Table of Content

10 January 2021, Volume 32 Issue 01

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Influences of Operating Parameters on Vaporization Characteristics and Properties of Liquid Films for Mechanical Seals

CHEN Huilong;GUI Kai;LI Xinwen;HAN Ting;XIE Xiaofeng;LU Juncheng

2021, 32(01):  2-11.  DOI: 10.3969/j.issn.1004-132X.2021.01.001

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To study the vaporization characteristics and sealing performance of liquid films for dynamic pressure mechanical seals, a computational model of liquid film vaporization in the sealing gaps was established involving the relationship between saturation temperature of water and pressure, viscotemperature effect and Newtonian fluid internal friction effect. Taking the spiral groove mechanical seal as an example, the influences of working conditions on the liquid film vaporization characteristics and sealing performance were analyzed. The results show that when the temperature of the medium increases, there is a critical temperature value where the average vapor phase volume fraction suddenly increases and the critical temperature value increases as the rotating speed increases. The increase of medium pressure and rotating speed has an inhibiting effect on vaporization. Increasing the rotating speeds tends to reduce the higher degree of vaporization quickly and a sudden change occurs at a certain rotating speed. The abrupt rotating speed may increase with the increasing of medium temperature. The sealing performance is obviously affected by the change of working conditions, especially the rate of change in sealing performance increases rapidly at critical vaporization temperature and abrupt rotating speeds. The liquid film vaporization first occurs in the leeward weir areas of spiral groove and rapidly covers the weir areas and advances to the dam areas with the increasing of medium temperature. With the increasing of rotating speeds, the circumferential distribution of the vapor phase of the lubrication film is more uniform and the high vaporization areas move to the outside diameter side.

CMSO for Multidisciplinary Design Optimization Method

YI Yongsheng1,2;LI Wei1;GAO Liang1;XIAO Mi1;QIU Haobo1

2021, 32(01):  12-17.  DOI: 10.3969/j.issn.1004-132X.2021.01.002

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In order to avoid complex time-consuming multidisciplinary analysis and cumbersome sensitivity calculation in solving complex engineering multidisciplinary design optimization problems, a CMSO method was proposed for multidisciplinary design optimization. Firstly, a collaboration model was used to filter sample points which might reflect the characteristics of the multidisciplinary design optimization problem better and to maintain the multidisciplinary consistency of the system. Then, adaptive surrogate models were constructed, verified and confirmed through the selected sample points. Then the best surrogate model was selected to approximate the multidisciplinary design optimization model and the sequence quadratic program method was used for optimization solution. The feasibility and effectiveness of the CSMO method were verified by a mathematical example and a cylindrical spiral compression spring design case, and the high efficiency of CMSO method was demonstrated by comparison with individual discipline feasible.

Swept-frequency ET and Innovative Feature Extraction of  Abrasion Defects for Thimble Tubes in Nuclear Power Plants

ZHANG Lei1;LIU Wujun3;XIE Shejuan1,4;WANG Xiaogang2;KONG Yuying2;MA Qiang2;CHEN Zhenmao1

2021, 32(01):  18-25.  DOI: 10.3969/j.issn.1004-132X.2021.01.003

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To avoid reactor coolant leakage because of abrasion defects of thimble tubes in nuclear power plants from micro-vibration abrasion, the depths of abrasion defects needed to be accurately quantified. A finite element model of thimble tubes ET was established. The effects of depth, axial length and circumferential angle of abrasion defects of thimble tubes on ET signals were analyzed by simulation. Results show that the phase angle features of ET signals are not independently related to the defect depths，which means that conventional single frequency ET may lead to large errors of defect depths. Thus, a swept-frequency ET method was proposed for abrasion defects of thimble tubes, and an innovative feature namely zero-crossing frequency feature was extracted. Results of simulation analysis show that zero-crossing frequency feature is highly independently related to the defect depths.

Damage Detection in Composite Based on Time Reversal Lamb Waves Method

XIA Xiaosong;ZHENG Yanping

2021, 32(01):  26-31，53.  DOI: 10.3969/j.issn.1004-132X.2021.01.004

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In order to detect damage of composites, focusing characteristics of time reversal Lamb waves method was adapted, and PZT sensors were mounted on a composite plate to excite and receive Lamb waves. The time reversal method may realize damage detection quickly and accurately without comparing reference signals. An improved damage imaging method was proposed to realize damage visualization. Experimental results demonstrated the effectivenesses of the detection method and superiority of the improved method.

