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The difficulty of obtaining a densely packed granular material as an initial condition is a very common problem in numerical simulations of granular materials. In this article, an Imaginary Coating Algorithm (ICA) is introduced. To avoid unreasonable particle deformation when using a longer time step and a lower Young’s modulus, the radii used in calculating the action forces in a binary collision are slightly larger than the real values. In other words, an imaginary coat is added to each particle or element. To validate this algorithm, simulations were carried out by using ÅDEM, and a A Discrete Element Method (DEM) software program was developed. Compared with traditional Simulated Annealing Algorithms (SAA), this technique can approach the densely packed state with less CPU/GPU time and is easy to operate.

International audience; The well-known synthesis of the two polymorphs of the {[Fe(Htrz)2(trz)](BF4)}n spin crossover coordination polymer is explored with new template-free methods that allow a control over the local synthetic conditions. A “one-pot” synthesis approach is developed, in which the solid reactants are mixed together before the addition of the solvent, which is expected to generate instantaneous supersaturation conditions favoring the nucleation of particles over their growth. In a second method, the addition of ultrasound pulses promotes the appearance of local “hot spots” that affect the local temperature and allow exploring a different region of the concentration–temperature phase diagram, leading to an increase in the phase purity of the product. These two syntheses are compared to the classical method in which the reactants are first dissolved in separate solutions before being mixed. The use of a one-pot synthesis, with or without ultrasound pulses, induces a downsizing of the particle size by a factor of 500 on their volume. The addition of ultrasound pulses allows moving from a mixture of polymorphs I and II of this compound to the pure phase I. These approaches open the way to more studies on the control over the size or phase purity in such molecular compounds, without the use of any surfactant.

The paper studies the process of obtaining swelled granular materials based on liquid glass under the action of microwave radiation and compares it with the process of obtaining these materials with traditional convective heating. It has been established that under the action of microwave radiation at the same temperatures with convective heating, swelling of granular material occurs twice as intensively. Thus, at a power of 650 W (T=115-120 °C), the swelling coefficient reaches its constant value of 2.86 already at the 6th minute of the process, while when grains swell during convective heating at the same temperature, the highest value of the swelling coefficient is 1.534, and it is reached after 11 minutes, which indicates the complexity of grain swelling under these conditions, due to the occurrence of competing processes of porization and dehydration. The acceleration of the swelling process and the possibility of carrying it out at lower temperatures are due to the fact that under the action of microwave radiation due to the excitation of ionic currents by the microwave field, diffusion processes of substances with ionic conductivity, which include liquid glass, are significantly intensified. The impossibility of carrying out the process at given temperatures during convective heating is explained by the fact that the main condition which ensures swelling during heat treatment is the coincidence in time of the pyroplastic state of the material with the most intense gas evolution. The pyroplastic properties of alkali soluble silicates are manifested in the temperature range of 120-250 °C, which corresponds to the maximum water removal, that is, at the temperatures of 115-120 °C, the process is just beginning. To confirm the effectiveness of the use of microwave installations, the energy consumption and efficiency ratio of the installations have been calculated and it is determined that the efficiency ratio of the microwave installation is almost twice the efficiency ratio of the drying installation. The paper also presents the types of industrial microwave installations in which it is possible to carry out the process of swelling of liquid glass grains., В роботі проводиться дослідження процесу отримання спучених зернистих матеріалів на основі рідинного скла під дією НВЧ випромінювання та порівняння його з процесом отримання цих матеріалів при традиційному конвективному нагріванні. Встановлено, що під дією НВЧ випромінювання за однакових температур з конвективним нагрівом вдвічі інтенсивніше відбувається спучення зернистого матеріалу. Так, при потужності 650 Вт (Т = 115–120 °С) коефіцієнт спучення досягає свого постійного значення 2,86 вже на 6-й хв процесу, тоді як при спученні зерен при конвективному нагріві за тієї самої температури найвище значення коефіцієнта спучення – 1,534 і досягається воно через 11 хв, що свідчить про складність спучення зерен за цих умов через перебіг конкуруючих процесів поризації та дегідратації. Прискорення процесу спучення і можливість його проведення за більш низьких температур пов’язані з тим, що під дією НВЧ випромінювання за рахунок збудження мікрохвильовим полем іонних токів значно інтенсифікуються дифузійні процеси речовин з іонною провідністю, до яких відноситься рідинне скло. Для підтвердження ефективності використання НВЧ-установок було розраховано енергоспоживання і ККД установок та визначено, що ККД НВЧ установки майже вдвічі перевищує ККД сушарної установки. Наведено види промислових НВЧ-установок, в яких можна здійснити процес спучення рідинноскляних зерен.

Silver–bismuth iodide (Ag–Bi–I) rudorffites are chemically stable and non-toxic materials that can act as a possible lead-free replacement for methylammonium lead halides in optoelectronic applications. We report on a simple route for fabricating Ag–Bi–I colloidal nanoplatelets approximately 160 nm in lateral dimensions and 1–8 nm in thickness via exfoliation of Ag–Bi–I rudorffite powders in acetonitrile. The valence band electronic structure of isolated Ag–Bi–I nanoplatelets was investigated using synchrotron radiation to perform X-ray aerosol photoelectron spectroscopy (XAPS). The ionization energy of the material was found to be 6.1 ± 0.2 eV with respect to the vacuum level. UV–vis absorption and photoluminescence spectroscopies of the Ag–Bi–I colloids showed that the optical properties of the nanoplatelets originate from I 5p to Bi 6p and I 5p to I 5p transitions, which is further confirmed by density functional theory (DFT) calculations. Finally, calculations based on the DFT and k · p theoretical methods showed that the quantum confinement effect is very weak in the system studied.

When developing flexible electronic devices, trade-offs between desired functional properties and sufficient mechanical flexibility must often be considered. The integration of functional ceramics on flexible materials is a major challenge. However, aerosol deposition (AD), a room-temperature deposition method, has gained a reputation for its ability to combine ceramics with polymers previously considered incompatible with the conventional high-temperature sintering process. In this work, 0.9Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$−0.1PbTiO$_3$ (PMN−10PT) thick films were deposited directly on a polyimide substrate using the AD method. As a result, dense and flexible relaxor-ferroelectric thick films were produced by a one-step direct-integration, suitable for large-scale production. After annealing of as-deposited PMN−10PT films at 400 °C, stress-relaxation occurs, which is responsible for the development of a relaxor-ferroelectric character. Achieved high polarization (38 μC·cm$^{−2}$), high dielectric breakdown strength (∼1000 kV·cm$^{−1}$), and low hysteresis losses lead to improved recoverable energy density and energy-storage efficiency of the annealed thick films, reaching 10 J·cm$^{−3}$ and 73% (at 1000 kV·cm$^{−1}$), respectively. The thick films were subjected to flexural bending tests, which showed high flexibility (1.1% bending strain) and high durability (10$^5$ bending cycles). This stable energy-storage operation makes ceramic-polymer layered structures promising for integration into a wide range of flexible electronic devices.

