Passive structural damage localization with the modal strain energy method applied to acoustic measurements

Abstract

The modal strain energy (MSE) method is a passive technique for detecting and localizing structural damage based on the analysis of the modal response of a structure. In the development of Generation IV nuclear reactors, several designs involve immersing steel cylindrical structures in fluids under extreme conditions, such as high temperatures and intense radiation. For the structural health monitoring of these components, acoustic sensors are being developed to inspect submerged structures through active and passive measurements using movable linear arrays. The primary objective of this paper is to extend the MSE localization method from surface-based vibration measurements to acoustic near-field measurements in the surrounding fluid. The approach also accounts for the linear geometric constraints of the sensor array and aims to detect relatively small or early-stage structural defects. As a proof of concept, an experimental setup was developed using a vibrating aluminum plate in air. Two types of measurements were performed. First, laser vibrometer measurements were conducted. Results of the MSE method applied to these surface data are used as a reference to validate the detection and localization of an added mass. Second, acoustic measurements were carried out with a linear array of sensors to capture the normal component of the acoustic velocity near the plate surface. The MSE localization method, based on the prediction of mode shapes from the measured acoustic pressure fields, successfully identifies the location of the added mass.