Table of Content

10 March 2021, Volume 32 Issue 05

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Effects of Warping Defects of Steel Plate Resistance Spot Welding on  Average Stress Intensity Factor

SONG Kai , SU Yulong, DU Zhanpeng, CHEN Shaowei

2021, 32(05):  505.  DOI: 10.3969/j.issn.1004-132X.2021.05.001

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Welding of car body might easily cause warping defects, which significantly affected the fatigue life. Aiming at influences of warping defects on the average stress intensity factor, solder joint model was modularized based on mechanics theory and finite element method. Qualified solder joints average stress intensity factor ΔKqua obtained by simulation and warping defect solder joints average stress intensity factor ΔKdef obtained by simulation were compared and analyzed. By looking for influence factors and influence rules, the definition of warping factor was proposed, and the applicability was verified through simulation. The average errors between the average stress intensity factors obtained by simulation analysis and theoretical derivation are less than 6%. Experiments show that the average accuracy of the warping defect solder joint ΔKdef corrected by warping factor is as 84.6%.

Bistable Vibration Characteristics of Rod Fastening Rotor with Internal Damping

WANG Longkai, WANG Ailun, JIN Miao, YIN Yijun,

2021, 32(05):  512-522,564.  DOI: 10.3969/j.issn.1004-132X.2021.05.002

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To reveal the complex bistable vibration characteristics for combined rotor with internal damping, a nonlinear governing equation of motion for rod fastening rotor containing disk contact, nonlinear oil film force, and internal damping was derived based on Lagrange equation. Nonlinear dynamic behavior and internal damping mechanism of the combined rotor were studied by the method of combining speed-up and speed-down, and the investigated operating rotation speed was over the 2nd critical rotation speed. The results show that the combined rotor has significant bistable vibration characteristics, which is the very undesirable phenomenon. The internal damping causes rotation speed range where the bistable response phenomena occur to move significantly to the lower rotation speed direction. As a result, internal damping effect should be considered when analyzing the vibration characteristics of the combined rotor, to effectively predict the occurrence of bistable phenomena.

Predictive Control of Plantar Force and Motion Stability of Hydraulic Quadruped Robot

LI Bing1;ZHANG Yongde1;YUAN Lipeng2;ZHU Guangqiang3;DAI Xuesong1;SU Wenhai3

2021, 32(05):  523-532.  DOI: 10.3969/j.issn.1004-132X.2021.05.003

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Aiming at the problem that plantar position of hydraulic quadruped robot is susceptible to rigid impacts when walking on hard roads, which is resulted in poor motion posture stability, a method for predicting plantar force of the hydraulic quadruped robot was proposed. On the basis of analyzing structure of the hydraulic quadruped robot, a force control model of hydraulic servo system according to kinematics and mechanics model was constructed. Then, an improved adaptive cuckoo optimized BP neural network algorithm was used to establish plantar force predictive control model, feasibility of the algorithm was verified with simulation and comparative analysis. Finally, a KL prototype of the hydraulic quadruped robot was used to test for the plantar force of rigid ground walking. The results show that the method may effectively enhance leg flexibility of the hydraulic quadruped robot and improve stability of motion posture.

High-speed Friction and Sealing Characteristics of Step Seal under Mixed Lubrication Conditions

LI Yongkang1,2;WANG Jun1;LIAN Zisheng1, 2

2021, 32(05):  533-539.  DOI: 10.3969/j.issn.1004-132X.2021.05.004

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 A numerical model of step seal was established which accounts for combined effects of fluid cavitation, elastic contact deformation, and micro asperity contact mechanics to accurately investigate high speed friction and sealing characteristics based on mixed lubrication theory. The effects of sealed pressure and reciprocating velocity on friction, leakage, as well as film thickness distributions were analyzed. Reciprocating experiment rig was conducted to verify the accuracy of the proposed model. The results show that experimental frictions are similar to numerical calculated frictions. The mixed lubrication model may simulate sealing characteristics of high-speed piston pair better. Fluid pressure and contact pressure affect sealing performance together, while contact friction of roughness is dominant.

