COMPOSITES SCIENCE AND ENGINEERING

A MICROGEOMETRIC STRUCTURAL MODEL FOR SPREAD TOW FABRIC

LI Bei-bei, LI Wei

2014, 0(8): 5-10.

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Based on reasonable geometric hypothesis, a two-dimensional geometric structural model of STF composite is proposed. Crimp of fiber tows in the STF can be predicted. An equation of fiber volume fraction of STF composite is also set up, and variation of fibre volume fraction with fiber crimp percentage is analysed. Comparison of the resulting analytical predictions with experimental results shows that the proposed model is valid.

INFLUENCE OF TREATMENT AGENT ON MECHANICAL PROPERTIES OF CARBON FIBER COMPOSITE

GAO Quan-xi, ZHENG Wei, KONG Ling-mei, QI Yan-yan

2014, 0(8): 11-15.

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Acetone was used to extract the treatment agents on the surface of T700 carbon fiber fabric, and the major chemical components of treatment agents were analyzed, where the relationships between the extraction time and the content of treatment agents on the surface of carbon fiber fabric were studied. Carbon fibers reinforced composites with different content of treatment agents were prepared by vacuum-assisted resin infusion molding (VARI) process, and their mechanical properties were tested. The results indicated that the main component of treatment agents was BPA epoxy resin, with content of ~1.5%. Additionally, the surface roughness was increased after solvent extraction, which improved the wettability of resin matrix. Moreover, the mechanical properties, especially the bending strength, were significantly increased.

EXPERIMENTAL STUDY ON THE BOND BEHAVIOR OF THE REINFORCEMENT CONCRETE SPECIMENS WITH NEAR-SURFACE MOUNTED CFRP RODS

DING Ya-hong, SHEN Cui-hong, XU Ping

2014, 0(8): 16-21.

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Perfect bonding is the key to guarantee the strengthening effect for the method of Near-surface mounted (NSM). The pull-out-test of the 13 concrete specimens reinforced by CFRP rods with NSM method was studied to test the bonding shear stress, failure modes and experiment phenomena. The effect of concrete strength and notch-groove size were analyzed. The results showed that the maximum shear stress appeared at the loading end under low loading. And the maximum shear stress would appear at the loading end of 100~200mm when the load reached the failure load. The bond strength increased with concrete strength if the failure occurred at the interface of the glue and the concrete. The slotting sizes had an important influence on the failure modes. The research provides the basis for the practical engineering.

THE TOUGHENING MODIFICATION OF CYANATE ESTERS RESIN MODIFIED BY EPOXY TERMINATED BUTADIENE-ACRYLONITRILE

FAN Qin, WANG Yong-li, ZHOU Quan, NI Li-zhong

2014, 0(8): 22-26.

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The bisphenol A dicyanate resins (CE) were modified by epoxy-terminated butadiene-acrylonitrile (ETBN) to improve their toughness. The chemical structure of the CE/ETBN blends was investigated by FT-IR and then the mechanical properties tests were performed. Finally, the relationship between the structure and mechanical properties was established. And the microstructure and mechanical properties were characterized by scanning electron microscopy (SEM). The results showed an excellent toughening effect of ETBN on CE resin. The flexural strength of CE-18 blend was 148 MPa, and the impact strength of the CE-25 blend were 35.07kJ/m² and 1.32MPa·m^1/2, respectively. SEM results showed that the ETBN as a dispersed phase was evenly distributed in the CE resin matrix, and had a good toughening effect. The CE/ETBN blends system possessed good water resistance with water absorption rate lower than 0.9% after 96 hours in boiling water.

STUDY ON THE FLEXURAL STRENGTH OF SiO₂/SiO₂ CERAMIC COMPOSITES

ZHOU Shao-jian, LIAN Yun-qing, YANG Jie, XIAO Chun

2014, 0(8): 27-30.

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2.5D SiO₂/SiO₂composites were fabricated by sol-gel method using silica fiber and silica sol as the starting materials. The mechanical performance of the SiO₂/SiO₂ composites and the effect under different service temperature,passivation technics are studied. And the properties of SiO₂/SiO₂ composites and the effective factors are also studied. The results show that the composite achieves the best mechanical properties when the heat treatment temperature is 650℃. After the passivation technics,the flexural strength were increased by 17%. The results indicate that the SiO₂/SiO₂ composites had well heat-resistant. An inflexion point for high temperature bending property of SiO₂/SiO₂ composites is between 600~800℃,which is related to the self-union of molten condition SiO₂. Whereas after 800℃, the bending property of SiO₂/SiO₂ composites decreased.

