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Particle morphology has great influence on mechanical behaviour and hydro/thermal/electrical conductivities of granular materials. Surface reconstruction and mesh generation are critical to consider realistic particle shapes in various computational simulations. This study adopts the combined finite- discrete element method (FDEM) to investigate single particle crushing behaviour. Particle shapes were reconstructed with spherical harmonic (SH) in both spherical and Cartesian coordinate systems. Furthermore, the reconstructed surface mesh qualities in two coordinate systems are investigated and compared. Although the efficiency of the two SH systems in reconstructing star-like shapes is nearly identical, SH in Cartesian coordinate system can reconstruct non-star-like shapes with the help of surface parameterisation. Meanwhile, a higher triangular mesh quality is generated with spherical coordinate. In single particle crushing tests, the low mesh quality produces more fluctuations on load–displacement curves. The particles with more surficial mesh elements tend to have a lower contact stiffness due to more contact stress concentrations induced by complexity of morphology features and more volumetric tetrahedral elements. The fracture patterns are also influenced by mesh quality and density, e.g. a particle with fewer mesh elements has a simpler fragmentation pattern. This study serves as an essential step towards modelling particle breakage using FDEM with surface mesh directly from SH reconstruction.

International audience; We experimentally investigated the packing of wet monodisperse spheres with controlled falling height. The packing fraction are found to decrease with smaller grain size and free fall heights. A model describing the effects of interparticle force and falling height on packing fraction is developed by introducing a dimensionless length scale, representing the extent of particle rearrangement towards a denser state due to impacts of falling grains. A universal law is observed for both wet particles where capillary forces dominate and dry powders where van der Waals forces govern the packing behaviour. This study deepens the understanding of packing of cohesive spheres and provide a simple experimental method for generating granular media with tailored packing fraction.

The dynamic contact angle of a gas–liquid–solid system depends on the contact line velocity and ignoring this effect could lead to inaccurate estimations of the capillary pressures in microporous media. While most existing coarse-grained molecular dynamics (CGMD) models use one particle to represent a few molecules, we present a novel CGMD framework to model microscale CO2/water flows in silica with each particle representing hundreds of thousands of molecules. The framework can reproduce the densities and viscosities of water and CO2, water–CO2 interfacial tension, and static contact angle over a wide range of pressures. The validated framework is applied to study the velocity-dependency of contact angle of the microscale CO2–water–silica system. The results indicate that the assumption in the molecular kinetic theory that liquid–solid interaction is similar to the reversible work of adhesion between liquid and solid may not hold for CO2–water–silica systems.

Water management remains one of the major challenges in optimising the performance of PEMFCs, in which liquid accumulation and removal in gas diffusion layers (GDLs) and flow channels should be addressed. Here, effects of GDL surface roughness on the water droplet removal inside a PEMFC flow channel have been investigated using the Volume of Fluid method. Rough surfaces are generated according to realistic GDL properties by incorporating RMS roughness and roughness wavelength as the main characteristic parameters. Droplet dynamics including emergence, growth, detachment, and removal in flow channels with various airflow rates are simulated on rough substrates. The influences of airflow rate on droplet dynamics are also discussed by comparing the detachment time and droplet morphology. The liquid removal efficiency subject to different surface roughness parameters is evaluated by droplet detachment time and elongation, and regimes of detachment modes are identified based on the droplet breakup location and detachment ratio. The results suggest that rough surfaces with higher RMS roughness can facilitate the removal of liquid inside flow channel. Whilst surface roughness wavelength is found less significant to the liquid removal efficiency. The results here provide qualitative assessments on identifying the key surface characteristics controlling droplet motion in PEMFC channels.

Normal contact behaviour between non-adhesive fractal rough particles is studied using a finite element method (FEM). A series of spherical grain surfaces with distinguished roughness features are generated by means of Spherical Harmonics. These surfaces are described by two roughness descriptors, namely, relative roughness (Rr) and fractal dimension (FD). The contact behaviour of rough spheres with a rigid flat surface is simulated using FEM to quantify the influences of surface structure and sphere morphology by focusing on contact stiffness and true contact area. The dependence of normal contact stiffness (k) on applied normal force (F) is found to follow a power law (k = αFβ) over four orders of magnitude, with both α and β being highly correlated with Rr and FD. With increasing load, the power exponent converges to that of Hertzian contact, e.g., 1/3, independent of Rr. Regions of true contact evolve through the formation of new microcontacts and their progressive merging, meanwhile the area distributions of contact island induced by various forces tend to obey similar Weibull distributions due to fractal nature in their surfaces. Contacts with larger values of Rr are found to produce contact contours with higher fractal dimension as calculated by a 2D box-counting method. Our results suggest that the correlation between radial lengths in a quasi-spherical particle should be considered in studying contact behaviour.

Magnesium alloys usually lack “operative deformation slip mechanisms” because of their hexagonal close-packed structure. Therefore, the mechanical behavior of magnesium alloys at different temperatures is dictated by other deformation mechanisms such as twinning, detwinning, secondary twinning, or dynamic recrystallization (DRX). Twinning and DRX can affect the development of grain size and orientation distribution, as well as the deformation behavior of magnesium alloys. The current understanding of the mechanisms and mechanics of these different deformation modes and their implementation in crystal plasticity-based modeling are highlighted in this article. Future directions in the development of constitutive models are also discussed.

When particle rings/shells are subjected to divergent explosive loadings, a dual overlapping particle jetting structure emerges during the shock interaction timescale which consists of a large number of minor jets initiated from the external interface at very early instants and a much reduced number of major jets formed from the internal interface at delayed times but overtaking the minor jets in later times. In the present work, the formation of the hierarchical particle jetting pattern is investigated numerically by discrete element method (DEM) coupled with finite element method (FEM), which execute the mechanical calculations of particles and the explosive/detonation gases, respectively. The numerical results find that the external jetting arises from the spallation of an outer layer pulled away by inward propagating rarefaction waves. Meanwhile an inner compact band re-compressed by a secondary shock remains densely packed while expanding outward. The fragmentation of the inner compact particle band, preceding the internal particle jetting, is caused by the profuse spiral shear failures expanding from the inner radius to the outer radius. The resultant jetting structure depends on the shear-band spacing and the grouping of the clockwise and counterclockwise shear bands as well. The former is a function of the bulk characteristics of the inner compact band, especially the resistance to the shear flows. The latter markedly varies with the microstructure of particle packing, especially the structural order. In the highly ordered extreme, the particle ring with global crystalline structure exhibits six groups of shear bands, probably giving rise to around six fragments. By contrast, the grouping of shear bands in the amorphous packing is far from definite, suggesting an increased number of much smaller fragments to be generated. The dual jetting structure would degenerate into a single jetting pattern if the inner compact band manages to entrain all the spall particles before the shear failure occurs. (C) 2019 Elsevier Ltd. All rights reserved.

