Crushing Of Grains Research Articles

Capillary suction predictions in granular materials subjected to 1D compression and triaxial loading with emphasis on projectile penetration

The role of partial saturation in penetration resistance of projectiles in granular materials is not clear due to experimental constraints imposed by high cost and special considerations in equipment design. In this work, granular material near the tip and far-field of the projectile is numerically simulated based on 1D compression and triaxial stress paths, respectively, using the finite discrete element method. The crushing of grains in 1D compression simulations is implemented by pre-inserting cohesive interface elements in regular finite element mesh. The capillary suction is numerically predicted by extracting the deformed granular assembly microstructure at different loading steps as an input to the pore morphology method. The results demonstrate the development of high capillary suction in 1D compression loading due to the significant crushing of grains. The evolution of capillary suction is negligible during triaxial loading compared to the 1D compression loading. This suggests that future simulations related to projectile penetration in partially saturated granular materials should account for coupled hydromechanical effects near the tip whereas the far-field can be approximated as a dry material. Finally, the capillary suction corresponding to extreme comminution near the projectile tip is estimated from a 3D assembly of spherical grains with a mean grain size of 1 µm.

Microstructure and mechanical properties of 7075 aluminum alloy during complex thixoextrusion

7075 aluminum alloy was used to obtain elbow parts by complex thixoextrusion and the microstructure evolution and mechanical properties during this process were studied by SEM, TEM and other analytical methods. The results show that different parts in 7075 aluminum alloy show quite different microstructures. The microstructure of the thin walls formed by back-extrusion is stratified, and the bottom of the parts formed by angular extrusion is obviously deformed. Shear forces contribute to the crushing of grains and the coarse second phase. The main strengthening phases in the material are η phase and E phase, whose amounts greatly decrease during heating to semi-solid and thixoextrusion. After heat treatment, they can precipitate evenly to improve the mechanical properties of the material. The average tensile strength of whole part after thixoextrusion and heat treatment is 485.49 MPa, while the average elongation is 5.49%.

Experimental Data of the Ear Threshing Process in a Pneumatic Device

Introduction. The current problem is the high level of grain injuries during the threshing process. Therefore it is necessary to develop the gentle methods for separating grains from ears. These methods shall exclude direct shock influence of operative parts of the threshing devices on cereal grains. The objective of research is to study the process of the wheatear threshing in the pneumatic device and to estimate the influence of device settings on cereal grain separation and damage. Materials and Methods. The experimental apparatus is a pneumatic threshing device. The threshing is carried out in case of the interaction of an ear and concave under the influence of the alternating high and low pressure of the airflow generating by the rotor’s blades. Separation is carried out by means of deriving light-load tailings into the reduced pressure chamber. Results. The grain damage decreases in reducing the speed of rotor blades motion and consequently the speed of ears motion in the threshing unit. Germ damage and grain breakage decrease almost to zero at a minimum blade motion speed of 13.5 mps. The range of blade speed between 13.5 and 20 mps is the most favorable for the pneumatic grain threshing in terms of the germ damage. The pneumatic threshing on the experimental device results in effective assorting of grains and light-load tailings of ears. Discussion and Conclusion. Process of the wheat ears pneumatic threshing has satisfactory results. The pneumatic threshing reduces grain endosperm damage by 10…12%. Grain germ damage decreases by 5%, practically to zero. Crushing of grain at rotor blades minimum speed is no more than 0.5%. Comparison of shares of the damaged and crushed grains when using the pneumatic threshing with shares of the damaged grains when using the traditional combine threshing has showed that the offered method of the threshing provides a reduction in grain damage.

Improvement of the soybean harvesting process as a way to increase the quality of seeds

The quality of seeds is the most important factor in increasing the yield of agricultural crops, including soybean. However, on the average, up to 2025% of soybean seeds, sown in the Amur re-gion, are substandard. At the same time, one of the main reasons for the decline in the quality of seed material is significant crushing and damage of soybean during harvesting and processing. Up to 10 different marks of combines, which allow a high degree of crushing of bunker grain, are used in harvesting soybean in the Amur region. The crushing of grain by combines of different marks varies in the range from 6,9 to 15,1 percent. Combines of Russian and foreign production are mainly single-drum by design and collect the threshed soybean grain in one bunker, while they do not separate seeds according to the biological diversity inherent in soybean. As a result, soybean yield losses reach 2,7-3,3 c/ha. In order to reduce grain losses from the crushing and obtaining high-quality seeds, a new device, based on a two-stage threshing combine with double-flow cleaning and with two bunkers, has been developed. The study of the operating modes of the threshing and separating device for threshing, separation and damage of soybean seeds along the length of the combine thresher was carried out in order to select and preserve the part of the biologically valuable and high-quality soybean seeds from the crushing during combine harvesting of soybean with reduced grain moisture (less than 12%). The conducted research with the use of the complete factorial experiment method and processing the results made it possible to create mathematical models of separation and seed damage, on the basis of which a nomogram was built to determine separation and the content of damaged soybean seeds, which are obtained in the zone of the first drum, depending on the techno-logical adjustments of the threshing apparatus, grain feed and grain moisture.

Bounding surface plasticity model for stress-strain and grain-crushing behaviors of rockfill materials

Crushing of grains can greatly influence the strength, dilatancy, and stress-strain relationship of rockfill materials. The critical state line (CSL) in the void ratio versus mean effective stress plane was extended to the breakage critical state plane (BCSP). A state void-ratio-pressure index that incorporated the effect of grain crushing was proposed according to the BCSP. Rowe’s stress-dilatancy equation was modified by adding the breakage void-ratio-pressure index, which was also incorporated into the formulations of the bounding stress ratio and plastic modulus. A BCSP-based bounding surface plasticity model was proposed to describe the state-dependent stress-strain behaviors and the evolution of grain crushing during shearing process of rockfill materials, and was shown to sufficiently capture the breakage phenomenon.

