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      20 October 2017, Volume 45 Issue 10 Previous Issue    Next Issue
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    VIEWPOINT
    One Generation of New Material, One Generation of New Type Engine:Development Trend of Aero-engine and Its Requirements for Materials
    Da-xiang LIU
    2017, 45 (10): 1-5.   DOI: 10.11868/j.issn.1001-4381.2017.100001
    Abstract ( 1927 ( PDF (698KB)( 830 Citation

    Based on the brief review of accelerated developing status of aircraft power technology in the world, the present status and developing trend of key materials technology for aero-engine were analyzed. In accordance with the idea of "one generation of new material, one generation of new type engine", development requirements for the materials technology of the system and main parts of aero-engine were proposed. Suggestions for improving development and application level of the materials technology in China were presented from aspects of quality stability and technical maturity, investigation and verification for engineering, materials system and data, composite materials, airworthiness certificate, etc.

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    RESEARCH ARTICLE
    Preparation of Graphene via Thermal Reduction and Its Adsorption Capacity for Heavy Metal Pb2+
    Yan-chun WANG, Xiao-shu ZENG, Zhi-qiang AO, Qiu-hong YUAN, Wen-qing YANG, Zuo-jian SHEN
    2017, 45 (10): 6-11.   DOI: 10.11868/j.issn.1001-4381.2016.000815
    Abstract ( 739 ( PDF (3349KB)( 276 Citation

    Graphene(GR) was obtained by reduced graphite oxide(GO) by instantaneous heating. Thermal reduced graphene was used to adsorb heavy metal Pb2+ ions in water to study the effect of adsorption time and pH value on the adsorption. The results show that the pH value greatly affects the adsorption capacity of graphene. When pH value is higher than 7, the adsorption capacity obviously increases. And the equilibrium reaches within five minutes. The analysis by scanning electron microscope (SEM) and transmission electron microscope (TEM) shows that graphene flake is very thin and with less layers. Experimental data are fitted by Langmuir and Freundlich adsorption isotherms model. According to the Langmuir adsorption isotherms model, the maximum theoretical adsorption capacity of Pb2+ is 86.5mg/g, the correlation coefficient R2 is 0.9982, and Langmuir constant KL is equal to 10.7. The Langmuir model agrees well with experimental data. It demonstrates that the adsorption reaction is a fast single molecular layer chemical process. The adsorption kinetics is better fitted to the pseudo-second-order kinetic model.

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    Synthesis and Photocatalytic Activity of Iron Doped CdS by Hydrothermal Method
    Yang-long LIU, Yu-ying ZHENG, Ning-ning CAO, xiang WANG
    2017, 45 (10): 12-17.   DOI: 10.11868/j.issn.1001-4381.2015.000498
    Abstract ( 801 ( PDF (4312KB)( 429 Citation

    Fe-doped cadmium sulfide was prepared by hydrothermal method in aqueous solution using cadmium nitrate, ferric nitrate and thiourea as raw materials. The samples were characterized by SEM, XRD, EDS and XPS. The photocatalytic degradation of methylene blue (MB) in aqueous solution was used as a target reaction to evaluate their photocatalytic activity. The experimental results show that the reaction temperature has a great effect on the morphology of cadmium sulfide, and spherical, flowerlike, clustered and rodlike cadmium sulfide are obtained in various reaction temperatures. Among them, the photocatalytic activity of flowerlike CdS is observed to be better than other CdS materials. The XRD indicates that Fe-doped cadmium sulfide is hexagonal crystal structure when the reaction temperature is 160℃. The experimental results also indicate that Fe-doped can obviously improve the photocatalytic activity of cadmium sulfide and when the doping ratio of Fe to Cd is 1:10, the photocatalytic effect is the best of all.