To model the effective conductivity of the solid and the pore phase of a lithium-ion battery (LIB) we make use of the resistor network method (RN). We recall the scheme on how resistor networks can generally be set up and numerically solved. Furthermore, we explain how this general method can be applied to an assembly of spherical particles where for the individual resistances between touching particles an analytical formula is being used. As a new feature, we use the same scheme to setup resistor networks for the pore phase of an assembly of spherical particles where we propose a simple geometric approach for the calculation of the individual resistances of pore throats. For the validation of this method we created several random particle structures with different size distributions and calculated effective conductivities with both the RN and the finite element method (FEM). On the one hand, the comparison between RN and FEM shows a very good performance of the RN because the mean error lies within 4%. On the other hand, the RN results always lie within the well-known theoretical bounds for the effective conductivity in porous media. As an important aspect, the RN has proven to be highly efficient concerning the computation time and the resource costs.

Multiphase flow through a porous medium involves complex interactions between capillarity, wettability and gravity during drainage process. In contrast to these factors, the effect of pore distribution on liquid retention is less understood. In particular, the quantitative correlation between the fluid displacement and the level of disorder has not yet been established. In this work, we employ direct numerical simulation by solving the Navier–Stokes equations and using volume of fluid method to track the liquid–liquid interface during drainage in disordered porous media. The disorder of pore configuration is characterized by an modified index to capture small microstructural perturbation, which is pivotal for fluid displacement in porous media. Then, we focus on the residual volume and morphological characteristics of saturated zones after drainage and investigate the effect of disorder under different wettability (i.e., the contact angle) and gravity (characterized by a modified Bond number) conditions. Pore-scale simulations reveal that the highly-disordered porous medium is favourable to improve liquid retention and provide various morphologies of entrapped saturated zones. Furthermore, the disorder index has a negative correlation to the characteristic curve index (n) in van Genuchten equation, controlling the shape of the retention characteristic curves. It is expected that the findings will benefit to a broad range of industrial applications involving drainage processes in porous media, e.g., drying, carbon sequestration, and underground water remediation.

In this research paper, smoothed particle hydrodynamics (SPH) with Johnson Holmquist damage model is adopted for modelling of the blast-induced fractures in Barre granite rock. The permeability of the blast-induced rock is then obtained using the implemented finite volume method code in OpenFOAM. It is found that the calculated permeability depends on the direction of fluid flow and with higher value in radial direction than the axial one. This is mainly due to the higher and larger connected pore network in the radial direction. This research work shows that the adopted SPH method along with finite volume method code can be effectively combined to qualitatively and quantitatively predict the fractured network, to analyse geometry of the fractured network, and to calculate the permeability of blast-induced rock.

Dynamic wetting plays an important role in the physics of multiphase flow, and has a significant influence on many industrial and geotechnical applications. In this work, a modified smoothed particle hydrodynamics (SPH) model is employed to simulate surface tension, contact angle and dynamic wetting effects at meso-scale. The wetting and dewetting phenomena are simulated in a capillary tube, where the liquid particles are raised or withdrawn by a shifting substrate. The SPH model is modified by introducing a newly developed viscous force formulation at the liquid–solid interface to reproduce the rate-dependent behaviour of the moving contact line. Dynamic contact angle simulations with the interfacial viscous force are conducted to verify the effectiveness and accuracy of this new formulation. In addition, the influence of interfacial viscous forces with different magnitude on the contact angle dynamics is examined by empirical power-law correlations; the derived constants suggest that the dynamic contact angle changes monotonically with the interfacial viscous force. The simulation results are consistent with experimental observations and theoretical predictions, implying that the interfacial viscous force can be associated with the slip length of flow and the microscopic surface roughness. This work demonstrates that the modified SPH model can successfully account for the rate-dependent effects of a moving contact line, and can be used for realistic multiphase flow simulations under dynamic conditions.

International audience; We experimentally study the drying of loosely packed wet glass beads at low initial water content. The drying rate is found to decrease at the start, corre- sponding to the decreasing rate period controlled by vapor diffusion, followed by a deviation in drying rate from the diffusion limited evaporation. The prop- agation of drying front associated with a sharp saturation gradient is identified through both image analysis and magnetic resonance imaging technique. The drying-induced collapse of granular medium is observed and quantified. The concentrated collapse at the end of drying suggests the existence of liquid in the form of liquid bridges in the apparent dry region until the end of drying process. Collapse event is found to be local, i.e., a clear boundary can be iden- tified for each collapse event, below which the loosely packed medium remains intact. This indicates the existence of a saturation gradient in the apparent dry region. The drying dynamics and collapse statistics suggest that the observed transition of drying regimes is due to Kelvin effect. This work demonstrates for the first time the drying enhancement phenomenon due to Kelvin effect even for grains with size of hundreds of micrometers, and provides insights on the drying process of partially saturated granular materials, especially near the final period of evaporation.

Hypothesis Control of capillary flow through porous media has broad practical implications. However, achieving accurate and reliable control of such processes by tuning the pore size or by modification of interface wettability remains challenging. Here we propose that the flow of liquid by capillary penetration can be accurately adjusted by tuning the geometry of porous media and develop numerical method to achieve this. Methodologies On the basis of Darcys law, a general framework is proposed to facilitate the control of capillary flow in porous systems by tailoring the geometric shape of porous structures. A numerical simulation approach based on finite element method is also employed to validate the theoretical prediction. Findings A basic capillary component with a tunable velocity gradient is designed according to the proposed framework. By using the basic component, two functional capillary elements, namely, (i) flow amplifier and (ii) flow resistor, are demonstrated. Then, multi functional fluidic devices with controllable capillary flow are realized by integrating the designed capillary elements. All the theoretical designs are validated by numerical simulations. Finally, it is shown that the proposed model can be extended to three dimensional designs of porous media

International audience; We study how grain shapes impact multiphase flow in porous media in the quasi-static regime using an extended pore-network model. The algorithm allows the explicit determination of different types of pore-scale instabilities and tracks the interface motion during fluid-fluid displacement process. It also includes the volume capacitance model, such that both the evolution of capillary pressure signal and sizes of Haines jumps can be captured. Further, it considers the pinning of menisci at sharp edges of grains, through which the distribution of effective contact angles can be obtained. Simulations are carried out across a wide range of wetting conditions for different particle shapes. Our results show that the effective contact angle distribution during displacement widens as the grain becomes more angular, which consequently modifies the macroscopic fluid invasion morphology. By analyzing various characteristic metrics during displacement, including capillary pressure signal, Haines jump size distribution, and fractal dimension, our results highlight the profound influence of particle shape on the multiphase flow.

