Table of Content

25 April 2020, Volume 31 Issue 08

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Review on Management at Mechanical Design and Manufacturing Discipline of NSFC in 2019

LAI Yinan;LI Hongwei;YE Xin;CAO Zhengcai

2020, 31(08):  883-889. 

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The applications, evaluations and funding of projects at mechanical design and manufacturing discipline(division Ⅱ of engineering science) of the NSFC in 2019, as well as the research progresses and fruits of the executing and finished projects were reviewed. Specific measures of mechanical design and manufacturing discipline were stated, such as the new age reform of scientific fund, academic exchange and cooperation, talent cultivation, and academic team construction and so on. Finally, the researches of the medium and long-term development planning and the 14th five-year development strategic plan was briefly introduced.

Design and Motion Simulation of Variable Stiffness Bending Soft Actuators Driven by Granular Flow

HAN Fenglin1,3；LI Peng1,3；LI Minghui1,3；TIAN Liang2,3

2020, 31(08):  890-897. 

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To improve the carrying capacity of soft robot, a variable stiffness bending soft actuator was designed by utilizing both of the characteristics, flow and jamming of granular matter. A prototype of variable stiffness bending soft actuator was designed and made based on the mechanics of granular matter. Elastoplastic joint model and Ogden hyperelastic constitutive model individually describing the granular matter and the deformation cavity materials were obtained through experiments. Finite element simulation methods of the soft actuator motion processes were proposed. The experimental platform of variable stiffness soft actuator was set up. Bending angle errors obtained by the experiments and simulations are about 15.6%. The carrying capacity may increase about 1.75 times by using granular jamming principle.

Load Distribution and Bending Fatigue Life Analysis of Hub Bearings Based on Modified L-P Model

LIN Fen1;TANG Jie1Z;HAO Youqun1;LI Jianlei1;ZANG Liguo2;CHEN Yuke1

2020, 31(08):  898-906. 

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The third generation hub bearings were taken as the object of study to deduce the contact deformations and contact loads among rolling body, inside and outside raceways under the actions of bending moment. A more accurate calculation model of contact load distribution was proposed. The circumferential distribution laws of contact load and contact angle of hub bearings under different working conditions were analyzed. Based on the first modification of load distribution in hub bearings, the contact fatigue of raceway materials and bearing rollers with different position angles was considered, and the modified L-P model of fatigue life of third generation hub bearings was obtained by using the product laws statistical interpretation. Meanwhile, combined with the ISO281—2007 life correction calculation method, second modification of the lubrication phenomenon were conducted, and the fatigue life model of the third generation wheel hub bearings was obtained, where the lubrication was modified. The bending fatigue tests of the bearings were carried out by rotating bending fatigue testing machine. The tests results show that the errors between the theoretical and testing values calculated by the proposed fatigue life model are less than 10%, and the correctness of the model is verified.

Study on Hydrodynamic Pressure Characteristics of Linear Hydrodynamic Pressure Polishing

ZHENG Zijun;XUE Kaiyuan;WEN Donghui;XU Yaoyao;YING Fuqiang

2020, 31(08):  907-914. 

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A linear hydrodynamic pressure polishing method was proposed based on the principle of hydrodynamic lubrication. Effects of polishing roller structures and processing parameters on the size and distribution uniformity of hydrodynamic pressure were studied by CFD numerical simulations. Results show that polishing roller with rectangular micro-structure will generate larger and more uniform hydrodynamic pressures on the workpiece surfaces. The larger diameter polishing roller get higher rotational speed and smaller polishing gap may obtain larger hydrodynamic pressures. At the same time， the uniformity of hydrodynamic pressure distribution will be worse. Finally， experimental platform was built and polishing experiments were carried out. Surface roughness value Ra of K9 glass is reduced from 45.41 nm to 0.91 nm after linear hydrodynamic pressure polishing.

Rigid-flexible Coupling Dynamics and Structure Optimization of Flexible Tractors

WANG Kunpeng1,2;XIAO Xiaohua1,2;ZHU Haiyan1,2;ZENG Jie1,2

2020, 31(08):  915-923,930. 