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    Synthesis, Characterization and Properties of Ag/InP Composites
    Shu-ling LIU, Xiao-li HAN, Jian-bo TONG
    2017, 45 (10): 18-22.   DOI: 10.11868/j.issn.1001-4381.2016.001198
    Abstract ( 619 ( PDF (2936KB)( 314 Citation

    InP microcrystal was successfully synthesized via a facile hydrothermal route, and then Ag nanoparticles were loaded on the surface of InP microcrystal using UV lamp to reduce silver versions. The as-prepared composites were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The results show that Ag/InP composite is composed of lots of spherical microcrystals with a size of 500nm and Ag nanoparticles with a diameter of 20 nm loaded uniformly on the surface of cubic phase InP microspheres, the surface is rough. Using Congo red as model organic pollutant, the photo-catalytic performance of Ag/InP microspheres is further detected by fluorescence and UV-vis spectra. It is found that the as-prepared composite exhibits a superior photo-catalytic degradation activity as compared to InP, which might be the effective separation of electrons and holes after Ag nanoparticles loaded on the surface of InP microspheres.In addition, the photo-catalytic performance of Ag/InP microspheres with different Ag loads was studied, and the results show that when the loading is 73.3%, the photocatalytic activity of the product is the best, and the degradation rate is 64%.

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    Mechanical Characteristic of Remanufacturing of FV520B Precipitation Hardening Stainless Steel Using MAG Surfacing Deposition
    Jian LIU, Sheng ZHU, Zhi-hai CAI, Ping ZHANG, Jun LIU, Hang QIN, Yong-gang TONG
    2017, 45 (10): 23-31.   DOI: 10.11868/j.issn.1001-4381.2017.000433
    Abstract ( 713 ( PDF (5473KB)( 215 Citation

    Surfacing deposition forming method was adopted to carry out remanufacturing experiment of FV520B precipitation hardening stainless steel. Then the mechanical property characteristic of the remanufacturing layer was tested and studied, contrasted with the corresponding property of substrate. The results show that the remanufacturing layer, formed with MAG surfacing of FV520B precipitation hardening stainless steel has mechanical characteristic with high strength and hardness, the tensile strength reaches 1195MPa, exceeds 1092MPa of substrate, yield strength is 776MPa and average hardness is 336HV, is close to the corresponding property of substrate which is 859MPa and 353HV respectively; however, the elongation and impact toughness of the remanufacturing layer is merely 8.92% and 61J/cm2 respectively, it has a large gap with the corresponding property 19.72% and 144J/cm2 respectively of substrate. Fracture and microstructure analysis on specimens shows that the microstructure of remanufacturing layer is fast cooling non-equilibrium crystallized lath martensite, and carbide precipitated strengthening phase such as NbC, MoC, M23C6, etc, which is the reason that remanufacturing layer has high strength and high hardness. But as lack of aging treatment and Cu strengthening phase, and the weak interface between contaminating brittle phase or large size spherical particles and substrate will deteriorate the deformability and induce stress concentration and cracking when the material is load-carrying, and is the main reason of the remanufacturing layer having lower static tensile elongation and impact toughness.

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    Effect of Rotation Rate on Microstructure and Properties of Underwater Friction Stir Welded 7A04-T6 Aluminum Alloy
    Wen WANG, Tian-qi LI, Ke QIAO, Rui-qi XU, Kuai-she WANG
    2017, 45 (10): 32-38.   DOI: 10.11868/j.issn.1001-4381.2015.001234
    Abstract ( 745 ( PDF (12771KB)( 342 Citation

    Underwater friction stir welding (FSW) on 7A04-T6 aluminum alloy plates was carried out, and the effect of rotation rate on microstructure and mechanical properties of joints was investigated. The results show that the minimum hardness of underwater FSW joints is located in the thermo-mechanically affected zone. The hardness of welded joints at the high rotation rate of 950r/min exhibits W-shaped distribution, and the average hardness value in the nugget zone is higher than that of welded joints at the low rotation rate of 475, 600, 750r/min. When the rotation rate increases from 475r/min to 750r/min with a constant welding speed of 235mm/min, the precipitated phases in the nugget zone gradually become coarse, and the ultimate tensile strength coefficient of the joint decreases from 89.71% to 82.33%; when rotation rate increases to 950r/min, the precipitated phases dissolve into aluminum matrix during welding, and age after welding. This produces the fine and homogeneous dispersed phases, which results in an increase of the strength coefficient to 89.04% and a certain enhancement of strain hardening capacity and elongation for the joints. All the tensile fracture surfaces exhibit the mixed characteristics of microporous polymerization and cleavage fracture.

