Long Range Inspection of Rail Using Guided Waves

Ultrasonic techniques have been used for many years for the inspection of rail. However large transverse cracks of the type likely to cause catastrophic failure can be detected but these are often masked by small non-critical cracks at shallow angles close to the running surface of the rail. Also, alumino-thermic welds are difficult to inspect due to the attenuation of the weld material at ultrasonic frequencies. A new technique for inspecting rail that makes use of guided acoustic waves is described. These waves travel along the rail, for tens or hundreds of metres, and are partially reflected by any defects that are present. They are particularly sensitive to transverse defects and because they are used at relatively low frequency they are not significantly attenuated by weld material. The guided wave modes that can exist in a rail are found using a 2-dimensional finite element (FE) technique. Experimental measurements have been used to identify a number of candidate modes that are suitable for long range testing. The interaction of these candidate modes with a wide variety of defect geometries is investigated with 3-dimensional time-marching FE models. This study enables characteristic mode conversion signatures for various defects and features to be obtained. A prototype transducer rig has been developed and tested on a variety of rail samples containing artificial defects and also on in-service rails. Results from these tests are presented and compared with FE predictions. For the covering abstract see ITRD E122683.