The size and shape of individual grains, play an important role in the mechanical behavior of granular materials such as the strength and stability of railway ballast. The aim of this research is to study materials from which uniform, reproducible grains with irregular convex geometry can be created by molding and additive manufacturing technologies in order to create reproducible artificial assemblies that can be used in experiments. Packings with determined grain shape results more controlled investigations contrarily to using natural grains with random geometry. Specimens were made from railway ballast materials, materials used in the construction industry, additively manufactured and molded polymers, and certain low-strength materials. Uniaxial compression and bending tests were conducted on these specimens. The mechanical properties of typical railway ballast materials (basalt and andesite) were compared with the properties of artificially produced materials. The results show that for grain reproduction the molding technology is recommended with the use of polyester-crushed stone composite and ceramic powder. Furthermore, the additive manufacturing was recommended with PolyJet or Multi Jet Fusion technology as they have the feasibility to produce grains with similar material properties to the properties of basalt and andesite.

Self-assembly at the macro-scale is a promising pathway for fabrication, but the assembly process and mechanisms are still poorly understood. We examine the vibration-induced assembly of hard cubic grains as a potential route for the rapid fabrication of architectured materials and structures. We performed assembly experiments with various combinations of vibration amplitudes and frequencies to map the different states of the system. The results show that the acceleration normalized by gravity cannot fully capture the phase transitions or the mechanisms governing cubes packing and that amplitude and frequency must be considered independently. We used discrete element modeling to duplicate experiments and then single-grain models to find the effective mechanisms involved in the packing and phase transition of cubes. Both cube rotation and bouncing govern packing, while bouncing has an additional role in the phase transition. These findings provide guidelines for the assembly of complex materials, for example, topologically interlocked materials.

Granular materials display significant differences in their acoustical response when tested in a standing wave tube, compared with the behavior of more traditional sound absorbing materials such as fibrous webs and foams. The latter materials can often be modeled as an equivalent fluid with the further assumption that the material properties do not depend on the input signal level. In contrast, the level dependence of the acoustical behavior of granular materials has been observed in measurements of glass bubbles, as reported in previous studies, for example. When the input level is low, the absorption coefficient of the glass bubble stack shows solid-like behavior with multiple peaks associated with modal response of the stack. On the other hand, when the input level is high, glass bubble stacks show fluid-like behavior, with the quarter wavelength resonance in the direction of the tube axis dominating the response. In the current work, the boundary conditions at the air/granule interface and the granule/tube wall boundary are studied, as is the mechanism causing the variation of the apparent stiffness of the granule stack. The proposed model is implemented with a finite difference approach, and the model predictions are compared with acoustic measurements of granule stacks.

Each year, the number of scrap tires disposed of in huge piles across the world continuously increases. Consequently, new recycling solutions for these materials have to be proposed. Among them, one possibility consists of shredding tires and mixing the obtained tire chips with sand, which can be used as alternative soils in various geotechnical applications, such as backfilling for retaining structures, slope and highway embankment stabilization, road constructions, soil erosion prevention, and seismic isolation of foundations. Such types of mixtures are highly heterogeneous due to the important difference in elasticity and deformability between the two constituents, which leads to complex mechanical behavior. In this article, the one-dimensional loading/unloading behavior of sand-rubber mixtures is investigated by laboratory strain-controlled experiments performed for different packing densities, particle sizes, rubber contents, and sand/rubber size ratios. After a global analysis of the increase of the packing deformation with the rubber fraction and the stress level, a novel criterion to classify the behavior of the mixture as sand-like or rubber-like was proposed, based on the concavity of the void ratio—log of vertical stress curve. The concavity increased with the stress level and the rubber fraction, up to the limits where the saturation of the voids due to their filling with rubber induces a rubber-like behavior. A simplified phase diagram, limited to the range of this study, is proposed. The one-dimensional confined stiffness and the swelling behavior were also analyzed.

Discrete element method (DEM) has been intensively used to study the constitutive behaviour of granular materials. However, to what extent a real granular material can be reproduced by virtual DEM simulations remains unclear. This study attempts to answer this question by comparing DEM simulations with typical features of experimental granular materials. Three groups of models with spherical and clumped particles are investigated from four perspectives: (i) deviatoric stress and volumetric behaviour; (ii) critical state behaviour; (iii) stress-dilatancy relationship; and (iv) the evolution of principal stress ratio against axial strain. The results demonstrate that DEM with spherical or clumped particles is capable of qualitatively describing macroscopic deviatoric stress responses, volumetric behaviour, and critical state behaviour observed in experiments for granular materials. On the other hand, some qualitative deviations between experiments and the investigated DEM simulations are also observed, in terms of the stress-dilatancy behaviour and principal stress ratio against axial strain, which are proven to be critical for constitutive modelling. The results demonstrate that DEM with spherical or clumped particles may not necessarily fully capture experimental features of granular materials even from a qualitative perspective. It is thus encouraged to thoroughly validate DEM with experiments when developing constitutive models based on DEM observations.

Strain localization is one of the key phenomena which has been extensively studied in geomaterials and for other kinds of materials including metals and polymers. This well-known phenomenon appears when structure/material is closed to failure. Numerous theoretical, experimental, and numerical studies have been dedicated to this subject for a long while. In the numerical aspect, strain localization inside periodic granular assembly has not been well studied in the literature. In this paper, we investigate the occurrence and development of strain localization within a dense cohesive-frictional granular assembly with high coordination number under bi-periodic boundary conditions by Discrete Element Modeling (DEM). The granular assembly is composed of 2D circular particles and subjected to biaxial loading scheme with constant lateral pressure. The results show that the formation of shear bands is of periodic type, consistent with the boundary conditions used. The occurrence and development of the shear band are originated from the irreversible loss of cohesive contacts. The latter is viewed as micro-cracking in the cohesive-frictional granular media, which is highly concentrated in the periodic shear zones and thus related to the strain localization observed at the sample scale. Finally, we also show that the strain localization is in perfect agreement with the kinematic field, displayed in terms of displacement fluctuation.

Strain localization is one of key phenomena which have been studied extensively in geomaterials and for different kinds of materials including metals and polymers. This well-known phenomenon appears when structure/material is closed to failure. Theoretical, experimental, and numerical research have been dedicated to this subject for a long while. In the numerical aspects, strain localization inside the periodic granular assembly has not been well studied in the literature. In this paper, we investigate the occurrence and development of strain localization within a dense cohesive-frictional granular assembly with high coordination number under bi-periodic boundary conditions by Discrete Element Modeling (DEM). The granular assembly is composed of 2D circular disks and subjected to biaxial loading with constant lateral pressure. The results show that the formation of shear bands is of periodic type, consistent with the boundary conditions. This formation has the origins of the irreversible losing of cohesive contacts, viewed as micro-crackings which strongly concentrated in the periodic shear zones. This micromechanical feature is therefore strongly related to the strain localization observed at the sample scale. Finally, we also show that the strain localization is in perfect agreement with the sample’s displacement fluctuation fields.

