2014 Vol. 31, No. 6

2014, 31(6): .
CaCO3 reinforced maleated castor oil resin and its foam plastics
WANG Hongjuan, RONG Teng, RONG Minzhi, ZHANG Mingqiu
2014, 31(6): 1383-1393.
Using maleated castor oil (MACO) as main raw material, enviromental friendly CaCO3/MACO composites and their foam plastics were prepared with inorganic filler calcium carbonate (CaCO3) particle as reinforcement. Effects of addition of CaCO3 on mechanical properties, dynamic mechanical performance and thermal stability of MACO were analyzed. And the interfacial interaction between inorganic particles and matrix was analyzed. The results show that CaCO3 content and the interfacial bonding between CaCO3 and MACO matrix are the key factors influencing the strength of composites. With increasing of CaCO3 content, stiffness of CaCO3/MACO composites increases significantly. At 60% mass ratio of CaCO3 loading, tensile and bending strength attain the maximum values of 26.7 MPa and 46.2 MPa, respectively, which are comparable to some general commercial plastics. Dynamic mechanical analysis and thermal stability analysis show that the addition of CaCO3 improves storage modulus, glass transition temperature and thermal decomposition temperature of maleated castor oil matrix plastics. These behaviors are attributed to the good interfacial adhesion between CaCO3 and the carboxyl, carbonyl of MACO resin by hydrogen bonding and coordination bonding. CaCO3 can also reinforce CaCO3/MACO composite foam plastics. When density of foam plastics is 0.24 g/cm3, by adding 20wt% of CaCO3, compared with pure foam plastics, the compressive strength and modulus of the composite foam plastics are increased by 142.0% and 211.5%, respectively. The addition of inorganic filler into castor oil derived polymer can reduce the usage of petroleum based components and the cost of material, while increase compatibility of CaCO3/MACO composites with environment.
Effects of glass fiber reinforcement type on property of phenolic foam
LU Jie, YANG Zhongjia, GU Yizhuo, LI Min, ZHANG Zuoguang
2014, 31(6): 1394-1401.
Aiming at the defects of phenolic foam, such as brittleness and low strength, three kinds of glass fiber reinforcement with different forms, i.e. short chopped glass fiber (SGF), glass fiber needle with phenolic resin impregnated and cured (GFN) and 3D spacer grille fabric with phenolic resin impregnated and cured, were adopted to reinforce phenolic foam. The effects of fiber content and length on the compressive property of phenolic foam were studied. The compressive and thermal insulation properties of phenolic foams reinforced by different glass fibers were compared. The results indicate that phenolic foam reinforced by 5% mass ratio of SGF with 3 mm length has the largest specific compressive strength, which increases by 21% than pure foam. Specific compressive strength of phenolic foam reinforced by 25% mass ratio of GFN with 5 mm length increases by 8%. Specific compressive strength of phenolic foam reinforced by 3D spacer grille fabric slightly reduces, while its compressive strength (0.239 MPa) meets the requirement of load-bearing phenolic foam. Compared with phenolic foam without fibers, the thermal conductivities of phenolic foams reinforced by SGF or GFN are a bit higher, but still meet the requirement of efficient thermal insulation materials, while the thermal conductivity of phenolic foams reinforced by 3D spacer grille fabric increases apparently.
Basalt fiber modified with graphene oxide and properties of its reinforced epoxy composites
YE Guorui, YAN Yiwu, CAO Hailin
2014, 31(6): 1402-1408.
To improve the interfacial properties of basalt fiber/epoxy composites, the graphene oxide modified with coupling agent was introduced into sizing agent, and the modified sizing agent was used to modify basalt fiber and the graphene oxide-basalt fiber/epoxy composites were prepared. The modification effect of graphene oxide was characterized by FTIR. The effect of modified sizing modification on surface of basalt fiber and composites cross-sectional morphologies and reaction mechanism were investigated using SEM. The results show that coupling agent is successfully grafted onto the surface of graphene oxide. Surface roughness and reactive functional groups are increased after basalt fiber being infiltrated in sizing agent modified by graphene oxide, and the mechanical interlocking and chemical bonding of the graphene oxide-basalt fiber/epoxy interface are enhanced, the interface bonding strength is improved, the fracture strength of basalt fibers is improved by 30.8% and the interlaminar shear strength of graphene oxide-basalt fiber/epoxy composites is improved by 10.6%.
Self-organization preparation of poly (lactic acid) poly (ethylene oxide) composites with compositional gradient structure based on non-equilibrium phenomenon
LI Ya'nan, YAN Xinping, CAO Xinxin, YANG Jia, LI Jigong, DAI Yahui
2014, 31(6): 1409-1415.
Based on thermodynamic non-equilibrium phenomenon, by setting the blend solution poly(lactic acid) (PLA)-poly(ethylene oxide)(PEO)-CHCl3 in the open system at non-equilibrium conditions to be dried, the compositional gradient phase-separation structures of internal PLA-PEO composites were successfully self-organized. The compositional gradient structure in the composite blend films was characterized by polarized optic microscopy (POM) and the attenuated total reflectance Fourier transformed infrared (ATR-FTIR) spectrum. It is found that the compositional gradient structure is formed in composite at thermodynamic non-equilibrium state. PLA concentrates at the air-side where the energy flows out while PEO at the bottom where the energy flows in, as the system is away from the equilibrium state. The composition of the resulted films distributes gradually along with energy movement direction and presents the tendency of increase with the system away from the equilibrium state. And thermodynamic equilibrium state is the major factor that affects the formation of compositional gradient structure.
