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28 June 2023, Volume 49 Issue 3 Previous Issue    Next Issue

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Materials Science and Engineering

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Comparison of corrosion resistance of MAO coatings fabricated on pure Magnesium and AZ91D Magnesium alloy WANG Zhan-ying, MA Ying, AN Shou-jing, WANG Sheng 2023, 49 (3):  1-8.  Abstract ( 236 )   PDF (6712KB) ( 209 )   Save Micro-arc oxidation (MAO) coatings were prepared in the silicate-containing electrolyte on pure magnesium and AZ91D magnesium alloy substrates, and different characterization methods were used to compare the corrosion resistance of the coatings on the two substrates. The results showed that the AZ91D-MAO coating has better formability and more Mg2SiO4 and MgF2 phases, resulting in better spotting and electrochemical corrosion resistance than that of Mg-MAO coating. The Mg-MAO coating exhibits overall corrosion in the whole deterioration process, but it basically loses the protection to the matrix in the late corrosion stage, for the AZ91D-MAO coating, localised corrosion occurs at the later stage of immersion, but the coating still can protect the substrate effectively. Due to the different electrode potentials of different elements after alloying, the selective arcing occurs on the α and β phase regions of the substrate surface. This alternating discharge phenomenon is conducive to the improvement of microstructure parameters such as the compactness, composition and defects of the coating, which results in a better corrosion resistance of the AZ91D-MAO coating. References | Related Articles | Metrics

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Corrosion behavior of inconel 625 alloy in the oxygen-rich and high-temperature slag JIA Jin-feng, WANG Jiang, CHEN Da-lin, LIU Jun-zhao, WANG Zhen-ming 2023, 49 (3):  9-14.  Abstract ( 132 )   PDF (3312KB) ( 89 )   Save In order to solve the problem of low service life of spray gun for nickel top-blown smelting, Inconel 625 alloy was used as a substitute material, corrosion behavior and mechanism of Inconel 625 alloy were studied under actual working conditions: oxygen flow rate 15 000~42 000 Nm3/h and slag temperature 1 400 ℃.The microstructure, element distribution and hardness of the samples were analyzed by OM, SEM, EDS, EMPA and micro-hardness tester. The results showed that the formation of oxide film such as Cr2O3 oxide hindered the corrosion process during 15~20 h. The severe corrosion zone of the alloy occur in 0 μm to 250 μm on the surface, and the heat-affected zone is in 250~1 650 μm. Nb-rich and Cr-poor areas are corroded first. With the continuous formation and decomposition of the complex oxide film system composed of Cr2O3, Fe2O3, Cr2S3, Nb0.1Ni0.9, [Mg, Fe]2SiO4, the main elements in the alloy are corroded off, and Mg and S elements in the oxide film are derived from slag. The hardness of the corroded alloy surface decrease obviously. References | Related Articles | Metrics

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Preparation mechanism and tribological performance of Ni-base composite coating on aluminum alloy surface YAN Cheng-qi, JIA Zhu-ying, LI Zhan-jun 2023, 49 (3):  15-22.  Abstract ( 111 )   PDF (9724KB) ( 94 )   Save To improve the surface wear resistance of aluminum alloy in the application, Ni-Al and three different Ni-Al-W composite coatings were prepared on the surface of aluminum alloy by mechanical milling method. The study showed that the inner tissues of the four composite coatings are evenly distributed with a thickness of about 50 μm to 100 μm. With the increase of W content, the ductile deformation surface of the particle gradually decreases. After heat treatment, Al3Ni and Al3Ni2 intermetallic compounds are generated in the Ni-Al compound coating, but only Al3Ni2 is produced in the remaining powder, and no fine powder remain. AlNi and Al3Ni2 are generated in the three Ni-Al-W composite coatings and coarse powder, and the Al3Ni2 intermetallic compounds in the fine powder gradually disappear with increasing W content. The microhardness of the composite coating increase with increasing W content, the friction coefficient of the three coatings is slightly higher than that of the aluminum alloy matrix and Ni-Al composite coating, between 0.6 and 0.75, however, its wear rate is much lower than that of matrix aluminum alloy and Ni-Al composite coating, about 0.2×10-3~0.4×10-3 mm3/(N·m), and slightly reduce with the increase of W content. The preparation of Ni-Al-W composite coating on aluminum alloy surface effectively improves the wear resistance of aluminum alloy surface. References | Related Articles | Metrics

