Table of Content

25 February 2016, Volume 44 Issue 2

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Architecture & Civil Engineering

P-δ Effect of Sliding Columns in Reinforced Concrete Structures with Partial Columns Sliding at Upper Ends

WU Bo Lü Wen-long

2016, 44(2):  1-7.  doi:10.3969/j.issn.1000-565X.2016.02.001

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In order to reveal the P-δ effect of sliding columns in reinforced concrete structures with partial columns sliding at upper ends,the validity of a simplified model with upper end joints is verified.Then,the characteristics of the second-order moment of the sliding column without sidesway caused by the P-δ effect are investigated in different cases,the boundary condition considering the second-order moment is presented,and a method to determine the increment coefficient of the bending moment for the sliding column without sidesway is proposed.Moreover,the concrete nonlinearity is taken into account primarily by amending the parameters in the proposed method,and some examples are finally analyzed.It is found that the friction support located at the upper end of the sliding column under minor earthquakes can be approximately treated as a joint; and that,in some cases,the column's maximum bending moment increases owing to the second-order moment of the sliding column without sidesway caused by the P-δ effect and that it can be easily determined by using the first-order moment of the sliding column without sidesway and the aforementioned increment coefficient.

Nonlinear Response of Reinforced Concrete Frame Structures Under Symmetrical Impact

WEI De-min LIU De-yuan LI Di

2016, 44(2):  8-13.  doi:10.3969/j.issn.1000-565X.2016.02.002

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Dealt with in this paper is the nonlinear dynamic response of reinforced concrete frame structures under symmetrical centralized impacts.In the investigation,first,two influencing factors,namely the initial impact velocity of the drop hammer and the beam-to-column linear stiffness ratio,are analyzed.Next,a nonlinear finite element analysis is performed to explore the variations of the impact force with time,the displacement response of the structure,the final deformation,the characteristics of the plastic deformation and the energy consumption of the structure.Then,the computational results are analyzed and a simplified model to estimate the final deformation of the impact point is put forward.Finally,a comparison is made between the results respectively obtained by the finite- element computation and the simplified model.It is found that ( 1) the influence of initial impact velocity on the structure's dynamic response is more evident than that of the beam-to-column linear stiffness ratio; ( 2) the plastic deformation of the frame structure mainly occurs at the two ends and in the midpoint of the beam,which greatly increases with the increase of the initial impact velocity; and ( 3) the horizontal displacement of the two frame columns is symmetrically outward and the plastic deformation of the column is relatively smaller than that of the beam.

Influence of Bond Length on Bonded Interface Performance of CFRP-C60 Concrete

HONG Lei DUO Run-min WANG Su-yan

2016, 44(2):  14-19.  doi:10.3969/j.issn.1000-565X.2016.02.003

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By using a self-designed loading device,the interface performance of CFRP ( Carbon Fiber-Reinforced Polymer) -C60 high-strength concrete under different bond lengths are investigated via double shear tests.Then,the concept of the minimum bond length is proposed and a model of the effective bond length is established.The results indicate that ( 1) with the increase of the bond length,both the ultimate bond load and the ultimate global slip response increase remarkably ,while the initial strip load and the initial strip response have no significant change; ( 2) with the increase of the load，the stress transfer area moves forward from the loading end and continuously prolongs,which presents a process of dynamic change; ( 3) the minimum bond length of C60 concrete is about 2 times the effective bond length; and ( 4) when the bond length is larger than the minimum value,the bearing capacity of the concrete can be fully used and the ductility is improved.

Nonlinear Temperature Distribution of Longitudinal Plate-Type Ballastless Track in Spring

DAI Gong-lian SU Hai-ting YAN Bin ZHU Jun-pu

2016, 44(2):  20-25,32.  doi:10.3969/j.issn.1000-565X.2016.02.004

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In order to reveal the time-dependent temperature distribution in the ballastless track structure on a curve line,a continuous observation of CRTS Ⅱ longitudinal plate-type ballastless track was carried out with temperature sensors.After the statistical analysis of a great amount of measured temperature data,the vertical and horizontal temperature gradients of the track were obtained.The results show that ( 1) the vertical and horizontal temperature distributions of the ballastless track are both nonlinear in the process of heat exchange with the outside; ( 2) the temperature of the track periodically changes with the environment temperature; ( 3) the time corresponding to the maximum temperature delays due to the increase of the distance to the track surface,even presents a 5 h delay at the bottom of the track structure in a comparison with the time on the surface; and ( 4) the vertical temperature gradient is in an exponential distribution,which matches the distribution curve suggested by the design standard for railway bridges and culverts in China.