Effects of surfactant on suspension property of diamond in resin and associativity between diamond and resin
CHEN Jing, WAN Long, SHI Dan, WANG Junsha, LIU Huijuan, FANG Wenjun
2014, 31(6): 1416-1421.
The surface modifications of diamond were carried out respectively by KH550 silane coupling and polyelectrolyte type surfactant polyethyleneimine (PEI), the effects of KH550 and PEI on surface potential performance of diamond, suspension property of diamond in polyamide imide resin liquid and associativity of diamond and resin were analyzed.The results show that compared to the original diamond abrasive, the surface electrical behavior of modified diamond changes significantly. Zeta potential of diamond increases observably under acid condition, and increases the repulsive force among particles. So it will improve the suspension stability of diamond in the resin liquid. Both surface wettability of resin to diamond and the interface combination are also improved, thus improving the cutting performance of wire saw. The modification effects of diamond modified by KH550 are better than that of PEI.
Degradation behavior of residual films of controlled release fertilizers with nano-TiO2 LDPE composites
LI Lixia, CAO Bing, LI Hongyan, XIAO Qiang, NI Xiaohui, XU Qiuming
2014, 31(6): 1422-1427.
Nano-TiO2 and low density polyethylene (LDPE) were combined to form coating fluids, and nano-TiO2-LDPE composite-coated controlled release fertilizers were prepared in a spouted fluidized bed coating equipment. Based on the research of their release characteristics via water immersion method, the mass loss rates were measured after different irradiation time by artificial accelerated ageing test. The effects of nano-TiO2 on photo-degradation behavior of residual films were systematically studied by using FT-IR spectroscopy, DSC and viscosimetry. And changes in molecular mass, carbonyl index and others during degradation were discussed. It is found that under the function of photo-catalyst, the urea release rate of controlled release fertilizer has a certain degree of delay, the release period becomes longer and the degradation of residual film is remarkably promoted by hydrophobic nano-TiO2. Furthermore, residual film shows the best degradation property when the mass fraction of hydrophobic nano-TiO2 is 1%. With the increasing of degree of residual film degradation, the carbonyl index and crystallinity of LDPE in residual film increase, and the viscosity-average molecular mass decreases.
Pultrusion process and interface performance of new light wood GFRP sandwich panels
SHI Dong, LIU Weiqing, QI Yujun
2014, 31(6): 1428-1435.
Alkali-free glass fiber bundle, chopped fiber, unsaturated resin and paulownia wood were selected to prepare light wood-glass fiber reinforced plastic (GFRP) sandwich panels. And the pultrusion process was investigated. Research shows paulownia wood-GFRP sandwich panels with good apparent performance can be prepared by suitable temperature of mould heating area (gel area) and pultrusion rate which are 160 ℃ and 10 cm/min, respectively. Compared with panels maded by vacuum infusion process, as for the sandwich panels with or without groove on surface of wood core, the interface bonding property between paulownia wood and GFRP panels was investigated by double cantilever beam (DCB) test. The results show that pultruded paulownia wood-GFRP sandwich panels are up to ones of vacumm process in interfacial bonding properties. The measure of groove on surface of core can effectively increase the energy release rate. And its effect is more obvious for panels made by vacumm infusion process. The resin is difficult to fill groove adequately to form resin nails in pultrusion process, and the groove can not improve the interfacial adhesion efficiently. So ungrooved core can reduce the production process and production difficulty when the interface performance requirements are not strict.
Effects of MAH on properties of dry method esterified starch/PLA composites
ZUO Yingfeng, GU Jiyou, YANG Long, TAN Haiyan, ZHANG Yanhua
2014, 31(6): 1436-1445.
Maleic anhydride (MAH) esterified starch was synthesized by dry method with corn starch and MAH as raw materials, and esterified starch/polylactic acid (PLA) composites were prepared by melt extrusion. Effects of MAH amounts on the degree of crystallinity and compatibility of composites were studied. At the same time, the influence of compatibility and degree of crystallinity change on thermal property, melt flow property, mechanical property, water resistance and rheology property of composites were investigated. FTIR results show that MAH esterified starches were successfully synthesized by dry method. Degree of substitution of esterified starch gradually increases with the increasing of MAH amounts, and the reaction efficiency is up to 90%. XRD and DSC results show that with the increasing of MAH amounts, the degree of crystallinity of composites decreases, which makes the compatibility between starch and PLA increase gradually. The decrease of degree of crystallinity and the improvement of compatibility cause the decreased glass transition temperature and the increased melt flow and water resistance. The mechanical properties and rheological properties are affected by the combination of the compatibility and degree of crystallinity. The tensile strength, bending strength, storage modulus and complex viscosity increase gradually when MAH amount increases from 0 to 1.0wt%, but these properties decrease gradually when the amount of MAH is more than 1.0wt%.