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    Preparation of High Quality Ti-6.5Al-1.4Si-2Zr-0.5Mo-2Sn Alloy Powder by Plasma Rotating Electrode Process
    Quan-bo KUANG, Li-ming ZOU, Yi-xiang CAI, Xin LIU, Jun CHENG, Jian-hong YI
    2017, 45 (10): 39-46.   DOI: 10.11868/j.issn.1001-4381.2016.001045
    Abstract ( 758 ( PDF (5739KB)( 330 Citation

    This research aims to prepare high quality powder of Ti-6.5Al-1.4Si-2Zr-0.5Mo-2Sn, which lays foundation for the following preparation of powder high temperature titanium alloy component.Ti-6.5Al-1.4Si-2Zr-0.5Mo-2Sn alloy ingots were prepared by vacuum arc remelting (VAR). The chemical compositions of ingots were examined. The loss of alloy elements, uniformity of composition, phase composition and microstructure of titanium alloy ingots were analyzed. Then powders were prepared by plasma rotating electrode process (PREP) with different rotating speeds. Alloy powders were sieved into different particle sizes. The relationship between rotating speed and physical and chemical properties of powder was studied. X-ray diffraction(XRD), scanning electron microscope(SEM) and metallurgical microscope(OM) were used to investigate the phase composition, morphology and microstructure of the powder. The results show that the composition distribution of titanium alloy ingot prepared by VAR is uniform and the content of alloy elements meets the requirements of national standard, through a unique pressing electrode. Microstructure of the ingot is lamellar structure with small amounts of silicide particles disperse in the matrix. The size distribution of the powders made by PREP method exhibits the normal distribution. The sphericity of the powder is excellent, and no hollow ball and satellite ball exists. With the increase of rotating speed, the proportion of small particles increases dramatically, the proportion of large particles decreases greatly. The phase composition of powder is mainly α' phase, and it is mainly composed of peritectic and small amount of dendrite structures. Compared with the alloy ingot, the elements of the powders have a slight loss, the content of O is less than 0.1%, which is beneficial to obtain high-performance powder titanium alloy.

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    Dynamic Mechanical Properties and Constitutive Equations of 2219 Aluminum Alloy
    Zi-qun ZHANG, Zhao-liang JIANG, Qing-yue WEI
    2017, 45 (10): 47-51.   DOI: 10.11868/j.issn.1001-4381.2016.000859
    Abstract ( 1529 ( PDF (834KB)( 421 Citation

    To analyze the deformation characteristics and the change rule of flow stress of 2219 aluminum alloy at high temperatures and high strain rates, the dynamic as well as quasi-static tensile response of 2219 aluminum alloy were investigated by using split Hopkinson pressure test(SHPB) and universal test machine. The true stress-strain curves of 2219 aluminum alloy under different strain rates and temperatures were obtained. The results show that the temperature sensitivity of 2219 aluminum alloy is high and the flow stress decreases with the increase of temperature. When the strain rates are within the range of 1000-3000s-1, the change of flow stress is not obvious. The parameters fitted by the Johnson-Cook model can predict well the flow stress.

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    Effect of Current Density on Quality of Electroformed Mold Inserts with Micro/Nano-cavities
    Can WENG, Fei WANG, Dong-jiao YANG, Hui LYU, Bing-yan JIANG
    2017, 45 (10): 52-58.   DOI: 10.11868/j.issn.1001-4381.2016.000104
    Abstract ( 625 ( PDF (4490KB)( 248 Citation

    Based on the COMSOL Multiphysics software, the electric field distribution and the growth front of electroformed layer on the cathode surface were simulated during the electroforming process. The simulation results show that the uniformity of electroformed layer with micro/nano-cavities can be effectively improved with a better replication quality by using a lower initial current density. Both nano-diaphragm and nanopillar array are selected as masters for the electroforming experiments. When the initial current density decreases from 4A/dm2 to 1A/dm2, the maximum deviation of characteristic width between the nano-diaphragm master and mold inserts dramatically decreases from 60nm to ±20nm. By setting proper current density and enhancing mass transfer near the cathode surface, the characteristic diameter dimension error of electroformed mold inserts for nanopillar array decreases from 6.27% to 2.49%. The replication quality of electroformed mold inserts with micro/nano-cavities can be significantly improved by these methods.