STUDY ON AGING PROPERTIES OF GLASS-FIBER REINFORCED PES/EPOXY COMPOSITES

MENG Ling-yu, XU Ren-xin, ZHENG Cong-wei, WANG Jun

2014, 0(8): 31-34.

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The composites of polyethersulfone (PES)/epoxy matrix have heat resistance and toughness. Many researches have been focused on the heat resistance and impact resistance, but researches on its aging properties are rare. This paper used dicyandiamide, dichlorophenyl dimethylurea as latent curing agent and accelerator. E-glass fiber reinforced PES/amine phenol tri-functional epoxy prepregs were prepared by wet process, and the composite materials were prepared by compression molding. Composite samples were tested by hydrothermal aging and UV aging. The changes of mechanical properties of composites after hydrothermal aging and UV aging test were studied. The results showed that after the hydrothermal aging treament of 28 days, the samples' tensile, bending, compressive and impact strength retention rate was 68.3%, 60.9%, 72.7% and 82.8%. After UV aging treament of 28 days, the samples'tensile, bending, compressive and impact strength retention rate was 83.9%,78.9%, 82.5% and 72.0%, respectively.

PREPARATION AND PROPERTIES OF CARBON FIBERS REINFORCED PTA COMPOSITES UNDER CATALYTIC CURING PROCESS

XU Jian-wen, WAN Li-qiang, ZHANG Cun-chao, GUO Bing

2014, 0(8): 35-40.

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To reduce the curing temperature and simplify the curing process, bromotris (triphenylphosphine) copper (Ⅰ) was added into the polytriazole resin system (PTA) as the catalyst. According to the relationship between the amount of catalyst and the gel time of PTA, the amount of catalyst was determined to be as 3‰ of the least molar amount of the monomer. Under catalytic conditions, PTA composites reinforced by T300B carbon fiber (C-PTA/T300B) were prepared in the curing process of 50℃/6h+100℃/2h+150℃/2h. The influences of catalyst to the glass transition temperature (T_g), 5%-weight-loss temperature (T_d5) and mechanical properties of C-PTA/T300B composites were studied. Compared with the non-catalytic PTA composites reinforced by T300B carbon fiber (PTA/T300B), the results showed that to aehieve same mechanical properties, the curing temperature of C-PTA-T300B composites decreased 30℃, which greatly simplifies the after-treatment process. Moreover, the T_g was 21℃ enhanced, and the T_d5 was 21℃ and 5℃ promoted in air and N₂ environment, respectively.

STUDY ON THE FEM SIMULATION FOR THE STATIC TEST OF WIND TURBINE BLADE

ZHAO Na, GAO Yang

2014, 0(8): 41-43.

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To make the deviation of the static test results and numerical simulation results meet the requirement of GL specification,the match of the station of numerical model and the static test is the key factor. Generally, when we do the blade structure analysis using finite element software, the boundary conditions are constraints on the blade root. However, in the static test, the blade is mounted on the wheel hub, where the hub and bearing are fixed together. And the hub is not rigid, so the model should consider its influence on the test results. This article takes MW blade as an example, compares the static test results and FEM calculation, and finally confirms the validity of this method.

ACOUSTIC EMISSION BEHAVIOR ON INTERLAMINAR DAMAGE OF COMPOSITE BASED ON WAVELET ANALYSIS

LIANG Xiao-min, ZHOU Wei, PANG Yan-rong, BAO Zheng-yu

2014, 0(8): 44-48.

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Acoustic emission (AE) testing technology was used to monitor defect evolutions of wind turbine blade composite with delamination under loading in real time. In order to obtain the acoustic emission response characteristics of interlaminar failure, the waveform data-flow cascaded by VBScript was analyzed. The results showed that during the interlaminar cracking process of mode Ⅰ the fiber was damaged, but to the mode Ⅱ, only matrix was damaged, which caused great differences of acoustic emission energy between mode Ⅰand mode Ⅱ during the delamination growth. The frequency spectrum of mode Ⅰ has two wave crests, while mode Ⅱ has only one. The frequencies corresponding to the two wave crests were the main frequencies to the damaged resin and fibers. This conclusion can provide a basis for identifying the delamination damage mode of wind turbine blade composite.

ANALYSIS ON DAMAGE EVOLVEMENT OF FIBER REINFORCED POLYMER BY WEIBULL PROBABILITY DISTRIBUTION

WI Yi-bin

2014, 0(8): 49-53.

