To overcome the unfavorable factors of ground wheel-driven chain transmission when a no-tillage planter operates on straw mulching fields,a friction wheel transmission based on ground wheel transmission was designed i...To overcome the unfavorable factors of ground wheel-driven chain transmission when a no-tillage planter operates on straw mulching fields,a friction wheel transmission based on ground wheel transmission was designed in this research.The stability,i.e.,the effects of friction wheel tyre pressure on stability of machine transmission was investigated via validation of main factors.The relationships among tyre pressure,deformation and load were determined via theoretical analysis.The tyre pressure extreme for transmission is 25.90 psi,the maximum pressure imposed on the friction wheel tyre is 14 kN,the maximum deformation of friction wheel is 8.7 mm.The stabilities of friction wheel slip rate and seeding distance were investigated via field tests and alteration of friction wheel tyre pressure.After processing the test data,it can be found that the minimum tyre pressure for acquisition of friction wheel slip rate was 24.35 psi.After processing the data of seeding distance,it can be validated that the tyre pressure was kept unchanged following the optimal transmission effect of the transmission through the abrupt change of working speed,which further proved the feasibility of the new friction wheel transmission.The transmission of friction wheel can reduce 14.67%in variation coefficient of seed spacing at the speed of 5 km/h,and 16.22%at the speed of 8 km/h.展开更多
By combining thermomechanical coupling finite element analysis with the characteristics of phase transformation [continuous cooling transformation （CCT） curve], the thermal fatigue behavior of train wheel steel unde...By combining thermomechanical coupling finite element analysis with the characteristics of phase transformation [continuous cooling transformation （CCT） curve], the thermal fatigue behavior of train wheel steel under high speed and heavy load conditions was analyzed. The influence of different materials on the formation of the phase transformation zone of the wheel tread was discussed. The result showed that the peak temperature of wheel/track friction zone could be higher than the austenitizing temperature for braking. The depth of the austenitized region could reach a point of 0.9 mm beneath the wheel tread surface. The supercooled austenite is transformed to a hard and brittle martensite layer during the following rapid cooling process, which may lead to cracking and then spalling on the wheel tread surface. The decrease in carbon contents of the train wheel steel helps inhibit the formation of martensite by increasing the austenitizing temperature of the train wheel steel. When the carbon contents decrease from 0.7% to 0.4%, the Ac3 of the wheel steel is increased by 45 ℃, and the thickness of the martensite layer is de creased by 30 %, which is helpful in reducing the thermal cycling fatigue of the train wheel tread such as spalling.展开更多
A finite element vibration model of a multiple wheel-rail system which consists of four wheels, one rail, and a series of sleepers is established to address the problem of rail corrugation in high-speed tracks. In the...A finite element vibration model of a multiple wheel-rail system which consists of four wheels, one rail, and a series of sleepers is established to address the problem of rail corrugation in high-speed tracks. In the model, the creep forces between the wheels and rail are considered to be saturated and equal to the normal contact forces times the friction coefficient. The oscillation of the rail is coupled with that of wheels in the action of the saturated creep forces. When the coupling is strong, self- excited oscillation of the wheel-rail system occurs. The self-excited vibration propensity of the model is analyzed using the complex eigenvalue method. Results show that there are strong propensities of unstable self-excited vibrations whose frequencies are less than 1,200 Hz under some conditions. Preventing wheels from slipping on rails is an effective method for suppressing rail corrugation in high-speed tracks.展开更多
The Udwadia-Kalaba formulation is proposed to model the dynamics of the rolling wheel. A unified approach that addresses both the slip and the stiction in the contact section is considered. Purely rolling constraints ...The Udwadia-Kalaba formulation is proposed to model the dynamics of the rolling wheel. A unified approach that addresses both the slip and the stiction in the contact section is considered. Purely rolling constraints are associated with stiction and are suitably lifted as slip occurs. An extended formulation for the Uwadia-Kalaba equations of motion is introduced for that matter. It resorts to the weighted minimum norm and the weighted semi-least-squares solutions of the constraints equations. This not only allows a bias on constraints, by an appropriate description of weight functions based on friction, it also leads to a smooth activation or deactivation of selected constraints without rewriting the equations of motion or upsetting their numerical integration.展开更多
基金supported by the 13th Five-Year Plan for National Science and Technology(Grant No.2016YFD0700302,20140309001NY)Science and Technology Project of Jilin Provincial Education Department(JJKH20170811KJ)Science and Technology Development Project of Jilin Province(20160307011NY).
