Thermo-mechanical effects in the formation mechanism of rail squats

Abstract

A three-dimensional elasto-plastic finite element (FE) tool has been developed to
study the thermo-mechanical originations of squats in rails. The initiation process of
rail squats is in principle related to the response of materials against cyclic loading.
The thermo-mechanical issues in this process are not yet clear, due to the
complicated wheel-rail interaction and the variability of the loads, parameters and material properties. This paper examines the role of thermo-mechanical-related causes on the formation mechanism of squats using numerical modelling. Assuming a range of material behaviour, thermal softening and temperature dependencies, the sliding wheel-rail contact problem is investigated using a three-dimensional FE tool. The temperature rise and thermal stress due to the frictional heat, generated at the contact surface of the wheel and rail, are taken into account. The magnitudes and distributions of thermo-mechanical stresses on rail surface are calculated for realistic loading conditions. Particular attentions are paid to the temperature rise, residual stress and plastic strain with thermal effects under high tractive forces. The outputs are used to scrutinise if the so-called white etching layer is formed as a result of the temperature rise, needed for structural phase change and to consider the role of plastic deformations.