FABRICATION AND TEST OF HIGH-TEMPERATURE HONEYCOMB CORE SANDWICH CONSTRUCTION

The primary objective of this program was the determination of the engineering properties of polybenzimidazole and polyimide honeycomb core sandwich constructions after aging at various temperatures. Both press and autoclave methods were evaluated for the fabrication of sandwich face sheets and honeycomb core sandwich composites. A pressure-point cure technique was developed which provided a controlled, efficient processing method for preparing polyimide and PBI laminates and sandwich composites. Technology was developed for fabricating sandwich composites by secondary bond, single stage cure, and multiple stage cure methods. The single stage cure method, using the pressure- pointytechnique, was selected for preparing the heat aging test specimens for both the polyimide and the PBI resin systems. Heat aging studies were conducted at 400F, 500F, and 600F. Polyimide sandwich composites exhibited excellent heat resistance at all test temperatures. The polyimide composites retained over 50 of their room temperature flexural shear strength values after 1400 hours aging at 400F. The PBI sandwich composites were susceptible to oxygen degradation during fabrication and during the heat aging study. Speciments heat aged at 600F exhibited complete failure within a 300-hour period. Oxygen attack was less at lower temperatures and PBI test specimens still retained over 50 of their room temperature strength values after 600 hours aging at 400F.