Throughout the world, dam and dikes are constructed to ensure energy production and security of the populations. Such hydraulic structures can be quite large, spanning over kilometers, and are often made of granular materials. The study of the latter has long been challenging because their behaviour emerges from complex phenomena occurring between grains, at the microscopic scale. Usual constitutive laws used for other materials, e.g. for steel, thus struggle to handle the variety of loading paths a granular material may be subjected to. More accurate models were developed by considering a non-continuous description of the material at the grain scale, making possible the inclusion of important microscopic phenomena. For instance, Discrete Element Method (DEM) directly models all constitutive grains, resulting in an expensive but also very accurate description of any granular material. Indeed, a cubic meter of granular material can contain tens of billions particles, requiring years of calculation on most super-computers. The structure scale is thus unreachable with DEM simulations.This thesis demonstrates how DEM can be used to describe the behaviour of granular materials within a continuum-based method, the Material Point Method (MPM), thus replacing the usual constitutive laws. Such a MPMxDEM coupling can be implemented to model earth dams and dikes at large scales with a DEM accuracy, even when deformations reach a point where the traditional Finite Element Method (FEM) is unable to continue the simulation. First, two DEM studies are performed on an artificial real-life material using the open-source software YADE. The angle of repose formed by a heap of particles and the role of rattlers at critical state are therein examined through the execution of many simulations. As for the MPM, a parametric study is performed after detailing its formulation, which is linked to the MPM open-source code used in this thesis (CB-Geo MPM). More precisely, the excessive dissipative properties of PIC-based MPM velocity update strategies are highlighted in the simple case of a bouncing elastic cube. A MPMxDEM formulation is next provided, including specifics of the quasi-static assumption made at the microscopic scale. Technical aspects on how our MPMxDEM implementation embeds the Python user interface available in YADE into the C++ source code of CB-Geo MPM are discussed. In particular, details are given on how a Python module developed during this thesis implements an interface for CB-Geo MPM and the MPMxDEM framework. A speed-up analysis of our MPMxDEM implementation performed on a server machine then assesses its performances, demonstrating that simulations can be considerably accelerated through parallelization. Our MPMxDEM implementation is shown to be capable of reproducing accurately pure DEM results in the case of a one cell triaxial test, performed on a numerical replica of Camargue's sand. The well-known case of the collapse of a granular column is finally investigated, using both pure MPM with the Mohr-Coulomb constitutive law and the MPMxDEM coupling, the latter using the best set of parameters determined in the former. An analysis of the deformation involved at each MPM iteration establishes that our quasi-static assumption is necessary to perform a MPMxDEM simulation at this scale, within a reasonable amount of time. It is highlighted that using MPM unrealistically decreases the collapse rate of the column, compared to experimental results as well as results obtained with other numerical methods. However, the final run-out of the collapsed column is found to be in accordance with the values obtained in the literature using a similar multi-scale model.; Des barrages et des digues sont construits à travers le monde afin d'assurer la production d'énergie et la sécurité des populations. De telles constructions peuvent avoir des tailles conséquentes, s'étendant sur des kilomètres, et sont souvent construites avec des matériaux granulaires. Leur comportement découle de mécanismes complexes ayant lieu à l'échelle du grain et s'en trouve difficile à décrire. Les lois constitutives utilisées habituellement pour d'autres matériaux plus homogènes, tels que l'acier, peinent à reproduire le comportement des matériaux granulaires pour des chemins de chargement quelconques. Des modèles plus précis ont été mis au point en se basant sur une description non continue du matériau à l'échelle du grain, permettant ainsi la prise en compte de phénomènes microscopiques importants. Parmi ces modèles, la Méthode des Éléments Discrets (DEM) décrit le comportement des matériaux granulaires avec une bonne précision en modélisant directement l'ensemble des grains qu'il contient. Le coût numérique de cette méthode est cependant assez élevé, un mètre cube de matériau granulaire pouvant contenir des dizaines de milliards de grains, ce qui nécessiterait des années de calculs sur la plupart des super-ordinateurs actuels. La DEM ne permet donc pas d'accéder à l'échelle des ouvrages.Cette thèse propose une façon d'utiliser la DEM pour décrire le comportement de matériaux granulaires au sein d'une méthode basée sur la continuité du matériau, la Méthode du Point Matériel (MPM), remplaçant ainsi de fait la loi constitutive phénoménologique. Un tel couplage MPMxDEM peut-être envisagé pour modéliser de grands ouvrages avec la précision de la DEM, même dans les cas où des déformations importantes empêcheraient la Méthode des Éléments Finis (FEM) de poursuivre son calcul.Dans une première partie, deux études DEM sont menées à l'aide du logiciel open-source YADE sur un matériau réel et concernent d'abord l'angle de repos formé par un empilement de grains soumis à la gravité puis l'implication des "rattlers" (particules avec 0 ou 1 contact) dans la description de l'état critique en l'absence de gravité. Ensuite, une analyse des paramètres fondamentaux de la formulation de la MPM est menée, dans le cadre de l'utilisation du code open source CB-Geo MPM. La dissipation excessive d'énergie que présentent certains schémas MPM est mise en évidence dans le cas simple d'un cube élastique qui rebondit. Dans une seconde partie, le couplage MPMxDEM est formulé explicitement, en détaillant l'hypothèse de quasi-staticité faite à l'échelle microscopique. Différents aspects de notre implémentation MPMxDEM sont discutés, notamment l'intégration de l'interface Python de YADE dans le code C++ de CB-Geo MPM. Cela inclut la présentation d'un module Python, développé dans le cadre de cette thèse, qui sert d'interface à CB-Geo MPM en intégrant les spécificités du couplage MPMxDEM. Une analyse des performances de notre implémentation montre par la suite que, si judicieusement paramétrée, une parallélisation du code peut considérablement accélérer les simulations MPMxDEM. Notre implémentation MPMxDEM est ensuite validée sur la base de résultats d'un essai triaxial pur DEM, réalisé sur un modèle numérique du sable de Camargue.Le cas de l'effondrement d'une colonne de sable est finalement étudié, en pure MPM avec le modèle de Mohr-Coulomb et en MPMxDEM. Une analyse de la déformation imposée par la MPM pour le calcul local DEM démontre que notre hypothèse de quasi-staticité est indispensable afin de réaliser une telle simulation en un temps raisonnable. Il est observé que la MPM ralentit excessivement la chute de la colonne, par rapport à des résultats expérimentaux mais aussi numériques, obtenus avec d'autres méthodes. Cependant, l'étalement final obtenu pour nos colonnes MPMxDEM est en accord raisonnable avec les résultats produits à l'aide d'une autre approche multi-échelles similaire.