Stress softening and dynamic properties of nano-graphite/natural rubber composites
FANG Qinghong, SONG Bo, GAO Yu, WANG Na, MA Chi, DAI Caiyun
2014, 31(6): 1446-1451.
The nano-graphite/nature rubber (NR) composites with different sizes of nano-graphite as fillers were prepared. The influence of nano-graphite with different sizes (30, 80, 150 nm) on the properties of nano-graphite/NR composites such as stress softening effect (Mullins effect), Payne effect, the dynamic heat generation and loss factor, were investigated. The results show that with the increase of size of nano-graphite, the effect of nano-graphite reinforcement on nano-graphite/NR composites is obvious and stress softening effect exhibites almost the same upward trend, dynamic loss factor increases while the Payne effect of composites decreases obviously, on the other hand, with the increasing of dynamic loss factor, the dynamic heat generation increases. The fact that the dynamic heat generation of composites closely relates to the filler network can be concluded. The results of SEM and Payne effect analysis demonstrate that the larger size nano-graphite has a good dispersion in rubber, while the smaller size nano-graphite is easy to aggregate.
Preparation and properties of modified MgO nanoparticles/PLLA composite films
CAO Xiuxiang, ZHANG Jing, WANG Liang, YANG Jinjun, CHEN Minfang
2014, 31(6): 1452-1456.
To improve the degradability of poly (L-lactic acid) (PLLA) and prepare the bone repair material with good mechanical properties, the composites consisting of PLLA and MgO nanoparticles (MgO-NPs) have been prepared. The result suggests that, compared with pure PLLA, modified MgO nanoparticles (g-MgO-NPs) significantly enhance its dispersion in PLLA matrix and its interfacial bonding with PLLA matrix. With addition of 4%(mass ratio) g-MgO-NPs, the tensile strength of film increases from 10.6 MPa to 30.1 MPa, and its elongation at break decreases from 71% to 59%. The pH of film tends to be a relatively stable value and be close to that of the physiological saline after degradation. It reveals that g-MgO-NPs improve the degradability and mechanical properties of polylactic acid composite films in a certain extent.
Fabrication of grape seed polyphenols/gelatin composite fibers in aqueous by electrospinning
XING Zuge, HAN Xiaotong, SI Shaoxiong, YAO Yongyi, ZHANG Qiyi
2014, 31(6): 1457-1466.
The grape seed polyphenols/gelatin composite fibers were prepared by electrospinning technique using self-designed heat-retaining device equipped system devices and using water as solvent. The influences of electrospinning process conditions including gelatin concentration, temperature, voltage, flow rate and the content of grape seed polyphenols on grape seed polyphenols/gelatin composite fiber morphologies were investigated. The results show that the average diameters of fibers decrease and then increase with the increasing of spinning temperature and voltage, and increase with the increasing content of grape seed polyphenols when the gelatin concentration is 24wt%. The work efficiency is improved significantly from 0.25 mL/h to 0.90 mL/h (spinning speed) by adding an appropriate amount of grape seed polyphenols. However, the beads appear on surface of the fibers, when the mass ratio of grape seed polyphenols to gelatin is over 1:30, the electrospinning solution even got worse and could not spin when mass ratio of grape seed polyphenol to gelatin is over 1:20. The composite fibers have the finest structure with average diameter of 515 nm when the concentration of gelatin is 24wt%, the mass ratio of grape seed polyphenols to gelatin is 1:50, the temperature is 55 ℃, the voltage is 20 kV, the distance is 12 cm and the flow rate is 0.90 mL/h. The addition of grape seed polyphenols not only improves the efficiency of spinning, but also causes composite nanofibers membrane to find important application in biomedical field, especially in wound dressings due to its good antimicrobial activity and crosslinking effect with gelatin.
Acoustic emission behavior of steel fiber reinforced fly ash geopolymer under uniaxial compression
TAO Xin, XIE Ziling, HAO Shengwang, ZHOU Huafei
2014, 31(6): 1467-1475.
In order to investigate the relationship between the macroscopic mechanical behavior and mesoscopic damage evolution characteristics of fiber reinforced geopolymer samples, a series of uniaxial compression tests were carried out on steel fiber reinforced fly ash geopolymer composites with different fiber volume contents (the volume ratios of fiber to mixture). Based on the acoustic emission technique, the acoustic emission behaviors during the compression process of samples were monitored. The influence of fiber volume contents on the failure behavior and the characteristics of acoustic emission of geopolymer under uniaxial compression was investigated. The results show that the strength, ductility, the increasing slope and average frequency of acoustic emission waveform increase as the fiber content increases, and the failure mode of the samples changes from brittle catastrophic pattern to ductile pattern gradually. In the earlier stage of destruction, the acoustic emission hit rate and energy release rate (abbreviate energy rate) of samples with the fiber volume content of 0 or 0.5% maintain a higher level, and finally leads to the catastrophic rupture of the samples. However, the fiber volume content of 2.0% makes the acoustic emission hit rate and the energy rate reach the peak at the inflection point of stress-time curve, and then decrease slowly, leads to the ductile rupture of samples finally. Therefore, predicting the occurring of catastrophic rupture depends on the rapid increasing of acoustic emission hit rate or energy rate simply, may gives false information sometimes.
