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28 April 2021, Volume 47 Issue 2 Previous Issue    Next Issue

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Materials Science and Engineering

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Study on magnetic properties of Fe-based amorphous composites ZHAO Yan-chun, WANG Bo, LI Ze-feng, SUN Hao, KOU Sheng-zhong 2021, 47 (2):  1-6.  Abstract ( 897 )   PDF (3215KB) ( 609 )   Save The Fe-15Mn-5Si-xCr-0.2C(wt.%) amorphous composite material was prepared by using water-cooled copper crucible smelting and copper mold suction casting. XRD was used to characterize the phase composition of the sample. Vibrating Sample Magnetometercombined with M-H and B-H curves were used to analyze the effect of the change of the Cr element content on the magnetic properties for amorphous composite material. The results show that the Fe-15Mn-5Si-xCr-0.2C (x=1, 2, 4, 6, 8, 10, 12, 13, 14) samples are composed of α-Fe phase, γ-Fe phase and the amorphous phase. As thecontent of Cr element increases, the mixing enthalpy decrease while the mixing entropy increase. The synergistic effect of α-Fe phase and the amorphous phase made the Fe-15Mn-5Si-14Cr-0.2C exhibit the best soft magnetic properties, which the coercive force and saturation magnetization are 16.12A/m and 5.1T, respectively. References | Related Articles | Metrics

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Effect of Cu content on the γ-Ni phase: First-principles studies LI Ya-min, JIANG Lu, LIU Hong-jun 2021, 47 (2):  7-12.  Abstract ( 354 )   PDF (2506KB) ( 361 )   Save In this work, first-principles density functional theory was applied to investigate the effect of variation of Cu Content on the γ-Ni Phase of nickel base alloy from the atomic scale. The total energy, formation enthalpy, cohesive energy,the density of the states and elect on density difference were calculated and used to study the stability of different system including before and after doping. The results show that the doping of Cu atoms reduces the absolute values of formation enthalpy and cohesive energy of the γ-Ni system, and with the increase of the doping concentration, the absolute values of the formation enthalpy and cohesive energy decrease correspondingly, indicating that the system stability reduced when introducing Cu, which is worse with the increasement of Cu. The doping of Cu reduces the hardness and deformation resistance of the system, as well as the oriented bond and bonding ability between atoms, resulting in the reduction of system's ductility. The essential reason for these changes is that the incorporation of Cu changed the charge distribution and interaction around Ni atoms in the system. The trend for experimental results are consistent with that for the first-principles calculation results. References | Related Articles | Metrics

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Phase field simulation of pearlite growth based on OpenCL parallel baffle ZHU Chang-sheng, LI Yu-jie, MA Fang-lan, FENG Li, LEI Peng 2021, 47 (2):  13-20.  Abstract ( 231 )   PDF (5930KB) ( 293 )   Save The KKSO model coupling of phase field and solute field was established. OpenCL parallel computing was used to simulate the eutectoid growth process of Fe-C alloy, and the influence of baffles with different shapes and positions on the co-growth of lamellar pearlite was studied. The results show that GPU computing efficiency reach up to 88 times faster than that of serial CPU, and as the simulation scale increases, acceleration performance is higher; the presence of baffles directly affects the evolution of pearlite morphology that is, the growth of pearlite under the bafflewas be restricted, and the morphology of the pearlite passing through the gap of the baffle changed; when the baffle is located directly above the interface between cementite and ferrite, the cementite on both sides of the baffle merges into an irregular shape; the carbon atoms in the front of the cementite phase cannot meet its growth requirements, so that the growth stops, and adjacent ferrites merge into one phase. Therefore, the presence of the baffle can control the growth morphology of pearlite. References | Related Articles | Metrics