Widely distributed aquifers have been proposed as effective storage reservoirs for compressed air energy storage (CAES). This aims to overcome the limitations of geological conditions for conventional utility-scale CAES, which has to date used caverns as the storage reservoirs. As a promising technology, compressed air energy storage in aquifers (CAESA) has received increasing attention as a potential method to deal with the intermittent nature of solar or wind energy sources. This article presents a selective review of theoretical and numerical modeling studies as well as field tests, along with efficiency and economic analyses, to assess the feasibility of the emerging technology. Although some field tests suggest that a large bubble could be created in aquifers to sustain the working cycles at target rates, challenges remain before the technology can be recommended for wide deployment. The geological critical safety factors affecting the gas bubble development and sustainability of operation cycles include the geological structure, aquifer depth, and hydrodynamic and mechanical properties, such as porosity, permeability, compressibility, and mineral composition. Moreover, the injection/withdrawal well configurations and oxidation reactions caused by the oxygen in compressed air should also be considered. The failed attempt of renewable energy combined with CAESA in Iowa is described and the lessons learned are summarized. Combining CAESA with thermal storage, using CO2 as cushion gas, horizontal wells or hydraulic fracturing, and man-made boundaries are proposed to improve CAESA efficiency but need further study for future applications.

The calendering step during manufacturing of lithium‐ion batteries is an essential process in the production, as it significantly influences the microstructure of electrodes and, therefore, the performance of the battery. Within this context, this article investigates the influence of particle shapes on the micromechanical responses during calendering and, in turn, their impact on the effective transport properties of battery electrodes. The electrodes are modeled using discrete elements. For this reason, a novel algorithm for the generation of random stress‐free particle assemblies consisting of superellipsoids is presented. The effective conductivities of solid and pore phase are calculated with a resistor network approach. In this context, a new analytical formula for calculating the individual resistance between two mechanically deformed ellipsoidal particles is presented. Furthermore, a geometrical approach is chosen for the pore phase for calculating individual resistances of pore throats in superellipsoidal particle assemblies. With the theoretical fundamentals, the effective conductivities of solid and pore phases of uniaxially compressed ellipsoidal particle assemblies are investigated. The mechanical response and its influence on the evolution of the effective conductivities are discussed. The deeper insight into the interplay between the calendering process and electrode microstructure can be a helpful information regarding a specific electrode design.

International audience; Tribological phenomena are governed by combined effects of material properties, topology and surface-chemistry. We study the interplay of multiscale-surface-structures with molecular-scale interactions towards interpreting static frictional interactions at fractal interfaces. By spline-assisted-discretization we analyse asperity interactions in pairs of contacting fractal surface profiles. For elastically deforming asperities, force analysis reveals greater friction at surfaces exhibiting higher fractality, with increasing molecular-scale friction amplifying this trend. Increasing adhesive strength yields higher overall friction at surfaces of lower fractality owing to greater true-contact-area. In systems where adhesive-type interactions play an important role, such as those where cold-welded junctions form, friction is minimised at an intermediate value of surface profile fractality found here to be in the regime 1.3-1.5. Our results have implications for systems exhibiting evolving surface structures.https://doi.org/10.1016/j.triboint.2015.09.016; Les phénomènes tribologiques sont régis par les effets combinés des propriétés des matériaux, de la topologie et de la chimie des surfaces. Nous étudions l’interaction des structures de surface multi-échelles avec les interactions à l’échelle moléculaire pour interpréter les interactions frictionnelles statiques aux interfaces fractales. Par discrétisation assistée par spline, nous analysons les interactions d’asperité par paires de profils de surface fractale en contact. Pour les aspérités se déformant élastiquement, l'analyse de la force révèle un frottement plus important sur les surfaces présentant une fractalité plus élevée, le frottement croissant à l'échelle moléculaire amplifiant cette tendance. L'augmentation de la force adhésive engendre un frottement global plus élevé sur les surfaces de fractalité inférieure en raison d'une plus grande surface de contact. Dans les systèmes où les interactions de type adhésif jouent un rôle important, tels que ceux où se forment des jonctions soudées à froid, le frottement est minimisé à une valeur intermédiaire de la fractalité du profil de surface qui se situe autour de 1,3–1,5. Les résultats ont des implications pour les systèmes présentant des structures de surface en évolution.https://doi.org/10.1016/j.triboint.2015.09.016

International audience; The present work explores water permeability of uniformly graded irregular grains using 3D printing with controlled shapes and fractal morphological features at low Reynold's number for viscous flow. From large amount of real 3D granular morphological data, a scaling law, in terms of fractal dimension, is found to be followed. With this universal law, sand grains with controlled fractal morphological features are generated using Spherical Harmonics, and then created using 3D printing technique for water permeability tests. A modified Kozeny-Carman equation is proposed through more accurate determination of specific area, as a function of relative roughness and fractal dimension, than approximation using the volume-equivalent sphere. By isolating the contributions from specific area, the shape coefficient is found to be insensitive to particle morphology. Through benchmarking the model prediction against experiments from both this work and past literature, we demonstrate the validity and wide applicability of the modified Kozeny-Carman equation.

International audience; Drying-induced cracking is widely encountered in nature and is of fundamental interest in industrial applications. During desiccation, the evolution of water content is nonlinear. Considering the inhomogeneous procedure of desiccation, it is worth considering whether water content will affect the crack pattern formation. To address this concern, in this paper, we report an experimental investigation on the effect of water content on the failure mode in drying colloidal films. A distinct failure transition from random cracking to curling is found when the initial water content increases gradually. When the water content is below a critical value for given film thickness, random desiccation cracking driven by shrinkage is observed. Beyond this critical water content, the film curls with the advent of several main cracks. It is also found that the critical water content corresponding to the transition point depends on the film thickness. In order to qualitatively interpret the experimental observation, a theoretical model is established by adopting the fracture mechanics based on the energy method. The model is found to agree well with the experimental results, elucidating the effects of initial water content on the crack patterns and the transition of failure modes.

