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Dr Nigel St John

TOPIC: Dimensional stability of composite materials

Authors: Nigel St John, Lauren Booth and Jeff Heath of the Defence Science and Technology Group, Australian Department of Defence

Presented by Dr Nigel St John, Defence Science and Technology Group, Australian Department of Defence


The major environmental factors that affect the dimensional stability of fibre reinforced polymer composites are temperature and moisture content. These factors act, primarily on the resin matrix and result in different behaviour in and out of the plane of the reinforcing fibres. While the dimensional changes may be small, they can be significant in applications where small tolerances are important – as in structures as diverse as composite propeller shaft bearings to space telescopes. Dimensional changes can also be significant when a composite is combined with different materials such as patches or joints, or when internal stresses need to be considered in combination with residual cure or thermal stresses from manufacture, such as spring back.

To explore the role of these environmental factors on dimensional stability, a study has been undertaken measuring the thermal and moisture expansion coefficients of a range of unidirectional glass and carbon epoxy composites, as well as a quadraxial glass reinforced composites. It was found that while for unidirectional composites the thermal expansion was similar transverse and through thickness, the moisture expansion was markedly different in the two directions which is not what has been traditionally assumed. The presentation will discuss these results; the background of measurement methods and issues; the effect of fibre type, tow size and resin content on the thermal and moisture expansion.

 Keywords: Thermal expansion, moisture expansion

Presenter’s resume

Nigel St John graduated with a B. Appl. Sci. from the Queensland University of Technology in 1989, B.Sc. (Hons) in 1990 and PhD in 1994 from the University of Queensland. He has over 20 years research and development experience working for the Defence Science and Technology Group (DST Group) in the field of polymer materials and composite structures for Defence applications including projects for the all composite Huon Class Minehunter Coastal ships, applications related to the Collins Class Submarines and new applications for the future fleet.