China Mechanical Engineering

Study on Dynamic Response Characteristic Simulation of EMCVT Actuators

LIU Junlong1;SUN Dongye1;LIU Xiaojun1;YE Ming2;YOU Yong1

2020, 31(03): 253-260.

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In order to study the reliability of the EMCVT and the influence factors of the response characteristics of the EMCVT speed ratios and driven pulley clamping forces, a dynamics model of the EMCVT actuator was established using MATLAB/Simulink. Then, the speed ratio feedback controller and driven pulley clamping force feedback controller were designed on the basis of the dynamics model. Finally, the simulations on dynamic characteristics of the electro-mechanical actuator under conditions of step change of CVT speed ratio and input torque were carried out with the designed controller. The results show that the overshoot and settling time of the speed ratio and driven pulley clamping force may meet the requirements of a CVT, and the response time of the driven pulley clamping force is less than 1 second and the maximum change rate of the CVT ratio reaches 2. Additionally, the response characteristics of the speed ratio and driven pulley clamping force are influenced by the torque loads and rotation directions of the execution DC motors.

Effects of Temperature on Secondary Fatigue Crack Initiation and Growth Behavior of High-speed Railway Wheel Steels

FANG Xiuyang;HUANG Wei;WANG Junguo

2020, 31(03): 261-266.

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School of Mechanical Engineering,Southwest Jiaotong University,Chengdu，610031
For high-speed railway wheel steels under severe service temperature conditions, fatigue crack initiation and growth behavior are important for planning maintenance interval and assessing residual lifetime. Fatigue tests were conducted under -60~60 ℃ test conditions for ER8C high-speed railway wheel steels and fracture morphologies were observed. The results show that the fatigue lifetime decreases as the temperature increases for both of wheel rim and web steels. Secondary fatigue crack initiation and growth area with shape of half ellipse exists under high testing temperature conditions. Furthermore, for wheel rim and web, the generation temperatures of secondary fatigue crack initiation and growth areas are different due to the diversity of steel strength and toughness, for wheel rim，this critical temperature is 50 ℃ while it is 30 ℃ for wheel web. Based on the comparison of growth characteristics between the main and secondary cracks, it may be concluded that the weak area changes from pearlite lamella to grain boundary of pearlite colony as the stress intensity factor range increases.

Experimental Study on Influences of Laser Shock Processing on Fatigue Performance of LZ50 Axle Steels

TANG Kai1;ZHOU Liucheng2;HE Weifeng2;WANG Wenjian1;GUO Jun1;LIU Qiyue1

2020, 31(03): 267-273.

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The present work aimed to improve fatigue performance of LZ50 axle steels by using LSP methods. LSP was applied to the surface of LZ50 axle steel specimens, the JD-1 wheel/rail simulation machine was used to explore the fatigue performance of LZ50 axle steels under LSP with different parameters. The surface hardness of two axle specimens with different parameters of LSP significantly increases at the rate about 18% and 27%, respectively. After LSP at the interference fitted surface of the LZ50 axle steel specimens, a plastic deformation layer was generated, resulting in a high residual compressive stress. After test, both sides of the interference fitted surfaces emerged annular band damages which presented plough and spalling, and the damage mechanism was abrasive wear, oxidation wear and delamination. The morphology feature of fracture surface before and after LSP is similar and fatigue crack initiation is multisource. Many of quasi-cleavage fracture in the propagation area are trans-granular fracture mode. A large number of dimples and second cracks appeares in the final fracture area. The fatigue life of the axle materials is obviously improved by LSP, and the fatigue life rate of the two treated axle specimens with different parameters increases by 31% and 21%, respectively.

Back-stepping Sliding Mode Control for an Electromagnetic Valve Actuator

FAN Aimin;CHANG Siqin;CHEN Huitao

2020, 31(03): 274-280,288.

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To satisfy the application requirements of the EMVAs, a new control scheme was presented based on the analysis of structural features and the establishment of mathematical model of the self-developed EMVA. The control method is a compound algorithm based on the back-stepping control, combining with the advantages of adaptive control and sliding mode control. The simulation results show that the proposed control method may achieve precise valve motions, and also has strong robustness to system parametric variations and external disturbances. An experimental set-up was used to verify the effectiveness of the proposed method. When the valve lift is set as 8 mm and the ideal transition time is set as 4.8 ms, the experimental results are in good accordance with the simulation results, and a transition time of 3.3 ms and a seating velocity of 0.055 m/s are obtained.

