Search Results (44)

This study reports a first-principles investigation of the structural, mechanical, electronic, and vibrational properties of In₃Sc in several crystal structures: AuCu₃ (Pm$\overline{3}$m), Al₃Ti (I4/mmm), Ni₃Sn (P6₃/mmc), and BiF₃ (Fm$\overline{3}$m), with a focus on pressure effects. Calculated equilibrium lattice constants, bulk, shear, and Young’s moduli show good agreement with experimental and theoretical data, especially for the cubic AuCu₃ phase. Elastic constants, examined with the Born stability criteria, reveal that the cubic (SG 221), tetragonal (SG 139), and hexagonal (SG 194) phases are mechanically stable at zero pressure, while the BiF₃-type cubic (SG 225) is unstable. Pressure-dependent variations in lattice parameters, bulk modulus, and elastic moduli, captured by polynomial fits, demonstrate stiffening effects and pressure-induced phase transitions. Band structures and density of states confirm metallicity in all stable phases, with In–Sc hybridization governing bonding. Phonon dispersions and Grüneisen parameters, calculated under compression, establish the dynamical stability of the mechanically stable structures and provide insight into vibrational and thermal behavior. Debye temperature and sound velocities highlight favorable thermal-transport features. Altogether, the results clarify the intrinsic mechanical and thermodynamic response of In₃Sc, supporting its potential as a promising intermetallic for structural and functional use under extreme conditions. Full article

In this study, we propose a novel energetic structural material, HfZrTi(TaNbV)_x (x = 0.1, 0.3, 0.5, 0.7, 0.9, Ta:Nb: V = 1:1:1), to improve the ductility and toughness of the HfZrTi high-entropy alloy (HEAs). The transformation of the single-phase Hexagonal Close-Packed (HCP) HfZrTi-based alloy into a Body-Centered Cubic (BCC) phase HfZrTiTaNbV alloy can be achieved by tuning the concentration of Group VB β-stabilizing elements. The proposed alloy combines the insensitivity and excellent mechanical strength of conventional inert alloys with the ability to react with air under high-velocity impact for energy release. The mechanical properties and energy release characteristics of HZTX_x (H = Hf, Z = Zr, T = Ti, X = TaNbV) at various strain rates are systematically investigated, and comprehensive microstructural characterization is performed, establishing a clear structure–property relationship. Under high-rate loading, the rapid oxidation of reactive elements, such as Hf and Zr, with atmospheric oxygen releases substantial chemical energy, which can be further enhanced by an adiabatic temperature rise, inducing local thermal softening through adiabatic shear bands. This study elucidates the connection between the deformation response mechanism of HZTX_x under dynamic loading and the microstructure, providing crucial insights for advancing the application of high-entropy alloys in energetic systems. Full article

Internal waves play a critical role in material transport, vertical mixing, and energy dissipation within stratified aquatic systems. Their dynamics are strongly modulated by thermal stratification and surface meteorological forcing. This study examines the influence of interannual meteorological variability from 1980 to 2010 on internal wave behavior using a series of numerical simulations in Lake Biwa in Japan. In each simulation, air temperature, wind speed, or precipitation was perturbed by ±2 standard deviations relative to the climatological mean. Power spectral analysis of simulated velocity fields was conducted for the surface, thermocline, and bottom layers, focusing on super-inertial (6–16 h), near-inertial (~16–30 h), and sub-inertial (>30 h) frequency bands. The results show that higher air temperatures intensify stratification and enhance near-inertial internal waves, particularly within the thermocline, whereas cooler conditions favor sub-inertial wave dominance. Increased wind speeds amplify internal wave energy across all layers, with the strongest effect occurring in the high-frequency band due to intensified wind stress and vertical shear, while weaker winds suppress wave activity. Precipitation variability primarily affects surface stratification, exerting more localized and weaker impacts. These findings highlight the non-linear, depth-dependent responses of internal waves to atmospheric drivers and improve understanding of the coupling between climate variability and internal wave energetics. The insights gained provide a basis for more accurate predictions and sustainable management of stratified aquatic ecosystems under future climate scenarios. Full article