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Ultrasonic testing of friction welded piston rod joints and two-dimensional reconstruction of defect contour ZHU Ming, ZHANG Hu-long, CHEN Yu-yu, SHI Yu, HOU Guo-qing, LIU Tao 2021, 47 (2):  21-25.  Abstract ( 221 )   PDF (1437KB) ( 272 )   Save For the incomplete fusion defect of the friction welded joint of the piston rod, the ultrasonic non-destructive testing method was used to testing the weld joint of the piston rod and then the ultrasonic echo signal containing noise was extracted. The wavelet noise reduction method was used to filter and reduce the defect signal containing noise.The two-dimensional contour reconstruction of the incomplete fusion defect is carried out by the method of analyzing multi-position and multi-point ultrasonic echo signal. The result shows that: 1) By optimizing the parameters of the wavelet threshold noise reduction algorithm, the signal-to-noise ratio of the ultrasonic echo signal can be improved, and the effectiveness and accuracy of the detection result can be improved. Also it can realize the noise reduction of the defect signal and ensure the integrity of the signal;2) Inspection data was theoretically calculatedto determine the edge points of the defect. Through fitting the edge points of the multi-position defect, the two-dimensional contour reconstruction of the incomplete fusion defect is realized, and the reconstruction result is basically consistent with the destructive inspection result. References | Related Articles | Metrics

Mechanical Engineering and Power Engineering

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Multi-objective maintenance for series-parallel production systems with multiple resource constraints LI You-tang, HUANG Zhao-kun 2021, 47 (2):  26-31.  Abstract ( 209 )   PDF (1504KB) ( 391 )   Save Aiming at the series-parallel production system with multi-resource constraint, a multi-objective dynamic maintenance model is established by considering the availability of the system under multi-resource constraint and taking the priority of each process resource requirement as the standard. By introducing the weight factor and using the reliability recovery factor to describe the reliability change process before and after the maintenance of each process equipment, a maintenance strategy with the maintenance cost and system availability as the optimization objective was established. The preventive maintenance and opportunity maintenance thresholds of the system in a given interval are solved by simulation sampling. The results show that the maintenance strategy can guarantee the maintenance cost and system availability of the complex degraded production system under multi-resource constraints. References | Related Articles | Metrics

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Effect of flue gas waste heat combined heating on performance of biomass direct combustion power generation system LI Jin-ping, YANG Xiao-yu, ZHANG Bo, HUANG Juan-juan, WANG Chun-long 2021, 47 (2):  32-38.  Abstract ( 247 )   PDF (3754KB) ( 331 )   Save Aiming at the situation that the biomass direct-fired power generation system has a large amount of water vapor and latent heat recovery potential, a combined heat and power system integrating biomass direct-fired power generation with an absorption heat pump and a water source heat pump is proposed for the first time. The composite heating system is modeled by TRNSYS software, and its stability of the systemwas analyzed. The exergy analysis of the system was performed,and the benefits of the system were finally analyzed. The results show that the composite heating system can stabilize the output heat for the user during the heating season, and the average coefficient of performance of the absorption heat pump in the heating season is 1.61, and the average coefficient of performance of the water source heat pump is 4.32. The exergy efficiency of the composite heating system is 41.85%.After adding the compound heating system, theenergy saving rate increased by 5.2%, the comprehensive energyutilization rate increased by 7.8%, the waste gas heat recovery rate increased by 15.5%, the system can save 6 416.5 t of standard coal annually, reducing16 682.98 t of CO2, 128.33 t of SO2, and 449.16 t of NOX each year. References | Related Articles | Metrics

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Defect size estimation of rolling bearings based on double impulses characteristic method YAN Chang-feng, ZHAO Wei-kun, MENG Jia-dong, WANG Wen-bin, WU Li-xiao 2021, 47 (2):  39-47.  Abstract ( 203 )   PDF (5422KB) ( 446 )   Save A defect size estimation method based on double impulses feature is proposed in this paper for rolling bearing. This method realizes accurate estimation of fault defect size according to extracted feature signals of the rolling bearing. Collected vibration signals are pre-whitened by an AR model, and the pre-whited signals are decomposedinto a series of Intrinsic Mode Functions (IMFs) by Variational Mode Decomposed (VMD). According to the kurtosis value and the mutual information being the largest, the step component and the impact component are extracted respectively. Then, the square envelope is applied to enhance characteristics of the signals. According to double impulsescharacteristics, the corresponding time when the rolling element enters or exits the defect is determined hereby, and the defect size estimation method of the fault bearing is put forward as a result. This paper also shows the influence of rotational speed and defect size on accuracy of above method, and analyzes possible causes of errors. The effectiveness of the proposed extraction method has been verified by experiments. The error of estimated defect size is less than 5%. It is verified that the defect size estimation method has higher accuracy. References | Related Articles | Metrics

