Table of Content

28 May 2017, Volume 0 Issue 5

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BASIC STUDY

DYNAMIC ANALYSIS OF SIMPLY SUPPORTED BEAMS STRENGTHENED WITH PRETENSION CFRP SHEETS

CHEN Feng, ZHOU Ding, LIU Duo, ZHANG Jian-dong

2017, 0(5):  5-10. 

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The elasticity method was used for analyzing the dynamic characteristics of simply supported beams strengthened with pretension CFRP sheets. The influence of various parameters on characteristics of free vibration of strengthened beams was discussed in detail. Firstly, the strengthened beam was divided into two parts: bare beam and CFRP sheet. The bare beam was studied based on two-dimensional elasticity, and the CFRP sheet was analyzed by the method of string theory. According to the continuity of the displacements and the stresses between the two parts, frequency equation of strengthened beams was obtained. Eigen-frequencies were given by the searching root method of determinant. Excellent consistency of the present solutions and the finite element solutions from the program ANSYS has been observed. The analysis shows that along with the increase of the layers and the pretension force, the reinforcing effect of CFRP on dynamic characteristics of simply supported beams increases.

EXPERIMENTAL STUDY OF ONLINE MONITORING CURING PROCESS OF EPOXY RESIN UNDER MEDIUM TEMPERATURE CONDITION BY ULTRASONIC TECHNIQUE

HU Yan, HUANG Gui-fei, LIANG Ke, XIE Jia-yu

2017, 0(5):  11-15. 

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Ultrasonic transmission technique is successfully employed to real-time online monitor curing process of epoxy resin under different conditions. The relationship between ultrasonic amplitude attenuation and curing time of epoxy resin as well as the effect of mould thickness and glass fiber on the curing reaction process of epoxy resin under medium temperature are investigated, respectively. Experimental results indicate that ultrasonic attenuation firstly increases then decreases and finally tends to be stable. As the curing reaction proceeds, the appeared time of gel point and the phase change process transformed from viscous-gel state to gel-glass state can be accurately measured by ultrasonic attenuation. It is shown that the curing time can be shorten by raising temperature, the appeared time of gel point can be delayed by adding thickness and glass fiber in some degree and their mechanisms are discussed. The ultrasonic online monitoring can provide a theoretical basis and important technical support for the molding and processing technology of epoxy resin composite materials.

THE STRUCTURAL ANALYSIS METHOD OF WIND TURBINE BLADE BASED ON MECHANICS OF COMPOSITE MATERIALS

GUO Xiao-feng, GUO Shi-rui, YANG Shu-feng, CAO Yan-long

2017, 0(5):  16-21. 

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The method of blade section structural analysis is the key to the optimization design of wind turbine blades. In the existing research methods, the engineering mechanics calculation method based on the basic mechanics of materials has a fast computation speed, while its calculation accuracy is restricted for the approximate equivalent of material structures and attributes. Another method is the finite element method. It was widely used in the structural analysis of blade, but for high time-consuming the modeling and calculating, it's not easily used in the optimization design of wind turbine blades. Based on the study of the laminate structure of the blades, the new method and formulas for calculating the tensile and shear stress of blade sections is developed. Taking a 1.5 MW blade as an example, the structural strength of the blade is studied with the ultimate loads of the blade, and compared with the test result. The feasibility of the new method was verified.

EXPERIMENTAL STUDY ON DEFORMATION AND FAILURE OF CARBON FIBER BRAIDED COMPOSITE

LU Bo-yuan, ZHAO Jing, WEI Zi-hui, ZHOU Wei

2017, 0(5):  22-27. 

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The damage evolution of carbon fiber braided composites was studied by using the acoustic emission (AE) and digital image correlation (DIC) method. The relationship between mechanical loading, deformation and strain field and acoustic emission characteristic parameters of carbon fiber braided composites was analyzed by collecting acoustic emission signals and damage deformation field information during tensile test. The results show that the displacement, strain field and the AE signal characteristic parameters of the composites can describe the damage accumulation and failure process of the composites during tensile test. The tensile process is divided into two stages: damage accumulation stage and damage stage. In the early stage of loading, low amplitude signals with the amplitude from 40 to 60 dB are generated. As the load increases, the number of cumulative hits increases dramatically, and high-amplitude, high-duration-time signal means that a variety of damages occur at the same time in damage stage. In addition, it is found that the displacement and the maximum tensile strain increase and then decrease in the same load increment measured by DIC.