The effects of wettability on multiphase displacement in porous media have been studied extensively in the past, and the contact angle is identified as an important factor influencing the displacement patterns. At the same time, it has been found that the effective contact angle can vary drastically in a time-dependent manner on rough surfaces due to the Cassie-Wenzel wetting transition. In this study, we develop a theoretical model at the pore scale describing the apparent contact angle on a rough interface as a function of time. The theory is then incorporated into the lattice Boltzmann method for simulation of multiphase displacement in disordered porous media. A dimensionless time ratio, Dy, describing the relative speed of the wetting transition and pore invasion is defined. We show that the displacement patterns can be significantly influenced by Dy, where more trapped defending ganglia are observed at large Dy values, leading to lower displacement efficiency. We investigate the mobilization of trapped ganglia through identifying different mobilization dynamics during displacement, including translation, coalescence, and fragmentation. Agreement is observed between the mobilization statistics and the total pressure gradient across a wide range of Dy values. Understanding the effect of the wetting transition during multiphase displacement in porous media is of importance for applications such as carbon geosequestration and oil recovery, especially for porous media where solid surface roughness cannot be neglected.

Fabric of a granular assembly represents the topology of the contact network. This paper investigates the evolution of contact anisotropy (fabric) and average coordination number for a granular assembly subjected to uniaxial compression through the Discrete Element Method (DEM). A monosize three-dimensional random close-packed granular assembly with periodic boundary conditions under uniaxial compression is considered in this work. The fabric evolution is studied by post-processing the output data of the DEM simulation. The influence of cyclic loading, strain rate, and Young’s modulus on the evolution of contact anisotropy and average coordination number is presented. The Young’s modulus of the particle shows a significant influence on the particle contact creation during compression of the granular assembly with high strain rate. Effect of inertia on the contact anisotropy is observed to be significant during the compression of granular assemblies with different Young’s modulus under high strain rate. The paper concludes with a semi-empirical model to predict the evolution of contact anisotropy as a function of the macroscopic stress state of the assembly during quasi-static uniaxial compaction. The model also introduces two microscopic non-dimensional parameters that are independent of friction between the particles and can be used to relate the macroscopic stresses with the contact anisotropy.

Liquid bridges are commonly encountered in nature and the liquid transfer induced by their rupture are widely used in various industrial applications. In this work, with the focus on the porous tip, we studied the impacts of capillary effects on the liquid transfer induced by the rupture through numerical simulations. To depict the capillary effects of a porous tip, a time scale ratio, R_T, is proposed to compare the competing mechanisms of spontaneous imbibitiona and external drag. In terms of R_T, we then develop a theoretical model for estimating the liquid retention ratio considering the geometry, porosity and wettability of tips. The mecahnism presented in this work provides a possible approach to control the liquid transfer with better accuracy in microfluidics or microfabrications.

International audience; In engineering practice, energy pile foundations are often designed for the lifetime of the building. Thermal exchange between a pile and the surrounding soil depends on the annual energy needs of the building, as heating mode in winter and cooling mode in summer. Thus, energy pile foundations will undergo a heating–cooling cycle per year. In the present work, an experimental method based on a small-scale pile model installed in saturated clay was used to study the thermo-mechanical behaviour of energy piles under thermal cycles. Thirty cycles were applied (to represent a 30-year period if the daily cycles are neglected) while a constant pile head load was maintained. Four tests were performed corresponding to pile head loads equal to 0, 20, 40 and 60% of pile resistance. The results obtained show an increase in irreversible pile head settlement with the thermal cycles. In order to interpret the experimental results better, the finite-element method is used to simulate the experiments numerically. This allows the important role of pile thermal contraction/expansion in the pile–soil interaction under thermo-mechanical loading to be highlighted.

This paper presents a new data processing method for calculating more reliable thermophysical properties of liquid using Green-Kubo Method based molecular dynamics (MD) simulation. In this study, MD simulations of water are first performed using three common water models. A new approach for analysing the simulation data is then developed to obtain statistically meaningful thermophysical properties such as thermal conductivity and viscosity. It is demonstrated that for a given desired standard deviation for a specific simulation, a suitable simulation box size can be determined. The proposed approach can assure the repeatability and reliability of the calculated thermophysical properties of liquid.

Imbibition is a commonly encountered multiphase problem in various fields, and exact prediction of imbibition processes is a key issue for better understanding capillary flow in heterogeneous porous media. In this work, a numerical framework for describing imbibition processes in porous media with material heterogeneity is proposed to track the moving wetting front with the help of a partially saturated region at the front vicinity. A new interface treatment, named the interface integral method, is developed here, combined with which the proposed numerical model provides a complete framework for imbibition problems. After validation of the current model with existing experimental results of one-dimensional imbibition, simulations on a series of two-dimensional cases are analysed with the presences of multiple porous phases. The simulations presented here not only demonstrate the suitability of the numerical framework on complex domains but also present its feasibility and potential for further engineering applications involving imbibition in heterogeneous media.

Fruit and nut shells can exhibit high hardness and toughness. In the peninsula of Yucatan, Mexico, the fruit of the Cocoyol palm tree (Acrocomia mexicana) is well known to be very difficult to break. Its hardness has been documented since the 1500 s, and is even mentioned in the popular Maya legend The Dwarf of Uxmal. However, until now, no scientific studies quantifying the mechanical performance of the Cocoyol endocarp has been found in the literature to prove or disprove that this fruit shell is indeed “very hard”. Here we report the mechanical properties, microstructure and hardness of this material. The mechanical measurements showed compressive strength values of up to ~150 and ~250 MPa under quasi-static and high strain rate loading conditions, respectively, and microhardness of up to ~0.36 GPa. Our findings reveal a complex hierarchical structure showing that the Cocoyol shell is a functionally graded material with distinctive layers along the radial directions. These findings demonstrate that structure-property relationships make this material hard and tough. The mechanical results and the microstructure presented herein encourage designing new types of bioinspired superior synthetic materials.

Surface bio-functionalization through covalent attachment of bioactive molecules is a promising approach to facilitate rapid bone-implant integration. Radical-rich plasma polymer interlayers are highly attractive as platforms that enable covalent biofunctionalization in a single-step, reagent-free manner. However, fabrication of mechanically robust plasma polymer films, particularly for biomedical devices that operate in corrosive body fluids, is not trivial. Here we show a facile approach to tune the robustness of ion-assisted plasma polymer (IPP) films via simply varying the nitrogen atomic concentration incorporated into their structure. X-ray photoelectron spectroscopy data indicated that the total sp3/sp2 ratio of carbon atoms decreases in the films with increasing nitrogen atomic concentration. Electron recoil detection analysis data provided evidence that the hydrogen content decreases as the nitrogen atomic concentration increases. Nano-indentation and nano-scratch tests, together with long-term stability studies in simulated body fluid, showed a strong correlation between the nitrogen atomic concentration and the robustness and stability of the films. We confirmed the potential of the optimized, nitrogen-rich IPP film to regulate osseointegration by covalent attachment of fibronectin followed by quantifying primary osteoblast attachment and proliferation. The IPP films developed here hold great potential as robust interfaces for biomimetic surface engineering of implantable biomedical devices, in particular bone implants.