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The traditional tractor support mechanisms were mostly rigid structures, which were easy to cause blockage problems in the hole. Based on this engineering background, a structural scheme of telescopic tractors with flexible support mechanisms was proposed based on inclined blocks. The tractor support mechanisms might keep locked with the pipe walls under the load forces, which was the key for the tractor crawled forward. A rigid-flexible coupling dynamics model of flexible support mechanisms was established under load forces, the influences of parameters such as span, width, thickness and chamfer on locking of flexible support mechanisms were revealed, and the optimum design method of flexible support mechanisms were obtained. The superiorities of rigid-flexible coupling model over rigid model were analyzed by rigid-flexible coupling dynamics simulations, and the maximum load forces of flexible support mechanisms under optimal span, width, thickness and chamfer were obtained. The test results show that the measured values are basically in agreement with the theoretical analysis ones and the simulation ones, which verify the validity of the traction locking laws of flexible support mechanisms and the rigid-flexible coupling model simulation.

Closing Effort Analysis of Sliding Doors Based on Co-simulation of ADAMS and Simulink

CHEN Ziming1,2;XUE Zhigang1,2;ZHANG Song3;LI Luoxing1,2

2020, 31(08):  924-930. 

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Aimed at the situation in lack of analysis tool to evaluate the closing effort of sliding doors in the early design stages, a co-simulation combined with dynamics analysis was proposed based on ADAMS and numerical iterative solution based on Simulink. A rigid-flexible coupled multibody model was built to perform dynamics simulation analysis on the sliding door systems; the differential equation of the changes in air pressure caused by airflow compressed by sliding doors in the closing processes was derived, and the iterative solution process was built in Simulink. The closing efforts of the sliding doors were performed by the co-simulation method with a result of 4.4 J, where the effort costs by air-binding and weather stripping are 48.9% and 36.6% respectively. At last, the accuracy of the co-simulation was verified as the errors of closing efforts from simulation and experiment are below 10%, which prove the co-simulation reliability.

Research on Development Algorithm for Doubly Curvature Hull Plates

CHEN Xingbu1,2;HU Yong1,2;HUANG Chaoyan1,2;WANG Yao3;WANG Jian3

2020, 31(08):  931-936. 

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In order to develop hull plates with doubly curvature, a geometric development algorithm was improved considering the characteristics of line-heating processes and large thickness of ship hull plates. Using the idea of finite element, the surfaces were segmented into strips firstly, and then the strips were separated into triangle planes for devolopment and splicing. In view of the characteristics of large thickness of ship hull plates, the developing surfaces were shifted from the profile surfaces to the neutral layers before development; in view of the characteristics of line-heating processes, the overlapping parts between the strips were eliminated and the gap parts were reserved during the splicing of the strips, so that the expansion areas were increased to compensate for the shrinkage of line-heating processes. In order to realize the automatic development of ship hull plates, the software was developed. And the development accuracy of the software was tested and verified by comparion with the results of TRIBON software. The results show that the errors of all test boards are between 1.0 mm and 1.8 mm, and the maximum error is not more than 2 mm, which may meet the actual production requirements.

Principle of Geometric Elements Constructed Tooth Pairs with Curve-surface Mesh

PENG Shuai1;CHEN Bingkui2

2020, 31(08):  937-943. 

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According to the contact characteristics of curve and surface, the principle of geometric elements constructed tooth pairs with curve-surface mesh for gear transmissions was put forward. The concepts of curve-surface contact and curve-surface mesh were provided and three key elements for curve-surface mesh were given. The fundamental principle of curve-surface mesh was presented. The corresponding conjugated curve was also deduced. By establishing a cross section profile on normal plane of every point of the curve, the tooth surface was constructed. Taking an internal helical gear of parallel-axis as an example, a new gear pair with curve-surface mesh was established by selecting a contact path on the internal helical gear and the general law for the mesh processes of the gear pair was analyzed. The results reveal that based on the principle of curve-surface mesh, a gear pair with point contact may be obtained by choosing appropriate design parameters. The principle of curve-surface mesh provides a method for the generation of tooth surfaces.

Modeling of Influences of Beam Creep Relaxation on Kinematic Accuracy Reliability of Gantry Boring-milling Machines

LI Guolong1;XIE Tianming1;REN Weixian1;CUI Gangwei2

2020, 31(08):  944-951. 