TENSILE FAILURE MODE INVESTIGATION OF POLYMER MATRIX 3D-WOVEN COMPOSITE

ZHANG Jian

2017, 0(5):  28-33. 

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Two fracture locations were normally observed on the tensile specimens when polymer matrix 3D-woven composites were tested under uniaxial tension. Moreover, one of the fracture locations was mostly at the gripping area and appeared to be compressive failure. With the use of explicit FEA and stress wave theory, the displacement and strain of the specimen after failure were studied. The result shows that the compressive strain caused by the stress wave at the gripping area was higher than the static compressive failure strain, which caused the fracture at the gripping area. This result provides insight into the failure mode discovered when using ASTM D3039 standard for obtaining the tensile properties of polymer matrix 3D-woven composites.

INTERFACIAL STRESSES AND FAILURE SIMULATION OF COMPOSITE HAT-STIFFENED PANEL

HUANG Ling-kai, ZHU Li-bao, ZHANG Xiang-ming, TANG Yu-hang

2017, 0(5):  34-40. 

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Based on CZM (Cohesive Zone Model), FEM model is built up to study the interfacial stresses and debonding failure of the composite hat-stiffened panel subjected to four-point bending. In the present model, the debonding failure of the adhesive layer between the skin and stiffener is considered by adding interface elements between the solid elements. The results indicate that: adhesive debonding is the main failure pattern of composite hat-stiffened panel, shear stress has a major effect on the debonding of bondline, and the failure of the adhesive layer can largely decrease the load-carrying capacity of the structure and lead to more serious damage.

NUMERICAL SIMULATION OF CURING RESIDUAL STRESS AND STRAIN OF COMPOSITE LAMINATES WITH TIME-DEPENDENT PHYSICAL PARAMETERS OF MATERIALS

HE Ji-lin, MENG Yuan-ming, WANG Te, WANG Xiao-fei

2017, 0(5):  41-47. 

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Residual stress formed during the curing process of thermoset resin composites is an important factor affecting the quality of material. A three-dimensional model based on the time-dependent physical parameters of materials during the curing process of composites was established.It contains thermal-chemical, resin curing kinetic model, and the residual stress model. On the basis,the time-dependent properties of material performances during the curing process were introduced into multi-field coupled calculation model. According to the comparison with experiment data in reference, the reliability of the model was verified. Then, the curing residual stress and strain of composite laminates were numerically simulated, the change rule of the curing residual stress and strain of composite laminates was studied, and the effect of process parameters on the stress and strain was analyzed. Through the comparison with the strain of pre-preg test, the correctness was verified. And the results show that the model can simulate composite curing process. Temperature, volume fraction of resin, and ply angle have significant impact on laminates stress and strain, and the affect of volume fraction of the resin is the most significant among these factors.

SPH-BASED NUMERCIAL SIMULATION OF COMPOSITE MATERIAL UNDER BIRD IMPACT

YU Yong-qiang, LI Cheng, TIE Ying

2017, 0(5):  48-52. 

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In this paper, high-velocity impacts for application to the bird-strike problem of composite laminates were studied. The progressive damage model is used to simulate composite laminates, in order to study the deformation and damage of composite laminates subjected to the bird strike. The process of composite laminates by bird impact is simulated through the smoothed particle hydrodynamics method (SPH) coupled explicit finite element method. This paper analyses the damage of bird when it hits the composite laminates. The progressive damage characteristics of a unidirectional composite laminates, and the damage of fiber and matrix of every layer in the composite laminates. The influence of absorbing energy of laminates is studied at the direction of different incident angle of bird. The analysis results show that the laminates layers' orientations should have corresponding change in order to improve the energy absorption of composite laminates.

INVESTIGATION OF LONG-TERM CREEP BEHAVIOR OF GLASS FIBER REINFORCED PLASTICS WITH DIFFERENT PLY LAYERS

LIU Qing, ZHU Si-rong, LIANG Na

2017, 0(5):  53-56. 

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With the wide application of glass fiber reinforced composites, the study of its creep properties has been one of the most significant projects. Meanwhile, the study of long-term performance of glass fiber reinforced plastics develops slowly, owing to the immaturity of experimental methods and theoretical researches. In this paper, based on the previous research, glass fiber reinforced plastics samples with different ply layers were prepared to explore the regularities of creep compliance's change with the increasing service time . The corresponding theoretical model with two parameter variables was established. The experimental data was fitted by the theoretical formula. The differences in creep properties of different ply layers were compared. The results show that the model and experimental data agree well with each other.

