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This study proposed a novel method for the fabrication of non-woven based microfluidic devices with a wax hydrophobic barrier. Current microfluidic devices were fabricated with glass or polymer material, and paper is also widely used for the fabrication of low-cost microfluidic devices. The application of non-woven fabric based microfluidic devices provides a new option of bulk materials for microfluidics. Compared with the glass or polymer material used in microfluidics, non-woven fabric is low-cost, easy to process and disposable. Fluid can penetrate through the non-woven fabric material with capillary force without the requirement of external pumps. As fiber-based material, comparing with paper, non-woven fabric material is more durable with higher mechanical strength, and various types of non-woven fabric material also provide a board choice of surface chemical/physical properties for microfluidic applications. In this study, the hydrophilic non-woven fabric is chosen as the bulk material for microfluidic devices, a wax pattern transfer protocol is also proposed in this study for the deposition of hydrophobic barriers. For a demonstration of the proposed fabrication technique, a microfluidic mixer was also fabricated in this study. [ABSTRACT FROM AUTHOR]

In this paper, synthesis of iron carbide in a recessed fuel oil electric arc between steel and graphite electrodes was carried out. As a result, FeC and Fe2C were found. Fe2C has a solid bulk structure. FeC is coiled into nanoballs 100–500 nm in size. The new steel will also include carbon nanotubes, which give the steel hardness and strength. [ABSTRACT FROM AUTHOR]

We present in this paper a numerical study of sandpile formation and angle of repose by considering the effect of particle shape. We analyze the micromechanical responses of sandpiles, which are crucial to the exploration of origin of angle of repose. The results show that the principal anisotropy directions of contact orientations for the left and right parts of sandpiles deviate increasingly away from the vertical direction as the particle shape becomes more irregular, and that the summation of their deviation angle $$\Delta \phi _n$$ relative to the vertical direction with angle of repose $$\alpha $$ , is approximately a constant regardless of the effect of particle shape. We find that the principal anisotropy directions of particle orientations for the left and right parts of sandpiles rotate as the irregularity of particle shape varies, and tend to reach a compromise state and to lie in the common horizontal direction at a characteristic aspect ratio AR = 0.6. We reveal that the mobilization of arching effect depends primarily on the inclined propagation of strong force chains. We also establish a relationship between the direction where the most intense arching phenomenon takes place and the principal anisotropy directions characterizing the distribution of microstructures and inter-particle force network. [ABSTRACT FROM AUTHOR]

In this paper, we report on the Boltzmann kinetic equation approach adapted for simulations of warm dense matter created by irradiation of bulk gold with intense ultrashort X-ray pulses. X-rays can excite inner-shell electrons, which triggers creation of deep-lying core holes. Their relaxation, especially in heavier elements such as gold (atomic number Z = 79 ) takes complicated pathways, involving collisional processes, and leading through a large number of active configurations. This number can be so high that solving a set of evolution equations for each configuration becomes computationally inefficient, and another modeling approach should be used instead. Here, we use the earlier introduced 'predominant excitation and relaxation path' approach. It still uses true atomic configurations but limits their number by restricting material relaxation to a selected set of predominant pathways for material excitation and relaxation. With that, we obtain time-resolved predictions for excitation and relaxation in X-ray irradiated bulk of gold, including the respective change of gold optical properties. We compare the predictions with the available data from high-energy-density experiments. Their good agreement indicates ability of the Boltzmann kinetic equation approach to describe warm dense matter created from high-Z materials after their irradiation with X rays, which can be validated in future experiments. [ABSTRACT FROM AUTHOR]

In this paper, the formulation of post-buckling of end-supported nanorods under self-weight was developed by the variational method. The surface stress effect was considered following the surface elasticity theory of Gurtin–Murdoch. The variational formulation involving the strain energy in the bulk material, the strain energy of the surface layer, and the potential energy due to self-weight was expressed in terms of the intrinsic coordinates. The variational formulation was accomplished by introducing the Lagrange multiplier technique to impose the boundary conditions. The finite element method was used to derive a system of nonlinear equations resulting from the stationary of the total potential energy, and then, Newton–Raphson iterative procedure was applied to solve this system of equations. The post-buckled configurations of nanorods under self-weight due to various boundary conditions were presented and demonstrated that the variational formulation expressed in terms of intrinsic coordinate is highly recommended for post-buckling analysis of end-supported nanorods. In addition, the surface stress effect significantly influenced the post-buckling response of nanorods and exhibited higher stiffness in comparison with nanorods without surface stress. The model formulation presented in this study is of special interest in the design and application of advanced technological devices. [ABSTRACT FROM AUTHOR]

Flow of fluids through porous media such as soil, rocks, bones, wood and concrete has been an area of interest for engineering communities that deal with porous materials. The tools developed to describe flow through porous regions are generally applied to bulk materials with single composition. In this paper, however, we demonstrate their applicability to an interface of any two contacting surfaces particularly those of the elastomer and metal in the context of sealing applications. We propose a relationship to account for change in the permeability and the thickness of the seal interface with contact pressure at the interface and fluid pressure of fluid flowing through the interface. We hence develop a porous-media-based model to describe leak of gas through metal–elastomer interface. We validate the model using nitrogen gas leak experimental data for different elastomer–metal interfaces. [ABSTRACT FROM AUTHOR]

