Effect Of Grain Shape Research Articles

AnisEulerSC: A MATLAB program combined with MTEX for modeling the anisotropic seismic properties of a polycrystalline aggregate with microcracks using self-consistent approximation

Seismic anisotropy of polycrystalline materials depends on the characteristics of microcracks as well as the crystallographic orientations of minerals. Here, we present a MATLAB-based software, AnisEulerSC (Anisotropy from Euler angles using Self-Consistent approximation), for modeling the anisotropic seismic properties of a polycrystalline aggregate with microcracks using the self-consistent approximation. In this program, several commands of MTEX (a MATLAB toolbox for texture analysis) are utilized to analyze constituent components of a rock sample based on experimental measurement data (e.g., electron backscatter diffraction) and to calculate and visualize seismic wave velocities and polarizations. We provide several examples of SC modeling to explore the effects of grain shapes on a polycrystalline aggregate and the effects of crack shapes and orientations on the anisotropic seismic properties of a polycrystalline aggregate.

Effect of grain shape to potential liquefaction

Earthqueke is one of the most frequent disaster in Indonesia, Earthqueke have caused losses both in terms of life and material. An earthquake also can trigger to soil liquefaction. Attention to liquefaction in Indonesia has raised after the Palu Earthquake in 2018. Liquefaction may happen in sandy soil in certain condition. Here, a series laboratory tests to study potentially liquefied in sandy soils is conducted. The liquefaction potential of sand are analyzed with the effect of the shape of the soil particles. The sandy sample is made up by special selected in three different shapes that are sharp, angular and round. Finally, it can be seen the effect of the shape of the soil grain on the liquefaction potential. The results of this study can be used to further investigation in order to mitigate the liquefaction.

Effects of grain shape on the standard penetration test and particle packing

Coarse soils can contain flaky grains in addition to rounded or angular grains, along with a varying fines content. Depending on the regional geology, however, the mica grain content can be remarkable, reaching 30 % or higher. Therefore, it is reasonable to expect that mica grains would affect the soil behaviour. In this study, soils of a delta deposit that are known to involve mica grains were examined. The river sand was considered as the host material and the mica grain contents were determined by means of the flotation technique. A correlation between the mica content as found using the flotation technique and XRD count numbers obtained using an X-ray diffraction test method for each soil sample was established. The standard penetration test (SPT) blow counts from various boreholes were interpreted from the mica content’s influence point of view. The results showed that the mica grains would reduce the SPT resistance at certain fines-content, host-sand, mica-grain combinations. The reduction in the SPT resistance as a result of the presence of mica grains might reach eight units at depths close to the ground surface. This influence is expressed by means of a dimensionless parameter (MCef); however, it diminished with an increasing effective stress and fines content. The findings of the present study show that the influence of particle shape on the overall soil behaviour deserves further study.

Grain morphology and strength dilatancy of sands

The presented experimental study, from micro to macro scale, assesses the effects of grain shape on the strength-dilatancy behaviour and physical properties of seven natural sands of different origins and mineralogical composition. The micro-scale has been characterised by processing two-dimensional image of grains, using the fractal analysis of particle contour to define their shape. The macroscopic material properties are evaluated performing direct shear tests at three different normal stresses, and measuring void ratios limit and angles of repose. An innovative method to interpret the experimental data obtained has pinpointed interesting relationships linking the morphological features of grains to the mechanical and physical properties of sands. Data confirm that the increase in grain shape irregularity produces an increase in all the variables investigated: void ratios limit, friction angles and dilatancy parameters.

