Tire slip angle has a great influence on peak values of both logitudinal and lateral adhesion coefficients as well as optimal slip ratios. Regression equations based on the experi- mental data from several countries...Tire slip angle has a great influence on peak values of both logitudinal and lateral adhesion coefficients as well as optimal slip ratios. Regression equations based on the experi- mental data from several countries are given to describe their dependencies. The peak value of longitudiinal adhesion coefficient has a linear relationship with tire slip angle, but peak value of lateral has a complicated relationship; the optimal slip ratio of longitudinal has an exponent function relationship, the optimal slip ratio of lateral almost has nothinng to do with tire slipangle.展开更多
Purpose–In response to the problem of insufficient traction/braking adhesion force caused by the existence of the third-body medium on the rail surface,this study aims to analyze the utilization of wheel-rail adhesio...Purpose–In response to the problem of insufficient traction/braking adhesion force caused by the existence of the third-body medium on the rail surface,this study aims to analyze the utilization of wheel-rail adhesion coefficient under different medium conditions and propose relevant measures for reasonable and optimized utilization of adhesion to ensure the traction/braking performance and operation safety of trains.Design/methodology/approach–Based on the PLS-160 wheel-rail adhesion simulation test rig,the study investigates the variation patterns of maximum utilized adhesion characteristics on the rail surface under different conditions of small creepage and large slip.Through statistical analysis of multiple sets of experimental data,the statistical distribution patterns of maximum utilized adhesion on the rail surface are obtained,and a method for analyzing wheel-rail adhesion redundancy based on normal distribution is proposed.The study analyzes the utilization of traction/braking adhesion,as well as adhesion redundancy,for different medium under small creepage and large slip conditions.Based on these findings,relevant measures for the reasonable and optimized utilization of adhesion are derived.Findings–When the third-body medium exists on the rail surface,the train should adopt the low-level service braking to avoid the braking skidding by extending the braking distance.Compared with the current adhesion control strategy of small creepage,adopting appropriate strategies to control the train’s adhesion coefficient near the second peak point of the adhesion coefficient-slip ratio curve in large slip can effectively improve the traction/braking adhesion redundancy and the upper limit of adhesion utilization,thereby ensuring the traction/braking performance and operation safety of the train.Originality/value–Most existing studies focus on the wheel-rail adhesion coefficient values and variation patterns under different medium conditions,without considering whether the rail surface with different medium can provide sufficient traction/braking utilized adhesion coefficient for the train.Therefore,there is a risk of traction overspeeding/braking skidding.This study analyzes whether the rail surface with different medium can provide sufficient traction/braking utilized adhesion coefficient for the train and whether there is redundancy.Based on these findings,relevant measures for the reasonable and optimized utilization of adhesion are derived to further ensure operation safety of the train.展开更多
Mathematical models of tire-lateral mad adhesion for use in mad vehicle dynamics studies are set up to express the relations of adhesion coefficients with slip ratio in lateral direction.The models of tire-lateral mad...Mathematical models of tire-lateral mad adhesion for use in mad vehicle dynamics studies are set up to express the relations of adhesion coefficients with slip ratio in lateral direction.The models of tire-lateral mad adhesion revolutionize the Pacejka's model in concept and therefore make it possible for applications in vehicle dynamics studies by the expression of lateral adhesion coefficient as a function of wheel slip ratio,instead of the wheel slip angle,taking into account in the mean time the influences of mad surface condition, vehicle velocity,vertical load,tire slip angle,and wheel camber angle.展开更多
The fundamental principle of road identification by using angular acceleration of driving wheels was demonstrated in this paper. Based on the analysis of energy conversion and parameters variation during the vehicle d...The fundamental principle of road identification by using angular acceleration of driving wheels was demonstrated in this paper. Based on the analysis of energy conversion and parameters variation during the vehicle drive slip process, the change of adhesion coefficient relative to the an- gular acceleration were theoretically studied experimentally validated. The variation shows that the change of adhesion coefficient relative to the angular acceleration and the change of slip ratio in the drive slip process have same trend-both of them exist an only optimal angular acceleration corre- sponding to the peak value of adhesion coefficient. The peak adhesion coefficient of the prototype vehicle is about 0. 14 on the ice-covered road surfaces, with the corresponding optimal angular accel- eration of about 23.5 rad/s2 and optimal slip ratio of about 9. 4%.展开更多