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Detection and analysis of roughness variation of laser cleaning to remove paint layer on Aluminum alloy ZHU Ming, HOU Xiao-fei, SHI Kun, ZHANG Hao, SHI Yu, FAN Ding 2023, 49 (3):  23-29.  Abstract ( 175 )   PDF (3229KB) ( 121 )   Save When 1 064 nm laser was used to clean 2024 aluminum alloy skin surface fluorocarbon paint layer, the change of surface roughness caused the alteration of absorption effect of paint layer on laser, which easily causes excessive absorption of heat to produce substrate damage. Therefore, for the detection and analysis of surface roughness in the laser cleaning process, the pulsed laser cleaning experimental system was designed. The generation mechanism of surface roughness morphology of fluorocarbon paint layer was analyzed under two laser cleaning modes, and the surface roughness was tested and characterized by laser scanning confocal microscope. The evolution of surface roughness was studied when the fluorocarbon paint layer was removed by laser. The result showed that: 1) The laser ablation mechanism and vibration mechanism will produce rough surface in the laser cleaning process; 2) With the increase in the times of laser cleaning, the surface roughness presents the nonlinear increase in the laser layer-by-layer cleaning process. After the laser cleaning 14 times, the roughness of the paint layer has reached 35.88μm, which is an increase of 370% compared to that of the first cleaning. 3) The presence of rough surface has a significant increase effect on the laser absorption rate in the process of laser layer by layer paint removal. After the laser cleaning 7 times, the absorption rate of the rough surface of the paint layer on laser increase by 32.8%. References | Related Articles | Metrics

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Influence of high rate charge and discharge cycle on the electronic performance and thermal safety of lithium ion battery LI Dong-qi, ZHANG Qing-song, ZHENG Shao-shuai 2023, 49 (3):  30-35.  Abstract ( 264 )   PDF (2624KB) ( 379 )   Save Lithium-ion batteries are widely used in electric vehicles and various energy storage devices. In this paper, cyclic aging and thermal runaway experiments under different charge-discharge rates were carried out, and the effects of large-rate charging and discharging on the performance and thermal safety of single lithium-ion batteries were studied. The results showed that the actual capacity of single lithium-ion battery is attenuated under the large-rate charge-discharge cycle, and the degree of attenuation is positively relevant to the charge-discharge rate. With the charge-discharge rate increasing, the constant current ratio is stepwise attenuation, but the coulombic efficiency still maintains in the range of 99%-100%, indicating that the reversible performance of lithium-ion batteries is normal. With the increase of the magnification, the thermal runaway trigger time, explosion pressure and jet flame temperature first increase and then decrease. The average surface temperature of the battery during explosion is 655.8 ℃, which is close to the melting point of aluminum. The explosion injection powder products are mainly metal aluminum, graphite and lithium cobalt oxide. References | Related Articles | Metrics

Mechanical Engineering and Power Engineering

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Influence analysis of inlet gas volume fraction and blade number of vortex pump on it’s inner flow field and hydraulic performance ZHANG Ren-hui, DUAN Peng, YANG Wei-feng 2023, 49 (3):  36-42.  Abstract ( 118 )   PDF (5808KB) ( 207 )   Save In order to analyze the influence of inlet gas volume fraction and blade number on the inner flow filed and the hydraulic performance of vortex pump during gas-liquid two-phase flow, the inner flow filed and the hydraulic performance of vortex pump with different inlet gas volume fraction (5%, 10%, 15%) and different blade number (20, 22, 24, 28) were analyzed by numerical simulation. The analysis results show that the head and efficiency of the vortex pump decrease with the increase of inlet gas volume fraction with the head decreased from 48.98 m to 36.19 m, and the efficiency decreased from 34.8% to 32.4%. The pressure in the side channel on each meridional plane is greater than that in the impeller channel. The pressure difference between the maximum pressure in the casing and the minimum pressure in the impeller gradually increases along the circumference from the inlet to the outlet of the impeller, which result that the gas-liquid separation on the meridional plane is becoming more and more serious. The gas volume fraction in the impeller increases gradually while the gas volume fraction in the side channel decreases gradually, and the gas accumulation near the impeller hub becomes more and more serious. With the increase of the blade number, the head and efficiency of the vortex pump increase first and then decrease. With the increase of inlet gas volume fraction, the sensitivity of vortex pump performance with the number of blades increases first and then decreases. References | Related Articles | Metrics

