Material Density Variation Research Articles

Modeling pore fluid pressure and deformation in unsaturated soils under gravitational compaction and cyclic loading

Cyclic loading of fluid-bearing soils often induces excess pore water pressure, leading to accumulation of strain in the solid matrix. Additionally, variations in material density and volumetric fraction due to gravitational effects generate momentum forces, which subsequently cause deformation in the soil. In this paper, we present a mathematical framework of poroelasticity that generalizes the simultaneous action of gravitational body forces and cyclic loading to analyze solid deformation and fluid pressure dissipation in partially-saturated porous media. To account for the effect of gravity, the gradient of the vertical displacement needs to be treated as an additional dependent variable alongside pore air and water pressures.We numerically solve a mixed strain-controlled and pressure-prescribed boundary-value problem using a finite difference scheme as a representative example to quantify the impact of gravitational forces. Our results show that gravitational compaction affects both total settlement and excess pore water pressure, with its influence being particularly significant at lower water saturations, regardless of excitation frequency, soil depth, or type. The effect of gravity is more pronounced in soils with higher compressibility but appears insensitive to excitation frequency. Notably, the gravitational effect correlates linearly with the depth of the soil deposit and, therefore, should be well integrated into the consolidation theory of poroelasticity.

In-plane density gradation of shoe midsoles for optimal energy absorption performance

Midsoles are important components in footwear as they provide shock absorption and stability, thereby improving comfort and effectively preventing certain foot injuries. A strategically engineered midsole designed to mitigate plantar pressure can enhance athletic performance and comfort levels. Despite the importance of midsole design, the potential of using in-plane density gradation (deliberate variation of material density across the horizontal plane) in midsoles has been rarely explored. The present work investigated the effectiveness of in-plane density gradation in shoe midsoles using novel polyurea foams as the material candidate. Different polyurea foam densities, ranging from 95 to 350 kg/m2 were examined and tested to construct density-dependent correlative mathematical relations required for optimizing the midsole design for enhanced cushioning and reduced weight. This study combined mechanical testing and plantar pressure measurements to validate the efficacy of density-graded midsoles. The methodology introduced here is relevant to realistic walking conditions, ensured by biomechanical tests supplemented by digital image correlation analyses. An optimization framework was then created to allocate foam densities at certain plantar zones based on the required cushioning performance constrained by the local pressure. The optimization algorithm was specifically tailored to accommodate varying local pressures experienced by different areas of the foot. The optimization strategy in this study aimed at reducing the overall weight of the midsole while ensuring there were no compromises in cushioning efficacy or distribution of plantar pressure. The approach presented herein has the potential to be applied to a wide range of gait speeds and user-specific plantar pressure patterns.

Implementation of the non-reflection boundary for the seismic response analysis in the framework of non-local general particle dynamics

A thorough understanding of the seismic response of geotechnical structures has always been an aspiration for all engineers. Recently, the non-local general particle dynamics (NLGPD), which considers the variation of material density, has exhibited excellent promise in modelling extremely large deformation and dynamic problems. To extend the capacity of NLGPD to carry out seismic response analysis, four non-reflection boundaries are newly added in the framework of NLGPD in this paper. The viscous boundary allows wave energy to be absorbed by dashpot, in which a stress input method is proposed to input the seismic motion. The viscous-spring boundary can capture the elasticity recovery ability of the far-field medium. The free-field boundary achieves the free-field motion at lateral boundaries in the process of absorbing wave, and the corresponding relation between the points of the main model and the free-field column is determined. The static-dynamic unified boundary is introduced to model the transformation process from fixed boundary conditions in a static state to free field boundary conditions in dynamic analysis. Several representative numerical examples are solved to validate the feasibility of the proposed method. The numerical results show that the NLGPD method provides robustness and broad applicability for the seismic response analysis.

