COMPOSITES SCIENCE AND ENGINEERING

VIBRATION-BASED DELAMINATION ASSESSMENT IN FIBER REINFORCED POLYMER BEAMS

ZHAN Chao, MA Xiao-jing, ZHANG Zhi-fang

2017, 0(9): 5-12.

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Delaminations in fiber reinforced polymer (FRP) beams were detected and assessed through the changes in natural frequencies before and after the damage occurred in beams. To assess the three delamination parameters, namely, the interface, lengthwise location and size, two different inverse algorithms, i.e. graphical technique and artificial neural network (ANN), were developed to inversely predict the delamination from a series of known frequency shifts. To verify the prediction efficiency and accuracy of the inverse algorithms, both numerical and experimental validation were conducted and the results were compared. The numerical validation results show that both algorithms can predict the delamination parameters successfully, although the accuracy of the graphical technique is noticed to be higher than that of the ANN. Experimental validation using the measured frequencies in literature shows that the graphical technique can predict the delamination with satisfactory accuracy using the measured frequencies which is noise polluted, while ANN is very sensitive to the experimental errors and can hardly predict the delamination with experimental data. In conclusion, it is recommended to use the graphical technique rather than artificial neural network to assess the delamination in FRP beam through frequency shifts.

ANALYSIS OF FIBRE GLASS REINFORCED FLEXIBLE PIPES UNDER INTERNAL PRESSURE

LIN Shan-ying, BAI Yong, FANG Pan

2017, 0(9): 13-18.

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A short-term burst pressure test is carried out and a 3D finite element model is established. An analytical solution of burst pressure of FGRFP is presented in the paper. The comparison of three methods shows that the stress of reinforced layers is much greater than that of inner and outer layers, indicating that the reinforced layers bear most of internal pressure. For the winding angle ranging from 45 to 80 degrees, the capacity to bear the internal pressure increases. The winding angle of 59 degrees of the reinforced layers is appropriate for the crossing section design. It is reasonable to reduce the diameter to thickness ratio of pipe for designing FGRFP.

TEMPERATURE EFFECT ON FATIGUE PERFORMANCE OF FIBER-REINFORCED POLYMER

XIE Gui-hua, BIAN Yu-long, TANG Yong-sheng, FENG Qian-hong

2017, 0(9): 19-24.

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Fiber Reinforced Polymer (FRP) has attracted much attention due to its high strength to weight ratio, strong resistance to chemical corrosion, while its anti-fatigue property varies with material characteristics, ambient environmental conditions and loading status. In this study, the performance of FRP on anti-fatigue was studied under different temperatures and loading stress level according to the phenomenology-based macro mechanical theories, and an equivalent model was proposed to estimate and predict the stiffness degradation and residue fatigue life of FRP under the synergy effect of temperature and fatigue stress level. Based on the experimental data, the verification of the model was carried out. The verified model was applied to predict the fatigue performance of the E-glass plain-weave fabric laminate. It is shown that the suggested model may efficiently predict the stiffness degradation and equivalent residue fatigue life of FRP. The temperature effect on fatigue property of FRP is obvious and this effect may even be more evident than that of the stress amplitude for FRP.

STRESS ANALYSIS AND STRUCTURE DESIGN OF THE MULTI-RING INTERMIXING COMPOSITE FLYWHEEL

LU Chen-xiang, SU Wei-guo, ZHANG Xian-biao, WANG Dong

2017, 0(9): 25-33.

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Based on plane stress full elastical model, a plane stress analysis model of the multi-ring intermixing composite flywheel is forwarded by considering the anisotropy of filament winding composites. 2D axisymmetric FEM is used to verify the validity of this model. The former plane stress analysis model is used to find out the quantitative relationship between the stress distribution of the rotor and these factors such as the different modulus ratio of rotor material, the quantities of rings, the thickness ratio of rings, the interference between rings on static or roating speed. The results show that the stress and strength distribution can be improved when the greatest modulus ratio of outermost or the radial thickness of outermost rings or the interference between hub and inner ring are increased in the multi-ring intermixing composite flywheel. Based on the former result, a three-ring intermixing composite flywheel with high energy density is designed by glass fibre, T700, and T800. 3D FEM is used to verify the validity of this structure.

NUMERICAL STUDY ON THE FRACTURE PROPERTIES OF SHORT-FIBER REINFORCED COMPOSITES BASED ON MICRO-MECHANICS

GAO Jian-hong, YANG Xiao-xiang

2017, 0(9): 34-39.

