Constitutive modelling of single crystal and directionally solidified superalloys

Successful attempts were made to model the deformation behavior of nickel base superalloys to be used in gas turbine engines based on both a macroscopic constitutive model and a micromechanical formulation based on crystallographic slip theory. These models were programmed as FORTRAN subroutines, are currently being used to simulate thermomechanical loading predictions expected at the fatigue critical locations on a single crystal turbine blade. Such analyses form a natural precursor to the application of life prediction methods to gas turbine airfoils

Thermoviscoplastic analysis of fibrous periodic composites using triangular subvolumes

The nonlinear viscoplastic behavior of fibrous periodic composites is analyzed by discretizing the unit cell into triangular subvolumes. A set of these subvolumes can be configured by the analyst to construct a representation for the unit cell of a periodic composite. In each step of the loading history, the total strain increment at any point is governed by an integral equation which applies to the entire composite. A Fourier series approximation allows the incremental stresses and strains to be determined within a unit cell of the periodic lattice. The nonlinearity arising from the viscoplastic behavior of the constituent materials comprising the composite is treated as fictitious body force in the governing integral equation. Specific numerical examples showing the stress distributions in the unit cell of a fibrous tungsten/copper metal matrix composite under viscoplastic loading conditions are given. The stress distribution resulting in the unit cell when the composite material is subjected to an overall transverse stress loading history perpendicular to the fibers is found to be highly heterogeneous, and typical homogenization techniques based on treating the stress and strain distributions within the constituent phases as homogeneous result in large errors under inelastic loading conditions

A domain-specific analysis system for examining nuclear reactor simulation data for light-water and sodium-cooled fast reactors

Building a new generation of fission reactors in the United States presents many technical and regulatory challenges. One important challenge is the need to share and present results from new high-fidelity, high-performance simulations in an easily usable way. Since modern multiscale, multi-physics simulations can generate petabytes of data, they will require the development of new techniques and methods to reduce the data to familiar quantities of interest (e.g., pin powers, temperatures) with a more reasonable resolution and size. Furthermore, some of the results from these simulations may be new quantities for which visualization and analysis techniques are not immediately available in the community and need to be developed. This paper describes a new system for managing high-performance simulation results in a domain-specific way that naturally exposes quantities of interest for light water and sodium-cooled fast reactors. It describes requirements to build such a system and the technical challenges faced in its development at all levels (simulation, user interface, etc.). An example comparing results from two different simulation suites for a single assembly in a light-water reactor is presented, along with a detailed discussion of the system's requirements and design.Comment: Article on NiCE's Reactor Analyzer. 23 pages. Keywords: modeling, simulation, analysis, visualization, input-outpu

Prediction of the cyclic durability as a function of cycle duration and temperature of an air plasma sprayed coating using inelastic strain

A detailed study of the failure mechanisms in an APS TBC was carried out involving over 1000 micrographs. As a result the kinetics of oxidation and rumpling were characterized. In addition it was found that the failure was always within the ceramic caused by progressive cracking. At approximately half the spallation life, crack linking became the dominant growth mode for cracks. This pattern of damage remained constants over the temperature range of 1066 °C to 1149 °C and for cycle durations of 0.5 hours to 50 hours. The change in temperature resulted in a variation in spallation life of a factor of 5 and the variation in hold time resulted in a variation in life of a factor of 7 and for the entire data set the ratio of the longest failure life to shortest was 17. Through the use of a finite element analysis (FEA) that used an experimentally validated viscoplastic model driven by imposed shape changes derived from measured oxidation and rumpling behavior as well as thermal expansion mismatch, the hot and cold inelastic strains were predicted and used to predict failure. It was possible to predict the entire data set using data from only two cyclic life tests at two different test conditions. The life as a function of temperature can be predicted from two experiments run with two different hot times at a single temperature. The life as a function of hold time can be predicted from tests run at two temperatures at a single hold time. This suggests that the hold time dependence and temperature dependence are closely tied to the factors controlling inelastic strain. The inelastic strains can be determined form a combination of measured and computed behavior. It was also found that the finite element results can be captured without running the FEA using simple expressions that are calibrated using a large set of FEA run

