Table of Content

10 November 2019, Volume 30 Issue 21

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Fatigue and Creep Life Prediction Method of Turbine Blades for Turbocharger

WANG Zheng;MA Tongling

2019, 30(21):  2521-2526. 

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According to the structural characteristics and operation profiles of radial turbines, the spatial distribution characteristics of load and stress of turbine blades were analyzed. For the failure mode of blade root fracture caused by fatigue and creep, the loadings and stress processes of blade roots of turbines were studied, and the methods for describing the load and stress of turbine blade roots were developed. Then, the life prediction methods of turbine blade root of turbochargers were studied and the life prediction model of turbine blade roots with the failure mode of fatigue and creep was derived. Finally, taking the turbine of turbocharger for automobile diesel engine, the model built was applied to analyze the life of turbine blade roots of turbocharger for vehicle applications.

Material Performance Tests of Q235 under Multiple Cyclic Loading Conditions

ZHANG Qingling1，2;JIN Miao1，2;ZHANG Rongqiang1，2;LI Qun1，2

2019, 30(21):  2527-2533. 

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The cyclic loading tests of Q235 steel with variable stress loading amplitudes and different pre-deformations and loading holding time were carried out, and the mechanics responses and material performances were analyzed. The results show that under cyclic stress loading Q235 steel shows cyclic softening characteristics and ratcheting, and the ratcheting strain mainly depends on loading levels. When the loading level increases step by step, the early deformations lead to the later ratcheting strain increase. When the loading level decreases step by step, the later ratcheting strain depends on the ratcheting strain under the maximum loading conditions, and the ratcheting strain rate is close to zero. When the response stress peak of the pre-deformations is smaller than the later stress loading peak, the pre-deformations have an inhibiting effect on the ratcheting. And the greater the pre-deformation the more obvious the inhibiting effect. The loading holding time increases both of the ratcheting strain and ratcheting strain rate, which accelerate the material failures.

Recursive Formula and Numerical Solution of Stability with n-stepped Crane Telescopic Booms

YAO Fenglin1;MENG Wenjun1;ZHAO Jie2;ZHANG Zhide3;SHEN Changhong3;YAN Junhui3;LIU Haibo3

2019, 30(21):  2533-2538. 

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Differential equations of n-stepped telescopic boom were established based on the vertical and horizontal bending theory. The recursive formula of the stability of n-stepped telescopic booms was deduced by the mathematical induction method. For the transcendental equation in recursive formula, combined with the structural force characteristics, the Levenberg-Marquardt numerical optimization algorithm was used to solve the equations with n unknowns. Length coefficients that solved by the method were compared with those in GB3811—2008 and the outcomes calculated by ANSYS 17.0. The results show that the accuracy of this algorithm is better than that of the other algorithms, and the length coefficient has certain nonlinearity. Therefore, linear interpolation is feasible in a small scope in practical processes. For the large sections of the stepped column, linear interpolation method will lead larger errors in critical forces.

Setup Planning Method Based on Intelligent Water Drops Algorithm

GAO Bo;HU Xiaoyu;PENG Zhenrui;LIU Junquan

2019, 30(21):  2539-2545. 

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To solve the setup planning problems in CAPP, a novel setup planning method was proposed based on intelligent water drops(IWD) algorithm. By analyzing the machining features, the machining unit and its constraint relationships were defined, and the setup planning model was constructed. The machining units of the parts were associated with the nodes of the flow path in IWD algorithm, and then the similarity between machining units was characterized by the amount of soil carried by the water-drop, thus the fitness function of IWD algorithm was constructed. Iterative computation was carried out in the feasible solution space selected by the sequential constraint matrix of the machining unit. The optimal solution was obtained by the amount of soil in the path of water droplet scour for several times, and the optimal setup planning was obtained after decoding. Setup planning process of the typical parts was illustrated to prove the effectiveness and feasibility of the proposed method.

Cylinder Consistency Control for Engines Equipped with Electromagnetic Valve Trains

XU Yaxuan;LIU Liang;CHANG Siqin;HU Maoyang

2019, 30(21):  2546-2553. 

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In order to improve the engine cylinder consistency, based on EMVT, a control method of individual cylinder air-fuel ratio was proposed to reduce the difference of air-fuel ratio and torque between engine cylinders. The fading Kalman filter algorithm was used to establish the individual cylinder air-fuel ratio observer under steady-state conditions. Parameter identification and the estimation of the individual air-fuel ratio were realized with only one universal exhaust-gas oxygen (UEGO) sensor based on the DE algorithm. Finally, according to the difference of individual air-fuel ratio, the EMVT was used to adjust the intake valve opening durations of each cylinder separately, and the consistency control of individual cylinder air-fuel ratio was realized. The engine model and the air-fuel ratio estimation and control model were built in GT-Power and Simulink respectively. The co-simulation results show that under steady-state conditions, the air-fuel ratio difference between cylinders decreases from 2.6% to 0.05%, the torque generation difference between cylinders decreases from 4.51% to 0.25%.