APPLICATION RESEARCH

EFFECT OF SHORT GLASS FIBER ON LAYER TEARING PROPERTIES OF MULTI AXIAL WARP KNITTED LAYER COMPOSITES

NIE Xiao-lin, MA Pi-bo, WANG Ya-bai

2017, 0(5):  57-61. 

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By using the glass fiber multi axial warp knitted fabric as reinforcement, epoxy resin as matrix and adding, short glass fiber to glass fiber fabric reinforced layer, multi-axial warp knitted fabric for composites containing short glass fiber between glass fiber layer was prepared. The short glass fibers between glass fiber fabrics were observed by using SEM after tests, the tensile and tear strength of the composite was tested and studied by the universal mechanical testing machine. The results show that under the same conditions, the layer tearing property of composites treated was obviously enhanced. The load displacement curve of initial slope is large, and the composites are not easy to be destroyed by tearing load form.

EFFECT OF SURFACE TREATMENT ON ADHESIVELY BONDED REPAIR OF ALUMINUM

YU Zhou-hui, WAN Qi

2017, 0(5):  62-67. 

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GFRP adhesive repaired damage aluminum, aluminum alloy surface was treated with different concentrations of the silane coupling agent KH550, KH560, and compared with non-treated aluminum sample. The repair effect was studied by tensile and humidity test. The results showed that two kinds of coupling agent KH550, KH560 have simular effect on repair sample. After treated with coupling agent of 1%~2% concentration, the repaired samples have a high initial strength and the heat-resistant properties are also improved. Humidity treatment has significant adverse effects on the mechanical properties, and the damage of hygrothermal environment for aluminum-layer interface is stronger than layer-GFRP interface. The decrease of adhesive strength between aluminum-layer interface is the main reason of sample performance degradation.

EXPERIMENTAL STUDY ON BOND BEHAVIOR BETWEEN FRP PLATE AND CONCRETE WITH GRID SHEAR BOND

ZONG Ming-ming, HAN Li-ting, LIU Wei-qing, TONG Gang

2017, 0(5):  68-71. 

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For the different interface connection form of FRP board and concrete for single shear test, focusing on the destruction of the form, the ultimate bearing capacity and damage mechanism and so on. The results show that increasing the number of connectors and reducing the spacing between the joints can improve the interface shear capacity and improve the overall elactic stiffness of the members when arranging the unidirectional shear connections. The proposed two-way gration shear connector can significantly improve the overall shear strength of the interface and enhance the overall stiffness of the elastic phase member.

STUDY ON PROCESSING PARAMETERS OF TAPE PLACEMENT FOR CONTINUOUS GF REINFORCED PPS

LI Jing, HONG Cheng, GUO Bing-bing, FANG Li

2017, 0(5):  72-79. 

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Orthogonal experiments and single-factor experiments were carried out to evaluate the effects of five processing parameters including temperature of hot air, tape laying speed, pressure of roller, temperatures of roller and platform on interlaminar shear strength (ILSS) and flexural strength of the laminates to get optimal parameters in tape placement process. The prepreg made of polyphenylene sulfide as matrix and continuous glass fiber as reinforcement was used. The results show that the pressure of roller has significant impact on ILSS and the temperature of platform has less impact on ILSS, while the tape laying speed has significant impact on flexural strength and the temperature of roller has less impact on flexural strength. Besides, higher ILSS and flexural strength can be achieved by improving the tape laying speed and pressure of roller properly and choosing the temperature of hot air, temperature of platform and temperature of roller in the suitable range for operation. When the optimal condition of the tape laying speed is 40 cm/min, the pressure of roller is 0.4 MPa, the temperature of roller is 240 ℃, the temperature of hot air is 340 ℃ and the temperature of platform is 240 ℃, ILSS and flexural strength of the laminate can reach 79.94 MPa and 1097.37 MPa, respectively.

DESIGN AND SIMULATION OF HANGING FIBER AUTOMATICALLY ON WINDING MACHINE BASED ON CREO AND ADAMS

TIAN Hui-fang, ZHOU Cheng-guang, ZHANG Jun-wei

2017, 0(5):  80-83. 

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Based on the summarization of the structure and working principle of the filament winding machine, the problems and shortcomings of the current filament winding machine are found. Then, the design of hanging fiber automatically on winding machine about cylinder is carried out in the modeling software Creo according to the actual production needs. The kinematical properties of the mechanism are obtained by simulating the threading of several common gas cylinder core molds by introducing the model into the ADAMS by MECH/PRO interface. The results show that the design of hanging fiber automatically on filament winding machine can meet the requirements of core mold with various sizes, which is of great significance to solve the problem of low degree of automation in filament winding machine.