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    Research on SiC Whisker Prepared by H-PSO
    Yao WANG, Yang CHEN, Ning QIAO, Xin LI, Wen-ting ZHANG
    2017, 45 (10): 59-64.   DOI: 10.11868/j.issn.1001-4381.2016.001112
    Abstract ( 633 ( PDF (11748KB)( 268 Citation

    SiC whiskers were prepared on the matrix of graphite by using high hydrogenous silicone oil(PSO) as raw material. The effect of surface conditions of graphite and heating temperature on the growth of SiC whisker was mainly studied in this paper. The main factor which affects the nucleation and growth of SiC whisker is the heating temperature, with the heating temperature rising, the production of SiC whisker increases. The surface condition of graphite matrix also influences the growth of SiC whisker. With the nucleation points provided by graphite matrix defects increasing, the production of SiC whisker incleases and SiC whisker starts to overlap with each other. The formation process of SiC whisker includes two steps:nucleation and growth. SiC whisker nucleates at low temperature and grows at high temperature, which follows the VLS (vapor-liquid-solid) growth mechanism.

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    Effect of Al-TiO2-C Grain Refiners on Refinement of Industrial Pure Aluminum
    Xiao-wei HAN, Rui-ying ZHANG, Peng WANG
    2017, 45 (10): 65-70.   DOI: 10.11868/j.issn.1001-4381.2015.000521
    Abstract ( 627 ( PDF (25848KB)( 219 Citation

    The Al-TiO2-C grain refiners were synthesized by the in-situ exothermic dispersion method by using TiO2, C and Al powders as raw materials. The microstructure of Al-TiO2-C refiners with different C/TiO2 was investigated by SEM, XRD and EDS. Grain refining test was carried out on industrial pure aluminum. The results show that Al-TiO2-C refiners are composed of Al3Ti, TiC and Al2O3. When the mole ratio of C to TiO2 is between 1:25 and 1:20, the amount of Al2O3 is moderate and its distribution is relatively dispersive. An excellent grain refining performance is obtained when adding 0.2% (mass fraction) Al-TiO2-C refiner with C/TiO2 is 1:20, the average grain size is about 142μm and there is no refining recession when holding 1h.

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    Fabrication of Aluminum-based Superhydrophobic Coating by Anodization and Research on Stability and Corrosion Resistance
    Shun-li ZHENG, Cheng LI, Teng-fei XIANG, Wei HU, Shi-bing DING, Jing WANG, Pan-jin LIU
    2017, 45 (10): 71-78.   DOI: 10.11868/j.issn.1001-4381.2016.000301
    Abstract ( 646 ( PDF (12512KB)( 327 Citation

    Aluminum (Al) can be easily contaminated or damaged after exposure in damp environments, which can adversely affect its aesthetic appearance and desired functionalities. To improve its corrosion resistance, a superhydrophobic coating was fabricated on Al by electrochemical anodization followed by modification with myristic acid. The surface morphology and chemical composition were characterized by using a field emission scanning electron microscope (FESEM) with attached energy dispersive X-ray spectrum (EDS). The surface wettability, mechanical stability as well as corrosion resistance were also investigated by contact angle measuring system, sandblasting test and electrochemical measurements. The results show that the optimal Al-based superhydrophobic coating with a static water contact angle of (155.2±0.5)° and a sliding angle of (3.5±1.3)° is obtained at the anodization voltage of 20V. The corresponding corrosion current density (Icorr) is reduced by 2 orders of magnitude and the corrosion potential (Ecorr) shifts from -0.629V to -0.570V compared to the bare Al substrate, indicating excellent corrosion resistance. Besides, the as-prepared optimal Al-based superhydrophobic coating also suggests good mechanical stability.

