Scaling complications of dual temperature cure resin prepreg systems in airplane part manufacture

Carbon and glass fabric epoxy prepreg with a highly accelerated curing system were compared and used to build a Boeing 737 flap hinge fairing production part. The prepreg materials, uncured and cured, were analyzed to determine physical and mechanical properties. Initial evaluations of the carbon prepreg indicated unique and desirable characteristics including dual temperature cure and excellent handling characteristics. Therefore, this material was selected for the use in the development of a production part. However, the part selected for manufacture, a Boeing 737 flap hinge fairing, required the use of both carbon and glass fabric prepregs. Therefore, the resin system, which was developed for carbon prepreg, had to also be impregnated into glass fabric. After cure of the part, it was found that areas on the part were scorched including the bagging material. This scorching led to an investigation of the exotherm produced by the accelerated resin in the cure of the carbon and glass prepreg materials. Two sets of test panels were made to simulate optimal and poor processing conditions for the glass and carbon fiber fabric prepregs. Thermocouples were placed in the layers of prepreg to track the temperature effects during the curing process. It was found that the glass fabric prepreg did not conduct the heat produced by the curing exotherm as well as the carbon material and therefore was the cause of material degradation or charring of the components in the composite system.