Investigation into Half Grout Sleeve Splicing for Rebars via Static Tensile Test

HUANG Yuan ZHU Zheng-geng HUANG Deng YI Wei-jian ZHANG Rui

2016, 44(2):  26-32.  doi:10.3969/j.issn.1000-565X.2015.02.005

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In order to investigate the mechanical properties of half grout sleeve splicing for rebars,14 specimens were tested under static tension,with such main parameters as bar diameter,sleeve dimension and rebar deviation being considered.The results show that ( 1) the tested half grout sleeves meet the strength requirements well; ( 2) the specimens are destroyed in three failure patterns including the tension fracture of the rebar,the rebar scratchplough pulling out of the rebar and the sliding wire of the sleeve; and ( 3) when the tension fracture of the rebar occurs,the rebar deviation has little effect on the bearing capacity of specimens.Based on the analysis of the test results,a design method is put forward to avoid the occurrence of the rebar scratch-plough pulling out and the sleeve sliding wire.

Mechanical Engineering

Investigation into Warpage Deformation and Corresponding Parameters in Expanding-Jointing Process of Air Conditioner Fin

XIA Qin-xiang LI Zhi-wei LONG Xiao-bin LONG Chuan

2016, 44(2):  33-39.  doi:10.3969/j.issn.1000-565X.2016.02.006

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In order to avoid the excessive warpage deformation of air-conditioner's heat exchanger fins in the expanding- jointing process,a finite element simulation was carried out to analyze the causes of warpage deformation,the deformation of the grooved fin and the groove structures in different locations on the fin.Then,on the basis of orthogonal experimental design,the primary and secondary factors affecting the warpage degree of the fin,including the dimensions of both the fin and the bulging ball,were analyzed,and reasonable parameters for the expandingjointing process were obtained.Finally,the rationality of the parameters optimized by the orthogonal experimental design method was verified through a trial produce and a heat-transfer finite element simulation.The results show that,as compared with the structure and the location of the grooves,the dimensions of the fin and the bulging ball both affect the warpage degree of the fin more significantly,and that the factors affecting the warpage degree are ranked as follows in the decreasing order of their seriousness: the long-axis length of the fin,the long-axis length of the bulging ball,the minor-axis length of the fin and the minor-axis length of the bulging ball.

Double-Pulse Multi-Phase Coordinative Control System of High-Power Twin-Wire GMAW

WU Kai-yuan LIANG Zhuo-yong HE Zu-wei HUANG Xi CHENG Jia

2016, 44(2):  40-45.  doi:10.3969/j.issn.1000-565X.2016.02.007

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In order to improve the forming quality of welding seam during the high-power twin-wire GMAW ( Gas Metal Arc Welding) ,a double-pulse waveform control method is proposed.The proposed method adopts the PWM ( Pulse Width Modulation) modules integrated in DSP ( Digital Signal Processor) to implement the direct digital control of PWM signals for the parallel master and the slave power supply in a software mode,so that the corresponding double-pulse waveform modulation is further achieved.Moreover,a double-pulse multi-phase coordinative control system is developed by using the I /O communication of DSP,and the coordinative control of synchronous,alternate and independent phase outputs of two pulses for high-power twin-wire GMAW is realized.Test results demonstrate that the developed double-pulse multi-phase coordinative control system meets the design requirements well and helps to achieve stable welding with decreased twin-arc interference,little splash and perfect welding seam with scaly appearance.

Analysis of Bicycling State Based on Linkage Model of Human-Bicycle

Wu Shangsheng

2016, 44(2):  46-52,59.  doi:10.3969/j.issn.1000-565X.2016.02.008

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According to physiological and cycling characteristics, a model of human-bicycle was built, and its parameters were obtained from body measurement and empirical formula. Through this model, the characteristics such as associated effect of bone, cycling efficiency, dead point and dead zone of cycling were analyzed. After that, the methods of Lagrangian and Newton-Euler were adopted to establish the kinematical and dynamical models and obtained the equivalent moment for bicycle driving as well as the forces and motions of joints. All that devoted to the theoretical basis for bicycle research and design.