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    Microstructure Evolution and Impedance Spectroscopy Characterization of Thermal Barrier Coating Exposed to Gas Thermal-shock Environment
    Wen-long CHEN, Min LIU, Ji-fu ZHANG, Jin-bing SONG
    2017, 45 (10): 79-87.   DOI: 10.11868/j.issn.1001-4381.2016.000713
    Abstract ( 602 ( PDF (17919KB)( 207 Citation

    Gas thermal-shock experiment of thermal barrier coatings (TBCs) was carried out in air up to 1250℃ in order to simulate the thermal cycling process of the engine blades during the start heating and shut down cooling. The growth of thermal growth oxide (TGO) layer and microstructure evolution of YSZ layer during thermal cycling process were investigated systematically by electrochemical impedance spectroscopy testing and SEM. The results show that the thickness of TGO layer increases when increasing the frequency of thermal cycling, and the impedance response of middle frequencies is more and more remarkable. Meanwhile, initiation and growth of micro-cracks occur in YSZ layer during the gas thermal-shock experiment. The corresponding impedance characterization of YSZ layer after 100 cycles is similar to the as-sprayed sample, indicating that micro-cracks in short time could heal since the YSZ micro-cracks sinter at high temperature. But after 300 cycles, the impedance spectroscopy of YSZ layer is quite different to the as-sprayed sample, with the corresponding impedance of particle-gap of YSZ more and more remarkable with the increase of the thermal-shock times, indicating that non-healing micro-cracks form in the YSZ layer, which may be the main reason to induce the failure of YSZ layer.

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    Self-lubricating Coating Prepared by Electro-spark Deposition Using Electrode with Drilled Holes at End Face
    Tong-kun CAO, He SUN, Xiao-ming WANG
    2017, 45 (10): 88-94.   DOI: 10.11868/j.issn.1001-4381.2016.000691
    Abstract ( 512 ( PDF (9857KB)( 397 Citation

    Cu-MoS2 self-lubricating coatings were prepared on high speed steel by electro-spark deposition (ESD) by electrode with drilled holes at the end of faces. The holes were filled with MoS2. The composition and micro morphology of the coatings were analysed. The effects of capacitance and deposition time on coating thickness were studied, and also the friction performance and wear mechanism were studied. The results show that there is nothing but MoS2 and Cu exist in the coating fabricated by this way. The micrographs show that the coating surface is uneven and many pores existing on the surface, showing typical characteristics of ESD; the surface quality is the best when it was prepared in the 3rd grade capacitance. Coating thickness firstly increases and then decreases with the increase of capacitance and deposition time. The self-lubricating coating prepared in the 3rd-grade capacitance has the lowest friction coefficient. The friction coefficients of the self-lubricating coatings prepared in the 1st and the 3rd grades stay almost constant with the increase of friction time. The friction coefficient of self-lubricating coatings prepared in the 5th grade show a clear upward trend when friction time increases. Scanning electron microscope images show shear-slip phenomenon on the wear surface.

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    Microstructure and Properties of Ti-5553 Alloy for Aerospace Fasteners
    Qing-yun ZHAO, Yang YOU, Li-dong WANG, Li-min DONG, Feng-lei LIU
    2017, 45 (10): 95-102.   DOI: 10.11868/j.issn.1001-4381.2016.000170
    Abstract ( 1065 ( PDF (19496KB)( 332 Citation

    The effect of heat treatment on microstructure and mechanical properties of Ti-5553 alloy was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that when the alloy is treated in α+β phase zone, tensile strength decreases with raising solution temperature due to decreasing the content of primary α-phase and increasing the size and volume fraction of β phase. A lot of secondary α-phase precipitates from grain boundary and intragranular with β phase transformation during aging treatment. The size of secondary α-phase has significant influence on tensile strength, secondary α-phase coarsens gradually with the increase of aging temperature, resulting in the decrease of tensile strength. It is suggested that for 1240MPa aerospace fasteners the solution temperature of Ti-5553 should be under Tβ, thus adequate β phase, where a lot of secondary α phase precipitates from, is good for the required high strength. Meanwhile, a certain percentage of primary α-phase is kept for acquiring good ductility and toughness. After solution treatment at 810-820℃ for 1.5h, water quenching plus aging at 510℃ for 10h, Ti-5553 shows a better mechanical property with tensile strength 1500MPa, elongation 14.8% and reduction of cross-section area 38.6%. Lots of dimples can be found in tensile fracture after solution treatment and solution+aging treatment, which demonstrate Ti-5553 with good ductility and toughness.