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The two-parameter Weibull distribution is first recommended for modeling both strength and stiffness properties by using statistical analysis and the goodness-of-fit in this paper. Based on the relationship between damage and tensile strength, a model of damage evolvement for fiber reinforced polymer(FRP) was founded. Combining existing experimental data and linear regression method, damage evolvement equation of FRP for different layers were given out, and it is indicated that the tensile strength was reduced with the increase of FRP layers, according to the same damage. And, the tensile strength of FRP with one layer is 10%, 20% and 25% higher than that with two,three and four layers respectively. Whereas, the infulence of additional layers on modulus can be neglected. Finally, a modified coefficient is suggested to take the effect of additional layers into consideration, and the value can be served as reference for strengthening design.

STUDY ON DIGITAL SIMULATION AND TEST VERIFICATION FOR DEBRIS IMPACT ON GFRP COMPOSITE

ZHOU Chun-ping, LI Xing-de, ZHU Shan

2014, 0(8): 54-58.

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This paper summarized the literatures related to debris impact on aircraft structures to obtain the velocity and energy parameters required for radome structures to bear, conducted runway debris impact test on composite panels, and built LS-DYNA model to simulate the test. By tuning the parameters in the simulation model, the test result can be reflected in the model for the composite panel. And through the user programming, the behavior of debris can also be finely repeated in the computation model. In future, in the process of radome to runway debris impact computation, all other parameters can remain unchanged in the simulation model, only the composite panel model needs to be replaced. Thus, we can get a set of quick and reliable method to get the rational result from simulation results based on LS-DYNA models for runway debris impact.

STUDY OF STRUCTURAL BEHAVIOUR OF REINFORCEMENT-FREE CONCRETE DECK STRUCTURE CONSTRUCTED WITH FRP

LI You, ZHENG Yu, YANG Jian-bin, WEI Mu-wang

2014, 0(8): 59-66.

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To enhance the durability of concrete bridge deck structure and reduce the maintenance cost, a reinforcement-free concrete deck structure based on FRP was invented in this study. In this deck structure, the loading-carrying mechanism is an arching action inside the deck slab. Because this structure is restrained by horizontal GFRP rods, there is no reinforcement provided in the concrete slabs. A series of one-third scale test models were conducted and tested with the variation in structural parameters, including supporting beams, spacing of lateral restraint rods and loading positions. The results were used to study the effect of arching action on loading-carrying capacity of deck structures by investigating the behaviour of test decks under wheel loads. Due to the accurate validation of the results from nonlinear finite element analysis and experimental tests, a further parametric study were conducted to investigate the influence of other structural variables, such as concrete strengths, arch depth and configuration of FRP rods.

EVALUATION ON LOCAL REPAIR OF DEBONDING DEFECTS IN COMPOSITE HONEYCOMB SANDWICH STRUCTURES

ZHANG Ya-ting, CHEN Liang, LI Jian-fang, FU Ping-jun

2014, 0(8): 67-71.

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A local-injecting repair is brought forward for debonding defects (Z≤100mm) in composite honeycomb sandwich structures. The repairing effect was studied based on the finite element model established based on ANSYS software and experiment. The results show that the compression strength can reach 80% of the original sample after local-injecting repair. Finite element model could estimate the compression strength and the failure mode of honeycomb sandwich plates exactly.

ENGINEERING PRACTICE OF FRPM PIPELINES ACROSS THE NATIONAL ROAD OR EXPRESSWAY

YANG Jian-ming, SHI Qiang, PAN Duo-jun, WU Xun

2014, 0(8): 72-76.

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This paper discusses glass fiber reinforced plastic mortar pipes (FRPM)'s construction technology for spanning the freeway and the importance and measures of quality management from the aspects of project profile, construction technology for installing of trench-less pipelines, the construction technology for installing pipelines in culvert and pressure test. Meanwhile, the paper analyzes some problems that may occur and provides the corresponding solutions for this two kinds of technology.

STUDY ON WET PROCESS FORMULA FOR ARAMID Ⅲ FIBER'S

HE Li, YIN Shu-bang, YANG Jie, LIU Xin-dong

2014, 0(8): 77-82.

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A matrix formula suitable for the wet winding technology of aramid Ⅲ fiber was studied and developed based on the mechanical property, thermal performance, wettability and processing property. The experimental results show that the formula had a low initial viscosity (430mPa·s) at 35℃ and long pot life(≥8h), which met the requirements of wet winding. The tensile strength, specific elongation and bending strength of the formula were 88.8MPa, 3.23% and 142.8MPa. The Martin heat resistant temperature was 155.1℃, and the glass-transition temperature was 171.5℃. The interlaminar shear strength, tensile strength and modulus of the matrix formula/aramid Ⅲ fiber NOL ring were 51.3MPa, 2102MPa and 96.1GPa. The performance factor and the fiber strength conversion ratio of the Φ150mm vessel were 34.8km and 68.9%, respectively, which could reach the level of aramid Ⅲ/R04 composites by dry winding.