Study on influence of grinding depth and grain shape on grinding damage of K9 glass by SPH simulation

This work use the SPH method to study the relationship between grinding depth and grinding force of K9 glass in ultra-precision grinding, and the effect of grain shape on material removal. The relationship between the force and the depth in the stable scratching stage is FR = 0.55078ap1.15356, which provides a basis for controlling the grinding depth by force. The material removal modes at different grinding depths were obtained, that is, plastic removal occurs below 0.2 μm, brittle transition occurs between 0.2 and 0.4 μm, and brittle removal occurs at more than 0.5 μm. It is found that the cutting resultant force of sharp grains is smaller and the normal force is smaller than the tangential force. By analyzing the plastic deformation depth and residual stress depth, it is found that the material removal mode with small deformation and little removal has the lowest cutting force fluctuation and the highest grinding quality. It provides a reference for the choosing of grain shape in rough grinding and ultra-precision grinding. The correctness and reliability of the simulation results were verified by the comparison of the simulation findings with the results obtained from varied-depth scratching experiments and the multi-shape indenter scratch experiments.

Grain shape effects on the mechanical behavior of compacted earth

The main purpose of this paper is to experimentally explore the effects of grain shape and size on the mechanical behavior of compacted earthen materials. Sand-earth, natural rounded gravel and crushed angular gravel are the three materials used in this study. Both gravels are from the same site and characterized by the same grain size curve. The uniaxial compression tests, the results of which are presented and discussed in this paper, were performed on cylindrical specimens of three materials: sand-earth mixture, rounded gravel-earth mixture and angular gravel-earth mixture. The tested specimens were prepared under optimum compaction references, using the Proctor test procedures. For each compression test, four parameters are determined: the compressive strength, the initial tangent modulus, the secant modulus at maximum stress and the peak axial strain corresponding to the maximum compressive stress. The results obtained show that the mechanical behavior of gravel-earth mixture may be influenced by grain shape of the gravel used, thus introducing a new parameter to be taken into account when preparing unstabilized rammed earth material. Further experimental studies are recommended to better assess these results.

Simulation of Lunar Soil With Irregularly Shaped, Crushable Grains: Effects of Grain Shapes on the Mechanical Behaviors

AbstractOne of the challenges to overcome in Moon mining operations, such as soil handling, drilling, excavation, and wheeled movement, is understanding the mechanical behaviors of lunar soil, which is composed of grains characterized by highly irregular shapes. The impracticality of performing mechanical experiments on lunar soil samples has made computational techniques useful for exploring the mechanical behaviors of lunar soil. This paper uses particle flow code and describes a procedure for simulating lunar soil grains with specific size, shape, and strength distributions. We adopt data from soil samples 64501 and 60501 retrieved in Apollo 16. Lunar soil samples are simulated as assemblies of different shapes of grains consisting of rigid spheres connected through parallel bonds. We classify grains into four categories based on their shape: agglutinate, breccia A, breccia B, and plagioclase. We simulate each grain based on available imaging studies on their shape characteristics. We reveal the significance of grain shape irregularity through angle‐of‐repose tests on samples with and without irregularly shaped agglutinates. Results show that the shape irregularity increases the angle of repose by 6°. We repeat the test under different gravitational acceleration ranging from 0.1 to 25 m/s2 and show that for values below about 10 m/s2, the angle of repose is inversely related to the gravity but above 10 m/s2, remains independent of the gravity. We perform triaxial compression tests to investigate behaviors of simulated samples under confined loadings. The confinement varies from zero to 15 kPa, corresponding to the lateral in situ stress at depths up to 250 cm. The cohesion and friction angle derived from the triaxial tests are shown to agree with the lab and in situ measurements. This numerical practice and presented methodology pave the way for full‐scale simulation of mining operations on the Moon surface.

A micromechanical analysis to the elasto-viscoplastic behavior of solder alloys

A small strain multi-scale elasto-plastic self-consistent constitutive model is developed to describe the rate and temperature dependent behavior of solder alloys. In the extended model, a modified Voce hardening law is proposed to describe the change of hardening rate as a function of accumulated shear strain. The developed model has been incorporated into finite element analysis to obtain the macroscopic behavior of polycrystalline materials. The stress updating algorithms of both microscopic and macroscopic scales are presented. The effect of grain shape on macroscopic behavior is investigated. The proposed model is verified with the Taylor factor and the experimental data of Sn-3.0Ag-0.5Cu and Sn-0.7Cu solder alloys at different temperatures and strain rates. In general, the numerical results can fit the experimental data with reasonable accuracy.