Microstructure and sound absorption property of diatomite/polyurethane porous composites
LIN Jian, GUO Jiao, ZHAO Yu, DUAN Lianfeng, JIN Songzhe
2014, 31(6): 1476-1480.
The diatomite/polyurethane composites with multiple aperture communicating channels were successfully prepared with diatomite and polyurethane. The effect of the contents of diatomite, foam stabilizer and plasticizer on the microstructure, compressive strength and sound absorption property of diatomite/polyurethane composites were studied. The results show that the diatomite/polyurethane porous composites have good compressive strength and sound absorption property. The diatomite/polyurethane composite with 65wt% diatomite exhibits excellent sound absorption property, the peak of sound absorption is around 1 600 Hz, and the sound absorption coefficient is greater than 0.9. The frequency width, whose sound absorption coefficient is higher than 0.56, is wider than 2 000 Hz.
Preparation of mesoporous tourmaline / TiO2 composites and their simulated sunlight photocatalytic activity
XIONG Jingjing, LI Kexin, HUANG Liming, YAN Liushui
2014, 31(6): 1481-1489.
A series of mesoporous tourmaline/TiO2 composites were prepared by using one-step sol-gel co-condensation combined with solvothermal synthesis technique, and their phase structure, morphology, porosity, optical absorption property, as well as composition and structure were characterized. The results show that the tourmaline/TiO2 composites exhibit pure anatase crystalline phase, uniform mesostructure, large surface area (205-242 m2·g-1), uniform pore size distribution (3.4-3.8 nm) and low band gap energy (3.0 eV). The as-prepared composites were successfully applied to the degradation of aqueous organic pollutants rhodamine B and norfloxacin under simulated sunlight irradiation. The degradation kinetics researches show that, the addition of tourmaline improves the photocatalytic quantum efficiency of TiO2 and reduces the band gap energy of TiO2. The composites with 1wt%-5wt% tourmaline loading exhibit the higher rates to the rhodamine B degradation and the degradation rates of tourmaline/TiO2 composites to the norfloxacin are higher than that of the pure TiO2.
Preparation and adsorption properties of ZnO nanowire/macroporous SiO2 composites
LI Xuefei, SHANG Chuanyang, ZHANG Ruifeng
2014, 31(6): 1490-1496.
Ternary mixture solution of Zn(Ac)2/polyethylene glycol 600 (PEG600)/H2O was used as precursor, Zn(Ac)2 was hydrolyzed via two-step heating processes at temperature range of 100-200 ℃ and finally ZnO seeds formed on hole wall of SiO2 by calcination at high temperature. Zinc-ammonia complex solution was used as zinc source, at 90 ℃ it was thermally decomposited and the resulted Zn(OH)2 was deposited in the channels. ZnO nanowires were in-situ prepared through hydrothermal synthesis at 100 ℃. The compositions of ternary precursor were changed to control the size and distribution of ZnO seeds which could further control the morphology of ZnO nanowires. And ZnO nanowires with diameter of 15-20 nm were eventually obtained, which were uniformly dispersed in the 3D macropores as random coil. XRD and Raman spectroscopy confirm that the nanowire has hexagonal wurtzite crystal structure. The adsorption properties of ZnO nanowire/macroporous SiO2 composites were investigated by testing its immobilizing ability against the porcine pancreatic lipase. The experimental results show that the adsorption capacity of composites is 5-6 times than that of macroporous SiO2 materials. The maximum of adsorption capacity is up to 286.8 mg·g-1 and the highest enzyme activity is 425.5 U·g-1. Both adsorption capacity and the immobilizing ability against lipase remain almost unchanged when the samples are soaked in buffer solution for 48 h.
Compression performances and interfacial properties of carbon fiber-foam metal sandwich beams with aramid fiber toughening
SUN Zhi, SHI Shanshan, SUN Shiyong, CHEN Haoran, HU Xiaozhi
2014, 31(6): 1497-1502.
To fully understand the underlying toughening and reinforcing effect of short aramid fibers to interfacial and structural properties of composite sandwich structures, experimental studies were carried out for investigating toughening effects and mechanisms of aramid fiber interfacial toughening on a sandwich beam, consisting of an foam aluminum covered with two carbon fiber/epoxy composite surface layers. Low-density short aramid fiber films were inserted at the interface during the sandwich fabrication process, to improve the interfacial bonding properties through the bridging effect of short fibers. In-plane compression tests were carried out to investigate the effect of short aramid fibers on structural properties and failure mode of sandwich beam. The critical energy release rates of face-core interface with various toughening parameters were measured under asymmetric double cantilever beam (ADCB) condition. According to the results, the in-plane compression strength of sandwich beams and critical energy release rates between face sheet and core were all improved for all specimens toughened with short Kevlar fibers, especially for specimens toughened with hybrid-length short Kevlar fibers. The interfacial toughening performance and underlying mechanisms for short aramid fiber toughening were discussed and analyzed using SEM.
Influence of pore distribution nonuniformity on strength of ceramic
FU Yunwei, ZHANG Long, NI Xinhua, LIU Xiequan, RAN Chao
2014, 31(6): 1503-1508.
