Controlling thermal expansion to obtain negative expansivity using laminated composites

It is confirmed, by considering a wide range of laminated composites containing a variety of fibres and matrices, that negative thermal expansion coefficients may be obtained. These are usually accompanied by a correspondingly large value of the in-plane axial Poisson’s ratio (PR). By making use of this large PR extremely negative values of expansivity may be obtained – much further negative than for any monolithic materials. The use of laminated composites also overcomes some of the previously reported limitations of a device to control thermal expansion when made with monolithic materials. The use of the device, as a platform to control the expansivity of an optical fibre containing a Bragg grating, is discussed in detail and it is shown that the required negative expansivity of −10−5 K−1 may easily be obtained with a number of composite systems.