Residual Stress of High Speed Cylindrical Grinding of 18CrNiMo7-6 Steel

ZHANG Yinxia1;YANG Xin1;YUAN Shaoshuai1;ZHU Jianhui2;WANG Dong1

2021, 32(05):  540-546.  DOI: 10.3969/j.issn.1004-132X.2021.05.005

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In order to investigate the effects of high-speed cylindrical grinding processes on the residual stress distributions of 18CrNiMo7-6 steel, high-speed grinding tests were carried out by using ceramic bond CBN grinding wheels, and single factor tests were carried out to analyze the influences of wheel speed vs, workpiece speed vw, radial feed rate vf and granularity of grinding wheels. An auxiliary split fixture used for cylindrical workpiece outer surfaces was designed and made. The X-Ray diffractometer was used to detect stress distributions of workpieces. The results show that the high-speed grinding processes may produce compressive stress on surfaces of the workpieces. The residual stress on the surface increases slightly with the increase of wheel speed vs. The effects of workpiece speed and feed speed on the surfaces stress is not obvious. The stress distributions in X and Y directions are almost the same, while the one in Y direction is slightly larger. The feed speed has a great influence on the stress distribution, with the thickness of the influenced layer reaching 100~150 μm, and the tensile stress appears. The influence of the wheel speed on stress distribution is less than the feed speed. When the wheel speed is 60 m/s, distribution of residual stress is “tower-shape” . The workpiece speed has no obvious influence rule. The granularity of 230/270 has a great influence on the stress distribution, depth of the stress influenced layer is 80～100 μm, and the granularity of 120/140 and W20 on the distribution is close. The auxiliary fixture effectively improves the accuracy and efficiency of the residual stress, and the detection efficiency is more than doubled.

Distinct Modeling and Identification Technology for Rotary Axes Geometric Error Elements of Five Axis Machining Centers

ZHENG Hualin1;XIANG Xiping1;HU Teng1;MI Liang2;LIU Yan3

2021, 32(05):  547-555.  DOI: 10.3969/j.issn.1004-132X.2021.05.006

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It was critical to precisely identify the rotary axis position-dependent geometric error elements(PDGE) and position-indendent geometric error elements(PIGE) for constructing volumetric error models of five-axis machining centers. A five-axis machining center was taken as the research object, and a distinct modeling identification method was proposed for rotary axes PDGE and PIGE. Actual kinematic models of the rotary axes were firstly constructed by using multi-body system theory and homogeneous transformation matrix. The variations of the formed spatial vector Euclidean norms at the end of the two kinematic chains were then derived, according to which the essential equations for identifying rotary axes PDGE and PIGE were established, where the required parameters for solving the identification basic equation were obtained via double ball bar tests. Combining with the essential equations, the coupling mechanism of the rotary axes PDGE and PIGE were revealed, based on which an iterative method was proposed to accurately decouple the rotary axes PDGE and PIGE. Finally, in order to verify the method, a numerical verification strategy was presented and carried out on the basis of a virtual prototype. The simulation results show that the coupling issues between rotary axes PDGE and PIGE are resolved by the proposed identification method, thus providing accurate data support for constructing volumetric error model of five-axis machining centers.

Correlationship between Contact Load and Efficiency of Cycloidal Transmission and Its Test Verification

SU Yuewen;GUO Caixia

2021, 32(05):  556-564.  DOI: 10.3969/j.issn.1004-132X.2021.05.007

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In order to study the correlationship between contact load and efficiency of cycloidal pin gear transmission, a theoretical analysis method was proposed based on Newton's method and elastic contact theory to determine accurate locations of multi-tooth mesh points, contact load distribution and transmission efficiency. Rigid body dynamic equations of cycloidal gear were built by the method herein to derive transmission efficiency, which could be expressed as a function of resultant external force of cycloidal gear. The contact loads of cycloidal gear were determined by relative geometric relationships and contact conditions of tooth profile discrete points, gear pin circle and output pin/hole of cycloidal gear. The contact loads of cycloidal gear were transferred into generalized forces to get the transmission efficiency function expressed by resultant external force/torque of cycloidal gear. A single-stage cycloidal reducer was taken as an example to analyze effects of design parameters and operating conditions on transmission efficiency. Comparative tests were tried on a special test bench. Results indicate that the theoretical calculated transmission efficiency does not change with the load. Under low load, the transmission efficiency is low, and rises rapidly when load increasing. Under high load, the transmission efficiency does not change much with load and tends to be a constant value, which is close to the theoretical one. The proposed method is accurate only for high load and may be a simple method to evaluate transmission efficiency of cycloidal pin gear.

