Reconstruction of radial pseudo-forces on cylinders via mono-laser scanning: Concept and application to characterization of damage

Abstract

Damage in a plate can cause perturbation to the equation of out-of-plane motion, which can be equivalently regarded as the transverse pseudo-force applied on the damage region. Thereby, the characterization of damage in the plate can be achieved by identifying the pseudo-force. Nevertheless, it is difficult to formulate the pseudo-force for the characterization of damage in a cylinder because its longitudinal, circumferential, and radial motions are coupled. Moreover, a conventional scanning laser vibrometer equipped with a single scanning head can measure the out-of-plane motions of a plate but is insufficient for measuring the 3D motions of a cylinder. The aforementioned limitation leads to a noticeable barrier to extending the pseudo-force approach from a plate to a cylinder. To overcome this barrier, a new concept of radial pseudo-force (RPF) is formulated to represent the damage-induced perturbation to the radial equilibrium of a cylinder, whose motions are dominated by its radial components. The RPF is applied on the lateral surface of the cylinder and is an ideal damage indicator because it appears in the damage region only and almost vanishes at intact locations. Furthermore, a novel method for reconstructing RPFs via mono-laser scanning is proposed. A correction matrix is formed to correct an undeflected-laser-axis mode shape component (MSC) that can be directly measured via mono-laser scanning, whereby the radial MSC of the cylinder can be obtained for the reconstruction of the RPF on the cylinder. The concept of the RPF is numerically proved using the finite element method. In addition, the applicability of the RPF approach is experimentally validated on a cylinder with internal damage. The numerical and experimental results reveal that the RPF approach can graphically characterize the occurrence, location, and approximate plane size of damage in cylinders.