Structural Design and Performance Analysis of Superconducting Magnetic Liquid Thrust Bearings

YAN Gang1;YUAN Xiaoyang1;CHEN Runlin2;JIA Qian1;JIN Yingze1

2021, 32(01):  32-39.  DOI: 10.3969/j.issn.1004-132X.2021.01.005

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In order to improve the efficiency and stability of large-scale flywheel energy storage systems, a thrust bearing which consisted of 16 superconducting shoes and 8 small orifice restrictors that were composed of static pressure tiles was designed, combined with superconducting magnetic force and hydrostatic fluid force. Firstly, an analysis model was established based on superconductor local model and hydrostatic fluid equation. And then, performance indexes such as stiffness of the composite bearings were analyzed by decoupling method, and the composite bearings were optimized. The results show that the composite bearings may ensure stable suspension and maintain high rigidity, and the power loss is within the acceptable ranges.

Fault Diagnosis Method of Rolling Bearings Based on Probability Output Flexible Convex Hull

YANG Luhang1;LI Baoqing1;WANG Ping2,3;WANG Jian2,3;YANG Yu1

2021, 32(01):  40-46.  DOI: 10.3969/j.issn.1004-132X.2021.01.006

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Aiming at the defects that the classification hyperplane of flexible convex hull were only formed by constraints of convex hull vertex and ignores decision-making contributions of most of the other sampling points, which led to the reduction of classification accuracy. A probability output flexible convex hull classification method was proposed. In this method, distance from all the samples to the hyperplane was calculated after the convex vertices were used to form the hyperplane. Through sparse mapping, cross entropy likelihood function was minimized and transformed into a posteriori probability output. When dealing with multi classification problems, output probability of each classifier was coupled in pairs, which further improved classification accuracy and robustness of the multi classification flexible convex hull. This method was applied to the fault diagnosis of rolling bearings, and the robustness was verified on different data sets, which may accurately identify the faults of rolling bearings.

Modeling and Simulation of Complex Ruled Surface Model for High Efficient Cutting with Wire Saw

XU Zhiteng;HUANG Hui;CUI Changcai

2021, 32(01):  47-53.  DOI: 10.3969/j.issn.1004-132X.2021.01.007

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 The shapes of the initial blanks and the final products are quite different in the complex curved surface machining for some brittle materials, such as natural stone and artificial crystal. The large removal of rough machining material leaded to the low processing efficiency and serious tool wear. A new solution was proposed based on the cooperative removal of wire saw cutting and point-cutting for the high-efficiency rough machining. According to the characteristics of wire saw processing, a new modeling method was proposed herein. The digital model of final product was layered, the polygons were used to envelope the two-dimensional outer contour curves of each layer, a ruled surface model was established with fitting the polygons between the layers. The influences of different ruled surface models constructed by different envelope polygon sides and connection methods on roughing processing time were analyzed. The simulation results show that although increasing the numbers of polygon sides or rotating between layers may reduce the volumes of remaining unprocessed materials, the overall rough machining time increases, which is not conducive to improving efficiency. The rough machining time may be used as a comprehensive evaluation index to optimize the construction of the ruled surface model.

Postprocessing Performance Regulation for Ceramic Part  Based on Controllable Binder Jet Printing Processes

CAO Shu1,2;HE Xueming3;XIE Fangxia1;YU Jinghu3

2021, 32(01):  54-64.  DOI: 10.3969/j.issn.1004-132X.2021.01.008

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It was difficult to control the structure of the ceramic parts or to realize a high-density green body, and the effects of postprocessing at atmospheric pressure were usually poor when forming ceramic green parts by commercial BJP system. The densification of Al2O3 green specimens were controlled by adjusting the formulation of molding powder materials, adjusting the thickness of powder layers and switching powder-dispensing method based on the self-developed BJP system and own material. The relatively density of the high-dense green specimens was reached 43.9%. Furthermore, the integrated post-processing procedure of “ceramic slurry infiltration and stepwise sintering” was used to study the infiltration-strengthening mechanism against different green bodies, and thereby, presintering processes were regulated to significantly improve the final performance of high density green bodies, having the relatively density, bending strength and compressive strength of 89.3%, 91.9 MPa and 813.2 MPa, respectively, after sintering under atmospheric pressures. The forming material, process procedures and equipment applied in this study had low threshold and were easy to operate, providing a flexible and quick technical scheme for the preparation of high-performance structural ceramics.

