Quasi-static Region Research Articles

Numerical derivation of pressure-impulse (P-I) diagrams of prefabricated RC columns with steel joints subjected to blast loads

In recent decades, terrorist attacks and accidental explosions have occurred frequently. The casualties are not only caused by the shock wave, but also by the structural collapse initialed from the failure of structural columns. In this paper, the dynamic response and damage mechanism of prefabricated reinforced concrete (RC) columns with steel joints (PRC) subjected to blast loads are numerically investigated. By comparing the numerical results with the experimental results, the accuracy of the finite element (FE) model is firstly verified. Then, dynamic responses and damage of PRC under blast loads induced by the TNT explosions and vapor cloud explosions (VCEs) are investigated and compared with each other. The results indicated that PRC damage under VCEs with 9.3 MPa is larger than that under TNT explosions. Conversely, the damage under VCEs with 7 MPa is smaller than that under TNT explosions, and the blast-induced damage and dynamic behavior of PRC under two types of explosions is different. Subsequently, parametric studies are further carried out to investigate the influence of key parameters of PRC, including longitudinal and transverse reinforcement ratio, column dimensions, concrete strength, steel sleeve dimensions on PRC damage. It is revealed that different parameters affect the damage for PRC column in different load regions of P-I diagrams, including the impulsive load region, dynamic load region and quasi-static load region. Increasing the sleeve length, sleeve ratio and transverse reinforcement ratio improves the shear-resistant performance of PRC, and these parameters more easily affected PRC damage in the impulsive load region. Increasing the concrete strength and column depth can increase the blast-resistant performance of PRC in three load regions. Based on parametric studies, pressure-impulse (P-I) diagrams for damage evaluation of PRC under VCEs and TNT explosions are proposed and verified. Finally, Blast-resistant design procedure of PRC based on P-I diagram is developed.

Stability of granular media impacts morphological characteristics under different impact conditions

Abstract In planetary surfaces, oblique impact events are commonplace, and their study holds significant importance for understanding planetary impact processes and aiding in the design of landers and impactors. Current research predominantly focuses on simplified models to study the force and motion under vertical impact craters in terms of scale and impact loading. For oblique impacts, investigations have primarily concentrated on the final crater shape. However, the specific influence of impact load motion on particle bed movement and the precise impact angle’s effect on the ultimate crater shape during the impact process remain unclear. In this study, we used a custom-built oblique impact experimental setup to analyze changes in the velocity field of the particle bed and the horizontal movement of the impact load. Using quasi-static region to assess ellipticity, we aimed to reveal the state of particle movement during oblique impacts and explore the impact of impact angles and energies on crater formation. The results indicate that under large impact angles, the obliquely acquired kinetic energy is minimal, leading to a predominant static point source movement of the particle bed. At higher energy levels, the impact load primarily excavates downward, resulting in the formation of circular impact craters. These findings underscore the sensitivity of particle bed motion to impact angles, making it a crucial metric for assessing the impact of oblique angles on final crater morphology.

Modeling the Magnetoelectric Composites in a Wide Frequency Range.

This article presents a general theory of the ME effect in composites in the low- and high-frequency ranges. Besides the quasi-static region, the area of electromechanical resonance, including longitudinal, bending, longitudinal shear, and torsional modes, is considered in more detail. To demonstrate the theory, expressions of ME voltage coefficients are obtained for symmetric and asymmetric layered structures. A comparison is made with the experimental results for the GaAs/Metglas and LiNbO3/Metglas structures. The main microwave ME effect, consisting of the FMR line shift in an electric field, for the ferromagnetic metals, their alloys, and YIG ferrite using various piezoelectrics is discussed. In addition to analytical calculations, in the article, finite element modeling is considered. The calculation methods and experimental results are compared for some composites.

Rheology of granular rafts.

Rheology of macroscopic particle-laden interfaces, called "granular rafts," has been experimentally studied in the simple shear configuration. The shear-stress relation obtained from a classical rheometer exhibits the same behavior as a Bingham fluid, and the viscosity diverges with the surface fraction according to evolutions similar to 2D suspensions. The velocity field of the particles that constitute the granular raft has been measured in the stationary state. These measurements reveal nonlocal rheology similar to dry granular materials. Close to the walls of the rheometer cell, one can observe regions of large local shear rate while in the middle of the cell a quasistatic zone exists. This flowing region, characteristic of granular matter, is described in the framework of an extended kinetic theory showing the evolution of the velocity profile with the imposed shear stress. Measuring the probability density functions of the instantaneous local shear rate, we provide evidence of a balance between positive and negative instantaneous local shear rate. This behavior is the signature of a quasistatic region inside the granular raft.

