Reference-free load-modulated longitudinal rail stress measurement using ultrasonic LCR waves

A method of in situ measurement of longitudinal stress in a railway rail, comprising:

• using an ultrasonic wedge sensor to measure a stress-free (unloaded) time-of-flight (t0) in the vertical direction of the rail, the wedge sensor having at least one receiver and one transmitter;
• applying a vertical load of known load value to the rail;
• while the vertical load is applied, using the ultrasonic wedge sensor to measure a stressed time-of-flight value;
• calculating the difference between the stress-free time-of-flight value and the stressed time-of-flight value to obtain a time-of-flight difference value (Δt);
• and
• based on the load value, the stress-free time-of-flight value, and the time-of-flight difference value, calculating the acoustoelastic constant, L;
• using the ultrasonic wedge sensor or another ultrasonic wedge sensor to measure time-of-flight in the horizontal (longitudinal) direction;
• and
• based on the stress-free time-of-flight value, the acoustoelastic constant, L, and a time-of-flight difference value from the time-of-flight in the horizontal direction, calculating the longitudinal stress.

A longitudinal rail stress measurement system, comprising:

• an ultrasonic wedge sensor having angled transducers that produce the required refraction of an ultrasonic wave for acquiring time-of-flight measurements in a railway rail;
• a load frame and actuator operable to apply a known load in the vertical direction to the rail;
• and
• a control and analysis system operable to perform the following tasks:
• to provide and receive ultrasonic signals from the wedge sensor, to calculate time-of-flight values in the rail unstressed in the vertical direction and stressed with the load in the vertical direction, and to calculate an acoustoelastic constant of the rail material based on the time-of-flight measurements.