An enhanced ultrasonic method for monitoring and predicting stress loss in multi-layer structures via vibro-acoustic modulation

Abstract

A sensitivity and reliability enhanced ultrasonic method for monitoring and predicting stress loss in pre-stressed multi-layer structures is developed in this study. The enhancement is based on the idea of leveraging the potential breathing effect of porous cushion materials in the structures to increase the sensitivity of the signal feature to stress loss, and is achieved via vibro-acoustic modulation by mixing a low-frequency pumping wave and an ultrasonic probing wave. A mathematical model correlating the stress state with the relative change in velocity of the coda portion of the received wave is derived. A pre-stressed five-layer mockup structure made of three materials with vastly different properties is manufactured and used for experimental investigation. Different stress states are simulated by bolting the structure with prescribed torques. Data are acquired for model calibration and verification. Independent data are further acquired to validate the prediction performance of the proposed method using the calibrated model. A thorough comparison between the proposed method and the conventional method is made. Results show that the proposed method offers improved accuracy, reliability, and sensitivity to stress change.