Impaction techniques have so far been efficiently used for formation of films from nanoparticles when coupled to synthetic process. However, this approach limits the choice of shapes and compositions of particles, so techniques of impaction of ready-made particles are desirable. To this end, the use of nanoparticle inks as a source of solid material is first described in this paper. The films are cast from dispersions of polar solvent-susceptible Si/SiOx nanoparticles. Water, ethanol, and acetonitrile are studied for solvents, and the latter two are shown to be suitable, as they possess lower surface tension and lower boiling points. Microscopically uniform films of nanoparticles are formed when aerosol and substrate are heated, with density of films approaching 40% of that of the bulk material. Higher stagnation pressure is beneficial for deposition, while further heating of the aerosol beyond the solvent evaporation can cause oligomerization of the solvent. Deposition of dense films in subsonic part of the jet appears possible with the technique. [ABSTRACT FROM AUTHOR]

This paper describes the Gdx−2BaxCu2x−2Oδ (x = 6, 7) cuprate system synthesis using the conventional solid-state reaction method. Rietveld analysis of X-ray patterns evidences that samples crystallize in Pmm2 (#25) space group at room temperature with lattice parameter a = 3.8807 Å, b = 3.8735 Å, c = 38.7094 Å for Gd4Ba6Cu10Oδ and a = 3.8680 Å, b = 3.8763 Å, c = 46.5065 for Gd5Ba7Cu12Oδ. Resistivity measurements evidence zero-resistance state, which is a typical behavior of superconducting materials at bulk critical temperature of 15.5 K for Gd4Ba6Cu10Oδ and 22.1 K for Gd5Ba7Cu12Oδ. [ABSTRACT FROM AUTHOR]

The paper presents research results of the defect nucleation and propagation in the structure of nanosized iron samples with a perfect body-centered cubic lattice under a uniaxial tension along different crystallographic directions. The molecular dynamics method is used in these investigations. It is found that the mechanisms of plasticity nucleation considerably depend on the sample orientation relative to the load direction. The yield point exceedance along the [11 2 ¯ ] crystallographic direction leads to the twin nucleation on one of the sample edges. In this twin, the formation of dislocations occurs. Localized face-centered cubic arrangements can appear at the front of twinning dislocations. A large number of twins having the high growth velocity and low thickness generate in the crystal during tension along the [1 1 ¯ 0] crystallographic direction. During tension, the twins tend to transform to dislocations. If tension occurs along the [111] crystallographic direction, the plastic strain generation has a well-defined dislocation nature. An avalanche of dislocations proceeding from tension causes the dislocation piercing of the free surface, leaving vacancies in the bulk material at their intersections. [ABSTRACT FROM AUTHOR]

Debonding of fiber/matrix interfaces, kinking on debonded matrix surfaces, and tearing of interfiber ligaments are three major failure modes in micro-scales often observed in the failure experiments of Fiber Reinforced Composites (FRC) under extreme transverse tensile loadings. Numerical simulations on these complex failure processes at micro-scales are critical for designing new FRC materials. However, it is difficult to simultaneously simulate all these failure modes especially for cases where bulk matrix materials are ductile and undergo large plastic deformation. To overcome this difficulty, we adopt an innovative DG-based interface-oriented finite element technique that is able to handle all three failure modes. In this paper, using this numerical technique, we successfully simulate a complete failure process characterized by all three fracture modes for a composite structure containing two fibers embedded in a ductile bulk matrix. Furthermore, the kinking of debonded matrix surfaces predicted from simulations agrees well with the experimental results. Finally, we have studied the impact of variation in the thickness of interfiber ligaments on the failure behaviors of FRC materials. By running four cases with varied ligament thicknesses, we have identified a beam-like mixed bending/shearing failure mode for the tearing of interfiber ligaments and the shearing influence on the failure may increase following the increase in ligament thickness. [ABSTRACT FROM AUTHOR]

This paper presents a hybrid additive manufacturing (3D Printing) process for fabricating functionally gradient materials. A multi-axis robot was integrated with microextrusion, picojet, and fiber laser systems to deposit conductive traces of different materials. Laser and furnace curing mechanisms were investigated to evaluate their effect on grain morphology and electrical resistivity of the traces. An increase in the number of laser passes resulted in microstructure evolution from a powder-like to densely packed structure for different materials (Ag, Ni, and C). The laser curing mechanism offered lower resistivity and rapid curing times (< 1 min) compared with furnace curing (> 2 h). Optimal sintering parameters were obtained for 4-pass laser at 18 W with comparable resistivity with bulk materials. Localized infiltration (doping) of nanoparticle silver within the micro-extruded carbon trace demonstrated a significant enhancement in electrical properties (two orders of magnitude reduction in resistivity). The energy dispersive x-ray spectroscopy (EDS) mapping of the infiltrated traces displayed uniform dispersion of nano-particulate silver within the carbon matrix. Multilayer-multi-material (MLMM) traces deposited displayed distinctive morphology of each constituent material based on in situ laser curing. Scanning electron microscopy revealed distinctive microstructure and graded elemental composition of different layers (FGM) based on targeted laser sintering of individual materials. The versatile hybrid AM platform provides a basis to fabricate functionally gradient materials (FGMs) for electronic components with several applications. [ABSTRACT FROM AUTHOR]

This paper presents a meta-material-based design method for bulk acoustic wave (BAW) resonators with enhanced characteristics compared to those obtained with the typical bulk material implementation. We demonstrate the novel use of empty inclusions (i.e., 'holes') in bulk materials for engineering their acoustic (mechanical) properties (e.g. Young's modulus E, Poisson's ratio ν and mass density ρ) to tune and achieve optimal acoustical performance/characteristics. Inclusions have been demonstrated before to produce phononic band gaps for wave trapping. We focus on the propagation characteristics of the meta-materials brought into being by these inclusions. We implement patterns of holes with different sizes and distributions, to effectively scatter acoustic waves in bar-type BAW resonators and to devise the desired resonator properties, e.g., the resonant frequency. While the available bulk material is homogeneous and isotropic, the bar consists of an equivalent non-homogeneous material that can for example be distributed by design in order to shrink the overall resonator size, enhance electromechanical transduction coefficients or reject spurious modes. Our paper compares two extraction methods for the equivalent material properties of a periodically hole-punched material: the steady-state mechanical simulation of a unit cell and its 'phase delay' counterpart. We discuss their validity and practical use for the design of bar resonators. [ABSTRACT FROM AUTHOR]