Timing Decision Method for Predecisional Remanufacturing of Backup Roll Considering Fatigue Damage

SONG Shouxu;YU Jiong

2021, 32(05):  565-571.  DOI: 10.3969/j.issn.1004-132X.2021.05.008

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Aiming at the problem of the uncertain quality of roll remanufacturing blanks, which leads to the uncertainty of performance before and after remanufacturing, a timing decision method was proposed for predecisional remanufacturing of backup roll considering fatigue damage. Combined with the existing roll grinding technology, the sizes of grinding were determined based on the coupling relationship of wear and fatigue cracks, and the effects of multiple grinding on fatigue strength were studied. The improved nonlinear continuous damage theory was applied to establish a timing decision model for predecisional remanufacturing of backup roll. Finally, the backup rolls in a four-high rolling mill were simulated and analyzed, and the predecisional remanufacturing timings of the roll surface and the roll neck were obtained, which verifies the feasibility of the method.

Temperature Field Model and Verification of Titanium Alloy Grinding under Different Cooling Conditions

WANG Xiaoming1;ZHANG Jianchao1;WANG Xuping2;ZHANG Yanbin2;LUO Liang3;ZHAO Wei4;LIU Bo5;NIE Xiaolin6;LI Changhe1

2021, 32(05):  572-578,586.  DOI: 10.3969/j.issn.1004-132X.2021.05.009

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To overcome bottlenecks of insufficient heat capacity for atomizing air carrying nanofluids in grinding zone, a new process coupled with cryogenic air and nanofluid minimum quantity lubrication was proposed. A finite difference model of temperature field was established. Temperature fields of grinding zone with three cooling methods such as cryogenic air, nanofluid minimum quantity lubrication, and cryogenic air nanofluid minimum quantity lubrication were numerically simulated. The results show that cryogenic air nanofluid minimum quantity lubrication has the strongest heat transfer capacity, followed by cryogenic air, and nanofluid minimum quantity lubrication is the weakest. Moreover, the temperature field of surface grinding was verified under three cooling method experiments with Ti-6Al-4V as workpiece. The model error is less than 5%, which verified accuracy of the theoretical model.

Influences of MQL System Parameters on Atomization Characteristics

KONG Xiaoyao1,2;YUAN Songmei1,2 ;ZHU Guangyuan1,2;ZHANG Wenjie1,2

2021, 32(05):  579-586.  DOI: 10.3969/j.issn.1004-132X.2021.05.010

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 During MQL cutting process, the atomization characteristics of the system affect the effect of mist particle penetration between interfaces.A laser particle size analyzer was used to test the atomization characteristics of the MQL system by a single factor test. The influences of system parameters such as air flow rate, injection distance, cutting fluid dosage and cutting fluid type on the average diameter and particle size distribution of fog particles were analyzed. Results show that air flow and spray distance are main influencing factors. When the air flow is maintained in 80~90 L/min and the spray distance is controlled in 40~50 mm， the atomization effect may be better. Based on aetor analysis method, a mist particle diameter prediction model was established under the condition of MQL. The error is less than 10%. It shows a good performance in describing the influence of MQL system parameters on atomization characteristics.

Influence of Defocusing Amount on Temperature and Stress Field of Hollow-ring Laser Cladding Layer

LI Guangqi1;ZHU Gangxian1;WANG Lifang2;ZHAO Liang1;SHI Shihong1

2021, 32(05):  587-593,599.  DOI: 10.3969/j.issn.1004-132X.2021.05.011

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To reduce residual stress of laser cladding layer based on inside-beem powder feeding laser cladding, the work aims to study influence of different defocusing amounts on temperature and stress field distribution of cladding layer. Numerical simulation and experimental verification were carried out to investigate temperature and stress distribution when defocusing amount was as 0, -1 mm, -2 mm, -3 mm, -4 mm. The results show that the temperature distribution is more uniform and the residual stress is lower with negative defocusing amounts. As defocusing amount increases, the residual stress along the laser scanning direction gradually decreases with the increases of cladding layer depth.

Method of Boundary Strengthening Design for Lattice Structure Filling Model

REN Limin;DAI Ning;CHENG Xiaosheng;GONG Sai

2021, 32(05):  594-599.  DOI: 10.3969/j.issn.1004-132X.2021.05.012

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For the parts filled with homogeneous lattice structure, failure usually occurs at beams which near the boundary connection, and external load cannot be transferred to interior of lattice structure effectively. To solve this problem, a parameterized boundary strengthening technique was proposed to realize the design of “lattice-part” optimization model with solid connection. Taking connecting rod part as an example, the optimized model was compared with the homogeneous lattice filling model with equal volume. The results show that the proposed method ensures the effective transfer of load, and the model has better firmer boundary connection.

