New and Refined Nondestructive Techniques for Graphite Billets and Shapes

This report summarizes the first year's effort to develop more sensitive techniques for detecting and evaluating flaws in graphite. On the basis of preliminary studies, it was concluded that the potential areas of improvement in the state-of-the-art lay both in the interrogative and interpretative aspects of NDT that is in the techniques of introducing the test energy and generating the test signal on one hand,and extracting it from other non-information bearing or noise signals on the other. In regard to improved interrogative techniques particular emphasis was placed upon developing a better understanding and control of ultrasonic focused pulse echo inspection techniques to provide maximum response to small defects and the demonstration of the feasibility of delta scan ultrasonic inspection for ATJ-S and AXF-9Q grades of graphite. Other areas of interest for this work were an investigation of laminographic X-ray techniques and a basic definition of eddy current parameters leading to a possible application of pulsed eddy current techniques to graphite inspection. In the area of interpretation, primary emphasis was on improved techniques for the deliniation of small defects on x-ray images and the * -plication of signal processing, especially spectrum analysis, technique for analyzing the ultrasonic responses received from various types of defects in graphite. Results of the first year's work have defined the limitations of "conventional" pulse echo testing and demonstrated the basic feasibil„ty of delta inspection for graphite inspection. A listing of advanced techniques for \-ray film enhancement is also included. Next year's work will explore more fully the area of utility of the delta system and spectrum analysis for ultrasonic inspection. Efforts will also be made to evaluate imre fully the capabilities of a modified laminographic for advanced applications such as graphite bonded to pyrolytic graphite for nose tips and rocket nozzles.