This paper proposes a practical and memory efficient method to model YBCO coated conductors by commercial finite element software. This method uses the H formulation to directly solve a magnetic field in a two-dimensional space. This model has been successfully used for bulk materials and thick wires, and is extended in this article to solve geometries with high aspect ratios such as coated conductors. The effect of mesh quality and order of element on the performance and accuracy of the model is discussed. A model using 2nd order single layer elements is chosen as the optimal setting for solving AC loss in coated conductors. Based on this setting, a series of simulations with the thickness of the tape varying from 1 μm (the actual thickness) to 120 μm have been performed to investigate the effect of artificially expanding tape thickness. The results obtained from our FEM model are compared with the classical analytical solutions. The discrepancies between the two are discussed and explained. The model proposed in this paper is able to give an accurate solution of AC loss for simple geometry (such as a single tape with expanded thickness) within just a few minutes. Even in the case of dealing with complex problems (such as a tape in its actual dimension or a stack of tapes under complicated magnetic conditions), the model would only require a few hours to solve the problems with excellent convergence properties. [ABSTRACT FROM AUTHOR]

In recent years, the discrete element method (DEM) has been used to model bulk material, especially brittle materials (such as rocks, ceramics, concrete, ice, etc.) with various mechanical properties or responses by setting serials of contact properties (such as bonds) in the particle assembly. These bonds can withstand a certain amount of force and/or moment, so that the stresses executed in the bond can be used for determining the initiation and propagation of micro-cracks. There are increasing evidences over the last 20 years that the DEM is becoming an effective numerical method to simulate the cracking, crushing, and deformation of continuous media under external loads. The DEM has now been widely used in the field of processing and machining of rock, ceramic, concrete, and other brittle materials. In this paper, the theoretical principles, formulations, and contact models as well as the numerical solving processes of DEM are introduced. The applications of DEM for the machining processes of brittle and rigid materials such as ceramics are described and reviewed in detail, and the future development trend is also discussed. [ABSTRACT FROM AUTHOR]

This paper derives an expression for pore pressure coefficient B in terms of a geomaterial's mesoscopic properties and jacketed and unjacketed macroscopic compressibilities. The mesoscopic properties include phase compressibilities and pressure distribution ratios. The pressure distribution ratios represent the geomaterial's meso-heterogeneity, while the difference between the unjacketed bulk compressibility and the solid grain compressibility represents macroscopic effects, such as solid grain rearrangement. The difference in phase compressibilities is shown to be the principal determinant of B , with the effects of meso-heterogeneity and macroscopic change relatively negligible. The unjacketed pore compressibility appears to be quite sensitive to the effects of both meso-heterogeneity and macroscopic change. Although B can be derived reliably from a measured value of unjacketed pore compressibility, unjacketed pore compressibility derived from a measured value of B is considered unreliable. The expression for B includes five elastic coefficients. The necessary and sufficient condition for constant porosity in an unjacketed test is proposed. The published expressions for B , the coefficient of fluid content and porosity change are recovered by introducing appropriate assumptions with regard to meso-heterogeneity and phase compressibilities. [ABSTRACT FROM AUTHOR]

Primitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects. [ABSTRACT FROM AUTHOR]

Electrospun fibrous mats, characterized by their large surface-to-volume ratios, have unique and beneficial properties for various applications. The micro or nanoscale architectures of these structures significantly affects the mechanical properties of the material. The lack of knowledge for predicting the mechanical behavior of electrospun fibrous mats may prevent applications utilizing the se mats from reaching their full potential. In this paper, we propose a new computational model to predict the mechanical behavior of an electrospun fibrous mat by considering its microstructure and the percentage of the cross-points that are bonded. The model of the electrospun mat with randomly distributed fibers is considered in uniaxial and biaxial tension. Three cases are studied: (1) no interaction in cross-points of intersecting fibers, (2) half of the cross-points are bonded, (3) all of the cross-points are bonded. The results show that along with the mechanical properties of individual fibers, the fusion bonding of fibers is a critical parameter for tuning the mechanical properties of the bulk material. In a predefined porosity, the interfiber fusion enhanced the stiffness of the mat by 60%, which is independent of the loading mode and the mechanical property of individual fibers. For all ranges of porosities, bonding increases the stiffness of the mat; however, the bonding is more effective at stiffening when the porosity of the mat is low. [ABSTRACT FROM AUTHOR]

The ordered mesoporous metal oxides as catalytic carrier or active center have been reported by many literatures. The large specific surface area and ordered mesoporous structure had caused great concern in the field of catalysis. In the catalytic reaction, the ordered mesoporous materials had great mechanical properties and the active centers had strong interaction between each other. There were obviously advantages of these ordered mesoporous materials than bulk materials or routine nano-materials in the catalytic conversion of volatile organic compound, CO, NOx and other polluting gases. At present, researchers prepared a variety of ordered mesoporous metal oxides by different synthetic methods. Based on the analysis and summary of the literature, this paper briefly reviewed the preparation methods and application of ordered mesoporous metal oxide catalysts and the prospect of future development is worth expecting. [ABSTRACT FROM AUTHOR]

