The effect of increasing void content (up to 30%) on the ultrasound attenuation coefficient, interlaminar shear strength and Mode I interlaminar fracture toughness properties of a glass fibre reinforced polymer (GFRP) composite were investigated. Also studied was the effect of increasing the thickness (up to 150 mm) of highly porous GFRP composites on ultrasound attenuation. A pulse-echo ultrasonics technique was used to measure the amount of attenuation through the GFRP, and this increased linearly with thickness up to 150 mm. Attenuation also increased rapidly with void content, and these measurements were used to further test the accuracy of models proposed by Martin and by Hale and Ashton for calculating the attenuation coefficient of porous composites. Poor agreement was found between the measured and calculated attenuation coefficients, and the causes for the discrepancies are discussed. As expected, the interlaminar shear strength and interlaminar fracture toughness decreased rapidly with increasing void content.
1. Cantwell, W.J. and J. Morton. 1992. "The significance of damage and defects and their detection in composite materials: A review,"Journal of Strain Analysis, 27(1):29-42.
2.
2. Stone, D.E.W. and B. Clarke. 1975. "Ultrasonic attenuation as a measure of void content in carbon-fibre reinforced plastics,"Non-destructive Testing, 8:137-145, April.
3.
3. 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.
4.
4. Bowles, K.J. and S. Frimbord. 1992. "Void effects on the interlaminar shear strength of unidirectional graphite-fiber-reinforced composites,"Journal of Composite Materials, 26(10): 1487-1509.
5.
5. Ghiorse, S.R.1993. "Effect of void content on the mechanical properties of carbon/epoxy laminates,"SAMPE Quarterly, 54-59, January.
6.
6. de 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.
7.
7. Wisnom, M.R., T. Reynolds and N. Gwilliam. 1996. "Reduction in interlaminar shear strength by discrete and distributed voids,"Composites Science and Technology, 56:93-101.
8.
8. Hou, M., L. Ye and Y.-W. Mai. 1996. "Effect of moulding temperature on flexure, impact strength and interlaminar fracture toughness of CF/PEI composite,"Journal of Reinforced Plastics and Composites, 15:1117-1130, November.
9.
9. Asp, L.E. and F. Brandt. 1997. "Effects of pores and voids on the interlaminar delamination toughness of a carbon/epoxy laminate,"Proceedings of the Eleventh International Conference on Composite Materials (ICCM-JJ), pp. II-322 to II-331.
10.
10. Tomasino, A.P. 1988. "The effects of porosity on the out-of-plane tensile strength of laminated composites," PhD Thesis, Virginia Polytechnic and State University.
11.
11. Jones, B.R. and D.E.W. Stone. 1976. "Towards an ultrasonic-attenuation technique to measure void content in carbon-fibre composites,"Non-Destructive Testing, 9:71-79, April.
12.
12. Prakash, R.1980. "Non-destructive testing of composites,"Composites, 11(10):217-224.
13.
13. Hsu, D.K.1988. "Ultrasonic measurements of porosity in woven graphite polyimide composites," in Review of Progress in Quantitative Nondestructive Evaluation, Vol. 7B, pp. 1063-1068.
14.
14. 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(1):13-26.
15.
15. Henneke, E.G.1990. "Ultrasonic nondestructive evaluation of advanced composites," in Non-Destructive Testing of Fiber-Reinforced Plastics Composites, Vol. 2, edited by J. Summerscales, Elsevier Applied Science, London, pp. 55-159.
16.
16. Jeong, H. and D.K. Hsu. 1995. "Experimental analysis of porosity-induced ultrasonic attenuation and velocity change in carbon composites,"Ultrasonics, 33(3):195-203.
17.
17. Jeong, H.1997. "Effects of voids on the mechanical strength and ultrasonic attenuation of laminated composites,"Journal of Composite Materials, 31(3):276-292.
18.
18. Fitting, D.W., C.M. Fortunko and C.M. Teller. 1990. "Ultrasonic nondestructive evaluation of composites used in marine applications," in Proceedings of the National Conference on the Use of Composite Materials in Load-Bearing Marine Structures, Vol. 2, pp. 219-234.
19.
19. Fortunko, C.M. and D.W. Fitting. 1991. "Appropriate ultrasonic system components for NDE of thick polymer-composites," in Review of Progress in Quantitative Nondestructive Evaluation, Vol. 10B, edited by D.O. Thompson and D.E. Chimenti, Plenum Press, New York, pp. 2105-2112.
20.
20. Bar-Cohen, Y.1991. Nondestructive Evaluation (NDE) of Fibreglass Marine Structures: State-of-the-Art Review, McDonnell Douglas Corporation, Report No. CG-D-02-91.
21.
21. Thompson, R.B., D.O. Thompson, D.K. Holger, D.K. Hsu, M.S. Hughes, E.P. Papadakis, Y.-M. Tsai and L.W. Zachary. 1991. "Ultrasonic NDE of thick composites," in NDE: Enhancing Analysis Techniques for Composite Materials, Vol. 10, American Society for Mechanical Engineering, pp. 43-57.
22.
22. Rubin, A.M. and K.L. Jerina. 1993. "Evaluation of porosity in composite aircraft structures,"Composites Engineering, 3:601-618.
23.
23. "Standard test method for apparent interlaminar shear strength of parallel fiber composites by short-beam shear," ASTM D2344-84 (Reapproved 1995), ASTM Annual Book of Standards, Vol. 15.03, American Society for Testing and Materials, Philadelphia, 1996.
24.
24. "Standard test method for Mode I interlaminar fracture toughness of unidirectional fiber-reinforced polymer matrix composites," ASTM 5528-94a, ASTM Annual Book of Standards, Vol. 15.03, American Society for Testing and Materials, Philadelphia, 1996.
25.
25. Hashemi, S., A.J. Kinloch and J.S. Williams. 1990. "The analysis of interlaminar fracture in uni-axial fibre-polymer composites,"Proceedings of the Royal Society of London, A427(1872): 173-199.
26.
26. Martin, B.G.1976. "Ultrasonic attenuation due to voids in fibre-reinforced plastics,"NDT International, 9(5):242-246.
27.
27. Hale, J.M. and J.N. Ashton. 1988. "Ultrasonic attenuation in voided fibre-reinforced plastics,"NDT International, 21(5):321-326.
28.
28. Martin, B.G.1977. "Ultrasonic wave propagation in fiber-reinforced solids containing voids,"Journal of Applied Physics, 48(8):3368-3373.
29.
29. Mar, J.W. and Lin, K.Y.1977. "Fracture mechanics correlation for tensile failure of filamentary composites with holes,"Journal of Aircraft, 14:703-704.