A review on flow and segregation of granular materials during heap formation

Segregation is an important process mainly used in industries during the flow of granular materials. A granular medium is repeatedly collected particles that have different properties like size, shape, and density. Heap formation in the industry occurs if particles with various sizes, forms, material densities or surface properties are made of bulk materials, then they spatially separate during formation of the heap. This paper provides a detailed understanding of segregation dynamics in granular flows within industrial processes. Focusing on the intricate interplay of particle characteristics, mixing phenomena, and heap formation methodology, the review delves into the essential aspects influencing the spatial separation of particles. Granular media, comprising particles with distinct properties such as size, shape, and density, undergo segregation during the flow processes commonly employed in industries. The formation of heaps becomes a consequential outcome when bulk materials consist of particles exhibiting variations in size, shape, material density, or surface properties. The comprehensive analysis within this review encompasses detailed insights into granular material flow, the intricacies of mixing, the mechanisms of segregation, and the profound effects of particle characteristics on these processes. Additionally, the paper scrutinizes various methodologies employed in industrial settings for heap formation, providing a holistic perspective on the key factors influencing segregation dynamics in granular flows. This review aims to contribute valuable insights to researchers, engineers, and practitioners involved in the optimization and control of granular material handling within diverse industrial applications.

Investigation of the unsteady thermal storage performance of metal foam dual-phase change unit thermal storage tanks in solar thermal utilization systems

The adoption of metal foam thermal energy storage (TES) tanks in solar thermal utilization systems is crucial for enhancing energy supply stability. In this study, to investigate the transient thermal storage performance of TES tanks, a model of a solar thermal utilization system integrated with solar collectors and TES tanks was established. The model was validated through a literature review and experiments. The effects of initial temperature variation of solar collectors and the addition of metal foam on the transient heat transfer characteristics and thermal efficiency of TES tanks were analyzed. The results indicate that the porous structure of metal foam restricts natural convection, thereby improving temperature drift caused by displacement due to phase change material density variation. Maintaining the same initial temperature of solar collectors, filling metal foam can avoid the occurrence of melting dead zones at the bottom of pure paraffin phase change units, leading to an enhancement in the thermal efficiency of TES tanks and a reduction of 48.44% in phase change completion time. Additionally, a low initial temperature of the solar thermal collection system contributes to improving the thermal efficiency of metal foam composite TES tanks.

Signal-Decay Based Approach for Visualization of Buried Defects in 3-D Printed Ceramic Components Imaged with Help of Optical Coherence Tomography.

We propose the use of Optical Coherence Tomography (OCT) as a tool for the quality control of 3-D-printed ceramics. Test samples with premeditated defects, namely single- and two-component samples of zirconia, titania, and titanium suboxides, were printed by stereolithography-based DLP (Digital Light Processing) processes. The OCT tomograms obtained on the green samples showed the capability of the method to visualize variations in the layered structure of the samples as well as the presence of cracks and inclusions at depths up to 130 µm, as validated by SEM images. The structural information was visible in cross-sectional images as well as in plan-view images. The optical signal measured from the printed zirconia oxide and titanium oxide samples showed strong attenuation with depth and could be fit with an exponential decay curve. The variations of the decay parameter correlated very well with the presence of defects and material variation. When used as an imaging quantity, the decay parameter projects the position of the defects into 2-D (X,Y) coordinates. This procedure can be used in real time, it reduces the data volume up to 1000 times, and allows for faster subsequent data analysis and transfer. Tomograms were also obtained on sintered samples. The results showed that the method can detect changes in the optical properties of the green ceramics caused by sintering. Specifically, the zirconium oxide samples became more transparent to the light used, whereas the titanium suboxide samples became entirely opaque. In addition, the optical response of the sintered zirconium oxide showed variations within the imaged volume, indicating material density variations. The results presented in this study show that OCT provides sufficient structural information on 3-D-printed ceramics and can be used as an in-line tool for quality control.

