The effects of voids on the mechanical strength and ultrasonic attenuation have been investigated on a number of laminated composite systems containing a wide range of void content. Graphite fiber reinforced specimens were fabricated both from unidirectional tape and woven fabric prepreg and their interlaminar shear strength and frequency dependent ultrasonic attenuation were measured together with a careful study of microstructure. The measured strength and attenuation slope were found to depend not only on the void content but on the void geometry associated with the prepreg structure of composites. A shear fracture criterion similar to the Mar-Lin equation for notched tensile fracture stresses was used successfully to correlate the fracture strength of porous laminates. The unidirectional laminates showed much higher void sensitivity than the fabric laminates, i.e., more reduction in shear strength and higher attenuation slope for a given void content. It was shown that the void content may be estimated from the measured attenuation slope and that a good correlation exists between the attenuation slope and the shear strength of porous composite laminates.
1. Stone, D. E. W. and B. Clarke. 1975. "Ultrasonic Attenuation as a Measure of Void Content in Carbon-Fiber Reinforced Plastics,"Non-Destructive Testing, 8:137-145.
2.
2. Hsu, D. K. and K. M. Uhl. 1987. "A Morphological Study of Porosity Defects in Carbon-Epoxy Composites,"Review of Progress in Quantitative Nondestructive Evaluation, 6B:1175-1184.
3.
3. Hsu, D. K.1988. "Ultrasonic Measurements of Porosity in Woven Graphite Polyimide Composites,"Review of Progress in Quantitative Nondestructive Evaluation, 7B:1063-1068.
4.
4. Rubin, A. M. and K. L. Jerina. 1993. "Evaluation of Porosity in Composite Aircraft Structures,"Composites Engineering, 3:601-618.
5.
5. Hancox, N. L.1977. "The Effects of Flaws and Voids on the Shear Properties of CFRP,"Journal of Materials Science, 12:884-892.
6.
6. Judd, N. C. W. and W. W. Wright. 1978. "Voids and Their Effects on the Mechanical Properties of Composites-An Appraisal,"SAMPE Journal, 14(1):10-14.
7.
7. Yoshida, M. J., J. Ogase and R. Hayashi. 1986. "Statistical Approach to the Relationship between ILSS and Void Content of CFRP,"Composites Science and Technology, 25:3-18.
8.
8. Tang, J.-M., W. I. Lee and G. S. Springer. 1987. "Effects of Cure Pressure on Resin Flow, Voids, and Mechanical Properties,"Journal of Composite Materials, 21:421-440.
9.
9. Bowles, K. H. and S. Frimfong. 1992. "Void Effects on the Interlaminar Shear Strength of Unidirectional Graphite-Fiber-Reinforced Composites,"Journal of Composite Materials, 26:1487-1509.
10.
10. Greszczuk, L. B. 1967. "Effect of Voids on Strength Properties of Filamentary Composites,"Proceedings, 22nd Annual Meeting of the Reinforced Plastics Division of The Society of the Plastics Industry, pp. 20-A.1 to 20-A.10.
11.
11. Uhl, K., B. Lucht, H. Jeong and D. K. Hsu. 1988. "Mechanical Strength Degradation of Graphite Fiber Reinforced Thermoset Composites Due to Porosity,"Review of Progress in Quantitative Nondestructive Evaluation, 7B:1075-1082.
12.
12. Gurdal, Z., A. P. Tomasino and S. B. Biggers. 1991. "Effects of Processing Induced Defects on Laminate Response: Interlaminar Tensile Strength,"SAMPE Journal, 27(4):39-49.
13.
13. Ghiorse, S. R.1993. "Effect of Void Content on the Mechanical Properties of Carbon/Epoxy Laminates,"SAMPE Quarterly, pp. 54-59.
14.
14. Ryshkewitch, E.1953. "Compression Strength of Porous Sintered Alumina and Zirconia,"Journal of American Ceramic Society, 36(2):65.
15.
15. Duckworth, W.1953. "Discussion of Ryshkewitch Paper,"Journal of American Ceramic Society36(2):68.
16.
16. Corten, H. T.1968. Fundamental Aspects of Fiber Reinforced Plastic Composites, R. T. Schwartz and H. S. Schwartz, eds., New York, NY: Interscience, pp. 89-107.
17.
17. Almeida, S. F. M. and Z. S. N. Neto. 1994. "Effect of Void Content on the Strength of Composite Laminates,"Composite Structures, 28:139-148.
18.
18. Hagemaier, D. J. and R. H. Fassbender. 1979. "Nondestructive Testing of Advanced Composites,"Materials Evaluation, 37(7):43-49.
19.
19. Prakash, R.1980. "Non-Destructive Testing of Composites,"Composites, 11:217-224.
20.
20. Hsu D. K. and S. M. Nair. 1987. "Evaluation of Porosity in Graphite Epoxy Composite by Frequency Dependence of Ultrasonic Attenuation," Review of Progress in Quantitative Nondestructive Evaluation, 6B:1185-1193.
21.
21. Nair, S. M., D. K. Hsu and J. H. Rose. 1989. "Porosity Estimation Using the Frequency Dependence of the Ultrasonic Attenuation,"Journal of Nondestructive Evaluation, 8:13-26.
22.
22. Jeong, H. and D. K. Hsu. 1995. "Experimental Analysis of Porosity-Induced Ultrasonic Attenuation and Velocity Change in Carbon Fiber Composites,"Ultrasonics, 33:195-203.
23.
23. Bar-Cohen, Y. and R. L. Crane. 1982. "Acoustic-Backscattering Imaging of Subcritical Flaws in Composites,"Materials Evaluation, 40:970-975.
24.
24. Blodgett, E. D., L. J. Thomas III and J. G. Miller. 1986. "Effects of Porosity on Polar Backscatter from Fiber Reinforced Composites,"Review of Progress in Quantitative Nondestructive Evaluation, 5B:1267-1274.
25.
25. Qu, J. and J. D. Achenbach. 1987. "Analytical Treatment of Polar Backscattering from Porous Composites,"Review of Progress in Quantitative Nondestructive Evaluation, 6B:1137-1146.
26.
26. Nondestructive Testing Handbook, Second Edition. 1991. Vol. 7, Ultrasonic Testing, P. McIntire, ed., Columbus, OH: The American Society for Nondestructive Testing.
27.
27. Dayal, V. and V. K. Kinra. 1991. "Leaky Lamb Waves in an Anisotropic Plate. II: Nondestructive Evaluation of Matrix Cracks in Fiber-Reinforced Composites,"Journal of the Acoustical Society of America, 89:1590-1598.
28.
28. Mar, J. W. and K. Y. Lin. 1977. "Fracture Mechanics Correlation for Tensile Failure of Filamentary Composites with Holes,"Journal of Aircraft, 14:703-704.
29.
29. Zak, A. R. and M. L. Williams. 1963. "Crack Point Singularities at a Bi-Material Interface,"Journal of Applied Mechanics, 85, Series E., pp. 142-143.
30.
30. Lagace, P. A. 1986. "Notch Sensitivity and Stacking Sequence of Laminated Composites,"Composite Materials: Testing and Design (Seventh Conference), ASTM STP 893, American Society for Testing and Materials, pp. 161-176.
31.
31. Carpino, G.1983. "On the Prediction of Residual Strength for Notched Laminates,"Journal of Materials Science, 18:2269-2273.