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Numerical simulation research on T300/69 composite laminate under multi-angle impact LIU Jian-hui, PAN Yi-chen, XUE Wen-zhuo, SUN Jian-ren 2023, 49 (3):  43-48.  Abstract ( 103 )   PDF (4556KB) ( 136 )   Save To investigate the effect of different impact energies/angles on the edge impact performance of T300/69 composite laminate, a numerical simulation of the edge low-velocity impact process of T300/69 composite laminate with different impact energies/angles is carried out based on the three-dimensional Hashin failure criterion of strain description with the help of Abaqus finite element analysis software and the modified VUMAT subroutine. The finite element model of the edge low-velocity impact of T300/69 composite laminate is established and the results of the finite element simulation show that the damage degree and energy absorption of the composite laminate decrease with the increase of impact angles with the same impact energies. Meanwhile, the damage degree and energy absorption of the composite laminate increase with the increase of impact energies in the condition of the same impact angles. And the modified VUMAT subroutine can better predict the low-velocity impact response and damage of T300/69 composite laminates. References | Related Articles | Metrics

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Study on mechanical characteristics of vascular bundle tower based on bamboo biological characteristics ZHENG Yu-ming, HE Zheng-wen 2023, 49 (3):  49-54.  Abstract ( 119 )   PDF (1677KB) ( 175 )   Save Bamboo has a strong survival ability, which is closely related to its unique biological structure. From a macroscopic perspective, the non-uniform distribution of bamboo nodules along the bamboo body is the most significant structural feature of bamboo, and the nodules increase the axial and radial compressive capacity of the bamboo material. The vascular bundle of bamboo nodes was further investigated from the microscopic point of view, and it was found that the vascular bundle of bamboo nodes was the main load-bearing structure of bamboo nodes. In consideration of the similarity between bamboo and wind turbine tower, the bamboo vascular bundle structure was applied to the tower structure to design the bamboo vascular bundle tower, and the static analysis of the bamboo vascular bundle tower and the conventional tower was carried out under the extreme working conditions. The results show that the maximum response stress of the bamboo vascular bundle tower is reduced by 22.12% and the maximum response displacement is reduced by 9.02% compared with the conventional tower, meaning that the bamboo vascular bundle structure improved the strength and stiffness of the bamboo vascular bundle tower. This study provides a theoretical basis for the practical engineering application of bamboo microstructure. References | Related Articles | Metrics

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A machine learning methods for identifying the properties of Chinese medicinal materials from infrared spectrum data TIAN Chun-ting, ZHAO Ning, QIN Jian-wei, MENG Xiao-feng 2023, 49 (3):  55-59.  Abstract ( 194 )   PDF (2953KB) ( 394 )   Save There are great differences in the characteristics of near-infrared and mid-infrared spectra of different kinds of traditional Chinese medicine. Due to the different chemical components such as inorganic elements and organic substances, even if the origin of the same traditional Chinese medicine is different, the labeling effect under near-infrared and mid-infrared spectral irradiation will have different spectral characteristics which can be used to classify Chinese herbal medicine and identify the origin of Chinese herbal medicine. With the help of MATLAB software tool and K-means clustering algorithm in SPSS classification tool, unsupervised machine learning is carried out on traditional Chinese medicine to classify traditional Chinese medicine; Using SPSS neural network multilayer perceptron and the random forest algorithm provided by Python language, 70% of the data set is used as the training set and 30% as the verification set to train the supervised machine learning model which is finally used to identify and predict the origin of traditional Chinese medicine. References | Related Articles | Metrics

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Thermal-structure coupling analysis of neutron target system of beryllium palladium copper composite based on fluent ZHANG jing, ZHOU Zong-tuan, WANG Sen, YANG Long-fei, LIU Wen-bo 2023, 49 (3):  60-66.  Abstract ( 128 )   PDF (6487KB) ( 104 )   Save In the field of electronic devices, the heat dissipation of high heat flux electronic devices has become an important factor restricting the development of high-tech. The neutron target system with simple structure can not meet the heat dissipation requirements of some kinds of electronic devices. Therefore, a new and efficient microchannel beryllium-palladium copper composite neutron target system is designed and developed to solve the heat dissipation problem of beryllium-palladium copper composite using liquid cooling technology. The flow field and thermal stress distribution of beryllium-palladium copper composite neutron target system with different structures were compared and analyzed by using the turbulence model in ANSYS Fluent and Static Structural simulation software, and the microchannel beryllium-palladium copper composite neutron target system with compact structure and good heat transfer performance was optimized. References | Related Articles | Metrics