A Novel Approach to Quantifying the Effect of the Density of Sand Cores on Their Gas Permeability

The density of moulding mixtures used in the foundry industry plays a significant role since it influences the strength, porosity, and permeability of moulds and cores. The latter is routinely tested in foundries using different solutions to control the properties of the moulding materials that are used to make moulds and cores. In this paper, the gas permeability of sand samples was measured using a custom-made setup to obtain the gas permeability in standard units instead of the usual permeability numbers (PN) with calibrated units. The aim of the work was to explore the effect of density variations in moulding materials on their gas permeabilities. Permeability in this work is quantified in SI units, square metres [m2]. The setup works based on Darcy’s law and the numbers obtained from the measurements can be used to deduce the gas permeability, k, of a sample. Two furan resin bonded mixtures with the same grain size distribution were hand-rammed with varying compaction forces to obtain a variation in density. Cylindrical samples (50 × 50 mm) were prepared using a silica sand aggregate sourced from a Swedish lake. The results of the measurement provided the difference in gas permeability between the samples that have varying densities. The results of permeability were then extrapolated by modifying the viscosity value of the air passed through the sample. In order to find the effect of apparent density variation on the pore characteristics of the samples, mercury intrusion porosimetry (MIP) was also performed. The results were in line with the gas permeability measurements.

Development of semiempirical equation of state of binary functionally graded materials and its influence on generation of ramp compression: Comparison with bilayer graded density impactors

Ramp wave study involving graded impactors with discrete or continuous variation of material density is of immense interest for investigation of shock induced structural changes in solids. Hydrodynamic simulation of ramp wave generated by continuously changing functionally graded materials (FGM) requires accurate knowledge of its equation of state (EOS) parameters. However, theoretical as well as experimental EOS data for the same are not readily available. Current work is an attempt towards development of semiempirical EOS model for binary FGM (bFGM) wherein the density is a continuous function of position, either linearly or quadratically. This has been achieved by deriving analytical functions for density dependence of hugoniot parameters using the recently proposed kinetic energy average (KEA) model as well as commonly employed interpolation based methods. Six bFGMs with Al, Mg, and paraffin as low-impedance components and Cu and W as high-impedance ones are considered for the present study. It is shown that shock impedance of linear and quadratic bFGM can be expressed as superlinear/superquadratic functions of position. Subsequently, hydrodynamic simulation results of impact loading of thus constructed bFGMs on ultrathin Ta target are reported. The time profile of target pressure displayed signatures of quasi-isentropic compression (shock ramp). Ramp profiles obtained in our simulation are compared with those generated by recently reported [Phys. Rev. B 99, 214105 (2019)] alternate material bilayer graded density impactor (blGDI) with programmable layer thicknesses. Time profile of ramp pulse is shown to have direct correlation with spatial profile of shock impedance. Influence of associated physical parameters, such as impedance of front layer material, impedance ratio of two components, impact velocity, and mixture model of EOS on shock-ramp adiabats are explored in great detail. The merits of using low and high impedance material as one component of bFGM or blGDI in lowering target heating and enhancing peak ramp pressure are investigated theoretically. Study reveals that paraffin based bFGM with quadratic density function produces the lowest temperature and entropy.

Thermal charge carrier driven noise in transmissive semiconductor optics

Several sources of noise limit the sensitivity of current gravitational wave detectors. Currently, dominant noise sources include quantum noise and thermal Brownian noise, but future detectors will also be limited by other thermal noise channels. In this paper, we study a thermal noise source which is caused by spatial charge carrier density variations in semiconductor materials. We provide an analytical model for the understanding of charge carrier fluctuations under the presence of screening effects and show that charge carrier noise will not be a limiting noise source for third-generation gravitational wave detectors.

