Damage Identification of Plates by using a Continuously Scanning Laser Doppler Vibrometer System

Abstract

A damage identification method for plates by using a continuously scanning laser Doppler vibrometer (CSLDV) system is presented. A new uniform-speed scan algorithm is proposed to create a two-dimensional scan trajectory and automatically scan a whole plate surface. Based on the new scan algorithm, the demodulation method is extended from one dimension for beams to two dimensions for plates to obtain a full-field operating deflection shape (ODS) of the plate from velocity response. The full-field ODS of an associated undamaged plate is obtained by using polynomials to fit the corresponding full-field ODS from the demodulation method. A curvature damage index (CDI) using differences between curvatures of ODSs associated with ODSs that are obtained by the demodulation method and the polynomial fit is proposed to identify damage. An experiment of an aluminum plate with damage in the form of 10.5% thickness reduction in a damage area of 0.86% of the whole plate scan surface area is conducted to investigate the proposed method. The damage can be successfully identified near an area with high values of a CDI