Influence of Low-Earth Orbit Exposure on the Mechanical Properties of Silicon Carbide

摘要

The influence of the Low-Earth orbit (LEO) environment on the mechanical strength of silicon carbide (SiC) was evaluated on two flight experiments as part of the Materials on the International Space Station Experiment (MISSE). SiC samples for modulus of rupture (MOR) and equibiaxial flexural strength (EFS) testing were flown on the Optical and Reflector Materials experiments (ORMatE) as part of MISSE-6 (launched on STS-123, March 2008; returned on STS-128, September 2009) and MFSSE-7 (launched on STS-129, November 2009; returned on STS-134, June 2011). Two different SiC vendors provided material for each flight experiment. The goal of the experiments was to measure mechanical properties of the flight samples and compare them to an equal number of similar samples in control and traveler sample sets. Complete characterization of the strength of brittle materials typically requires many more test specimens than could be reasonably accommodated on the ORMatE sample tray and statistical models based on few samples include large uncertainties. Understanding the results of the mechanical tests of MISSE samples required comparison to results from a statistically valid number of samples. Prior testing by The Aerospace Corporation of material supplied by the same four vendors was used to evaluate the MISSE results, including flight and control samples. The results showed that exposure to LEO over the durations covered by MISSE 6 and 7 (approximately 18 and 20 months, respectively) did not alter the mechanical strength of the silicon carbide for any of the vendors' materials.