The propagation of Quasi-static region during granular impact

In this paper, through experiments and DEM simulations, it is found that there is a ring-shaped region named Quasi-static Region between the particles expanding outward and the particles collapsing inward during the impact process. Quasi-static Region is always generated from the impact point at the same time, and then spreads out at a uniform speed. During the propagation of Quasi-static Region, the velocity of the particles in the particle extend region varies linearly in space and time. And the change rate is only related to the properties of the particle system. The simulation results show that the particle flow in Quasi-static Region is elastic-inertial flow, while the particle flow expanding outward and collapsing inward is inertial flow.

Anomalies of Brillouin Light Scattering in Selected Perovskite Relaxor Ferroelectric Crystals.

Compositionally disordered perovskite compounds have been one of the exotic topics of research during the past several years. Colossal piezoelectric and electrostrictive effects have been observed in disordered perovskite ferroelectric materials. The key ingredient in the physical behavior of disordered perovskites is the nucleation and growth of the local dipolar regions called polar nanoregions (PNRs). PNRs begin to nucleate far above the temperature of the dielectric maximum Tm and exhibit varied relaxation behavior with temperature. The evidence for the existence of various stages in the relaxation dynamics of PNRs was revealed through the study of the temperature evolution of optical phonons by Raman scattering. The quasi-static regime of PNRs is characterized by the strong coupling between the local polarization and strain with the local structural phase transition and the critical slowing of the relaxation time. Strong anomalies in the frequency and the width of the acoustic phonons, and emergence of the central peak in the quasi-static region of the relaxation dynamics of PNRs have been observed through Brillouin scattering studies. In this review, we discuss the anomalies observed in Brillouin scattering in selected disordered perovskite ferroelectrics crystals such as Pb(Mg1/3Ta2/3)O3, Pb(Sc1/2Ta1/2)O3, 0.65PIN-0.35PT and Sr0.97Ca0.03TiO3 to understand dynamical behavior of PNRs.

Recognition of a quasi-static region in a granular bed impacted with a sphere

Various characteristics such as stationary, laminar, and turbulent flow exist in the granular flow and it is critical to recognize the flow features based on the full-field velocity measurement to reveal the complex motion of granular flow. We propose a Dilated Convolution UNet++ (DC-UNet++) framework modeling of flow field images, which can recognize the features within the region in sphere impact on granular beds without using Particle Image Velocimetry (PIV). When compared with the results of the thresholding method, the accuracy of feature recognition using this model is improved by 8.3%. The accuracy of feature recognition reaches 73.44% for the flow field of transparent glass beads, which is difficult to analyze using PIV. This suggests that DC-UNet++ has a wide range of applications for granular materials that are difficult to handle using PIV and is a new tool for developing a feature recognition model for granular flow.

Static MLC transmission simulation using two-dimensional ray tracing.

PurposeWe investigated the hypothesis that the transmission function of rounded end linearly traveling multileaf collimators (MLCs) is constant with position. This assumption is made by some MLC models used in clinical treatment planning systems (TPSs) and in the Varian MLC calibration convention. If not constant, this would have implications for treatment plan QA results.MethodsA two‐dimensional ray‐tracing tool to generate transmission curves as a function of leaf position was created and validated. The curves for clinically available leaf tip positions (−20 to 20 cm) were analyzed to determine the location of the beam edge (half‐attenuation X‐ray [XR]) location, the beam edge broadening (BEB, 80%–20% width), as well as the leaf tip zone width. More generalized scenarios were then simulated to elucidate trends as a function of leaf tip radius.ResultsIn the analysis of the Varian high‐definition MLC, two regions were identified: a quasi‐static inner region centered about central axis (CAX), and an outer one, in which large deviations were observed. A phenomenon was identified where the half‐attenuation ray position, relative to that of the tip or tangential ray, increases dramatically at definitive points from CAX. Similar behavior is seen for BEB. An analysis shows that as the leaf radius parameter value is made smaller, the size of the quasi‐static region is greater (and vice versa).ConclusionThe MLC transmission curve properties determined by this study have implications both for MLC position calibrations and modeling within TPSs. Two‐dimensional ray tracing can be utilized to identify where simple behaviors hold, and where they deviate. These results can help clinical physicists engage with vendors to improve MLC models, subsequent fluence calculations, and hence dose calculation accuracy.