Multiscale Observation of the Fatigue‐Induced Damage Mechanisms in Carbon‐Black Filled Styrene‐Butadiene Rubber

AbstractFilled rubber materials exhibit a complex macroresponse characterized by stress softening, hysteresis, and dissipative heating when they are cyclically loaded. The relationship of these inelastic features to the microstructure changes is far from being fully established. This paper deals with the damage mechanisms in sulfur‐vulcanized styrene‐butadiene rubber (SBR) specimens in the diablo form reinforced with carbon‐black (CB) and zinc‐oxide (ZnO) fillers, and submitted to tension cyclic loading at room temperature. The microstructure alteration is characterized at different relevant scales and at different zones of the diabolo specimen by means of various technologies in the aim to report valuable insights about the mechanisms responsible for the macroresponse of this rubber‐filler material system. IR absorption spectra reveal that increasing filler content induces more interfacial interaction between CB and SBR chains. The environmental scanning electron microscopy (ESEM) observations show relevant altered morphologies of elastomeric chains with a predominant effect of both CB and ZnO fillers. A mesoscale observation of material density variation is presented using X‐ray computed tomography and the results are compared with those issued from ESEM.

Indentation-Induced Structural Changes in Vitreous Silica Probed by in-situ Small-Angle X-Ray Scattering

The transient (or permanent) structural modifications which occur during local deformation of oxide glasses are typically studied on the basis of short-range data, for example, obtained through vibrational spectroscopy. This is in contrast to macroscopic observations, where variations in material density can usually not be explained using next-neighbor correlations alone. Recent experiments employing low-frequency Raman spectroscopy have pointed-out this issue, emphasizing that the deformation behavior of glasses is mediated through structural heterogeneity and drawing an analogy to granular media. Here, we provide additional support to this understanding, using an alternative experimental method. Structural modification of vitreous silica in the stress field of a sharp diamond indenter tip was monitored by in-situ small-angle X-ray scattering. The influenced zone during loading and after unloading was compared, demonstrating that changes in the position of the first sharp diffraction peak (FSDP) directly in the center of the indent are of permanent character. On the other hand, variations in the amplitude of electron density fluctuations appear to fully recover after load release. The lateral extent of the modifications and their relaxation are related to the short- to intermediate-range structure and elastic heterogeneity pertinent to the glass network. With support from Finite Element Analysis, we suggest that different structural length scales govern shear and isotropic compaction in vitreous silica.

A comparison of the abrasive sanding dust emission characteristics of oil palm wood and rubberwood

With the increasing interest in using oil palm wood (OPW) in the manufacture of value-added wood products in the South East Asian region, the subject of dust emission in relation to the variable density of OPW is a matter of concern. Therefore, this study evaluated the dust emission characteristics of untreated and phenol-formaldehyde-treated OPW during the abrasive sanding process. Rubberwood was the solid wood material used in this study for comparison purposes. The abrasive sanding process was carried out using an orbital sander with aluminium oxide abrasive paper with a grit size of 150. The sample boards were weighed before and after sanding to determine the amount of stock removed. The dust concentration and dust particles diameter was influenced by the material type, material density variation, and material hardness. The study revealed that both untreated and treated OPW produced higher dust concentration and higher proportions of fine respirable dust particles compared with rubberwood during the abrasive sanding processes, and therefore, it is important for a more stringent permissible exposure level (PEL) standard for dust emission to be established for OPW processing. In this context, the existing PEL of 5 mg/m3 of dust is inappropriate and needs a revision if OPW is to be successfully used in the value-added wood products industry.