Chemical Industry and Light Industry

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Effects of plasma activated water on the quality and antioxidant enzyme activities of fresh-cut apples CAI Meng, TIAN Li-peng, LI Chun-ai, WAN Qiang-gui, WANG Ting, PU Lu-mei 2023, 49 (3):  67-74.  Abstract ( 123 )   PDF (4411KB) ( 248 )   Save The paper aims to explore the effects and mechanisms of plasma activated water (PAW) on the preservation of fresh-cut apples. PAW was prepared by treating 0.2 mg/mL Na2SO4 sterile solution using glow discharge plasma under DC voltage of 500 V, 550 V, and 600 V for 30 min, respectively. The concentration of active species in PAW such as H2O2 and ·OH were determined by colorimetric method. The effects and mechanisms of PAW on preservation of fresh-cut apples were investigated by measuring the quality indexes and metabolic parameters of PAW soaked fresh-cut apple during storage. The results showed that the concentrations of H2O2 and ·OH in PAW increased with the increase of discharge voltage during 500 V and 600 V. The PAW could make the quality indicators such as hardness, color and acidity of fresh-cut apples stable during storage. The content of malondialdehyde (MDA) was lower than that of the control group, and the activities of lipoxygenase (LOX) and polyphenol oxidase (PPO) decreased significantly, with the superoxide dismutase (SOD), catalase (CAT) and Peroxidase (POD) activities significantly increased (P<0.05). Therefore, PAW has excellent preservation performance for fresh-cut apples. References | Related Articles | Metrics

Automation 'Technique and Computer 'Technology.

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The speed regulation method of hybrid permanent magnet memory machine throughout different stage of all speed range LI Yan-hong, BAO Guang-qing, XIE Ping, MENG Qing-cheng 2023, 49 (3):  75-82.  Abstract ( 114 )   PDF (3194KB) ( 164 )   Save Aiming at the problems of high power consumption, high demagnetization risk, and narrow speed regulation range of permanent magnet motor for top-driving drilling system, a novel direct-drive variable frequency top drive system with hybrid permanent magnet memory machine (HPM-MM) as the core is proposed. According to the corresponding relationship between permanent magnet flux linkage and speed under different magnetization states of HPM-MM, combined with the coordinated control of online written pole and leading angle magnetic weakening, a zoning speed control strategy is realized. In addition to the excellent characteristics of a permanent magnet synchronous motor, a wide range of smooth speed regulation characteristics is available in the HPM-MM system. By calculating the turning speed, the operation area is divided into constant torque low-speed area and constant power high-speed area. In the low-speed region, the motor is in the forward saturation magnetization state, so as to obtain the maximum output torque. The high-speed area includes weak magnetic field Ⅰ area and weak magnetic field Ⅱ areas, where the former realize high-efficiency speed regulation through backward magnetization state adjustment of soft magnetic material, and the latter adopts the leading angle flux weakening control to further widen the speed regulation range by redistributing the stator current. References | Related Articles | Metrics

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Research on the properties of fuzzy reverse triple Ⅰ method for residual intuitionistic fuzzy reasoning XU Xiao-fu 2023, 49 (3):  83-87.  Abstract ( 66 )   PDF (625KB) ( 50 )   Save With the help of the reverse triple Ⅰ method for intuitionistic fuzzy inference (IFMP), the continuity and robustness of the reverse triple I method of intuitionistic fuzzy inference (IFMP) is studied. The IFMP problem of the reverse triple Ⅰ method of intuitionistic fuzzy inference (IFMP) under intuitionistic fuzzy distance is verified, which has good continuity approximation property and robustness. References | Related Articles | Metrics

