Progress in Quantitative Nondestructive Evaluation

The objective of this study was to increase the understanding of damage in composite materials with through-the-thickness reinforcements. As a first step it was necessary to develop new ultrasonic imaging technology to better assess internal damage of the composite. A useful ultrasonic imaging technique has been successfully developed to assess the internal damage of composite panels. The ultrasonic technique accurately determines the size of the internal damage. It was found that the ultrasonic imaging technique was better able to assess the damage in a composite panel with through-the-thickness reinforcements than by destructively sectioning the specimen and visual inspection under a microscope. Microscopic determination of crack location and lengths in a composite panel with through-the-thickness reinforcements was almost impossible. Five composite compression-after-impact panels were tested. The compression-after-impact strength of the panels with the through-the- thickness reinforcements was almost twice that of the comparable panel without through-the-thickness reinforcement. REFERENCES 1. B.T. Smith, J.S. Heyman, A.M. Buoncristiani, Earl D. Blodgett, J.G. Miller, and S.M.

Freeman, Correlation of the Deply TechniQue with the Ultrasonic Imaging of Impact Damage in Graphite/Epoxy Composites, Materials Evaluation, vol. 47, NO. 12, December 1989, pp 1408-1416. 2. NASA Tech Briefs, June 1987, p. 28. 3. P.M. Gammel, Improved Ultrasonic Detection using Analytic Signal Magnitude. Ultrasonics, Vol. 19, March 1981, pp 73-76. 4. R.C. Heyser, Determination of Loudspeaker Signal Arrival Times Part ~ Journal of the Audio Engineering Society, Vol. 19, Dec. 1971, pp 902-905.