A P-I Diagram Approach for Predicting Dynamic Response and Damage Assessment of Reactive Power Concrete Columns Subjected to Blast Loading

Reactive power concrete (RPC) possesses high compressive strength, toughness, and durability, and it is increasingly being used in important buildings. The column is an important load-bearing member of a building, and its failure under blast loading results in building collapse. Based on these attributes, the dynamic response and the degree of damage to the RPC column are critical in assessing building performance. Due to the lack of methods, the progress of the study is relatively slow. In order to solve these issues, the dynamic response of the RPC column is studied based on the equivalent single-degree-of-freedom method and P-I curve in this paper. During the model validation phase, the deformation of the RPC column predicted using the ESDOF approach correlates well with the explosion simulation and test results. The P-I curves of the typical RPC column were also determined, and some data were analyzed to evaluate the influence of different key parameters, such as slenderness ratio, cross-sectional dimension, and axial compression ratio. The results show that the RPC column is susceptible to shear, bending, and bending-shear failure in the impulse load region, quasi-static load region, and dynamic load region, respectively. The cross-sectional dimension and slenderness ratio exhibit the greatest influence on P-I curves among the five parameters. With the increasing cross-sectional dimension and slenderness ratio, the overpressure asymptote of bending response increases by 4.2 times and decreases by about 57.3%. Furthermore, combined with the P-I curve features, it is found that reasonably increasing the cross-sectional dimensions and RPC strength could simultaneously improve the comprehensive anti-blast performance of RPC columns. This study was carried out to obtain the effect of the five parameters mentioned above on the degree of damage under different blast loading, which can provide a valuable reference for the dynamic response of RPC columns.

Synthesis of an Al – Er Addition Alloy and Its Effect on the Structure and Physico-Mechanical Properties of AMg5 Alloy

Adoption of structural materials that combine high strength with low specific weight ensures a better energy efficiency of industrial machines and equipment. An aluminium part is almost three times lighter than its steel counterpart. However, it takes high-strength materials to replace critical components that are made of steel. There are high-strength aluminium alloys that contain scandium. However, they only find limited application because of high initial cost of scandium. Erbium works similarly to scandium in terms of strengthening of aluminium alloys, and its cost is 32 times lower. The problem of developing Al – Er alloys is of relevance today. At the same time, more study is necessary to understand the effect of erbium on the overall properties of aluminium alloys. The authors looked at the effect of erbium on the structure, mechanical properties and the fracture pattern of AMg5 alloy (Al – Mg system). Due to the melting temperature difference, erbium was introduced in the aluminium melt as part of an addition alloy produced by an advanced hydriding process. This paper describes a combined study into the obtained addition alloys and as-cast and as-deformed alloys. The authors examined the alloys following a classical pattern of materials research: i.e. composition – structure – properties. Special attention was given to understanding the structure. Thus, conventional optical techniques and scanning electron microscopy were applied, including energy dispersive analysis and electron backscattered diffraction technique. Following a uniaxial tensile test, a positive effect of erbium was observed on the strength of AMg5 alloy in the quasi-static loading region. The obtained results indicate that erbium can potentially be used as a doping element for aluminium alloys. Certain actions are proposed aimed at process optimization to maximize the strengthening effect of erbium in aluminium industry.This research was funded by the Ministry of Education and Science of the Russian Federation under Governmental Assignment no. FSWM-2020-0028.This research was carried out using the facilities of the Tomsk Regional Centre of Shared Knowledge at Tomsk State University and the funding by the Ministry of Science and Higher Education of the Russian Federation received under Contract No. 075–15-2021–693 (No. 13.ЦКП.21.0012) dated 26/07/2021.

Deformation mechanism of copper reinforced by three-dimensional graphene under torsion and tension

The mechanical behaviors of uniaxial torsional and tensional copper nanorod embedded with sp2-type hybrid graphene nanosheets (3DG/Cu) were investigated systematically using molecular dynamics methods. During the torsion process, graphene expanded the plastic deformation region of copper, while the plastic deformation in monocrystalline Cu cases was limited to a smaller area. 3DG/Cu responded to the torsion by one more plastic stage when plastic deformation spread along the length after the elastic response. Graphene improved the torsional loading capacity of the composite material, greatly extending the effective response range of the material by distributing the deformation of copper along with the graphene rather than being concentrated at a certain position like monocrystalline Cu. Generally, as the length of the model increased, this enhancement decreased. The copper portion of 3DG/Cu was divided into three areas during uniaxial tensile, a static region, a quasi-static region of the middle portion where the shear and necking occurred, and a dynamic area near the loading end. However, the inside graphene kept continuous until fracture. Furthermore, graphene improved the yield strain of copper by maintaining intact after copper failure. The greater the pre-loaded torsion angle, the smaller the yield strength and Young’s modulus of 3DG/Cu.

