Ultrasonic Thread Surface Inspection of Railroad Car Wheels and Locomotive Tires Using Rayleigh Waves

Abstract

Ultrasonic surface inspection of cylindrical objects using the Rayleigh wave echo method has many advantages. Despite strict requirements for surface cleaning, the method is widely implemented in industries and transport, for example on the all-rolled wheel thread or tires of railroad rolling stock. Taking into account the ability of the Rayleigh wave transducer to receive waves with a side ("back") lobe of the ray diagram, the influence of possible contamination or excess of contact fluid on the input surface on the control results, it becomes particularly difficult to explain the position and amplitude of the signal. Using mathematical modeling and experimental studies, the ray diagrams of Rayleigh wave piezoelectric transducers with the "back lobe" characteristic of piezoelectric transducers of this type were obtained. The efficiency of emission and (or) receiving depends on the parameters of control and apparatus; this effect is more evident if the width of the transducer piezoelement deviates (e.g., during fabrication) and the frequency varies within 20 %, allowed by GOST R 55724-2013. The acoustic path of the Rayleigh wave reflected from the flaw with a diameter of 7 mm on the wheel thread is experimentally constructed and tested on the model. It is shown that the amplitude of the echo-signal changes nonuniformly, the local maxima obtained experimentally reach 9 dB relative to the exponential relation characteristic of propagation over a boundless surface. The reason for such phenomena lies in multiple re-reflections of waves from the boundaries on the tread surface of railway wagon wheels and locomotive tires (rim chamfer, ridge to ridge transition) and their further interference.