Distributed model based thermal control for optimal curing of the large composite structures

The high loaded aircraft composite structures are produced by the autoclave and closed mould processes at which the consolidation of the fibers and matrix is done at the same time as the component is shaped. Full curing schedule include a pre-warming to the resin viscosity reaches a minimum, next applying of pressure to remove the gas bubbles and removal of excess resin, and finally consolidation of resin at elevated temperature to its full polymerization. The change in the states of the composite should be made as possible uniformly across the thick-walled products. The main processing problems encountered in closed molding of articles with large variations in thickness include porosity, resin-rich areas, resin-dry areas, insufficient consolidation, degraded mechanical properties, and distortion which can arise from uneven cure. Many of the problems can be resolved by correct timing of application of temperature and pressure. But the process control is complicated due to unobservability of the rheological state and temperature of material in a closed volume of a mould. In this paper we propose a mathematical model for epoxy-based thick-walled composite structure curing. PDE system linking a kinetic equation of the resin cure with heat transfer equation, take into account heating caused by excessive exothermic reactions, a phase transition of resin from liquid to gel and further to the solid state, where required temperature field is supported by the independently controlled heat sources. To synthesize the optimal control law we use the genetic algorithm which performs the transient analysis of the developed model on each iteration steps.