چكيده به لاتين
Continuous welded rails are always exposed to tensile and compressive stresses. These stresses, if they have been in critical condition, cause buckling or breakage of the rail and consequently derailment and damage. This is becoming more important when the train speed and train axle force increase. For this reason, the use of methods for assessing these stesses with the aim of preventing damage is of interest to the railways. In general, stress measurement methods are divided into two non-destructive and destructive classes. The ultrasonic method is important, due to its non-destructive nature, its portability, its low cost, fast measurements, and the ability to measure stresses at depth. Types of ultrasonic methods include the birefringence of shear waves, the difference in the velocity of two horizontal transverse waves, the polarization, the velocity change of the longitudinal waves, and the velocity change of the transverse waves.
In this thesis, the aim of the feasibility study of non-destructive stress measurement on the rails, the velocity change of ultrasonic wave under different stresses has been investigated in both laboratory and theory. In a laboratory study, tensile measurements in a steel plate with dimensions of 596×120×20/1 mm, under different tensile stresses up to 100 MPa and 5 MHz probe were carried out using a longitudinal velocity change method. With a tensile increase of 0 to 100 MPa, the longitudinal wave velocity decreases by 0.12%.
In a numerical study, using the Comsol software, the relationship between ultrasonic wave velocity change with natural frequency and longitudinal stress of a steel beam was simulated and compared with theory. Also, with a two-dimensional modeling, the change in ultrasonic wave velocity in a steel sheet under stress has been investigated. In addition, a sensitivity analysis has been carried out for velocity variables of longitudinal wave in the direction of stress (V_11).