Automatic Positioning of Multi-Stage Sheet Forming Based on Constrained Projection

CHEN Jiang CHEN Wen-liang BAO Yi-dong

2016, 44(2):  53-59.  doi:10.3969/j.issn.1000-565X.2016.02.009

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Proposed in this paper is a fast automatic positioning method based on the constrained projection of meshes,which is embedded in the framework of multi-job submitting system.In order to get a more accurate initial position between the sheet and the tool,the real forming result of the previous stage is utilized to replace the initial sheet to adjust the tool position before the current stage is submitted to the solver.As compared with some other positioning methods for multi-stage simulation,the proposed method is of low time cost,good stability and high positioning accuracy,and it effectively solves the positioning problem caused by the vertical wall of tools.Simulated results of the multi-stage forming process of an automobile body demonstrate that the proposed method is feasible.

Optimization Design of Rivet Head for Shaft Riveting Assembly of Hub Bearing Unit

QU Jie ZHANG Guo-jie XU Xiao-qin

2016, 44(2):  60-66,73.  doi:10.3969/j.issn.1000-565X.2016.02.010

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In order to overcome the nonlinearity and instability of the shaft riveting assembly process of wheel hub bearing units,an optimization strategy based on the surrogate model was proposed for the optimization design of the rivet head.In the investigation,first,the finite-element modeling parameters were determined through the tensile test,the ring upsetting test,the on-site axial feeding displacement test,the on-site axial riveting force test and the theoretical derivation about the space trajectory of the rivet head.Next,a comparison between the simulated and the tested results of the axial riveting force and the hub shaft's ultimate deformed shape was made to verify the effectiveness of the proposed finite element model.Then,on the basis of the existing design experiences and the life theory of hub bearing units,the parametric equations and the optimization objective were determined.Moreover,on the basis of the Latin hypercube sampling strategy and the finite element simulation results,a support vector machine regression model,which takes into consideration the maximum radial deformation of inner ring,the axial preload,the acting force between the hub shaft and the rivet head as well as the forming surface parameters of the rivet head,was established.Finally,a verification of the optimization design was performed,with an improved performance of the hub bearing unit being achieved.

Fault Diagnosis of Rolling Bearing Under Gear Noise Interference and Variable Rotating Speed

ZHAO De-zun LI jian-yong CHENG Wei-dong

2016, 44(2):  67-73.  doi:10.3969/j.issn.1000-565X.2016.02.011

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In order to improve the fault diagnosis accuracy of rolling bearings that are commonly interfered by gear noise and variable rotating speed,a fault diagnosis method based on the ensemble empirical mode decomposition ( EEMD) and the instantaneous dominant meshing Multiply ( IDMM) is proposed.The proposed method employs EEMD to eliminate the gear noise in bearing vibration signals,transfers IDMM into an instantaneous rotating frequency,and uses the order tracking to overcome the decrease of diagnosis accuracy due to rotating speed variation.Simulated and experimental results show that the proposed method is effective in eliminating the interferences caused by gear noise and rotating speed variation,thus improving the characteristic order amplitude of faults.Accordingly,the installation of tachometers can be avoided.

Effects of Tool Wear on Surface Integrity of Pure Iron Material Under Finish Turning

KONG Jin-xing HU Kun XIA Zhi-hui LI Liang

2016, 44(2):  74-80.  doi:10.3969/j.issn.1000-565X.2016.02.012

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The finish turning of pure iron material with uncoated carbide tools under minimal-quantity lubrication was performed to investigate the tool wear and its effects on the surface integrity of pure iron material turned respectively by the tool with an average flank wear of 0. 12 and 0. 21 mm.The results show that ( 1) the life of the tool used in the finish turning of pure iron material is greatly influenced by the turning speed; ( 2) the nose wear and the notch wear on the flank surface are two main wear modes of the tool; ( 3) the surface roughness rapidly increases with the tool wear at a high turning speed but first increases and then changes a little with the tool wear at a low turning speed; ( 4) both the tangential and the axial residual stresses on the tool surface first decrease and then increase with the increase in the tool wear at the turning speeds of 100 and 300m/min,while the surface microhardness first increases and then decreases; and ( 5) with the increase in tool wear,both the distortion and the tensile plastic deformation of grains in the surface layer increase,and serious tearing and plastic flow defects appear on the workpiece surface.

