Research On Tribological Behavior Of Friction Blocks Of High-speed Trains In Gravel Environment

As an important part of high-speed trains,the braking system plays a key role in the process of smooth deceleration and safe stopping of trains.The train brake system is mainly composed of brake discs and brake pads.The brake pads include brake friction blocks and back plates.Brake friction blocks are the parts that directly contact and friction with brake discs and their tribological performance is directly related to the braking performance of the train.In recent decades,many scholars at home and abroad have studied the brake tribological behavior such as vibration noise and friction heat during braking,but most of the interface environment of their research is dry friction under normal working conditions.Few studies have been conducted on the braking process of trains in harsh environments(wind,sand,rain,snow,etc.),and a comparatively systematic theory of brake tribology has not yet been formed.Many of the main railway lines in northwest and north of China are in the environment of wind and sand all year round.Poor external conditions make the friction environment of the train brake interface more complicated.In addition to the debris generated by normal wear,the brake interface may also be affected by gravel,which poses a great potential threat to the safe operation of the train brake system.Therefore,exploring the tribological behavior and mechanism of brake friction blocks in the gravel environment is of great significance to enrich the friction theory of friction blocks under harsh environments and achieve safe and reliable operation of high-speed trains in complex environments.This research is based on a customized disc brake small-scale test bench of the high-speed train.Three types of gravel(desert gravel,Gobi gravel,quartz gravel)on the surface of the Lanxin Line are investigated,exploring the effect of gravel type on the tribological behavior(wear,heat distribution,vibration noise,etc.)of the friction blocks.Then,taking desert sand as an example,the effect of gravel size on the tribological behavior of the friction block is studied.At last,the perforated friction block is introduced into the experiment to investigate the influence of the friction block hole structure on the tribological behavior of the interface under the gravel environment,and explain its mechanism.The main conclusions are as follows:1.Of the three types of gravel,the desert sand involved in the friction environment has the greatest impact on the braking tribological behavior of the friction block,the friction block surface wears the most,the outer ring appears a large area of spalling,the surface heat distribution is the most uneven,and squeal with high frequency is excited.In other grit environments,the wear is relatively slight,and only low-frequency vibration noise is excited.2.The analysis of the influence of the size of the gravel on the tribological behavior of the friction block shows that the gravel with small size can quickly accumulate at the friction interface,which causes the material to peel off in a large area after repeated extrusion and friction,reducing the actual contact areas of the friction interface;Grooves and scratches are formed on the surface of the friction block by medium-size gravel,the gravel and abrasive debris are compacted in the low-lying area,which together with the contact platform bears the interface friction force;it’s difficult for the large-sized gravel to intervene in the friction interface,most of them are embedded in the material pores or spalling pits and participate in interface friction in the form of "micro-convex body".At the same time,large-sized gravel destroys the contact platform on the surface of the friction block,resulting in local concentration of contact pressure and alternating stress,thus screaming noise with high strength and high frequency is excited.In addition,the study found that in the area where gravel and abrasive debris accumulated,the gravel accumulation layer becomes the main load-bearing platform in this area,and the repeated rubbing between the gravel causes the surface temperature of this area to be higher.3.By studying the effect of the hole structure on the tribological behavior of the friction block in the gravel environment,the result shows that the hole structure on the surface of the friction block accumulates a large amount of gravel,which gradually accumulates around the circular hole during the braking friction process to form a gravel accumulation layer.The layer becomes the main bearing platform of the interface,resulting in a higher surface temperature in this area.At the same time,due to the repeated rubbing of the gravel at the braking interface,the material on the surface of the friction block fell off to a large extent.