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    Influences of PAN Fiber on Performance of Automobile Friction Materials
    Bo-wei LIU, Ya-lin LI, Yong LIU, Yang YANG, Bing TANG, Xiang-ming KUANG
    2017, 45 (10): 103-110.   DOI: 10.11868/j.issn.1001-4381.2015.001439
    Abstract ( 726 ( PDF (6576KB)( 215 Citation

    The PAN (Polyacrylonitrile) fiber enhanced friction materials were prepared by hot-press method based on a low metal formula, and the influences of PAN fiber content on the physical performance mechanical property, friction and wear properties and brake noise of the friction materials were investigated. The results show that as the PAN fiber content increase, the density decrease, and the porosity, shear strength and compress deflection of the friction material increase firstly then decrease; adding PAN fiber to the friction material has little influence on the nominal friction coefficient, but will reduce the anti-high temperature wear performance, and as the content increases, the friction coefficient increases; however, adding PAN fiber will improve the friction and wear rate of materials, but with the PAN fiber content increasing, friction and wear rate exhibits the tendency of decreasing firstly and then slightly increasing; adding adequate PAN fiber is conducive to the suppression of noise generation, when the PAN fiber content is about 3%-5%, the noise performance is the best.

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    Acrylic Acid Improved Nylon 66 Fabric by Electron Beam Irradiation-induced Grafting
    Wei SANG, Lan ZHOU, Xin-xing FENG, Jian-chun ZHANG
    2017, 45 (10): 111-116.   DOI: 10.11868/j.issn.1001-4381.2015.001319
    Abstract ( 648 ( PDF (4326KB)( 266 Citation

    Acrylic acid was grafted onto nylon 66 fabric by the electron beam irradiation method. Effects of different grafting conditions on grafting reaction were investigated. Fourier transform infrared spectroscopy(FTIR), thermo gravimetric analyzer(TGA), scanning electron microscope(SEM) and YG065 type fabric strength tester were used to characterize the chemical structures, thermal properties, surface morphology and mechanical properties of these prepared nylon 66 fabric samples. And the anti-dripping performance was evaluated by the vertical burning. The results show that in FTIR spectrum new absorption peeks at 1720.2 cm-1 and other wave numbers are assigned to the carboxyl groups, which imply that acrylic acid is successfully grafted to the nylon 66 molecular. The anti-dripping performance of nylon 66 fabric is improved significantly after grafting. It can be attributed to the cross-linked char layer which subsequently provides a support for the melting fiber. However, the mechanical properties of grafted samples decrease to some extent. With the increase of grafting ratio, the onset temperatures of grafted samples decrease gradually, while the char-forming performance enhances significantly. Besides, the damage length and droplet velocity of grafted samples become shorter and lower, and the tensile strength at break increases slightly.

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    Evaluation and Application of Tensile Strength Prediction for CFRP Bars
    Bin WANG, Yong-xin YANG, Qing-rui YUE, Bin ZENG
    2017, 45 (10): 117-123.   DOI: 10.11868/j.issn.1001-4381.2015.001435
    Abstract ( 671 ( PDF (870KB)( 248 Citation

    Based on the prediction formula of tensile strength for CFRP bars, weight of influence of the typical factors on material strength was evaluated, and the mechanism of intensity compensation in the process of preparing CFRP bar was proposed. The results show that the effect of typical factors of carbon fiber tensile strength and volume fraction effect on the tensile strength of CFRP bars is most significant (influence rate:39.1%-46.7% and 43.5-52.6%). They are the most important factors that determine the tensile properties of CFRP bars. Nominal diameter has a certain effect on the tensile strength of CFRP bars (influence rate:7.1%-15.4%). Influence of resin matrix strength on the tensile strength of the CFRP bar is not obvious (influence rate:0.3%-1.0%). Compared to the other three factors, the influence of the tensile strength of resin can be nearly neglected. According to the intensity compensation rule of the typical factors, the strength and volume fraction of carbon fiber in CFRP bars can be easily inferred.

