Railway Wheelsets: Theory, Experiments and Design Considering Temperatures, Stresses and Deformations as Induced by Braking Loads and Contact Forces
Doctoral thesis, 1993
Railway wheelset components exposed to braking loads and contact forces have been studied. The work has been performed in close cooperation with the Swedish wheelset manufacturer ABB SURA Traction AB, and it has resulted in one brake disc prototype and two different wheel prototypes. Theoretical and numerical investigations have been performed using analytical models and commercial FE-programs. The results are verified through full-scale laboratory and field experiments. An inertia dynamometer for testing of brake components (wheels, discs, pads) has been designed and constructed within the present project.
A linear analytical model for calculating transient axisymmetric temperature distributions in finite hollow cylinders has been established. The model is used to calculate temperature histories during and after braking in a nonventilated solid steel disc and in a ventilated disc made of cast iron. The theoretical results agree reasonably well with the experimental results from dynamometer testing. The conclusion is that, under Swedish driving conditions, a forged solid steel disc may be a possible substitute for the more complicated and expensive ventilated disc.
A railway wheel using flexible S-shaped steel spokes between hub and rim is suggested. The vertical dynamic behaviour of a two-axle freight car with such wheels is analyzed and compared to that of a freight car with standard solid wheels. Full-scale field experiments have been performed using wheels without and with wheelflats instrumented for measurement of transient vertical wheel/rail contact forces. Accelerations and strains in the track structure were measured in parallel. The location of the travelling instrumented wheelset in relation to the instrumented portion of the track was determined at each instant of time. Different train speeds and axle loads were tested. The flexible wheel was found to considerably reduce the impact loads in the presence of a wheelflat.
In contrast to a standard solid wheel, no thermally induced residual stresses from block braking will occur in the rim of the flexible wheel. The wheel was also found to radiate less noise than a solid wheel. Calculated temperatures and deformations are verified through experiments on the inertia dynamometer.
The performance of a so-called low stress wheel with hub-rim offset is investigated. By use of a two-level fractional factorial design, the influences of six selected geometrical variables (describing disc thickness, rim thickness, and hub-rim offset) are quantified. It is found that a low stress wheel offers high resistance to thermal and mechanical loads. Based on the present study, a first set of twelve forged rim-quenched low stress wheels has been produced. Brake tests have been performed and field testing is underway.