This study numerically investigates the solid–liquid mixing characteristics in solid–liquid stirred tanks with solid volume fraction as high as 35%, focusing on the effect of impeller and baffle configurations on solid and liquid flow behaviors. Three stirred tanks with different capacities and impellers were analyzed to evaluate liquid flow field, solid suspension, and free surface profiles. It has demonstrated superior shear rate uniformity in the multi-impeller systems compared to the single-impeller, attributed to the enhanced fluid circulation. Multi-impeller systems can achieve near-complete off-bottom suspension, while the single-impeller configuration exhibited band-shaped particle accumulation above the impeller. Free surface vortices, significantly deeper in the 6 m³ multi-impeller tank due to high blade tip velocities, were mitigated through the integration of four circumferentially arranged triangular baffles. The existence of baffles can suppress surface turbulence, promote axial flow patterns, and eliminate particle accumulation at the tank bottom, improving shear rate and solid concentration homogeneity. These findings provide a beneficial guideline for the optimization of solid–liquid mixing efficiency the similar flow system or processes. Full article

An absolutely conflicting value for the incorporation of the Lode parameter into a fracture criterion was reported in the literature when predicting the ballistic resistance of metallic plates failing through shear plugging. In this study, a combined experimental–numerical investigation was conducted to understand the dynamic shear fracture behavior under compression–shear stress states. Flat-hat-shaped specimens of 30CrMnSiNi2A high-strength steel were loaded using a Split Hopkinson Pressure Bar apparatus, combining the ultra-high-speed photography technique, digital image correlation method, and microstructure observation. Parallel finite element simulations were performed using both a modified Johnson–Cook (MJC) fracture criterion or an extended Xue–Wierzbicki (EXW) fracture criterion with Lode dependence to reveal the value of the Lode parameter incorporation. It was found that deformed shear bands with a width of approximately 0.14 mm form at a critical impact velocity. The EXW criterion correctly predicts the critical fracture velocity and estimates the fracture initiation instants within an error of 5.3%, whereas the MJC fracture criterion overestimates the velocity by 14.3%. Detailed analysis shows that the EXW criterion predicts a combined failure mechanism involving ductile fracture and material instability, while the MJC fracture criterion attributes the failure exclusively to material instability. The improved accuracy achieved by employing the Lode-dependent EXW fracture criterion may be attributed to the compression–shear stress state and the accurate prediction of the failure mechanism of the dynamic shear fracture. Full article

Bands of interdendritic porosity and positive macrosegregation are commonly observed in pressure die castings, with previous studies demonstrating their close relation to dilatant shear bands in granular materials. Despite recent technological developments, the micromechanism governing dilatancy in the high-pressure die casting (HPDC) process for alloys between liquid and solid temperature regions is still not fully understood. To investigate the influence of fluid flow and the size of externally solidified crystals (ESCs) on the evolution of dilatant shear bands in HPDC, various filling velocities were trialled to produce HPDC samples of Al8SiMnMg alloys. This study demonstrates that crystal fragmentation is accompanied by a decrease in dilatational concentration, producing an indistinct shear band. Once crystal fragmentation stagnates, the enhanced deformation rate associated with a further increase in filling velocity (from 2.2 ms⁻¹ to 4.6 ms⁻¹) localizes dilatancy into a highly concentrated shear band. The optimal piston velocity is 3.6 ms⁻¹, under which the average ESC size reaches the minimum, and the average yield stress and overall product of strength and elongation reach the maximum values of 144.6 MPa and 3.664 GPa%, respectively. By adopting the concept of force chain buckling in granular media, the evolution of dilatant shear bands in equiaxed solidifying alloys can be adequately explained based on further verification with DEM-type modeling in OpenFOAM. Three mechanisms for ESC-enhanced dilation are presented, elucidating previous reports relating the presence of ESCs to the subsequent shear band characteristics. By applying the physics of granular materials to equiaxed solidifying alloys, unique opportunities are presented for process optimization and microstructural modeling in HPDC. Full article

