTURE BASEDON TWO-LEVEL OPTIMIZATION METHOD

LIU Bo, LU Zhen-yu, YUAN Dong-ming, MA Jing-wei

2016, 0(4): 31-35.

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In order to reduce the weight of wing structure of composite unmanned aerial vehicle(UAV), a method of two-level optimization which uses MSC.PATRAN and MSC.NASTRAN is proposed in this paper. In the first level, a response surface method is used to optimize the location of the longitudinal wing spars. In the second level, a genetic algorithm is used to optimize the lay parameter of wing structure. As an example, a layout optimization of one type of high aspect-ratio wing structure is calculated. The result shows that about 25% weight of wing structure is reduced. It can be concluded that the two-level optimization method can significantly reduce the wing structure weight, which can satisfy the design requirements.

STUDY ON DAMAGE BEHAVIOR OF THREE KINDS OF COMPOSITE SANDWICHSTRUCTURE PANEL UNDER BENDING LOAD

FANG Lu-ping, LU Chun, CHEN Ping, QI Ming-xue

2016, 0(4): 36-40.

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In this paper, three types of composite sandwich panels, hat, bubble, and Ⅰ were fabricated, and the bending performance of composite sandwich panels were studied. Finite element analysis (FEM) method was used to investigate the stress distribution on composite sandwich panels suffering from bending load, and Tsai-Hill failure criteria was used to predict the failure mechanism of the composite structures. Results show that the bending stiffness and maximum load of hat sandwich panel is the highest among the three sandwich structures. The damage zone of three kinds of sandwich are different. The damage zone of hat sandwich structure occurred at the edge of indenter and core corner below the loading zone. The damage zone of bubble sandwich occurred in the support region of core. The damage zone of Ⅰsandwich is located at the support region of bottom plate.

THE WIND-INDUCED VIBRATION RESPONSE ANALYSIS OF COMPOSITE MATERIALCHIMNEY BASED ON MODAL SUPERPOSITION

WANG Qi-xing , ZHU Si-rong, WANG Ying-jun, WANG Hong

2016, 0(4): 41-44.

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The FRP composite material chimney has the advantages of light weight and good corrosion resistance. It is a new type of composite chimney structure, which is combined with the steel outer cylinder. In the latest "chimney design code", it is not involved. And there is no design standard for this kind of structure. Because of the difference of stiffness between the steel outer cylinder and the inner cylinder, the chimney structure is difficult to design and calculate. And the wind load is one of the main loads of tall and slender structure. Its response is the main basis for the design of chimney. In this paper, the fine finite element model of the steel-FRP chimney structure is established. The response of this new type of chimney under the along-wind impulsive wind is analyzed by using modal superposition method. The random vibration response of the structure is obtained. For the wind resistant design of the new type of composite material chimney structure, an effective method is proposed.

STUDY ON DIELECTRIC PROPERTIES OF QUARTZ FIBER REINFORCED5284RTM EPOXY RESIN COMPOSITES

HE Xian-cheng, ZHONG Xiang-yu, LI Ye, BAO Jian-wen

2016, 0(4): 45-50.

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Quartz fiber reinforced epoxy resin QW220/5284RTM composite laminates with four different fiber volume fractions were fabricated via RTM process. The relationship between dielectric properties of the composites and temperature, moisture absorption, frequency, fiber volume fraction of composites and post cure were investigated. The results showed that within the temperature range of 30 to 150℃, dielectric constant and dielectric loss of QW220/5284RTM composites increased with increasing temperature. When fiber volume fraction of the composite was 53%, saturated moisture absorption rate of the composite was about 0.44%, and dielectric constant and dielectric loss of the composites increased after moisture absorption. At room temperature, dielectric constant and dielectric loss of the composites did not show any obvious and regular changes with frequency changing from 7 to 18 GHz. Dielectric constant and dielectric loss of the composites respectively increased and decreased with increasing fiber content. Dielectric constant and dielectric loss of the composites decreased after post curing. QW220/5284RTM composite has good dielectric properties which has good environmental characteristics, and can be used for aircraft wave-transparent structure.

MANUFACTURING OF CARBON FIBER COMPOSITE FRONT FLOOR OF AUTOMOTIVE

CHEN Gang, TU Li-yan, CHEN Ming-da, LIU Dong

2016, 0(4): 51-54.

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This paper describes a manufacturing process of automotive front floor made of carbon fiber reinforced plastic (CFRP). The structure of CFRP front floor was determined from the design based on metal Body-in-White. With the development of material selection, molding process and preform production, a multi-point injection rapid RTM mold has been designed and built for the purpose. A front floor made of carbon fiber reinforced thermosetting epoxy has been fabricated from the device. The sample succeeded in the stiffness, rigidity, and modal tests, combining with a significant weight reduction. The resultant product meets the manufacturer′s technical requirements, indicating that carbon-fiber-composite as the primary structural material in automotive applications is proved to be feasible.

