Comparison of Acoustoelastic Methods to Evaluate Stresses in Steel Plates and Bars

Abstract

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. This work presents the application of shear and longitudinal waves in the determination of 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 cross-sectional area. The comparison between the theoretical and experimental results shows that it is possible to correlate tensile stresses and velocity with both methods, although the longitudinal critically refracted LCR waves have greater sensitivity to the stress.

Internal Stress Monitoring of In-Service Structural Steel Members with Ultrasonic Method

“…The most common application of this approach is for residual stress measurement after welding. Welding residual stress results from complex thermo-plastic deformations in the material [ 19 , 20 , 21 ]. The sensitivity of ultrasonic waves to stress has been tested by Egle and Bray [ 18 ] with a pearlitic steel bar under tensile and compressive loads.…”

“…Therefore, the Lcr wave method has been the focus of many studies recently. Bray and Santos [ 19 , 20 ] used Lcr waves to detect the residual stresses of an aluminum welded seam and a steel welded seam. The results confirmed the relaxation phenomenon of welding residual stress, and that the stress relaxation of the aluminum welded seam was less than that of the steel counterpart.…”

Comparison of the L cr wave TOF and shear‐wave spectrum methods for the uniaxial absolute stress evaluation of steel members

“…This result is consistent with previous research results and thus verifies the accuracy of Equation . The calibrated factor in this work is the SATD factor, which is different from that of certain references, in which the fitted parameter is the acoustoelastic constant . The SATD factor contains the information of the Lcr wave path and reflects the relationship between the stress and the Lcr wave TOF difference ( B = σ /( t L 0 − t L )), whereas the acoustoelastic constant relates the stress and the Lcr wave TOF change rate ( K = (( t L 0 − t L )/ t L 0 )/ σ ).…”

“…Thus, the same procedure may result in a variation in the stress of approximately ±33.5 and ±10.5 MPa using the Lcr wave and shear wave, respectively. A possible explanation for this dispersion is the small variations in the microstructure where the measurements were recorded …”

“…The longitudinal critically refracted (Lcr) wave, which is generated by longitudinal wave mode conversion, can travel below the surface of a material with a penetration depth relating to the excitation frequency. Among all ultrasonic waves, the Lcr wave exhibits the greatest sensitivity to stress, that is, the velocity of the Lcr wave that travels parallel to the stress changes most obviously with stress . Thus, the time‐of‐flight (TOF) method is often used to measure the change in Lcr wave flight time along a fixed acoustic path.…”