Ultrasonic Signal Analysis of Composite Structures Using the Entire Waveform

Abstract

Composite structures are often desirable for their strength and weight characteristics. Since composites are not as well characterized mechanically as metallic or ceramic structures, much work has been performed to obtain that characterization and to develop methods of determining the mechanical properties of a composite nondestructively. Most of the work in the literature to date has been performed on nonenclosed structures on which several promising nondestructive evaluation (NDE) techniques have been used to predict the integrity of the composite.1,4 An increased use of composites in enclosed geometries has led to the desire to transfer and further develop the most promising NDE techniques used on nonenclosed geometries to enclosed geometries.5,6 As part of the further development of ultrasonic inspection techniques, a high-speed data-acquisition system has been assembled which digitizes an entire RF signal waveform at each point on a Kevlar-epoxy composite structure. The complete data set of ultrasonic A-scans is then available for analysis of particular features which might ordinarily have been overlooked when only the maximum amplitude is recorded from data in a preset gate. The system provides a three-dimensional view of the data in which either the XY, YZ, or XZ planes can be displayed using pseudo color or gray scale to indicate the maximum signal amplitude in a gate set under program control. Depth information can be displayed on the XY data plane, and various image display techniques can be implemented to enhance certain material or defect conditions.