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Automatic verification and realization of MBD data set 3D annotation WANG Hong-shen, WANG Dao-jun 2021, 47 (2):  48-53.  Abstract ( 415 )   PDF (2481KB) ( 448 )   Save In view of the lack of correctness verification of MBD function 3D annotation in commercial CAD software at present, this paper studies the problems of 3D dimension labeling and validation inspection based on the geometric modeling core of OpenCASCADE. By extracting the geometric features of the annotated object and combining the information annotation rules, the matching between the annotated content and the annotated object is judged, and then the correctness of the annotation is judged. The hierarchical data structure is designed to store the annotation information, and the annotation information is associated with the shape elements, which avoids the repetitive annotation, and also provides the possibility for automatic extraction of product semantic information during subsequent virtual assembly, processing and manufacturing and service. The annotated information is stored in XML format, which is convenient for information transmission and access, which lays a good foundation for further research on digital twin technology. References | Related Articles | Metrics

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Analysis of thrust and velocity variation of permanent magnet synchronous linear motor under variable load SHEN Hao, ZHANG Wang, TAN Wei-rong, DANG Sheng-hui 2021, 47 (2):  54-59.  Abstract ( 719 )   PDF (1152KB) ( 1282 )   Save Taking the permanent magnetic synchronous linear motor as the research object, its force was analyzed; mathematical model was established, and the simulation model of the linear motor by using Matlab/Simulink in order to study the thrust and speed change of the linear motor when different loads are applied. The results show that with the increase of the workpiece’s mass, the state response time and maximum deviation of the linear motor increased; the response time curve of the speed is flat; the response time curve of thrust changed obviously; the overshoot curve of thrust increase flatly; the overshoot curve of velocity increased stably, the overshoot curve of speed is obvious.When the quality of the workpiece is 240 kg, the over-adjusting amount of motor speed exceeds 30%, which seriously affects the operation of the motor. In order to reduce the effect of load change on linear motor stability, the maximum load quality and maximum motor thrust are calculated. References | Related Articles | Metrics

Chemical Industry and Light Industry

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Stress variation law of buried collecting and transporting pipeline under rock collapse CUI Yi, MA Hong-qiang 2021, 47 (2):  60-64.  Abstract ( 221 )   PDF (2256KB) ( 355 )   Save Based on the theory of elastic-plastic mechanics and finite element analysis method, the analysis model of buried gathering pipeline under the action of rock collapse is established, and the influence law of different factors on the stress of buried gathering pipeline under the action of rock collapse is studied. The results show that the impact load increases exponentially with the increase of the side length of the block. When the side length of the cube changes by 1.4 m, the impact load can be changed by 22.4 MPa. Operation pressure, temperature and pipeline laying slope have little influence on pipeline wall stress, while impact load and corrosion are the main factors affecting the safety of buried gathering and transportation pipelines. When the impact load is greater than 10.5 MPa, the pipe will enter the plastic deformation zone. When the rock collapse impact load is large, the maximum equivalent stress on the pipe wall decreases with the increase of the pipe diameter thickness ratio. When the diameter thickness ratio changes 3.8, the maximum equivalent stress on the pipe wall can be reduced by 44 MPa; when the rock collapse impact load is small, the maximum equivalent stress on the pipe wall appears a minimum point. References | Related Articles | Metrics

