Ultrasonic Field Measurements for Flaw Analysis

Abstract

The purpose of this paper is to introduce experimental sonic field measurement procedures that can be used to analyze ultrasonic transducer wave generation characteristics and wave reflection patterns from specially shaped flaws in solid materials. This work is essential for understanding principles of ultrasonic nondestructive evaluation in homogeneous isotropic materials as well as advanced composites and multilayered bonded structures. Very little work to date has been done on this subject except for the work related to the classical flat bottom hole equivalent that is so widely used in ultrasonic inspection test standards today. It is shown in the paper that sonic field pressure profiles obtained in both pulse-echo and through-transmission modes can be used to characterize flaw shapes, sizes, and locations. The following details are included: (1) Experimentally obtained pressure profiles in solid blocks are compared with results obtained from a theoretical solution for wave propagation in a solid material. The effects of transducer frequency, diameter, and type on the sonic field pressure profile are discussed. (2) Experimental ultrasonic field pressure profile measurements are compared with results obtained from a finite difference two-dimensional computer code for elastic wave propagation across a rectangular flaw in a solid block. Applications of the computer code to other problems in flaw detection are presented. (3) Ultrasonic pressure profiles are presented for wave reflection patterns across such flaws as cracks and elliptically and circularly shaped holes. Guidelines for establishing inspection standards based on this work are presented.