An Expert System for Autoclave Curing of Composites

Abstract

A rule based expert system was developed for controlling the autoclave temperature and pressure during cure of fiber reinforced thermosetting matrix composites. Rules were established which ensure that the temperatures and pressures remain within the required limits, the laminate is fully compacted and fully cured, the void content is minimum, and the residual (curing) stresses are low. The inputs to the expert system are the measured instantaneous autoclave temperature and pressure, the composite midpoint and surface temperatures, composite thickness, and ionic conductivity. These inputs are examined by preestablished rules and, on the basis of decisions dictated by the rules, the autoclave heater, cooler and pressure controllers are adjusted to the appropriate settings. An algorithm was written and hardware was developed for collecting and processing the data, for applying the rules, for making the decisions, and for controlling the autoclave. The software and hardware were integrated into a control system which was validated by simulated as well as actual cures of flat graphite-epoxy laminates ranging in thickness from 0.1 to 6.5 inches. The tests showed that the control system (designated as SECURE) performed all its required functions well, resulted in reduced cure times, and produced laminates whose mechanical properties were as good as those cured by conventional methods.