Anisotropic oxidation due to aging in a triaxially braided composite and its influence on tensile failure

The service life of Polymer Matrix Composite Materials can be severely affected by long exposures to elevated temperatures. This study investigated the high temperature durability of a carbon/MVK10 triaxially braided textile composite. The goal was to monitor, analyze and quantify the evolution of physical and chemical aging processes to verify if Federal Aviation Administration (FAA) regulations for maximum service temperature ensure the safe use of such materials. Tensile tests were performed at the maximum service temperature on aged samples in two material directions to evaluate the progression of stiffness and Ultimate Tensile Strength (UTS) degradation. Aging induced damage was observed with the help of microscopic observations on the edges and cross-sections of tensile samples prior to loading. It was found that aging had a significant effect on UTS. It was also observed that the rate of deterioration was different for samples cut along different material directions, pointing towards anisotropic degradation mechanisms promoted by the braiding architecture. The investigated material had performances similar to existing high temperature composites, albeit at a lower temperature. It would therefore seem that FAA rules for setting the operating temperature are suitable for this material when aging effects are taken into consideration at the design stages.