Methodology for examining system aging due to interactions between chemically211 incompatible materials

摘要

We start with a stored and unused population of fielded engineered units that are211u001ecomposed of chemically incompatible materials. The units age primarily through 211u001eheterogeneous chemical reactions between the materials resulting in possible 211u001edegradation in performance. The engineered units are unused in storage, but may 211u001ebe called into actual service at any time. We sample several units from the 211u001epopulation per year and perform a number of non-destructive evaluation (NDE) 211u001etechniques, such as radiography, low-frequency vibration analysis, and ultrasonic 211u001eimaging on the selected units. From those units, some are selected for 211u001edestructive testing (D-test) involving disassembly and testing of internal parts 211u001eand components. Chemical analyses, mechanical properties measurements and other 211u001etests are performed. All of the above steps provide information that is used in 211u001ethe system simulation mathematical model. The system simulation model 211u001eincorporates chemical reactions and gas-solid transport processes, along with 211u001echanges in both the surface and bulk properties of the solids. Model results are 211u001eused to suggest improvements in NDE analyses of the units and improvements in 211u001ecomponent and material analyses. Model results give trending indications of 211u001eindividual component and overall system changes over time, plus some 211u001eunderstanding of the mechanisms involved which allow science-based predictions of 211u001ethe aged state of the units in future times. The NDE, D-test, and model results 211u001ecan also be used to assess statistically the reliability and performance of the 211u001eoverall aging population of units.