A laser ultrasonic system for real-time cure monitoring of a graphite-epoxy composite is proposed. The system contains an array of fiberized laser ultrasonic sources, and an embedded fiber optic Sagnac ultrasonic sensor, and is integrated with a Resin Transfer Molding machine. The use of an optical switch allows ultrasonic generation at several locations of the composite part. Ultrasound generated by the laser source is transmitted into the composite and is detected by the embedded sensor. The cure state is inferred from measurements of ultrasonic velocity. The results of ultrasonic measurements during manufacturing of a composite specimen are presented. The laser ultrasonic cure monitoring system described in this paper has the ability tooperate in a high temperature and high pressure environment; is small enough to be incorporated into molds; and measures the cure state at several locations within the composite part.
1. Hunston, D. and McDonough, W. et al. (1988). Cure Sensors for Composite Materials: State of Art Assessment, Report to National Center for Manufacturing Sciences. Report No. NCMS-88-MPM-12. Gaithersburg, MD: National Institute of Standards and Technology (NIST).
2.
2. Bujard, M., Tittmann, B.R., Ahlberg, L.A. and Cohen-Tenoudji, F. (1987). Dynamic Viscosity Measurements of Fluids Employing Resonance Characteristics of a Piezoelectric Element Vibrating in the Shear Mode. In: Thompson D.O. and Chimenti D.E. (eds.), Review of Progress in Quantitative Nondestructive Evaluation, Vol. 6B. pp. 1267–1276. Plenum Press, New York.
4. Hertz, T.G., Dymling, S.O., Persson, H.W. and Lindstrom, K. (1990). A Non-Invasive Ultrasonic Method for Viscosity Measurements, IEEE Ultrasonics Symposium Proceedings, 299–302.
5.
5. Rogers, W.P. (1995). Elastic Property Measurement using Rayleigh-Lamb Waves, Research in Nondestructive Evaluation, 6(4): 185–208.
6.
6. Kawashima, K., Watanabe, M., Fujii, I. and Gomi, F. (1995). Identification of Anisotropic Elastic Constants of Aluminum Composites Reinforced with Short Alumina Fibers by Double Transmission Ultrasonic Method. In: Thompson D.O. and Chimenti D.E. (eds.), Review of Progress in Quantitative Nondestructive Evaluation, Vol. 14B. pp. 1225–1232. Plenum Press, New York.
7.
7. Hosten, B. and Baudouin, S. (1995). Ultrasonic Measurements of Elastic Constants in Polymeric Matrix/Glass Composite Materials versus Temperature. In: Thompson, D.O. and Chimenti, D.E. (eds.), Review of Progress in Quantitative Nondestructive Evaluation, Vol. 14B. pp. 1209–1216. Plenum Press, New York.
8.
8. Hosten, B., Hutchins, D.A. and Schindel, D.W. (1996). Measurement of Elastic Constants in Composite Materials using Air-Coupled Ultrasonic Bulk Waves, J. Acoust. Soc. Am., 99(4): 2116–2123.
9.
9. Winfree, W.P. and Parker, R.F. (1985). Measurement of the Degree of Cure in Epoxies with Ultrasonic Velocity. In: Thompson, D.O. and Chimenti D.E. (eds.), Review of Progress in Quantitative Nondestructive Evaluation, Vol. 5B. pp. 1055–1061. Plenum Press, New York.
10.
10. Parker, R.F. and Winfree, W.P. (1985). Acoustic Characterization of Composite Cure, Review of Progress in Quantitative Nondestructive Evaluation, Vol. 5B. pp. 1063–1067. Plenum Press, New York.
11.
11. Krautkramer, J. and Krautkramer, H. (1969). Ultrasonic Testing of Materials, Springer-Verlag, Berlin.
12.
12. Lindrose, A.M. (1978). Ultrasonic Wave and Moduli Changes in Curing Epoxy Resin, Experimental Mechanics, 6: 227–232.
13.
13. Winfree, W.P. (1983). Ultrasonic Characterization of Changes in Viscoelastic Properties During Cure, IEEE Ultrasonic Symposium Proceedings, 1: 866–869.
14.
14. Rokhlin, S.I., Lewis, D.K., Graff, K.F. and Adler, L. (1986). Real-Time Study of Frequency-Dependence of Attenuation and Velocity of Ultrasonic-Waves During the Curing Reaction of Epoxy-Resin, J. Acoust. Soc. Am., 79(6): 1786–1793.
15.
15. Matsukawa, M. and Nagai, I. (1996). Ultrasonic Characterization of a Polymerizing Epoxy Resin with Imbalanced Stoichiometry. J. Acoust. Soc. Am., 99(4): 2110–2115.
16.
16. Krishnaswamy, S. (1998). Fiber-Optic Sensors for Process Monitoring. In: Birnbaum, G.A. and Auld, B.A. (eds.), Sensing for Materials Characterization, Processing and Manufacturing, pp. 345–362. ASNT publications.
17.
17. Powell, G.R., Crosby, P.A., Waters, D.N., France, C.M., Spooncer, R.C. and Fernando, G.F.(1998). In-Situ Cure Monitoring Using Optical Fibre Sensors – A Comparative Study, Smart Materials and Structures, 7: 557–568.
19. Davis, A., Ohn, M.M., Liu, K. and Measures, R.M. (1991). A Study of an Opto-Ultrasonic Technique for Cure Monitoring. In: Udd, E. (ed.), Fiber Optic Smart Structures and Skins IV. Proceedings of SPIE, 1588: 264–274.
20.
20. Ohn, M.M., Davis, A., Kexing, L. and Measures, R.M. (1992). Embedded Fiber-Optic Detection of Ultrasound and its Application to Cure Monitoring. In: Udd, E. (ed.), Fiber Optic Smart Structures and Skins V, SPIE proceedings, 1798: 134–143.
21.
21. Chen, J.-F., Hoa, S.V., Jen, C.K. and Wang, H. (1999). Fiber-Optic and Ultrasonic Measurements for In-Situ Cure Monitoring of Graphite/Epoxy Composites, Journal of Composite Materials, 33(20): 1860–1881.
22.
22. Dorighi, J.F.Krishnaswamy, S. and Achenbach, J.D. (1997). A Fiber Optic Ultrasonic System to Monitor the Cure of Epoxy, ASNT’s Research in Nondestructive Evaluation, 9: 13–24.
23.
23. Scruby, C.B. and Drain, L.E. (1990). Laser Ultrasonics: Techniques and Applications, Adam Hilger, New York.
24.
24. Fomitchov, P., Kromine, A., Krishnaswamy, S., Achenbach, J.D., Kim, U.K. and Daniel, I.M.(2000). Laser Ultrasonic Enabled “Smart” Mold for Composite Parts Manufacturing. In: Thompson, D.O. and Chimenti, D.E. (eds.), Review of Progress in Quantitative Nondestructive Evaluation, AIP Conf. Proc. Vol. 20B. pp. 1808–1814.
25.
25. Pavel Fomitchov, Krishnaswamy, S. and Achenbach, J.D. (2000). Extrinsic and Intrinsic Fiber-Optic Sagnac Ultrasound Sensors, Opt. Eng., 39(7): 1972–1984.
26.
26. Kim, Y.K. and Daniel, I.M. (2002). Cure Cycle Effect on Composite Structures Manufactured by Resin Transfer Molding, Journal of Composite Materials, (accepted).
27.
27. Um, M.K. and Daniel, I.M. (2000). A new Kinetic Mode for Degree of Cure and Viscosity in Liquid Molding Application, 45th International SAMPE Symposium, Vol. 45. pp. 1598–1610.
