Design and development of an automatic residual stress measuring device

This thesis describes the design and development of prototype automatic devices for the measurement of residual stress in magnetic materials. The device, called an \Automatic Rotation Rig\" or ARR for short uses the principal of magnetic anisotropy to determine the difference in the principal stresses and their direction at the surface of the material. The stress measurement is averaged over an area of approximately 5 mm by 5 mm to a depth of about 1 mm. Three such devices have been built in the period from January 1987 to February 1989. These have been designed for the measurement of residual stress in railway wheels and tracks. Railway wheels may fail if the rim becomes sufficiently tensile hence the device may be used to detect unsafe wheels and allow for their removal from service. Continuous railway tracks are welded together to induce tension along their length. This tension counteracts compression due to heating of the rail. Thus the ARR may be able to be used to determine the \"stress free\" temperature of the rail. This can be used to find whether or not the welding has induced sufficient tension into the rail or at what ambient temperature the rail may buckle due to excessive longitudinal compression. The residual stress measuring device can also be used for other applications where the difference imprincipIe stresses needs to be measured on reasonably flat ferrous materials. The device is portable and reasonably cheap and easy to produce. Prototype ARR's have proven to be reliable in field trials thus leading to the possibility of their being manufactured commercially."