The paper presents the transmission electron microscopy (TEM) investigations of the thin film structure and phase composition of the heat-affected zone (HAZ) of a weld joint produced by manual metal arc welding (MMAW) of 0.12C–18Cr–10Ni–1Ti–Fe austenite steel exposed then to plastic deformation. The test machine INSTRON-1185 is used to perform quasi-static tensile tests at room temperature and a 1.7∙10–4 s–1 strain rate up to 5 and 37% deformations. TEM investigations are carried out within the HAZ, at a 1 mm distance to the weld line, in the direction of the parent metal and at 0.5 mm distance to the weld deposit. It is shown that MMAW results in the formation of ε-martensite both in the parent metal and weld deposit regions. In the latter, γ → ε phase transformation occurs faster. Plastic strain ranging between 0–5% throughout the HAZ leads to further γ → ε phase transformation. In the weld deposit of the HAZ region, this phase transformation is also more intensive. Further increase in the degree of plastic strain from 5 to 37% results in γ → ε → α phase transformation and an elastoplastic lattice distortion of the α-phase. The plastic flexure remains in the crystal lattice of the γ-phase. The bulk material in the HAZ region satisfies the following conditions: scalar dislocation density is higher than the excess, and internal shear stresses are higher than long-ranging. [ABSTRACT FROM AUTHOR]

This paper shows how Partial Least Square Regression (PLS) methods can be used to model sensor data of spectral character. The modelling approach has been applied on a tumbling mill where a strain gauge sensor measures the deflection of a lifter bar when it hits the charge. The deflection of the lifter bar during every mill revolution gives rise to a characteristic signal profile that is shown to contain information on both the charge position and grinding performance. As a signal pre-processing method the discrete wavelet transform is used. It distinctly shows a capability of signal feature extraction where both time and frequency are of interest. Its well-known ability to achieve good data compression without loss of information is also demonstrated, a data reduction ratio of 20:1 is obtained here. Modelling results demonstrate that different operating conditions are well distinguishable from each other and by that the finding of proper operating regimes are highly feasible. Grinding parameters that are normally measured in the laboratory are now readily modelled from the on-line signal. A further objective of this paper is to link the experimentally obtained strain gauge sensor data with computational data from a discrete element mill model (DEM). This enables to visualise the charge motion and helps to interpret the complex phenomena that take place inside a grinding mill measured by the strain gauge sensor. The approach taken is to simulate the behaviour of a rubber lifter when it is exposed to forces from the grinding charge in a two-dimensional DEM mill model using a particle flow code. The deflection profile obtained from the DEM simulation shows a reasonably good correspondence to pilot mill measurements. [ABSTRACT FROM AUTHOR]

The knowledge of Biot's effective stress coefficient is of particular importance to simulate the effects of pore pressure variations during reservoir depletion and injection operations. Direct experimental evaluation of this parameter can be limited by the availability of good quality cores. The experiments can also be expensive and time-consuming particularly in low-permeability formations. This paper presents a method to evaluate a 3D spatial model of Biot's effective stress coefficient based on well logs and the empirical correlation between dynamic and static Young's modulus in the wells. To estimate static Young's modulus, uniaxial compression tests are performed on the cores obtained from Asmari reservoir in the Gachsaran oil field and the correlation between static and dynamic Young's moduli is established. The mineral volume fraction in the wells is obtained from mineralogy log and validated using thin-sections, XRD, XRF, and SEM studies. Bulk and solid bulk modulus are estimated and a 1D model was built for 47 wells in the field, which is validated using two samples in one of the wells. An empirical relation has been obtained to estimate Biot's effective stress from total porosity log. Then, a 3D spatial model of Biot's effective stress coefficient has been presented by Sequential Gaussian Simulation (SGS) in the Gachsaran oil field, southwest of Iran. [ABSTRACT FROM AUTHOR]

Theoretical investigation into bonded granulates is of great importance to modern geomechanics. This paper presents an interpretation of the internal length in Chang’s couple-stress continuum for bonded materials (Chang et al., Eng Fract Mech 69(17):1941–1958, 2002; Chang and Shi, J Eng Mech ASCE 131(2):120–130, 2005). First, a micro-model for bonds between particles is proposed, in which a pair of bonded particles is in contact over a width B and this bond contact width is continuously distributed with the normal/tangential basic elements (BE) (each BE is composed of spring, dashpot, bond, slider or divider). Second, a couple model for the bonds is established to describe the relationship between relative particle rotation and couple. Third, Chang’s couple-stress continuum for bonded material is analyzed in the case of a hexagonal packing structure of a monodisperse bonded material. The study shows that the internal length in Chang’s couple-stress continuum for bonded monodisperse material is equal to $${\sqrt 3}B/6$$ , while other usual elastic constants of the continuum can also be linked to B. In addition, those constants can be associated with a size-independent parameter proposed in this paper. [ABSTRACT FROM AUTHOR]

This paper discusses possible models for probability distributions of contact force magnitudes in loaded granular media. Many authors have studied such distributions, based on experiments with real particles as well as simulations in 2D and 3D. This has led to various and partly contradicting suggestions for the form of those distributions, which are described in the present paper. Its new theoretical investigations start from the empirically justified assumption that the components of contact forces follow exponential distributions with a certain dependence structure. This leads to distributions of force magnitudes similar to Gamma distributions with shape parameters depending on space dimension, which is in good agreement to results from experiments and numerical simulations. Also the analytical and statistical difficulties of the problem of determination of distributions of force magnitudes are discussed. [ABSTRACT FROM AUTHOR]