Power & Electrical Engineering

Calculation Model and its Verification for Cable Emergency Time of 10 kV Three-Core Cable

LIU Gang WANG Peng LI Wen-xiang

2016, 44(2):  81-88.  doi:10.3969/j.issn.1000-565X.2016.02.013

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transient thermal circuit model of 10kV three-core cables directly laid in soil is established and simplified into an equivalent first-order RC thermal circuit.Then,the relationship between the emergency time and the core temperature is deduced by using the established model,and the temperature rising experiments of the cable are designed and carried out to measure the emergency time under different emergency loads.Finally,the measured values are compared with the calculated ones to verify the correctness of the theoretical calculation,discover the causes of error and reveal the variation of cable's emergency time under different emergency loads.The present study provides a theoretical foundation for the operation of power cables in power sectors.

Fixed-Frequency Hysteresis Control Based on Optimal Space Vector

ZENG Jiang CHEN Hao-ping GU Zhi-peng Huang Hai-ying

2016, 44(2):  89-96,106.  doi:10.3969/j.issn.1000-565X.2016.02.014

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Proposed in this paper is a novel hysteresis current control method based on the optimal space vector for active power filters with constant switching frequency.In this method,the hysteresis width of the next cycle is linearly predicted by the previous switching time,and the switching phase is aligned with a clock signal with fixed frequency,thus achieving the discontinuous SVPWM ( Space Vector Pulse Width Modulation) based on optimal space vector.Moreover,two kinds of discontinuous SVPWM modes are used alternately to further reduce the current error.The effectiveness of the proposed method is finally verified by means of PSCAD/EMTDC simulation.

Dynamic Reactive Power Optimization of Distribution Network Containing Special Load Based on Time Decoupling

OUYANG Sen YANG Jia-hao AN Xiao-hua CHEN Xin-hui

2016, 44(2):  97-106.  doi:10.3969/j.issn.1000-565X.2016.02.015

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The expansion of special loads in power distribution networks results in uncertain power flow distribution,great voltage fluctuation and difficulties in the control of reactive power.In order to solve this problem,a dynamic reactive power optimization method of the distribution network containing special loads is proposed.In the investigation,first,the uncertainty of power flow in the distribution network containing special loads is described via the calculation of probabilistic load flow.Next,in order to overcome the strong space-time coupling of dynamic reactive power optimization issue created by the action constraints of the discrete control equipment,a time decoupling strategy is proposed,which transforms the original problem into a continuous optimization decision in each period.Then,a voltage quality penalty function and an equipment switch penalty function are designed based on the probabilistic voltage distribution information and the equipment adjustment ability.The optimization goal fully considers the network loss,the probabilistic voltage distribution and the equipment adjustment ability,so that the reactive voltage of the distribution network can be optimized according to the optimization process of control variables and state variables.Finally,a case study on IEEE 33-bus system is performed to verify the effectiveness of the proposed method.

Real-Time Selection of Dynamic Load Model Parameters Based on Multiple Linear Regression

HUANG Yu-long LIU Ming-bo CHEN Xun

2016, 44(2):  107-116.  doi:10.3969/j.issn.1000-565X.2016.02.016

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This paper analyzes the factors influencing the load model parameters and proposes a real-time selection method of dynamic load model parameters based on the multiple linear regression.In the investigation,first,all historical load disturbance data measured in a certain duration are identified to obtain the load model parameters,and the identified parameters are used to construct a model parameter database that is further classified into three sub-databases respectively corresponding to small,common and large disturbances.Then,the parameters matching the real-time operation condition best are found from the sub-databases with correct disturbance type and the fitting accuracy is further analyzed.Finally,the effectiveness and accuracy of the proposed method are verified with the field measurement data collected from two substations in a metropolitan area in China.

Effects of H₂O/CO₂ Addition to Acetylene Flame on Soot Particle Size Distribution

LIU Jin-ping WEI Ming-rui GUO Guan-lun LI Song

2016, 44(2):  117-123,146.  doi:10.3969/j.issn.1000-565X.2016.02.017

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In this paper,first,a mathematical model based on the particle population balance theory,which takes into consideration the nucleation,coagulation,surface growth and oxidation of particles,is established to describe the dynamic evolution of soot particles in one-dimension laminar premixed flames.Next,the model is solved by means of Monte Carlo stochastic method.Then,based on a detailed chemical kinetic mechanism,a computation platform of particle size distribution is established.With this platform,the effects of CO₂ and H₂O addition on the soot formation in laminar acetylene /air premixed flames are analyzed,and the particle size distribution affected by the CO₂ /H₂O dosage ( 0%,20% and 40%) is obtained8.The results show that the addition of CO₂ and H₂O slows down the soot formation when the equivalence ratio remains unchanged at 2. 5,especially at a H₂O addition of 40%; and that fewer particles in large size may form due to the addition of CO₂ and H₂O.