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Fast garbage images classification model based on depthwise separable convolution combined with multi-channel attention WANG Xing, YAN Rong-jing 2023, 49 (3):  88-93.  Abstract ( 134 )   PDF (3244KB) ( 168 )   Save Aiming at the problems of complex structure and poor real-time performance of traditional garbage image classification models, a fast garbage images classification model based on depthwise separable convolution combined with a multi-channel attention mechanism was proposed. Firstly, depthwise separable convolution is constructed by using deep convolution and pointwise convolution, and the training time overhead of the mode is reduced by reducing the number of convolution parameters. Then the multi-channel attention mechanism is introduced to make the model pay more attention to the features with strong classification ability. Finally, the test is performed on open-source garbage image classification data sets such as TrashNet、Garbage-classify, and GINI. The experimental results show that the model has a lower time overhead than the current mainstream garbage image classification models while maintaining a higher recognition accuracy. References | Related Articles | Metrics

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Research on noise addition and precision analysis in differential privacy WANG Xiao-shi, KANG Hai-yan 2023, 49 (3):  94-103.  Abstract ( 189 )   PDF (2751KB) ( 364 )   Save Differential privacy, as a definition of privacy protection with a strong mathematical background and rigorous mathematical derivation, has received great attention and has been widely studied. However, up to now, there is a lack of strict and clear proof and derivation processes for the definition of differential privacy and the basic mechanism used in China, which makes it difficult for scholars to get started. Therefore, in this paper, the Laplace and exponential mechanism in differential privacy are analyzed in detail by means of analysis, proof, and application examples, and a complete mathematical derivation process and application examples are given to address this gap. It is pointed out that there is a problem of excessive scaling in the accuracy formula of the Laplace and exponential mechanism. After proving the accuracy formula of Laplace and the exponential mechanism, the reason why this paper considers excessive scaling is given. It is not difficult to conclude from experiments that the Laplace mechanism precision formula and the exponential mechanism precision formula are formulas with an excessive range of accuracy. References | Related Articles | Metrics

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Design of a fully automatic verification system for microcontroller after silicon HE Ji-ai, GOU Bin 2023, 49 (3):  104-108.  Abstract ( 92 )   PDF (1697KB) ( 166 )   Save Post-silicon verification plays a significant role in the pre-silicon procedure, which can find out the escape errors accurately. As the complexity of microcontrollers increases, there exists a large number of test cases and parameters, which makes the process inefficient and time-consuming. The use of automated system management and regression testing is an effective method. A fully automatic post-silicon verification system of microcontrollers based on the cooperation of epigynous and hypogynous machines is proposed. The hypogynous machine of system is the hardware platform to be tested. The epigynous machine designs the TLV (type-length-value) message protocol based on Unittest, and the automatic control of oscilloscopes and logic analyzers are realized through Pyvisa and Saleae libraries. The HTMLTestRunner library is used to generate visual test reports, and one-button automatic regression and control are realized by using Unittest. The advantages of the system are low-test cost, high test efficiency, and strong reusability. References | Related Articles | Metrics

Architectural Sciences

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Experimental study on mechanical properties of undisturbed frozen soil on different depths in permafrost region BI Gui-quan, XIONG Meng, CHAI Ming-tang, HU Yang, YU Hong 2023, 49 (3):  109-114.  Abstract ( 96 )   PDF (2709KB) ( 98 )   Save In order to investigate the strength and deformation characteristics of the undisturbed sample of permafrost under vertical and outward loading, uniaxial tests and consolidation tests were performed on undisturbed samples of permafrost with different depths to analyze the compressive strength, Elastic Modulus, failure pattern, and thawing characteristics of frozen soil. The test shows that the stress-strain curve of the shallow soil is an irregular nonlinear curve and the stress-strain curve of the deep soil is a parabolic curve in the uniaxial test. As the ice content increases and the sand content decreases, the bearing body of load is developed from the soil particle skeleton to ice crystals, and the compression strength and elastic modulus decrease first and then increase with the increase of soil depth. Failure of frozen soil is divided into three types: there are no obvious cracks on the outside when ductile failure occurs, and only compression deformation occurs; shear failure on the weak surface leads to the lateral cracks and lateral compression deformation; cracks of brittle failure expand from the middle part to the axis. In the consolidation test, the main consolidation generally occurred in the first 100 minutes; the consolidation strain and thawing coefficient of the deep soil are larger than those of the shallow soil layer and the deep soil layer thawing settlement coefficient is greatly affected by the load. References | Related Articles | Metrics