The response of partially saturated granular cargoes during maritime transportation has resulted in the capsize and sinking of 27 bulk carriers at sea and the loss over 90 seafarers’ lives in the last decade. The partially saturated granular material response to energy imparted during cargo loading, ship engine vibrations and vessel rolling motions from sea states causes a change in state of the granular cargo, which can lead to vessel instability and ultimately capsize. However, the mechanisms driving the response of partially saturated granular cargos within a bulk carrier hold are not well understood. This paper presents results from an experimental study of rolling table centrifuge model tests on a partially saturated silica sand to contribute to improved understanding of the response of granular cargoes during maritime transport. Observed settlement, pore pressure, moisture content and density changes during and/or following a sequence of large amplitude rolling motions are presented. The results indicate that for the conditions considered, a progressive upwards migration of pore water during rolling led to creation of a free surface of water above the granular sample that was left in a denser, lower moisture content sample compared to its initial state. Sloshing of free water on top of even a competent cargo during rolling motions of the ship can contribute to loss of ship stability and ultimately capsize. [ABSTRACT FROM AUTHOR]

The kinetics of state switching fronts plays an important role in controlling nanodevices and the properties of many quasi-one-dimensional objects in physics, chemistry, and biology. In active media, this process is accompanied by the interaction of the state switching front with excitations in the bulk of the material. The propagation of the metastable-state switching front from the sample boundary with the absorption of spontaneously forming new-phase domains in the bulk is considered. The corresponding statistical-kinetic problem is solved by calculating the distribution functions of the "relay-race" path lengths and travel times for the edge-domain boundary. The related problem of the influence of uncontrolled noise on the propagation of signals in transmission lines is discussed. [ABSTRACT FROM AUTHOR]

This paper is aimed at investigating and improving material removal rate (MRR) and surface quality in wire electrical discharge machining (WEDM) based on specific discharge energy and magnetic-assisted method. A set of a single-factor experiment is implemented to analyze the effects of carbon content and discharge parameters on machining characteristics. The concept of specific discharge energy (SDE) is proposed to reveal the fundamental influence of workpiece material properties on material removal rate and to obtain the optimal machining feed rate. The mathematical model between SDE and the physical properties of workpiece material is also fitted out. Additionally, it can be found that, in subsurface material, the recast layer is with the maximal hardness followed by bulk material and heat-affected zone. Ra and RLT firstly increase and then decrease with the increase of carbon content, and they have a positive correlation with discharge peak current and pulse-on time. Finally, verified experiment shows that, comparing with other machining feed rates, the method of optimal machining feed rate according to SDE can simultaneously achieve the fastest actual machining speed and the lowest surface roughness. In addition, the method of magnetic-assisted trim cutting can almost eliminate recast layer and reduce heat-affected zone to less than 20 μm. [ABSTRACT FROM AUTHOR]

In this paper the applicability of selected silica-supported early transition metal oxides in photocatalysis is discussed. The catalytic properties of highly dispersed transition metal oxides often differ strongly from their corresponding bulk material. The structural and photophysical properties can often be linked to those changes. [ABSTRACT FROM AUTHOR]

The volumetric visualization of materials and inner boundaries of a joint is one of the fields in which long-focus high-frequency beams are used. Visualization is carried out using beams that passed through the immersion–sample interface and changed their geometry due to differences in the refraction of rays being incident at different angles on the interface. The beam structure is substantially distorted upon refraction and transforms into a caustic. The problem of spatial resolution in the formation of acoustic images of the microstructure in the material bulk is relevant. This paper presents a theoretical analysis of the spatial resolution with consideration for refractive aberrations in the formation of images of interfaces that are located at a considerable depth in the sample bulk. The results of the experimental visualization of the interface between jointed materials are presented. It is shown that the theoretical estimate is in good agreement with the experimental value of the resolution for beams of longitudinal waves converging in the sample volume. [ABSTRACT FROM AUTHOR]

This paper reports the results of experiments carried out to explore the effects of particle form, sometimes referred to as sphericity, on the depositional density and subsequent shear behaviour of granular material. Previous experimental studies have generally neglected this important control, considering only rotund or bulky particles. However, the results of a few numerical studies have suggested its importance. Pluviated granular materials were tested in triaxial compression under free-end conditions, achieved using enlarged lubricated platens, which allowed specimens to be taken to high axial strain levels without strain localisation. Strains were measured locally. The results show that the limiting void ratios, $$e_{max}$$ and $$e_{min}$$ , the void ratio range ( $$e_{max}- e_{min})$$ and the depositional anisotropy increase as particles become platy. Almost all aspects of behaviour during shear are significantly affected by particle form, including mobilised friction at the onset of dilation, peak state and ultimate (or critical) state, dilation and particle breakage. For extremely platy material it appears that dilatancy may be completely suppressed, even for dense packings of particles. [ABSTRACT FROM AUTHOR]

This paper presents the results of an intensive series of experiments on various types of sands using cyclic direct shear testing apparatus. Two different grain shapes (rounded and angular) of sands having distinct sizes (0.25-0.5 and 1.0-2.0 mm) were tested in an automated constant normal load cyclic direct shear testing apparatus at an 100 kPa vertical effective stress, and two rates of shearing (2.0 and 0.025 mm/min). Experiments on the specimens resulted in sharp decreases followed by gradual increases in shear stress values. The results suggest that these successive drops and formations give a stick-slip nature to the fluctuations, which might be attributed mainly to the rate of loading, shape of grains, size of grains, and fines contents. [ABSTRACT FROM AUTHOR]

