Table of Content

28 January 2017, Volume 0 Issue 1

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BASIC STUDY

EXPERIMENTAL STUDY ON ENERGY ABSORPTION OF THE FOAM SANDWICH COMPOSITE ENHANCED LATTICE WEB UNDER QUASI-STATIC COMPRESSION

FAN Zi-yan, FANG Hai, ZHUANG Yong, LIU Wei-qing

2017, 0(1):  5-10. 

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Composite sandwich structure has the characteristics of light weight, high strength, bending stiffness, corrosion resistance, good designability, impact resistance, energy absorbing, etc. Lattice web reinforced foam sandwich composite specimens are produced by vacuum infusion, with glass fiber reinforced polymer (GFRP) for the panels and lattice webs, polyurethane foam for core. Holding the specimen plane size constant and changing the distance, height and thickness of the webs and the density of foam, specimens are tested under quasi-static axial compression to study their performance of energy absorption. It is shown that with the increase of the volume ratio of web, the yield bearing capacity and energy absorption performance of the composite sandwich structure increase. In addition, the lattice web plays a role in strengthening the core and absorbing energy.

SHEAR CAPACITY OF RC SHORT BEAMS STRENGTHENED BY ETS METHOD

LI Jin-song, LIU Hua-xin, ZHAO Lin, XUE Jia-yu

2017, 0(1):  11-15. 

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This paper explores the destruction progress, failure modes and shear capacity for the reinforced concrete beams shear strengthened with ETS method, according to the study and analysis on 4 RC beams. According to relative analysis between "Code for design of concrete structures (GB 50010—2010)" and "Building Code Requirements for Structural Concrete (ACI 318-05) and Commentary (ACI 318R-05)", calculated values are more conservative than experimental values. The results indicate that reinforced bars can delay the development cracking, improve the cracking load and shear capacity of the beam. The RC beams strengthened by ETS method show good mechanical and deformation properties.

STUDY ON THE BEHAVIOUR OF CONCRETE BRIDGE DECK SLABS STRENGTHENED WITH NEAR SURFACE MOUNTED FIBER REINFORCED POLYMER BARS

ZHENG Yu, XIA Li-peng, YANG Jian-bin, TONG Bing

2017, 0(1):  16-24. 

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To study the behaviour of concrete bridge deck slabs strengthened with Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) bars, an experimental test of this strengthened concrete deck slab was carried out. In this experimental test, the material of strengthening FRP and strengthening configuration were varied to investigate the influence of those structural parameters. It was found that the ultimate strengths of strengthened concrete deck slabs were enhanced significantly by using the NSM strengthening method. Interestingly, the variation of strengthening FRP bar materials had no strong effect on the behaviour of strengthened concrete deck slabs due to the lateral restraint stiffness. To develop further study of the behaviour of NSM strengthened concrete deck slabs, a finite element analysis (FEA) of the test specimens was proposed. In the comparison of the results from numerical analysis and the test results, the FEA results showed good correlation with the test results. Thereafter, a series of parametric study was conducted with this numerical model, which included concrete strengths, lateral restraint stiffness, span-to-depth ratio, elastic modulus of FRP bars, strengthening percentage and reinforcement percentage. It was shown that increasing the lateral restraint stiffness and reinforcement percentage would result in higher loading-carrying capacity but weakened the strengthening effect. In addition, the ultimate capacity of strengthened concrete deck slabs was enhanced by increasing the concrete strengths and elastic modulus of FRP bars. As expected, the ultimate strengths of concrete deck slabs were reduced by increasing the span-to-depth ratios. Based on the study of experimental and numerical results, it can be concluded that the material properties of FRP and strengthening percentages should be determined according to the concrete strength, lateral restraint stiffness and reinforcement ratio of deck slabs in the structural design.

EFFECT OF HOT AIR AGING ON MECHANICAL PROPERTIES OF PBO/T700 HYBRID COMPOSITES

ZHANG Cheng-shuang, BAO Yan-ling, LIU Ning, WANG Jian

2017, 0(1):  25-29. 

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The effects of hot air aging on static and dynamic mechanical properties of PBO/T700 hybrid composites were studied in this paper by using a universal testing machine and dynamic mechanical analysis (DMA). The static mechanical properties testing results indicate that the tensile strength and compressive strength of PBO/T700 hybrid composites declined after hot air aging, with maximum drop of 12.7% and 6.9%, respectively. The tensile modulus increased from 126 GPa to 145 GPa, while the flexural strength and modulus and the interlaminar shear strength of the composites show little changes. The DMA result shows that the heat-resistance property and rigidity of PBO/T700 hybrid composites increased to some extent after hot air aging. However, the E' and E″ of the composites shift toward low temperature and high temperature, respectively, with the increase of the aging time, which means some decline of heat-resistance property and rigidity of the composites.