Transient adhesion effects in rolling–sliding contacts influence all aspects of train–track interaction.This is of high importance specifically when these effects result in critically low adhesion,which poses a risk...Transient adhesion effects in rolling–sliding contacts influence all aspects of train–track interaction.This is of high importance specifically when these effects result in critically low adhesion,which poses a risk to traction and braking of railway vehicles.This study presents a model that can replicate the transient changes of the coefficient of adhesion with tested water and solid particle mix.The experimental data for the model are measured using a commercial ball-on-disc tribometer.The experimental results showed a liquid reservoir in front of the contact area that slowly reduces in size.This observation was used in the modelling approach to divide the calculation into two stages where the reservoir is present and when it disappears.The model was able to reproduce the occurrence of low adhesion region seen in experimental results with different particle concentrations.展开更多
Ultra-high-strength steels have been widely utilized in the aviation industry due to their superior mechanical and physical properties.However,the intense friction occurring at the tool–workpiece interface can result...Ultra-high-strength steels have been widely utilized in the aviation industry due to their superior mechanical and physical properties.However,the intense friction occurring at the tool–workpiece interface can result in significant tool wear,impacting both the machining efficiency and surface quality.Therefore,a deep understanding of the tribological behavior at the tool–workpiece interface is crucial for extending tool life.The current study proposed a novel open tribo-system to simulate the intermittent contact conditions between the tool and the workpiece during the milling process.An improved friction model was established to calculate the real friction coefficient under intermittent contact conditions.Tribological comparative experiments on ultra-highstrength steel and cemented carbide were conducted under various cooling conditions:dry,high-pressure air cooling(HPAC),air atomization of cutting fluid(AACF),and ultrasonic atomization of cutting fluid(UACF).The influences of various cooling conditions on the tribological characteristics were investigated,with a focus on the depth of the wear mark,height of the pile-up,measured force,adhesion friction coefficient,and wear morphology.The results reveal that the depth of the wear mark,height of the pile-up,and measured forces play pivotal roles in determining the adhesion friction coefficient.The synergistic action of airflow and droplets results in the formation of a liquid film,improving the friction at the interface between the ball and the workpiece.Compared with the AACF condition,the UACF condition results in a 7.7% reduction in the adhesion friction coefficient due to its excellent film-forming ability stemming from its small droplet size and uniform droplet size distribution.Abrasive wear,adhesive wear,and oxidative wear are the primary wear types for cemented carbide,regardless of the cooling conditions.The effective cooling and lubrication capability provided by the uniform liquid film in UACF contributes to improving the wear resistance of cemented carbide,offering valuable insights for mitigating tool wear.展开更多
文摘Tire slip angle has a great influence on peak values of both logitudinal and lateral adhesion coefficients as well as optimal slip ratios. Regression equations based on the experi- mental data from several countries are given to describe their dependencies. The peak value of longitudiinal adhesion coefficient has a linear relationship with tire slip angle, but peak value of lateral has a complicated relationship; the optimal slip ratio of longitudinal has an exponent function relationship, the optimal slip ratio of lateral almost has nothinng to do with tire slipangle.
文摘Purpose–In response to the problem of insufficient traction/braking adhesion force caused by the existence of the third-body medium on the rail surface,this study aims to analyze the utilization of wheel-rail adhesion coefficient under different medium conditions and propose relevant measures for reasonable and optimized utilization of adhesion to ensure the traction/braking performance and operation safety of trains.Design/methodology/approach–Based on the PLS-160 wheel-rail adhesion simulation test rig,the study investigates the variation patterns of maximum utilized adhesion characteristics on the rail surface under different conditions of small creepage and large slip.Through statistical analysis of multiple sets of experimental data,the statistical distribution patterns of maximum utilized adhesion on the rail surface are obtained,and a method for analyzing wheel-rail adhesion redundancy based on normal distribution is proposed.The study analyzes the utilization of traction/braking adhesion,as well as adhesion redundancy,for different medium under small creepage and large slip conditions.Based on these findings,relevant measures for the reasonable and optimized utilization of adhesion are derived.Findings–When the third-body medium exists on the rail surface,the train should adopt the low-level service braking to avoid the braking skidding by extending the braking distance.Compared with the current adhesion control strategy of small creepage,adopting appropriate strategies to control the train’s adhesion coefficient near the second peak point of the adhesion coefficient-slip ratio curve in large slip can effectively improve the traction/braking adhesion redundancy and the upper limit of adhesion utilization,thereby ensuring the traction/braking performance and operation safety of the train.Originality/value–Most existing studies focus on the wheel-rail adhesion coefficient values and variation patterns under different medium conditions,without considering whether the rail surface with different medium can provide sufficient traction/braking utilized adhesion coefficient for the train.Therefore,there is a risk of traction overspeeding/braking skidding.This study analyzes whether the rail surface with different medium can provide sufficient traction/braking utilized adhesion coefficient for the train and whether there is redundancy.Based on these findings,relevant measures for the reasonable and optimized utilization of adhesion are derived to further ensure operation safety of the train.
