TABLE OF CONTENTS This chapter deals with the use of piezoelectric wafer active sensors (PWAS) to detect structural damage using wave propagation techniques. This application of PWAS technology builds on the wealth of knowledge accumulated in the conventional nondestructive inspection (NDI), nondestructive testing (NDT), and nondestructive evaluation (NDE) fields. The main difference between our approach and conventional NDE is that our approach used permanently attached unobtrusive, minimally intrusive PWAS transducers, whereas the conventional NDE approach uses relatively large and expensive conventional ultrasonic transducers. For this reason, we see our approach as leading to an emerging new technology: embedded ultrasonic NDE. The embedded ultrasonic NDE will facilitate on-demand interrogation of the structure to determine its current state of health and predict the remaining life.
The emerging new technology of embedded ultrasonic NDE is enabled by the PWAS transducers. Because the PWAS transducers are essentially different in their operation from conventional NDE transducers (as shown in previous chapters), the development of embedded ultrasonic NDE requires the development of new ultrasonic interrogation and interpretation methods. This chapter will cover these issues and highlight new research directions that need to be explored in order to mature the embedded ultrasonic NDE concept.
After a review of the main conventional NDE ultrasonic methods, the chapter will present some simple 1-D modeling and experiments involving PWAS-generated guided waves propagating in a thin metallic strip. The PWAS transducers will be used as both transmitters and receivers. The modeling will be done with the finite element method (FEM)...
