Effects of Transverse Stitching and Hygrothermal Environment on Composite Wing T-Joints

Abstract

The present paper deals with the effects of transverse stitching and hygrothermal environment at the web-skin interface of composite wing T-joints that are made of carbon fibre composite (CFC) materials. The T300 carbon fibres are considered for the transverse stitching. The statistical bundle strength based on the Weibull distribution function is used for the estimation of the joint strength. A thick composite shell finite element is specially developed taking into account the hygrothermal effects and is used for a detailed finite element analysis of composite T-joints. T-joints may be exposed to moisture and temperature during their service life. Under such circumstances moisture and temperature diffuse into T-joints. As a consequence, the stiffness and strength properties of the laminates are degraded. Moreover, since the laminas in the laminate cannot deform freely, residual stresses are introduced. All the normal and shear stresses are computed and the failure loads are also computed using various failure criteria to get better insight into the behaviour of laminated T-joints. Additional stresses due to hyghrothermal forces are also computed. The T-joint is supported along the length and a pull-out force is applied on the top of the web. It is found that the web-skin interface where load transfer is out of plane, is the critical zone for failure due to high transverse normal and shear stresses. Also, higher temperature and moisture levels introduce additional transverse normal and shear stresses that make the zone more critical. The present study also shows how the transverse stitching at the web-skin interface zone adds to the transverse strengthening of the interface laminates and helps the T-joints to sustain higher loads.

References

1. Stickler, P.B., Ramulu, M. and Johnson, P.S. (2000). Experimental and Numerical Analysis of Transverse Stitched T-Joints in Bending , Composite Structures, 50: 17-27 .

2. Iwahori, Y. and Ishikawa, T. (1999). Stitch Parameter Effects on Interlaminar Fracture Toughness of CFRP Laminates , 44th International SAMPE Symposium, 23-27 May.

3. Larsson, F. (1997). Damage Tolerance of a Stitched Carbon/Epoxy Laminate , Composite Part A (Elsevier Science Limited), 28A: 923-934 .

4. Barrett, D.J. (1996). The Mechanics of z-Fibre Reinforcement , Composite Structures, 36: 23-32 .

5. Tada, Y., Matsushima, M., Ishikawa, T. and Iwahori, Y. (1995). Stitching Effect Upon Strength of Composite Laminates . In: Kimpara, I., Miyairi, H. and Takeda, N. (eds), Composite 95: Recent Advances in Japan and the United States, Proc. Japan-U.S. CCM-VII, Kyoto.

6. Adanur, S. and Tsao, Y.P. (1994). Stitch Bonded Textile Structural Composites , 26th International SAMPE Technical Conference, 17-20 October.

7. Tsai, G.C. (1991). Global/Local Stress Analysis of Stitched Composite Laminate , 23rd International SAMPE Technical Conference, 21-24 October.

8. Harris, H., Schinske, N., Krueger, R. and Swanson, B. (1991). Multiaxial Stitched Preform Reinforcements for RTM Fabrication , 36th International SAMPE Symposium, 15-18 April.

9. Dow, M.B. and Smith, D.L. (1989). Damage-Tolerant Composite Materials Produced by Stitching Carbon Fabrics , 21st International SAMPE Technical Conference, 25-28 September.

10.

10. Pelstring, R.M. and Madan, Ram C. (1889). Stitching to Improve Damage Tolerance of Composites , 34th International SAMPE Symposium, 8-11 May.

11.

11. Mayadas, A., Pastor, C. and Frank, Ko K. (1985). Tensile and Shear Properties of Composite by Various Reinforcement Concepts , 30th National SAMPE Symposium, 19-21 March.

12.

12. Fukuda, H., Tomatsu, H. and Yasuda, J. (1995). Three-Dimensional Micromechanical Approach to the Strength of Unidirectional Composites , In: Proceedings of 7th Japan-U.S. Conference on Composite Materials, p. 255 .

13.

13. Rispler, A.R., Steven, G.P. and Tong, L. (1997). Failure Analysis of Composite T-Joints Including Inserts , Journal of Reinforced Plastics and Composites, 16(18).

14.

14. Kumari Shyama and Sinha, P.K. Finite Element Analysis of Composite Wing T-Joints , J. Reinforced Plastics and Composites, accepted for publication.

15.

15. Kumari Shyama and Sinha, P.K. (2002). Hygrothermal Analysis of Composite Wing T-Joints , Aircraft Engineering and Aerospace Technology: An International Journal, 74: 23-37 .

16.

16. Chiao, T.T. and Moore, R.L. (1970). A Tensile Test Method for Fibres , J. Composite Materials, 4: 118-122 .

17.

17. Brewer, J.C. and Lagace, P.A. (1988). Quadratic Stress Criterion for Initiation of Delaminations , J. Composite Materials, 22: 1141-1155 .

18.

18. Thuis, H.G.S.J. and Wiggenraad, J.F.M. (1992). Investigation of the Bond Strength of a Discrete Skin-Stiffener Interface, NLR TP 92183 U.

19.

19. Wiggenraad, J.F.M. and Bauld, N.R. Jr. (1991). Interlaminar Stress Analysis at the Skin/Stiffener Interface of a Grid Stiffened Composite Panel, NLR TP 91011 U.

20.

20. van, Rijn J.C.F.N. (1998). Failure Criterion for the Skin-Stiffener Interface in Composite Aircraft Panels, NLR TP 98264.

21.

21. Shenoi, R.A., Read, P.J.C.L. and Jackson, C.L. (1998). Influence of Joint Geometry and Load Regimes on Sandwich Tee Joint Behavior , Journal of Reinforced Plastics and Composites, 17: 725-740 .

22.

22. Turaga, U.V.R.S. and Sun, C.T. (2000). Failure Modes and Load Transfer in Sandwich T-Joints , Journal of Sandwich Structures and Materials, 2: 225-245 .

23.

23. Bathe, K. (1997). Finite Element Procedures, Prentice Hall of India Private Limited, New Delhi .

24.

24. Cook, R.D., Malkus, D.S. and Plesha, M.E. (1989). Concepts and Applications of Finite Element Analysis, John Wiley & Sons, New York .

25.

25. Jones, R.M. (1999). Mechanics of Composite Materials, Taylor & Francis, Philadelphia .

26.

26. Broutman, L.J. and Krock, Richard H. (1967). Modern Composite Materials, Addison-Wesley Publishing Company, Reading, Massachusetts .

27.

27. Irwin, G.R. (1963). Relatively Unexplored Aspects of Fracture Mechanics, Univ. of Illinois, TAM Report No. 240, Section V.