Depth Detection of Internal Defects for Arc Additive Products Based on Laser Ultrasound

YUAN Jiuxin;QIN Xunpeng;ZHANG Jinpeng;WANG Xiaokai

2021, 32(01):  65-73.  DOI: 10.3969/j.issn.1004-132X.2021.01.009

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Aiming at the problems of poor surface quality of additive products and difficulty of on-line detection of internal defects, the research of laser ultrasonic detection of internal defects for arc additive manufacturing test block was carried out. In order to ensure the accuracy of defect detection results, defect reflection method and synchronous movement of excitation source and receiving source way were adopted. The theoretical calculation, the simulation analysis and experimental results were contrasted, the propagation paths and detect wave type were determined. Defects in A sweeping reflection amplitude and defects in B scan reflected wave imaging were obtained respectively, according to the amplitude size and the imaging results. In depth of 10 mm, the internal defects 1 mm diameter were accurately detected, the influence laws of defect depth were obtained. The research results have a good reference value for the on-line detection of additive manufacturing.

Universal Post-processing for Five-axis 3D Printing

RAO Yongjian1,3;FU Guoqiang1,2,3;TAO Chun1,3;GAO Hongli1,3;DENG Xiaolei4

2021, 32(01):  74-81.  DOI: 10.3969/j.issn.1004-132X.2021.01.010

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Firstly, the structural parameters of the printer were introduced to represent the positions of two rotational axes and the workpiece in frame coordinate system. The general forward kinematics model of table-tilting five-axis 3D printer was established by exponential product theory. Secondly, the specific expressions of double solution of the rotational axis angles were obtained by combining the periodicity of the trigonometric function, the rotational axis travel and the five-axis structure features. The selection principle was proposed to obtain the optimal combination of the rotational axis angles based on the shortest path of the rotational angle. The displacements of each translational axis were obtained by the selected rotational axis angles. All the motions obtained were absolute motions based on zero position of each axis, and then the NC printing codes used directly for machining were generated, which might be processed without the help of rotational tool center point functions. Then, the general post-processing method was studied in combination with three different types of five-axis 3D printers: table-tilting, spindle/table-tilting, and spindle-tilting. Finally, the proposed method was applied for five-axis 3D printing, five-axis CNC machining experiments and five-axis machining simulations of various structure types were carried out to verify the correctness and generality of the method.

Research on Deep Drawing of Sheet Metal Using EPM Blank Holder Technique

ZHANG Hongsheng1,2;QIN Siji1;CHENG Xiao1;CAO Liqin2

2021, 32(01):  82-91.  DOI: 10.3969/j.issn.1004-132X.2021.01.011

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 In order to overcome the problems that the conventional blank holder could not apply BHF independently, and the overheating problem of electromagnetic blank holders, a novel blank holder technique was proposed based on EPM technology.  According to the characteristics of EPM technology and deep drawing processes, a deep drawing die with magnetic cushion was designed and manufactured. The magnetization and demagnetization states of magnetic pole unit and the cushion were simulated by finite element analysis(FEA). Based on the coupling analysis of magnetic field and mechanics field, the distributions of contact pressures applied on the sheets by magnetic forces were determined. By using FEA, the deep drawing processes of cylindrical cups were simulated with conventional blank holder and the new technique respectively. The results show that the strain distributions of the drawn parts obtained by the two blank holder methods is basically the same. Using EPM blank holder, the drawing experiments of 08Al sheets (thickness is as 0.98 mm) with diameters of 180 mm and 195 mm were carried out, where the drawing heights were as 48 mm. The results demonstrate that the large enough BHF may be applied independently using the new EPM blank holder method. Finally, the energy consumption of the conventional blank holder, the electromagnetic blank holder and the EPM blank holder method were calculated respectively. Among them, the EPM blank holder method has the best energy saving effectiveness. Compared with the electromagnetic blank holder, the energy saving rate using the new blank holder method is as high as 95%.

