Research
PRECCAP students working at LANL Summer 2019
Research Team: Norman Love, Calvin M Stewart, and Yirong Lin (UTEP), Tom Robinson (KCNSC)
Background: Polymeric foam materials are prevalent throughout the business and serve a number of functions including (1) the distribution and relieving stress (2) to mitigate the effects of shock and vibration; (3) accommodate dimensional changes caused by thermal variations and (4) maintaining position of surrounding parts by applying the appropriate spring force and (5) encapsulation applications [4]. Of particular interest are foams made from polysiloxanes [5] due to their relatively high thermal stability and chemical resistivity. With the shift to additive manufacturing processes where 3d structures are built layer by layer with each layer being 200 microns or less, there is a need for pore formers with average sizes in the range of 5-100 microns.
Objective: To develop a process for making hollow polysiloxane spheres, such as polydimethylsiloxanes, that average in the desired size range that could ultimately be scaled up to a production process. Emulsion polymerization [6] processes along with the use of sonic transducers are possible approaches to be investigated. Characterization of the generated microspheres would include size and size distribution, sphere wall thickness, thermal and mechanical properties of the spheres.
Approaches: This project is a collaborative effort between KCNSC (Dr. Thomas Robison) and UTEP (Drs. Yirong Lin, Norman Love, and Calvin Stewart). The synthesis of hollow polysiloxanes will involve emulsion polymerization process with the feasibility of controlling hollow polysiloxane sphere diameters, wall thickness, and size distribution. Once the spheres are synthesized, they will be characterized using SEM, XRD, and Laser based particle size distributor analysis tools. 3D printing process will be carried out including, but not limited to FDM, SLA where polymer porous structures with designed porous structures will be printed. Upon completion of printing, various testing such as mechanical testing including static failure testing, dynamic failure testing, and impact testing will be carried out to characterize the printed pilysiloxane structures. These properties at various temperature ranges will be carried out to determine its temperature influence on the mechanical property. Upon completion of testing, improvement on synthesis and 3D printing will be carried out to improve the property of the fabricated structures.
Research Team: Yirong Lin, Norman Love, and Calvin M Stewart (UTEP), Dennis Eichorst (KCNSC)
Background: Glass and glass-ceramics are used in a variety of connectors for DOE/NNSA applications requiring hermeticity at elevated temperatures and/or pressures [1]. Significant characterization of material performance for use in solid oxide fuel cells (SOFC) has been undertaken by national labs and academia [2]. However, basic material properties at conditions of interest are not well understood for hermetic electrical connectors. This project involves two major activities: 1) material characterization, and 2) component evaluation. Materials evaluation activities consist of evaluating mechanical (modulus of rupture) and electrical performance (resistivity) as a function of temperature. Potential temperature range is -50 to 500°C or beyond. Sealing glasses will be limited to commercially available (or KCNSC supplied) glasses for sealing to 316 or 304 stainless steels. Glass-ceramics within the lithium alumino-silicate system shall be evaluated. These glasses have a range in the coefficient of thermal expansion (CTE) as a result of processing conditions; processing will need to be developed to produce a range of CTE values from approximately 12 – 18 ppm/C. Glass-to-metal (or glass/ceramic-to-metal) seals are used in a variety of high performance or high reliability devices to provide a hermetic environment for both commercial industrial and DOE/NNSA applications. Examples of such devices include airbag actuators, lightning arrestor connectors, electrical feedthroughs for vacuum equipment or space systems [3]. Frequently, component designs are selected from a limited selection of commercially available glasses (or glass-ceramic materials) largely based on material properties measured near room temperature. However, performance over a much wide range of pressures and/or temperatures may be required, particularly for critical safety devices that may be expected to survive accident scenarios (e.g., crash or fire).
Objective: This research will evaluate thermal, electrical, and mechanical material properties as function of temperature and/or pressure. This data will be essential in understanding changes in glass properties (e.g., viscoelastic relaxation) that may occur at elevated temperatures and not typically considered in finite element modeling.
Approaches: Component level testing will involve the Helium leak testing of connectors for hermeticity and high voltage breakdown between the electrical feedthrough and shell. A fixture needs to be designed upon which the connector can be welded to. This fixture needs to be portable enough to be placed within an environmental chamber and/or split tube furnace. The pressure needs to be tunable such that a variety of pressures can be applied. Once the fixture is designed and fabricated, connectors will be welded on and a targeted test matrix of accelerated aging tests performed. During these tests a variety of pressure and temperature profiles will be exerted on the connector to simulate a harsh service life in an accelerated fashion. Once aging tests are completed, the connector will be placed into a designated chamber and helium leak rate tests performed where helium is pumped into the fixture and leaks are detected according to differential pressure decay method. Simultaneous to these measurements, voltage breakdown will be measured. Ideally, the experiment setup will be configured to evaluate leak rates while at a variety of pressures and temperatures. The geometry and interfacial reactions between the various metals and glass within a connector are unique to the model of connector. Unexpected complications are likely to arise. At this early stage it is not clear how many different connectors might need to be evaluated during this collaborative effort. It may be that a series of fixture need to be designed to accommodate a variety of connector types and materials. It is envisioned that a modular design will be created, the makes it easy to quickly size the fixture or a given connector
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