Measurement of the consolidation and shrinkage processes in composites manufacture

The Problem

It is very important in controlling the processing of advanced composites to develop an understanding of the consolidation and resin shrinkage processes throughout the cure cycle. For typical aerospace epoxies this requires the simultaneous application of pressure up to a few Bar and temperatures up to about 180°C to a prescribed cycle. Equipment is available to do this such as Thermo Mechanical Analysers (TMA), but their sample sizes are very small and interpreting their outputs can be problematical.

The Solution

To achieve a reliable set of data a pair of heaters was mounted in a die set so that a prescribed temperature and pressure could be applied to a composite sample nominally 4mm thick. Targets were attached to the steel plates in contact with the sample and their position monitored throughout the five hour cure cycle. The processes going on at each stage in the cure could be identified in a reliable and reproducible way over a long cure cycle.

Advantages of the Video Gauge

The experiments were very quick and simple to set up, whilst other approaches could be used to measure the displacement of the system difficulties might be expected with the temperature range required and the possibilities for baseline drift over a five hour cure cycle. The resolution of the data allowed consolidation due to flow and due to resin cure shrinkage to be separated and permitted the expansion coefficients of the composite to be established at various critical places in the cure cycle. The expansion coefficients measured in this way agreed closely with measurements made in more conventional ways.