Accurately measuring river flow is not only crucial for hydrologists monitoring hydrological processes but also important for all professionals involved in hydrological research. The ultrahigh frequency (UHF) band enables the surface flow velocity measurement at a deeper effective water depth, so it is less susceptible to the influence of wind drift. However, in curved river channels, the spatial variation in surface velocity is caused by the uneven erosion of the water flow, and this variation is influenced by both air shear stress and the curvature of the river. To mitigate the impact of water level on cross-sectional flow velocity estimation and address the nonlinear relationship between cross-sectional area and water level, this paper proposes a model that is independent of river water level. The nonlinear relationship between cross-sectional area and water level is calculated using a Taylor series expansion. The model was validated using experimental data collected from the Xiantao section of the Han River in Hubei, China, from March to July 2018. The data were discussed separately for high-flow and low-flow periods and were divided into training and validation sets in an 8:2 ratio. Compared to the previous method, our improved method reduces the Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE) by approximately 2%. In the estimation of flow during the dry season, the improved method achieved a correlation coefficient of 0.9523, representing an increase of 0.1243 compared to the original method. The RMSE was 23.0383, and the MAPE was 0.0232, showing reductions of 23.144 and 0.0241, respectively, compared to the original method. In the estimation of discharge during the wet season, the improved method achieved a correlation coefficient of 0.9908, an increase of 0.0575 compared to the original method. The RMSE was 65.4929, and the MAPE was 0.0391, reflecting reductions of 75.1271 and 0.0338, respectively, compared to the original method. This advancement further enhances the application of UHF radar for discharge measurement in meandering rivers. Full article

The transition from ductile to brittle for metals is usually encountered during fast machining operations, in low-temperature environments, and in all situations involving very high strain rates. Traditionally, classical material models used in the dynamic structural analysis focus on the plastic-stress-versus-strain rate. As a result, those models cannot incorporate sudden changes in failure strains and strengths triggered by material behavior transition. The ability to predict realistically the dynamic behavior of structures based on physical constitutive equations depends on having a comprehensive understanding of such drastic changes in material behavior. This transition is described by the DAMP-PLAST model, incorporating constitutive equations and governed by the shear band speed parameter at a finite time. After the development of the equation set, the material model is tested in regard to its ability to produce three distinguished material responses: elastic-plastic, elastic–plastic with strain-rate sensitivity, and brittle with increased dynamic failure strength. The study identifies metal dynamic brittleness linked to a critical loading rate influencing the plastic flow process. Based on this relation, the identification of the critical loading rate using split Hopkinson bar apparatus, and material constitutive equation is proposed. Full article

The relationship between acoustic parameters and the microstructure of a Cu30Zn brass plate subjected to plastic deformation was evaluated. The plate, previously annealed at 550 °C for 30 min, was cold rolled to reductions ranging from 10% to 70%. Linear ultrasonic measurements were performed on each of the nine specimens, corresponding to the nine different reductions, using the pulse-echo method to record the times of flight of longitudinal waves along the thickness axis. Subsequently, acoustic measurements were conducted to determine the nonlinear parameter $\beta$ through second harmonic generation. Microstructural analysis, carried out by X-ray diffraction, Vickers hardness testing, and optical microscopy, revealed an increase in deformation twins, reaching a maximum at 40% thickness reduction. At higher deformations, the microstructure showed the generation and proliferation of shear bands, coinciding with a decrease in the twinning structure and an increase in dislocation density. The longitudinal wave velocity exhibited a 0.9% decrease at 20% deformation, attributed to dislocations and initial twin formation, followed by a continuous increase up to 2% beyond this point, resulting from the combined effects of twinning and shear banding. The nonlinear parameter $\beta$ displayed a notable maximum, approximately one order of magnitude greater than its original value, at 40% deformation. This peak correlates with a roughly tenfold increase in twinning fault probability at the same deformation level. Full article

