Measurement of Thermal Stress in Railroad Rails Using Ultrasonic SH waves

The use of ~elded joints in railroad tracks has led to problems of rail buckling brought about by the development of large compressive stresses during hot days. On cold days, tensile stresses can actually fracture the rail. In order to prevent this source of derailments, it is desirable to develop an easily used instrument to measure the level of stress in an arbitrary section of track in the field. Ultrasonic bire-fringence, acoustic emission and certain magnetic phenomena have all been used to attack this problem but they all suffer from the necessity for calibrating the sensor under stress-free conditions in order to correct for metallurgical structure variations. A ne ~ ultrasonic techniqL· ~ based on using surface skimming shear horizontal ultrasonic ~aves generated and detected by EMATs ~as investigated here because it rigorously eliminates the effects of metallurgical texture as ~ell as unreliable coupling of the transducer to the part. Tests on sections of rail mounted in a 200,000 pound testing machine at the University of Ne ~ Mexico demonstrated that the theory for the basic phenomenon is correct and that the stress level can be measured in spite of the presence of considerable texture in the rail microstructure