Simulation and Tests on Hot Forming Process Optimization for Door Anti-collision Beams

HU Jian1;CHEN Zezhong1;LIU Tao2;YANG Jinhua3

2021, 32(01):  92-100.  DOI: 10.3969/j.issn.1004-132X.2021.01.012

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Based on the hot stamping module of DYNAFORM software, the hot forming process of one vehicle door anti-collision beam made of B1500HS steel was studied. By introducing the thermal physical parameters of H13 die steel, the variation formula of temperature field element was obtained by the method of multi-step difference, taking the latent heat of phase transformation into account. The structural characteristics of the door anti-collision beams were analyzed, two kinds of thermal-mechanical-metallurgical coupling models were established. After comparing and analyzing the stress fields, temperature fields and thickness distributions of the overall and typical M-shaped-section of the schemes, it is found that the scheme with pad is more suitable for hot stamping, because of their uniform distribution after hot forming and quenching. Finally, the hot stamping experiments were carried out, referring to relevant parameters of the scheme with pad, and the experimental results show that microstructures of the door anti-collision beam are all martensite. In addition, the martensites lath at the bottom and top is finer, and the Vickers hardness reaches above 450HV, which meets the performance standard of hot stamping parts.

Effects of Q235 Coated Tubes on Bulging Behavior of AA5052 Aluminum Alloy Base Tube with Granular Medium

CHEN Guang1;ZHAO Changcai 1;YANG Zhuoyun 1;DONG Guojiang2;CAO Miaoyan3

2021, 32(01):  101-110.  DOI: 10.3969/j.issn.1004-132X.2021.01.013

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The AA5052 aluminum alloy extruded tube was used as inner base tube, the Q235 carbon structure steel coil welded tube was used as outer cladding steel/aluminum composite tube, and the particle media bulging behavior of the composite tubes was studied. The influences of tangential friction forces between tubes and the normal pressures on the stress of the base tubes during the bulging processes were analyzed through plastic theory. Numerical simulation was used to analyze the comprehensive influences of the friction coefficients between tubes and the anisotropy of the coated tubes on the strain forming limit of the base tubes. In addition, the wall thickness reduction of the single tubes and composite tubes and the stress and strain distribution of the base tubes during the bulging were given. Through the high-pressure bulging tests in the tube granular medium, limit bulging ratios of aluminum alloy tubes were compared under single tube and composite tube bulging conditions. The deformation compatibility of the composite tubes was analyzed. Results show that by applying Q235 carbon structural steel clad tubes, the bidirectional tensile stresses are reduced at the middle section of the bulging zones of the AA5052 base tubed, the wall thickness reduction of the base tube bulging zones is decreased, and the bulging ratio is increased by 22%. The maximum thinning rate of the base tubes under the composite tube is as 17.5%. The forming performance is significantly improved.

Development of Excitation Sources for Liquid High Frequency Sinusoidal Pressure Based on Piezoelectric Stack

LI Bo1;YANG Jun1;ZHANG Heyu1;ZHANG Zhaojing2;GONG Zheng3

2021, 32(01):  111-116,125.  DOI: 10.3969/j.issn.1004-132X.2021.01.014

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The sinusoidal motions of liquid in sealed cavity were driven by piezoelectric stack to realize the sinusoidal changes of pressure in hydraulic cavities. According to the piezoelectric effect and cavity resonance principle, the excitation sources of high frequency sinusoidal pressure with single piezoelectric stack and double piezoelectric stacks were designed, the two devices were compared. The results show that the double piezoelectric stacking device with a novel way of generating sinusoidal pressure may generate a large sinusoidal pressure amplitude and a small sinusoidal distortion. The working frequency of the device is up to 30 kHz. The amplitude and waveform of sinusoidal pressure may be adjusted at the same frequency. The device may meet the measurement and calibration requirements for dynamic pressures of pressure sensors and testing systems.

Design of P2 Hybrid Engine Start Control

MO Chongxiang;XIU Caijing;LIANG Wanwu

2021, 32(01):  117-125.  DOI: 10.3969/j.issn.1004-132X.2021.01.015

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Based on analysis of engine start control theory of P2 hybrid powertrain with double clutch transmissions, the control strategies of P2 hybrid powertrain engine start dynamic condition was designed. The target powertrain control value calculations and the analysis corresponding to those each control phases were proposed. It is proved that the designed control strategy may realize the engine start effectively through the simulation and vehicle tests. According to the vehicle longitudinal acceleration curves of the real vehicle tests, the designed control strategy also achieves good results in vehicle ride comfort.