A newly developed pure rolling fatigue test rig with three contact points for bearing bails was used to perform rolling contact fatigue (RCF) tests. The fatigue properties of GCrl5 steel bails and two kinds of Si3N4...A newly developed pure rolling fatigue test rig with three contact points for bearing bails was used to perform rolling contact fatigue (RCF) tests. The fatigue properties of GCrl5 steel bails and two kinds of Si3N4 ceramic balls (GSN-200 and NBD-200) produced with different technologies were compared. Ball surfaces were examined after failure with optical microscope and scanning electron microscope (SEM). It was identified by tests that the failure mode of ceramic balls was surface spail. The main factor of ceramic bail failure was principal tensile stress. Life tests data, summarized in accordance with the Weibull theory, showed that the life of GSN-200 balls was close to that of GCrl5 balls, whereas the life of NBD-200 balls was much longer than those of GSN-200 and GCr15. Under the same working condition, the temperature rise of all ceramic bails was lower than that of steel balls, and their crack propagation rates were slower than that of steel balls.展开更多
The manipulation and constraint equations are established by considering the pure rolling motion in a dexterous hand as two passive joints. According to mapping relation among the motion of the system, the differentia...The manipulation and constraint equations are established by considering the pure rolling motion in a dexterous hand as two passive joints. According to mapping relation among the motion of the system, the differential kinematics and mobility are studied. The minimal structure for realizing the task motion of the object is obtained, and the conditions for dexterous manipulation are presented. Finally, some rolling manipulations are used as examples to demonstrate the applicability of approach proposed.展开更多
Using an optical interferometric technique,the grease film distribution under a pure rolling reciprocating motion is observed on a ball‐disk test rig,to explore the transient response of grease,which is expected to f...Using an optical interferometric technique,the grease film distribution under a pure rolling reciprocating motion is observed on a ball‐disk test rig,to explore the transient response of grease,which is expected to fill the contact with thickener fiber and run for a long time under steady‐state conditions.It is found that the reciprocating motion reduces the accumulation of the thickener fiber gradually with time.The maximum film thickness forms around the stroke ends.After 1,000 working cycles,very severe starvation occurs so that either the central or minimum film thickness becomes nearly constant over one working period.Thus,the life of grease lubrication under a transient condition is far below that under steady‐state conditions.However,it is also found that by selecting a smaller stroke length,the thickener fiber spreads out in the contact instead of being removed from the contact at the 1,000th working period.When increasing the maximum entraining speed of the reciprocating motion to a certain value,during which the thickener fiber is not expected to accumulate under a steady‐state condition,severe starvation occurs very quickly,causing surface damage.展开更多
Asymmetric rolling(ASR), as one of severe plastic deformation(SPD) methods, was widely used to make ultra-fined materials with enhanced performance. Internal marks were used to show the shear deformation during asymme...Asymmetric rolling(ASR), as one of severe plastic deformation(SPD) methods, was widely used to make ultra-fined materials with enhanced performance. Internal marks were used to show the shear deformation during asymmetric rolling with pure aluminium as a model material. Effects of reduction ratio and mismatch ratio on the shear deformation were studied. With the observed shear deformation results, equivalent strain was calculated. For lager shear deformation, rolling equipment was modified to increase friction between specimen and the rollers. Consequently, extremely fine grains with size of 500 nm are obtained in pure aluminium. With improved asymmetric rolling, the ability of grain refinement of ASR is greatly improved.展开更多
We investigated the influences of process parameters on the head curvature of pure titanium sheet in hot rolling process and proposed the controlling means. First, the thermal simulation experiments for pure titanium ...We investigated the influences of process parameters on the head curvature of pure titanium sheet in hot rolling process and proposed the controlling means. First, the thermal simulation experiments for pure titanium TA1 were carried out to investigate the hot deformation behaviors of pure titanium in the temperature range of 700-800 ℃ with strain rate range of 1-20 S-1, and the processing map was established to determine optimized deformation parameters. Then, the finite element model has been constructed and used to analyze the effect of process parameters on the direction and severity of head curvature of pure titanium sheet. The process parameters considered in the present study include workpiece temperature, work roll diameter, pass reduction, oxide scale thickness of workpiece surface, and interface friction coefficient. The simulation results show that the workpiece temperature and the interface friction coefficient are the two main factors. The proposed controlling means was carried out on a hot rolling production line and solved the head curvature problem effectively. The rolling practices indicate that the rolling yield is improved greatly.展开更多
Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking...Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.展开更多
A newly developed pure rolling fatigue test rig with three contact points is used to test the rolling contact fatigue properties of silicon nitride ceramic balls. Ball surfaces are examined after failure with optical ...A newly developed pure rolling fatigue test rig with three contact points is used to test the rolling contact fatigue properties of silicon nitride ceramic balls. Ball surfaces are examined after failure with optical microscopy and scanning electron microscopy. The failure cause, fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material and propagate, to form elliptical fatigue spalls under the action of principal tensile stresses. The principal tensile stress increases with increasing contact load, causing spall formation and reduction of rolling contact life. The greater the principal tensile stress is, the more severe the peeling of near surface is. Under the same condition, the closer volume defects are to the surface, the more likely failure occurs, the shorter the rolling contact life is.展开更多
针对无人驾驶车辆采用纯跟踪算法对不同曲率路径跟踪时,出现道路适应能力弱和跟踪精度差的问题,提出一种基于代价的滚动预瞄模型(rolling preview model,RPM),以提高纯跟踪算法跟踪精度与鲁棒性。首先,根据车辆运动学与阿克曼转向几何,...针对无人驾驶车辆采用纯跟踪算法对不同曲率路径跟踪时,出现道路适应能力弱和跟踪精度差的问题,提出一种基于代价的滚动预瞄模型(rolling preview model,RPM),以提高纯跟踪算法跟踪精度与鲁棒性。首先,根据车辆运动学与阿克曼转向几何,提出预瞄轨迹的确定方法以及预瞄轨迹与待跟踪路径间的几何约束;其次,设计道路弯曲度加权项并构建目标函数对预瞄轨迹进行优化,以获得预瞄距离的最优值;最后,在ROS/Gazebo仿真环境下设置不同初始状态与不同曲率的工况进行对比仿真实验,并在空旷环境中对8字形路径进行实车跟踪实验。实验结果表明,所提出的滚动预瞄模型能够根据预瞄轨迹与待跟踪路径的几何关系有效调节预瞄距离,相较于麻省理工(Massachusetts Institute of Technology,MIT)算法和Stanley算法,滚动预瞄模型在特殊初始状态、大曲率道路下有利于跟踪精度的提高。展开更多
基金Project supported by the Science Foundation of Shanghai Municipal Commission of Science and Technology (Grant No.05KJB460106), and the Provincial University Natural Science Foundation of Jiangsu, China (Grant No.0152nm031)
文摘A newly developed pure rolling fatigue test rig with three contact points for bearing bails was used to perform rolling contact fatigue (RCF) tests. The fatigue properties of GCrl5 steel bails and two kinds of Si3N4 ceramic balls (GSN-200 and NBD-200) produced with different technologies were compared. Ball surfaces were examined after failure with optical microscope and scanning electron microscope (SEM). It was identified by tests that the failure mode of ceramic balls was surface spail. The main factor of ceramic bail failure was principal tensile stress. Life tests data, summarized in accordance with the Weibull theory, showed that the life of GSN-200 balls was close to that of GCrl5 balls, whereas the life of NBD-200 balls was much longer than those of GSN-200 and GCr15. Under the same working condition, the temperature rise of all ceramic bails was lower than that of steel balls, and their crack propagation rates were slower than that of steel balls.
基金This project is supported by Scientific Research Foundation for ReturnedOverseas Chinese Scholars, Education Ministry of China and ProvincialNatural Science Foundation of Shanxi, China (No.2000C37).
文摘The manipulation and constraint equations are established by considering the pure rolling motion in a dexterous hand as two passive joints. According to mapping relation among the motion of the system, the differential kinematics and mobility are studied. The minimal structure for realizing the task motion of the object is obtained, and the conditions for dexterous manipulation are presented. Finally, some rolling manipulations are used as examples to demonstrate the applicability of approach proposed.
基金supported by the National Natural Science Foundation of China through grants No.51875298 and No.51275253
文摘Using an optical interferometric technique,the grease film distribution under a pure rolling reciprocating motion is observed on a ball‐disk test rig,to explore the transient response of grease,which is expected to fill the contact with thickener fiber and run for a long time under steady‐state conditions.It is found that the reciprocating motion reduces the accumulation of the thickener fiber gradually with time.The maximum film thickness forms around the stroke ends.After 1,000 working cycles,very severe starvation occurs so that either the central or minimum film thickness becomes nearly constant over one working period.Thus,the life of grease lubrication under a transient condition is far below that under steady‐state conditions.However,it is also found that by selecting a smaller stroke length,the thickener fiber spreads out in the contact instead of being removed from the contact at the 1,000th working period.When increasing the maximum entraining speed of the reciprocating motion to a certain value,during which the thickener fiber is not expected to accumulate under a steady‐state condition,severe starvation occurs very quickly,causing surface damage.
