Study and analysis of the stress state in a ceramic, button-head, tensile specimen

The final results are reported for a study to identify and correct the causes of nongage-section failures (notably button-head failures) in ceramic tensile specimens observed in several laboratories. Numerical modeling of several candidate specimen gripping systems has shown inherent stress concentrations near the specimen button head at which the maximum stress may approach 75 to 100% of the gage-section stress for certain grip conditions. Empirical comparisons of both tapered- and straight-collet gripping systems revealed compromises in both systems. The straight-collet system, with deformable collets, is simpler to use but produces statistically significant greater average percent bending for all tests than those produced for the tapered-collet system, which is slightly more difficult to use. Empirical tensile tests of {approximately}50 aluminium oxide and {approximately}50 silicon nitride specimens were conducted to evaluate the loading capability of both gripping systems, the percent bending in each system, and the potential of consistently producing successful test results. These tests revealed that, due to variations in individuals specimens or the individual specimen/grip interfaces, neither of the gripping systems can consistently produce bending of less than 3 to 4% at failure although occasional values of {approximately}0.5% bending were attained. Refinements of grinding procedures and dimensional measurement techniques have shown critical details in both the practices and consistency of machining necessary for achieving the dimensional tolerances while minimizing subsurface damage. Numerical integration techniques indicate that up to a consistent 5.0% bending during fast- fracture tests can be tolerated before large influences are detected in the determination of the Weibull modulus and the Weibull characteristic strength

Microtearding mode study in NSTX using machine learning enhanced reduced model

This article presents a survey of NSTX cases to study the microtearing mode (MTM) stabilities using the newly developed global reduced model for Slab-Like Microtearing modes (SLiM). A trained neutral network version of SLiM enables rapid assessment (0.05s/mode) of MTM with $98\%$ accuracy providing an opportunity for systemic equilibrium reconstructions based on the matching of experimentally observed frequency bands and SLiM prediction across a wide range of parameters. Such a method finds some success in the NSTX discharges, the frequency observed in the experiment matches with what SLiM predicted. Based on the experience with SLiM analysis, a workflow to estimate the potential MTM frequency for a quick assessment based on experimental observation has been established

The Ceramic Manufacturability Center: A new partnership with US industry

The Ceramic Manufacturability Center (CMC) is a new facility at the Oak Ridge National Laboratory (ORNL) established as a direct response to current US industry needs. It was created as part of a highly integrated program jointly funded by the US Department of Energy Defense Programs, Energy Efficiency and Renewable Energy, and Energy Research divisions. The CMC is staffed by personnel from ORNL and the Y-12 Plant, both managed by Martin Marietta Energy Systems, Inc. (Energy Systems). Its mission is to improve the technology needed to manufacture high-precision ceramic components inexpensively and reliably. This mission can be accomplished by strengthening the US machine tool industry and by joining with ceramic material suppliers and end users to provide a path to commercialization of these ceramic components

Utilization of fractography in the evaluation of high temperature dynamic fatigue experiments

The slow crack growth properties of six structural ceramics were measured by dynamic fatigue in air and inert atmospheres over a range of elevated temperatures. The material response varied from no strength degradation as a function of stress and environment to significant strength degradation by slow crack growth (SCG) and by a combination of SCG and creep. The fractographic investigation showed that SCG was evidenced by growth of isolated cracks and often by an intergranular fracture mode, while creep was evidenced by accumulated damage such as void formation and opening of the microstructure at grain boundaries and triple junctions. For the materials in which the strength was unaffected by the stress and environment, the fracture surfaces were essentially indistinguishable from the inert fracture surfaces

Industrial thermal insulation: an assessment

A large variety of thermal insulation materials is manufactured for application in various temperature ranges and environments. Additional and improved thermal insulation for steam systems is a key area with immediate energy conservation potential in several of the larger energy-consuming industries. Industrial thermal insulation technology was assessed by obtaining input from a variety of sources including insulation manufacturers, system designers, installers, users, consultants, measurement laboratories, open literature, and in-house knowledge. The assessment identified a number of factors relevant to insulation materials and usage that could contribute significantly to improved energy conservation