Publications

Variations in the neutron generator encapsulation process can affect functionality. However, instead of following the historical path in which the effects of process variations are assessed directly through functional tests, this study examines how material properties key to generator functionality correlate with process variations. The results of this type of investigation will be applicable to all generators and can provide insight on the most profitable paths to process and material improvements. Surprisingly, the results at this point imply that the process is quite robust, and many of the current process tolerances are perhaps overly restrictive. The good news lies in the fact that our current process ensures reproducible material properties. The bad new lies in the fact that it would be difficult to solve functional problems by changes in the process.

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A polyurethane foam used in the H1616 shipping container provides impact energy absorption and fire protection in hypothetical accident conditions. This study was undertaken to determine the estimated lifetime of the foam as a function of temperature. The foams were aged at temperatures ranging from 65°C to 95°C for periods of time ranging from 6 months to 6 years. Both destructive and nondestructive Dynamic Mechanical Analyses (DMA) were used to evaluate the performance of the foams as a function of time and temperature. In addition, color changes and weight loss were recorded. Three properties of the foam show a definite trend with aging time: weight loss, nondestructive G’ (measured at 100°C), and glassy G’. A time temperature superposition analysis shows a reasonable trend with temperature for both the weight loss and glassy G’. The acceleration factors for weight loss and glassy G’ did not correlate with each other, however. A prediction of the behavior of G’ as a function of aging time at 25°C was derived from an extrapolated value of the acceleration factor. In addition to providing a quantitative estimation of the aging process, the curve also provides a description of the qualitative features of the aging process. First, the aging process appears to proceed smoothly as a function of aging time. There are no discontinuities or sharp breaks in the glassy G’ as a function of aging time at any of the temperatures. Second, the rate of change of the glassy G’ appears to decrease as the aging time increases.

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The autonomic healing ability of an epoxy adhesive containing micro-encapsulated dicyclopentadiene (DCPD) was evaluated. The epoxy resin used was Epon 828 cured with either Versamid 140 or diethylenetriamine (DETA). Variables included total weight percent of microcapsules (MCs) and catalyst, as well as the catalyst to DCPD ratio. The degree of healing was determined by the fracture toughness before and after ''healing'' using double-cantilever beam analysis. It was found that the degree of self-healing was most directly related to the contact area (i.e. crack width) during healing. Temperature also played a significant role. Observed differences between the results of this study and those in literature are discussed.

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