Pores, inclusions and other defects in ceramics are inevitable due to the special process, and they generally ununiformly distribute, this nonuniformity has big impact on ceramic properties. Base on the pore distribution characteristic in ceramics, the parameter uniformity was defined to quantize the uniformity of pore and inclusions distribution, and an image processing method was introduced to confirm the uniformity. According to the image processing results, ceramic was divided to two parts, the effective matrix phase enriched pores and the effective grain phase without pores. Based on interact direct derivative (IDD) estimate, the relationship between strength and uniformity was analyzed. The results indicate that uniformity has significant influence on the strength of ceramic, the strength reduces with uniformity decreasing, especially when the uniformity is lower than 0.2, and influence of uniformity is limited when it is higher than 0.5.
Effect of Bi2O3 flux on properties of CaO-B2O3-SiO2/Al2O3 glass-ceramic composites
FANG Yihang, WANG Huanping, LI Zhigang, HUANG Xiaohua, ZHAO Xianrui, LI Qintao
2014, 31(6): 1509-1515.
CaO-B2O3-SiO2(CBS) glass powder and Al2O3 ceramic powder were used as the raw materials. Appropriate amount of Bi2O3, which was used as flux, was added into the glass-ceramic composites consisting of CBS and Al2O3 with a fixed mass ratio of 50:50. The effects of Bi2O3 flux on the sintering character, dielectric properties, bending strength and thermal expansion coefficient of CBS/Al2O3 composite were investigated. The results show that Bi2O3 flux can lower the transition temperature and the viscosity of CBS glass, which promotes the densifying of CBS/Al2O3 composites, and results in the CBS/Al2O3 composite which has relatively dense structure and less porosity can be prepared by sintering at 880 ℃. However, the excess addition of Bi2O3 will deteriorate the sintering character, dielectric properties and bending strength of CBS/Al2O3 composites for the viscosity of CBS glass is too low. When the additive amount of Bi2O3 is 1.5wt% of CBS/Al2O3 composite, the densest CBS/Al2O3 composite which has a density of 2.82 g·cm-3can be obtained by sintering at 880 ℃. This CBS/Al2O3 composite also has excellent dielectric properties (dielectric constant is 7.21, dielectric loss is 1.06×10-3), the bending strength is 190.34 MPa, and the thermal expansion coefficient from 0 to 300 ℃ is 3.52 ×10-6 K-1.
An accurate modeling method based on cord/rubber composite material micromechanics
REN Jie, ZHONG Jianlin, MA Dawei
2014, 31(6): 1516-1524.
To study the compression expansion mechanical characteristic of adaptive base, an accurate modeling method based on fiber cord/rubber composite material micromechanics was proposed. The method was based on the precise estimation for material parameters of cord and rubber. The Mooney-Rivilin constitutive model was used to discribe rubber material, and correctness of constitutive model was verified by tension tests. Amending of cord tension modulus was based on bundle cord tension test rule. Based on the methods above, numerical simulation and experimental study of adaptive base compression expansion process were conducted. Results show that the accurate modeling method can simulate the compression expansion characteristics of base effectively. The distributions of stress and strain of cord and rubber materials in base, and their variation laws can be obtained. The study can provide technical support for further research and actual application of adaptive base.
Effect of opening and boundary conditions on compressive buckling properties of composite one-third cylindrical shell
WU Pengfei, CHENG Xiaoquan, ZHANG Jikui, ZHANG Tao, XU Yahong
2014, 31(6): 1525-1531.
The compressive buckling properties of three types of composite one-third cylindrical shells were studied, including intact shell, shell with reinforcement around the opening hole and shell with opening hole and cover. The effect of opening and cover on compressive stability of cylindrical shell was analyzed through the axial compressive buckling strength of three typical composite cylindrical shells. The results show that the opening hole significantly decreases the axial compressive buckling strength. Although axial compressive buckling strength can be restored partly by applying a cover, it can hardly be restored as it was. Axial compressive tests of warp knitting fabric composite one-third cylindrical shells with opening hole and cover were conducted. Compared with the identical structures made of flat knitting composites, the axial compressive buckling strength decreases obviously. In order to explore the cause for the serious axial compressive buckling strength drop, finite element analysis of composite one-third cylindrical shell model with nonuniform loading was conducted. The numerical results show that nonuniform boundary loading decreases the bearing capability and designing the boundary loading according to shell stiffness distribution can improve the bearing capability.
Mechanical property analysis of composite adhesively bonded sandwich pipe joints
TAN Chao, LI Yulong, GUO Yazhou
2014, 31(6): 1532-1542.
An analytical model for the joints of composite honeycomb sandwich pipes widely used as the aviation structures, which is the most vulnerable part, was developed to investigate the mechanical characteristics of adhesively bonded composite honeycomb sandwich pipe joints. Equivalent elastic parameters of the honeycomb core were obtained according to Gibson's correction formula, and the governing equations were acquired by using the classic composite shell theory and linearly elastic theory, and it was solved through the state space method. The adhesive shear stress and peel stress of pipe joint under torgue and bending moment were calculated by the proposed analytical model. And finite element method was used to simulate the model and the simulated results were compared with the model calculated results. In addition, the influence of overlap length on adhesive stress was analyzed.