Ice Load Identification Method of Ship Structures and Experimental Verification

KONG Shuai;CUI Hongyu;JI Shunying

2020, 31(03): 281-288.

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Ice loads were important environmental loads which might influence the structural safety of the ships during the navigation in the ice-covered waters. The ice pressures on the ship were generally monitored by the strain sensors and the reasonable layout of the strain sensors was the foundation of reconstruction of ice loads. Through the comparison between the impact loads and measured strains of the different measurement schemes in the tests of shell structures of the ship, the optimal measurement schemes were determined. The dynamic responses between the strains and impact loads of shell structures of the ship were established by means of Green kernel function and the analysis of the ill posed problems during the load identification due to noise was performed. The Tikhonov regularization method was adopted to overcome the numerical instability during the processes of load identification. At last, the measured responses were applied in the load identification. The identified loads may reveal signal features of the impact loads in time domain and the accuracy of identified loads is good.

Research on Hybrid Control Strategy for Intelligent Vehicle Path Tracking

CAI Yingfeng1;LI Jian2;SUN Xiaoqiang1;CHEN Long1;JIANG Haobing2;HE Youguo1;CHEN Xiaobo1

2020, 31(03): 289-298.

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In order to solve the problems of traditional single control algorithm might not effectively coordinate the lateral control performance requirements of intelligent vehicles under different steering conditions, a hybrid control strategy of intelligent vehicle path tracking was designed based on PID control and model predictive control by combining with the different system characteristics of intelligent vehicles under high-speed and low-speed steering conditions. The control strategy selected PID control in low-speed mode and model predictive control in high-speed mode, The path following control mode was determined by vehicle speed, and then a switching mechanism of control mode with stable supervision was designed to realize smooth switching of lateral control system. Based on Carsim and MATLAB/Simulink simulation platform, the hybrid control strategy of intelligent vehicle path tracking was simulated and verified. Then, the real vehicle tests were further completed. Simulation and real vehicle test results show that the designed hybrid control strategy may ensure the performance of the intelligent vehicle path tracking at different speeds, and has good tracking accuracy, real-time performance and vehicle running stability.

Vehicle Shifting Process Analyses in Consideration of Walking Elasticity

ZHU Yutian;WANG Zonglei;LIU Zhao

2020, 31(03): 299-305,313.

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In order to study the influences of walking elasticity on the shifting processes of construction vehicles, a vehicle walking dynamics model was established considering the influences of driving wheel tire deformations on vehicle walking elasticity, which was suitable for shifting process analyses. The dynamic shifting processes of typical loaders were calculated and analyzed, and the calculated change processes of acceleration and instantaneous impacts of the vehicle with and without considering the walking elasticity were compared respectively. The results of gearbox input and output speed variations and clutch sliding friction power characteristics in the processes of gear shifting with the consideration of walking elasticity were compared with those of gear shifting processes without the consideration of walking elasticity. The results show that compared with the situations without considering of walking elasticity, the changes of vehicle acceleration during gear shifting processes are more gentle. The shift into the clutch has two sliding processes, less impact, longer shift time. The impact of clutch engagement is related to the connection time. The sliding friction work is smaller.

Research on Prediction Technology for Tool Rotation Profile Errors in Flank Milling

YU Hangzhuo1;QIN Shengfeng1,2;DING Guofu1;JIANG Lei1;LIANG Hongqin1

2020, 31(03): 306-313.

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In the flank milling processes, it is difficult to accurately predict the tool rotation profile errors caused by tool wears and deformations before actual machining. A identification test method of workpiece shape-tool profile mapping was proposed to obtain the tool rotation profile errors and the error data under different working conditions were obtained through the multi-factor orthogonal tests. A prediction model for tool rotation profile error was established by the LS-SVM technology based on the error data. The genetic algorithm (GA) was used to optimize the model parameters including kernel function parameters and error warning factors, which were very important to the proposed model. A LS-SVM model was established based on GA optimization(GA-LS-SVM)，which was compared with a LS-SVM model without GA optimization. The testing results show that the GA-LS-SVM prediction model is more suitable for tool rotation profile error prediction.

Multiaxial Fatigue Life Prediction Considering Additional Hardening Effects and Mean Stains

LIU Jianhui1;LYU Xin1;WEI Yaobing1;CHENG Jinhui2

2020, 31(03): 314-320.