Research Progresses of HVIW Technology

DU Fei;WANG Xinyun;DENG Lei;XIA Juchen;JIN Junsong

2021, 32(05):  600-610.  DOI: 10.3969/j.issn.1004-132X.2021.05.013

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Different from the traditional welding processes, HVIW might effectively reduce the formation of heat-affected zones and continuous intermetallic compounds, thus the mechanics properties of the bonding zones were ensured. HVIW might almost achieve the connection between arbitrary metal materials, which had a wide range of possibilities for further developments and applications. HVIW might be divided into two processes: driving flyer plate moving at high speed and impact welding. HVIW included explosive welding, magnetic pulse welding, laser impact welding and vaporizing foil actuator welding. The basic principles, characteristics and application fields of four kinds of impact welding processes were briefly introduced. The metallurgical studies, interface phenomena, mechanics properties, welding window and numerical simulation in impact welding processes were summarized. Some problems in current researches were analyzed, which provide a basis for further researches.

Numerical Analysis of Shear-lag Effect on Curing Deformation of Composites

QIAO Wei1;YAO Weixing1,2

2021, 32(05):  611-616,623.  DOI: 10.3969/j.issn.1004-132X.2021.05.014

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 By analyzing the multi-field coupling of thermal, chemical shrinkage and material properties during curing, a three-dimensional numerical simulation model for curing deformation of composites was established. By comparing the predicted results with the experimental ones, it is proved that the simulation model has high computational accuracy. Based on the established simulation model, the physical mechanism and influences of the shear-lag effect were analyzed. Results show that the shear-lag effect increases with the increase of the part thickness, while the influences of the part corner radius on the shear-lag effect are insignificant. The shear-lag effect is an important factor affecting the curing deformation of parts, and the curing deformation decreases with the enhancement of shear-lag effect.

Fault Diagnosis Method of EDG in Nuclear Power Plants Based on Energy Operator Gradient Neighborhood Feature Extraction

JIANG Zhinong1;WANG Zijia1;ZHANG Jinjie2;Huang Yifei3;MAO Zhiwei2

2021, 32(05):  617-623.  DOI: 10.3969/j.issn.1004-132X.2021.05.015

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Valve clearance fault was a typical EDG faul that might lead to degradation in performance, mechanical faults, et al. The traditional methods of manually unpacking and checking the valve clearance were time-consuming and laborious. Using the transient vibration identification ability of Teager energy operator and the variation law of vibration shock energy, an online diagnostic method was proposed for valve clearance faults in EDG based on k-th maxima on Teager energy operator gradient(k-TEOG) adaptive and accurate extraction of vibration shock starting points. The reference thresholds of fault recognition herein were EDG design parameters. Experiments on a 12-cylinder V-type diesel engine show that the proposed method may effectively diagnose valve failure and has the ability to track valve clearance. The research provides an effective new way for EDG online monitoring and diagnosis.

Design and Test Analysis of PMT Detonation Defensive Equipment

MENG Lingcun1,2;YAN Ming1;DU Zhipeng2;ZHANG Lei2

2021, 32(05):  624-629.  DOI: 10.3969/j.issn.1004-132X.2021.05.016

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PMT was the core component of neutrino detection. It was arranged to work in deep water environments and withstand high hydrostatic pressure. If a PMT breaks and implosions, it would cause the surrounding PMT to burst. For this problem, a kind of PMT detonation defensive equipment was designed, and the detonation tests of PMT with defensive equipment were carried out. During the tests, image acquisitions and measurements of shock wave data of PMT implosion with defensive equipment were completed, and the mechanism of PMT implosion with defensive equipment was analyzed. Results show that the defensive equipment persist for about 400 ms to cause the overall damages after detonating the PMT, and the PMT detonation does not occur. The failure mode of defensive equipment is different from that of PMT. After broken, the defensive equipment becomes a large piece of debris, which reduces the inrush velocity of the water current and implosion energy. The implosion shock peak value of the PMT with defensive equipment is equal to 1/20 that of the bare PMT, and the pulse width is equal to 1/2 that of the bare PMT. These prove that the defensive equipment may effectively reduce the intensity of PMT implosion shock wave, and provide a reference for the design of PMT detonation defensive equipment.