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The distribution characteristics of PM2.5, alkanol and their correlation with meteorological factors in Xigu district of Lanzhou ZHANG Guo-zhen, LI Dan-dan, YUE Yong-li, LIU Peng-fei 2021, 47 (2):  65-71.  Abstract ( 232 )   PDF (3320KB) ( 310 )   Save The PM2.5 data of Xigu district of Lanzhou in 2019 were collected, and the organic components in PM2.5 were analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry (GC-MS). The distribution characteristics of PM2.5 and alkanol were mainly discussed. Relationship between PM2.5 and alkanols distribution and meteorological parameters was assessed by correlation (Pearson) and non-parametric analysis (Spearman) methods, and the applicability of the two methods was compared simultaneously. The results showed that the annual mean concentration of PM2.5 in 2019 was 51 μg/m3, which was 1.5 times of China’saverage annual air quality standards (Grade Ⅱ,35 μg/m3 ) in which the alkanols in PM2.5 was accounting for 0.3%. For seasonal trends, both PM2.5 and alkanols were all decreased in the order of winter>spring>autumn>summer. Pearson and Spearman’s analysis of temperature and relative humidity were consistent, while their calculation results of wind speed were slightly different in terms of significance level, and the statistical results of atmospheric pressure were significantly different. References | Related Articles | Metrics

Automation Technique and Computer Technology

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CPS attack detection based on SAE-SVM WANG Zhi-wen, CAO Xu, HUANG Tao 2021, 47 (2):  72-79.  Abstract ( 300 )   PDF (1995KB) ( 335 )   Save Cyber-physical system (CPS) is widely used in industrial control and critical infrastructures. Because of its vulnerability, the security of CPS is especially important. In order to improve the accuracy of CPS attack detection, an attack detection method combining sparse autoencoder (SAE) and support vector machine (SVM) is proposed in this paper. For the purpose of dimension reduction of data in CPS, SAE is used to learn and reduce dimension of the data, and the unsupervised method is adopted to reconstruct the new representation of features. On this basis, in order to establish an optimized detection model, improved bacterial foraging algorithm(IBFA) is employed to optimize parameters of SVM. The Tennessee-Eastman process model is utilized as simulation foundation to simulate a malicious attack to CPS, and the proposed algorithm is then used to detect the attack. Results coming out of above simulation and detections indicate that the proposed algorithm can detect occurrence of attacks effectively, which not only shorten detection time but also improve security performance of CPS. References | Related Articles | Metrics

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A modular multilevel converter circulation suppression method based on SOGI ZHANG Ming-guang, CHANG Jian-hua, YANG Cheng-ming, LIU Zi-lin 2021, 47 (2):  80-86.  Abstract ( 332 )   PDF (2679KB) ( 313 )   Save The high voltage direct current based on modular multilevel converter (MMC-HVDC) has occupied an important position in the power field, but modular multilevel converter has a circulating current, which can increase the rated capacity and system loss of switches and other components, seriously affecting the working characteristics of MMC. In order to suppress the circulation, the main higher harmonics in MMC circulation are analyzed, for the second and fourth harmonics, a multi-harmonic filter based on the second order generalized integrator (SOGI) was first designed to extract the harmonic components in the circulating current, then circulating current suppressing controller based on proportional resonant was designed to suppress harmonic components. Finally, a 21 level MMC-HVDC simulation model is built in PSCAD, and compared with the traditional circulation suppression method, the results show that the proposed method can suppress circulation more effectively. References | Related Articles | Metrics

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Copy-move image blind forgery algorithm based on quaternion convolutional neural networks with dual-tree complex wavelet LI Ce, LI Lan, JIN Shan-gang, GAO Wei-zhe, XU Da-you 2021, 47 (2):  87-96.  Abstract ( 201 )   PDF (7241KB) ( 114 )   Save With the popularity of image editing software, people can forge images by Copy-move. However, existing Copy-move blind forensics algorithms are difficult to extract consistency features of color images with results depending on manually adjusting parameters, which leads to low locate accurate. Therefore, using the advantage of quaternion convolutional network on extracting spatial consistency of color images and double-tree complex wavelet on extracting image local features, Copy-move blind forensics algorithm based on quaternion convolutional network with double-tree complex wavelet is proposed. Firstly, images represented as quaternions were input to quaternion convolutional network to extract consistency features of color images, and the high-frequency subbands of double-tree complex wavelet transform were connected with feature maps of the convolutional network to learn local features. Next, similarity scores in feature vectors are calculated. Then, convolutional network is extracted features with higher scores to locate similar areas, which solves the problem of adjusting parameters during matching. Besides, an auxiliary branch is constructed to locate the tampered areas. Finally, similar and tampered areas are fused to distinguish copy and paste. The subjective and objective experiments on CoMoFoD and CASIA CMFD datasets show that the proposed algorithm improves the performance of Copy-move blind forgery. References | Related Articles | Metrics

