6.11: Summary

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In this TLP we have looked at the approaches taken to go about deriving the in-plane, on-axis elastic constants, in particular the axial and transverse Young's Moduli and the Poisson's ratios , for a composite. From these, we went onto consider the strengths and failure modes of fibre-aligned composites and explore the question as to why they exhibit high strength and toughness , even though the constituent materials tend to be brittle.

With this basic understanding we were able to extend our consideration to laminates , which have a possible advantage of being isotropic, and we have seen how to calculate the elastic constants for an arbitrary in-plane stress state. Off-axis loading presents us with the problem of tensile-shear interactions and coupling stresses in laminates, as a result of which balanced symmetric laminates are preferred. Then in the last section we applied the Maximum Stress Criterion and the Tsai-Hill Criterion to predict the required stress state for laminate failure.

The greatest advantage of composite materials is strength and stiffness combined with lightness and durability; and these properties are the reasons why composites are used in a wide variety of applications.

Going further

Books

Hull D. and Clyne T.W. An Introduction to Composite Materials, CUP 1996

Clyne T.W. and Withers P.J. An Introduction to Metal Matrix Composites Materials, CUP, 1993

Piggott M.R. Load Bearing Fibre Composites, Pergamon Press 1980

Chawla K.K. Ceramic Matrix Composites, Chapman and Hall 1993

Chou T.W. Microstructural Design of Fibre Composites, CUP, 1992

Harris B. Engineering Composite Materials, Institute of Metals 1986

Kelly A. Concise Encyclopedia of Composite Materials, Pergamon Press 1994

Ashby M.F. Materials Selection in Mechanical Design, Pergamon Press, 2nd ed. 1999

Nye J. F. Physical Properties of Crystals-Their representation by Tensors and Matrices. Clarendon: Oxford, 1985

Websites

National Composites Network