In this paper, the embedded discontinuity approach is applied in finite element modeling of rock in compression and tension. For this end, a rate-dependent constitutive model based on (strong) embedded displacement discontinuity model is developed to describe the mode I, mode II and mixed mode fracture of rock. The constitutive model describes the bulk material as linear elastic until reaching the elastic limit. Beyond the elastic limit, the rate-dependent exponential softening law governs the evolution of the displacement jump. Rock heterogeneity is incorporated in the present approach by random description of the mineral texture of rock. Moreover, initial microcrack population always present in natural rocks is accounted for as randomly-oriented embedded discontinuities. In the numerical examples, the model properties are extensively studied in uniaxial compression. The effect of loading rate and confining pressure is also tested in the 2D (plane strain) numerical simulations. These simulations demonstrate that the model captures the salient features of rock in confined compression and uniaxial tension. The developed method has the computational efficiency of continuum plasticity models. However, it also has the advantage, over these models, of accounting for the orientation of introduced microcracks. This feature is crucial with respect to the fracture behavior of rock in compression as shown in this paper. [ABSTRACT FROM AUTHOR]

Recently, bimetallic clusters have attracted a great deal of attention from research community because clusters yield intriguing properties ranging from the molecular and the bulk materials, which have extensive applications in nanomaterials. Clusters with tailored properties are governed by cluster size, geometrical structures, and elemental composition. Motivated by that we systematically investigated the structural, relative stable, and electronic properties of PbnSbn (n = 2-12) clusters by means of density functional theory. In this paper, the ground state structures, average binding energies, fragmentation energies, HOMO-LUMO gaps, and density of states were theoretically calculated. The results demonstrate that the large clusters adopt distorted ellipsoid structures with no symmetry. The average binding energies tend to be stable when cluster size n ≥ 4. Pb5Sb5 and Pb9Sb9 clusters are more chemically stable compared with the neighboring PbnSbn clusters, which may serve as the cluster assembled materials. The density of states of PbnSbn (n = 2-12) clusters moving toward more negative energy levels with the growing cluster size n, which also becoming more nonlocalized as the clusters size n increasing. [ABSTRACT FROM AUTHOR]

Effective stress laws and their application are not new, but are often overlooked or applied inappropriately. The complexity of using a proper effective stress law increases when analyzing stress variation in coal as a result of gas production or mining. In this paper, an effective stress law is derived analytically for coalbed methane reservoirs, combining the concepts of matrix shrinkage/swelling and external stress by including the effect of sorbing gas pressure on the elastic response of the reservoir. The proposed law reduces to that of Terzaghi when the compressibility of bulk material is sufficiently greater than the compressibility of the solid grain, and without the strain associated with matrix shrinkage/swelling effect. Moreover, it is shown that the Biot coefficient ( α) can have a value larger than unity for self-swelling/dilation materials, such as coal. The proposed stress-strain relationship was validated using experimental results. Overall, the effective stress law for deformation was extended for sorptive materials, providing a new and unique technique to analyze the elastic behavior of coal by reducing three variables, namely, external stress, pore pressure and matrix shrinkage/swelling along with the associated stress, down to one variable, 'effective stress'. [ABSTRACT FROM AUTHOR]

Modeling the deformation of structures containing pressure-sensitive adhesive (PSA) joints can be a challenging task because of the dependence of the deformation mechanism on a) PSA adhesive properties and b) the bonding substrate's surface properties, such as surface energy and surface roughness. These parameters have significant and unique effects on the mechanical response of the joint. This paper is part of a two-part series, where a mechanism-based predictive modeling approach, supported by empirical observations, is presented for modeling the uniaxial tensile mechanical behavior of single-layered PSA joints based on acrylic PSA materials. This paper (Part I) addresses the stress-strain response, while Part II of this series will address the creep behavior. The underlying model is based on multiple mechanisms: i) cavity nucleation and growth in the bulk adhesive material of the PSA system, as well as at the interfaces between the PSA and the substrate; ii) fibrillation of the cavitated adhesive layer and iii) interfacial slippage between the adhesive and the bonding substrate; iv) PSA delamination from the substrate. This predictive model can be used as a virtual testing tool to generate stress-strain curves for constitutive models of PSA joints under different tensile loading conditions. [ABSTRACT FROM AUTHOR]

In this paper a study on the operations of a bulk material port is carried out to develop a decision support model, which deals with the dynamics of port and aids in better decision making at different scenarios. Here, we describe various decisions taken by port authorities pertaining to the import of coal at the terminal. We optimize these decisions with the aim of minimizing the unloading time of ships at the port, congestion in the stockyard, and loading time of the rakes. A practice-oriented decision support model is proposed to assist port planners in making these decisions. Various operational rules are embedded within the model, for carrying out the modelling of various port operations. The utility of the developed model is demonstrated using a case study which helps in achieving efficient utilization of berths, stockyard and rake loading stations. [ABSTRACT FROM AUTHOR]

For both single-phase and multiphase metallic materials, it is necessary to understand the mechanical behavior on the grain-size scale in detail to get information that is not obtainable from macro-scale mechanical characterizations. This paper presents a methodology for uniaxial tensile testing of micro-specimens isolated from a bulk material. The proposed concept of multiple parallel micro-tensile specimens at the tip of a macro-sized wedge reduces the alignment work and offers an easy way for specimen handling. The selection of site-specific specimens is based on detailed microstructural and crystallographic characterization. Three kinds of representative specimens are presented to illustrate the wide range of application of the methodology for a variety of materials. Accurate, reproducible measurement of force (2.5 μN resolution) and displacement (~10 nm resolution) is demonstrated, while accurate alignment (in-plane rotational and out-of-plane tilt misalignment of <0.2°) limits the stress due to bending to <0.2% of the imposed uni-axial stress. Combined with detailed material characterization on both sides of the micro-specimens, this method yields detailed insights into the micro-mechanics of bulk materials which is hard to obtain from traditional macro-mechanical tests. [ABSTRACT FROM AUTHOR]