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Aiming at the influences of the beam creep deformations on the accuracy retention of the gantry boring-milling machines, a kinematic reliability assessment model of the gantry boring-milling machines was established. The multi-process continuous simulations of the beam residual stress were carried out by utilizing finite element software, and the validity was verified by the blind hole method. The geometric accuracy degradation model of the gantry boring-milling machines was constructed based on the error representation relationship between the beam guide and the ram seat, and the degradation trajectory of y direction geometric errors was determined by the creep simulation data. Combining the machine tool spatial position errors and the error degradation trajectory, the kinematic reliability assessment model was established to predict and assess the kinematic reliability of the gantry boring-milling machines under different residual stress states during the service period. The results show that the beam creep deformations cause the kinematic reliability of machine tools to decline as a power law function, and the decrease is more obvious under the greater stress before aging.

Prediction Method of Performance of Intelligent Hydraulic Components Based on Lubrication Mechanism

LIU Siyuan1,2;WANG Guangda1,2;SUN Hongmei3;LIU Jianxun4;JIANG Wanlu1,2

2020, 31(08):  952-959. 

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The hydraulic pump was taken as an example, and the slipper pair, the weakest link were the research object, and the wear of slipper was used as the causes of performance degradation. The oil film lubrication characteristic equations of the shoe wear processes were established by combining the mathematical description equation of the wear of slipper, the leakage flow formula and the instantaneous change model of piston chamber pressure. The failure mechanism of hydraulic pump performance was revealed and the failure critical points were calculated. The performance degradation states of hydraulic pump were divided into different regions, and the variation law of slipper wear, oil film lubrication characteristic parameters and performance degradation parameters of the hydraulic pump in different states were analyzed, a performance prediction model was established. The correctness of the theoretical model was verified by simulation analyses, and the validity and accuracy of the prediction model were verified by hydraulic pump performance tests. The results show that the built model may accurately predict hydraulic pump performance.

Research on FLC in CNC Single Point Incremental Forming of Aluminum Sheets

HOU Xiaoli;LI Yan;YANG Mingshun;BAI Lang;SHI Xun;ZHANG Chengxing

2020, 31(08):  960-967. 

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When CNC single point incremental forming of thin-walled complex components was carried out, sheet metal was prone to cracking, wrinkling and other defects, and the evolution of material deformation mechanism was complex, which was very sensitive to loading conditions. It was difficult to predict and control the fracture of sheet metals in CNC single point incremental forming. Therefore, 1060 aluminum sheet was selected as the research material, and the forming performance of the sheet metals in CNC single point incremental forming technology was studied experimentally to realize the prediction and control of fracture. Spatial deformation of parts was transformed into plane deformation by rubbing method. The grid data of rubbing parts were measured and extracted by digital microscope. The data were fitted by interpolation method and polynomial fitting method. Finally, the FLC in CNC single point incremental forming of 1060 aluminum sheets was obtained. The strain distributions in the break area and safe area were obtained by analyzing the FLC. The prediction and control of the rupture for the workpieces were realized. In order to further improve the forming limit of 1060 aluminum sheets, ultrasonic vibration was introduced into single point incremental forming. The FLC of ultrasonic vibration assisted incremental forming and traditional incremental forming were compared by tests. The testing results show that the forming limit of 1060 aluminum sheet increases by 11% when the vibration power is as 120 W and the vibration frequency is as 25 kHz.

Design and Performance Analysis of Turbodrill Blade Based on Joukowski Transformation

ZHANG Xiaodong;LIN Meng;GONG Yan;HAO Renjie;YANG Lin

2020, 31(08):  968-974. 

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In order to improve the performances of turbodrill blades and to innovate blade design theory, a new method of turbodrill blade design was proposed based on the combination of Joukowski conservative angle transform airfoil design theory and the classic hydraulic airfoil. Taking 127 turbodrill blade as research object, 5 kinds of 127 turbodrill airfoil design were completed by using built turbodrill blade parametric design platform and self-designed turbodrill performance test bench. The flow characteristics corresponding to 5 kinds of blade were discussed in detail. Then the performance tests of the designed blades were carried out. Finally, actual performances of the design airfoils and a 127 turbine blade serving in Xinjiang Tarim Oilfield were compared and analyzed. The experimental and simulation results show that single-stage torque of NACA-0012 type thickened blades which are designed based on a new method reaches 5.83 N·m under the test conditions of 600 r/min rorate speed and 15 L/s flow rate. Comparing with the ones serving in Xinjiang Tarim Oilfield under the same conditions, single stage torque increases 6.4% and stage efficiency increases 1.16%, which show overall performance improvements.

Forward Design Method of Electric Vehicle Body Stiffness Based on Thin-walled Beam Structure

ZHONG Haolong;ZHANG Xiaolong;LIU Zijian

2020, 31(08):  975-982. 

