Mode-II Fracture at the Interface between a Base and a Repair Graphite/Epoxy Laminates

Abstract

Experimental investigation of the characteristics of the interface between a base laminate [0₈] _T and a repair laminate [0₈] _T was carried out through Mode II fracture tests, compliance calibration tests, and microscopic observations. The material used for manufacturing the test samples is unidirectional carbon fiber prepreg (Newport Composites NCT-301 graphite/epoxy). The laminate lay-up used in all experiments was [0₁₆] _T .The specimens were subjected to variations in the autoclave pressure in the repair curing cycle. A standard sample (reference) was subjected to the manufacture recommended cure cycle. The repair samples were subjected to the manufacturer recommended curing cycle (for temperature) with different values for pressure.

Results show a significant effect of pressure. However, the effect of the magnitude of the pressure is not significant after some threshold values. More than 28% drop in the fracture toughness is experienced by the lack of bonding between the older previously cured matrix and the newly added composite laminate. There is some difference between the Mode-II test and compliance calibration test, but no preference, in terms of accuracy, can be given to what method to be used to obtain Mode II fracture toughness.

Get full access to this article

View all access options for this article.

References

1. Beehag, A. and Ye, L. , 1996, “Role of Pressure on Interlaminar Fracture Properties of Comingled CF/PEEK Composites,” Composites, Part A, Vol. 27A, No. 3, pp. 175-182.

2. Benzeggagh, M. and Charentenay, F. X. De , 1983, Fracture Mechanics of Mode I Delamination in Composite Materials, Technomic Publishing Co., Inc., Vol. 6.

3. Chai, H. , 1986, “On the Correlation between the Mode I Failure of Adhesive Joints and Laminated Composites,” Engineering Fracture Mechanics, Vol. 24, No. 3, pp. 413-431.

4. Hwu, C. and Kao, C. J. , 1995. “Delamination Fracture Criteria for Composite Laminates,” Journal of Composite Materials, Vol. 28, No. 15, pp. 1962-1987.

5. Jarrah, M. A. and Hoa, S. V. , 1998, “Characteristics of the Interface between a Base Laminate and a Repair Laminate Subjected to Variation in Pressure in the repair Curing Cycle,” Journal of Reinforced Plastics and Composites, Vol. 17, No. 6, pp. 512-526.

6. Krawczak, P. and Pabiot, J. , 1995, “Fracture Mechanics Applied to Glass Fiber/Epoxy Matrix Interface Characterization,” Journal of Composite Materials, Vol. 29, No. 17, pp. 2231-2253.

7. Madhuker, M. S. and Drzal, L. T. , 1992, “Fiber Matrix Adhesion and Its Effect on Composite Mechanical Properties: IV, Mode I and Mode II Fracture Toughness of Graphite/Epoxy Composites,” Journal of Composite Materials, Vol. 26, No. 7, pp. 926-968.

8. Madhuker, M. S. and Drzal, L. T. , 1991, “Fiber Matrix Adhesion and Its Effect on Composite Mechanical Properties: II, Longitudinal (0°) and Transverse (90°) Tensile and Flexure Behavior of Graphite/Epoxy Composites,” Journal of Composite Materials, Vol. 25, No. 7, pp. 958-991.

9. Papanicolaou, G. C. and Bakos, K. , 1996, “Interlaminar Fracture Behaviour of Sandwich Structure,” Composites, Part A, Vol. 27A, No. 3, pp. 165-173.

10.

10. Pipes, B. , 1992, Composites Design Encyclopedia, Technomic Publishing Co., Inc., Vol. 6.

11.

11. Tsai, M. Y. , Morton, J. and Matthews, F. L. , 1995, “Experimental and Numerical Studies of a Laminated Composite Single Lap Adhesive Joint,” Journal of Composite Materials, Vol. 29, No. 9, pp. 1154-1175.

12.

12. Waterbury, M. and Drzal, L. , 1989, “Determination of Fiber Volume Fraction by Optical Numeric Volume Fraction Analysis,” Journal of Reinforced Plastics and Composites, Vol. 8, pp. 627-636.

13.

13. White, S. R. and Kim, Y. K. , 1995, “Stage Curing of Composite Materials,” Composites, Part A, Vol. 27A, No. 3, pp. 219-227.

14.

14. Zimmerman, K. and Liu, D. , 1995, “Geometrical Parameters in Composite Repair,” Journal of Composite Materials, Vol. 29, No. 11, pp. 1473-1487.