Bias-Dependent Intrinsic RF Thermal Noise Modeling and Characterization of Single-Layer Graphene FETs

In this article, the bias dependence of intrinsic channel thermal noise of single-layer (SL) graphene field-effect transistors (GFETs) is thoroughly investigated by experimental observations and compact modeling. The findings indicate an increase of the specific noise as drain current increases, whereas a saturation trend is observed at very high carrier density regime. Besides, short-channel effects, such as velocity saturation (VS) also result in an increment of noise at higher electric fields. The main goal of this work is to propose a physics-based compact model that accounts for and accurately predicts the above experimental observations in short-channel GFETs. In contrast to long-channel MOSFET-based models adopted previously to describe thermal noise in graphene devices without considering the degenerate nature of graphene, in this work, a model for short-channel GFETs embracing the 2-D material’s underlying physics and including a bias dependence is presented. The implemented model is validated with deembedded high-frequency data from two short-channel devices at quasi-static (QS) region of operation. The model precisely describes the experimental data for a wide range of low-to-high drain current values without the need of any fitting parameter. Moreover, the consideration of the degenerate nature of graphene reveals a significant decrease of noise in comparison with the nondegenerate case and the model accurately captures this behavior. This work can also be of utmost significance from the circuit designers’ aspect since noise excess factor, a very important figure of merit for RF circuits implementation, is defined and characterized for the first time in graphene transistors.

Footstep Planning for Hexapod Robots Based on 3D Quasi-static Equilibrium Support Region

Footstep Planning for Hexapod Robots Based on 3D Quasi-static Equilibrium Support Region

Quasi-static secondary flow regions formed by microfluidic contraction flows of wormlike micellar solutions

This study investigates the effects of yield stress (τ0) and shear banding on the fluidic behaviors of cetyltrimethylammonium bromide/sodium salicylate wormlike micellar solutions flowing through a microfluidic planar contraction (8:1) geometry. Test solutions with different surfactant concentrations (Cd = 75, 87.5, and 100 mM) at a fixed molar ratio of salt to surfactant (R = 0.32) were characterized by shear and extensional rheometry. While the lower concentrated test solution (Cd = 75 mM) with low τ0 (≈ 0.02 Pa) and no shear banding showed a Newtonian-like flow behavior for Mach number, Ma < 1, the flow with corner vortices was formed when Ma exceeds unity. For higher Cd (87.5 and 100 mM), new fluidic phenomena are documented: (i) even at a low volumetric flow rate (Q), the fluid velocity at upstream corners was slower than that of Newtonian-like flows and (ii) at higher Q, the secondary flow with a quasi-static condition was formed at Ma well lower than unity. Micro-particle image velocimetry showed the lower shear rates at upstream corners, which can be understood by the effects of contraction entry, shear thinning, and high yield stress. The quasi-static secondary flow region was not induced by generation of elastic shock waves; instead the shear banding was found to be the underlying mechanism for the separation of the region from the main flow. In addition, the length of secondary flow regions showed a close correlation with the Deborah number, which was calculated using the extensional relaxation time.

Failure Behavior Analysis of Single-leaf Blast-resistant Door by Explosion Loads

For a blast-resistant structural system with concrete slab as the primary structural member, edge rotation based on flexural failure is generally used as an index to evaluate its structural performance. However, it has been predicted that short-span single-leaf blast doors are vulnerable to shear failure. In this study, limitations on the general application of the edge rotation as a performance evaluation index were reviewed using a finite element (FE) method. The results demonstrated that shear failure was dominant in the impulsive and dynamic response regions, while shear failure or flexural-shear combined failure was dominant in the quasi-static region. In the case of short-span single-leaf blast door, the concrete slab is vulnerable to shear failure, and therefore, the door should be designed considering pressure-impulse curves based on shear failure. For further study, several explosion tests and FE analyses will be required to verify the structural responses and failure level changes according to various specifications of the blast door, and to obtain a general evaluation index for its structural performance.