Impact of granular slugs on rigid targets: Effect of grain shape and fracture

Abstract The effect of grain shape and fracture on the interaction of high velocity granular slugs with rigid stationary targets is analysed for targets in normal and inclined orientations. The granular slugs comprise spherical, rod-shaped or cubic grains and are constructed by connecting together spherical sub-particles with either rigid or beam connectors . The case when grain fracture is suppressed (rigid connectors between sub-particles) is first analysed. With increasing grain aspect ratio, the grains tend to slide rather than roll on the target surface and this increases frictional interactions with the target surface. However, these enhanced frictional forces do not affect the momentum transmitted into normally oriented targets due to the symmetry of the problem. By contrast, the break in the symmetry for inclined targets results in the transmitted momentum increasing with grain aspect ratio. Fracture of the grains (as modelled by the fracture of the beam connectors between sub-particles) is shown to affect the momentum transmitted into the inclined targets. This is a consequence of fracture resulting in a change in grain shape. In this case the simulations show that the transmitted momentum is a function of the initial grain shape, the fracture properties of the grains and the impact velocity. In fact, grain fracture results in an enhanced transmitted momentum for initially cubic grains but fracture of grains with a high initial aspect ratio results in a reduction in transmitted momentum as these grains fragment into more spherically shaped grains.

A NUMERICAL STUDY OF THE MICROSCALE PLASTIC STRAIN LOCALIZATION IN FRICTION STIR WELD ZONES

A crystal plasticity approach was used to study the effects of grain shape and texture on the deformation behavior of friction stir weld (FSW) microregions. The explicit stress-strain analysis was performed for two representative grain structures with equiaxed and extended grains. Grain orientations were assigned to simulate no texture or a weak or strong cubic texture. Calculations have shown that the texture gave rise to earlier plastic strain localization on a larger scale. The highest stresses were found to develop in a non-textured specimen with equiaxed grains where the grain boundaries served as a barrier to dislocation motion. In both equiaxed and extended grain structures with a strong cubic texture no pronounced strain localization was seen on the grain scale but mesoscale shear bands appeared early in the deformation process. The calculations have shown that the microstructure-based simulation is a reasonable tool to study the deformation behavior of FSW materials, which is difficult to be predicted within macroscopic models alone.

Impact of Grain Shape and Multiple Black Carbon Internal Mixing on Snow Albedo: Parameterization and Radiative Effect Analysis

AbstractWe quantify the effects of grain shape and multiple black carbon (BC)‐snow internal mixing on snow albedo by explicitly resolving shape and mixing structures. Nonspherical snow grains tend to have higher albedos than spheres with the same effective sizes, while the albedo difference due to shape effects increases with grain size, with up to 0.013 and 0.055 for effective radii of 1,000 μm at visible and near‐infrared bands, respectively. BC‐snow internal mixing reduces snow albedo at wavelengths < ~1.5 μm, with negligible effects at longer wavelengths. Nonspherical snow grains show less BC‐induced albedo reductions than spheres with the same effective sizes by up to 0.06 at ultraviolet and visible bands. Compared with external mixing, internal mixing enhances snow albedo reduction by a factor of 1.2–2.0 at visible wavelengths depending on BC concentration and snow shape. The opposite effects on albedo reductions due to snow grain nonsphericity and BC‐snow internal mixing point toward a careful investigation of these two factors simultaneously in climate modeling. We further develop parameterizations for snow albedo and its reduction by accounting for grain shape and BC‐snow internal/external mixing. Combining the parameterizations with BC‐in‐snow measurements in China, North America, and the Arctic, we estimate that nonspherical snow grains reduce BC‐induced albedo radiative effects by up to 50% compared with spherical grains. Moreover, BC‐snow internal mixing enhances the albedo effects by up to 30% (130%) for spherical (nonspherical) grains relative to external mixing. The overall uncertainty induced by snow shape and BC‐snow mixing state is about 21–32%.

