Experimental and numerical studies on low velocity impacts detection and damage identification in metal and composite structures using ultrasonic waves propagation (Lamb waves)

Abstract

In this thesis a theoretical base required for the development of a reliable structural health monitoring system based on ultrasonic guided waves is considered. An exact theory is used for relatively rapid calculation of the PZT driven surface motion in a plate recorded in an ultrasonic experiment. The theoretical results are compared with those obtained from an explicit finite element code for their mutual verification, showing excellent agreement. Important characteristics of the ultrasonic signals recorded by the PZT patches in an experiment are carefully extracted and modeled to identify the behavior of the PZT patches used in the experiment. Some applications are presented mainly concerning composite plates subjected to low velocity impact damage or more general hidden defects. Finally an application to the beam forming technique is presented.