Modelling of Heat and Mass Transfer for Wire-Based Additive Manufacturing Using Electric Arc and Concentrated Sources of Energy

The paper presents a model developed by the authors and aimed to describe heat and mass transfer during wire-based additive manufacturing, when electron beam, plasma or arc are used as energy sources in case of non-consumable electrode welding. The model describes non-stationary and non-equilibrium conjugated processes of heat and mass transfer in free-surface liquid metal. The solution of differential equations of viscous fluid motion (Navier-Stokes), with convective terms and at laminar flow, has become the model base. Melting and crystallization of the metal is recognized by heat release in a two-phase region. The material density variation during phase transitions of the first and the second order can be described by introducing a certain dependence on temperature. The model is able to consider the use of preliminary and additional induction heating by changing the initial temperature and establishing an additional distributed bulk heat source. Variables for the simulation of heat and mass transfer during additive formation are the intensity and type of the heat source, the plate initial temperature, the power density distribution, the intensity of the additional bulk heating, the dependence of material thermal and physical characteristics on temperature, the characteristics of the phase transitions, the motion velocity of the heat source, the rate of wire feeding.

Efficient fault detection and diagnosis of distillation column using gamma scanning

This paper presents an efficient approach for automated fault detection and diagnosis of the distillation column by analyzing the gamma intensity variations. Gamma-ray scanning is one of the most common techniques that is used in industrial radioisotopes applications. It is used to get signals that reflect the inner details of a distillation column. These signals are gamma intensity variation that comes from material density variation in the column. In the proposed approach, the signals of each distillation column are divided into frames. Each frame contains the signal of just one column tray. Therefore, the position of the defected tray can be determined exactly in the column. Discrete wavelet transform, power density spectrum, higher order statistics (HOS), area under the curve (AUC) and correlation between signals are features that are extracted to be used in artificial neural network. The proposed results prove that the selection of HOS with correlation and AUC effectively achieves the fault detection and diagnosis approach in different high noise environments.

The role of anisotropy on the static and wave propagation characteristics of two-dimensional architectured materials under finite strains

In the current work, we analyze the role of anisotropy on the static and wave propagation characteristics of architectured materials. In particular, we study the mechanical behavior of nearly isotropic, moderately and highly anisotropic metamaterials under finite shear and normal strains. Thereupon, we quantify the effect of finite deformations with respect to their magnitude and loading direction, relating the metamaterials' initial degree of anisotropy to its finite strain static attributes. We distinguish between the effect of finite shear and normal strains, noting that highly anisotropic material designs do not uniquely entail shear strain sensitive structural behaviors. Contrariwise, we observe that finite normal loads in certain loading directions can lead to instabilities at rather low strain magnitudes already for moderately anisotropic material designs. Moreover, we show that strain-induced instabilities can be detected as negative phase velocity increments before the stiffness matrix loses its positive definiteness. What is more, we demonstrate that anisotropy and non-reciprocity can be used as mechanisms for wave propagation tuning. We provide evidence that for enhanced tuning capabilities to be observed, inner material density variations need to be exploited. The latter require the application of normal rather than shear strains, as shear deformations are volume preserving.

Numerical and experimental study on free vibration of 3D-printed polymeric functionally graded plates

The paper presents the free vibration analysis of simply supported 3D printed polymeric functionally graded (FG) plates with variation of material stiffness and density along their length. The analytical formulation based on Higher- Order Shear Deformation Theory (HSDT) accounts for both the shear deformation and thickness stretching effect by a sinusoidal variation of the displacement field across the thickness. The problem is then modelled using the finite element (FE) method. The FE solutions are obtained using linear hexahedral solid elements with spatially graded property distribution at different Gauss points, which is implemented by a subroutine (USDFLD) in the ABAQUS FE software. In order to validate the proposed graded FE solutions, experimental tests using Portable Digital Vibrometer (PDV) performed to capture the first natural frequency of designed and manufactured 3D printed polymeric FG plates. It can be concluded that the presented analytical formulation is not only accurate, but also provides for simple prediction of the free vibration of FG plates. Also, the good agreement found between the numerical models and experimental results demonstrates the effectiveness of graded solid elements in the modelling of FG plate vibration.

