SEARCH · Engineering Papers
Results for “equations of state”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
High-pressure phase transition of olivine-type Mg 2 GeO 4 to a metastable forsterite-III type structure and their equations of state
Germanates are often used as structural analogs of planetary silicates. We have explored the high-pressure phase relations in Mg 2 GeO 4 using diamond-anvil cell experiments combined with synchrotron X-ray diffraction and computations based on density functional theory. Upon room temperature compression, forsterite-type Mg 2 GeO 4 remains stable up to 30 GPa. At higher pressures, a phase transition to a forsterite-III type (Cmc2 1 ) structure was observed, which remained stable to the peak pressure of 105 GPa. Using a third-order Birch Murnaghan fit to the experimental data, we obtained V 0 = 305.1(3) Å3, K 0 = 124.6(14) GPa, and $K'_0$ = 3.86 (fixed) for forsterite-type Mg 2 GeO 4 and V 0 = 263.5(15) Å 3 , K 0 = 175(7) GPa, and $K'_0$ = 4.2 (fixed) for the forsterite-III type phase. The forsterite-III type structure was found to be metastable when compared to the stable assemblage of perovskite/post-perovskite + MgO, as observed during laser-heating experiments. Understanding the phase relations and physical properties of metastable phases is crucial for studying the mineralogy of impact sites, understanding metastable wedges in subducting slabs, and interpreting the results of shock compression experiments.
A Proposed Common Model of Multi-phase Strength and Equation of State for a Tri-laboratory Collaboration (Working Draft 1.1)
The proposed simple common model for multiphase strength and EoS (CMMP) is meant to be sufficiently simple that each of the collaborating labs can share in a common starting point. Another objective is to start with relatively simple assumptions, which will not necessarily capture details of the physical processes, and incrementally add complexity in order to identify the minimal-needed technical detail. Through this co-evolution of model and experiment, we will better learn the importance of various theoretical approximations and where to invest future resources in experiment and model development. This simple framework is based on pressure and temperature equilibrium of all co-existing phases combined with deviatoric stress averaging through a volume fraction weighted ow stress and a volume fraction weighted shear modulus. Implementations of the framework based on equilibrium phase fractions (i.e. instantaneous kinetic rate) and for finite rate transition kinetics are proposed.
Uncertainty Quantification in High Explosives Equations of State [Slides]
In order to fit models to data, we need a way to simulate the data given a model. Our projects involved simulators for the Manganin gauge experiment and for cylinder tests, which we use to calibrate models to experiments. We call the parameters we seek to optimize the degrees of freedom (DOF). We use a Bayesian approach with its associated UQ benefits.
Polymer Equations of State and Shock-Driven Decomposition [Slides]
Summary of presentation: Polymers decompose under shock loading; Details affected strongly by porosity; and, Polymer decomposition produces non-trivial wave evolution.
A Limited-Ranged Two-Phase Iron Equation of State Model
This report describes the construction of a two-phase EOS for Fe that includes both (hcp) and liquid phases, and which is meant to be valid over the restricted range: V ϵ [4 : 7] °A 3 /atom, and T ϵ [1000 : 20000] K. It was recently used as the basis for a theoretical study of liquid → solid phase transformation kinetics in Fe which appeared in the Supplemental Material for a paper describing a series of NIF shock + ramp compression experiments aimed at constraining the high-P melt curve of Fe.
An Introduction to EOS and Navigating SESAME Equation of State Data [Slides]
Abstract not provided.
Equation of state methods for the development of accurate models in support of Co-Optima.
Abstract not provided.
Platinum equation of state to greater than 2 terapascals: experimental data and analytical models.
Abstract not provided.
GnarlyX: Eulerian multi-material hydrodynamics coupled to equation of state and hyperelastic, plastic constitutive models
GnarlyX is a new hydrocode for direct numerical simulations of the microstructural behavior of high explosives at the mesoscale. We summarize the computational framework for multidimensional, Eulerian multi-material hydrodynamics coupled to EOS and hyperelastic, plastic constitutive models. We present 1D verification tests of multi-material only and combined multimaterial and strength capabilities with comparisons to exact solutions of shock states resulting from an incident shock impacting the material interface of PBX9502 and aluminum. We show that GnarlyX performs well in capturing the resulting shock waves in examining numerical convergence with exact solutions. In later work, we will summarize the thermomechanics and multi-dimensional, parallel computing capabilities in GnarlyX with multi-dimensional verification tests.
SESAME 2163: an updated tin equation of state
This writeup summarizes a new tin EOS, which we refer to as SESAME 2163. The new EOS is very similar to SESAME 2162, containing the β, γ, δ, and ϵ solid phases and the liquid phase. The main differences in 2163 compared to 2162 are: (1) the β-γ phase boundary has been moved slightly higher in pressure, to better agree with recent measurements by Hinton et. al (2020), (2) the γ-δ phase boundary has been moved to slightly lower pressures, (3) the δ-ϵ phase boundary has been adjusted at pressures above 200 GPa to exclude the possibility of melt from the ϵ phase, with δ existing at pressures exceeding roughly 800 GPa, and (4) the melt curve has been moved to lower temperatures based on measurements and recommendations by Briggs et. al. Importantly, we also point out thatthe windows used for multiphase constructionhave changed to the δ phase. We summarize changes in plots showing comparisons of 2162 and 2163 to the relevant experimental data.
Platinum equation of state > 2 TPa: experimental data and analytical models.
Abstract not provided.
Validation of the compression regime of a new nickel equation of state.
Abstract not provided.
Structures and equation of state of gadolinium using in-situ x-ray diffraction.
Abstract not provided.
Optimization to generate equations of state for hydrogen production
Explore the source record for details and available documents.
New Equation of State for Iridium
Explore the source record for details and available documents.