文摘Mathematical models of tire-lateral mad adhesion for use in mad vehicle dynamics studies are set up to express the relations of adhesion coefficients with slip ratio in lateral direction.The models of tire-lateral mad adhesion revolutionize the Pacejka's model in concept and therefore make it possible for applications in vehicle dynamics studies by the expression of lateral adhesion coefficient as a function of wheel slip ratio,instead of the wheel slip angle,taking into account in the mean time the influences of mad surface condition, vehicle velocity,vertical load,tire slip angle,and wheel camber angle.
基金Supported by the National"Eleventh Five"Project of China(40401040302)
文摘The fundamental principle of road identification by using angular acceleration of driving wheels was demonstrated in this paper. Based on the analysis of energy conversion and parameters variation during the vehicle drive slip process, the change of adhesion coefficient relative to the an- gular acceleration were theoretically studied experimentally validated. The variation shows that the change of adhesion coefficient relative to the angular acceleration and the change of slip ratio in the drive slip process have same trend-both of them exist an only optimal angular acceleration corre- sponding to the peak value of adhesion coefficient. The peak adhesion coefficient of the prototype vehicle is about 0. 14 on the ice-covered road surfaces, with the corresponding optimal angular accel- eration of about 23.5 rad/s2 and optimal slip ratio of about 9. 4%.
基金support within the COMET K2 Competence Centers for Excellent Technologies from the Austrian Federal Ministry for Climate Action(BMK)the Austrian Federal Ministry for Labour and Economy(BMAW),the Province of Styria(Dept.12)and the Styrian Business Promotion Agency(SFG).
文摘Transient adhesion effects in rolling–sliding contacts influence all aspects of train–track interaction.This is of high importance specifically when these effects result in critically low adhesion,which poses a risk to traction and braking of railway vehicles.This study presents a model that can replicate the transient changes of the coefficient of adhesion with tested water and solid particle mix.The experimental data for the model are measured using a commercial ball-on-disc tribometer.The experimental results showed a liquid reservoir in front of the contact area that slowly reduces in size.This observation was used in the modelling approach to divide the calculation into two stages where the reservoir is present and when it disappears.The model was able to reproduce the occurrence of low adhesion region seen in experimental results with different particle concentrations.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.92160301,92060203,52175415,and 52205475)the Science Center for Gas Turbine Project,China(Grant No.P2023-B-Ⅳ-003-001)+3 种基金the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20210295)the National Key Laboratory of Science and Technology on Helicopter Transmission(Nanjing University of Aeronautics and Astronautics,NUAA,China)(Grant No.HTL-A-22G12)the Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant No.KYCX21_0189)the Funding for Outstanding Doctoral Dissertation in NUAA,China(Grant No.BCXJ22-07).
文摘Ultra-high-strength steels have been widely utilized in the aviation industry due to their superior mechanical and physical properties.However,the intense friction occurring at the tool–workpiece interface can result in significant tool wear,impacting both the machining efficiency and surface quality.Therefore,a deep understanding of the tribological behavior at the tool–workpiece interface is crucial for extending tool life.The current study proposed a novel open tribo-system to simulate the intermittent contact conditions between the tool and the workpiece during the milling process.An improved friction model was established to calculate the real friction coefficient under intermittent contact conditions.Tribological comparative experiments on ultra-highstrength steel and cemented carbide were conducted under various cooling conditions:dry,high-pressure air cooling(HPAC),air atomization of cutting fluid(AACF),and ultrasonic atomization of cutting fluid(UACF).The influences of various cooling conditions on the tribological characteristics were investigated,with a focus on the depth of the wear mark,height of the pile-up,measured force,adhesion friction coefficient,and wear morphology.The results reveal that the depth of the wear mark,height of the pile-up,and measured forces play pivotal roles in determining the adhesion friction coefficient.The synergistic action of airflow and droplets results in the formation of a liquid film,improving the friction at the interface between the ball and the workpiece.Compared with the AACF condition,the UACF condition results in a 7.7% reduction in the adhesion friction coefficient due to its excellent film-forming ability stemming from its small droplet size and uniform droplet size distribution.Abrasive wear,adhesive wear,and oxidative wear are the primary wear types for cemented carbide,regardless of the cooling conditions.The effective cooling and lubrication capability provided by the uniform liquid film in UACF contributes to improving the wear resistance of cemented carbide,offering valuable insights for mitigating tool wear.
