NPL worked with LMAT to develop a modified PVT cell to measure shrinkage of the composite. PVT is a technique which allows control of pressure, volume and temperature conditions.
The instrument was adapted from one previously used by NPL for characterising behaviour of thermoplastic materials used in injection moulded parts. The instrument was redesigned by NPL to take measurements to characterise shrinkage of thermoset resin systems, and manufactured by a contractor commissioned by LMAT.
NPL tested the cell on two materials provided by LMAT, one which cures at room temperature and one which cures at high temperature. The instrument is a cell, into which the composite material is placed, with a plunger located on top. As the material shrinks or expands during the curing process, the plunger is displaced in a way that follows the movement of the material, providing measurement of shrinkage.