NEW PROCESS FOR MAKING SMART COMPOSITE MATERIALS
Stephen Bush
UMIST Centre for Manufacture
England UK
Keywords: L.176, SMARTFORM, Session 12
ABSTRACT OF PAPER FOR PPS-19
Melbourne, Australia July 7-10, 2003
For Session 12
NEW PROCESS FOR MAKING SMART COMPOSITE MATERIALS
by
S F Bush, D R Blackburn and K J Jamieson
Polymer Engineering Research Laboratory
Centre for Manufacture
UMIST, P.O.Box 88, Manchester M60 1QD
This paper describes a new process for the production of certain types of smart composite materials, which under prescribed temperature fields spontaneously adopt prescribed shapes. These shapes are quite stable at room temperature plus about 50șC. At or near the forming temperatures the shapes may revert to their original forms. Articles of this type can thus be seen as the polymer composite equivalent of a bimetallic strips or shape memory metal alloys.
The purpose of this process which is under commercial development under the acronym SMARFORM© , is to be able to make shapes from straight rods and flat sheet feedstock which are either impossible to mould or very expensive to do so by conventional processes. The key to the new process is the placing of mixtures of heat shrinkable synthetic and natural fibres in precise positions in the cross-section of pultruded profiles notably rods and sheet. When subsequently cut to size, the rods or sheet elements are passed on belts through a series of heating zones for prescribed times which cause them to curl or twist into the shapes required. The process is economical since both the pultrusion stage and the thermal forming stage are continuous, not requiring manual intervention.
Among a number of fibre properties, the heat shrinkage is particularly important. Drawn Poly(ester terephthalate) fibres are used in a number of cases since the degree of shrinkage obtainable at say, 200șC, is strongly dependent on the draw ratio for this fibre. PET fibres with different degrees of draw are readily available commercially so that the process economics are not imperilled. Natural fibres such as cotton or linen can also play a part in ensuring the post-thermal forming shapes are maintained in the face of intermittent mechanical stress and temperature increases above ambient of say, 50șC.
The purpose of the paper is to demonstrate how the observed post-thermal forming shapes can be predicted mathematically from the properties of the different fibres used in combination in the matrix, and the geometrical positioning of the fibres in the matrix cross-section.