18TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS

High performance composite structures produced by the processes at which the consolidation of the fibres and matrix is done at the same time as the component is shaped. Full curing schedule include a pre-warming for resin liquefaction, next apply of pressure to remove the gas bubbles, and finally consolidation of resin at elevated temperature to its full polymerization. The change in the state of the composite should be made as possible uniformly across the thick-walled products. The complexity of process control is due to unobservability of the rheological state of material in a closed volume of a mould. In this paper we propose a mathematical model of epoxy-based thick-walled composite structure curing. PDE system linking a kinetic equation of the resin cure with heat transfer equation, take into account a phase transition from liquid to gel and further to the solid state. On the basis of transient analysis of the developed model we optimize the temperature control law. 1 The Problems of Thermoset Composite Cure The manufacturing processes for thermoset composites are subject to extensive research [1- 3] and the number of models has been proposed for mould filling/consolidation and cure for several manufacturing methods. The purpose of these models is the optimization of the production process to ensure the specified properties of the material, to reducing the residual stress and shape distortions. In an industrial process, it is economically advantageous to minimize the cure time [4] by increasing the cure temperature and providing a faster crosslinking reaction. But this can lead to significant loss of the composite product quality, which appears in the forms of large shape distortions and delaminations. In general, residual stresses and shape distortions will increase with increased cure temperature [5]. Moreover, at some conditions in a thick-walled epoxy based composite pieces at high cure temperature the cracks in the resin can be observed due to cure shrinkage. To avoid this problem, instead of using a single step cure schedule, in the some cases gelled the resin at low temperature and slow increased the temperature by a linear ramp up to its maximal value [6]. We consider here the problem of optimizing the cure cycle on an example of a composite spar of th