X-ray based displacement and strain measurements for hostile environments

A completely new method of non-contacting, hostile environment displacement and strain measurement based on the focus and scanning of x-rays, has been developed and demonstrated. The new technique has the ability to overcome many of the limitations associated with available methods. The system is based on the focus and scanning of low energy, hard x-rays such as those emanating from table top copper or molybdenum sources. The x-rays are focused into a narrow and intense line image which can be swept onto targets that fluoresce secondary x-ray radiation. By monitoring the secondary radiation intensity and comparing it with the focused x-ray image's position as it is swept over the target edge, the position of the target edge relative to the focused image can be determined. The present system has a resolution of 0.5 micron, which has been shown to be limited by bearing backlash (or 'yaw' error) in the linear translation table. Its use has been demonstrated in the presence of an open flame with a resultant target temperature in excess of 2000 degrees Fahrenheit (1000 degrees Celsius). Strain measurements have been conducted in a laboratory environment at both room temperature and at a specimen temperature of 1300 degrees Fahrenheit, with an accuracy of within 20 microstrain (primarily a function of the 0.5 micron resolution limit). The main advantage of the technique lies in the penetrating, non-refractive nature of x-rays, which are virtually immune to the presence of refracting gas layers, smoke, flame or intense thermal radiation

Development of Sensors Using Evanescent Wave Interactions in Sapphire Optical Fibers

The development of tunable diode laser absorption sensors for measurements in industrial boilers, both through direct absorption and evanescent wave absorption have been performed in the work presented here. These sensors use both direct and indirect absorption through the use of evanescent interactions within a coal firing combustion environment. For the direct absorption sensor, wavelength modulation absorption spectroscopy with second-harmonic detection was implemented within a physical probe designed to be placed with the flue stack of a power plant. Measurements were taken of carbon dioxide and water vapor concentration during operation at a local industrial facility. The design of this sensor probe overcomes problems of beam steering and permits a reference gas measurement. Extracted concentration data and design elements from the direct absorption measurements are presented. In addition, development of a sapphire fiber-based sensor using evanescent wave absorption along the outside of the fiber is presented. Evanescent absorption allows for the laser transmission to be maintained in the fiber at all times and may alleviate problems of background emission, beam steering, and especially scattering of the laser beam from solid particles experienced through free path direct absorption measurements in particulated flows. Laboratory measurements using evanescent fiber detection are presented

Second language (L2) gains through digital game-based language learning (DGBLL): A meta-analysis

Studies on digital game-based language learning (DGBLL) have increased in numbers, creating a pool of studies that can be meta-analyzed to measure the overall effect of digital gaming on second language (L2) development. The current meta-analysis targets digital games that were available to the public at the time of data collection, January of 2020, aggregating their effects on L2 development overall and across a number of moderator variables. These moderator variables include the game developers’ intended purpose of the game (educational or entertainment), outcome measures (e.g., vocabulary, overall proficiency), and several game design features such as the type of player interaction (single player, multiplayer, massively multiplayer online), among others. Results indicate that DGBLL has had a small to medium positive effect (Cohen’s dweighted = 0.50) for between-groups designs and a medium effect (dweighted = 0.95) for within-group designs. Games designed for entertainment were found to be more effective than those designed for L2 education, although there is some overlap in the 95% confidence intervals of the two groups. The overall findings and those from additional moderator analyses are discussed in light of previous DGBLL findings while offering direction for future research and recommendations for improving the methodological rigor and transparency in DGBLL research

Chemical and physical properties of bulk aerosols within four sectors observed during TRACE-P

Chemical and physical aerosol data collected on the DC-8 during TRACE-P were grouped into four sectors based on back trajectories. The four sectors represent long-range transport from the west (WSW), regional circulation over the western Pacific and Southeast Asia (SE Asia), polluted transport from northern Asia with substantial sea salt at low altitudes (NNW) and a substantial amount of dust (Channel). WSW has generally low mixing ratios at both middle and high altitudes, with the bulk of the aerosol mass due to non-sea-salt water-soluble inorganic species. Low altitude SE Asia also has low mean mixing ratios in general, with the majority of the aerosol mass comprised of non-sea-salts, however, soot is also relatively important in this region. NNW had the highest mean sea salt mixing ratios, with the aerosol mass at low altitudes (\u3c2 km) evenly divided between sea salts, non-sea-salts, and dust. The highest mean mixing ratios of water-soluble ions and soot were observed at the lowest altitudes (\u3c2 km) in the Channel sector. The bulk of the aerosol mass exported from Asia emanates from Channel at both low and midaltitudes, due to the prevalence of dust compared to other sectors. Number densities show enhanced fine particles for Channel and NNW, while their volume distributions are enhanced due to sea salt and dust. Low-altitude Channel exhibits the highest condensation nuclei (CN) number densities along with enhanced scattering coefficients, compared to the other sectors. At midaltitudes (2–7 km), low mean CN number densities coupled with a high proportion of nonvolatile particles (≥65%) observed in polluted sectors (Channel and NNW) are attributed to wet scavenging which removes hygroscopic CN particles. Low single scatter albedo in SE Asia reflects enhanced soot