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
Transient photovoltage(PV) technique was applied to investigate the separation and the transport mechanism of the photo-induced charge carriers on nano-TiO_ 2 film electrode. The positive PV transients were observed w...Transient photovoltage(PV) technique was applied to investigate the separation and the transport mechanism of the photo-induced charge carriers on nano-TiO_ 2 film electrode. The positive PV transients were observed whenever the light was incident from the gauze platinum(top illumination) or the ITO electrode(bottom illumination). This implies that the photo-induced electrons always accumulate near the ITO. Simultaneously, it is found that under the singe pulse illumination, PV transient at bottom illumination needs a shorter time to reach its maximum than that at top illumination. This indicates that the photo-induced carriers are separated faster on TiO_ 2/ITO interface than that in the bulk of the TiO_ 2 film. These demonstrate the existence of the contact potential on the TiO_ 2/ITO interface, with the downward band bending from the TiO_ 2 to ITO, which may cause the excess carriers to be separated by drift. Under the repeated pulses illumination, the PV transients at top illumination remained unchanged, while those at bottom illumination changed significantly. This results from the trapping of the excess electrons on the TiO_ 2/ITO interface.展开更多
The transient response to longitudinal impact of flexible rods with Hertz contact is closely related to the extent of deformations with different impact parameters. By means of LS-DYNA, for different radius and differ...The transient response to longitudinal impact of flexible rods with Hertz contact is closely related to the extent of deformations with different impact parameters. By means of LS-DYNA, for different radius and different speeds, the longitudinal impact of a hammer with a rounded end on a drill rod is numerically simulated in this article. Simulations demonstrate that there is an obvious dif-ference between analytical solution and numerical solution on condition of short curvature radius. In the circumstance contact pressure increases, the boundary of the yield zone exceeds that of the contact zone, and the significant plastic deformation reduces the intensity of contact pressure pulse. Contact force-time curves in loading and unloading phases shift down. The numerical solution is in good agree-ment with analytical solution on condition of large curvature radius and impact speeds. The deforma-tion of yield region is constrained by the surrounding elastic region and no significant plastic deforma-tion appears.展开更多
Existing studies primarily focus on stiffness and damping under full-film lubrication or dry contact conditions.However,most lubricated transmission components operate in the mixed lubrication region,indicating that b...Existing studies primarily focus on stiffness and damping under full-film lubrication or dry contact conditions.However,most lubricated transmission components operate in the mixed lubrication region,indicating that both the asperity contact and film lubrication exist on the rubbing surfaces.Herein,a novel method is proposed to evaluate the time-varying contact stiffness and damping of spiral bevel gears under transient mixed lubrication conditions.This method is sufficiently robust for addressing any mixed lubrication state regardless of the severity of the asperity contact.Based on this method,the transient mixed contact stiffness and damping of spiral bevel gears are investigated systematically.The results show a significant difference between the transient mixed contact stiffness and damping and the results from Hertz(dry)contact.In addition,the roughness significantly changes the contact stiffness and damping,indicating the importance of film lubrication and asperity contact.The transient mixed contact stiffness and damping change significantly along the meshing path from an engaging-in to an engaging-out point,and both of them are affected by the applied torque and rotational speed.In addition,the middle contact path is recommended because of its comprehensive high stiffness and damping,which maintained the stability of spiral bevel gear transmission.展开更多
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.
文摘Transient photovoltage(PV) technique was applied to investigate the separation and the transport mechanism of the photo-induced charge carriers on nano-TiO_ 2 film electrode. The positive PV transients were observed whenever the light was incident from the gauze platinum(top illumination) or the ITO electrode(bottom illumination). This implies that the photo-induced electrons always accumulate near the ITO. Simultaneously, it is found that under the singe pulse illumination, PV transient at bottom illumination needs a shorter time to reach its maximum than that at top illumination. This indicates that the photo-induced carriers are separated faster on TiO_ 2/ITO interface than that in the bulk of the TiO_ 2 film. These demonstrate the existence of the contact potential on the TiO_ 2/ITO interface, with the downward band bending from the TiO_ 2 to ITO, which may cause the excess carriers to be separated by drift. Under the repeated pulses illumination, the PV transients at top illumination remained unchanged, while those at bottom illumination changed significantly. This results from the trapping of the excess electrons on the TiO_ 2/ITO interface.
基金supported by the National Natural Science Foundation of China (No. 50475056)
文摘The transient response to longitudinal impact of flexible rods with Hertz contact is closely related to the extent of deformations with different impact parameters. By means of LS-DYNA, for different radius and different speeds, the longitudinal impact of a hammer with a rounded end on a drill rod is numerically simulated in this article. Simulations demonstrate that there is an obvious dif-ference between analytical solution and numerical solution on condition of short curvature radius. In the circumstance contact pressure increases, the boundary of the yield zone exceeds that of the contact zone, and the significant plastic deformation reduces the intensity of contact pressure pulse. Contact force-time curves in loading and unloading phases shift down. The numerical solution is in good agree-ment with analytical solution on condition of large curvature radius and impact speeds. The deforma-tion of yield region is constrained by the surrounding elastic region and no significant plastic deforma-tion appears.
基金This research was supported by the National Natural Science Foundation of China(NSFC,No.51875369)by the Chongqing Key Industry General Key Technology Innovation Special Major R&D Projects(No.cstc2017zdcy-zdzxX0001)Wei Pu would also like to thank the Fundamental Research Funds for the Central Universities(No.YJ201752)。
文摘Existing studies primarily focus on stiffness and damping under full-film lubrication or dry contact conditions.However,most lubricated transmission components operate in the mixed lubrication region,indicating that both the asperity contact and film lubrication exist on the rubbing surfaces.Herein,a novel method is proposed to evaluate the time-varying contact stiffness and damping of spiral bevel gears under transient mixed lubrication conditions.This method is sufficiently robust for addressing any mixed lubrication state regardless of the severity of the asperity contact.Based on this method,the transient mixed contact stiffness and damping of spiral bevel gears are investigated systematically.The results show a significant difference between the transient mixed contact stiffness and damping and the results from Hertz(dry)contact.In addition,the roughness significantly changes the contact stiffness and damping,indicating the importance of film lubrication and asperity contact.The transient mixed contact stiffness and damping change significantly along the meshing path from an engaging-in to an engaging-out point,and both of them are affected by the applied torque and rotational speed.In addition,the middle contact path is recommended because of its comprehensive high stiffness and damping,which maintained the stability of spiral bevel gear transmission.