Innovative Design of Human Computer Interaction System for CNC Machine Tools Based on Performance Incentive Mechanism

LIU Minyang1,2;HUANG Yanqun1;ZHANG Dawei1

2019, 30(21):  2554-2559. 

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In the context of China's manufacturing transformation, in order to improve the operational performance of the first-line operators of CNC machine tools and their positive psychological emotions, based on performance incentive mechanism a human-computer interaction system for CNC machine tools was designed as an innovative management method of enterprise human resource. In order to realize the system design, the corresponding system structure design strategies were proposed. The system connected four parts, namely CNC machine tools, an upper monitor, cloud platform and mobile APP through network technology, which calculated and compared the production process data of CNC machine operators and used real-time visual feedback to transmit to the corresponding worker users and management users. In order to test the effectiveness of the system, experiments were conducted in two manufacturing plants. The results show that the system significantly improves participants' job motivation, job satisfaction, and operational performance.

Johnson Distribution Fitting Method Based on Minimum Sample Space

ZHANG Qi1;WU Yizhong2;LIU Xin2;QIAO Ping2

2019, 30(21):  2560-2566,2576. 

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When calculating the reliability index based on the stress-strength interference model, statistical methods were used to obtain the probability distribution of stress and strength. However, in the design processes of complex electromechanical products, the acquisition of each sample values was an expensive evaluation, so, the acquisition of a large number of sample values would be confronted with serious problems such as time consuming. Aiming at this problem, the parameterized Johnson distribution family function was introduced to fit the probability distribution, and the Johnson distribution fitting method was studied based on the minimum sample space. The parameters of the Johnson distribution family function were solved by percentile matching method and the minimum sample space was determined based on the hypothesis testing principle. To ensure the fitting accuracy, K-S test was introduced to analyze the consistency between the real distribution and the fitted distribution. The results of engineering applications show that the method may quickly obtain the distribution of samples based on a small number of expensive evaluation samples, which lays a foundation for the rapid calculation of reliability index.

Performance Evaluation and Optimization Analysis for Integrated Active and Passive Seat Belts

SONG Zhiqiang1;CAO Libo1;OUYANG Zhigao1;QIU Yangdi2;CHEN Kai2

2019, 30(21):  2567-2576. 

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Aiming at the situations of multi-function and low integration of advanced driver assistance system(ADAS), an integrated active safety system was proposed, which integrated reversible preloading seat belt with lane departure warning system, forward collision warning system and fatigue driving monitoring system. On the basis of discussing the working principles and control strategies of the integrated system, three factors influencing driver's subjective feeling were studied by volunteer real-road tests, which were the TTC threshold for triggering forward collision warning system, the pre-tightening forces of seat belts, and working noises generated during seat belt pre-tightening. By comparing and analyzing the subjective evaluations of volunteers and tests data, the results show that the control strategy of the integrated system is logical and it may be actively triggered to alert and restrain the occupants under various working conditions, but the driver's subjective feeling is affected by the high frequency of warning and large noises. The driver's subjective feeling was improved by lowering the TTC threshold and optimizing the transmission structures of seat belts. The integrated active safety system may effectively assist the drivers to drive and satisfy the subjective acceptability of passengers.

Efficiency Calculation and Test for a Two-step Sine Movable Tooth Transmission

YANG Jinan;XU Lizhong

2019, 30(21):  2577-2582,2589. 

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According to force analysis of the movable tooth meshing pair of a two-step sine movable tooth transmission, the expressions of the output torque of the movable tooth transmission system were deduced, and then the formulas for calculating the transmission efficiency of the system were given. The transmission efficiency of the system was analyzed by using the efficiency formula, and the variation laws of the transmission efficiency of the system were established. The results show that in order to improve the transmission efficiency, the amplitude of sine tracks and the circumferential radius of the center of the movable tooth should be increased, and the transmission ratio should be allocated reasonably. In addition, a two-stage sinusoidal movable tooth transmission prototype was developed, and the transmission efficiency experiments were carried out. The experimental efficiency is close to the calculation efficiency, which verifies the correctness of the theoretical analysis.

Fatigue Analysis of Commercial Vehicle Frames Based on Six-dimensional Wheel Loads

LIU Jun1;ZHANG Haijian1;WANG Wei1;LIU Yajun1;ZHOU Fugeng2

2019, 30(21):  2583-2589. 