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The strain energy release rates of cracks with different directions in short-fiber reinforced composites were calculated using vitual crack propogation method combined with finite element method. The influence of mesh size as well as the crack length, fiber length, fiber radius and fiber content on the calculation results were studied. It is shown that, the mesh size has little effect on the calculation results; the strain energy release rates of cracks in different regions of composites vary differently with the crack length; it presents a regular change pattern with the variation of crack direction and the minimum of propagation resistance happens in the sliding crack; and the strain energy release rates increases as the increasing of fiber length, fiber radius and fiber content.

SEISMIC RESPONSE ANALYSIS OF STEEL OUTER CYLINDER-FRP INNER CYLINDER COMPOSITE MATERIAL CHIMNEY

GAO Ming, ZHU Si-rong, WANG Ying-jun, WANG Qi-xing

2017, 0(9): 40-45.

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FRP composite materials, because of its corrosion resistance and other advantages, are widely used. By using glass fiber reinforced plastic inner cylinder and steel outer cylinder together, a new type of composite chimney structure was formed. However, the analysis of the FRP composite chimney structure is rare. And, our country has no corresponding specification, so its design and calculation is more difficult. In this paper, we can only refer to the design and calculation method of chimney structure such as concrete chimney or steel chimney. ANSYS finite element analysis software is applied to analyze the dynamic characteristics and seismic response of steel tube-FRP inner tube composite chimney structure under seismic action by mode decomposition response spectrum method. Strength analyses are proceeded according to Tsai-Wu failure criteria based on the laminated shell theory of composite materials. And, the results are compared with those of steel chimney of the same structure size under earthquake action. Its advantages and feasibility of the new chimney structure are discussed, which provides reliable references for the aseismic design of the new composite chimney structure.

STUDY ON THE ENGINEERING APPLICATION OF THE SENSOR BASED ON THE PIEZO-RESISTANCE EFFECT OF CFRP

HUANG Jun-jie, LIU Rong-gui, XU Zhao-hui, XIE Gui-hua

2017, 0(9): 46-51.

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The piezo-resistance effect of Carbon Fiber Reinforced Plastic (CFRP) has been explored and verified in both experimental and theoretical fields. The new CFRP sensing material made by improving the formula of the epoxy resin matrix, which was tested by its piezo-resistance effect, has been proved feasible as the sensor. However, in the practical engineering, the stress condition of the load-bearing material is much more complicated than the tensile test. In this paper, we have designed an experiment by putting the CFRP sensing material at the tensile zone of the beam, which could simulate the practical stress condition of the steel at the maximum degree. We found out that in the practical application, the CFRP sensing material could well and intuitively reflect the information of the structure such as the load, crack and other state situations. The CFRP sensing material show a good linear relationship between the out load of the beam and the resistance, which is the basic feasibility of the smart material with both load-bearing and sensing characteristic. The sensitivity of CFRP is smaller than it in the tensile test but is enough to measure and could be improved in the further process. Especially, in the low loading stage, the CFRP could reflect the load of the beam well by the piezo-resistance effect, which means the sensor is quite practical.

RESEARCH ON FAILURE BEHAVIOR OF UNBALANCED ADHESIVE JOINT IN CARBON FIBER DRIVE SHAFT

HONG Tao, HU Ye-fa, TAN Jian, LIU Can

2017, 0(9): 52-57.

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A finite element model was established to analyze the failure behavior of unbalanced adhesive joint in carbon fiber drive shaft under torsion loading. Then the failure torque and failure mode of the unbalanced adhesive joint was predicted from the finite element model. It is found that the failure torque, failure mode in the torsion experiment were in close agreement with the result from finite element analysis. The effect of shear modulus ratio and wall thickness ratio between metal shaft head and carbon fiber tube on the failure behavior of unbalanced adhesive joint are discussed, which provides available reference in designing adhesive bonded joints in carbon fiber drive shaft.

COMPARATIVE STUDY ON JOINING COMPOSITE AND ALUMINUM ALLOY WITH ROLLING RIVETING AND BOLTING

HUANG Zhi-chao, HE Jun-hua, FENG Jia

2017, 0(9): 58-62.

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The connection experiments and static tensile tests of composite and aluminum alloy were carried out by the rolling riveting and the bolt connection. The effects of washer and bonding on the joint strength and the energy absorption were compared. The experiment results show that the peak loads of the two joints are almost the same, but the failure displacement of the bolt joint is longer than that of the rolling riveting joint when the washer exists. Furthermore, the energy absorption value of bolt joint is 16.29% higher than that of the rolling riveting joint, and it has a stronger capacity to absorb vibration. The factor of bonding has little effect on the tensile strength of the two joints. In addition, the peak load of bolt connection is slightly higher than that of the roller riveting connection, and the failure displacement and energy absorption of the two joints are basically the same.

