Effect of Stitching on Impact and Interlaminar Properties of Graphite/Epoxy Laminates

Abstract

Effects of through-the-thickness stitching on the impact damage resistance, impact damage tolerance, and interlaminar fracture toughness (Mode I and Mode II) of plain woven and uniweave textile graphite/epoxy laminates were investigated. The uniweave textile was formed by weaving dry carbon-fiber tows with fiberglass fill tows. The content of fiberglass fill tows was 2.5% by weight. The plain woven laminates were manufactured using resin infusion molding and the uniweave laminates by resin transfer molding. Kevlar and glass yarns of various yarn numbers were used for stitching. Static Indentation-Flexure, Compression-After-Impact, Double Cantilever Beam and End-Notched Flexure tests were conducted. Stitching did not have any effect on the onset of impact damage. However, stitching leads to significant improvement (25-40%) in impact damage tolerance as measured by CAI strength and impact damage area. Mode I fracture toughness as characterized by critical strain energy release rate (G,_Ic) was found to increase by at least an order higher (15-30 times) than the unstitched laminates. Mode II fracture toughness (G_IIc) increased by 5-15 times over the unstitched laminates. New methods to estimate the Mode II critical strain energy release rate in the stitched laminates are presented. The stitched textile advanced composites are considered potentially superior to prepregs for high-volume, low-cost and high-performance structural materials.

References

1. Jackson, W. C. and C. C. Poe, Jr. 1993. "The Use of Impact Force as a Scale Parameter for the Impact Response of Composite Laminates," Journal of Composites Technology and Research, JCTRER, 15(4):282-289.

2. Kwon, Y. S. and B. V. Sankar . 1992. "Indentation-Flexure and Low-Velocity Impact Damage in Graphite/Epoxy Laminates," NASA-CR 187624, University of Florida, (March).

3. Prasad, C. B. , D. R. Ambur and J. H. Starnes, Jr. "Response of Laminated Composite Plates to Low-Speed Impact by Air Gun-Propelled and Dropped-Weight Impactors," AIAA Paper 93-1412-CP, pp. 887-900.

4. Teh, K. T. and J. Morton . "Impact Damage Development and Residual Compression Performance of Advanced Composite Material Systems," AIAA Paper 93-1401-CP, pp. 877-886.

5. Guild, F. J. , P. J. Hogg and J. C. Prichard . 1993. "A Model for the Reduction in Compression Strength of Continuous Fiber Composites After Impact Damage:" Composites, 24(4):333-339.

6. Sierakowski, R. L. and G. M. Newaz . 1993. "Key Elements in Damage Tolerance Concept for Polymeric Composites," Proceedings of the 8th Annual Technical Meeting of the American Society for Composites, Cleveland, OH, pp. 640-649.

7. Lagace, P. A. and E. Wolf . "Impact Damage Resistance of Several Laminated Material Systems," AIAA Paper 93-1524-CP, pp. 1862-1872.

8. Mignery, L. A. , T. M. Tan and C. T. Sun . 1985. "The Use of Stitching to Suppress Delamination in Laminated Composites;" ASTM STP 876, American Society for Testing and Materials, Philadelphia, pp. 371-385.

9. Dexter, H. B. and J. G. Funk . 1986. "Impact Resistance and Interlaminar Fracture Toughness of Through-the-Thickness Reinforced Graphite/Epoxy," AIAA Paper 86-1020-CP.

10.

10. Pelstring, R. M. and R. C. Madan . 1989. "Stitching to Improve Damage Tolerance of Composites," 34th International SAMPE Symposium, (May), pp. 1519-1528.

11.

11. Byun, J.-H. , J. W. Gillespie and T.-W. Chou . "Mode I Delamination of a Three-Dimensional Fabric Composite," Journal of Composite Materials, 24(3):497-518.

12.

12. Chen, V. L. , Wu, X. X. and C. T. Sun . 1993. "Effective Interlaminar Fracture Toughness in Stitched Laminates," Proceedings of the 8th Annual Technical Meeting of the American Society for Composites, Cleveland, OH, pp. 453-462.

13.

13. Ogo, Y. 1987. CCM Report Number 87-17, Center for Composite Materials, University of Delaware, Newark, (May), pp. 1-188.

14.

14. Dow, M. G. and D. L. Smith . "Damage-Tolerant Composite Materials Produced By Stitching Carbon Fabrics," International SAMPE Technical Conference Series, 21:595-605.

15.

15. Conrad, E. G. 1983. "3-D Reinforcement of Thin Composite Laminates for Low-Velocity Impact Damage Tolerance," M.S. thesis, University of Texas at Arlington, (Dec.), pp. 1-83.

16.

16. Carlsson, L. A. and R. B. Pipes . 1987. "Experimental Characterization of Advanced Composite Materials," Prentice-Hall, Inc., Publication, pp. 157-193.

17.

17. Sharma, S. K. and B. V. Sankar . 1995. "Effect of Through-the-Thickness Stitching on Impact and Interlaminar Fracture Properties of Textile Graphite/Epoxy Laminates," AEMES-TR-95-1-05, Department of Aerospace Engineering, Mechanics and Engineering Science, University of Florida, (Jan.), pp. 1-118.

18.

18. Portanova, M. A. , C. C. Poe and J. D. Whitcomb . 1990. "Open Hole and Post-Impact-Compression Fatigue of Stitched and Unstitched Carbon/Epoxy Composite," NASA-TM-102676, (June), p. 29-29.