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A frame of a commercial vehicle was taken as the research object, and six-dimensional force transducers were fixed on the three axles of the vehicle. Tests were completed at Dingyuan test field with several typical roads to get six-dimensional force. The finite element model of the frame was built by HyperMesh and the stress field of the frame under unit load was obtained by using the inertia release theory. Rigid-flexible coupled multi-body dynamics model of the vehicle was built by ADAMS and the load spectrums of the junctions between frame and suspensions were obtained based on the six-dimensional force signals of the wheel hub. According to the linear cumulative damage theory, combining the stress distribution under unit load of the frame, the load spectrums of the junctions between the frame and the suspensions and the strain(ε)-fatigue life(N) curve of materials of the frame, fatigue simulations of the frame were carried out by nCode and the results show that the reliable life of the frame meets the relevant national safety regulations and the design requirements.  The simulation results are also verified by experiments.

Research on Fatigue Damage of Automobile Coil Springs under Actions of Two Demensional Random Loads

TENG Ruipin1;SONG Xiaolin1;LIU Guoyun2;ZENG Junwei2

2019, 30(21):  2590-2597. 

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The expandation of two dimensional random load spectrums was researched, three expandation methods were presented. The probability density function of equivalent loads of two-dimensional random loads were deduced,  as the mean loads of the two-dimensional random loads following Gaussian distribution, and the amplitude following Weibull distribution under the conditions of shape parameter α=1 and dimensional parameter ε=0, the math models of the probability density functions were presented.Take a city sport utility vehicle(SUV) as object , the load spectrum data on reinforced pavement was aquired in test ground. Sample interception method was presented for parameter estimation of radom loads. Parameter checking shows that the method may realize a good fitting on middle and high load regions. The acquired two dimensional random loads were expanded by load date segmentation method. Fatigue damage was analyzed under the expandation loads. The influences of different segmentation methods on the result of fatigue damage calculation was studined.The results show,when the segments of amplitude is less than 20,the fatigue damage will be high deviation to a smaller result,and the influences of the segment number of mean loads will be less that of the segment number of amplitudes.

A Macroscopic and Microscopic Integrated Decision-making Model for Evaluating Process Compatibility of Additive Manufacturing

LIU Xiaochen1;SUN Yu1;JING Shikai2;QIE Longfei2

2019, 30(21):  2598-2603. 

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Additive manufacturing(AM) has outstanding problems such as difficult to manufacture in suspended areas, difficult to predict the formability of parts with different structures and different performance requirements, thus it is significant to evaluate the matching and rationality of the process in advance. A decision-making model that integrated macroscopic and microscopic factors was proposed to evaluate the formability of parts from the perspective of additive manufacturing processes, and to deduce the optimized forming strategy according to the effectiveness of printed parts. A mathematical model of the relationship between design requirements and manufacturing processes was established in the macro-decision stage, to judge the degree of matching of processes from the perspective of formability. The mathematical model of surface roughness, support structure volume and printing time was established in the micro-decision stage to optimize the printing processes from the perspective of print quality. Finally, a topologically optimized beam part was taken as an example. The established model was used to optimize the printing processes, and the results are consistent with the simulation printing results, which verify the validity of the mathematical model.

Effects of Load on Friction and Wear Properties of Cf/SiC Composites Prepared by SLS

FU Hua;ZHU Wei;ZHENG Shenwei;YAN Chunze

2019, 30(21):  2604-2610. 

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Carbon fiber reinforced silicon carbide composites were prepared by SLS and liquid phase silicon infiltration. The composite microstructure consisted of three phases of C, SiC and Si. The density and flexural strength of the Cf/SiC composites were 2.89±0.01 g/cm3 and 237±9.8 MPa, respectively. The friction and wear properties of Cf/SiC composites under different loads (10N, 30N, 50N and 70N) were studied by UMT TriboLab multi-function friction and wear tester. The results show that the wear mechanism of the Cf/SiC composites caused by micro-protrusions and SiC hard sports is abrasive wear when the load is small (10 N). When the load is as 30N, the composites have the best comprehensive friction and wear properties, showing the average friction coefficient of 0.564, and low wear rate of 5.24×10-7 cm3/（N·m）. The main wear mechanism is abrasive wear and adhesive wear formed by plough. When the load is increased to 70 N, the wear is serious, and the particles fall off to form pits and cracks. It has a high wear rate (8.68×10-7 cm3/（N·m）). The wear mechanism is mainly brittle shedding.

Optimal Design for Rocket Bourrelets Aiming at Minimizing Initial Disturbances

YANG Qi;ZHEN Wenqiang;JI Yongqiang

2019, 30(21):  2611-2615. 