Related Plasmon Oscillations in a Cluster of Two Silver Nanocylinders of Different Diameter

A two-dimensional problem of the diffraction of a plane wave of the light range on a cluster consisting of two self-similar, silver nanocylinders of different diameter is considered. The frequency characteristics of the scattering diameter, the spatial distribution of the field components, and the scatterplot are calculated by strict numerical methods. The influence of the angle of incidence, the cylinder distance, the coefficient of self-similarity and silver loss on the spectra of the scattering diameter, and the scatterplot in the light wavelength range is studied. It is shown that the maximum value of the electric field component in the quasistatic region at the output of such a system cannot be more than ten times the values of the incident field.

Metamaterial With Local Resonators Coupled by Negative Stiffness Springs for Enhanced Vibration Suppression

In recent years, metamaterials for the applications in low-frequency vibration suppression and noise reduction have attracted numerous research interests. This paper proposes a metamaterial system with local resonators from adjunct unit cells coupled by negative stiffness springs. Frist, a lumped parameter model of the system is developed, and a stability criterion is derived. The band structure of the infinite lattice model is calculated. The result reveals the appearance of extra band gaps in the proposed metamaterial. A parametric study shows that the first extra band gap can be tuned to ultralow frequency by controlling the negative stiffness of the coupling springs. A transmittance analysis of the finite lattice model verifies the predictions obtained from the band structure analysis. Subsequently, the work is extended to a distributed parameter metamaterial beam model with the proposed configuration of coupled local resonators. The stability analysis shows that the infinitely long metamaterial beam becomes unstable as long as the stiffness of the coupling spring becomes negative. For the finitely long metamaterial beam, the stability could be achieved for negative coupling springs of given stiffnesses. The effects of the number of cells and the lattice constant on the system stability are investigated. The transmittance of the finitely long metamaterial beam is calculated. The result shows that due to the restriction on the tunability of negative stiffness for the proposed metamaterial beam, a quasistatic vibration suppression region can only be achieved when the number of cells is small.

Buckling Behavior of Long Strips under Various End Conditions in Quasi-Static and Dynamic Loading-Velocity Region

Buckling Behavior of Long Strips under Various End Conditions in Quasi-Static and Dynamic Loading-Velocity Region

Reduction of Thermal Conductive Flux by Non-local Effects in the Presence of Turbulent Scattering.

The heat flux in a plasma is determined by the degree of anisotropy in the particle distribution function, which is in turn driven by gradients in the ambient density and temperature. When the mean free path at the thermal speed is substantially smaller than the scale length associated with the temperature variation, the heat flux simply depends on the local value of the temperature gradient. However, when the temperature scale length and mean free path are comparable, heat conduction becomes substantially non-local in character: the magnitude of the heat flux now depends on the overall temperature profile and is generally smaller than the locally determined value. In the presence of angular scattering associated with turbulence, the mean free path (and its velocity dependence) can be significantly smaller than its collisional value; this makes the expression for the heat flux more local in character, but also results in a heat flux that is lower than that obtained through a purely collisional analysis. Therefore, whether or not turbulence is present, the heat flux is generally smaller than the value obtained from a local collisional analysis. We here present an analytic expression for the conductive heat flux in terms of a convolution of the local heat flux with a non-local kernel function that incorporates both Coulomb collisions and turbulent scattering. We comment on the need to include both non-local and turbulent scattering effects in the modeling of quasi-static active region loops and in the conductive cooling of post-flare loops.

Investigation of the influence of frictional viscosity regularization on quasi-static gas-solid flow predictions in a conical spouted bed with non-porous draft tube

The stress in the quasi-static particle flow is often modeled through the Mohr-Coulomb failure criterion. In the extension to complex three-dimensional flows, a granular viscosity is introduced through a tensorial rheology and the deviatoric frictional stress tensor is assumed aligned with the strain rate tensor. This granular viscosity is singular as the shear rate approaches zero, regardless of the local rheology. We discuss the influence of regularizing such a frictional viscosity on the particle circulation rate and other measured characteristics in a laboratory scale draft tube spouted bed. The friction between particles is modeled either with a constant Coulomb rheology or using a local particle pressure and strain-rate based friction known as μI-rheology. The predictions appear very dependent on the regularization parameter introduced by the method. The mean properties of the flow (e.g. circulation and pressure drop) monotonically converge towards the measurements when the regularization parameter tends to zero. In other respects, the two regularization models regarded in this study induced similar hydrodynamics within the spouted bed of interest. But the analysis of the conditional averages of the inertial number and the fraction of the solids in the quasi-static regime shows that the extent and staticity of the quasi-static region is sensitive to changes to the regularization parameter or regularization function.