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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.

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990 records · Page 55
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Coupling dynamic in situ X-ray micro-imaging and indentation: A novel approach to evaluate micromechanics applied to oil shale

Oil and gas shales are a system where understanding the mechanical properties at the microscale is of paramount importance, e.g. to better understand the behavior of proppant-shale contacts and their role in the evolution of propped fractures in unconventional reservoirs. Here we show for the first time an experiment coupling indentation testing with in situ X-ray imaging in a Green River shale sample. A full compliance curve has been measured with the sample in water, allowing to visualize the indentation of the sample in function of axial load, in a purpose-built system for combined in situ indentation and X-ray imaging. A series of 3D datasets were used for a digital volume correlation study to obtain local strain fields. This analysis has been complemented with the analysis of cracks. Finally, geomechanical modeling has been carried out to replicate and generalize the observed behavior in the shale. This study validated this experimental approach, providing a breakthrough in understanding micro-mechanics in shales, and demonstrates how this class of experiments can be important for studies involving the prediction of the evolution of propped fractures in shale reservoirs, with possible applications in a much larger number of application fields (geothermal, materials science, etc.)

04 OIL SHALES AND TAR SANDS↗
DOE OSTI2020

Effect of nickel on the kinematic stability of retained austenite in carburized bearing steels – In-situ neutron diffraction and crystal plasticity modeling of uniaxial tension tests in AISI 8620, 4320 and 3310 steels

The presence of kinematically metastable retained austenite in the microstructure of bearing components can significantly affect the macro and micro-mechanical material response. In the present work, the influence of Ni on the stability of the retained austenite within three different grades of high carbon bearing steel using in-situ neutron diffraction is investigated. For the first time, the results show that presence of Ni increases the stability of the austenite in the elastic regime whereas the transformation rate remains unaffected. Crystal plasticity finite element (CPFE) modeling was used to study the deformation in these three steels and shows that the predominant factor causing the difference in mechanical behavior of these steels is the austenite stability. Finally, the elastic and plastic response of the matrix martensite was found to be identical among all specimens while the austenite demonstrates similar elastic behavior but remarkably different stabilities under monotonic loading.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Modeling plasticity-mediated void growth at the single crystal scale: A physics-informed machine learning approach

Modeling the evolution of voids during plastic flow as well as their effects on plastic dissipation is critical for both component manufacturing and lifetime estimation purposes. To this end, we propose a rate-dependent constitutive model to homogenize the effects of semi-randomly distributed voids on single crystal plasticity whilst capturing void interaction and plastic anisotropy. Here, this present work focuses on the case of face centered cubic crystals to introduce an anisotropic gauge function applicable within the crystal plasticity formalism. The approach combines analytical methods to describe the micromechanics of the system in combination with symbolic regression to capture analytically intractable mechanisms from data. The hybrid framework uses a physics-informed genetic programming-based symbolic regression algorithm to solve a multiform optimization problem simultaneously producing a new gauge function and a new strain rate equation. This is also a multi-objective optimization problem with many competing objectives. A new search and selection step is introduced to the genetic algorithm that promotes convergence toward a global solution that better satisfies all the objectives. Overall, the symbolic equations produced leverage data-driven methods to achieve greater accuracy than comparable alternatives on an analytically intractable problem while maintaining model transparency.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Plasticity and fracture behavior of Inconel 625 manufactured by laser powder bed fusion: Comparison between as-built and stress relieved conditions

In this work, the influence of stress relief on the plasticity and fracture behavior of Inconel 625 fabricated through laser powder bed fusion additive manufacturing (AM) was investigated. The as-built versus stress relieved microstructures were compared, showing similar grain structures but the presence of ~10 vol % δ phase in the stress relieved condition, and no δ phase in the as-built condition. Mechanical tests under plane strain tension were performed on the stress relieved samples, and an anisotropic plasticity model was calibrated and validated using finite element simulations. Uniaxial and notched tension tests were performed on both as-built and stress relieved samples to probe the effect of stress relief on stress state- and direction-dependent fracture behavior. It was found that on average, the fracture strain of the stress relieved samples along the build direction was 30% higher than that along the perpendicular build direction in the stress state range studied, and the stress relief heat treatment resulted in a 45% decrease in fracture strain. The fracture strain in stress relieved samples was more strongly dependent on stress state than in as-built samples.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Comparison of cracking behavior of nanocrystalline Cu film on substrates of different plastic deformation mechanisms

Nanocrystalline (NC) metallic thin films on metal substrates usually undergo substantial cracking at applied strains of a few percent due to strain concentration at the film/substrate interfaces. In this work, we show that the cracking of a nanocrystalline Cu film can be significantly inhibited by a NiTi substrate. NC Cu films are deposited on 304 stainless steel, Kapton and NiTi substrates, in which plastic deformation occurs via dislocation slip, molecule chain disentanglement and collective lattice shear, respectively. NC Cu film on NiTi substrate starts to show observable cracks at an applied strain of 24%, in contrast to 6% for that on steel and 15% for that on Kapton. Further, the crack density in the film on NiTi substrate is two to three orders lower than the counterparts. The discrepancy is suggested to attribute to the reduced local strain concentration enabled by the uniform lattice shear and high strain hardening of the NiTi substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nonlinear deformation and elasticity of BCC refractory metals and alloys

