Generation and Analyzes of Guided WAVES in Planar Structures

E Sotja,P Malkaj,Dh Sotja

doi:10.4236/eng.2011.35062

Abstract

Guided wave in plate propagates like shear waves and Lamb waves. Both kinds are very dispersive waves. Generation and analysis of dispersion curves is very important. Those are used to predict and describe the relation between frequency, thickness with phase velocity, group velocity and wave mode. For a stainless steel plate with thickness 5.89 mm we built dispersion curves for shear and Lamb waves. A method based on peak frequency shifts of the shear waves along with the thickness was applied. In line with dispersion curves of shear waves phase velocity was seen that mode of waves translate in some points, have experiment performance much better than other points.

Highlights

Low frequency ultrasonic waves propagate in long distance in the league, with small loss of energy, which are called “directed waves”.Guided waves monitor large areas from a single position even when the objects are not fully physically accessible, and they propagate standing localized between surfaces of a thin-walled structure, and even it is curved
In line with dispersion curves of shear waves phase velocity was seen that mode of waves translate in some points, have experiment performance much better than other points
Guided waves are cited as elastic waves that propagate in the samples where the axial dimension is many times greater than the dimensions of the section

Summary

Introduction

Low frequency ultrasonic waves propagate in long distance in the league (meters compared to millimeters in conventional techniques in UT), with small loss of energy, which are called “directed waves” (guided wave). Guided waves monitor large areas from a single position even when the objects are not fully physically accessible, and they propagate standing localized between surfaces of a thin-walled structure, and even it is curved. These properties make them important for the ultrasonic control of facilities of special importance as airplanes, helicopters, spaceship, pressure vessels, and oil deposits. In order to predict the relation between frequency, the thickness of the structure and other parameters mentioned above there are used dispersion curves (so called because the change of the frequency brings the change of wave velocity and vibrations tent to disperse during the spread) The data in these curves are used to do the tests controlling the structures, ranging from defining the generating equipment parameters of the guided waves in the structures until the final calculations [4]

Overview of the Propagation of the Guided Waves in the Plan Structures

H Z x k

Techniques of the Guided Wave Generation at the Dispersion Curves

Direct Method of Testing a Planar Structure with Guided Waves