Shear wave velocity in sand: effect of grain shape

Whether the shear wave velocity in sand is dependent on grain shape is a basic question of considerable interest, yet remains open owing to the lack of solid experimental evidence. This technical note presents results from an experimental study where the effect of grain shape was carefully isolated from other factors and the grain shape was accurately measured using laser scanning technology. It is shown that, under otherwise similar conditions, shear wave velocity or the associated small-strain stiffness tends to decrease as sand grains become rounded, and that a fairly good correlation exists between stiffness parameters and a shape index known as overall regularity that accounts for grain shape in a collective manner. The study suggests that the laboratory finding reported in the literature, that a decrease in roundness of sand grains leads to a decrease in shear wave velocity or stiffness, was most likely attributable to varying gradation of tested materials rather than to varying grain shape.

Crystal plasticity finite element simulation of NiTi shape memory alloy based on representative volume element

Crystal plasticity finite element method based on a representative volume element model, which includes the effect of grain shape and size, is combined with electron backscattered diffraction experiment in order to investigate plastic deformation of NiTi shape memory alloy during uniaxial compression at 400 °C. Simulation results indicate that the constructed representation of the polycrystal microstructure is able to effectively simulate macroscopically global stress-strain response and microscopically inhomogeneous microstructure evolution in the case of various loading directions. According to slip activity and Schmid factor in {110} , {010} and {110} slip modes, slip modes are found to play a dominant role in plastic deformation, while slip mode is found to be a secondary slip mode. In addition, the simulation results are supported well by the experimental ones. With the progression of plastic deformation, the (001) [ $$0\bar 10$$ ] texture component gradually disappears, while the γ-fiber ( ) texture is increasingly enhanced.

Effect of Particle Morphology, Compaction, and Confinement on the High Strain Rate Behavior of Sand

The effect of grain shape, size distribution, intergranular friction, confinement, and initial compaction state on the high strain rate compressive mechanical response of sand is quantified using Long Split Hopkinson Pressure Bar (LSHPB) experiments, generating up to 1.1 ms long load pulses. This allowed the dynamic characterisation of different types of sand until full compaction (lowest initial void ratio) at different strain rates. The effect of the grain morphology and size on the dynamic compressive mechanical response of sand is assessed by conducting experiments on three types of sand: Ottawa Sand with quasi-spherical grains, Euroquartz Siligran with subangular grains and Q-Rok with polyhedral grain shape are considered in this study. The adoption of rigid (Ti64) and deformable (Latex) sand containers allowed for quasi-uniaxial strain and quasi-uniaxial stress conditions to be achieved respectively. Additionally, the effect of intergranular friction was studied, for the first time in literature, by employing polymer coated Euroquartz sand. Appropriate procedures for the preparation of samples at different representative initial consolidation states are utilized to achieve realistic range of naturally occurring formations of granular assembly from loose to dense state. The results identify material and confining sample state parameters which have significant effect on the mechanical response of sand at high strain rates and their interdependency for future integration into rate dependent constitutive models.

Pore scale evaluation of thermal conduction anisotropy in granular porous media using Lattice Boltzmann method

PurposeThermal conduction anisotropy, which is defined by the dependency of thermal conductivity on direction, is an important parameter in many engineering and research studies such as the design of nuclear waste depositional sites. In this context, the authors aim to investigate the effect of grain shape in thermal conduction anisotropy using pore scale modeling that utilizes real shapes of grains, pores and throats to characterize petrophysical properties of a porous medium.Design/methodology/approachThe authors generalize the swelling circle approach to generate porous media composed of randomly arranged but regularly oriented elliptical grains at various grain ratios and porosities. Unlike previous studies that use fitting parameters to capture the effect of grain–grain thermal contact resistance, the authors apply roughness to grains’ surface. The authors utilize Lattice Boltzmann method to solve steady state heat conduction through medium.FindingsBased on the results, when the temperature field is not parallel to either major or minor axes of grains, the overall heat flux vector makes a “deviation angle” with the temperature field. Deviation angle increases by augmenting the ratio of thermal conductivities of solid to fluid and the aspect ratios of grains. In addition, the authors show that porosity and surface roughness can considerably change the anisotropic properties of a porous medium whose grains are elliptical in shape.Originality/valueThe authors developed an algorithm for generation of non-circular-based porous medium with a novel approach to include grain surface roughness. In previous studies, the effect of grain contacts has been simulated using fitting parameters, whereas in this work, the authors impose the roughness based on the its fractal geometry.