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Call option elastic contract with information asymmetry under stochastic prices LU Sheng-wei 2021, 47 (2):  97-106.  Abstract ( 224 )   PDF (796KB) ( 287 )   Save In this paper, we aim to explore whether the supply chain could coordinate under the condition of random fluctuation of both market price and wholesale price. First, we construct a new call option elastic contract model based on the combination of the call option contract and quantity elastic contract, and a call option elastic contract model for emergency supply chain is constructed respectively in view of the information asymmetry caused by suppliers’ hiding supply cost information and manufacturers’ hiding manufacturing cost information in order to look for optimal pricing and ordering decisions, and analyze the influence of asymmetric information on the optimal decision and performance of supply chain and supply chain members by comparing to the complete information case. And the results show that participants in the supply chain with unilateral information advantage can make profits by hiding private cost information when the call option elastic contract coordinates the supply chain based on rising future prices of commodities caused by emergencies, but it will bring damage to the other side of the supply chain as well as the whole supply chain. Meanwhile, we also get the conclusion that the new contract formed by the combination of call option contract and quantity elastic contract is better than the quantity elasticity contract in coordinating the supply chain. Finally, we verify these conclusions by examples. References | Related Articles | Metrics

Architectural Sciences

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Effect of different specimen size on raw soil materials ZHANG Kun, WANG Yi-hong, PU Yong-hong, WAN Tian-ya, YANG Zhan-she 2021, 47 (2):  107-112.  Abstract ( 359 )   PDF (2199KB) ( 337 )   Save The compressive strength of parts is an important mechanical indicator of raw soil-based building materials. For the purpose of studying the size effect of cube specimens of raw soil materials, this research explores the influence of different sizes of specimens on compressive strength of the materials. Compressive strength tests of three kinds of cube raw soil specimens with the same sample preparation method, maintenance method and loading method were carried out to investigate failure pattern and compressive strength of the specimens. The regularity and mechanism of effect of different specimen sizes on the strength are investigated, and the strength relation coefficients of the three sizes of specimens are calculated hence by statistical screening method. Results from our researches indicate that the failure process of specimens with small size is obvious. The compressive strength of the material decreases with increase of specimen size, exhibiting a linear relationship. The strength conversion coefficient between 100 mm specimen and 150 mm specimen is 0.67, and that between 100 mm specimen and 200 mm specimen is 0.42. The compressive strength of raw soil-based materials is significantly affected by size effect. References | Related Articles | Metrics

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Impact resistance and damage evaluation of reinforced concrete deep beam under low velocity impact XIANG Chang-sheng, SUN Wei, ZHOU Yu 2021, 47 (2):  113-121.  Abstract ( 258 )   PDF (7082KB) ( 96 )   Save In order to study the impact resistance and damage mechanism of reinforced concrete deep beams under low-speed impact, the structural response of deep beams at different impact speeds was simulated by finite element software ANSYS/LS-DYNA. The dynamic damage process and the damage distribution of the cross section of the deep beam were analyzed, and the damage of it was quantitatively evaluated by the section damage factor. The influence of boundary conditions and impact position on the impact resistance and damage of deep beams were further analyzed. The analysis results show that the model established is capable of simulating the dynamic response of deep beams under low-speed impact reasonably, under which circumstance, the damage is formed in local area firstly, and then, it expands to the whole structure, the local damage increases again at the impact position ultimately. The impact velocity has a significant influence on the local damage degree at the impact position. Strengthening boundary conditions can improve the bearing capacity of deep beams under low-speed impact and reduce damage degree. The impact position has a significant impact on the vertical deformation and damage position of the deep beam, while it has little influence on the damage degree. References | Related Articles | Metrics