Magnetic viscosity experiments have been performed in order to investigate the magnetization reversal in Sr nanoferrite particles (nanoscale SrFe12O19) and interacting Sr/Co nanoferrite particles (SrFe12O19–CoFe2O4 nanocomposites). The magnetic viscosity S = d M ( t ) / d l n ( t ), where M ( t ) is the magnetization as a function of time, has been collected. For Sr nanoferrite S shows a maximum close to the coercive field, reflecting the relation between S and the energy barrier distribution. We evidence that magnetic viscosity experiments on Sr nanoferrite and interacting Sr/Co nanoferrite particles provide reliable qualitative results for the different magnetic field sweep rate and saturating field H s a t considered. In addition, the activation volumes extracted from the magnetic viscosity experiments performed at different temperatures on Sr nanoferrite are quantitatively correlated to anisotropy changes.

A granular material is a collection of discrete, solid particles. This substance is ubiquitous in nature and industry, with examples ranging from soils, jointed rocks, foodstuffs, ball bearings, powders, and even asteroids. As such, understanding granular materials is necessary for making sense of the physical world. Tremendous progress has been made in directly simulating granular materials in the previous decades, in particular via the discrete element method (DEM). Nevertheless, there remains ample opportunity for manipulating granular materials to achieve specific outcomes by leveraging the DEM. The research presented in this thesis utilizes DEM simulations to develop tools and strategies for manipulating granular material to achieve desired attributes. These attributes include the shape of individual grains, the structure of granular tunnels, and mesoscopic packing characteristics such as packing fraction and coordination number. Optimization of granular materials is considered at 3 different scales: at the single grain scale (100 grains), at the scale of granular structures such as arches (101 grains), and at the mesoscopic scale (103 grains). The first component of this thesis considers automated design of individual grain shapes that embody user-specified morphological properties via genetic algorithms. Next, excavation in granular materials is considered. It is studied how ants can so successfully manipulate granular materials to achieve stable systems by mapping the forces around real ant tunnels. Ant tunnels are simulated using a DEM which can handle arbitrary shaped grains: the Level-Set Discrete Element Method (LS-DEM). Finally, tools are developed for controlling mesoscopic attributes of granular materials as a function of grain shape. To do so, genetic algorithms and a deep generative model are combined with LS-DEM. The methodologies introduced in this thesis serve as a foundation for controlling granular material attributes. Such techniques can be leveraged to engineer granular materials, with applications ranging from swarm robotics, robotic grippers, mechanically tunable fabrics for armor, and robotic excavation.

To improve the understanding of the mixing performance of double shaft, batch-type paddle mixers, the discrete element method (DEM) in combination with a Plackett–Burman design of experiments simulation plan is used to identify factor significance on the system’s mixing performance. Effects of several factors, including three material properties (particle size, particle density and composition), three operational conditions (initial filling pattern, fill level and impeller rotational speed) and three geometric parameters (paddle size, paddle angle and paddle number), were quantitatively investigated using the relative standard deviation (RSD). Four key performance indicators (KPIs), namely the mixing quality, mixing time, average mixing power and energy required to reach a steady state, were defined to evaluate the performance of the double paddle mixer. The results show that the material property effects are not as significant as those of the operational conditions and geometric parameters. In particular, the geometric parameters were observed to significantly influence the energy consumption, while not affecting the mixing quality and mixing time, showing their potential towards designing more sustainable mixers. Furthermore, the analysis of granular temperature revealed that the centre area between the two paddles has a high diffusivity, which can be correlated to the mixing time.

This PhD thesis focuses on the flows on granular materials, such as sand, glass beads, and powders, which are sheared at low speeds with gravity perpendicular to the flow direction. The study is conducted using a combination of experiments, simulations, and theory, with the goal of developing a unifying theory of granular materials that can be described by continuum models. The main objective is to understand how microscale physics propagate to macroscale phenomena and to address issues related to setting boundary conditions and predicting timescales from unsteady to steady states. This research primarily aims to investigate stress variations in granular materials as a function of shear rate, encompassing both steady and unsteady states. Additionally, the thesis examines the phenomena of wall force anomalies and vortex flows. In Couette cell experiments and vertical plane shear simulations, granular material demonstrates a downward flow near the vertical shearing wall and an upward flow adjacent to another static vertical wall. Interestingly, this vortex flow causes a change in the direction of vertical shear stress when wall shearing commences, contradicting the prevalent assumption that particles consistently apply a downward force on the vertical wall. The study concludes with key findings, including the observation that normal and shear stresses on the shearing wall increase slowly after the initiation of shearing, and that steady-state values for these stresses are independent of the shearing speed within a certain range. The study also found that the height of particles near the shearing wall decreases gradually with the presence of vortex flow, and that the shear rate near the moving wall is initially high and decreases slowly to reach a steady state. Additionally, we used a non-local constitutive model and Boussinesq approximation to predict the downward flow that is driven by gravity and variations in the solid fraction near the shearing surface, as well as the decay profile of velocity in an infinitely wide box for the steady state. Overall, this thesis contributes to our understanding of granular materials in the slow flow regime, providing insights into their behavior under shear. The non-local model accurately predicts the downward flow and velocity decay profile, indicating its potential as a valuable tool for future research.

Due to their chemical composition, richness in calcium carbonate, chitin, proteins, and pigments, and nanoporous structure, crustacean shell waste shows great potential for a wide variety of applications. Large quantities of waste shells are produced annually, meaning that they can be considered a renewable source of ecofriendly biogenic materials, which can be turned into value-added byproducts. In this paper, an IR-based technique is developed to differentiate various biogenic powders originated from crude or food- processed crustacean shells. The validity of the method is supported by cross-checking with XRD, NMR, and SEM–EDX analyses. Our goal was to determine changes in properties of waste crab shells after the two most common treatments, deproteinization and milling. We discovered that deproteinization with NaOH could be tracked from the IR absorbance intensity ratio of the υ(CH2, 3) and υasym(CO32–) bands while milling time less influenced this ratio but induced changes in powder particle size distribution and morphology. The relative organic/inorganic ratio was different for different colored shells. Unexpectedly, waste shells stored for an average of 6 months or more were found to contain hydrated calcium carbonate (monohydrocalcite), which was absent in equivalent fresh shell composition. Deproteinization caused changes in mechanical properties of shells, making them more brittle, which resulted in a larger fraction of fine particles after powdering.

Granular materials like cereals and sands are widely present in different industrial fields like food and agricultural industry. Capacitive planar sensors for granular materials suffer from an additional source of uncertainty related with the random distribution of the grains inside the sensitivity volume. In this letter, we propose a capacitive planar sensor with a new electrode geometry for increasing the sensitivity volume, thus improving the accuracy of the measurements. The geometry is optimized through a design based on numerical simulations in order to maximize the sensitivity volume without reducing the dynamics of the capacitance variation. Experimental results obtained by considering two different granular materials show a reduction of the standard deviation due to granularity of 20% with respect to a classical interdigital electrode structure. Finally, it is experimentally shown that the increased accuracy of the proposed geometry can be fruitfully used for contaminant detection in a mixture of granular materials.