THE OPTIMAL DESIGN OF COMPOSITE CROSSED BEAM STRUCTURE

ZHANG Guo-qi, GUAN Xin, ZHANG Yu-sheng, LI Yu

2017, 0(5):  84-88. 

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Based on the numerical method, the work of optimizing composite crossed beam structures in spacecraft was conducted in this paper. The load-transferred path was optimized depending upon the load-bearing structure components. Furthermore, the enhanced region and lay-up of T700 unidirectional carbon/epoxy prepregs were reasonably presented, while the specimen was fabricated integrally by manual molding technology. The experimental results demonstrate that the weight of this crossed beam is reduced from 966 g to 436 g, up to 37.5%; the maximum deformation is reduced from 0.33 mm to 0.19 mm under the 6000 N compressive load, which satisfied the stiffness demand.

IMPACT RESISTANCE STUDY OF POLYUREA ELASTOMER/GLASS FIBER REINFORCED VINYL RESIN COMPOSITE

HE Hong-ying, NI Ai-qing, WANG Ji-hui, YANG-bin

2017, 0(5):  89-92. 

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Glass fiber reinforced resin composite materials in service is vulnerable to external impacts, which will cause composite structure damage,and thus severly threaten the safety service life of composite.In this paper, the improvement of impact resistance of glass fiber reinforced resin composite materials through coating a layer of polyurea elastomer was investigated. Charpy impact test machine, and optical microscopy were carried out on the specimens of no coating, front coating and back coating, respectively. The results show that the elastic deformation and fracture failure of polyurea coating can dramatically increase impact energy consumption and improve the impact strength of specimens.With the same thickness of coating, the coating of polyurea elastomer of front coating specimens does not completely fracture and absorb impact energy mainly through the elastic deformation, playing a buffer role. Conversely, the back coating specimens can absorb more impact energy due to fracture failure of polyurea coating, which will lead to lowest impact damage and higher impact strength.

INVESTIGATION ON THE HONEY COMB CORE SANDWICH WATER INTAKE AND ELECTRICAL PERFORMANCE OF MA60 AIRCRAFT RADOME

WANG Zheng-gang, XIA Wei-wei, ZHAO Bing, HUI Chen-peng

2017, 0(5):  93-98. 

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Radar radome of MA60 Aircraft is situated at the front of its fuselage, and it is a GFRP with honeycomb sandwich structure which was made by hands with the treatment of wet process. The radar radome is not only a functional device with the feature of electromagnetic wave penetrating, but also a vulnerable structural device. And water-logging of the honeycomb sandwich is one of the most severe damages. This paper combined all the fault phenomenon of electrical performance deterioration during the usage of radar radome in MA60 aircraft in outside field, and conducted simulating experiments of raining and soaking on the defective radar. By analyzing and comparing the weights and electrical performances of the radar radome before the simulating experiment as well as after that, and we found that in those situations water could infiltrated into the honeycomb sandwich through small damages (even some subtle damages) to deteriorate the electrical performances of the radar radome in a short time. Based on these experiment results, we analyzed the reasons which cause water accumulation in the honeycomb sandwich, and with the help of electromagnet theory, we studied the harms that water did to the electrical performances of radar radome; therefore, we concluded that dealing with all the outside and inside surface damages of radar radome is crucial for us to maintain its perfect alectrical performances.

REVIEW

APPLICATION OF INDUCTION WELDING TECHNOLOGY IN CIVIL AIRCRAFT THERMOPLASTIC COMPOSITES

YUAN Xie-yao, YANG Yang, JIAN Xue-zhen, XU Jie

2017, 0(5):  99-104. 

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In recent years, the application of thermoplastic composites in civil aircraft is rapidly developed. Welding technology is an important connection process for thermoplastic composites manufacturing and essential process from single component to part. The induction welding technology introduced in this paper is one of the several welding methods used recently. In this technology, the induction coil is used to generate high frequency electromagnetic field, and then the susceptor material is heated. Induction welding is a stable process and can be realized continuously. The whole process is rarely affected by personnel factor. It is an important development direction to connect thermoplastic composites component in the future. Based on the nature of induction welding technology, this paper introduces the latest development of this technology. At the same time, this also introduces some experimental processing and devices. Finally, the temperature field distribution in the welding area is also briefly described, to help to evaluate the processing parameters.