This work examines challenges associated with the accuracy of machine-learned force fields (MLFFs) for bulk solid and liquid phases of d-block elements. In exhaustive detail, we contrast the performance of force, energy, and stress predictions across the transition metals for two leading MLFF models: a kernel-based atomic cluster expansion method implemented using sparse Gaussian processes (FLARE), and an equivariant message-passing neural network (NequIP). Early transition metals present higher relative errors and are more difficult to learn relative to late platinum- and coinage-group elements, and this trend persists across model architectures. Trends in complexity of interatomic interactions for different metals are revealed via comparison of the performance of representations with different many-body order and angular resolution. Using arguments based on perturbation theory on the occupied and unoccupied d states near the Fermi level, we determine that the large, sharp d density of states both above and below the Fermi level in early transition metals leads to a more complex, harder-to-learn potential energy surface for these metals. Increasing the fictitious electronic temperature (smearing) modifies the angular sensitivity of forces and makes the early transition metal forces easier to learn. This work illustrates challenges in capturing intricate properties of metallic bonding with current leading MLFFs and provides a reference data set for transition metals, aimed at benchmarking the accuracy and improving the development of emerging machine-learned approximations. [ABSTRACT FROM AUTHOR]

This paper studies asymmetric strong coupling effect in two parallel exclusion processes, which is a generalization of previous works of Kolomeisky group (Pronina and Kolomeisky in Physica A 372:12, ; Tsekouras and Kolomeisky in J. Phys. A 41:465001, ). It is shown that with different configurations of hopping rates, the two-lane system exhibits diverse phase diagram and density profiles. Specifically, it shows how the phase diagram changes from having seven phases, via six phases, to three phases. Moreover, it shows that the phase diagram could have only one phase, which exhibits quadrilateral or triangular density profile. The vertical cluster mean-field approach is used to get the stationary-state bulk densities and phase diagrams. Extensively Monte Carlo simulations are carried out, and theoretical predictions are in excellent agreement with simulation results. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of role of particle creation and bulk viscosity on evolution of homogeneous and anisotropic model of the universe represented by Bianchi type I space time metric. Particle creation and bulk viscosity have been considered as separated irreversible processes. In order to discuss physical and geometrical behaviour of the model, a new set of exact solutions of Einstein's field equation have been obtained in non-causal, truncated and full causal theories. Dynamical behaviours of models have also been discussed. [ABSTRACT FROM AUTHOR]

This paper examines the effect of mechanical activation by impact and attrition milling in planetary and ball ring mills on the phase composition of gypsum. Partially dehydrated powders obtained without heat treatment contain up to 60–70% β-CaSO4 · 0.5H2O (impact milling) and up to 40–47% α-CaSO4 · 0.5H2O (attrition milling). On the addition of a set retarder (maleic acid + poly(vinyl alcohol)), such materials acquire high strength during hardening: up to 11–17 MPa in compression and 7–12 MPa in bending. [ABSTRACT FROM AUTHOR]

The packing of granular particles is investigated using a combined finite-discrete element approach. One of the aims of this paper is to present an application of a recently improved numerical simulation technique for deformable granular material with arbitrary shapes. Our study is focused on the influence of the effect of the particle shape on (1) the emergent properties of a granular pack (packing density, coordination number, force distribution), and on (2) the spatial distribution of the stress. A set of simulations that mimick the sedimentation process is carried out, with varying input parameters, such as contact friction and particle shape. It is shown that the eccentricity of the particles not only significantly influences the final density of the pack but also the distribution of the stress and the contact forces. The presence of surface friction increases the amount of disorder within the granular system. Stress heterogeneities and force chain patterns propagate through the particles more efficiently than for the frictionless systems. The results also suggest that for the monodisperse systems investigated the coordination number is one of the factors that controls the distribution of the stress within a granular medium. [ABSTRACT FROM AUTHOR]

The formation of strain localization influences the stability and stiffness of the soil mass or geosystem. The thickness of shear bands provides insight about overall strength and stiffness inside the granular body, and the shear band angle gives information about the failure surface in a given soil or soil mass. Thus, it is important to be able to predict when a shear band forms and how this zone of intense deformation is located and oriented within the granular medium. A rational finite element analysis for capturing the formation and development of shear bands has been performed and implemented by using a Cosserat continuum in finite element simulations. An extension of plane strain Drucker–Prager elastoplasticity to Cosserat continua is implemented in ABAQUS by using its User-defined ELement (UEL) option. The finite element formulation is discussed in the companion paper. The length scale–size effect relation has been investigated to understand the micro–macro structure relation. Several practical engineering problems are simulated in two dimensions by using the finite element code ABAQUS together with analyst-supplied extensions. The effect of Cosserat parameters on the finite element simulations has been simulated. [ABSTRACT FROM AUTHOR]

The formation of strain localization influences the stability and stiffness of the soil mass or geosystem. The thickness of shear bands provides insight into overall strength and stiffness inside the granular body, and the shear band angle gives information about the failure surface in a given soil or soil mass. Thus, it is important to be able to predict when a shear band forms and how this zone of intense deformation is located and oriented within the granular medium. A rational finite element analysis for capturing the formation and development of shear bands has been formulated by using a micropolar continuum in finite element analysis. Hardening parameters including nonsymmetric stress and length scale are implemented for a realistic stress–strain analysis. Implementation and simulations of the model will be discussed in the Part II of this research. The micro–macro structure relation for finite element analysis based on this formulation paper will be simulated in the corresponding paper. [ABSTRACT FROM AUTHOR]