RESEARCH ON PERMEABILITY PREDICTING FORMULA OF NON-CRIMPED FABRICS WITH FIBERS OF ELLIPSE EDGE

KANG Ning, LIANG Xuan-yong

2017, 0(1):  30-35. 

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The results of CFD (Computational Fluid Dynamics) were applied to fit the ellipse edge formula for predicting permeability of NCF while the edge of fibers was approximated as semi-ellipse. Orthogonal tests of 5 factors and 5 levels were carried out on the NCF unit cell. The average error between numerical and the ellipse edge formula's results is 1.91% for quadratic arrangement and 1.90% for hexagonal arrangement. The error between experimental and the ellipse edge formula's result is 0.22%, which is smaller than the error of 3.96% between experimental and the rectangle edge formula's result. The ratio between the result of ellipse edge formula and rectangle edge formula is over 1.1, when the ratio between the width W₁ between fiber bundles and the major semi-axis c₁ of ellipse edge is less than 0.8. The results verified that the ellipse edge formula was more accurate and the application was broader.

INFLUENCE OF MOLECULAR STRUCTURE ON MELT VISCOSITY AND FEATURES OF POLYIMIDE FOAM

HU Ai-Jun , LI Ke-di, LI Shu-shu , YANG Shi-yong

2017, 0(1):  36-43. 

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In a 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA) polyimide (PI) foam system, we studied the influence of thermal treatment temperature, calculated molecular weight and dianhydride molecular structure on the melt viscosity of precursor resin and the features of foam. We found that in a-BPDA/m-PDA/NA system, we were able to make uniform foam with outstanding features when precursor resin calculated molecular weight is 1500 g/mole, foam density is 100 kg/m³ and thermal treatment is 260 ℃/1 hr. The foam has 89% closed-cell content, 1.34 MPa compression strength and 37.1 MPa compression modulus. Partially introducing ODPA or BTDA into this PI foam system can reduce the cost, and maintain those good features and closed-cell content of the foam.

A FATIGUE ASSESSMENT METHOD FOR VARIABLE CROSS-SECTION FIBER REINFORCED PLASTIC BEAM

NIU Mu-hua, CHEN Cheng

2017, 0(1):  44-52. 

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A fatigue assessment method for variable cross-section fiber reinforced plastic beam under complex loads is studied. The blade of horizontal axis wind turbine is a typical reinforced plastic beam. Blade fatigue load cases are identified and loads are calculated by GH Bladed software, which is specified at the IEC61400 international specification and GL (Germanisher Lloyd) regulations. In order to resolve the problem resulting from the changing loads with time and beam span, stress analysis is performed with a finite element method (FEM). Considering Saint-Venant's principle, uniform cross section FEM model is built at each critical zone. Stress transformation matrixes (STM) are set up by applying six unit load components on FEM model separately. The total fatigue damage of each laminate on the critical point is counted by rain-flow counting method and Miner’s damage law based on general S-N curves. A comparison of the performance of this method is made with far more costly business software FOCUS. The results show that the fatigue damage of multi-axis FRP could be assessed conveniently by this FEM-STM method. And this proposed method gives a reliable and efficient method to analyze the fatigue damage of slender composite structure with variable cross-sections under irregular loading.

INFLUENCE OF INGREDIENT OF HIGH FRICTION COEFFICIENT COMPOSITE MATERIAL ON THE TRIBOLOGICAL PERFORMANCE

XU Xiang, YANG Ming, ZHANG Shi-wei, GONG Qian-jiang

2017, 0(1):  53-57. 

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The high friction composite materials with different proportion were prepared by orthogonal design. The influence of ingredient on the friction coefficient and elastic modulus were studied by range analysis. The friction tests were performed using MMS-2A friction tester. The surface morphology of friction materials were analyzed by 3D Measuring Laser Scanning Microscopy OLS4100 and the discipline of ingredient with material were studied. The thermal weight loss of materials were analyzed by TG/DTA7300 thermal analyzer and mechanical properties were tested by the SANS testing machine. The results show that the major affecting factors affecting friction coefficient is confidential filler and nitrile rubber, while the minor factor is Fiber. Fiber is the main factor affecting the elastic modulus, and confidential filler is the minor factor. Multiple regression analysis of friction coefficient and elastic modulus were built, and R2 are 0.94 and 0.955, respectively. The thermal decomposition temperature of composite materials is about 300℃, and the heat resistance decreased with the increase of the nitrile rubber. The main wear mechanisms were different for different composite materials by the analysis on surface morphology.

