An ultrasonic coda wave method for stress loss prediction in pre-stressed strongly heterogeneous multi-layer structures

A coda wave method is proposed to predict the stress loss of pre-stressed strongly heterogeneous multi-layer structures using ultrasonic testing. The method is centered on the basis that ultrasound can be multiply scattered and form the decaying coda waves in the strongly heterogeneous multi-layer structure. As the stress loss of the pre-stressed structure can alter the inter-layer contacting state and the mechanical strain of the propagation media, the signal features subject to the stress loss can be amplified in the process of multiply scattering and encoded in the coda wave. A theoretical model is developed to evaluate the stress of the muti-layer structure using the relative change in velocity of the ultrasonic coda wave. Experimental testing is performed on a five-layer pre-stressed mockup structure made of three different materials with vastly different mechanical and physical properties. Model parameters are obtained using testing data. An independent set of testing data is used to validate the developed model. The accuracy of the model is compared with an existing reference model. Results show that the proposed method can predict the stress accurately and outperform the reference model.