Compressive Behavior of a Thermoplastic Composite (GR/PEEK)

Abstract

The compressive properties of a graphite/thermoplastic composite (IM6/APC-2) were experimentally determined using unidirectional and multidirectional laminates. The notch sensitivity and damage tolerance of multidirectional laminates were also investigated by comparing the behavior of notched and impacted specimens with unflawed specimens. Whitney's average stress criterion was used to characterize the reduc tion in the compressive strength due to the presence of notches, while damage tolerance of impacted panels was compared directly using strength reduction. Resistance to low velocity impact was compared using a proposed empirical damage resistance parameter, γ, which was determined experimentally.

The observed failure mechanisms were typical for a tough-resin composite. In general, the damage was limited to a small region immediately surrounding the source of the stress concentration and only minor delamination was observed. The unidirectional specimens failed due to a band of fiber kinking at a large angle to the applied load, while delamina tion was the dominant failure mechanism in the multidirectional laminates. C-scans of im pacted specimens indicated minimal damage compared with other thermoplastic and un toughened graphite-epoxy composites.

The compressive properties of IM6/APC-2 compare favorably with similar commer cially available materials. The compressive longitudinal modulus (146 GPa) and strength (1062 MPa) are high and the notch sensitivity as measured by the characteristic length (a_o = 2.37 mm) is good. In particular, resistance to the initial impact was excellent when compared with untoughened graphite/epoxy systems [1].

Keywords

thermoplastic composites compression impact notch sensitivity damage tolerance.

References

Sohi, M.M. , H.T. Hahn and J.G. Williams 1987 "The Effect of Resin Toughness and Modulus on Compressive Failure Modes if Quasi-Isotropic Graphite/Epoxy Laminates," Toughened Composites, ASTM STP 937, American Society for Testing and Materials , pp 37-60

Pope, G.G. 1986 "Structural Materials in Aeronautics Prospects and Perspectives , Part 1," Aerospace, 13(4) 16-22

Modern Plastics Encyclopedia 1988 Rosalind Juran , ed , 64(10A).

Hartness, J.T. 1983 "Polyetheretherketone Matrix Composites," SAMPE Quarterly, 14(2).33-37

Munjal, A.K. 1986 "Use of Fiber-Reinforced Composites in Rocket Motor Industry ," SAMPE Quarterly, 17(2) 1-11.

Hahn, H.T. and J.G. Williams 1986. "Compression Failure Mechanisms in Unidirectional Composites ," Composite Materials Testing and Design (Seventh Conference), ASTM STP 893, American Society for Testing and Materials, pp 115-139

Awerbuch, J.A. and M.S. Madhukar 1985 "Notched Strength of Composite Laminates Predictions and Experiments-A Review," Journal of Reinforced Plasties and Composites, 4 3-159

Whitney, J.M. and R.J. Nuismer. 1974. "Stress Fracture Criteria for Laminated Composites Containing Stress Concentrations ," Journal of Composite Materials, 8 253-265

Adsit, N.R. and J.P. Waszczak 1979 "Effect of Near-Visual Damage on the Properties of Graphite/Epoxy ," Composite Materials Testing and Design (Fifth Conference), ASTM STP 674, American Society for Testing and Materials, pp 101-117

10.

Cordell, T.M. and P.O. Sjoblom 1986 "Low Velocity Impact Testing of Composites," Proceedings of the American Society of Composites, First Technical Conference, pp 297-312

11.

Demuts, E. , R.S. Whitehead and R.B. Deo 1985 "Assessment of Damage Tolerance in Composites," Composite Structures, 4(1) 44-58

12.

Garrett, R.A. 1986 "Effect of Manufacturing and Service-Induced Damage on the Strength of Aircraft Composite Structures ," Composite Materials Testing and Design (Seventh Conference), ASTM STP 893, American Society for Testing and Materials, pp. 5-33.

13.

Labor, J.D. 1979 "Impact Damage Effects on the Strength of Advanced Composites," Nondestructive Evaluation and Flaw Criticality for Composite Materials, ASTM STP 696, American Society for Testing and Materials, pp 172-184

14.

Levin, K. 1986 "Effect of Low-Velocity Impact on Compressive Strength of Quasi-Isotropic Laminate," Proceedings of the American Society of Composites, First Technical Conference, pp 313-326.

15.

Spamer, G.T. and N.O. Brink. 1988 "Investigation of the Compression Strength After Impact Properties of Carbon/PPS and Carbon/APC-2 Thermoplastic Materials ," Proceedings of the 33rd International SAMPE Symposium, pp. 284-295

16.

Starnes, J.H. , Jr., M.D. Rhodes and J.G. Williams. 1979 "Effect of Impact Damage and Holes on Compressive Strength of a Graphite-Epoxy Laminate," Nondestructive Evaluation and Flaw Criticality for Composite Materials , ASTM STP 696, American Society for Testing and Materials , pp 145-171

17.

Williams, J.G. 1983. "Effect of Impact Damage and Open Holes on the Compression Strength of Tough Resin/High Strain Fiber Laminates," Tough Composite Materials, NASA Conference Publication 2334, proceedings of a workshop held at NASA Langley Research Center, Hampton, VA, pp. 61-79

18.

1983 Standard Tests for Toughened Composite Materials , Revised Edition, NASA Reference Publication 1092

19.

Tsai, S.W. 1987 Composites Design, Third Edition Dayton, OH

Think Composites Publishers

20.

Nuismer, R.J. and J.D. Labor 1979 "Applications of the Average Stress Failure Criterion Part II-Compression," J Composite Materials, 13 49-60

21.

Kim, K.S. and D.G. Seidensticker 1988 "Mechanical Properties of the IM6/APC-2 Thermoplastic Composite," Final Report for McDonnell Aircraft RFP-0387-3, Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, PA

22.

Lee, S.M. 1986 "Compression-After-Impact of Composites with Toughened Matrices," SAMPE Journal, 22(2) 64-68

23.

Vinson, J.R. and R.L. Sierakowski 1987 The Behavior of Structures Composed of Composite Materials Dordrecht. Martinus Nijhoff Publishers

24.

Han, Y.M. and H.T. Hahn 1987 "Ply Cracking in Thermoplastic Composites," interim report prepared for E I du Pont de Nemours & Co , Department of Engineering Science and Mechanics, The Pennsylvania State University , University Park, PA

25.

Hahn, H.T. , D.G. Hwang , H.C. Cheng and S.Y. Lo 1981. "Flywheel Materials Technology: Design Data Manual for Composite Materials," UCRL-15365 Vol 1, Lawrence

Livermore Laboratory

26.

Jiang, Z. and R.C. Tennyson 1989 "Closure of the Cubic Tensor Polynomial Failure Surface ," J. Composite Materials, 23 208-231.