Application of isotropic pressure or uniaxial strain alters the elastic properties of materials; sufficiently large strains can drive structural transformations. Linear elasticity describes stability against infinitesimal strains, while nonlinear elasticity describes the response to finite deformations. Here, it was previously shown that uniaxial strain along [100] drives refractory metals and alloys towards mechanical instabilities. These include an extensional instability, and a symmetry-breaking orthorhombic distortion caused by a Jahn-Teller-Peierls instability that splays the cubic lattice vectors. Here we analyze these transitions in depth. Eigenvalues and eigenvectors of the Wallace tensor identify and classify linear instabilities in the presence of strain. We show that both instabilities are discontinuous, leading to discrete jumps in the lattice parameters. We provide physical intuition for the instabilities by analyzing the changes in first-principles energy, stress, bond lengths, and angles upon application of strain. Electronic band structure calculations show differential occupation of bonding and antibonding orbitals, driven by the changing bond lengths and leading to the structural transformations. Strain thresholds for these instabilities depend on the valence electron count.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Deformation behavior of crystalline/amorphous Al-Si nanocomposites with nanolaminate or nanofibrous microstructures

Deformation mechanisms in sputter-deposited crystalline Al/amorphous Si nanocomposites with nanolaminate or nanofibrous morphology are characterized by nanoindentation, micropillar compression testing and transmission electron microscopy (TEM). The nanofibrous composite having crystalline Al nanofibers with ~40–50 nm in length and 15–20 nm in diameter embedded in amorphous Si exhibits strain hardening to a maximum flow stress of 2.9 GPa and no shear band (SB) formation in compression up to plastic strain exceeding 24%. On the other hand, nanolaminate composite that is composed of 80 nm crystalline Al layers and 20 nm amorphous Si layers exhibits catastrophic SBs starting at plastic strains in the range of 5–10%. Cross-sectional TEM of the deformed samples reveals a high density of stacking faults and twin boundaries in Al nanofibers and no microshear bands in the nanofibrous composite, suggesting plastic deformation in amorphous Si phase and crystalline Al nanofibers. Further, molecular dynamics simulations revealed that the plastic deformation in amorphous Si phase in the cosputtered films could be favored by the decrease in flow strength of amorphous Si with increasing Al solute concentration trapped in Si.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Adaptation of Wallace's approach to the specific heat of elemental solids with significant intrinsic anharmonicity, particularly the light actinide metals

The quasiharmonic approximation is the most common method for modeling the specific heat of solids; however, it fails to capture the effects of intrinsic anharmonicity. In this study, we introduce the “elastic softening approximation,” an alternative approach to modeling intrinsic anharmonic effects on thermodynamic quantities, which is grounded in Wallace's thermodynamic framework that tracks entropy changes resulting from the continuous change (e.g., softening) of phonons as a function of temperature. A key finding of our study is a correlation between Poisson's ratio and the differential rate of phonon softening at finite frequencies, compared to lower frequencies relevant to elastic moduli measurements. We observe that elemental solids such as α -Be, diamond, Al, Cu, In, W, Au, and Pb, which span a wide range of Poisson's ratios and exhibit varying degrees of intrinsic anharmonicity, consistently follow this trend. When applied to α -U, α -Pu, and δ -Pu, our method reveals unusually large anharmonic phonon contributions at elevated temperatures across all three light actinide metals. These findings are attributed to the unique combination of enhanced covalency and softer elastic moduli inherent in the actinides, potentially influenced by their 5 f -electron bonding. Published by the American Physical Society 2025

36 MATERIALS SCIENCE↗
DOE OSTI2021

Unveiling enhanced oxidation resistance and mechanical integrity of multicomponent ultra–high temperature carbides

The development of a new class of multicomponent ultra-high temperature ceramics (MC-UHTCs), often referred to as high-entropy UHTCs, has gained increased interest due to the possibility of improved thermomechanical and oxidation properties. In this study, a systematic approach by gradual addition in the UHTC components ranging from a binary to a dense quaternary (Ta,Nb,Hf,Ti)C is synthesized using spark plasma sintering (SPS). The solid solutioning was the critical factor in homogenizing the composition in the multicomponent system. The segregation of NbC and HfC was seen in binary and ternary UHTC systems, while a single-phase homogeneity was observed in the quaternary UHTC improving its hardness up to 34.8 GPa. The presence of closely spaced slip lines in the MC-UHTCs enhances resistance to indentation damage up to 72% at an applied load of 200 N. The formation of complex mixed oxide phase of Hf6Ta2O17 ensued in the lower to negligible oxidation even up to 3 min of plasma exposure with temperature exceeding 2800°C. In sum, though the entropy remains medium (0.96R) for the selected system, the quaternary UHTC system undoubtedly has significantly better thermomechanical performance when compared to established baseline UHTCs. Furthermore, this raises the debate on the justification for calling a multicomponent system a “high entropy” to be seen in a new light. The developed MC-UHTCs elicits the paradigm of this new class of UHTCs expanding their potential in thermal protection systems for hypersonic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

In Situ Synchrotron X-ray Study of the Mechanical Properties of Pure Mg Produced by Powder Metallurgy

In this study, in situ synchrotron X-ray experiments with wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) detectors were performed on two pure magnesium materials produced by powder metallurgy. According to SAXS analysis, each of the two materials has a porosity of less than 0.5%. Line broadening analysis was performed on diffraction patterns collected by WAXS to analyze the dislocation evolution during material deformation. In both materials, $<$a$>$-type dislocation activities dominate the tensile deformation. The influence of grain size and texture on the different tensile behaviors of these two materials is also discussed.

line profile analysis (LPA)↗