Static and vibration analysis of sandwich cylindrical shell with functionally graded core and viscoelastic interface using DQM

Abstract In the present paper, elasticity solution for static and free vibration analysis of sandwich cylindrical shell with functionally graded (FG) core and viscoelastic interface is carried out. Variation of Young's Module and material density of FGM core layer are assumed to obey power-law of radial coordinate with the Poisson's ratio holds to be constant. Imperfect interfaces are modeled according to the Kelvin-Voigt viscoelastic law. State space differential equations are derived using differential equations of motion as well as stress-displacement relations. For sandwich cylindrical shell with simply supported boundary conditions, these equations are solved analytically by using Fourier series expansion along the axial and circumferential direction. Whereas they are solved semi-analytically for the other cases of boundary conditions by using one dimensional differential quadrature method (DQM) along the axial coordinate. Time-dependent behavior is determined by solving first-order differential equation of sliding displacement at the viscoelastic interfaces. Numerical results are computed and compared with the reported results in literature to validate the present approach. In addition, effects of solid, elastic interfaces, different boundary conditions, time and mid radius to thickness ratio on the bending and vibration behavior of the sandwich shell are studied.

An analysis of the impact of native oxide, surface contamination and material density on total electron yield in the absence of surface charging effects

The effects of the presence of a native oxide film or surface contamination as well as variations in material density on the total electron yield (TEY) of Ru and B4C were assessed in the absence of any surface charging effect. The experimental results were analyzed using semi-empirical Monte Carlo simulations and demonstrated that a native oxide film increased the TEY, and that this effect varied with film thickness. These phenomena were explained based on the effect of the backscattered electrons (BSEs) at the interface between Ru and RuO2, as well as the lower potential barrier of RuO2. Deviations in the material density from the theoretical values were attributed to the film deposition procedure based on fitting simulated TEY curves to experimental results. In the case of B4C, the TEY was enhanced by the presence of a 0.8-nm-thick surface contamination film consisting of oxygenated hydrocarbons. The effect of the low potential barrier of the contamination film was found to be significant, as the density of the B4C was much lower than that of the Ru. Comparing the simulation parameters generated in the present work with Joy’s database, it was found that the model and the input parameters used in the simulations were sufficiently accurate.

High temperature two-phase thermal conductivity of ceramic sponges with stagnant fluid – Experimental results and correlation including thermal radiation

Experimental results for the two-phase thermal conductivity (often called “effective thermal conductivity”) with stagnant fluid at temperatures up to 1200 K for different ceramic sponges (variation of material, porosity and cell density) are presented in this publication. A two-plate test facility was used for the experiments. Samples investigated have porosities higher than 75% and cell densities in the range of 10–45 ppi (pores per linear inch). They are made of alumina, mullite and oxidic-bonded silicon carbide. The two-phase thermal conductivity is strongly dependent on temperature, porosity and cell sizes of the sponge sample. A model based on the superposition of the two heat transfer mechanisms, thermal conduction and thermal radiation is used to predict the two-phase thermal conductivity of ceramic sponges. A model based on combination of thermal resistances is suggested for predicting the thermal conductivity. The so-called Rosseland equation is used as an initial model for predicting the part of thermal radiation on the two-phase thermal conductivity. Measurements of material properties are included in this work as model implementation requires an exact knowledge of sponge data.

Compton back scatter imaging for mild steel rebar detection and depth characterization embedded in concrete

A novel non-destructive Compton scattering technique is described to ensure the feasibility, reliability and applicability of detecting the reinforcing steel bar in concrete. The indigenously developed prototype system presented in this paper is capable of detecting the reinforcement of varied diameters embedded in the concrete and as well as up to 60mm depth, with the aid of Caesium-137(137Cs) radioactive source and a high resolution HPGe detector. The technique could also detect the inhomogeneities present in the test specimen by interpreting the material density variation caused due to the count rate. The experimental results are correlated using established techniques such as radiography and rebar locators. The results obtained from its application to locate the rebars are quite promising and also been successfully used for reinforcement mapping. This method can be applied, especially when the intrusion is located underneath the cover of the concrete or considerably at larger depths and where two sided access is restricted.