Stress Measurement in Seven-Wire Strands using Higher Order Guided Ultrasonic Wave Modes

Abstract

This paper investigates the use of higher order longitudinal guided modes for stress measurement within individual wires of a steel strand. The effect of stress on the phase velocity of higher order modes is studied using an approximate theory, which does not require the solution of dispersion curves. To validate the proposed approach, a prestressing bed was designed to apply a tensile load to a strand up to 25% ultimate tensile strength while recording guided wave signals. Guided waves were excited within individual wires of a strand, and the stress sensitivity of their phase velocity was used for stress measurement. Stress measurement was performed with higher order modes using the approximate theory with parameters for a steel of similar carbon content (Hecla 17), as well as with calibrated parameters. Using the Hecla 17 parameters, roughly 15% mismatch in stress was observed, whereas roughly 5% error was observed using calibrated parameters. Stress measurement was also performed using the fundamental mode, in order to compare the accuracy of higher order modes with the mode used previously in the literature. The greater stability of higher order modes across mode and frequency yielded significantly increased stress measurement accuracy, using both Hecla 17 and calibrated parameters.

Stress monitoring of prestressing strands in corrosive environments using modulated higher-order guided ultrasonic waves

“…Some researchers have studied the effect of nonuniform stress on guided waves. 32,33 From these considerations, future work should also study guided waves under plastic strain, while perhaps considering a nonuniform strain distribution.…”

Stress evaluation in seven-wire strands based on singular value feature of ultrasonic guided waves

“…Treyssède and colleagues 21–23 developed the semi-analytical finite method (SAFE) for calculating dispersion curves of unloaded and loaded seven-wire strand, which explained the notch frequency discovered by Kwun et al 18 In addition to the unexplained nonlinear dependence of the fundamental mode at lower stress, higher order modes have also been studied for potential damage detection in strands. 24,25…”