Influence of temperature on adhesion coefficient and bonding strength of leaf films: A twin disc study

Abstract

In the autumn, train operations in the UK are likely to be unstable due to the low adhesion coefficient between the wheel and rail, and fallen leaves on the line have been known as the main cause of this problem. In this study, the temperature effects on the adhesion coefficient as well as the bonding strength of the leaf film were investigated using a twin disc machine, to develop a potential prevention and mitigation method. The high surface temperature of the disc seemed to improve the adhesion when the leaf powder suspension was present, forming a linear relationship between the surface temperature. The surface temperature around 240 °C could be enough to attain the required level of traction. The high temperature could decrease the bonding energy between the leaf film and rail, possibly decelerating the chemical reaction for the leaf film formation. Continuous drag braking in the autumn was proposed as a countermeasure. Two effects can be expected for this method: prevention of leaf contamination by removing the leaf residue on the wheel surface and improvement of the adhesion level by braking heat.

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

“…Leaf particles are thereby shredded and ejected off the disc surface. In this case, both the mechanical aspect (associated with the increase of the shear stresses undergone by the third bodies) and physicochemical aspects (associated with the increase of RH) appear to affect the reactivation of the adhesion, as mentioned by Ishizaka [32] and White [38]. RH ≈ 50%:…”

“…Interestingly, the main difference between a RH of leaves of 35% and 85% lies in the difference of the quantity of water initially available in the external third body (indicated by the measure of the RH). The presence of water is one of the main components needed to activate physico-chemical reactions between organic components of leaves and steel regarding variations of adhesion in the wheel-rail contact [7,32]. Thus, reducing the amount of water found in leaves can decrease the physico-chemical effect in favor of mechanical changes of leaves under a RH below 35%.…”

“…14), the adhesion measured at low RH is always higher than that measured at high RH. However, the color change of the layer formed translates the occurrence of physico-chemical reactions, as explained in Section 1 and in [7,13]. We can therefore assume that the difference of power dissipated by friction at RH<35% and RH>85% is the power needed to activate the chemical reaction between lignin, cellulose, and polysaccharides (see also Sect.…”

“…The elements presented in this article can be positioned in relation to the recent work of Ishizaka [13], which mainly focused on studying the physico-chemical reactions involved in the transformation of dead leaves in connection with the loss of adhesion of a train. Spectroscopic analyses (i.e., the study of the interaction between matter and electromagnetic radiation as a function of the wavelength or frequency of the radiation) such as Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS) were performed after grinding and drying dead leaves in aqueous solution.…”

An improved degraded adhesion model for wheel–rail under braking conditions

“…The low adhesion state often occurs when the rail surface is slightly wet because of oil pollution, mist, light rain or condensation, and the most serious rail surface pollution is the adhesion reduction caused by wet defoliation coverage (Ishizaka et al , 2020). When the braking force exceeds the adhesion between wheel and rail, a large sliding will occur.…”