Corrective techniques for the ultrasonic nondestructive evaluation of ceramic materials

When acoustically measuring properties for armor materials, such as alumina or silicon carbide, it is important to incorporate all factors to ensure accurate results. Ultrasonic nondestructive evaluation (NDE) is a widely used technique which makes use of point analysis and property mapping. Material properties usually calculated include attenuation coefficient, ultrasonic velocities, Young's modulus, and other elastic properties. While the overall measurement style is similar between different facilities, several post processing details can be estimated, held constant, or disregarded completely. Each property which is ultrasonically evaluated needs an input of sample thickness. When mapping elastic property values it is important to have precise thickness measurements at each point. A difference in thickness of only one percent can translate into a variation of material velocity up to 100m/s. Attenuation coefficient, a measure of the loss of ultrasound energy through a sample, is not only affected by the accuracy of knowing sample thickness but is also affected by inherent loss factors. The loss factors which must be incorporated to understand a sample's true attenuation coefficient are reflection and diffraction. By correcting for each of these factors the true values of the material properties can be understood. This paper investigates the variations in acoustic signals due to sample thickness, reflection coefficient, and beam diffraction.