EXPLORATION OF WIND TURBINE BLADE LEADING EDG′S BONDING STRUCTUREDETECTING USING ULTRASONIC TECHNIQUE

WANG Chang-sheng, ZHOU Ke-yin, XU Ping, MENG Ling-min

2016, 0(4): 55-58.

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The wind turbine blade leading edge is a bonding structure, and the adhesive quality of this structure directly influences the service life of the blade. In this paper, the ultrasonic testing technology is used to detect the leading edge of the blade, and the factors affecting the results of ultrasonic testing are analyzed by CIVA simulation. The designed ultrasonic double crystal probes was used to detect the block of wind turbine blade leading edge. Analysis results show that ultrasonic double crystal probe can obtain obvious flaw echo of bonding region, and can easily detect the deboning defects of the blade leading edge.

THE DESIGN OF CONTROL SYSTEM ABOUT THE POLISH-SPRAY PRODUCTION LINEOF CARBON FIBER COMPOSITES BASED ON PLC

LI Gao-peng, ZHANG Hong-sheng, CHEN Ming-da, TU Li-yan

2016, 0(4): 59-63.

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According to the surface treatment process of carbon fiber composites, the overall plan of the production line about the carbon fiber composites surface polishing and spaying was designed, including the component and functional planning of control system, the design of program flow chart, the selection of PLC analysis, the design of I/O contact distribution, robot communication configuration, and the design of human-machine interface. The whole system design of the production line about the carbon fiber composites surface polishing and spaying were finally realized by the whole machine debugging.

QUANTITATIVE ASSESSMENT METHOD STUDY IN THE PRESSURE BEARINGLIFE OF FIBERGLASS SIMULATION CASE

LI Jing, ZHANG Xuan, CHEN Guo-jun

2016, 0(4): 64-67.

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Fiberglass simulation cases have undergone heat accelerated aging test and hydraulic blasting tests in different temperature conditions. By blasting pressure-aging time regression analysis in different aging temperature, aging equation and performance coefficient of variation were obtained. Based on the aging equation and performance coefficient of variation regression analysis, case performance coefficient of variation in normal temperature was extrapolated, and then the internal pressure bearing age equation in normal temperature was obtained. The relationship between the regression curve judged by the relevant index was obvious. Based on the blasting pressure data of simulation cases after accelerated aging test in heat-humid environment and natural storage case, aging equation was fixed. Studies have shown that fiberglass case burst pressure and reservoir simulation time performed logarithmic relationship, full-size fiberglass shell burst pressure was 9.97 MPa in the initial state, and it was predited that the full-size fiberglass shell burst pressure decreases 9.5% 20 years later.

STUDY ON HIGH TEMPERATURE CURING EPOXY RESIN SYSTEM MOULDING BY VARI

ZHANG Lian-wang, BAO Jian-wen, ZHONG Xiang-yu, LI Ye

2016, 0(4): 68-71.

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A high temperature cured epoxy resin system (5284VARI) moulding by VARI was designed. Curing reaction characteristics of this epoxy resin were tested by DSC (Differential Scanning Calorimeter). The operation characteristics of this epoxy resin system were analysed by rheometer. The mechanical properties of this resin system and its composite were tested by mechanical testing machine. The results demonstrated that 5284VARI epoxy resin system has low viscosity on moulding temperature and can maintain long duration. This resin system is appropriate for moulding composites by VARI. Besides, this epoxy resin has good properties under wet-and-hot conditions.

EFFECT OF PRESSURE APPLYING MOMENT ON MECHANICAL PROPERTIES OF CARBON FIBER REINFORCED MODIFIED BISMALEIMIDE COMPOSITE MATERIA

WEN Qiong-hua, MA Kai-wei, LI Bo, WEN You-y

2016, 0(4): 72-76.

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Differential scanning calorimetry (DSC) was adopted to analyze the curing process of the modified bismaleimide resin system. The resin viscosity was tested and analyzed, and then three different temperature values, 100℃,110℃ and 120℃, were selected to investigate the effect of pressure applying moment on mechanical properties. The results show that the mechanical properties get a little better with the lower temperature of pressure applying moment. Different mechanical property shows different sensitivities to the change of pressure applying moment and tensile properties are more sensitive than compressive properties, flexural properties and interlaminar shear properties in this research. This research provides important reference value for further study on process properties of modified bismaleimide resin system and mechanical properties of carbon fiber reinforced modified bismaleimide composite material.

INFLUENCE OF CURING EXOTHERMIC TEMPERATURE AND CURING TIMEON FINAL Tg OF NOVOLAC VINYL ESTER

YANG Yong-quan, GENG Xing, TIAN Hai-chang

2016, 0(4): 77-81.