In this paper, we study the contact stiffness of a fractal rough surface compressed by a rigid flat plane. A numerical model based on the analysis of flat punch indentation is proposed for simulated hierarchical surfaces, which are generated using statistical and fractal descriptors collected by surface profilometry. The contact stiffness of surfaces under increasing normal load is determined on the basis of the total truncated area at varying heights. The results are compared with experimental data from nanoindentation on four types of treated rough surfaces, showing good agreement with experimental observations below a certain truncation depth. Furthermore, the limits of the model's validity are discussed by focusing on surface geometries and deformation of contacting asperities. With this proposed truncation method, we present a parametric analysis to establish a correlation between contact stiffness and surface roughness descriptors. The contact stiffness shows a unified power-law scaling with respect to the applied load over a wide range for simulated surfaces with distinct sets of roughness descriptors. The exponent of the power-law relationship is found to correlate positively to the fractal dimension while its amplitude is inversely correlated to the surface roughness amplitude. This study provides an easily implemented and computationally efficient method to connect mechanical behaviour with multi-scale surface structure, which can be utilized in design and optimization of engineering applications involving rough contacts.

The structure of mono-sized sphere packings (diameter d) in cylindrical containers (diameter D and height H) both with and without inner cylinders (diameter Di) has been investigated in detail by means of advanced X-ray computed tomography. The geometrical parameters were varied in a wide range; in all experiments 1d vertical vibration was applied. Five experiments were selected with characteristically differing local packing structures. The influence of container geometry, filling and vibration procedures on the formation of regular packings is discussed and a simple correlation is presented to assess whether structured packings occupy a significant fraction of the total packed volume. For a packing with moderate densification, the regular structures are restricted to small wall zones and a random packing exists in the largest part of the packing volume. By selecting appropriate vibration parameters, the zones with regular structures can increase considerably and can persist in the total packed volume. The increasing crystallisation causes an increase of the container packing fraction. For cylinders with H/D ≫ 1 and moderate D/d, regular structures develop preferentially in radial direction from a hexagonal layer at the concave wall. For H/D < 1 and D/d ≫ 1, hexagonal dense structures grow preferentially above the flat bottom plate and can occupy a great portion of the total volume. The role of granular convection on these crystallisation processes has been addressed. Previous statements that the thickness of wall zones is ≈(4–5)d are not generally valid for mono-sized sphere packings; the development of a comprehensive correlation is the task of a future work. Structural details of the packings close to concave, plane and convex walls are analysed via void fraction distributions, sphere centre positions, contact angle distributions, coordination numbers, radial distribution function and Voronoi tessellation. The combination of these methods provides a comprehensive understanding of structural details. Only a few characteristic results are presented; special topics will be the subject of forthcoming publications.

International audience; Fluid-filled porous materials are widely encountered in natural and artificial systems. A comprehensive understanding of the elastic behavior of such materials and its dependence on fluid diffusion is therefore of fundamental importance. In this work, a multiscale framework is developed to model the overall elastic response of fluid-filled porous materials. By utilizing a two-dimensional micromechanical model with porosity at two scales, the effects of fluid diffusion and the geometric arrangement of pores on the evolution of effective properties in fluid-filled porous materials are investigated. Initially, for a single-porosity model the effective elastic properties of the dry and fluid-filled porous materials with ordered pores are obtained theoretically by considering a geometrical factor, which is related to the distribution of pores in the matrix. Model predictions are validated by finite element simulations. By employing a double-porosity model, fluid diffusion from macro- to micro-scale pores driven by a pressure gradient is investigated, and the resulting time-dependent effective elastic properties are obtained for both constant pressure and constant injection rate conditions. It is found that the presence and diffusion of pressurized pore fluid significantly affect the elastic response of porous materials, and this must be considered when modeling such materials. It is expected that the proposed theoretical model will advance the understanding of the fluid-governed elastic response of porous materials with implications towards the analysis of geophysical, biological and artificial fluid-filled porous systems.https://doi.org/10.1016/j.ijsolstr.2018.11.028; Les matériaux poreux remplis de fluide sont largement rencontrés dans les systèmes naturels et artificiels. Une compréhension globale du comportement élastique de tels matériaux et de sa dépendance à la diffusion de fluide revêt donc une importance fondamentale. Dans ce travail, un cadre multi-échelles est développé pour modéliser la réponse élastique globale des matériaux poreux remplis de fluide. En utilisant un modèle micromécanique bidimensionnel avec une porosité à deux échelles, on étudie les effets de la diffusion de fluide et la disposition géométrique des pores sur l'évolution des propriétés effectives dans les matériaux poreux remplis de fluide. Initialement, pour un modèle à une seule porosité, les propriétés élastiques effectives des matériaux poreux secs et remplis de fluide à pores ordonnés sont obtenues théoriquement en considérant un facteur géométrique, qui est lié à la distribution des pores dans la matrice. Les prévisions du modèle sont validées par des simulations par éléments finis. En utilisant un modèle à double porosité, on étudie la diffusion de fluide à partir de pores de macro à micro échelle, entraînés par un gradient de pression, et on obtient les propriétés élastiques effectives dépendantes du temps qui en résultent, à la fois pour des conditions de pression constante et de vitesse d'injection constante. On constate que la présence et la diffusion de fluide interstitiel sous pression affectent de manière significative la réponse élastique des matériaux poreux, ce qui doit être pris en compte lors de la modélisation de tels matériaux. Le modèle théorique proposé devrait permettre de mieux comprendre la réponse élastique des matériaux poreux régie par les fluides, avec des implications pour l'analyse de systèmes poreux remplis de fluides géophysiques, biologiques et artificiels.

In this study, we investigate the impact of topological disorder on liquid distribution and transport phenomena in three-dimensional unsaturated granular media using the Shan-Chen lattice Boltzmann method. Distinct samples of disordered media are generated, characterized by the disorder index I v . Under different I v , varied liquid cluster distributions are demonstrated in a gravity-driven vapour-liquid system. Gradually increasing the initial liquid phase in the simulation domain allows the full range of saturation. The focuses are placed on the liquid cluster statistics from the connectivity, total cluster number, largest cluster and mean cluster volume at an increasing saturation. Meanwhile, the interfacial area, liquid retention curves and relative permeability-saturation curves are produced at diverse I v and wettability. It is found that the slopes of retention curves are well correlated with the proposed capillary index I c that unifies both disorder and wettability. The proposed generalized correlation between capillary index and slope index is useful in terms of determining the capillary pressure-saturation curve and relative permeability-saturation curve for a given granular system at varied contact angles. Additionally, the cohesive strength-saturation curves are also obtained with the aid of the interfacial area and negative capillary pressure, which elucidates that a packing with a higher I v experiences a relatively larger cohesive strength. These results enhance the understanding of disorder effect and will be beneficial for the exploration of many retention curves-related phenomena such as liquid transfer and stress-strain relation for wet granular media.