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Considering the physical significance of crack formations and propagations under multiaxial loading conditions , a multiaxial equivalent linear fatigue life prediction model was proposed based on Miner rule and critical plane method. The ratio of cyclic yield stress to static yield stress was used to reflect the cyclic strengthening capacity of the materials, and the additional hardening factor was defined. The influences of phase differences and loading conditions on the non-proportional additional hardening effects were considered, and the mean strains under asymmetrical loadings were corrected. Multiaxial fatigue lifes of smooth and notched samples for five kind of materials were estimated by equivalent strain prediction model, maximum shear strain amplitude model and the proposed model, and the estimated results were compared with the testing results. The results show that the three models may achieve good effectiveness under proportional loadings, but the proposed model performs better than that of the other two models under non-proportional loadings. Meanwhile, it also verified that the proposed additional hardening factor may reflect the influences of phase differences and material properties on additional hardening effects.

SOC Estimation for Lithium-ion Batteries Based on EKF

LI Wei1;LIU Weiwei1;DENG Yelin2

2020, 31(03): 321-327,343.

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Aiming at the problems that it was difficult to accurately estimate SOC, the EKF method was used to improve the accuracy of SOC estimation. Firstly, the PNGV equivalent circuit models of lithium iron phosphate batteries were established, and the model parameters were obtained by charging and discharging experiments and off-line identification method. The polynomial function relationships among open circuit voltage, Ohmic internal resistance, polarization internal resistance, polarization capacitance and SOC were established. Then, the models were verified and the accuracy of the models was analyzed. Finally, under actual operation conditions, the SOCs of lithiumion batteries were estimated by EKF and compared with the results calculated by the Ampere-Hour method. The results show that the maximum errors of estimating SOC of lithium-ion batteries based on the proposed PNGV model combined with EKF are only 2.78%, which will improve the accuracy of battery SOC.

Cooling and Lubrication Performance of scCO2 Mixed with OoW in TC4 Milling

LIANG Xu;CAI Chongyan;AN Qinglong;CHEN Ming

2020, 31(03): 328-335.

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The milling tests of titanium alloys were carried out under three green cutting conditions: dry cutting, scCO2, scCO2 mixed with OoW. The effects of milling parameters and cooling lubrication methods on cutting force, cutting temperature and surface roughness were analyzed by single factor test and the cooling and lubrication performances of scCO2 mixed with OoW in titanium alloys milling were studied. The results show that under each cooling lubrication conditions, the cutting force and the cutting temperature increase with the increase of cutting speed, feed per tooth and radial cutting width. When the cutting speed is further increased, the cutting force and temperature have a tendency to slow down and decrease according to the high-speed machining theory. Under the various processing parameters, compared with dry cutting, scCO2 and scCO2 mixed with OoW cooling the cutting force and cutting temperature may reduce and a good machined surface is obtained, which has good cooling and lubrication performance.

Maintenance Policy Optimization for a Cold Standby System Based on Semi-Markov Process

QI Faqun1;ZHOU Hongming1;PANG Jihong1;XU Wenjie2

2020, 31(03): 336-343.

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In order to improve reliability of the systems, a cold standby system consisting of two components was constructed, and a semi-Markov process-based preventive maintenance model for a cold standby system was presented. Minor repair, major repair and preventive maintenance were applied in considering random failures and deterioration failure modes. State transition processes of the system were analyzed based on semi-Markov theory and regeneration point technique, and then the Markov renewal equations were established. By the application of Laplace transform to solve these equations, the mean time to the first system failure and the steady-state availability of the system were derived, and then the optimal preventive maintenance policy was identified by maximizing the two reliability performances of the system respectively. Finally, experiments were carried out to analyze the influences of different parameters on the system reliability and the optimal preventive maintenance cycle. Results indicate that the proposed model has guiding significance for cold standby system of maintenance decision-making problems.

Layout Optimization of Large Marine Power Component Production Workshops Based on DMPSO Algorithm

ZHANG Qinglei1;ZHANG Fan2;DUAN Jianguo1

2020, 31(03): 344-351.

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Large ship power components should possess good internal organization and strict dimensional accuracy requirements. Reasonable workshop layout might effectively improve the processes and reduce the costs of material handling between equipment. In order to reduce the costs of material handling in workshop layout, a two-dimensional vector was used to represent the space position of the equipment, the corresponding layout mathematical model was established, and the model was solved by DMPSO algorithm. The algorithm dynamically changed the size of the inertia factor according to the distribution of particles and the iterative stage of the algorithm located and adjusted the flight of each particle to improve the probability of the particle searching for the global optimal solution. Selection of optimal acceleration factors was completed by comparing three sets of acceleration factors to improve the optimization quality of the algorithm. Finally, an example of marine crankshaft workshop layout was given, and the optimized layout was obtained according to the actual situation of the workshop, and the 3D visual modeling of the optimized workshop layout was carried out. The results show that the algorithm has strong optimization ability and may effectively reduce the costs of material handling. It is feasible in the layout of practical workshop equipment.