Cement hydration within particle bed concrete 3D printing processes can be benefited by storing water in the otherwise dry aggregate bulk material. Additional water also has the advantage of acting as a source of passive cooling. However, even small amounts of liquid lead to detrimental effects on bulk properties, such as the flowability. For that reason, this study proposes implementing dry water (DW) in order to store large amounts of water in a bulk material of non-absorbent, coarse sand whilst maintaining its initial bulk properties. DW is essentially created by mixing water and hydrophobic fumed silica in a high shear process, leading to water droplets surrounded by a protective silica shell. Herein, several DW variants, distinguished by their deionised water to hydrophobic silica ratio, were mixed with non-absorbent, coarse sand particles. In addition, mixtures were produced to contain a specific overall water content of up to wH2O = 5% within the bulk material. It was shown that dry water can be used to incorporate large amounts of water into a granular bulk material and simultaneously preserve flow properties. The decisive factor is the proportion of hydrophobic silica for a given water content as the DW capsules may otherwise not endure mechanical stress during mixing. However, even minimal quantities of silica can prevent liquid capillary bridges from forming and, thus, inhibit bulk property degradation.

This paper follows up on a reference paper that inspired MDPI’s topic “Stochastic Geomechanics: From Experimentation to Forward Modeling”, in which the authors populated a spatio–temporal database of boundary displacement fields from a series of triaxial sand specimens using three-dimensional (3D) digital image correlation analysis. The database was curated and is currently available to the scientific community for further study. This paper uses a subset of this database, in which the experimental conditions were similar, to statistically investigate the dominant kinematic phenomena observed on the boundary of triaxial sand specimens under compression. The first-order 3D kinematic operators under the cylindrical coordinates, comprised of the divergence, curl, and gradient, were applied to the boundary displacement fields to illustrate the localization deformation patterns including the translational, rotational, shearing, and volumetric behaviors throughout the triaxial compression processes. Subsequently, the first-order statistics of the kinematic results are estimated, with the aim of revealing the evolution of associated localization effects as well as their corresponding uncertainties in space and time. The results of this research provide an innovative statistical interpretation of the localization effects on soil specimens under three-dimensional stress conditions. The proposed approach advances the interpretation of granular material’s responses under triaxial compression experimental conditions, while opening an opportunity to reproduce the material’s kinematic responses under the triaxial experimental conditions through constitutive modeling or machine learning techniques.

International audience; NaGaS2 is a newly discovered compound that has already shown great promise for a variety of applications because of its layered structure and ion exchange properties. In this work, crystalline NaGaS2 has been synthesized by an alternative method to what has been previously published, namely, by mechanochemistry, either by a direct one-step process or by a two-step process. In the one-step process, crystalline NaGaS2 is directly formed by milling sodium sulfide Na2S and gallium(III) sulfide Ga2S3. However, an amorphous material is present in majority together with the crystalline phase. In the two-step process, amorphous NaGaS2 is first obtained by mechanical milling and then heated above its glass transition temperature to obtain a glass–ceramic mainly composed of crystalline NaGaS2. For the two-step process, changes of the local atomic-level structure in amorphous NaGaS2 and after crystallization were analyzed by high-field solid-state nuclear magnetic resonance (NMR) spectroscopy as well as by X-ray total scattering and pair distribution function (PDF) analysis. Based on quantitative analysis on the 23Na NMR spectra, modifying the annealing treatment can promote the formation of the crystalline phase up to a molar fraction of 83.8%.

Particle image velocimetry has been applied to measure particle velocities on the free surface of a bed of particles within a rotating cylinder during avalanching. The particle velocities were used to examine the validity of existing avalanche models and to propose an alternative model. The movement of particles depends on their location on the surface of the bed: Particles located near the center of the bed travel the farthest, while the distance traveled decreases at an increasing rate for particles located farther from the center. The start of an avalanche can be determined to a single initiation point that can be located on the bottom half of the bed; the avalanche quickly propagates through the entire free surface with 90% of the surface in motion within 257 ms (approximately 20% of the total duration of an avalanche). The experimental insight is used to formulate a geometric model, in which three equal-sized sections flow down the bed surface during an avalanch. The predictions of the model are validated by experimental mixing measurements. ISSN:1539-3755 ISSN:1063-651X ISSN:1095-3787 ISSN:1550-2376

An onshore vibro driving testing of large-scale piles (2.5 m diameter) was carried out in order to validate an innovative foundation design that is needed to overcome challenging soil conditions encountered at an offshore wind farm in France. The foundation concept named DSD (drill-sand-drive) is to replace the hard soils using drilling by engineered granulars that are then compacted to design density though which monopiles are vibrodriven. Three tests were conducted covering different levels of soil compaction from low to very high and that was closely controlled using CPT. The pile driving monitoring comprised PDA sensors, vibro hammer parameters, crane hook load as well as water pressure along the external pile shaft to evaluate the liquefaction extent. The tests ultimately produced the confinement configuration induced by the drilled hole and the surrounding stiff soils and provide evidence of its impact on noticeable amplification of vibro compaction and vibro driving.

The application of recycled materials from the automotive industry in the field of the construction industry is a suitable alternative application for these materials and the use of their acoustic and thermal insulation properties. The output of recycling is granular, or chopped materials that can be used as a substitute for conventional materials. One of the important features of building materials is their acoustic properties. The measurement and evaluation of acoustic properties is carried out using an impedance tube as equipment. Measuring compact materials is quite simple and requires the preparation of a sample. Measuring the acoustic properties of granular bulk materials is more complicated and requires the development and production of a special test cartridge. Recycled bulk materials from the automotive industry such as rubber granules and chopped textiles can be applied as fillings for dividing structures. The aim of this paper was to assess the acoustic properties of different fractions of recycled rubber granules and textile chopped material and to compare acoustic properties with compact rubber and textile panels. To evaluate and compare sound absorption coefficient (α) and sound transmission loss (R) parameters, we used basic statistical methods and hypothesis testing methods. The production of compact panels is quite expensive since it is necessary to use special synthetic binders in production, and the content of these substances can also have negative effects on the environment. Based on the results of measuring the acoustic properties of bulk recycled materials and comparing them with compact materials, we can conclude that bulk recycled rubber and textile materials have very good values for their acoustic properties, which enables them to be used in several areas of industry.