Effect of Grain Shape on Texture Formation during Severe Plastic Deformation of Pure Copper

In this study, the authors use a combination of electron backscattered diffraction and polycrystal plasticity modeling to study the effect of grain shape on texture development in high pressure torsion and high pressure double torsion in high purity Cu. With varying applied pressures and after a large amount of strain corresponding to two to four turns, the average aspect ratios of the grains has changed from being elongated under higher pressures to nearly equiaxed for lower pressures, while keeping the average grain size similar among all samples analyzed. Polycrystal modeling is used to help isolating the deformation effect from the grain shape effect. The authors show that grains with elongated shapes form shear textures with a predominant C component, whereas those with largely equiaxed grains possess conventional shear textures.

The influence of sintering additives on the microstructure and material properties of silicon nitride ceramics investigated by advanced simulation tools

In multi‐phase bulk ceramics, the separate influence of individual phases on the overall macroscopic properties can often hardly be studied by purely experimental observations. However, once a realistic microstructure model exists, computer simulations allow for that by varying the properties of individual phases and, thus, for studying their role independently. In the present article, the microstructure of liquid phase sintered silicon nitride ceramics was created using a voxel‐based structure generator. These generated microstructures have been meshed with a special tool so that thermal conductivities and elastic properties of these ceramics could be calculated using standard finite element simulations. Variations of the properties of individual phases were considered in a realistic range for the experimental optimization of silicon nitride ceramics and, therefore, their respective influence on macroscopic properties could be studied. It turns out that a high volume fraction of the primary ‐SiN ‐phase has the largest positive impact on both stiffness and thermal conductivity, whereas the effect of grain shape and anisotropic material properties of the ‐SiN ‐grains is rather low. However, the thermal conductivity of the secondary phase plays a significant role in the overall thermal conductivity, provided that it drops beyond 10 W mK−1. Nevertheless, experimentally the thermal conductivity of silicon nitride ceramics is dominated by the thermal conductivity of the ‐SiN ‐grains, where the latter is controlled by impurities which can be incorporated into the silicon nitride lattice during sintering. Thus, inverse simulation can be used as a powerful tool to investigate individual phase properties in multiphase ceramics, for example, estimating a decreased thermal conductivity of the primary phase (‐SiN ‐grains).

Scaling laws in elastic polycrystals with individual grains belonging to any crystal class

In this paper, we develop unifying scaling laws describing the response of elastic polycrystals at finite mesoscales. These polycrystals are made up of individual grains belonging to any crystal class (from cubic to triclinic) and are generated by Voronoi tessellations with varying grain sizes. Rigorous scale-dependent bounds are then obtained by setting up and solving Dirichlet and Neumann boundary value problems consistent with the Hill–Mandel homogenization condition. The results generated are benchmarked with existing numerical results in special cases and the effect of grain shape on the scaling behavior is investigated. The convergence to the effective elastic properties with increasing number of grains is established by analyzing 5180 boundary value problems. This leads to the notion of an elastic scaling function which takes a power law form in terms of the universal anisotropy index and the mesoscale. Based on the scaling function, a material scaling diagram is constructed using which the convergence to the effective properties can be analyzed for any elastic microstructure.

Effect of grain shape on the jamming of two-dimensional silos

We present discrete element method simulations of the discharge of silos in two dimensions. We study the effect of the grain shape on the clogging of small apertures, considering regular polygons and disks of equal mass. In particular, we analyze the avalanche size distribution and the jamming probability for disks, triangles, squares, pentagons, hexagons and heptagons as a function of the aperture size. We show that the jamming probability presents a non-linear response as a function of the number of vertexes of the polygons.

Discrete element simulation of dynamic behaviour of partially saturated sand

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 (<20 %) in LS-DYNA; however, a number of questions remain open about the effect of grain shape, grain crushing and viscosity.