ABSTRACT
This chapter discusses the basis for materials evaluation methods that rely on the use of sound waves of different frequencies, including frequencies above the audible range (ultrasound). There are several variants on the theme of the use of ultrasonics in materials evaluation. These include the use of ultrasonics in measurement of thickness, in which the time of flight of an ultrasonic wave front through a material is measured, and, if the velocity is known, then the distance traveled can be calculated. Ultrasonics can be used to determine the elastic modulus of the material, assuming that the material density is known. Ultrasonic resonance can be used, at lower frequencies, to determine elastic properties, speed of sound, or sample dimensions. The reflection of an ultrasonic wave front from an interface or discontinuity can be used to detect the presence of flaws, such as defects, cracks, or other inhomogeneities in materials; and, finally, ultrasonics can be used to produce an image of the location of inhomogeneities in materials.