Materials Science & Technology

Ｒesearch Progress in Nanocellulose as a Rubber Reinforcing Filler

GU Ju LIANG Xiao-rong HUANG Fei WANG Juan HUANG Shi-wen

2016, 44(2):  124-132.  doi:10.3969/j.issn.1000-565X.2016.02.018

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As a new type of reinforcing filler with environment friendliness,biodegradability,extensive sources and formability for various nanoparticle forms and properties,nanocellulose has been paid much attention to in the field of polymer.However,most studies on nanocellulose focus on its application to plastic rather than to rubber.In fact,nanocellulose in rubber can improve not only such mechanical properties as strength and modulus but also the processing properties.It also gives good biodegradability for rubber,thus reducing the environmental pollution caused by traditional fillers.At present,a large amount of researches have concentrated on the mechanical properties of nanocellulose-reinforced rubber instead of its hygroscopicity,barrier properties,electrical conductivity and dynamic mechanical properties.The hydrophilic nature and dispersion property in many non-polar matrixes of cellulose nanoparticles are the challenging obstacles in the fabrication of such nanocomposites.This paper summarizes the recent progress in the researches on nanocellulose-reinforced rubber at home and abroad,introduces the studies of the authors about the replacement of carbon black or silica with nanocellulose in rubber,and discusses the application prospects of nanocellulose-reinforced rubber to tires.

Effect of Precipitation Phase on Microstructure and Properties of Nb-V-Ti Micro-Alloyed Steel

PANG Qi-hang TANG Di ZHAO Zheng-zhi XU Mei

2016, 44(2):  133-139.  doi:10.3969/j.issn.1000-565X.2016.02.019

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This paper deals with the microstructure and properties of Nb-V-Ti micro-alloyed steels with different Nb,V and Ti contents by means of SEM and TEM.It mainly investigates the morphology and formation mechanism of the diphase precipitate and explores the effect of diphase precipitate on the microstructure and properties of the steels.The results show that the simultaneous addition of Nb and V with a small dosage may remarkably improve the ductility and toughness of the steel with 0. 15% Ti; and that,when the tensile strength is 1200MPa,the percentage elongation after fracture achieves 13% and the impact energy achieves 102 J at － 20℃.Two types of Nb- V-Ti particles in the diphase precipitate are revealed.One is the large particle with a grain size of about 100nm and the other is the ( Nb,V,Ti) C particle with a grain size of about 35 ～ 50nm.It is found that the latter is of stronger precipitation strengthening ability.

Investigation into Deformation Mechanism of Medium Manganese Q&P Steel Based on Stacking Fault Energy

LIN Zhang-guo CHEN Jia-yong TANG Di JIANG Hai-tao DUAN Xiao-ge

2016, 44(2):  140-146.  doi:10.3969/j.issn.1000-565X.2016.02.020

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In this paper,first,the stacking fault energy of the retained austenite in medium manganese Q&P steels respectively with a Mn content of 5% and 7% were calculated by using the thermodynamic model of stacking fault energy,and the effect of carbon partition during the heat treatment on the stacking fault energy was analyzed.Then,the deformation mechanism of the steel under tensile strain was investigated by means of XRD,SEM and TEM,and the relationship between the stacking fault energy and the deformation mechanism was explored.The results show that ( 1) carbon partition should be considered during the calculation of the stacking fault energy of medium manganese Q&P steels; ( 2) the stacking fault energy of 7Mn-1. 5Si-0. 2C sample is 4. 55mJ /m²,and that of 5Mn-1. 5Si-0. 2C sample is 17. 8 mJ /m² ; ( 3) there is a linear relationship between the natural logarithm of retained austenite content and the deformation; and ( 4) TRIP effect is the main deformation mechanism of medium manganese Q&P steels,which is also verified by the calculated results of the stacking fault energy.