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Dynamic stability analysis of reinforced retaining wall based on strength reduction method JIA Liang, LIANG Rong 2021, 47 (2):  122-126.  Abstract ( 256 )   PDF (2563KB) ( 418 )   Save The stability of the reinforced retaining wall under earthquake action is one of the main contents of the retaining wall design. A numerical simulation of a 5 m high geogrid-reinforced retaining wall was carried out by using FLAC 3D numerical simulation software, which was based on the Lagrangian finite difference principle and the strength reduction method. The final displacement of the retaining wall, the time history displacement of the key points, the settlement of the soil, the maximum tensile force for each layer of geogrid and the distribution of the tensile force for the single-layer geogrid were analyzed under the dynamic and strength reduction. The results showed that the displacement of the key point has a good correspondence with the reduction factor. The strength reduction coefficient of the reinforced retaining wall under critical stability can be used as the dynamic stability factor of the reinforced retaining wall. After breaking through the stability factor, all parameters changed significantly. References | Related Articles | Metrics

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Effect of soil parameter uncertainty of loess slope reinforced by frame anchor on reliability LI Zhong, DING Sheng-huan, YE Shuai-hua 2021, 47 (2):  127-131.  Abstract ( 228 )   PDF (1668KB) ( 321 )   Save In order to study the effect of soil parameters such as cohesion force (c), internal friction angle (φ) and density of the soil (γ) on the reliability index of loess slope strengthened by frame anchors, based on the limit equilibrium theory, relying on the slope engineering example, using GeoStudio 2012 finite element software, the calculation model of reinforced slope is established, and the above analysis process is completed by Monte Carlo test simulation. The results show that when the coefficient of variation of two parameters is fixed and the coefficient of variation of the other parameter is changed, the coefficient of variation of φ has the greatest influence on the reliability index of the slope, and the coefficient of variation of γ has the least influence on the reliability index of the slope. When fixing the coefficient of variation of one of the parameters and the coefficient of variation of the other two parameters change simultaneously, the coefficient of variation of the internal friction angle φ and the density of the soil γ simultaneously has the greatest influence on the reliability index of the slope. The coefficient of cohesion force c and density of the soil γ have the least influence on the reliability index of the slope. References | Related Articles | Metrics

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Improvement of calculation method for stiffness coefficient of soil anchor ZHOU Yong, SHI Zhan-zhe 2021, 47 (2):  132-137.  Abstract ( 333 )   PDF (1429KB) ( 289 )   Save The stiffness coefficient of anchor is composite stiffness obtained by considering the deformation of free section, anchorage section and relative displacement of anchor to soil. In the derivation of the existing formulas for calculating the stiffness coefficient of anchor, only the deformation of free section and the anchorage section were considered, while the deformation of soil was not taken into account. The relationship between the actual displacement of anchor head and the internal force can not be truly reflected. Based on the coordinated deformation of anchor and soil, the formulas for calculating the stiffness coefficient of anchor rod considering the deformation of free section, anchorage section and soil were derived by using Mindlin solution, and the calculated codes was compiled with the software of MATLAB. Finally, combined with an engineering example, Plaxis2D was used to simulate the stiffness coefficients of anchor. The stiffness coefficients of anchor were solved by displacement and internal force. Compared with the calculation method and the standard method in this paper. The results show that the calculation method in this paper is more consistent with the simulation results. References | Related Articles | Metrics

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Preparation of composite emulsified asphalt and its properties of micro-surface mixtures SHI Fu-zhou, JIA Xiao-jun, WANG Zhen, LIU Xiao-pei, WU Jia-yun 2021, 47 (2):  138-143.  Abstract ( 346 )   PDF (2508KB) ( 522 )   Save In order to improve the road performance of ordinary emulsified asphalt in the micro surface mixture, the emulsified asphalt with high performance was prepared by the method of emulsification first and then modification. The addition method of modifier and the proportion of modifier blending were determined by using the indexes of ductility and softening point, and then it is used as cementing material for the micro-surface mixture. The performance of resistance to water damage and wear resistance of the wet wheel were verified by the wear test (WTAT), and its crack resistance and shear resistance were verified by splitting test and high-temperature rut test. The results show that the softening point and ductility of the composite modified emulsified asphalt are better than ordinary emulsified asphalt, while the blending ratio of SBR with waterborne epoxy resin is 3.5% to 2.5%, ductility and softening point can reach 400 mm and above 70 ℃.The performance test of the mixture showed that the micro surface mixture made of modified emulsified asphalt had significant advantages in water loss resistance/wear resistance, crack resistance and shear resistance compared with the ordinary micro surface mixture. References | Related Articles | Metrics