APPLICATION RESEARCH

CHARACTERISTICS AND CALCULATION METHODS OF CONCRETE BEAM STRENGTHENED WITH INMOUNTED CFRP-PCPs

DENG Yu, LIU Nan, YANG Yong, ZHANG Peng

2017, 0(1):  58-62. 

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Experimental studies on eight reinforced concrete beams strengthened with near-surface mounted(NSM) CFRP-PCPs reinforcement have been tested with load. Comparing with plastering CFRP to strengthen prestressed, the technique to strengthen concrete beams with near-surface mounted CFRP-PCPs reinforcement has specialties as rigidity. In addition, according to the test load-deflection relation curves, under the the identified trilinear moment-curvature model, deducing the CFRP-PCPs reinforcement embedded in reinforced concrete beam deflection calculation formula, the calculated value was compared with the test results, and the results match well.

PREPARATION AND FRICTION PERFORMANCE OF ND-DOPE ANATASE TITANIUM DIOXIDE/CYANATE ESTER COMPOSITES

YAO Huan-ying, ZHU Bao-lin

2017, 0(1):  63-67. 

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The surface modification of Nd-cyanate ester was realized by doping titanium dioxide (M Series) through the multi-step grafting method. A series of M series particles/cyanate ester (CE) composites were prepared. The friction properties and Rockwell hardness of the composites were studied. The result shows that the friction performance of CE can be improved by adding a little M particle (mass fraction<4%). When the M-2 particle mass fraction is 3wt%, the friction coefficient of the composite can be decreased by about 36%, and the friction consumption can be decreased by about 60%. The wear resistance of the composites was enhanced. When the M-2 particle content is 4wt%, the composite system Rockwell hardness is increased by 10.4%.

THE CURING RESEARCH OF COMPOSITE PIPE BASED ON BRAIDING-WINDING-PULTRUSION PROCESS

XU Jia-zhong, YUAN Ya-nan, ZHANG Bo-wen, LI Qiang

2017, 0(1):  68-76. 

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This paper makes research on the curing of the composite pipe which is produced based on braiding-winding-pultrusion process. According the principle of composite curing, this paper sets heat transfer model and cure kinetic model, which is based on composite braiding-winding-pultrusion process. The ANSYS and APDL language are used to develop the curing process numerical simulation procedure. Through the simulation of three-dimensional resin thin-walled pipe and the experimental verification, the process parameters affecting the curing temperature and curing of the process of forming the new pipe were analyzed. The influence law of initial temperature of pipes, heating process and pultrusion speed on solidification process of the new process for pipes is attained by the simulation analysis for the fitting. The on-line temperature testing is operated on the new process pipes, and the result shows that the simulation is identical with the actual production process, which can guide the actual production.

RTM PROCESSING OF THE A-SHAPED COMPOSITE STIFFENED FRAME

YUAN Chong-xin, GAO Li-min, CHEN Kai, LI Yong-hang

2017, 0(1):  77-79. 

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As the application of composites has been broaden from the secondary structures to the primary structures of aircrafts, the stiffeners such as stringers and frames are made of composites rather than metals. To develop the primary structure of the pylon of civil aircrafts, a stiffener with A shape is experimentally studied using the RTM processing. The mold design, the layup design, the choice of the inlet and outlet, and the injection parameters optimization are studied, based on which the A stiffener is machined successfully.

MULTILAYER 2D BIAXIAL BRAIDED LAYER COMPOSITE MESOSCOPIC GEOMETRICAL MODEL AND A CALCULATION METHOD OF THE TENSILE MODULUS

KE Chang-yi, QIN Xiao-hong, YAN Jian-hua

2017, 0(1):  80-85. 

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In this paper, a reasonable and effective mesoscopic geometrical model for 2×2 biaxial braided composite structure, and a calculation method for tensile modulus were eatablished. The geometrical model, which applys to single or multi-layer composites, was based on the practical factors such as cross-sectional performance, buckling of braided yarn bundle, actual weaving process and forming solidification. The calculation method of tensile modulus was also established, the simulation results are tend to be consistent with the actual numerical results, which proved the effectiveness of established model. The results show that the method is effective and feasible. The above results show that the meso-geometric model fit the structural characteristics of the monolayer and multi-layer 2×2 braided composites structure well. The equivalent mechanical model can reflect the tensile behavior of the composites and the tensile modulus can be accurately predicted.