STUDY ON THE GAS THERMAL DE-ICING SYSTEM OF WIND TURBINE BLADES

LV Qing, NING Li-wei, WEI Ke-xiang, ZHOU Zhou

2017, 0(9): 63-66.

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Based on the principle of gas thermal method, a blade de-icing system is designed to solve the icing problem of wind turbine blades in this paper. First, the design of the gas thermal de-icing system is introduced. Then, the feasibility of the system is studied in the laboratory. Finally, the reliability of the gas thermal system is analyzed by combining the actual situation and experimented with the de-icing system on field test of wind farm. The experimental results show that the design of the system is feasible, the wind turbine gas thermal system is running reliably without exception during the test, and the effect of de-icing is obvious. This system could be applied to de-icing of wind turbine blades.

THE STUDY OF SURFACE METALLIZATION PROCESS OF FIBER GLASS/EPOXY COMPOSITE

XING Ling-bing, SUN Shi-yong, YANG Rui, SUN Guo-zhong

2017, 0(9): 67-72.

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A simple method of electroless plating on fiber glass/epoxy composite surface is proposed. A layer containing short fibers with nickel plating was coated on the composite surface. The composite and layer were co-cured in the same process condition. Experimental results show that a uniform nickel coating was successfully deposited on the fiber glass/epoxy composite substrate by electroless plating after appropriate mechanical roughening and acidification. A three dimensional surface profiler was adopted to measure the surface morphology and roughness of the composite after mechanical roughening. In addition, SEM and digital microscope with large depth-of-field were employed to observe the surface microstructure and cross-sectional micrograph of nickel coating. Effects of electroless plating time and loadage on the coating morphology, coating thickness and deposition rate were discussed. The tensile tests were performed to determine coating adhesion strength. Under the process conditions with coating time of 8 h and loadage of 1.25 dm²/L, the experimental results indicate that the coating thickness and coating adhesion strength can reach 38.96 μm and 8.45 MPa, respectively.

RESIDUAL DEFORMATION OF COMPOSITE PRESSURE VESSELS AFTER AUTOFRETTAGE AND ITS FINITE ELEMENT ANALYSIS

SHU Ming-jie, LI Yun-zhong, LIU Chong

2017, 0(9): 73-77.

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It is of great significance to carry out research on the trend of axial residual deformation of composite material pressure vessels as well as revealing the influence mechanism and the reasonable on axial residual deformation of pressure vessels, which is helpful to control dimensional stability of composite pressure vessel in service. In this paper, the important part is to have finite element analysis and experimental research on the axial residual deformation of composite material pressure vessels since the process of autofrettage. The results show that the plastic deformation occurrs in the titanium liner under work pressure. In order to ensure the head curve of continuous coordination in the progress of autofrettage, the head liner inward concave and pressure vessels have the trend of axial shortening deformation. In addition, the change of yield strength of titanium liner has obvious effects on the trend of the axial residual deformation of pressure vessel. With the increase of titanium liner material yield strength, axial residual deformation of composite pressure vessel (shorten) decreases, and the better consistency between finite element analysis with experimental prediction results has been proven.

EXPERIMENTAL STUDY ON STRENGTH OPTIMIZATION OF FRPM PIPES RESIN MORTAR

CHEN Zhao-nan, WEI Lian-yu, PEI Ya-nan, LI Chun-xiao

2017, 0(9): 78-81.

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FRPM pipe, as a kind of flexible non-metallic composite materials, has excellent mechanical properties and good economic efficiency, which has broad application prospect in highway culvert engineering. Due to the long term heavy load of the vehicle, the strength of the buried culvert is more demanding, and the quality of FRPM pipe sand layer is very important. But, there are some problems existing in the FRPM pipe sand layer produced by many enterprises. The strength of the sand layer were optimized by making different graded samples, and fracture surface morphology of the samples was analyzed by stereomicroscope. The results show that the optimum mechanical properties of fourth groups of gradation sample, the better the quartz sand and resin binder, resin filling, which provides scientific basis for the quality control of FRPM pipe production in highway culvert engineering application.

THE STUDY OF ACCELERATED AGING OF ARTIFICIAL XENON ARC LAMP ON THE BURSTING AND TEARING PROPERTIES OF POLYESTER FIBER/PVC FLEXIBLE COMPOSITE

WEI Qu-ping, NI Ai-qing, ZHANG Hong , YANG Xiu-li

2017, 0(9): 82-88.

