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

This article investigates a guided ultrasonic wave–based data fusion approach for nondestructively monitoring stress redistribution in strands under active corrosion. Within this approach, the stress dependence of velocity (i.e. the acoustoelastic effect) is leveraged for stress measurement, while targeting advantageous frequencies of higher-order modes. To accommodate practical scenarios, where artificial velocity shifts are introduced by sensor reattachment/replacement, a technique called modal modulation is also proposed. To demonstrate the approach, accelerated corrosion testing was carried out on a prestressed strand while measuring higher-order modes in the core wire. The strand was subjected to 29 cycles of accelerated corrosion, with the last cycle resulting in peripheral wire fracture. Data from several higher-order modes yielded multiple estimations of corrosion-induced stress change, which were processed into a single estimate using data fusion and outlier analysis. The data fusion estimate decreased uncertainty (quantified with Gaussian process regression) and showed good agreement with measured values, especially where a large stress increase due to fracture was identified. The results demonstrated that higher-order modes were well suited to data fusion and also confirmed the value of modal modulation.