Experimental study of the influence of the relative humidity of leaves and their link to adhesion losses in the wheel-rail contact

Abstract

Every autumn, low levels of wheel–rail contact adhesion caused by leaves on the railhead surface are reported by train drivers. These incidents cause problems for the safety and regularity of rail traffic and occur predominantly at the beginning and end of the day when high humidity levels are achieved. At those moments the air temperature reaches the dew point temperature creating moisture on the railhead and oxides which react chemically with dead leaves found on the railhead surface. This article presents the results of a test campaign performed on a ring-on-disc tribometer with the aim of reproducing and studying the development of a loss of adhesion at an imposed slip rate. This type of tribometer enables a realistic approximation of the tribological circuit of a rail–wheel contact. Several samples of pollution responsible for adhesion losses were collected on the French railway network during fall and reproduced in a laboratory on a tribometer under imposed relative humidity and slip conditions. The results indicate the presence of reproducible phenomena modulated by variations in hygrometry and imposed slip rates. The decrease in hygrometry of the external third bodies introduced into the contact is at the origin of the generation of debris from the first bodies in contact. This presence of wear debris is reflected by an increase of the power dissipated by friction. Conversely, increasing the hygrometry decreases the ability of the third body to raise adhesion levels on contact and reduces the generation of debris from the first bodies. The results obtained from the analysis of the force and power quantities related to the contact reproduced in the laboratory allow the authors to confirm that the presence of water has a significant effect on the mechanical and physico-chemical evolution of the adhesion of a rail–wheel contact polluted by a third external (leaf-like) body.

Experimental Evaluation of Effect of Leaves on Railroad Tracks in Loss of Braking

“…The presence of worn and said 3BL causes the traction coefficient to drop less at the beginning and have a steeper increase. Similar observations and conclusions were made by the authors who have tested the traction recovery aspects of a leaf-contaminated rail environment [24][25][26]. This makes it essential to understand traction recovery in the presence of wear and naturally generated 3BL.…”

“…However, the ANOVA analysis performed by the researchers suggests no significant influence in the interaction between the amount of leaves and humidity but indicates individual factors alone have significance. Similarly, Guidoum et al [24] have experimentally studied the tribological aspects of leaves in the presence of moisture. They have concluded that the slip rate and percentage humidity strongly influence adhesion.…”

“A novel methodology for developing ultra-low adhesion leaf layers on a full-scale wheel/rail rig”

“…A nominal slip of 3% was used with the intention of creating the layer more effectively as higher slip values might accelerate the development of leaf layers. 31 Images from the layer creation are shown in Figure 2. The ambient conditions were 20.1°C and a relative humidity of 51%.…”

Numerical investigation of wheel‐rail adhesion using a simplified three‐dimensional model considering surface roughness and temperature

“…12 Many researchers have conducted studies to investigate the effect of 3BL on wheel-rail adhesion. [13][14][15][16] Khan 17 studied the effect of third bodies on friction and wear at the wheel-rail interface using a handheld tribometer. Meierhofer 18 introduced the definition of 3BL into the creep force model and compared the results with experimental results at large creepages.…”

“…Researchers have noted that the decrease in the adhesion‐creepage curve was mainly attributed to the change of shear stress caused by temperature in the third body layer (3BL) 12 . Many researchers have conducted studies to investigate the effect of 3BL on wheel‐rail adhesion 13–16 . Khan 17 studied the effect of third bodies on friction and wear at the wheel‐rail interface using a handheld tribometer.…”