The higher order surface wave, or Sezawa wave, is evaluated as the detection and measurement mechanism for traffic hardened Iayers in used rails. Hardness tests were conducted on rail specimens with known traffic volume (in terms of million gross tons) to determine surface and subsurface hardness gradients, prior to ultrasonic testing. Metallographic analyses were also undertaken on these rail specimens. The performance specification was defined in terms of the three rolling contact fatigue crack growth stages that occur in these layers: Stage 1- characterized by micro cracks 0.25 mm (0.01 in.) deep that grow slowly Stage II- defined by rolling contact fatigue cracks that grow from 1 to 3 mm (0.04 to 0.12 in.) at an accelerated rate Stage III - rolling contact fatigue branching that may occur in the traffic hardened layer with accelerated crack propagation in the vertical direction at depths between 4 and 7 mm (0.16 and 0.28 in.). The tests using the Sezawa wave technology demonstrated the ability to interrogate and resolve traffic hardened layers in the depth ranges of 0 to 1 mm, 1 to 3 mm and 4 to 7 mm (0 to 0.04, 0.04 to 0.12 and 0.16 to 0.28 in.). The minimum Brinell hardness (HB) gradient, between the hardened layer and underlying rail, required to support Sezawa wave generation was also investigated and determined to be greater than 20 HB. Finally, the technology was tested on lubricated rails, showing that Sezawa waves, unlike Rayleigh waves, can travel on such surfaces with excellent signal-to-noise ratio and therefore, can be applied to both dry and lubricated rails.
Rail surface characterization
Charakterisierung von Schienenoberflächen
Materials Evaluation ; 66 , 11 ; 1144-1151
2008
8 Seiten, 10 Bilder, 4 Tabellen, 5 Quellen
Article (Journal)
English
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