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In order to study the influences of rocket bourrelets structural parameters on the rocket initial disturbances, a dynamic simulation model of the interaction between rocket and rail was established. Taking minimizing initial disturbances as goals, and nonoccurrence of impact between rocket body and rail as constraint, launch dynamic simulation and optimal analysis of the rocket bourrelets were performed. The optimal design parameters of the rocket bourrelets were obtained. The optimal results show that the rocket bourrelets width has a large influence on initial disturbances, and the optimization of the bourrelets structural parameters may minimize initial disturbances of rocket to a great extent. The optimal method and results will provide reference to rocket bourrelet design.

Multi-objective Design Optimization of Pad-iron Positions for Three-point Supporting T-shaped Bed Machine Tools

DING Xiaohong;ZHANG Jun;ZHANG Heng

2019, 30(21):  2615-2621. 

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For the optimal position problems of the three-point supporting machine tools, a optimal method was proposed to optimize the locations of the three-point supporting. The detailed design processes were introduced with a T-shaped bed of a CNC cylindrical grinder which was taken as the research object. Firstly, the initial supporting positions were determined by the method of dividing bottom plane of the bed and finding the centroid of each region, and the pad-iron positions were parameterized, then the parameter ranges were specified according to the position limit conditions. Secondly, the multi-objective optimization mathematical model of pad-iron positions was established, and the optimal solution was obtained to achieve the optimal static and dynamic performances of the bed. Finally, by analyzing the relationship between the three pad-iron positions obtained from Pareto frontier and the bed geometric sizes, the arrangement rule of three-point support for this model was obtained. The results show that the static and dynamic performances of the bed are improved by this suggested method.

Direct Integral Method for Solving Axisymmetric Sheet Forming Problem Based on Incremental Theory

QIN Siji;KONG Xiaohua;YANG Li

2019, 30(21):  2622-2628. 

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By taking the initial configuration as reference, a differential equation of equivalent strain increment was obtained on the basis of plane stress assumption, incremental deformation theory using parametric analysis method. The differential equation was generally difficult to solve using theoretical methods because the first derivative terms of the equivalent strain increment of curved parts also existed as an implicit function. So, the first derivative of the equivalent strain increment was expressed as a function of the equivalent strain increment, parameter and itself. According to Taylor series expansion and the definition of the integral，a stepwise integral solution method was given to solve sheet metal forming problems such as bulging, flanging and deep drawing for axisymmetric parts. Taking the deep drawings of cylindrical parts and conical parts as examples, the total deformation was divided into several incremental steps and gradually loaded. Incremental theory solution was used to track the deformation particles and strain was added, and the strain distributions in the flange and the die radius regions were obtained. The analyzing results obtained by using the method under proportional loading condition and incremental theory respectively were compared with experiments. It is shown that the calculation results by incremental theory are closer to the experimental ones than those under the proportional loading conditions.

Directional Internal-cooling Tools and Their Machining Performances

PENG Ruitao1;JIANG Haojian1;TANG Xinzi1;ZHANG Shan2

2019, 30(21):  2629-2635,2642. 

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In view of surface burns in cutting of nickel-based superalloy, the directional internal-cooling cutting methods were proposed to improve the cooling effects of cutting fluid in cutting areas. The flow and temperature field model of the directional internal-cooling tool were established by FLUENT software, and the effects of micro-channel structures on heat transfer ability of the tool were studied. Based on the simulation results, the micro-channel structures were designed, and the directional internal-cooling cutting systems were developed. Cutting experiments of nickel-based superalloy with different cooling methods, i.e. dry, flood cooling and directional internal-cooling, were carried out under same cutting parameters. The influences of cooling methods on cutting force, cutting temperature, surface roughness and surface topography were studied respectively. The results show that the internal-cooling method may effectively reduce the cutting force and cutting temperature. Under directional internal-cooling conditions, lower surface roughness and more favorable surface topography with regular textures are obtained.

Research on Failure Mode of Welding Spots between Hot-formed Steel Sheet and Dual-phase Steel Sheet

NIE Xin;CHEN Huanhuan

2019, 30(21):  2636-2642. 

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The failure mode of welding spots between hot-formed steel sheet and dual-phase steel sheet was studied by tests and numerical simulations, finite element(FE) model was built to simulate the resistance spot welding(RSW) process. So as the welding lobe got, the effects of welding time and positive deviation of fusion zone(FZ) on mechanics properties of welding spots were researched. As the tensile-shear test shown, with the increase of welding time, the failure mode of welding spots transited from interface fracture(IF) to pullout failure(PF) . At the same time, it is found that the positive deviation of FZ has a great influence on starting positions of PF. when the thin sheet welded with thick sheet, the welding spots were easier to be pulled out from the thin sheet sides, when the sheet thickness is the same, the welding spots were easier to be pulled out from the hot-formed steel sides. Finally, the welding spot mechanics model was established based on experimental data, the welding spot failure criteria was obtained.