Keywords: carbon fibre reinforced plastics, viscoelastic material, damping layer, interleaving technique, ultrasonic testing.

Impacts on grafite/epoxy laminated composites can lead [1] to special type of damage in laminated structures where a barely visible indentation is produced [2,3]. The impact resistance of the grafite/epoxy laminated composites can be enhanced inserting a proper inter layer between the plies [4]. The interleaved layers used in this work, are made by different viscoelastic materials, selected for their promising damping properties. Thus, a set of viscoelastic embedded coupons have been manufactured and, successively, they have been tested in order to study their impact resistance. The tests have been performed both from a mechanical point of view, by measuring their capability to absorb energy, and also by detecting any induced damage using ultrasonic pulse echo testing (PE) [5,6,7] and optical microscopy. Impact tests have been carried out in accordance with the standard method ISO 6603-1985 [8]. The set up used was a drop-weight tester Fractovis (CEAST) which induces impacts by the fall, with a defined velocity and from a defined height, of a weight [9,10]. The results obtained have demonstrated that the viscoelastic layers can strongly limit the damaged area, effectively reducing the inter-lamina damage propagation [11].

1

R.E. Evans, J. Masters, "A New Generation of Epoxy Composites for Primary Structural Applications: Materials and Mechanics", Toughened composites, ASTM STP 937, 413-436, 1987. doi:10.1520/STP24391S

2

S. Abrate, "Impact on composite structures", Cambridge University Press, 1998.

3

S.H. Yang, C.T. Sun, "Indentation law for composite laminates", ASTM STP 787, 425-449, 1982. doi:10.1520/STP28494S

4

H. Kishi, M. Kuwata, S. Matsuda, T. Asami, A. Muratami, "Damping properties of thermoplastic-elastomer interleaved carbon fiber-reinforced epoxy composites", Composites Science and Technology, 64, 2517-2523, 2004. doi:10.1016/j.compscitech.2004.05.006

5

J. Krautkramer, H. Krautkramer, "Ultrasonic Testing of Materials", Springer-Verlag, 1990.

6

C.F. Buynak, T.J. Moran, "Characterization of impact damage in composites", Review of progress in quantitative non-destructive evaluation, 6B, 1203-1211, 1986.

7

R.T. Potter, "The Significance of Defects and Damage in Composite Structures", AGARD Conference proceedings, No. 355, 1983.

8

ISO 6603-1985 Plastics, "Determination of multiaxial impact behaviour of rigid plastics- Part 1: Falling dart method".

9

E. Wu, K. Shyu, "Response of composite laminates to contact loads and relationship to low-velocity impact", Journal of Composite Materials, 27(15), 1443-1464, 1993. doi:10.1177/002199839302701502

10

W.J. Cantwell, J. Morton, "The impact resistance of composite materials - a review", Composites, 22(5), 347-362, 1991. doi:10.1016/0010-4361(91)90549-V

11

E. Milella, C. Toscano, F. Lenzi, M. Iannone, "Composite laminated plates embedded with a viscoelastic material, manufacturing process and applications", Patent application No. IT-MI2009A001537, filed on 04/09/2009.

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