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The frame structures of automobile body were composed of thin-walled beams. Therefore, the thin-walled beam theory was applied to the forward development of vehicle body. Based on the improvement of the body stiffness design method in references, the mechanics relationships among 14 state vectors and 15 section properties of thin-walled structure including double moment and warping function were deduced herein. The stiffness analysis model of the body beam elements was established including main section properties and rigid chain mechanics model of vehicles with the coupling of body joints. Comparing the finite element analysis results of the same models with the ones of stiffness chain calculations in references, the rationality of the calculation method of the stiffnesses of the thin-walled structure body proposed herein was verified. Finally, with the constraints of body bending and torsional stiffnesses, and with the objective function of vehicle body quality, the genetic algorithm was used to solve the problem. The vehicle body lightweight design effectiveness was obtained，which is better than that in references.

Ablation Hole Characteristic of 2.5-dimensional Cf/SiC Composites Processed by Nanosecond Laser

JIAO Haowen1;CHEN Bing1;LUO Liang1;LI Jinbang2,3

2020, 31(08):  983-990. 

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In allusion to difficult machining problems of new 2.5-dimensional carbon fiber reinforced ceramic-based(Cf/SiC) composite materials by conventional machining, the 2.5-dimensional Cf/SiC composite materials were ablated by nanosecond laser. After ablating, the morphology of ablation hole characteristics were observed by scanning electron microscope, and the ablation removal mechanism was analyzed. The influences of laser parameters on the ablation hole were discussed. The results show that the ablation phenomena of Cf/SiC composites occur in the laser ablation area, such as ablation holes, resolidification, fiber fracture, end swelling, and elliptical material performance change area with long axis along fiber direction. Oxidation reaction may be found during laser ablation processes of Cf/SiC composites materials. The ablation hole diameter increases with the increasing ablation power and ablation time. When the ablation time and ablation power are large enough, there may be a case where the ablation hole is blocked or partially blocked by the resolidification materials. The beam waist radius of nanosecond laser was calculated to be as 223 μm, and the ablation threshold of Cf/SiC composite materials is 0.32 J/cm2 by nanosecond laser.

Research on CFRP Milling Considering Continuity of Left-handed Cutting Edges

WANG Zegang;WANG FujiLU Xiaohong;ZHAO Meng;FAN Junfeng

2020, 31(08):  991-996. 

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When CFRP was machined by a right-handed cutting edge milling tool, the fiber layers were subjected to unidirectional axial forces and was liable to cause delaminations and burr damages. Multi-tooth milling tool with the left and right-handed cutting edges coexisting the two-way axial forces on the fiber layers might effectively restrain the damages. However, how to ensure that each layer of fibers was subjected to the cutting actions of left and right-handed cutting edges becomes the key to suppressing damages. Herein, selecting the multi-tooth milling tool as the research object, three types of multi-tooth milling tools with continuous, overlapping and discontinuous cutting area of left-handed cutting edge were obtained by designing different angles of left-handed helical grooves. The testing results show that there are a few burrs and flanges on the surfaces of CFRP when the cutting area is continuous. When the cutting area overlaps, there is no burrs and tear damages on the surfaces of CFRP. When the cutting area is discontinuous, there are a lot of burrs and tear damages on the machined surfaces. In addition, the surface roughness increases as the angle of left-handed helical groove increases.

Current Research and Development Trends in Constitutive Relation for High Strength Aluminum Alloys in Hot Plastic Deformation

CHEN Minghe;WANG Ning

2020, 31(08):  997-1007. 

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In addition to temperature, strain rate and strain effects, microstructure evolution might be considered in hot plastic constitutive relation for deformation behavior characterization of high strength aluminum alloys in hot forming processes. Constitutive relation researches of high strength aluminum alloys in hot plastic deformation were summarized. The research results show that the widely applied phenomenal constitutive models may couple the effects of strain, temperature and strain rate by modifying model parameters and provide accurate prediction for the flow stresses. However, the phenomenal constitutive model prediction accuracy might not be guaranteed under the wide ranges of temperature and strain rate or out of the experimental scopes due to lacks of explanation on the deformation mechanism. The physical based constitutive models may calculate the flow stresses based on modeling the microstructural deformation behaviors such as dislocation density, grain size and dynamic recrystallization, which shows great ability in predicting both of macro and micro behaviors. Thus, this is the research trend of the constitutive relation for high strength aluminum alloys in hot plastic deformation.