文摘To overcome the unfavorable factors of ground wheel-driven chain transmission when a no-tillage planter operates on straw mulching fields,a friction wheel transmission based on ground wheel transmission was designed in this research.The stability,i.e.,the effects of friction wheel tyre pressure on stability of machine transmission was investigated via validation of main factors.The relationships among tyre pressure,deformation and load were determined via theoretical analysis.The tyre pressure extreme for transmission is 25.90 psi,the maximum pressure imposed on the friction wheel tyre is 14 kN,the maximum deformation of friction wheel is 8.7 mm.The stabilities of friction wheel slip rate and seeding distance were investigated via field tests and alteration of friction wheel tyre pressure.After processing the test data,it can be found that the minimum tyre pressure for acquisition of friction wheel slip rate was 24.35 psi.After processing the data of seeding distance,it can be validated that the tyre pressure was kept unchanged following the optimal transmission effect of the transmission through the abrupt change of working speed,which further proved the feasibility of the new friction wheel transmission.The transmission of friction wheel can reduce 14.67%in variation coefficient of seed spacing at the speed of 5 km/h,and 16.22%at the speed of 8 km/h.
基金High-Tech Research and Development Programof China (863 Program) (2006AA03Z514 and 2008AA030703)
文摘By combining thermomechanical coupling finite element analysis with the characteristics of phase transformation [continuous cooling transformation （CCT） curve], the thermal fatigue behavior of train wheel steel under high speed and heavy load conditions was analyzed. The influence of different materials on the formation of the phase transformation zone of the wheel tread was discussed. The result showed that the peak temperature of wheel/track friction zone could be higher than the austenitizing temperature for braking. The depth of the austenitized region could reach a point of 0.9 mm beneath the wheel tread surface. The supercooled austenite is transformed to a hard and brittle martensite layer during the following rapid cooling process, which may lead to cracking and then spalling on the wheel tread surface. The decrease in carbon contents of the train wheel steel helps inhibit the formation of martensite by increasing the austenitizing temperature of the train wheel steel. When the carbon contents decrease from 0.7% to 0.4%, the Ac3 of the wheel steel is increased by 45 ℃, and the thickness of the martensite layer is de creased by 30 %, which is helpful in reducing the thermal cycling fatigue of the train wheel tread such as spalling.
基金supported by the National Natural Science Foundation of China(No.51275429)
文摘A finite element vibration model of a multiple wheel-rail system which consists of four wheels, one rail, and a series of sleepers is established to address the problem of rail corrugation in high-speed tracks. In the model, the creep forces between the wheels and rail are considered to be saturated and equal to the normal contact forces times the friction coefficient. The oscillation of the rail is coupled with that of wheels in the action of the saturated creep forces. When the coupling is strong, self- excited oscillation of the wheel-rail system occurs. The self-excited vibration propensity of the model is analyzed using the complex eigenvalue method. Results show that there are strong propensities of unstable self-excited vibrations whose frequencies are less than 1,200 Hz under some conditions. Preventing wheels from slipping on rails is an effective method for suppressing rail corrugation in high-speed tracks.
文摘The Udwadia-Kalaba formulation is proposed to model the dynamics of the rolling wheel. A unified approach that addresses both the slip and the stiction in the contact section is considered. Purely rolling constraints are associated with stiction and are suitably lifted as slip occurs. An extended formulation for the Uwadia-Kalaba equations of motion is introduced for that matter. It resorts to the weighted minimum norm and the weighted semi-least-squares solutions of the constraints equations. This not only allows a bias on constraints, by an appropriate description of weight functions based on friction, it also leads to a smooth activation or deactivation of selected constraints without rewriting the equations of motion or upsetting their numerical integration.
