Foundations of Acoustic Methods Used in Non-Destructive Inspection of Laminated Materials

Foundations of Acoustic Methods Used in Non-Destructive Inspection of Laminated Materials

Kononov, A.V.

De Borst, R. (promotor)

Applied Sciences

2004-01-13

Ultrasonic inspection has become one of the most popular nondestructive testing technique because of its versatility and easy operation. It can detect internal cracks and inclusion type defects in homogeneous or layered materials, often without much difficulty. Layered materials, which are also called laminated materials, have become widely used in the aerospace industry, naval engineering and many other industries, and thus have attracted considerable interest of researchers in the last two decades. The present work can logically be subdivided into two parts: conventional ultrasonic methods and laser driven techniques. First, the conventional ultrasonic methods applied to a planar laminated structure immersed in a fluid are considered from a general point of view. Next, the study is extended to laser ultrasonic methods. An extended physical description of phenomenon of elastic wave excitation due to laser irradiation is given. Then, the focus is shifted to the directivity of laser generated ultrasound and various methods of control. As a means to achieve a narrow directivity of radiation the moving laser sources is introduced. Special properties of the radiation due to moving sources such as directivity and spectrum are described and analyzed thoroughly. Considerable part of the work is devoted to the theoretical study of ultrasound generation in laminates by moving laser sources. The following cases have been investigated: a) rectilinear motion of the laser beam; b) oscillatory motion of the beam; c)saw-tooth motion; d) uniform circular motion of the beam. Finally, in the last chapter we introduce more realistic laminates with anisotropic elastic properties. Such laminates consist of one or many fiber-reinforced lamina that are bonded together in order to achieve better structural properties and performance over conventional materials.

non-destructive inspection
planar laminate
laser ultrasonics
moving load
moving laser beam
transition radiation
diffraction radiation

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doctoral thesis

(c) 2004 A.V. Kononov