Volume 3, Issue 5 (May 2006)
Proficiency Testing for Evaluating Aerospace Materials Test Anomalies
ASTM G 86 “Standard Test Method for Determining Ignition Sensitivity of Materials to Mechanical Impact in Ambient Pressure Liquid Oxygen and Pressurized Liquid and Gaseous Oxygen” and ASTM G 74 “Standard Test Method for Ignition Sensitivity of Materials to Gaseous Fluid Impact” are commonly used to evaluate materials susceptibility to ignition in liquid and gaseous oxygen systems. However, the methods have been known for their lack of repeatability. The inherent problems identified with the test logic would either not allow precise identification or the magnitude of problems related to running the tests, such as lack of consistency of systems performance, lack of adherence to procedures, etc. Excessive variability leads to increasing instances of accepting the null hypothesis erroneously, and so to the false logical deduction that problems are nonexistent when they really do exist. This paper attempts to develop and recommend an approach that could lead to increased accuracy in problem diagnostics by using the 50 % reactivity point, which has been shown to be more repeatable. The initial tests conducted indicate that PTFE and Viton® A5 (for pneumatic impact) and Buna S (for mechanical impact) would be good choices for additional testing and consideration for interlaboratory evaluations. The approach presented could also be used to evaluate variable effects with increased confidence and tolerance optimization.