Perovskite oxyhydride SrVO₂H (V³⁺, d²) is a Mott insulator with a strong two-dimensional correlation due to anion ordering. In this study, we attempted electron doping by aliovalent substitution. Although Sr₁–xLaxVO₃ thin films (x ≤ 0.4) on a SrTiO₃ substrate were topochemically reduced using CaH₂, vanadium of the reduced films retained the trivalent state. Combined with the results of secondary ion mass spectroscopy, we conclude that Sr₁–xLaxVO₂+xH₁–x is obtained, where the apical oxygen site is partially replaced by hydride anions. First-principles theoretical calculations highlight the role played by compressive biaxial strain in stabilizing the charge-compensated Sr₁–xLaxVO₂+xH₁–x phase, rather than the electron-doped Sr₁–xLaxVO₂H. The present study demonstrates that topochemical reactions combined with substrate strain provide various opportunities to widen the compositional space in mixed-anion compounds.

The discrete element method (DEM) is a well-established approach to study granular materials in numerous fields of application; each granular particle is modelled individually to predict the overall behaviour. This behaviour can be then extracted by averaging, or coarse graining, the sample using a suitable method. The choice of appropriate coarse-graining method entails a compromise between accuracy and computational cost, especially in the large-scale simulations typically required by industry. A number of coarse-graining methods have been proposed in the literature, and these are reviewed and categorized in this work. Within this contribution, two novel porosity coarse-graining strategies are proposed including a voxel method where a secondary dense grid of “pixel cells” is implemented adopting a binary logic for the coarse graining and a hybrid method where both analytical formulas and pixels are utilized. The proposed methods are compared with four coarse-graining schemes that have been documented in the literature, including the particle centroid method, an analytical method, a method which solves the diffusion equation and an approach which employs averaging using kernels. The novel methods are validated for problems in both two and three dimensions through comparison with the “accurate” analytical method. It is shown that, once validated, both the proposed schemes can approximate the exact solutions quite accurately; however, there is a high computational cost associated with the voxel method. The accuracy of both methods can be adjusted allowing the user to decide between accuracy and computational time. A detailed comparison is then presented for all six schemes considering “accuracy”, “smoothness” and “computational cost”. Optimal parameters are obtained for all six methods, and recommendations for coarse-graining DEM samples are discussed.

Domestic and foreign relevant literatures of granular column collapse movement models are concluded to analyze the effects of initial spatial characteristics, essential physical properties of particles, boundaries, and environment conditions of model on the movement and accumulation characteristics of granular columns. Besides, the related mechanisms of movement and accumulation characteristics of granular columns are also analyzed. Remarkable linear and power relationships exist between the movement distance and the aspect ratios of initial height to initial width. Similarly, remarkable linear and power relationships exist between accumulation height and aspect ratio of initial height to initial width. The movement patterns and energy consumption mechanisms for granular columns with large aspect ratios are significantly different from those with small aspect ratios. A consensus has basically been reached concerning the effect of particle size, particle stiffness, particle breakage, and wet particles on the movement and accumulation characteristics of granular columns. Some preliminary research achievements of the effects of different wall constraints, fluidization phenomenon due to the gas mixing and water condition on the movement and accumulation characteristics of granular column are obtained. However, there still exist disagreements in the conclusions about the influences of initial porosity of granular column, particle friction, and wall friction on the movement and accumulation characteristics of granular column. A review of the current research indicate that the research in the future will be focused on the relationship between forces acted on particles and movement regimes. The mechanisms of the effect of complex particle shape, surface, particle density, and water movement conditions on the movement and accumulation characteristics of granular column collapse will also be focused on in the future.

International audience; Une méthode numérique multi-échelles est proposée afin de modéliser de manière précise les matériaux granulaires soumis à des chargements importants. En effet, les mécanismes agissant à l'échelle microscopique dans le matériau sont décrits à l'aide de la Méthode des Éléments discrets (DEM), traduisant rigoureusement le comportement du matériau. De plus grandes échelles sont atteintes en couplant la DEM avec la Méthode du Point Matériel (MPM), dévelopée pour des matériaux sujets à de grandes déformations, et dont le comportement dépend de leur histoire. Le couplage MPMxDEM est comparé à une simulation pure DEM contenant 30,000 sphères dans le but d'évaluer la fiabilité et l'efficatité du couplage. Un aperçu du comportement du matériau est donné à différents endroits dans l'échantillon, en tirant profit de la modélisation précise des structures microscopiques par la DEM.

We study the transmission of compressive and tensile stresses, and the development of stress - induced anisotropy in entangled granular structures composed of nonconvex S-shaped hooks and staples. Utilizing discrete element simulations, we find that these systems exhibit fundamentally different behavior compared to standard convex particle systems, including the ability to entangle which contributes to a lower jamming packing fraction and facilitates the transmission of tensile stresses. We present direct evidence of tensile stress chains, and show that these chains are generally sparser, shorter and shorter-lived than the compressive chains found in convex particle packings. We finally study the probability distribution, angular density and anisotropic spatial correlation of the minor (compressive) and major (tensile) particle stresses. The insight gained for these systems can help the design of reconfigurable and recyclable granular structures capable of bearing considerable loads, without any need for reinforcement., Granular Matter, 24 (3), ISSN:1434-5021, ISSN:1434-7636

Rapeseed is one of the most important sources of vegetable oil worldwide. Knowledge of the dielectric properties of rapeseed may be beneficial for moisture content determination and the optimization of microwave treatment processes. The aim of this research was to examine the complex dielectric permittivity spectra of rapeseed of moisture content from 8.3% to 16.1%. The measurements were performed in the 20 MHz–3 GHz frequency range with the use of a vector network analyzer and a coaxial transmission-line cell. The real part of dielectric permittivity significantly depended on the water content of the seeds. The obtained spectra were modeled with the use of a three-pole Debye model with bulk electrical conductivity. Because the highest-frequency pole was found near the high-frequency measurement band limit, the spectra were additionally modeled with the use of an approximate ABC model with two in-band Debye poles. The determined model parameters were found to be highly dependent on the water content of the seeds. The relations between these parameters and water content were analyzed.

Particle and continuum methods are usually coupled to handle particle-structure contact problems and transitional material behavior between discontinuous and continuous.In this work, we reformulate the surface and volume coupling methods based on a micro-macro transition technique called coarse-graining(CG).For surface coupling, coarse graining allows distributing the coupling forces beyond the elements that the particles are locally coupled with, e.g., from contact points to the neighboring integration points.For volume coupling, coarse-graining enriches the homogenization operation with a non-local contribution from the particles.The generalized coupling terms contain one user-defined parameter, namely, the CG width, setting a length scale for the coarse-grained fields.The advantages of CG in surface and volume coupling are demonstrated via two numerical examples: an elastic cube falling on a granular bed and wave propagation between discrete and continuum media.In this paper, we focus on how the conservation properties of the coupled system are influenced by the CG width.Together with other numerical parameters relevant to the coupling, we show that the CG-enriched formulations lead to better numerical stability and less computational cost for a given energy dissipation ratio.