EFFECT OF THE BF'S SURFACE MODIFICATION ON BF/BAMBOO/WOOD COMPOSITE'S BONDING PROPERTIES

XIANG Yan-yan, SHEN Shi-jie, JIN Ting-ting

2017, 0(1):  86-91. 

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Bonding performance of wood composite material is important parameters in the use of wood composite structural material. In this study, in oder to reinforce the bonding properties of BF/bamboo/wood composite, we use silane coupling agent KH550, plasma (PL), maleic anhydride (MA), salt ester etching (AE) and a combination of the above methods to modify the basalt fiber surface.The results showed the combination treatment on reinforcing the surface of basalt fiber has a better prefermance, and the order of effecting the BF/bamboo/wood composite bonding properties is as follows: MA550>PL550>AE550>KH550. After the KH550 and maleic anhydride-grafted combination treatment, the shear strength of bamboo-fiber layer reached 8.64 MPa, and the shear strength of wood-fiber layer reached 8.47 MPa; MA550 combination treatment increased by 50.45% than individual KH550 treatment, whereas wood-fiber glue had no fiber release.

STUDY ON PROCESS PERFORMANCE OF EPOXY STRUCTURAL ADHESIVE FOR THE WIND TURBINE BLADE

WANG Zhi-hua, SONG Qiu-xiang

2017, 0(1):  92-96. 

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This paper studies the effect of waiting time after mixture, curing degree, mixture ratio and the thickness of adhesive on bonding performance of epoxy structural adhesive for the wind turbine blades. The bonding performance of epoxy structural adhesive were characterized by tensile shear strength and equivalent peel strength. The results show that structural adhesive mixture with the waiting time of 90 min has the highest bonding strength. After glass transition temperature reaches 60 ℃, bonding strength is in a stable state. Within ±5% of the theoretical ratio of adhesive, the bonding performance of epoxy structural adhesive is stable. With the increase of the adhesive thickness, the shear strength shows a linear downward trend, while the peel performance is basically stable. The study provides technical basis for wind blade bonding process optimization.

STUDY ON THE METHOD OF MEASURING THE THICKNESS OF COMPOSITE MATERIALS BASED ON ULTRASONIC WAVE

LIU Mo, YANG Yu-qing, LU Ming-hui, ZHANG Yi-ping

2017, 0(1):  97-100. 

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Because of the small proportion, specific strength and modulus, composite materials have been widely used in aerospace, automotive, chemical, textile, mechanical manufacturing, medical and other fields. The composite products in service, due to the long time of differentiation and corrosion or products in the presence of delamination defects and other reasons, will result in changes in the thickness of the material. For high attenuation composite, this paper puts forward a method to measure the velocity of sound by using the time difference between the ultrasonic wave and the first floor, and then the thickness of the material is obtained. The experimental results show that the thickness of several materials is measured by a bottom wave method, and the error is about ±0.15 mm. It is feasible to use this method to measure the thickness of the composite material with high attenuation. It has great guiding significance for the field thickness measurement of high attenuation composites.

REVIEW

RESEARCH PROGRESS AND DEVELOPMENT TREND OF SECTIONAL WIND TURBINE BLADES

QIN Zhi-wen, YANG Ke, WANG Ji-hui, SONG Juan-juan

2017, 0(1):  101-108. 

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Application of sectional wind turbine blades is an effective access to conquer restraints of transportation and manufacturing of long blades. This paper firstly reviews fundamental research, and then the applications related to sectional wind turbine blades, joint figuration and their characteristics of various types of joint patterns employed in sectional blades are summarized and analyzed, and the trends of sectional blade techniques are prospected.

RESEARCH PROGRESS ON SHEAR STRENGTH OF CONCRETE BEAMS REINFORCED WITH FRP REBARS AND STIRRUPS

LIU Zong-quan, YUE Qing-rui, LI Rong, CHEN Xiao-bing

2017, 0(1):  109-115. 

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Fiber reinforced polymer (FRP) attracted wide attention in civil engineering field worldwide as a new type of high performance reinforcement for concrete structures. Shear strength of FRP reinforced concrete beams is effected by the unique characteristics of FRP rebars and FRP stirrups. Based on a number of experimental researches, several codes and design guidelines from different countries have provided computing equations of shear strength of FRP reinforced concrete beams, including Chinese GB 50608—2010, Japanese JSCE 1997, British BISE 1999, Italian CNR-DT 203/2006, American ACI 440.1R-06, and Canadian CSA.S 806-12. In order to evaluate the reliability of these equations, the computing results from these codes were compared with experimental values obtained from 33 experimental beams.