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Study on bearing capacity of foundation pile considering friction enhancement effect under combined load SONG Xiao-chun, DUAN Xin-guo, HUANG Rui, ZHU Yan-peng 2023, 49 (3):  115-120.  Abstract ( 79 )   PDF (3237KB) ( 127 )   Save At present, the pile bearing capacity analysis method of single load acting separately and then effect superimposing is adopted in the code, which ignores the coupling between vertical and horizontal loads and does not conform to the real stress situation. In order to investigate the bearing mechanism of foundation pile under combined load, based on the beam theory of elastic foundation, the expression of resistance moment caused by friction was derived considering the friction enhancement effect and displacement increment under load, and the displacement-internal force control equation of foundation pile was established. Use Mathematica software to analyze the existing cases and verify the correctness of the theory. The results show that under the condition of small deformation, considering the friction enhancement effect and displacement increment, the calculation accuracy of pile deformation and internal force is very good, and the accuracy is greatly affected by the change of calculation parameters. The results show that the deformation and internal force calculated by considering the friction enhancement effect and displacement increment have good accuracy when the pile is in small deformation under combined load. With the increase of the free section of the pile, the relative error of the calculated bending moment is still less than 10%. The research results provide a new idea for the calculation of bearing capacity of foundation piles, and enrich the analysis theory of bearing capacity of foundation piles under combined loads. References | Related Articles | Metrics

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Improved general limit equilibrium when considering the suction of unsaturated soil matrix CHOU Ya-ling, LIU Qiang, ZHU Shu-shun 2023, 49 (3):  121-126.  Abstract ( 79 )   PDF (1101KB) ( 111 )   Save The limit equilibrium strip method is currently a method widely used in slope stability analysis, and the General Limit Equilibrium (GLE method) has the most complete theory and the most relaxed conditions. The shear strength and earth pressure of unsaturated soils are greatly affected by the matrix suction. Therefore, when applying the GLE method, the role of matrix suction cannot be ignored. Based on this, the article makes the following improvements to the GLE method: ① the shear strength of the soil adopts the extended Mohr-Comlonb strength criterion; ② the inter-strip force function adopts a constant relationship similar to the strength criterion of the soil. Through the analysis of the calculation example, it can be known that the safety factor obtained by the improved GLE method is greater than that before the improvement. Therefore, the GLE method underestimates the anti-sliding force of the slope, which further illustrates the influence of matrix suction on slope stability is great. References | Related Articles | Metrics

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Mechanical properties impact analysis of simply supported steel beam with torsional system under uniform load GUO Yi-qing, ZHANG Wen-fu 2023, 49 (3):  127-134.  Abstract ( 120 )   PDF (1505KB) ( 114 )   Save In order to study the mechanical properties of simply supported steel beam with torsional system in the span under uniform load, the double variant stationary value theory of total potential energy was used to derive the correlation calculation formulas between critical uniform load of steel beam and torsion rigidity coefficient of torsional system. At the same time, the ANSYS finite element model is established to perform the buckling model analysis of simply supported steel beam with different torsion rigidity coefficients in the span. The theoretical calculation results and finite element analysis results both show that with the increase of the torsion rigidity coefficient, the critical uniform load of simply supported steel beam is improved effectively. References | Related Articles | Metrics

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Study of field test of cement-modified soil road bed in collapsible loess area JIN Ming-liang, WEI Zheng-peng 2023, 49 (3):  135-139.  Abstract ( 103 )   PDF (1214KB) ( 138 )   Save In order to solve the problem of reflective cracks often existed in the pavement structure layer, the construction effect of cement-improved soil pavement bed under the action of ordinary roller and large vibration force roller was compared by taking the construction of an expressway in Longdong region of Gansu Province as an example. Through rolling combined process and compaction parameters, the optimum filling thickness of cement-modified soil under the action of high vibration force roller is obtained. Through the different arrangement of construction period of pavement structure layer on the top surface of pavement bed, the effective way to reduce the reflection crack is studied. The test results show that: Influenced by the hydration reaction of cement-modified soil, with the increase of delay time, its maximum dry density decreases, while its optimum moisture content increases gradually. It is beneficial to improve the compaction degree of cement-improved soil by adopting strong vibration of high-exciting force road roller and increasing the number of compaction times. Due to the development of construction machinery, the compaction thickness can be appropriately increased on the basis of the limit specified in the specification. The reflective cracks of the pavement structural layer are obviously reduced with the increase of the placement time of the formed road bed. The test results can provide reference for the construction of cement improved soil road bed. References | Related Articles | Metrics