Numerical prediction of tensile properties and damage evolution of three dimensional-four directional braided CMCs
SHI Duoqi, JING Xin, YANG Xiaoguang
2014, 31(6): 1543-1550.
A numerical method was developed to simulate the effective elastic properties, strength and progressive damage evolution of three dimensional-four braided ceramic matrix composites(3D-B-CMCs). Firstly, the elastic properties of yarns were predicted using the composite cylinder assemblage (CCA) model and the strength were predicted by the global load sharing (GLS) model considering the strength distribution of fibers. Then a three dimensional unit-cell finite element model was constructed based on the geometric data from micro-CT images. After that, anisotropic damage model has been adopted in the fiber tows with Hashin failure criteria and damage evolution law based on the characteristic length of element. The model was coded as the ABAQUS/UMAT subroutine program and implemented into monotonic tension simulation of 3D-B-CMCs. The stress-strain curve was predicted and correlated well with the experimental curve, which verified the rationality of the method and the validity of the UMAT subroutine program. At the same time, more insights of the influence of different damage process on material mechanical behavior were concluded from the simulation, which provide information for the progressive damage evolution of the material fatigue and creep.
Roll deformation process simulation and rolling force calculation formula of copper clad aluminum composites
LI Jianyong, LUO Junting, SHEN Jianglong, GU Yongfei
2014, 31(6): 1551-1557.
A bimetallic composite rolling deformation partitioning model was established based on the finite element simulation of roll deformation process of copper clad aluminum bimetallic composites. The deformation zone was divided into five parts, namely, elastic region, single material plastic zone, back slip zone, knead rolling area and forward slip zone. On the basis of theoretical calculation formula of rolling load for single material, the rolling load calculation formula for bimetallic composites was proposed by simulating the rolling process of copper clad aluminum composites with variables of different Cu volume fractions. The rolling load formula was verified by rolling test and the finite element simulation of rolling process for copper clad aluminum composites with different reduction rates.
Thermal bending deformation of grid sandwich beam
ZHANG Rui, SHANG Xinchun
2014, 31(6): 1558-1565.
Considering internal heat conduction, the thermal bending deformation of grid sandwich beam when one side was heated was studied. It is assumed that the webs in the middle layer of the sandwich beam did not bend when the beam deformed. Taking the periodic character of the grid beam structure into account, the relationship of the internal force and the displacement was got through the equilibrium equation and the deformation coordination of the cell. By transfer matrix, the expressions of internal force and deformation of the sandwich beam depending on temperature were stablished. Using present model, the deformation of cantilever grid sandwich beam whose upper surface was heated was calculated. For the case that the number of cell is larger, the height of webs is smaller and the thickness of webs is close to one of panels,the deflection results computed by the presented model are in good agreement with finite element results.
Preparation and heat transfer performance of Ba(OH)2·8H2O/copper foam phase change composites
SHENG Qiang, XING Yuming
2014, 31(6): 1566-1572.
The compatibility of Ba(OH)2·8H2O with aluminum alloy and copper was studied by SEM and X ray energy dispersive spectrometer analysis methods after 50 thermal cycles. Results show that Ba(OH)2·8H2O displays a certain amount of corrosion in combination with aluminum alloy. Ba(OH)2·8H2O and copper present excellent compatibility. A simple method of successive vacuum absorption and padding was employed to prepare Ba(OH)2·8H2O/copper foam phase change composites. An experimental setup was built to study the heat transfer performances of Ba(OH)2·8H2O with and without copper foams. The steady state and transient heat transfer performances of Ba(OH)2·8H2O/copper foam composites were experimentally measured at room temperature. The results show that Ba(OH)2·8H2O/copper foam phase change composites have higher heat transfer rate, better heat transfer performance and lower supercooling degree than the pure Ba(OH)2·8H2O. The heat transfer experiments indicate that the thermal storage capacity of the composites decreases with the increase of ambient temperature in the high-temperature thermotank. When the ambient temperature is higher than the phase change temperature, some insulation measures should be considered for the phase change composites.
TiB2-50Co coatings prepared by high velocity oxygen fuel and their properties
CHEN Xiao, WANG Hongtao, JI Gangchang, WANG Yuwei, BAI Xiaobo
2014, 31(6): 1573-1580.
Three kinds of TiB2-50Co coatings were fabricated by high velocity oxygen fuel method at three different oxygen flow rates, including 322, 402 and 462 L/min.The microstructure and phase structure of TiB2-50Co coatings were analyzed by SEM and XRD. The microhardness was tested, and the properties of thermal shock resistance were tested by water quenching method. The corrosion resistance to molten Al-12.07wt%Si alloy and abrasive wear were investigated. Results show that the phases of three kinds of TiB2-50Co coatings are TiB2 and Co. Three kinds of TiB2-50Co coatings have denser structure, especially the coating prepared under oxygen flow rate 322 L/min has much denser microstructure, the lowest porosity(1.76%) and the highest hardness value (558±90) HV0.3. The coating prepared under oxygen flow rate 462 L/min has the worst thermal shock resistance performance with obvious microcrack. And the coatings have good durability in the molten Al-12.07wt%Si alloy after 60 h immersion test. The coatings have good abrasive wear performance after abrasive wear test with 6 N load, especially the coating prepared under oxygen flow rate 322 L/min has the best abrasive wear performance.