Along with the familiar Rossby–Haurwitz waves, two-dimensional flows on the surface of a rotating sphere in the regime of zonostrophic turbulence harbor another class of waves known as zonons. Zonons are wave packets produced by energetic large-scale Rossby–Haurwitz wave modes ‘enslaving’ other wave modes. They propagate westward with the phase speed of the enslaving modes. Zonons can be visualized as enslaving modes’ ‘ringing’ in the enslaved ones with the frequencies of the former, the property that renders zonons non-dispersive. Zonons reside in high-shear regions confined between the opposing zonal jets yet they are mainly attached to westward jets and sustained by the ensuing barotropic instability. They exchange energy with the mean flow while preserving their identity in a fully turbulent environment, a feature characteristic of solitary waves. The goal of this study is to deepen our understanding of zonons’ physics using direct numerical simulations, a weakly non-linear theory, and asymptotic analysis, and ascertain that zonons are indeed isomorphic to solitary waves in the Korteweg–de Vries framework. Having this isomorphism established, the analysis is extended to eddies detected in the atmospheres of Jupiter and Saturn based upon the observed mean zonal velocity profiles and earlier findings that circulations on both planets obey the regime of zonostrophic macroturbulence. Not only the analysis confirms that many eddies and eddy trains on both giant planets indeed possess properties of zonons, but the theory also correctly predicts latitudinal bands that confine zonal trajectories of the eddies. Full article

The formation of flow-induced, oriented structures in two-phase systems, as in this study, is a phenomenon of considerable interest to the scientific and industrial sectors. The main difficulty in understanding the formation of bands of droplets is the simultaneous interplay of physicochemical, hydrodynamic, and mechanical effects. Additionally, banded structure materials frequently show multiple length scales covering several decades as a result of complex time-dependent stress fields. Here, to facilitate understanding a subset of these structures, we studied water in oil emulsions and focused on the effects of three variables specifically: the confinement factor$(Co=2R/H)$, the viscosity ratio $\left(p\right),$ and the applied shear rate $\left(\dot{\gamma }\right)$. The confinement $\left(Co\right)$ is the ratio between the drop’s diameter ($2R$) and the separation of (the gap between) the circular rotating disks ($H$) containing the emulsion. We carried out (a) observations of the induced structure under different simple shear rates, as well as (b) statistical and morphological analysis of these bands. At low shear rates, the system self-assembles into bands along the direction of the flow and stacked normal to the velocity gradient direction. At higher shear rates is possible to observe bands normal to the vorticity direction. Here, we show that a detailed analysis of the dynamics of the band structures is amenable, as well as measurements of flow field anomalies simultaneously observed. The local emulsion viscosity varies in time, increasing in regions of higher droplet concentration and subsequently inducing velocity components perpendicular to the main flow direction. Thus, the emulsion morphology evolves and changes macroscopically. A relatively plausible explanation is attributed to the competitive effects of coalescence and the rupture of drops, where $p$ values less than one predominate coalescence. Full article

The temporal and spatial evolution of shear banding during startup and steady-state shear flow was studied for solutions of entangled, linear, monodisperse polyethylene ${\mathrm{C}}_{3000}{\mathrm{H}}_{6002}$ dissolved in hexadecane and benzene solvents. A high-fidelity coarse-grained dissipative particle dynamics method was developed and evaluated based on previous NEMD simulations of similar solutions. The polymeric contribution to shear stress exhibited a monotonically increasing flow curve with a broad stress plateau at intermediate shear rates. For startup shear flow, transient shear banding was observed at applied shear rates within the steady-state shear stress plateau. Shear bands were generated at strain values where the first normal stress difference exhibited a maximum, with lifetimes persisting for up to several hundred strain units. During the lifetime of the shear bands, an inhomogeneous concentration distribution was evident within the system, with higher polymer concentration in the slow bands at low effective shear rate; i.e., $\dot{\gamma }<{\tau }_R^{-1}$, and vice versa at high shear rate. At low values of applied shear rate, a reverse flow phenomenon was observed in the hexadecane solution, which resulted from elastic recoil of the molecules within the slow band. In all cases, the shear bands dissipated at high strains and the system attained steady-state behavior, with a uniform, linear velocity profile across the simulation cell and a homogeneous concentration. Full article

