A guided wave-based inspection methodology for high speed train hollow axles

This work proposes a hollow axle inspection approach based on guided wave phenomena in thick-walled cylindrical structures, for potential applications in high-speed train maintenance. The developed inspection procedure employs multiple rings of transducers permanently mounted at the bore of the axle which allow for selective scanning of the axle sections. To achieve an effective inspection of locations prone to the fatigue crack initiations i.e. surface underneath the wheel/gear seats and the geometrical transitions, near-field wave enhancement effect is explored and adopted. Changes in the local wave enhancement phenomenon, due to the 'quasi-surface' wave interaction with the outer diameter transition in the axle, are used as a signature of the on-surface defect. In addition to the wave enhancement effect analyses, the well-established guided wave damage localisation approach based on pulse-echo signals is incorporated in the inspection methodology. To validate the proposed procedure, a numerical model of a railway axle was investigated for different damage scenarios including various sizes and locations. Preliminary experimental work was also carried out on a thick-walled hollow cylinder with varying outer diameter using flexible Macro Fiber Composite transducers for guided wave generation.