Realization methods of computational homogenization for thermal conductivity coefficient of composites
ZHANG Rui, WEN Lihua, YANG Linya, XIAO Jinyou
2014, 31(6): 1581-1587.
The computational homogenization method has been proved to be a valid method which can be used to predict the equivalent thermal conductivity coefficient of periodical-structure composites. Due to the unconventional load item form of the control equations, there is no corresponding load forms in general finite element software, and it is difficult to solve directly. An analogy method of constitutive relationships and field variables was presented, and it proves that the homogenization equations of equivalent thermal conductivity coefficient and equivalent elastic modulus are equivalent in this analogy. By utilizing the thermal strain method for homogenization equations of solving equivalent elastic modulus, a novel computational solving approach for equivalent thermal conductivity coefficient of homogenization equations was proposed. The equivalent thermal conductivity coefficient of unidirectional fiber reinforced composites and metallic honeycomb panel were calculated by using ABAQUS as platform, the calculation results agree well with reference results. This method provides a simple way for the computational homogenization of equivalent thermal conductivity coefficient of composites in common finite element software.
Numerical simulation and experiment for acoustic-optical fiber based detection of interfacial damage in FRP-retrofitted structures
XU Ying, LIU Zhian, SHAO Changjun
2014, 31(6): 1588-1596.
To ensure the reliability and safety of fiber reinforced plastic (FRP)-retrofitted structures, the detection of interfacial debonding is an important part of any reinforce quality inspection process. The principle and methodology of an acoustic-optical fiber non-destructive evaluation (NDE) technique based on free vibration theory of a thin plate was proposed for the detection of interfacial damage in FRP-retrofitted structures. A focused sound beam generated from variable frequency loudspeaker source can be controlled to form a locally vibration field of the surface of FRP-retrofitted structures. Local vibration anomalies caused by interfacial damage in the structure can be measured by surface-mounted optical fiber interferometer, and thus, interfacial damage can be detected, mapped, and quantified. Based on the results from both numerical and experimental studies, the feasibility of interfacial damage detection in FRP-retrofitted structures with the proposed technique is demonstrated.
Rheological properties and retardant mechanisms of two types of new inorganic composite flame retardant modified asphalts
WANG Chaohui, Li Rui, ZHAO Juanjuan, HE Hai
2014, 31(6): 1597-1603.
In order to solve the main problems about high toxicity, expensive cost and poor thermostability of asphalt flame retardants currently, two types of new inorganic composite flame retardants consist of metallic oxide and metal hydroxide were prepared. The high temperature rheological properties, low temperature rheological properties and the viscosity characteristics of the two types of new flame retardant modified asphalts were studied deeply through dynamic shear rheological test, bending beam rheological (BBR) test and Brookfield rotational viscosity test. On this basis, the flame retardant mechanisms of the two types of flame retardant modified asphalts were studied using DSC, and the economic benefits of the two types of flame retardants were compared with the flame retardants in common use. Results show that the effect of restraint smoke of the two types of inorganic composite flame retardants is good, the high temperature rut resistance and the viscosity of the asphalts can be improved, and the low temperature performance of asphalt mastic can be strengthened significantly by the two types of flame retardants. The rut resistance factor of the two types of flame retardants shows good correlation with temperature. The incorporation of the two types of flame retardant makes the asphalts require more energy in phase changing, and modified asphalts are more stable in heating process at high temperature.
Geometric modeling for 3D 4-directional braided composites based on preform boundary reflection method
MA Ming, WANG Qi, CHEN Li, WANG Jianming, ZHANG Ronghua
2014, 31(6): 1604-1611.
Owing to the complexity of the yarn paths inside the preform, the geometric modeling for it is always time consuming. An efficient method, namely preform boundary reflection (PBR) method, was proposed, and the computation time to establish the model of yarns motion in geometric modeling process was shortened effectively. Furthermore, CAD simulation system was developed based on the SolidWorks software. Integral geometric descriptions of 3D braided preform with different parameters could be simulated. Compared with the traditional method, the PBR method significantly shor-tens the simulation time without affecting the precision of preform geometric modeling. As a result, the efficiency of braiding process design is effectively accelerated. The new method establishes the foundation of microstructure and mechanical properties analysis of the preforms with complex geometric structures.
Biomineralization of polyurethane-coated titanium and cell behaviors
GUO Zhijun, ZOU Qin, WANG Lijun, ZHOU Bin, LI Yubao, ZHANG Li
2014, 31(6): 1612-1617.
According to the failure of Ti dental implant due to the interface mismatching in clinic, polyurethane (PU) polymer coating was prepared by pulling Ti from PU solution in order to mimic the function and properties of human periodontal tissue. Then, PU-coated Ti was biomineralized by being immersed into supersaturated Ca-P solution for different periods. The physico-chemical properties of the biomineralized PU were characterized and analyzed by means of SEM, EDX, IR, XRD, DSC-TG and water contact angle testing, and the behaviors of MG63 cells were studied by co-culture test. The results indicate that the deposit on PU is formed by the agglomeration of microspheres made of nano-flake crystals and its main ingredient is proved to be poorly crystallized and non-stoichiometric hydro apatite crystals. Also, the biomineralized PU coating has better biocompatibility than PU coating and is more favor of the proliferation and growth of MG63 cells.