Fly ash-based geopolymers incorporated with 2% nano-SiO2 (NS)/nano-TiO2 (NT) particles were subjected to microstructural and statistical nanoindentation analysis. With the addition of both types of nanoparticles, the compressive strength of geopolymer and the micromechanical properties of N-A-S-H gel were increased. NS exhibited higher reinforcement effect than NT on macro-strength. However, NT more significantly enhanced gel micromechanical properties. NT and especially the NS were found to have a positive effect on the early reaction rate of geopolymer. After 28 days, the gel proportion obtained by Backscattered electron (BSE) images analysis was close values of 49.16%, 55.69% and 54.02% for reference sample and NS, NT reinforced geopolymer, which were more than two times of that from the statistical nanoindentation. The effects of NS and NT on microstructure, gel proportion and gel micromechanical properties were discussed to reveal the macro-strength reinforcement mechanism. The results obtained from different techniques were also compared and discussed.

Pore fluid adsorption-induced deformation of mesoporous materials is an important physical phenomenon. Experimental results show that the adsorption-induced elastic deformation can be quantified in terms of pore-load modulus (i.e., the radio between pore pressure and overall strain). In practical applications, most mesoporous materials are functionalized by post-fabrication processes such as surface coating. In this paper, we develop a theoretical model to predict the adsorption-induced deformation of ordered mesoporous materials with uniform and functionally graded coatings. Closed-form solutions of the pore-load modulus are obtained as a function of porosity, elastic properties of bulk materials and coating phases, thickness of coating, and geometrical arrangement of pores. Deformation of a coated triangular lattice of cylindrical pores representing the mesoporous materials with inner fluid pressure is also simulated by the finite element method, showing excellent agreement with the established theoretical solutions. The proposed model provides a general description of the elastic response of heterogeneous mesoporous materials subjected to the inner pressure loading.

The discrete element method (DEM) together with the finite element method (FEM) in LS-DYNA was employed to investigate the dynamic behaviour of sand under impact loading. In this approach, the partially saturated sand was modelled in DEM with capillary forces being taken into account through an implicit capillary contact model, while other solids were simulated using FEM. A slump test was first performed with dry sand to calibrate the contact parameters in DEM. Low velocity impact tests were then conducted to investigate the effect of water saturation on the shape and height of sand piles after impact, and to validate the simulations. It was found in the experiments that an increasing water saturation (in the range between 10 and 30 %) affected the height of sand pile for a given drop height due to an increasing cohesion between particles. The simulations captured the experimental ejecta patterns and sand pile height. Finally, a low confinement split Hopkinson pressure bar test from earlier literature was modelled; the DEM–FEM simulations could reproduce the trends of experimentally observed stress–strain curves of partially saturated sand under high strain rate loading, indicating that it was feasible to model dynamic behaviour of dry and wet sand with low saturation (

Effective thermal conductivity is an important property of granular materials in engineering applications and industrial processes, including the blending and mixing of powders, sintering of ceramics and refractory metals, and electrochemical interactions in fuel cells and Li-ion batteries. The thermo-mechanical properties of granular materials with macroscopic particle sizes (above 1 mm) have been investigated experimentally and theoretically, but knowledge remains limited for materials consisting of micro/nanosized grains. In this work we study the effective thermal conductivity of micro/nanopowders under varying conditions of mechanical stress and gas pressure via the discrete thermal resistance method. In this proposed method, a unit cell of contact structure is regarded as one thermal resistor. Thermal transport between two contacting particles and through the gas phase (including conduction in the gas phase and heat transfer of solid-gas interfaces) are the main mechanisms. Due to the small size of particles, the gas phase is limited to a small volume and a simplified gas heat transfer model is applied considering the Knudsen number. During loading, changes in the gas volume and the contact area between particles are simulated by the finite element method. The thermal resistance of one contact unit is calculated through the combination of the heat transfer mechanisms. A simplified relationship between effective thermal conductivity and loading pressure can be obtained by integrating the contact units of the compacted powders.

Geothermal energy piles have emerged as a cost effective and efficient solution for heating and cooling buildings through renewable energy. Although significant research effort has been dedicated to investigating the performance of these systems, the effect of ground mineralogy has received little attention. This study examines the likely performance of energy piles in dense sand with varying mineralogy. A 3D thermal discrete element model is used to determine the dry thermal conductivity of quartz, feldspar and mica rich sand. This is then used in a 2D finite element analysis to estimate the dissipation/extraction capacity of the soil surrounding a typical energy pile. A 35% increase in quartz content is predicted to result in 51% improvement in the thermal performance of a pile.

This paper aims to provide a coupled finite element method (FEM) and smoothed particle hydrodynamics (SPH) approach capable of reproducing the blast response in rock. In the proposed approach, SPH is used to simulate large deformation and fracture of rock at the near detonation zone, while the FEM is adopted to capture the far field response of the rock. The explosive is modelled explicitly using SPH. The numerical simulations are carried out using LS-DYNA. The interaction of the SPH particles and FEM elements was modelled by the node to surface contact, and for the interactions between explosive and rock SPH parts node to node penalty based contact was used. In the present study, the Johnson and Holmquist constitutive model is used for rock. Jones–Wilkins–Lee model is used for TNT explosive. It is found that the preliminary numerical simulation reproduces some of the well-known phenomena observed experimentally by other researchers. The numerical results indicate that the coupled SPH-FEM approach used in this work can be applied to simulate effectively both compressive and tensile damage of rock subjected to blast loading.