On the basis of the revised Goodman–Cowin theory, dry granular mass flows are modeled as elasto-visco-plastic continua with microstructural effects. In particular, hypoplasticity is incorporated to account for the plastic deformations and internal-friction characteristics of the material. The constitutive equations comprise of the equilibrium and non-equilibrium parts. A thermodynamic analysis, based on the Müller–Liu entropy principle, is performed to derive the ultimate equilibrium expressions of the constitutive variables, while the non-equilibrium responses are postulated by use of a quasi-linear theory. Results show that the revised Goodman–Cowin theory can appropriately be extended to take the frictional and plastic effects into account. These are revealed in the additonal plastic contributions in the equilibrium expressions of the Cauchy stress tensor and the balance equations of two internal variables. It is also shown that the present model is capable of describing the complex elasto-viscous-plastic behaviour of granular materials in static/quasi-static as well as in dynamic situations. This paper is devoted to the derivation of the thermodynamically consistent constitutive model. Its applications to benchmark problems and the justified evaluation of its performance and limitations are deferred to the other further paper. [ABSTRACT FROM AUTHOR]

Abstract  The paper examines asymmetric rolling of aluminum powder and granules on driving rolls of different diameters at the same angular velocity. The ratio of roll diameters is 1.1 to 1.4. It is established that asymmetric rolling of powder material allows removing drawbacks peculiar to traditional asymmetric rolling. These drawbacks are roll camber and destruction caused by nonuniform distribution of contact stresses across the roll width. Thereby it is possible to substantially reduce rolling defects and improve the quality of roll. [ABSTRACT FROM AUTHOR]

In a recent paper, the effect of cyclic shearing on forced shear localization in an infinite granular strip between rough boundaries was numerically investigated. The present paper focuses on the evolution of spontaneous developed shear localization within an granular body under plane strain conditions, constant lateral pressure and cyclic vertical compression-extension. For a simulation of the mechanical behavior of a cohesionless granular material, a micro-polar hypoplastic constitutive is used which takes into account particle rotations, curvatures, non-symmetric stresses, couple stresses and the mean grain diameter as a characteristic length. The proposed model captures the essential mechanical features of granular bodies in a wide range of densities and pressures with a single set of constants. For the calibration of the constitutive constants, the data of a medium quartz sand are used. The attention of numerical simulations is laid on the influence of the number of cycles, the magnitude of the vertical deformation amplitude and the initial density on the evolution of shear zones in an initially prismatic granular specimen. [ABSTRACT FROM AUTHOR]

Thermal conductivity of particulate beds is an important property for many industrial handling processes as well as for storage of particulate materials. This paper presents a new theoretical model that is based on heat transfer between particles in three modes: heat conduction through contact area, heat conduction through voids and radiation through voids. The model is further adjusted in order to obtain effective thermal conductivity of a particulate bed by using empirical augmentation factors for the heat transfer coefficient of each one of the heat transfer mechanisms. Comparison of the results predicted by the semi-empirical model to our experimental results show good agreement. The theoretical model was investigated to examine the effect of various parameters (such as: particle elasticity and surface roughness, particle and gas thermal conductivity and particle diameter), on the effective thermal conductivity of various particulate beds. Our results show the significant effect of the contact area (that is a clear function of the compression load) between particles on the effective thermal conductivity. [ABSTRACT FROM AUTHOR]

Shear in the annular space between drums is a well-known model for particle-laden flows. When this technique was introduced by Bagnold, it was assumed that the shear rate and particle concentration were uniform within the annular space. It is now known that this is not generally the case, in part because the distribution of particles in the annulus is influenced by hydrodynamic lift, which is discussed in the paper. The shear stress attributable to solids is also found to be influenced by different boundary conditions, and all these factors affect the usefulness of drum experiments for predicting other flow configurations. [ABSTRACT FROM AUTHOR]

When a load is applied to a granular material, the stress is not uniformly distributed but concentrates into quasi-linear particle assemblies known as ‘‘force chains.’’ By the time they can be observed, force chains are apparently quasistatic in the sense that they persist over time scales much longer than elastic timescales (such as a contact time) over which an unstable chain breaks apart. But many force chains attempt to form, but are unstable and break apart after a few contact times. Stability requires that each particle in the chain be pressed against its neighbors by the forces in the chain. Furthermore, each particle must also be in quasistatic equilibrium in the sense that all forces on it must roughly balance. This paper examines a simple linear string of particles in an attempt to estimate how much force is required to hold the chain together and how large a force imbalance can be tolerated. There are two modes of instability, a simple case in which an overloaded contact pushes its particles apart breaking the chain as they separate, and a more complicated mode requiring the interaction of elastic waves traveling along the chain. Overall, dissipation acts as a stabilizing factor, first by reducing the initial energy of the overloaded contact as it unloads, and subsequently, by reducing the energy of the elastic waves. [ABSTRACT FROM AUTHOR]

In this paper, we consider the complex problem of how to simulate particle contacts, taking into account the cohesion effect. In accordance with the molecular dynamics models, we propose a novel expression for the repulsive force which controls dynamically the transfer and dissipation of energy in granular media. This expression is formulated under fractional calculus, where a fractional derivative accumulates the whole history of the virtual overlap over time in weighted form. We then discuss and illustrate the basic properties of the repulsive force in a normal direction to the contacting surfaces. This approach allows us to perform simulations of arbitrary multiparticle contacts as well as granular cohesion dynamics. [ABSTRACT FROM AUTHOR]