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    Tensile Property and Influence Parameters of Bonded Repaired Composite Laminates
    Heng-chang NIE, Ji-feng XU, Zhi-dong GUAN, Zeng-shan LI, Xin WANG
    2017, 45 (10): 124-131.   DOI: 10.11868/j.issn.1001-4381.2015.000802
    Abstract ( 653 ( PDF (8618KB)( 267 Citation

    Bonded repair is efficient and widely-used repair technique for composite structures. Tests were conducted to study the tensile property of scarf repaired and external bonded repaired composite laminates with different repair parameters. The results show that the recovery of failure strength of scarf repaired laminates is about 66%-91% while external bonded repaired laminates is about 44%-61%.When reducing scarf ratio, repairing in double sides, curing in autoclaves, the scarf repair specimens can reach a higher recovery rate of failure strength. When repairing in double sides, enlarging the size of patches, the external bonded repaired specimens can also reach a higher recovery rate of failure strength. Based on the test results, finite element models were established to predict the failure loads and failure modes of specimens, and to analyse the stress distribution and progressive damage process of specimens, which can provide a reference to the designing in the repair projects.

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    Nonlinear Ultrasonic Characterization for Intergranular Corrosion Susceptibility of 304 Austenitic Stainless Steel
    Tian-yu HOU, Ping LI, Lei CHEN, Jie ZHAO, Ting-ju LI
    2017, 45 (10): 132-137.   DOI: 10.11868/j.issn.1001-4381.2016.000130
    Abstract ( 800 ( PDF (4462KB)( 318 Citation

    The variation law of nonlinear ultrasonic parameters for the samples sensitized at 650℃ for 2, 6, 10h was discussed using nonlinear ultrasonic testing technique and XRD pattern as well as microstructure. The results indicate that normalized nonlinear parameters(β/β0) of the samples show a monotonous growth trend with the increase of the sensitized time, and normalized nonlinear parameters(β/β0) of the samples sensitized with 2, 6, 10h increase to 28%, 32% and 43% respectively compared with that of the base material, meaning that it is feasible to use nonlinear parameter to characterize the sensitivity degree. It is analyzed that the mismatch between the carbide (Cr23C6) precipitated on the grain boundary and the austenitic matrix causes the local strain fields which interfere with the propagation of ultrasonic wave in the solid sample. In addition, the increment of precipitation phase exacerbates further the distortion of the ultrasonic with prolonging of the sensitization time.

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    Acoustic Emission Characteristics of Hydrogen Charged Cr-Mo Steel During Deformation
    Quan-quan TENG, Yue WANG, Yi-liang YOU, Zheng ZHANG
    2017, 45 (10): 138-144.   DOI: 10.11868/j.issn.1001-4381.2015.001146
    Abstract ( 664 ( PDF (6978KB)( 232 Citation

    Tensile test was conducted on 2.25Cr-1Mo steel specimens that were electrochemically hydrogen charged and acoustic emission signals were collected in the real-time stretching process. The results show that tensile strength of 2.25Cr-1Mo steel with hydrogen charging is 536.30MPa, decreased by approximately 57MPa and reduction of area is 43.62%, decreased by 7%, compared with the specimens without hydrogen charging. Hydrogen embrittlement-induced regions known as "fisheyes" and quasi-cleavage morphology are observed on the tensile fracture surface. The AE signals activity in the elastic stage of hydrogen charged 2.25Cr-1Mo steel is enhanced, but the acoustic emission signals activity in the yield stage is decreased. The cumulative absolute energy of AE signals of hydrogen charged specimens during deformation is almost one order magnitude lower than that without hydrogen charged specimens. The AE signals amplitude generated by the hydrogen charged specimens is about 0.33mV lower than that of the specimens without hydrogen charging during tensile deformation, and that the bandwidth of signal is reduced by 0.06MHz. Though the analysis of AE signals, it is found that tensile deformation microscopic mechanism of hydrogen charged specimens is that dislocation emission and motion is enhanced but dislocation cross-slip is inhibited by hydrogen.

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