Sequential heat release: an innovative approach for the control of curing profiles during composite processing based on dual-curing systems

Abstract

The sequential heat release (SHR) taking place in dual-curing systems can facilitate thermal management and control of conversion and temperature gradients during processing of thick composite parts, hence reducing the appearance of internal stresses that compromise the quality of processed parts. This concept is demonstrated in this work by means of numerical simulation of conversion and temperature profiles during processing of an off-stoichiometric thiol–epoxy dual-curable system. The simulated processing scenario is the curing stage during resin transfer moulding processing (i.e. after injection or infusion), assuming one-dimensional heat transfer across the thickness of the composite part. The kinetics of both polymerization stages of the dual-curing system and thermophysical properties needed for the simulations have been determined using thermal analysis techniques and suitable phenomenological models. The simulations show that SHR makes it possible to reach a stable and uniform intermediate material after completion of the first polymerization process, and enables a better control of the subsequent crosslinking taking place during the second polymerization process due to the lower remaining exothermicity. A simple optimization of curing cycles for composite parts of different thickness has been performed on the basis of quality–time criteria, producing results that are very close to the Pareto-optimal front obtained by genetic algorithm optimization procedures.Postprint (author's final draft

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