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Dynamic response of cement concrete pavement with crack under vehicle load based on analytic method GAO Yuan-yuan, WANG Wei-yu, ZHAO Qing-xin, JIAO Yan-peng 2021, 47 (2):  144-150.  Abstract ( 243 )   PDF (1491KB) ( 390 )   Save Bottom crack in cement concrete pavement is one of the major pavement diseases. The main purpose of this study is to propose the theoretical basis for evaluating the status of the pavement. In order to simplify the problem, the cement concrete pavement was modeled as an elastic plate on winkle foundation. To solve the governing equations, the Fourier transform and Laplace transform were introduced to transform the partial differential equations to ordinary differential equations. The residual theorem and dislocation density function were used to derive the singular integral equations. Lobatto-Chebyshev integration formula, as a numerical method, was used to gain the results of the singular integral equations. The numerical solution of dynamic stress intensity factor at the crack tip was obtained. In order to get the factors that affect the crack propagating, numerical analyses were carried out for a cement concrete pavement with a bottom crack. References | Related Articles | Metrics

Scientific

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Small R-projective modules WANG Yong-duo, LI Xia 2021, 47 (2):  151-155.  Abstract ( 274 )   PDF (741KB) ( 391 )   Save The concepts of small N-projective modules and small R-projective modules are introduced, basic properties of these modules are studied. It is proved that a ring R is a semiprimitive ring if and only if every right R-module is a small R-projective module. References | Related Articles | Metrics

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The boundedness of multilinear Marcinkiewicz operator in variable index Herz-Morrey space YE Xiao-feng, HAN Jing 2021, 47 (2):  156-162.  Abstract ( 241 )   PDF (729KB) ( 396 )   Save The boundedness of multilinear Marcinkiewicz operators with variable kernels was studied on variable index Herz-Morrey spaces, which is also the generalization of classical Marcinkiewicz operators on variable index Herz-Morrey spaces. By using the eigenfunction and the space decomposition principle, the operator is divided into four parts in this paper, and then the operator is estimated one by one by using the size condition satisfied by the kernel functions. The boundedness of the operator on the variable index Herz-Morrey space is therefore obtained. References | Related Articles | Metrics

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Existence of global attractors for a kind of Kirchhoff type wave equation with strong damping NIU Li-fang, WEI Qian-rui 2021, 47 (2):  163-167.  Abstract ( 232 )   PDF (692KB) ( 286 )   Save Study a class of strongly damped Kirchhoff wave equations with critical growth exponent. In a given Sobolve space, the existence of global attractors for global solutions of the system is proved by using Galerkin method and operator semi-group theory. References | Related Articles | Metrics

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Study on SAF 2707HD fatigue performance in rotating bending YU Shu-rong, CHENG Yue, HE Yan-ni, SONG Wei 2021, 47 (2):  168-172.  Abstract ( 241 )   PDF (2983KB) ( 374 )   Save The rotational bending fatigue test of SAF 2707HD duplex stainless steel was carried out. The fatigue limit is determined by the up-and-down method, and the stress-lifetime (S-N) curve is hence drawn according to the experimental data. The fatigue fracture surface of the specimen is observed by scanning electron microscope (SEM), and the type of fatigue crack initiation and the corresponding fracture mechanism are analyzed respectively. Statistical data show that the fracture caused by crack origins on the surface of the specimen occurs basically at or within in 105 cycles, while the fracture caused by internal crack origins occurs basically at about 106 cycles, with a difference of nearly one order of magnitude. For this reason, the fatigue life is then predicted by using the finite element software. All predicted results are compared with the experimental S-N curve, which confirms the reliability of our fatigue life analysis. References | Related Articles | Metrics