Effects of Prior Aging on the Creep Response of Carbon Fiber Reinforced PMR-15 Neat Resin at 288 C in an Air Environment

摘要

The mechanical response of carbon fiber reinforced PMR-15 neat resin with a + or - 45 fiber orientation was investigated at 288 C. Mechanical testing was performed on unaged specimens and specimens that were aged up to 1000 hours in an air environment. Tensile tests were performed to determine Young's modulus of elasticity and Ultimate Tensile Strength. Creep tests were performed at creep stress levels of 30 and 60 MPa. Creep periods of at least 25 h in duration were followed by recovery at zero stress. Duration of the recovery period was at least twice the time of the creep period. Oxidation layer growth and weight loss measurements were also taken as a function of aging time. Unaged test specimens accumulated creep strains of approximately 1.7% at 60 MPa and approximately 1.1% at 30 MPa. After 1000 h of aging the test specimens accumulated creep strains of approximately 0.5% at 60 MPa and approximately 0.1% at 30 MPa. It is clear that with prior aging time, there is a reduction in creep strain accumulation. Prior aging did not appear to significantly influence recovery at zero stress. The experimental data revealed that weight loss and oxidation layer growth increase with increasing aging time at elevated temperature. After 500 h of aging, the rectangular plus or minus 45 carbon fiber reinforced PMR-15 composite had '0.95% weight loss compared to '0.5% at 250 h. The oxidation layer growth at 500 h was '0.97 mm for the cut surface and '0.32 mm for the molded surface. After 1000 h the oxidation layer growth was '1.5 mm for the cut surface and '0.33 mm for the molded surface. It is apparent that the cut side of the specimen with the fibers exposed to the oxidizing environment experiences a thicker oxidation layer growth.