New stopping criteria for crack detection during fatigue tests of railway axles

• Fatigue test were performed for railway axles, and two axles resulted broken.
• Vibration measurements were taken during the tests.
• Some increasings in energy are found in cycles where the axle is cracked.
• Changes of energy observed can be used for crack detection.

There are several EN standards that regulate railway axles’ design, manufacturing, and maintenance since axles are one of the most important elements in a railway vehicle in terms of safety [1]. Fatigue tests are included in the standards, and they are widely used in this area to verify whether fatigue limits surpass certain specified values. Fatigue tests can be performed using test machines in which the axle rotates or more frequently, using Sincotec resonance test machines. For both types of test machines, fatigue tests aim to check if a crack appears in an axle within 107107 loading cycles, thus it is necessary to establish stopping criteria in case a crack appears during the test. In the case of resonance test machines, the axle is determined to have been cracked when the testing frequency drops more than 0.5 Hz. For rotating axle tests, there are alarm levels for the displacement of the center of the axle, axle temperature, and variation of the load applied. However, in both cases, stopping criteria have shown low sensitivity to cracks: when the machine stops, defects are very large. Thus, testing can involve a waste of energy and time, and risk of catastrophic failure of the axle, which raises safety concerns and could lead to serious damage of the machine and its environment. This paper addresses a new methodology based on vibration measurements to establish more precise stopping criteria for crack detection during fatigue testing of railway axles. The use of one of the latest developments of the wavelet transform, the Wavelet Packets Transform, allows a crack to be detected many cycles before the conventional methods. The methodology has been successfully applied to a machine where the axle rotates, with very promising results.