Numerical Analysis of Guided Wave Transmission Through a Rail Containing Numerous Small Cracks

Guided wave ultrasound is used to monitor continuously welded rail track in a system which transmits guided wave ultrasound between alternate transmit and receive stations along the rail and triggers an alarm if the signal is not received. During field testing, a section of rail was encountered where transmission through one rail was poor. Visual inspection showed that there was considerable flank wear and numerous gauge corner cracks. These cracks, while small, occurred roughly every 5 mm over a length of a few meters so the total number of cracks would be of the order of 1000 cracks. The scattering from the numerous small cracks was investigated using the hybrid 3D finite element - semi-analytical finite element technique. A substructuring approach was used, with reduction of internal degrees of freedom, to enable the analysis of a long section of rail with numerous cracks. The numerical analysis was used to investigate the transmission coefficient of the operational mode used in the monitoring system to determine if the presence of the small cracks could cause the observed poor transmission. It was found that significant transmission loss can occur but the transmission coefficient did not decrease monotonically with increasing number of cracks. This unexpected behavior requires further investigation.