Tension/torsion ultrasonic fatigue testing on a railway wheel

Abstract

Fatigue is one of the main causes for in service failure of mechanical components and structures. The need for the weight reduction of components and a growing need for greater lifespans of equipment, forced the understanding of the fatigue behaviour of materials under multiaxial loading cycles and increased number of loading cycles. It is generally recognized that multiaxial stresses occur in many full-scale structures, being rare the occurrence of pure uniaxial stress states. Nevertheless, the high cost of fatigue materials testing under multiaxial loading and for very high number of cycles, was a serious drawback for the research under these testing conditions. This study is a description of the present status of fatigue testing machines working at a frequency of 20 kHz, and the research that can be carried out in order to perform multiaxial fatigue tests under bi-axial stress states and very high cycle fatigue. Special emphasis will be given to the performance of multiaxial fatigue tests under axial/torsion and in plane bi-axial testing using low cost piezo-electric transducers either in classical cylindrical or in cruciform specimens and associated instrumentation. Together with the description of the testing machines, experimental results of fatigue tests will be presented in order to compare the behaviour of a metallic material from a Railway wheel under multiaxial tension/torsion at very high cycle fatigue.