Using data generated by a differential scanning calorimeter, the heat of reaction, the rate of cure, and the degree of cure of Fiberite 976 resin were determined at the constant temperatures of 413, 423, 433, and 443°K (isothermal scanning). The ultimate heat of reaction was also measured at the constant heating rate of 2°K/min (dynamic scanning). Using a disc and plate type viscometer, the viscosity was measured as a function of time at the temperatures of 413, 423, 433, and 443°K. Expressions were also developed which represent the rate of cure, the degree of cure, and the viscosity data.
Tests were performed measuring the temperature, ionic conductivity, and compaction in 16 to 200 ply thick graphite-epoxy laminates made of either Fiberite T300/976 (tape or fabric) or Hercules AS/3501-6 (tape). The data were compared to results calculated by the Loos-Springer CURE model. Good agreement was found between the model results and the data indicating that the model can be used to select the cure cycle. It is also shown that the cure cycle recommended by the manufacturer may result in ex cessive temperatures and in incomplete compaction and cannot be used to manufacture "thick" or even moderately thick composites.
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 ndl 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.
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