INVESTIGATION INTO TOE HIGH-TEMPERATURE STRENGTH DEGRADATION- OF FIBER-REINFORCED RESIN COMPOSITE DURING AMBIENT AGING

摘要

It was discovered earlier on NASA and Air Force programs that aging in a room tem¬perature environment can significantly reduce the high-temperature strength properties of graphite- and boron-reinforced epoxy composites. The primary objective of this pro¬gram was to study the phenomenon and determine the causes of these high-temperature strength losses.nA better understanding of this aging problem has been provided by this program. All commercial epoxy resins evaluated degrade as a result of exposure to water vapor. By separating the resins into categories of high-temperature resistant and general-purpose systems, excellent correlation was obtained. Composite flexure and sheer strength retention at elevated temperature after 24-hour water boll showed excellent agreement with cast resin flexural modulus retention after three-week humidity. This correlation confirms that water absorption by the resin matrix is the principal factor causing the ambient aging problem in reinforced epoxies. Surface contamination of graphite fibers and adsorption of water on the fiber surface can also be contributing factors.