Complete In-plane Elastic Characterisation under Tensile Tests of Angle-Ply Laminates Composed of Polymer-Matrix Layers

Abstract

In this paper we present a new strategy to completely characterise the in-plane elastic properties of a large range of angle-ply laminates using only unidirectional tests. We consider laminates having the same number of identical plies in the α and –α directions. This new method uses some preceding results found by Verchery for orthotropic laminates, namely the conditions of existence of a specific direction ω, in which the shear-extension coupling is null. The characterisation of the laminate is then made using the results of three tensile tests: two in the orthotropy axes, and the third one in the ω direction, in order to have always a pure one-dimensional state of stress. We show that for the most common unidirectional fibre-reinforced materials, the angle ω is, in most cases, close to the α direction of the fibres. This result permits a complete experimental characterisation of the laminate, which then does not need any a priori knowledge of the elastic properties of the elementary layer. In addition, it provides a simple method to verify the predictions of the laminate behaviour obtained by the Classical Laminated Plate Theory (CLPT) when the elementary layer is completely known. The paper ends with numerical examples and with the results of some experimental tests.

References

Gommers

, Verpoest

and Van Houtte

, “Determination of the mechanical properties of composite materials by tensile tests. Part I: elastic properties,” Journal of Composite Materials, 32, No. 4, (1998) 310–334.

Araujo

A.L.

, Mota Soares

C.M.

, Moteira de Freitas

M.J.

, Pedersen

and Herskovits

, “Combined numerical-experimental model for the identification of mechanical properties of laminated structures,” Composite Structures, 50, (2000) 363–372.

Marin

J.C.

, Canas

, Paris

and Morton

, “Determination of G₁₂ by means of the off-axis tension test. Part I: review of gripping systems and correction factors,” Composites Part A, 33, (2002) 87–100.

Jones

R.M.

, “Mechanics of composite materials,” New York: McGraw-Hill (1975).

Verchery

and Gong

X.J.

, “Pure tension with off-axis tests for orthotropic laminates,” in Proceedings of ICCM12 (Twelfth International Conference on Composite Materials), Paper 572, Paris (1999).

Verchery

, “Les invariants des tenseurs d'ordre quatre du type de l’élasticité,” in Proceedings of Euromech Colloquium115, Villard-de-Lans (1979). Published in Paris by Editions du CNRS in 1982, pp. 93-104 (in French).

Verchery

, “Designing with anisotropy. Part 1. Methods and general results for laminates,” in Proceedings of ICCM 12 (Twelfth International Conference on Composite Materials), Paper 734, Paris (1999).

Vannucci

and Verchery

, “A special class of uncoupled and quasi-homogeneous laminates,” Composites Science and Technology, 61, (2001) 1465–1473.

Vannucci

and Verchery

, “Stiffness design of laminates using the polar method,” International Journal of Solids and Structures, 38, (2001) 9281–9294.

10.

Valot

, “Anisotropie du comportement à rupture de composites à structure isotrope (Anisotropy of failure behaviour of composites with isotropic structure),” PhD report in French with English abstract, University of Burgundy, France (2002).

11.

Kandil

and Verchery

, “New methods of design for stacking sequences of laminates,” in Proceedings of Computer Aided Design in Composite Materials 88, Southampton, UK, (1988) 213–227.

12.

K.M.

and Avery

B.L.

, “Fully isotropic laminates and quasi-homogeneous anisotropic laminates,” Journal of Composite Materials, 26, (1992) 2107–2117.

13.

Grédiac

, “A procedure for designing laminated plates with required stiffness properties. Application to thin quasi-isotropic quasi-homogeneous uncoupled laminates,” Journal of Composite Materials, 33, (1999) 1939–1956.