International audience; The "incremental shear strain chain" concept (simply called "shear chain") has been proposed recently to quantitatively account for local kinematic features of granular materials. At the microscopic scale, contacts can slide and particles can rotate; while at the macroscopic scale, shear bands appear as a typical localized failure mode. Despite visual spatial distribution features, the direct links from microscopic to macroscopic shear behaviors are still missing. This paper investigates shear characteristics appearing at the micro, meso and macro scales in granular materials, and tries to elucidate how they can be correlated by adopting the shear chain concept. Based on the spatial statistics tools, the shear chain and the shear band orientations are compared by demonstrating that the shear band is influenced by the sample aspect ratio while shear chain orientation only depends on the stress state. Shear chains experience a relative steady and high fabric anisotropy, irrespective to the stress state. Micro contact sliding and particle rotation mainly exist in the shear chain connection positions, which gives possible clues on shear chain forming. In conclusion, the shear band is eventually conjectured to be formed of a collection of crossing shear chains at meso scale, according to detailed analysis and discussion on the correlations of shear behaviors across scales.

International audience

International audience; Up to now, the possible occurrence of a cationic ordering on the tetrahedral sublattices of stoichiometric double scheelite-type oxides was not settled, with somewhat contradictory X-ray diffraction and optical measurements [Blasse, G. J. Inorg. Nucl. Chem. 1968, 30, 2091]. Using two different synthesis routes, both ordered and disordered forms of fergusonite La2SiMoO8 were prepared. The crystal structure of the ordered form was determined using powder X-ray and neutron diffraction, which clearly evidence a tridimensional ordering between [SiO4] and [MoO4] tetrahedra. The crystal chemistry of ordered double sheelite-type LaIII2(SiIVO4)(MoVIO4) can be seen as an intermediate between those of simple regular scheelite or fergusonite LnIII(NbVO4) and of ordered triple scheelite BiIII3(FeIIIO4)(MoVIO4)2. The structure of the disordered La2SiMoO8 phase was analyzed using powder X-ray diffraction. A few small and larger diffraction peaks or bumps are observed in addition to the sharper peaks of a simple fergusonite cell. DIFFaX and FAULTS programs helped showing that these faint peaks originate from stacking faults between 2D ordered layers. The intermediate 2D–3D nature of SiO4/MoO4 ordering in seemingly disordered compounds might explain the previous discrepancy between optical and X-ray diffraction measurements.

The morphodynamic evolution of the shape of dunes and piles of granular material is largely dictated by avalanching phenomena, acting when the local slope gets steeper than a critical repose angle. A class of degenerate parabolic models are proposed closing a mass balance equation with several viscoplastic constitutive laws to describe the motion of the sliding layer. Comparison among them is carried out by means of computational simulations putting in evidence the features that depend on the closure constitutive assumption and the robust aspects of the models. The versatility of the model is shown applying it to the movement of sand in presence of walls, open ends, columns, doors, and in complicated geometries.

International audience; The objective of the study is to analyze the thermomechanical response of a two-dimensional monodisperse granular system made of thermoplastic polyurethane (TPU) cylinders with elliptical cross-section. Cyclic confined compression tests were performed while an infrared (IR) camera measured the temperature changes at the surface of the cylinders. Thermoelastic coupling and mechanical dissipation were distinguished in the thermal evolution. The former was mainly evidenced as a consequence of stress concentrations in the interparticle contact zones. The latter was highlighted at specific contacts, which can be explained by strong friction in these zones. The higher the number of applied mechanical cycles, the higher the temperature rise as a consequence of an accumulation of heat due to mechanical dissipation production. © 2021 Int. J. Mech. Eng. Rob. Res

This article studies the influences of particle morphology on the behaviors of granular materials at both macroscopic and microscopic levels based on the discrete element method (DEM). A set of numerical tests under drained triaxial compression was performed by controlling two morphological descriptors, i.e. ratio of the smallest to the largest pebble diameter, ξ, and the maximum pebble–pebble intersection angle, β. These descriptors are vital in generating particle geometry and surface textures. It was found that the stress responses of all assemblies exhibited similar behavior and showed post-peak strain-softening. The normalized stress ratio and volumetric strains flatten off and tended to reach a steady value after an axial strain of 40%. While the friction angles at peak state varied with different morphological descriptors, the friction angles at critical state showed no significant variation. Moreover, evolution of the average coordination numbers showed a dramatic exponential decay until an axial strain of about 15% after which it stabilized and was unaffected by further increase of axial strain. In addition, stress ratio q/p and strong fabric parameter ϕ d s / ϕ m s were found to follow an approximately linear relationship for each assembly. These findings emphasized the significance of the influences of particle morphology on the macroscopic and microscopic responses of granular materials.

International audience; To understand the importance of the particle size on the stabilization of metastable tetragonal ZrO2, ultrafine ZrO2 nanocrystals were synthesized via (i) the precipitation method in supercritical water using nitrate precursors, (ii) the sol–gel method in a supercritical ethanol–water mixture, and (iii) the borderline nonhydrolytic sol–gel route in supercritical ethanol using propoxide precursors. The obtained nanocrystals displayed a variation of the monoclinic versus tetragonal molar fractions from 100 wt % down to ≈10 wt % of monoclinic phase. This variation was concomitant with an overall size decrease of the nanocrystals, ranging from 7 to 2 nm depending on the synthesis procedures. Phase contents were quantified by refinement analysis of X-ray scattering data sets and crosschecked with Raman spectroscopy. Our results suggest that an upper limit of ≈90 wt % of the tetragonal ZrO2 phase is possible, even for ultrafine nanoparticles (2 nm). These findings thus question the existence of any critical size limit below which stabilization of pure t-ZrO2 is attainable at low temperatures.

The complex three-phase composition of lithium-ion battery electrodes, containing an ion-conducting pore phase, a nanoporous electron-conducting carbon binder domain (CBD) phase, and an active material (AM) phase, provides several avenues of mesostructural engineering to enhance battery performance. We demonstrate a promising strategy for engineering electrode mesostructures by controlling the strength of adhesion between the AM and CBD phases. Using high-fidelity, physics-based colloidal and granular dynamics simulations, we predict that this strategy can provide significant control over electrochemical transport-relevant properties such as ionic conductivity, electronic conductivity, and available AM-electrolyte interface area. Importantly, the proposed strategy could be experimentally realized through surface functionalization of the AM and CBD phases and would be compatible with traditional electrode manufacturing methods.

International audience; Data of quasi-specular reflection of cold neutrons, prompt-γ neutron analysis, X-ray Raman scattering (XRS), and neutron pair distribution function (PDF) analysis with powder of detonation nanodiamonds are analyzed to collect their structural properties and chemical composition. Both as-synthesized and purified samples were studied using fluorination samples. Removal of both the sp2 amorphous carbon shell and the hydrogen atoms is evidenced respectively by the change of neutron-nuclei optical potentials of nanoparticles and the increase of their neutron reflectivity. Moreover, sp3 diamond cores of nanoparticles stay intact during the fluorination as revealed by similar scattering patterns, PDF, and XRS data. Quasi-specular reflection, PDF, and XRS data are complementary for the study of nanomaterials and in good agreement with conventional characterization techniques (infrared spectroscopy and solid-state NMR).