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The paper studies the influence of different curing exothermic temperature and curing time on the final Tg of novolac vinyl ester. Thus, we design two extreme curing process, i.e, the resin cured in good heat conductive material of stainless steel mold and insulation materials of plastic beaker. Tg, curing degree and the double bond surplus ratio of oligomer and styrene are analyzed. Further, the change of performance parameter mentioned above is investigated through prolonging curing time at room temperature and high temperature post curing. As a result, in contrast to the resin cured in insulation materials of plastic beaker, Tg of the resin cured in good heat conductive material of stainless steel mold is lower and is difficult to reach the former Tg through prolonging curing time at room temperature and high temperature post curing.

ELECTRICAL PERFORMANCE DESIGN AND EXPERIMENTAL STUDY OFPMI FOAM CORED SANDWICH COMPOSITE

SHAN Zhong-wei, BIAN Jia-yan, CHENG Xiang, LIU Jun

2016, 0(4): 82-87.

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Radome is used to protect the antenna from the influence of natural environment, while at the same time, radome needs to guarantee the normal working of the antenna. Therefore, radome not only needs to has good mechanical performance, but also need excellent electrical performance. Thus, it is important to choose suitable materials and structure of radome. The polymethacrylimide (PMI) foam cored sandwich composite material has an excellent broadband penetration performance, and it is widely used to product radomes. Previous studies have found that electrical performance of radomes is connected with material system, structure type, thickness of face and thickness of core. In order to design a radome which meets the broadband penetration requirement, this paper chooses suitable material system, favorable structure type, optimum combination of thicknesses of face and core. Based on the principle of composite materials structure, the structure type is A-type sandwich structure, the face of the sandwich composite is quartz glass reinforced epoxy resin composite materials and the core of the sandwich composite is PMI foam. Both the materials of face and core have lower dielectric constant, lower dielectric loss and higher strength than most other material systems. Next, the effects of thicknesses of face and core on the wave permeability of A-type sandwich structure are calculated by CST software. Insertion loss-frequency curve can be obtain by putting thicknesses of face and core and frequency region into the CST software. According to the result of CST software, the theoretically optimum structure is obtained. In this paper, the theoretically optimum thicknesses of face and core are 0.5 mm and 15.6 mm. Then the A-type sandwich composite plate specimen is produced by vacuum bag molding process to test and verify the theoretically optimum structure. Further plate experimentation suggests that the experimental data agrees well with software test values. Therefore, the A-type PMI foam cored sandwich structure composite in this paper can meet the broadband penetration performance of a certain type of radome.

RESEARCH AND DEVELOPMENT IN SEISMIC PERFORMANCE OF FRP REINFORCED CONCRETE COLUMNS AND STRUCTURES

DENG Zong-cai, GAO Lei

2016, 0(4): 88-92.

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Compared with ordinary steel rebars, FRP bars have the characteristics of high tensile strength, light weight and non-corrosive. However, FRP bars have low elastic modulus, being linear elastic materials and having great brittleness at failure, which limit the application of FRP reinforced concrete columns, especially the structural engineering in the seismic region. This paper briefly introduces the main progresses in the studies on seismic performance of FRP reinforced concrete columns and structures, in which the experimental and numerical simulation investigations are included. The results show that it is practicable to arrange FRP bars instead of steel rebars in concrete columns, concrete frames and frame joints. FRP reinforced concrete structures can develop better ductility and deformation capacity when FRP bars are arranged properly in the elastic range. In the end, this paper proposes conducting further researches on the failure modes, calculation method of shear resistance, ductility assessment and design theory of FRP reinforced concrete columns. It is of theoretical significance and practical value to investigate the basic theory and design method of FRP reinforced concrete columns systematically

THE RESEARCH STATUS OF MODIFICATION OF PHENOLIC RESINS WITH PLANT OILS

SONG Jin-mei, TIAN Mou-feng, WANG Wen, ZHANG Dan

2016, 0(4): 93-97.

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Structure of plant oils, characters of phenolic resin and modification methods of phenolic resin with plant oil in recent years were summarized in order to design and apply new phenolic resin. Based on reaction principles, modification methods using formaldehyde solution method, epoxidation, conjugate copolymerization, esterification and amination were reviewed. Compared with advantages and disadvantages of different modification methods, now modification methods which can be industrialized were formaldehyde aqueous solution method and the amination method. As a result, using plant oil instead of non-renewable oil product to synthesize and modify phenolic resin not only protected the environment, but also reduced cost. At the same time, the modified phenolic resin with plant oil improved adhesive force, flame retardancy and mechanical properties of resin, and reduced water imbibitions. Applications of modified phenolic resins with soybean oil, tung oil, cashew phenol oil and cashew nut shell oil in friction material, printing ink, line copper clad, and laminated board were discussed, and their future prospects were previewed.

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