International audience; One of the many attributes of 3D printing is the ability to produce particles with independent control of morphology and material properties, parameters that are inexorably entwined in naturally occurring geomaterials. In this paper we describe the 3D printing of surrogate granular materials, show examples of the particles produced and present results showing their ability to capture real soil behaviour. Three approaches are demonstrated for the three dimensional generation of model grains. The first method involves the superimposition of a fractal surface with higher level stochastic features on the face of a closed volume such as a geodesic spheroid. The second method involves the use of Fourier descriptors or fractal geometry generated from 2D cross sections and their interpolation to produce simulated geomaterial particles in three dimensions. The third method involves the generation of complex particles by the aggregation of polyhedral elements such as cubes or octahedra which is suitable for the simulation and fabrication of porous or branching particles. Finally, we discuss applications of the fabrication of surrogate materials by 3D printing for use as standardised, printable geomaterials in future up-scaled geotechnical experiments and other geomechanical research.https://doi.org/10.1680/jgeot.15.P.034; L'un des nombreux attributs de l'impression 3D est la capacité de produire des particules avec un contrôle indépendant de la morphologie et des propriétés du matériau, paramètres inextricablement liés dans les géomatériaux naturels. Dans cet article, nous décrivons l'impression 3D de matériaux granulaires de substitution, montrons des exemples de particules produites et présentons les résultats montrant leur capacité à capturer le comportement réel du sol. Trois approches sont démontrées pour la génération tridimensionnelle de grains modèles. La première méthode implique la superposition d'une surface fractale avec des caractéristiques stochastiques de niveau supérieur sur la face d'un volume fermé tel qu'un sphéroïde géodésique. La deuxième méthode implique l'utilisation de descripteurs de Fourier ou de géométrie fractale générés à partir de sections transversales 2D et leur interpolation pour produire des particules de géomatériau simulées en trois dimensions. La troisième méthode implique la génération de particules complexes par l'agrégation d'éléments polyédriques, tels que des cubes ou des octaèdres, qui conviennent à la simulation et à la fabrication de particules poreuses ou ramifiées. Enfin, nous discutons des applications de la fabrication de matériaux de substitution par impression 3D pour une utilisation en tant que géomatériaux imprimables et normalisés dans de futures expériences géotechniques à grande échelle et autres recherches géomécaniques.https://doi.org/10.1680/jgeot.15.P.034

As an important inorganic material, geopolymer has been widely used for ceramics and sustainable cement in concrete. Sodium aluminosilicate hydrate (N-A-S-H) gel known as the zeolite precursor gel has the most critical impact on the performance of geopolymer. The nano/micromechanical properties of N-A-S-H have been investigated in several studies, but the resutls are always inconsistent. A novel “compromise approach” using Maximum Likelihood Estimation (MLE) for deconvolution of nanoindentation data is introduced to fundamentally further understand this issue in this study. Correlation and difference of different statistical techniques are compared to clarify the rationality of this method. Multiple characterization techniques including microstructure observation at micro -and nano-scale, element analysis, and crystal identification are applied to reveal the mechanisms. The results indicate that the elastic modulus and hardness of the N-A-S-H gel in geopolymer under different silica modulus and curing conditions vary in a small range from 10.50 to 14.30 GPa and from 0.40 to 0.57 GPa, respectively. When applying statistical nanoindentation in geopolymer, two kinds of spurious phases, mixed phases and sub-phases are unavoidable. For the MLE method adopted, the errors generated from analytical technique were estimated to be only 0.68 and 0.13 GPa for elastic modulus and hardness, respectively.

Cemented sands are not only widely found in nature, but also artificially made broadly for various engineering applications. We experimentally studied underlying breakage behaviour of artificially cemented sands under different loading paths at particle scale. Two types of sands (Leighton Buzzard sand and crushed limestone particles) and two types of bond materials (gypsum plaster and Portland cement) were used to prepare artificially cemented particles. Three typical loading paths, resulting in different breakage modes of specimens, including (1) uniaxial compression, (2) combined compression-pure shear (shorted by ‘pure shear’) and (3) combined compression-shear-bending (shorted by ‘bending’) were applied. It was found that when catastrophic failure occurred, cracks propagated roughly parallel to the loading axis in both particles and their bridging cementation in uniaxial compression tests. While under pure shear loads, the macroscopic fracture initiated at and evolved along particle-bond interfaces. By contrast, bending moment induced shear bands of which crack planes only occurred in cementation and were nearly parallel to each other in bending tests. For the intact samples before compression tests as well as fragmentations after breakage, Scanning Electron Microscope (SEM) images were taken for samples prepared by four kinds of materials, and multiscale rotational Haar Wavelet Transformation (HWT) was implemented to quantify their fabric including fabric value and direction. It is concluded that fracture surfaces of particle materials had more distinct fabric than intact particle surface. Meanwhile, due to sliding shear-dominant longitudinal bond fracture surfaces had more evident fabric than their corresponding tensile-dominant horizontal fracture surfaces. Consequently, our developed apparatus combined with the fabric quantification method sheds new light on cemented granular materials at the particle scale.

Static nanoindentation and Maximum Likelihood Estimation (MLE) were applied for the nano/micromechanical properties investigation of alkali-activated fly ash (AAFA) in this study. Some critical issues of statistical nanoindentation were fully discussed, including properties of pure gel phase, influence of bin size when using least-square estimation (LSE), and suitable number of components for deconvolution. Results indicate that the model estimated by MLE method can effectively reflect the micromechanical distribution of AAFA. The number of components needed to separate sodium aluminosilicate hydrate (N-A-S-H) gels is sometimes more than the normally used 3 or 4, depending on the sample and testing factors. The gel phase does not always display as a prominent peak in the histogram and is easy to be mixed with other adjacent peaks even if the bin size is small, indicating the challenges of employing the LSE method to investigate the gel phase in highly heterogeneous materials, such as geopolymer.

The purpose of this study is to determine the key properties of Australian hemp particles which are used for manufacturing hempcrete. Hemp characteristics have a wide variability due to the influence of the environment conditions in various farmed areas. This study focuses on the measurements of the mechanical, thermal and acoustic performances of three Australian hemp: unretted hemp hurd, retted hemp hurd, and hemp fines. Hemp hurd is usually used in non-load bearing building walls, and hemp fine, which is the by-product of hemp manufacturing industry, is usually incorporated into a render. The experimental results show that the main impact of the retting process is a decrease in bulk density and leading to an improvement in thermal and acoustic properties. Without compaction, the bulk density is ranged from 97 and 118.8 kg.m−3, the max sound absorption coefficient from 0.88 and 0.99, and the thermal conductivity from 64 to 97 mW.m-1. K-1. Hemp fines have excellent thermal and acoustic properties and appear to be an efficient aggregate to produce an insulating render. Australian hemps investigated in this study have shown very similar characteristics to European hemps.

Concrete is the most-used cementitious material and usually considered a three-phase composite with a mortar matrix, aggregates, and interfacial transition zones, all of which can fracture and even fragment. In this paper, the combined finite and discrete element method (FDEM) benchmarked with an in-situ X-ray micro-computed tomography and diffraction experiment is applied to bridge this gap in the meso-scale concrete fracture behaviour. To this end, algorithms are developed for realistic-shaped particle, packing, and high-quality FEM mesh- generation based on Voronoi tessellation and spherical harmonics. Using comprehensive simulations of virtually generated meso-scale concrete samples, it is found that rough particulates in concrete can increase its stress bearing capacity by enhancing intra-aggregate fracture paths. Results show that, the hierarchical aggregate morphology expressed by the fractal dimension more directly determines the compressive strength. Among the accessible conventional shape indices, convexity is the most effective parameter to correlate the global concrete fracture stress.