Montmorillonite clay (MMT) has been widely used in engineering and environmental applications as a landfill barrier and toxic waste repository due to its unique property as an expandable clay mineral that can absorb water easily. This absorption process rendered MMT to be highly exothermic due to electrostatic interactions among molecules and hydrogen bonds between surface atoms. A detailed study of a large supercell model of structural clay enables us to predict long-term nuclear waste storage. Herein, a large solvent MMT model with 4071 atoms is studied using ab initio density functional theory. The DFT calculation and analysis clarify the important issues, such as bond strength, solvation effect, elasticity, and seismic wave velocities. These results are compared to our previous study on crystalline MMT (dry). The solvated MMT has reduced shear modulus (G), bulk modulus (K), and Young’s modulus (E). We observe that the conduction band (CB) in the density of states (DOS) of solvated MMT model has a single, conspicuous peak at −8.5 eV. Moreover, the atom-resolved partial density of states (PDOS) summarizes the roles played by each atom in the DOS. These findings illuminate numerous potential sophisticated applications of MMT clay. Full article

In order to compare and analyze the seismic response characteristics of a safety-related nuclear structure on a non-rock site in the condition of raft and pile group foundations under unidirectional and multidirectional seismic motion input, a large-scale shaking table test of the soil-nuclear structure system was carried out in this paper. In the test, the soil was uniform silted clay, and the shear wave velocity was 213 m/s. Considering the similarity of the superstructure natural frenquency, the actual nuclear power structure was simplified to a three-story frame shear wall structure model. The annular laminated shear model box was used to take the boundary effect of soil into consideration; the seismic motions = were input in only one horizontal direction or three directions at the same time for the shaking table test, and the results were analyzed. The results of the test show that the acceleration response of the safety-related nuclear plant is affected by the directions of input seismic motion and the forms of the foundation. When the seismic motion is input simultaneously in three directions, the acceleration responses of the horizontal motion and vertical rocking of the safety-related plant are larger than those of the single-direction input. The acceleration response of the horizontal motion and vertical rocking of the safety-related structure with the pile group foundation is smaller than that with the raft foundation. The values of most frequency bands in the horizontal acceleration Fourier amplitude spectrum at the top of the pile-foundation structure are smaller than that at the top of the raft-foundation structure, while the displacement is basically the same as that of the raft-foundation structure. This is related to the relation between the frequency component of input seismic motion and the natural frequency of the structure system. Therefore, it is more reasonable to use three-dimensional seismic input in the seismic response analysis of nuclear power plants. The seismic performance of nuclear power plants can be enhanced by using pile group foundations. Full article

This contribution introduces a computerized semi-automated procedure coupled with a dedicated algorithm to improve shear wave velocity assessment and the on-site elastic damping ratio estimation of ground materials. The standard equipment of the downhole method is integrated with a horizontal geophone (guardian) placed on the field surface. Mask tapering and band multi-filter functions improve first arrival, recognizing and isolating SH-wave trains to estimate damping ratio profiles. These are computed by treating signals using a frequency–time combined approach (frequency–time packets method). The signals are corrected to consider the different source pulse amplitude, the effects of the propagation path, and scattering. The damping ratio profile is statistically computed in terms of the local drift of trend on the amplitude ratio series that would otherwise have a normal distribution centered on zero. These profiles intercept the lithology changes in the test sites and meet the damping values stemming from previous field tests and the laboratory experimental tests available in the literature regarding materials such as the ones investigated here. Full article