COMPARISON OF ACOUSTOELASTIC METHODS TO EVALUATE STRESSES IN STEEL PLATES AND BARS

摘要

Fabrication processes and events in service may cause residual stresses. Most of the methods for determining residual stresses inside metallic solids are destructive, which is undesirable. The ultrasonic technique provides a useful nondestructive tool in the evaluation of stresses. In bodies under traction like pressure vessels and bridges or railroad wheels, the technique can be used to prevent catastrophic failure. This work presents the application of shear and longitudinal waves in the determination of the stress state in a steel bar. A bar stressed by a hydraulic system is used to simulate the effect of the tensile stress. The stresses are recorded and compared with the real value calculated using the force and the bar transversal area. The comparison between the theoretic and experimental results shows that it is possible to correlate the tensile stresses and velocity with both methods, although the longitudinal critically refracted (L_(CR)) waves have greater sensitivity to the stress. For both techniques, there was less error at higher stress levels (above 40 MPa). Using LCR waves it is possible to get stresses with an error of less than three percent at the higher levels. For the birefringence (shear wave) technique, the error ranges from 0.2 to 31 percent.