基金Project(5067062) supported by the National Natural Science Foundation of ChinaProject(NCET-04-0386) supported by New Century Scholarship of the Ministry of Education of China
文摘Asymmetric rolling(ASR), as one of severe plastic deformation(SPD) methods, was widely used to make ultra-fined materials with enhanced performance. Internal marks were used to show the shear deformation during asymmetric rolling with pure aluminium as a model material. Effects of reduction ratio and mismatch ratio on the shear deformation were studied. With the observed shear deformation results, equivalent strain was calculated. For lager shear deformation, rolling equipment was modified to increase friction between specimen and the rollers. Consequently, extremely fine grains with size of 500 nm are obtained in pure aluminium. With improved asymmetric rolling, the ability of grain refinement of ASR is greatly improved.
基金Funded by the National Natural Science Foundation of China(51275445)
文摘We investigated the influences of process parameters on the head curvature of pure titanium sheet in hot rolling process and proposed the controlling means. First, the thermal simulation experiments for pure titanium TA1 were carried out to investigate the hot deformation behaviors of pure titanium in the temperature range of 700-800 ℃ with strain rate range of 1-20 S-1, and the processing map was established to determine optimized deformation parameters. Then, the finite element model has been constructed and used to analyze the effect of process parameters on the direction and severity of head curvature of pure titanium sheet. The process parameters considered in the present study include workpiece temperature, work roll diameter, pass reduction, oxide scale thickness of workpiece surface, and interface friction coefficient. The simulation results show that the workpiece temperature and the interface friction coefficient are the two main factors. The proposed controlling means was carried out on a hot rolling production line and solved the head curvature problem effectively. The rolling practices indicate that the rolling yield is improved greatly.
基金finically supported by the National Natural Science Foundation of China (No. 51474127)the Chinese Scholar Council (No. 201408210289)the Key Laboratory Open Project of Liaoning Province (USTLKFSY201504)
文摘Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.
基金This project is supported by Provincial University Natural Science Fund of Jiangsu, China (No. 05KJB460106)Municipal Science and Technology Development Fund of Shanghai, China (No. 0152nm031)Municipal Natural Science Fund of Nantong, China (No. Z5005).
文摘A newly developed pure rolling fatigue test rig with three contact points is used to test the rolling contact fatigue properties of silicon nitride ceramic balls. Ball surfaces are examined after failure with optical microscopy and scanning electron microscopy. The failure cause, fatigue phenomenon and mechanics are analyzed. The research shows that subsurface cracks play a dominant role in the formation of spalling failure. These cracks originated from volume defects of the material and propagate, to form elliptical fatigue spalls under the action of principal tensile stresses. The principal tensile stress increases with increasing contact load, causing spall formation and reduction of rolling contact life. The greater the principal tensile stress is, the more severe the peeling of near surface is. Under the same condition, the closer volume defects are to the surface, the more likely failure occurs, the shorter the rolling contact life is.
文摘针对无人驾驶车辆采用纯跟踪算法对不同曲率路径跟踪时,出现道路适应能力弱和跟踪精度差的问题,提出一种基于代价的滚动预瞄模型(rolling preview model,RPM),以提高纯跟踪算法跟踪精度与鲁棒性。首先,根据车辆运动学与阿克曼转向几何,提出预瞄轨迹的确定方法以及预瞄轨迹与待跟踪路径间的几何约束;其次,设计道路弯曲度加权项并构建目标函数对预瞄轨迹进行优化,以获得预瞄距离的最优值;最后,在ROS/Gazebo仿真环境下设置不同初始状态与不同曲率的工况进行对比仿真实验,并在空旷环境中对8字形路径进行实车跟踪实验。实验结果表明,所提出的滚动预瞄模型能够根据预瞄轨迹与待跟踪路径的几何关系有效调节预瞄距离,相较于麻省理工(Massachusetts Institute of Technology,MIT)算法和Stanley算法,滚动预瞄模型在特殊初始状态、大曲率道路下有利于跟踪精度的提高。