Thermomechanical analysis of laser-generated ultrasonics in thin structures by finite element method

Abstract

Ultrasonic guided waves have been widely utilized for the structural health monitoring (SHM) of structural components such as plates and pipes; Lamb wave as one of means for nondestructive test-ing and evaluation has emerged to provide a new way for the inspection of thin structures. In partic-ular, the noncontact excitation of the pipe surfaces using laser pulses has shown several advantages in experiments by eliminating the bonding process of the dielectric patches on the curved surfaces and the complicated interpretation of the temperature effect on the bonding layers. However, the numerical simulation of the methodology requires thermo-mechanical coupling and large-scale computation. Therefore, the numerical efficiency of the spatial partitioning by deploying thermo-mechanical elements and mechanical elements is investigated. The formation and propagation of the guided waves are also represented numerically.

A multi-scale simulation technique for three-dimensional wave propagation through pipe-like struc-tures is developed considering the noncontact excitation by a short duration laser pulse. Using this technique, the displacement fields in pipes, both with and without a notch, are calculated and ana-lyzed. In particular, the heat flux is applied to a micro-scale model, and then the temperature profile is obtained. The obtained temperature profile is imposed as the thermal boundary of the macro-scale global model. By applying the temperature profile to an intact pipe, the displacement fields are compared with experimental results in a literature. On the other hand, it is found that the existence of a notch makes effects on the propagation of waves. Therefore, the interaction causes some devia-tion of the displacement fields. The dissimilarity in the displacement fields with different notch depths is investigated using a statistical signal processing technique. Based on the investigation, a damage detection technique that evaluates the existence of a notch...