Development of a dilatometer for shrinkage analysis of thermosetting resin systems at accurate processing conditions of liquid composite moulding processes and exemplary results of the effects of varying processing conditions on chemical shrinkage of an epoxy resin

The processing of thermosetting resin systems in liquid composite moulding is accompanied by a change in density through chemical and thermal shrinkage during the curing reaction of the resin and cooling of a part from processing to operating temperature. These effects cause residual stresses and an undesired characteristic surface pattern in endless fibre reinforced plastics. However, the accurate measurement of the chemical and thermal shrinkage is challenging with state-of-the-art measurement devices, especially for highly reactive thermosetting resin systems. The main disadvantage is that it is not possible to recreate the processing conditions of modern liquid composite moulding processes during the measurement of the thermosetting resin systems and has therefore limited use for process optimisations. In this paper the development of a dilatometer, which is capable of measuring the shrinkage in highly reactive thermosetting resins providing the processing conditions of liquid composite moulding is presented. The effects of processing pressure and internal mould release agents on chemical shrinkage are analysed with the developed dilatometer for different epoxy resins. The trials demonstrate a significant effect of processing pressure on chemical shrinkage