TENSILE PROPERTIES OF HYBRID C/BFRP RODS

CAO Sheng-hu, WU Zhi-shen, MA Kai, WANG Xin

2014, 0(8): 83-87.

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In this paper,the tension performances of carbon fiber, basalt fiber and their different hybridization reinforced vinyl ester composite tendons were experimentally studied. The test results show that the fracture strain of the hybrid composite tendons increased when the basalt fibers increase gradually, and was higher than that of single carbon fiber composite tendons, showing a positive hybrid effect. But the elastic modulus of the hybrid composite tendons increased if carbon fibers was increased, basically following the law of mixture, while the experimental value of the tensile strength of hybrid composite tendons was higher than the theoretical value.

EXPERIMENTAL RESEARCH ON LONG-TERM MECHANICAL BEHAVIOR OF GFRP BARS IN DIFFERENT ENVIRONMENTAL CONDITIONS

SUN Can, QIU Wen-hao, ZENG Xian-bin, ZHENG Yu

2014, 0(8): 88-91.

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An around one-year experimental test of long-term mechanical behaviour of GFRP bars in different environments was carried out, including concrete environment, alkaline solution and natural UV radiation, respectively. This study is designed to verify the reliability of usual accelerated aging tests on GFRP bars and simulation of the actual time-dependent property of GFRP bars embedded in concrete. The experimental results showed that the degeneration in the mechanical property of the GFRP bars packaged in concrete and exposed to the natural environments was not so significant, while the property of the GFRP bars storing in the alkaline solution was degenerated by around 20%.

STUDY ON THE TENSILE STRENGTH OF TRIAXIALLY BRAIDED COMPOSITES

ZHANG Ping, GUI Liang-jin, FAN Zi-jie

2014, 0(8): 92-96.

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The tensile strength of triaxially braided composites was studied through integrated meso/macro-mechanical analysis. First, the braiding architecture was simplified appropriately. Secondly, the meso-mechanical model was proposed. Finally, the tensile strength of triaxially braided composites was predicted by using the commercial FEM software. The analysis method was verified with the test results. Based on the analysis method, the effects of braiding parameters (such as braiding angle, the ratio between axial yarn size and braiding yarn size) on the tensile strength were studied. This work provides valuable help in studying the structural mechanics of the braided composites.

CHEMORHEOLOGY RESEARCH OF VINYL ESTER RESIN FOR RTM

ZHAO Wei-sheng, SUN Chao-ming, WANG Wen-jing, YANG Kai

2014, 0(8): 97-100.

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The chemical rheological behavior of the modified vinyl ester resin system for RTM was studied in this paper. Using DTA and viscosity measuring instruments, the curing characteristics of the resin system and the curing process of the relationship between viscosity and temperature were investigated. According to the rheological properties of resin systems, a Dual-Arrhenius viscosity model with constant temperature was established. The results indicate that, the simulation results were consistent with the experimental results. It has revealed the viscosity variation of the resin system at different temperature conditions, predicted the low-viscosity window with quantitatily, reasonable development of RTM process parameters to ensure product quality to provide the necessary scientific basis.

DISCUSSION ON THE CHINESE STANDARD AND SPECIFICATIONS OF FRP BAR PRODUCTS

LI Wei-jie,LI Biao, YANG Yong-xin, YUE Qing-rui

2014, 0(8): 101-104.

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This paper compares the Chinese standard of FRP bar products with the American catalogue for the major mechanical specifications. Based on the results of comparison and related research, this paper points out that the requirements of FRP bars' tensile strength in the current Chinese standard has some deficiencies, and requirements of transverse shear strength and bond strength are absent so far. Suggestions on revising the Chinese standard of FRP bar products and further research are given.

RESEARCH PROGRESS OF COMPOSITE REPAIR TECHNIQUE

XU Fei, LIU Bin, LI Wen-ying, XIE Wei

2014, 0(8): 105-112.

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To begin with, this paper introduced the background, key technique, project design and repair tolerance of the composite repair. Then, the research status of composite repair at home and abroad were summarized and evaluated in two aspects, i.e., the computational research of analytical method, FEM and optimization, and the experiment and measurement. At last, some key fields and development tendency were pointed out on the basis of the newest technique of the composite repair.

Industry information contents

2014, 0(8): 113-128.

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