Phase change material (PCM) based latent heat thermal energy storage (LHTES) systems have been a technology of increasing interests. Extensive experimental and numerical studies on the heat transfer enhancement of PCM have been reported. However, a thorough analysis of the effects of PCM heat transfer enhancement in combination with geometric optimization on the overall storage performance of an LHTES system is still lacking. In this work, a performance index, the effective energy storage ratio Est, based on the effectiveness-NTU theory, which set up a standard to compare TES systems, was adopted to evaluate the effective energy storage density of an LHTES system. Using the conjugate heat transfer analysis, we investigated the impact of the key parameters and flow conditions, including the geometric parameters (tube length-diameter ratio L/di, PCM volume ratio λ), turbulent versus laminar flow conditions of HTF, and the effective PCM thermal conductivity keff, on the performance indicator Est. It was found that the effective energy storage ratio increases with tube length-diameter ratio, and an optimal PCM volume ratio exists. Increasing the effective PCM thermal conductivity is only effective in enhancing the effective energy storage ratio when PCM volume ratio is above certain value. Over 500 sets of parametric studies were performed to optimize the PCM volume by maximizing the effective energy storage ratio. The results show that for both laminar and turbulent flow, optimal PCM volume ratio and maximal effective energy storage ratio increases with tube length-diameter ratio and effective PCM thermal conductivity. The enhancement of effective PCM thermal conductivity only noticeably increases maximal effective energy storage ratio when tube length-diameter ratio is above a certain threshold, i.e., around 800 for laminar flow and around 600 for fully turbulent flow. The fully turbulent flow greatly enhances the charging rate by 50 times and increases the capacity effectiveness at optimal PCM volume ratio to 0.6-0.9 from 0.2-0.8 at laminar flow conditions, but the maximal effective energy storage ratio of fully turbulent flows are generally lower than those of laminar flows. This work is the first systematic numerical analysis of the complete ensemble design factors of a shell-and-tube LHTES system, and it is recommended that the method could be a standard one for the engineering design of an LHTES system.

The behaviour of droplets on porous media, combining the spreading above and imbibition into the medium, is of foundational interests for a series of applications. In this work, we combine the lattice Boltzmann method (LBM) and pore-network method (PNM) to develop an efficient and robust numerical framework in which the coarse-scale multiphase transport in porous media are modelled by the PNM while the fluid dynamics containing multiple components are resolved by the LBM. An effective transport mechanism has been implemented to ensure mass conservation and pressure continuity across the interface. This method is ideally adapted to flow domains, with two distinguishable characteristic length-scales. The numerical framework is validated by comparison with experimental observations of droplets on flat porous surfaces. Moreover, the behaviour of droplets on non-flat porous surfaces has been also investigated, demonstrating the influence of surface curvature on the competing mechanisms of droplet spreading and imbibition.

International audience; Spontaneous liquid transport has a wide variety of applications, including fog harvesting , microfluidics, and water-oil separation. Understanding of the droplet movement dynamics on structured surfaces is essential for enhancing the transport performance. In this work, we develop a theoretical model describing the movement process of droplets on surfaces with prescribed wedge shapes. Agreement is observed between the predictions from the model and experimental results. Through theoretical analysis and quantitative comparison between the transport performance of different wedge shapes, we identify the factors affecting the movement process and provide guidelines for wedge shape optimisation for spontaneous droplet transport.

In this study, arc melting was used to precipitate (Ti, Zr, Nb, Ta)C and (Ti, Zr, Nb, Ta, Hf)C particles in-situ within a steel matrix. Energy dispersive X-ray spectroscopy revealed that these particles are solid-solutions of their constituents (TiC, ZrC, NbC, TaC and HfC) while crystal orientation data from electron backscatter diffraction showed that the particles are either single crystals or an agglomerate of a few crystals. X-ray diffraction revealed that their lattice constants can be approximated using the rule of mixtures. The hardness of (Ti, Zr, Nb, Ta, Hf)C measured using nano-indentation was found to closely match that of TiC (the hardest and stiffest of the monocarbide constituents), indicating that the hardness is higher than what the rule of mixtures suggests. Nonetheless, better homogenization of the high entropy carbide should lead to significantly better properties. Additionally, considering the high melting points of TaC and HfC, (Ti, Zr, Nb, Ta, Hf)C may have interesting high temperature applications. Furthermore, using this approach, it should be possible to design new (Ti, Zr, Nb, Ta, Hf)C-reinforced steel matrix composites for a variety of engineering applications.

The objective of this study is to develop and test a coarse-grained molecular dynamics framework to model microscale multiphase systems with different inter-particle interactions and recover emerging thermodynamic and mechanical properties at the microscale. A water-vapor model and a fused silica model are developed to demonstrate the capability of our framework. The former can reproduce the water density and surface tension over a wide range of temperatures; the latter can reproduce experimental density, tensile strength, and Young’s modulus of fused silica. Therefore, the deformable solid model is implemented in the proposed framework. Validations of spatial scaling methods for solid, liquid, and multiphase systems suggest that the proposed framework can be calibrated at an arbitrary microscale and used at a different length scale without recalibration. Different values of wettability for a solid-liquid-vapor system that is characterized by the contact angle can be achieved by changing the solid-liquid inter-particle potential. Thanks to these features, the proposed coarse-grained molecular dynamics framework can potentially find applications in modeling systems in which multiple phases coexist and have substantial interactions.

Structural characteristics are considered to be the dominant factors in determining the effective properties of granular media, particularly in the scope of transport phenomena. Towards improved heat management, thermal transport in granular media requires an improved fundamental understanding. In this study, the effects of packing structure on heat transfer in granular media are evaluated at macro- and grain-scales. At the grain-scale, a gas-solid coupling heat transfer model is adapted into a discrete-element-method to simulate this transport phenomenon. The numerical framework is validated by experimental data obtained using a plane source technique, and the Smoluschowski effect of the gas phase is found to be captured by this extension. By considering packings of spherical SiO2 grains with an interstitial helium phase, vibration induced ordering in granular media is studied, using the simulation methods developed here, to investigate how disorder-to-order transitions of packing structure enhance effective thermal conductivity. Grain-scale thermal transport is shown to be influenced by the local neighbourhood configuration of individual grains. The formation of an ordered packing structure enhances both global and local thermal transport. This study provides a structure approach to explain transport phenomena, which can be applied in properties modification for granular media., 11 figures, 29 pages