Research on Crashworthiness of Minivans Based on Refined Multi-rigid Body Model

YAO Zuoping;WEI Yong;LYU Juncheng;LIU Changye;LIANG Yongbin

2020, 31(03): 352-359,372.

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Aiming at the problems of the finite element model with accurate simulation results and long calculation time, the multi-rigid body model with short calculation time and inexact simulation results, a refined multi-rigid body model for the whole vehicles was proposed. The reliability of the refined multi-rigid body model was verified by the platform tumbling tests. By analyzing the intrusion amounts of the key structure on the top of the vehicles, the stress distribution, the transmission path of the forces during the collision processes and the specific energy absorption of each structure, the key structures of the vehicles under the tumbling conditions were determined, which were the A-pillar and the front-retaining beam. Through the establishment of the refined multi-rigid body model of the target vehicles, a tumbling crashworthiness optimization scheme was proposed based on the vehicle A-pillars and the front-retaining beam. The optimization results show that the total masses of the A-pillar and the front-retaining beam are decreased by 6.8%, the bending amount of the front-retaining beam is decreased by 17.1%, the energy absorption is increased by 15.5%, and the intrusion of the vehicles living spaces is decreased by 17.7%.

Optimization of Twin-roll Thin Strip Vibrating Casting Screw-down Control Systems Based on Improved PSO Algorithm

SUN Minghan;XU Zhe;ZHENG Likang;XU Zhiqiang;DU Fengshan

2020, 31(03): 360-366.

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The periodic vibrations of the cast-rolling were the main factor that induced the fluctuation of Kiss points, which might also cause the rolling forces to fluctuate, eventually resulting in uneven thickness of the casted strips. To this end, the constriction factor PSO added extremum disturbed factor was created based on the PSO algorithm. Simulation based on four different type of test functions was made, which combined with AMESIM-MATLAB co-simulation model for verification. The algorithm was applied to the hydraulic screwdown control system of twin-roll thin strip vibration cast-rolling mill for experimental verification. The results show that the constriction factor PSO added extremum disturbed factor is superior to the basic PSO, constriction factor PSO and extremum disturbed PSO algorithms in convergence speed and solution precision, where the errors of the actual roll seam width are decreased to 0.1mm. It is suitable for the pilot production of twin-roll strip vibration cast-rolling, which enhances the stability of the processes.

Bead-on-plate Welding Deformation Prediction Technology Based on Initial Deformation Defects of Metal Sheet

GUO Nan1;MA Xiqiang1;YIN Xianqing2;YU Yongjian1

2020, 31(03): 367-372.

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For the influences of the initial deformations of the metal sheet on the dimensional accuracy of the welded structures, based on digital image correlation technology an optical detection method was proposed to study full-field dynamic accuracy prediction of bead-on-plate welding deformations. Firstly, the structural light scanning method was used to obtain the initial deformation profiles of the welded structures, and then the welding deformation prediction was performed based on the initial deformation model. Finally, the influences of the initial deformations of the structures on the welding deformations were studied through the ideal plate model and the initial deformation model prediction data. The results show that the plate model based on the initial deformation structure has higher precision in single-point dynamic and full-field static deformations compared with the ideal structure model. Both models are saddle-shaped after welding, but the initial deformations promote the deformations of the welding evolution processes. The initial deformations affect the longitudinal residual compressive stress distribution, which is the root cause of different welding deformations.

Effects of Fiber Direction on Grinding Performances for Unidirectional C/SiC Composites

ZHANG Lifeng;WANG Sheng;LI Zhan;ZHANG Jin;ZHEN Tingting;WANG Ying

2020, 31(03): 373-377.

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In order to study the material removal mechanism of carbon fiber braided composites and to explore the influences of fiber weaving direction on the grinding performances, a unidirectional composite C/SiC was designed and prepared, and the grinding experiments were carried out along the typical direction of the fiber. The results indicate that the tangential grinding force ,normal grinding force and surface roughness show following rules when grinding the unidirectional composite materials: the tangential grinding force and the normal grinding force conform to the normal grinding>longitudinal grinding>transverse grinding, and the surface roughness of the machining conforms to the regular longitudinal grinding>normal grinding >transverse grinding. The micro-multi-directional material removal mechanism of ceramic matrix composites was revealed by analyzing the microstructures of the machined surfaces.

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