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Because of outdoor application, polyester fiber/PVC flexible composite materials are tend to age under solar radiation, and the mechanical properties will then be affected. Artificial xenon arc lamp gives a good simulation of outdoor environment, so the influence of accelerated aging by artificial xenon arc lamp on the bursting and tearing properties of polyester fiber/PVC flexible composite were investigated. The bursting and tearing properties of the aged and un-aged composites, as well as the failure mechanism, were investigated by static mechanical tests. The failure mechanism of two different tearing modes were compared. The change of the peak position and intensity were illustrated by FTIR, and the micro-morphology were examined by SEM. It is found out that carbonyl compound and conjugated double bond are mostly formed in the polyester fiber/PVC flexible composite accelerated aging by artificial xenon arc lamp. The tearing property of the flexible composite decreases significantly with aging time. Different tearing modes result in significant difference in tearing force.

STUDY ON PROCESS AND MECHANICAL PROPERTIES OF THE VARI FORMING FOAM-CORE SANDWICH COMPOSITE BY DIFFERENT HANDING METHODS

SUN Yu, LIU Qiang, HUANG Feng, MA Jin-rui

2017, 0(9): 89-92.

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In this paper, two kinds of methods were taken: grooves and holes to process foam core in advance, VARI molding process was used to prepare foam-core sandwich composite, the non-destructive test, the molding efficiency, the surface quality and the mechanical properties of the foam-core sandwich composite were studied. The results show that grooves and holes could improve the molding efficiency of the foam-core sandwich composite effectively, whose surface quality was good. The combine between foam core and skin of sandwich of three kinds of foam-core sandwich composite was tight, and poor glue and delaminations were not existing. The peel strength of the foam-core sandwich composite was decreased somewhat, while the bending strength and the edge compressive strength were increased slightly after the handing methods of grooves. The peel strength, the bending strength and the edge compressive strength of the foam-core sandwich composite were all decreased to some extent after the handing methods of holes. In general, different processes have little influence in mechanical properties of the VARI forming foam-core sandwich composite.

STUDY OF THE IMPACT ON WIND POWER BLADE ROOT BOLT FATIGUE PROPERTY OF CERAMIC GASKET

JI Le, LI Cheng-liang, LU Xiao-feng, Tang Jin-qian

2017, 0(9): 93-96.

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Wind power blade root model was built up using Catia, meshed by professional mesh tool, analyzed by commercial FEM software, based on which the FEA result is eventually got. Using the FEA result and load Markov matrix, the root bolt′s damage can be obtained by fatigue code in Matlab. In this article, bolt stress are compared between with and without ceramic gasket, and the impact on bolt fatigue property of gasket is explored. It is indicated that bolt damage is obviously reduced by putting ceramic gasket under the nut from the result of simulation, while fatigue life is effectively elongated.

SIMULATION OF THE RESIN FLOW PROCESS OF THE COMPOSITE K/T TYPED JOINTS USING VACUUM ASSISTED RESIN TRANSFER MOLDING

ZHAO Qing-hua, WANG Chang-chun, YUE Guang-quan, LIU Jian-guang

2017, 0(9): 97-100.

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The large-span structure has obtained a rapid development during the advance of urbanization, which requires pipeline structures with good mechanical properties and corrosion resistance. The conventional pipe part is composing of metal concrete structure, which has the disadvantages in the wet and corrosive cases. The composites have widely regarded as the promising materials in civil engineering design for the high specific strength and corrosion resistance, which has greatly hindered the application in the fields of cost control. In this study, the composite K/T typed joints were obtained using the vacuum assisted resin transfer molding (VARTM) process and the suitable resin injection method was determined based on the simulation results of resin flow front shape and injection time for the four injection methods, which was compared with the testing result with the determined injection method. Both of these results present good agreement with each other, which can avoid the high cost of the trial and error method.

CURRENT STATUS ON DRILLING TECHNOLOGY OF FIBER REINFORCED COMPOSITES

SUN Qiao-ru, LIU Xiao-dong, WANG Tian-chen, YAO Wen-hao

2017, 0(9): 101-105.

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Due to its characteristics of mechanical anisotropy, poor thermal conductivity ability, drilling defects such as delaminations, tear and other defects are produced during the drilling process of fiber reinforced composites. This paper reviews the effects such as drilling thrust, drilling parameters and tool geometry on drilling defects of fiber reinforced composites. Furthermore, the current status of drilling technology is analyzed. Finally, reasonable technology parameters, tool geometry and new drilling technology which are important to improve the quality of drilling technology is proposed.

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