Numerical simulation on mechanism of viscoelastic encapsulation in polymer multiphase stratified flows
ZHOU Guofa, WANG Meimei, ZHANG Yu
2014, 31(6): 1618-1625.
Against the viscoelastic encapsulation induced thickness uniformity controlling technical problems of composite coextruded products, the influencing rule and mechanism of viscoelastic rheological parameter on polymer co-extrusion viscoelastic encapsulation were studied by the numerical simulation. Research results show that the viscoelastic encapsulation is induced by the second normal stress difference driven secondary flow in co-extrusion multiphase stratified flows, and depends on the direction and strength of melt secondary flow. The direction of melt secondary flow depends on the sign of secondary normal stress difference, and its strength is proportional to secondary normal stress difference. The viscoelastic encapsulation increases with increasing of polymer melt relaxation time. The theoretical premise of eliminating viscoelastic encapsulation is elimination of the secondary flow in co-extrusion multiphase stratified flows, and the secondary flow can be eliminated by means of making the second normal stress difference tend to zero. The transformation of the no-slip adhesive coextrusion multiphase stratified shear flow into the full-slip non-adhesive gas assisted coextrusion multiphase stratified plug flow is the theoretical prerequisite of making the second normal stress difference tend to zero, and the air cushion wall full slip of gas-assisted co-extrusion molding process is an effective technique to achieve this transformation.
Compressive allowables of composite laminates subjected to low-velocity impact
YANG Xu, HE Wei, HAN Tao, WANG Jin
2014, 31(6): 1626-1634.
In order to evaluate the compressive allowables of composite laminates made from two types of carbon fiber/epoxy composite laminates with the fiber of T300 and T800, which are commonly used in aeronautical structures, low-velocity impact and compressive after impact tests were carried out for composite laminates made from the two composite systems with different thicknesses and stacking sequences. The relationships between impact energy, dent depth, damage area and residual compression strength etc were discussed, and the effects of thickness, stacking sequence, surface protection etc were also investigated. The condition for the barely visible impact damage (BVID) formation and the residual strengths of the composite laminates containing BVID were specially concerned. The results show that the laminate thickness and stacking sequence can affect the dent depth-impact energy relationship greatly, while their influences on the compressive strength after impact-dent depth and compressive failure after impact strain-dent depth relationships are much smaller. In the condition of the same layup proportion, impact energy for the BVID formation increases linearly with the laminate thickness. The performances of laminates with different materials vary that the X850 laminates have a better impact damage resistance than the CCF300/5228 laminates, but their damage tolerance performances are similar. Surface treatment such as adding the bronze and painting, can enhance the impact damage resistance of the laminates greatly, while it has little influence on the damage tolerance performances. The compressive failure strain of all the CCF300/5228 samples are more than 4 000 με, while they are more than 3 000 με for X850 samples, when the damage is not more than BVID.
Performance of chromium-poisoning resistance of Gd0.2Ce0.8O2-impregnated LaNi0.6Fe0.4O3-δ cathode materials
YUAN Meng, WANG Xiaoying, HUANG Bo, LI Yang, ZHANG Zhiqiu, LIU Zongyao, TANG Xuchen, ZHU Xinjian
2014, 31(6): 1635-1641.
The symmetric cell LaNi0.6Fe0.4O3-δ (LNF)/Sc0.1Zr0.9O1.95 (ScSZ)/LaNi0.6Fe0.4O3-δ (LNF) was fabricated with screen printing and co-sintering methods. Using cerium nitrate and gadolinium nitrate as raw materials, citric acid as fuel, LNF cathode modified by impregnating with 21.3% mass fraction of Gd0.2Ce0.8O2 (GDC) was prepared using combustion method. Electrochemical impedance spectra (EIS) show that, specific polarization resistance is 0.70 Ω·cm2and 0.13 Ω·cm2 for LNF and 21.3% mass fraction of GDC-impregnated LNF cathode at 750 ℃, respectively. Specific polarization resistance of LNF cathode in absence of Cr-base alloy at 750 ℃ after holding of 500 h attains to 2.36 Ω·cm2 while that of the 21.3% mass fraction of GDC-impregnated LNF in the same conditions after holding of 1 200 h attains to 0.40 Ω·cm2. The impregnation of GDC speeds up the diffusion process of triple-phase boundary reaction area at gas/cathode/electrolyte and reduces cathode polarization resistance. In presence of Cr-base alloy, compared with 21.3% mass fraction of GDC-impregnated LNF, there is strong Cr2O3 deposition at LNF/ScSZ interface, which slows down the diffusion of active particles at triple-phase boundary. LNF exhibits far greater specific polarization resistance than that of 21.3% mass fraction of GDC-impregnated LNF. 21.3% mass fraction of GDC-impregnated LNF cathode has high tolerance towards Cr poisoning.