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Effect of skeletal flow-independent viscosity on the propagation characteristics of body waves in saturated foundations REN Yuan-yuan 2023, 49 (3):  140-146.  Abstract ( 69 )   PDF (2728KB) ( 70 )   Save Based on the research results of saturated porous medium, considering the influences of flow-independent viscosity of natural soil, the propagation behaviors of body waves in viscoelastic saturated foundation were studied in the present work. The viscoelastic dynamic coupling model of saturated soil were established by employing Biot model and Kelvin-Voigt linear viscoelastic model. The characteristic equations of body waves in viscoelastic saturated foundation were theoretically derived by Helmholtz potential function decomposition theorem with introducing displacement potential function. The variations law of the wave velocity and attenuation coefficient of body waves with physical parameters such as flow-independent viscosity relaxation time of soil, frequency and permeability were analyzed using a numerical example. The results show that the wave velocity and attenuation coefficient of P1, P2 and S waves increase with the extension of relaxation time of soil causes . Frequency and permeability in different ranges have different effects on the wave velocity and attenuation coefficient of P1, P2 and S waves. References | Related Articles | Metrics

scientiiric

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Hopf bifurcation and stability for an autocatalytic reversible biochemical reaction model with time delay GUO Fei-yan, GUO Gai-hui 2023, 49 (3):  147-152.  Abstract ( 99 )   PDF (1610KB) ( 156 )   Save Based on the Hopf bifurcation theory, an autocatalytic three-molecular reversible biochemical reaction model with time delay is considered. First, the stability of the equilibrium and the existence of Hopf bifurcation are obtained by choosing the delay τ as parameter. Secondly, the direction and stability of Hopf bifurcation are determined by the normal form theory and the center manifold theorem. Finally, some numerical simulations are presented to verify the theoretical results. References | Related Articles | Metrics

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Optimum post-warranty random maintenance policy based on working cycles SHANG Li-jun, DU Yong-jun, ZHANG Bi-wen 2023, 49 (3):  153-164.  Abstract ( 119 )   PDF (1530KB) ( 120 )   Save By incorporating both limited number of working cycles and a refund into renewing pro-rata replacement warranty (RPRW), a two-dimensional renewing pro-rata replacement warranty with refund (2DRPRW with R) is proposed, which can help manufacturers to ensure product reliability performance. Besides, by extending 2DRPRW with R to the post-warranty maintenance, a post-warranty random maintenance is modeled from consumers’ perspective to sustain post-warranty reliability, which is called random periodic replacement (RPR) policy. The cost rate model produced by RPR is constructed, and some special cost rates are obtained. Finally, the sensitivities of the proposed approaches are analyzed in numerical experiments. It shows that the warranty cost of 2DRPRW with R can be controlled by limiting the number of working cycles compared to RPRW. References | Related Articles | Metrics

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Transverse free vibration characteristics of thermoelectric material circular plate in a thermal environment TENG Zhao-chun, YANG Wen-xiu 2023, 49 (3):  165-172.  Abstract ( 83 )   PDF (2882KB) ( 182 )   Save In order to obtain the transverse free vibration characteristics of a thermoelectric material circular plate in a thermal environment, based on the classical plate theory and the inherent properties of thermoelectric materials, the governing differential equation of axisymmetric free vibration of thermoelectric material circular plate in thermal environment is established. The dimensionless governing differential equation and its boundary conditions are transformed by differential transformation method (DTM) to obtain the dimensionless natural frequencies of the transverse free vibration of thermoelectric material circular plate under pin-restrained and fixed-restrained conditions, respectively. Compared of the natural frequency of free vibration of isotropic circular plate before and after degradation, the validity of research method is verified. The effects of moments, input heat flux and applied current density on the transient temperature field of thermoelectric circular plate are discussed, as well as the effects of upper surface temperature and the applied current density on the dimensionless natural frequency. The results show that the dimensionless natural frequency of thermoelectric circular plate decreases with the increase of upper surface temperature and increases with the decrease of applied current density. The stronger the boundary constraints, the larger the natural frequency. References | Related Articles | Metrics