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Results for “heterogeneity”
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Spatial and temporal heterogeneity of geochemical controls on carbon cycling in a tidal salt marsh
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Secondary magnesite formation from forsterite under CO2 sequestration conditions via coupled heterogeneous nucleation and crystal growth
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CrossVis: A visual analytics system for exploring heterogeneous multivariate data with applications to materials and climate sciences
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Strength and plasticity of amorphous ceramics with self-patterned nano-heterogeneities
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Attribution of heterogeneous stress distributions in low-grain polycrystals under conditions leading to damage
In high-purity polycrystalline metallic materials, voids tend to favor grain boundaries as nucleation sites due to the elevated stress states produced by granular interactions and the weakened grain boundary from the relative atomic disorder. To quantify the key factors of this elevated stress state, simple compression of a small multi-grain cylinder of body-centered cubic tantalum was simulated using a single crystal plasticity model that incorporates non-Schmid effects. Four increasingly complex synthetic microstructures were created to tractably incorporate grain boundary interactions, and a statistically significant number of combinations were performed by varying the initial crystallographic orientations of the microstructure. Most of these simulations produce the maximum von Mises stress on a grain boundary and less frequently at the multi-grain junctions. To build a statistical model for the maximum von Mises stress at the grain boundary, physically based features that could contribute to the elevated stress state were selected. Then, a learning algorithm based on information theory was used to identify which of these features contributed the most information to the data set. The identified features include a grain’s propensity to accommodate both elastic and plastic deformations and their directional components. The misalignment of the direction of each grain’s mechanical response was found to be strongly correlated to the magnitude of the stress near the grain boundary. For all of the synthetic microstructures, the statistical models produce a residual distribution that is nearly Gaussian with a variance of, at most, 10% of the prior distribution. The successful performance of the statistical model implies the correct identification of the physical features that cause severe stress localization in polycrystalline materials. The statistical models constructed here can be used to formulate a physically motivated void nucleation model which is sensitive to a microstructure’s propensity to produce elevated stress states. As a result, these statistical models also enable the design of material microstructures, in which the crystallographic orientation is chosen to resist void nucleation.
Modelling gas flow in clay materials incorporating material heterogeneity and embedded fractures
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Understanding the Role of Surface Heterogeneities in Electrosynthesis Reactions
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Recommendations to standardize reporting on the synthesis of heterogeneous catalysts
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An asymptotically compatible probabilistic collocation method for randomly heterogeneous nonlocal problems
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Adaptive multilevel space-time-stepping scheme for transport in heterogeneous porous media (ADM-LTS)
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Support for utility-scale solar: Effects of information and heterogeneity among public officials, the general population, and landowners
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Modeling the two-way coupling of stress, diffusion, and oxidation in heterogeneous CMC microstructures
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Heterogeneous Diels–Alder tandem catalysis for converting cellulose and polyethylene into BTX
Producing biomass-derived aromatic hydrocarbons via controllable Diels–Alder reactions is a promising approach to recover energy and chemicals from waste streams. A tandem Diels–Alder catalysis consisting of SAPO-34 and Fe/HZSM-5 (stacked catalysis or mixed catalysis) was evaluated for thermochemical conversion of cellulose and polyethylene blends into benzene, toluene, and xylenes (BTX). Aromatization catalyst type significantly affected the activity of tandem catalysis, and the BTX obtained from the HZSM-5 stacked catalysis was ~2.3 times higher than that of the USY stacked one. An introduction of Fe active promoters into HZSM-5 increased the Lewis to Brønsted acid sites molar ratio (L/B) from 0.4 to 4.1. The comparison between Fe/HZSM-5 stacked catalysis and parent HZSM-5 single catalysis indicated that the former was more effective for BTX production, obtaining a nearly two-fold increase in yield with a high selectivity of 82.8%. A close proximity between Fe/HZSM-5 and SAPO-34 in the mixed catalysis increased the BTX enhancement to 1.8. A synergistic effect was provided by the coordination of Lewis and Brønsted acid sites in the Fe/HZSM-5 mixed catalysts for facilitating BTX generation, achieving a maximum of 25.9% at a Fe/HZSM-5 to SAPO-34 mass ratio of 1:1 with a theoretical L/B of 7.2. Finally, this work provides a sustainable strategy to produce biomass-derived aromatic hydrocarbons.
Quantifying 3D time-resolved kinematics and kinetics during rapid granular compaction, Part II: Dynamics of heterogeneous pore collapse
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Strength-ductility synergy through microstructural and compositional heterogeneity in directed energy deposition additive manufacturing of face-centered cubic materials
Directed energy deposition (DED) is an additive manufacturing (AM) process based on welding technology and offers the advantages of large build volume, high deposition rate, and ability to fabricate multi-material parts. Epitaxial continuous columnar grain growth is a characteristic microstructural feature of DED processed alloys. In this study, a bamboo-like microstructure (periodic alternation of equiaxed and columnar structure) was produced by adopting an intermittent deposition strategy in 316L stainless steel and Inconel 625. The formation of a bamboo-like alternating microstructure was confirmed through electron backscattered diffraction (EBSD) analysis. Hardness mapping showed that the columnar to equiaxed transition (CET) occurred at the region right below the fusion line. A finite element (FE) model was used to investigate the relationship between the temperature gradient (G) and the solidification rate (R). The FE model showed a low G/R ratio at the region right below the interface promoting the CET. The grain size and material-dependent deformation behaviors are analyzed using digital image correlation (DIC). The lower deformation on the fine-grain regions observed in DIC analysis is attributed to a higher strain hardening rate, which is confirmed through dislocation density analysis on a tensile-interrupted specimen. The periodically alternating grain size coupled with the microstructural changes caused by intermittent deposition strategy result in a better strength-ductility synergy in both single-material and bimetallic specimens.