International audience; 3D printed sand molds for the casting industry play a vital role in manufacturing intricate parts from a computer model. The possibility of producing fairly significant structural castings using a small job-box 3D sand mold printer is another advantage compared to the direct metal 3D printing processes. It is important to identify the relationship between the process parameters and the properties of the sand mold in order to produce a mold with the required strength, permeability and stiffness; to reduce gas emissions during casting and minimize the mass of combustible materials in the mold. Hence, it is possible to create an excellent casting by improving the design of such molds for liquid alloy filling and solidification. The relationship between the printing parameters and the properties of the mold can be a great tool for foundrymen, primarily to optimize the strength and permeability properties of these molds and therefore to provide exact boundary conditions for the solidification simulation prior to a casting trial. This paper reports on a study of a basic outline to quantify the role of the sand mold printing process parameters, particularly the recoater speed and print resolution, on the mold strength and permeability, and their impacts on the anisotropic behavior of the printed sand molds.

Stress-oftening is one of the significant features experienced by cohesive-frictional granular materials subjected to deviatoric loading. This paper focuses on mesoscopic evolutions of the dense granular assembly during a typical drained biaxial test conducted by DEM, and proposes mesoscopically-based framework to interpret both hardening and softening mechanisms. In this context, force chains play a fundamental role as they form the strong contact phase in granular materials. Their geometrical and mechanical characteristics, as well as the surrounding structures, are defined and analyzed in terms of force chain bending evolution, local dilatancy, rotation and non-coaxiality between the principal stress and the geometrical orientation of force chains. By distinguishing two zones inside and outside shear band, force chain rotations are shown to be of opposite sign, which may contribute to the observed macroscopic softening as one of the origin of the structural softening.

Vibroflotation includes densification of loose sands by means of shear deformation processes imparted by horizontal vibrations of vibrator probes. 1g model tests replicating the vibroflotation process were conducted using a model vibrator to identify online compaction control parameters. The effectiveness of the compaction was evaluated by means of a cone penetration test. An accelerometer and a trigger were installed in the model vibrator to measure the amplitude of the vibrator and the phase angle of the eccentric mass during compaction. The variation of amplitude and phase angle during compaction was studied and it was observed that amplitude and phase angle reduced with the increasing density of sand. Two tests were conducted with and without considering amplitude as a compaction control parameter. One test included a pre-determined fixed compaction time and the other used amplitude as a compaction completion indicator. It was observed that tests conducted considering amplitude as a compaction control parameter led to reduced compaction time. Coupled Eulerian-Lagrangian-based numerical simulations were carried out to study the feasibility of amplitude-controlled compaction under realistic stress state conditions.

In this study, mechanical testing of glass bead (GB), glass fiber (GF), and hybrid (GB/GF) composites was carried out. Following that, drilling tests were undertaken on glass bead/fiber-reinforced hybrid Polyamide 66 (PA66) polymer composites. The purpose of this study is to determine the mechanical properties of the cutting elements and the effect of cutting parameters (spindle speed and feed rate) and reinforcement ratios on thrust force and surface roughness (Ra). The contribution of the cutting parameters to the investigated outcomes was determined using statistical analysis. Optical microscopy and scanning electron microscopy (SEM) was used to inspect the hole quality and damage mechanisms. The results revealed that the feed rate was the most contributing factor to thrust force (96.94%) and surface roughness (63.59%). Furthermore, in comparison to other hybrid composites, the lowest Ra value was obtained as 0.95 µm in samples containing 30% GB, while the Ra value was 1.04 µm in samples containing 10% GF + 20% GB. Polymer PA reinforced with 30% GF had the highest strength, modulus of elasticity, impact strength, and hardness. © 2022 by the authors. Licensee MDPI, Basel, Switzerland. Karabük Üniversitesi: FDT-2020-2340 Funding: This research was funded by Karabük University, grant number FDT-2020-2340.

A series of medium-sized cyclic triaxial tests were performed to investigate the permanent deformation properties of granular materials. The strain rate was then plotted against loading cycles to classify the permanent deformation properties of granular materials under different cyclic stress ratios (CSRs). It was found that (1) the permanent strain rate dεp/dN was linearly correlated with loading cycles N using a double-log coordinate on the condition of CSR < 60%; (2) the deformation tendency factor β, which was extracted from the linear relationship between dεp/dN and N, significantly varied with CSR and, thus, can be adopted to identify the deformation states; (3) β > 1 implying that permanent strain accumulation ceases in limited cycles and corresponds to the plastic shakedown range, while 0 < β ≤ 1 indicates the temporary steady state, corresponding to the plastic creep range; (4) sluggish decrease or remarkable increase in dεp/dN appeared as CSR ≥ 60%, leading to soil collapsed in limited loading cycles and resulting in an incremental collapse range. The new approach was validated by the crushed tuff aggregates and subgrade materials reported previously. It is expected that the new approach will have wider applicability than the traditional one and can provide technical guidance for the design and construction of substructures in roadway and railway engineering.

Granular materials promise opportunities for the development of high-performance, lightweight vibration-damping elements that provide a high level of safety and comfort. Presented here is an investigation of the vibration-damping properties of prestressed granular material. The material studied is thermoplastic polyurethane (TPU) in Shore 90A and 75A hardness grades. A method for preparing and testing the vibration-damping properties of tubular specimens filled with TPU granules was developed. A new combined energy parameter was introduced to evaluate the damping performance and weight-to-stiffness ratio. Experimental results show that the material in granular form provides up to 400% better vibration-damping performance as compared to the bulk material. Such improvement is possible by combining both the effect of the pressure–frequency superposition principle at the molecular scale and the effect of the physical interactions between the granules (force-chain network) at the macro scale. The two effects complement each other, with the first effect predominating at high prestress and the second at low prestress. Conditions can be further improved by varying the material of the granules and applying a lubricant that facilitates the granules to reorganize and reconfigure the force-chain network (flowability).

The acoustical behavior of granular materials, such as activated carbon and silica gel, has drawn attention in recent studies, due to their favorable properties such as good low frequency sound absorption. Like other more traditional porous materials, granular materials can also be tested in a standing wave tube for a convenient assessment of their acoustical properties. However, the behavior of granular materials stacked in a standing tube is more complex than that of traditional materials. For example, the response of lightweight glass bubbles reveals a clear dependence on the sound pressure level of the input signal. Also, when tested in standing wave tubes of different diameters, the same type of granular materials displays differences in their behavior. The apparent stiffness of granule pack is also related to the depth of the stack. In the present work, a model based on Biot theory is proposed, together with a consideration of the effect of the change of boundary conditions and the granule stack stiffness in different test configurations. The model is realized by using a finite difference method, and the simulation results are compared with measurements of different types of granular materials.