Graphite is commonly used in brake pads. The use of graphite powder has the main goal of solid state lubrication and friction coefficient stabilization. In this article results on resin bonded brake pads with focus on noise performance and heat dissipation are presented. Experimental tests are based on model friction materials with a known formulation and a reduced number of components for a better identification of the role of the graphite type. Results clearly indicate that both noise performance and thermal conductivity are strongly affected by the type of graphite. Guidelines for the selection of graphite types for optimized friction materials are given.

This article presents a prediction of the residual stresses that are introduced by the heat treatment in the manufacture of railway wheels. It is well known that this treatment induces the formation of a layer of residual circumferential (hoop) compressive stresses on the tread surface. This stress field may be reversed during service loading, especially tread braking. Tensile stresses at the wheel tread that arise from repeated braking may lead to the initiation of surface cracks. The work presented here defines a methodology for determining the as-manufactured residual stress field prior to service loading. A thermal and mechanical finite element model was used to study the residual stress evolution during the heat treatment. The heat transfer coefficient during quenching was determined by means of a dedicated experimental setup. The results show that the numerically computed residual stresses correlate strongly with the experimental residual stresses determined by ultrasound when the model material includes time-dependent effects such as creep or viscoplasticity.

Squeal from railway wheels occurring in short radius curves produces a very intense and highly annoying noise in the range 400–8000 Hz. When the excitation, due to lateral forces acting on the wheel, cannot be avoided, additional systems can be added on the wheel to limit acoustic emission. A very economical approach is the use of metal rings inserted into grooves machined in the wheels. Unfortunately the effectiveness of these so called damping rings varies from one wheel to another and for different rings. Because the mechanisms of attenuation are not well understood, these variations have not to date been explained. The aim of this paper is to clarify the attenuation mechanisms for damping rings especially for the first three axial wheel modes, which are the predominant sound radiated ones in curve passage and for which the effectiveness of the treatment is lower. It has been generally assumed that friction between the ring and the groove has been the mechanism for squeal noise attenuation. Here it is shown that the vibration attenuation is due to modal coupling between the wheel and the ring. The validity of this proposed mechanism is investigated using experimental measurements and theoretical and numerical models. The results presented here will provide an avenue for optimization of the damping ring noise control treatment to obtain significant levels of squeal noise attenuation notably for the first three axial modes.