Experimental and numerical evaluation of CBM potential in Jharia Coalfield India

Geophysico-mechanical characterization of coal data are important in the economic success of CH4 extraction as well as a CO2 injection in deep coal seam reservoir. The heterogeneous nature of coal makes the CH4 removal quite challenging because of the complex behaviour of the seam at in situ as well as applied stress level. Coal matrix behaviour depends on several parameters as permeability, porosity, pore pressure, gas content, structural features, etc. plays a leading role in methane extraction. Therefore, extensive laboratory investigation is handiest approached to anticipate the behavior of coal effectively. This paper presents the results of coal characterization, gas permeability, adsorption/desorption capacity of coal as well as the performance of CBM production well in the replicated model of JH-MD-XVI-T coal seam at a depth of 580 m. The coal characterization was determined to evaluate the prospects of methane in the study area. The gas permeability was determined in a triaxial experimental set up using Darcy’s approach to in situ conditions. The decrease in permeability with an increase in confining as well as gas pressure was observed in all coal samples due to the crushing of grain, coal deformation and narrowing of fractures as well as cleats leading to hinder the flow of fluid through it. The well performance was evaluated to determine the gas rate as well as cumulative gas volume over twenty-five years of well life. Mutual relation between permeability, in situ confining pressure as well as gas pressure, has been established statistically.

Quantification of the crushing of grains by the calculation of the surfaces

The quantification of the grain’s crushing has often been neglected in the past, today it is a necessary asset in the selection of use of granular materials. The Kick and Rittinger theories on energy reduction in the size of a grain combined with the model proposed by Fukumoto who represents mathematically the particle size distributions, allowed us to calculate the area between the grain size distributions curves before and after tests. The aim of this work is to identify the amount of crushed grains on local materials (pegmatite, clayey schist and sandstone) in order to quantify the breaking of their grains. The evolution of the particle size distribution, particle breakage, of these materials was investigated through performing a three series of tests (oedometer, shear and Proctor tests). This grain size spreading obtained after the test, called the crushing surface, shows that the crushing evolves with not only the increase of load, presence of water and grain size, but also with the material (mineralogy) and the stress path.

Study of crushing of grains of limestone under the effect of cyclic loading with the fractal dimension

The grains can be of very diverse nature (size, shape, mineralogy, etc), indeed even if each grain is a fairly simple object, the set of grains is a very complex system in which the geometrical and physical properties of the grains, their forces and their orientations play a crucial role in their mechanical behavior. The measurement of their shape in soil mechanics has historically required the use of standards and diagrams to which the different grains can be compared. However, these methods are approaches and remain insufficient and incomplete for the actual measurement of their form and the understanding of their behavior remains a task far from being completed.
 This work is in this context and proposes to analyze the shape and size of the grains with the fractal theory using the Box Counting method. It also makes it possible to study their influence on the crushing of the grains of the calcareous material under the effect of the cyclic loading-unloading during the oedometer test. The obtained results show that the variation of the fractal dimension, corresponding to the crushing effect of the grains, is strongly influenced by their shape, their size, their particle size distribution and the variation in the number of loading-unloading cycles.

Effect of texture of carbonate soils in South Iran coasts on aggregate crushing

ABSTRACTAggregate crushing is a phenomenon occurring in carbonate soils under shear and compressive loads resulting in settlement of the offshore structures such as piers, bridges, waterfronts, wharfs, and oil and gas extraction platform foundations. Therefore, it is of significant importance to address the above-mentioned issue through a comprehensive study. In the present research, the texture of carbonate soil in south Iran coasts and its effect at high hydrostatic pressure (2 MPa) on aggregate crushing was studied. The physical properties of coastal soils, such as the effective grain size, shape index, and angularity were then characterized to investigate their effect on grain crushing grade. The results showed that the effective grain size, shape index, angularity, and calcium carbonate content are the main parameters affecting the crushing of grains and consequently settlement of marine soils. Based on the above parameters, a relationship is proposed to estimate grain crushing in carbonate soils.

Stress drop effects in time dependent behavior of quartz sand

Time effects in granular materials relate to crushing of grains, which is a time dependent process. Depending on the proximity of the load applied to a grain relative to the instantaneous failure load of the grain, the time increases as the load is decreased below the failure load. A study of grain crushing associated with stress drop-creep and stress drop-stress relaxation experiments on dense Virginia Beach sand consisting mainly of quartz grains is presented. In these experiments the triaxial specimens are isotropically consolidated to 8000 kPa, sheared at a constant rate up to a given deviator stress followed by either creep or stress relaxation over a given time period. After dismantling the triaxial specimens, the grain size distributions are determined and their changes, as expressed through Hardin's relative breakage factor, are related to the amount of energy input. Results of the stress drop-creep tests and the stress drop-stress relaxation tests show that creep deformations and the amount of stress relaxation are considerably reduced with increasing amounts of stress drop. Depending on the amount of stress drop, a delay is detected before creep deformation or stress relaxation is initiated. Multiple stress drop-creep experiments are also performed. Structuration effects, which describe changes in yield surface location during creep or stress relaxation and are due to change in grain configuration and interlocking with time, are not observed in the specimens of Virginia Beach sand.

Simulation of railway ballast using crushable polyhedral particles

The need to understand and predict the long- and short term behavior of railway ballast calls for extensive experimental programs as well as the development of reliable numerical models. From the modeling point of view, the granular nature of ballast in connection with the high onset speed of dynamic loading makes it ideal for the application of the Discrete Element Method (DEM).The paper describes the employment of the DEM to simulate ballast behavior in large-scale oedometric testing. Ballast grains are represented by convex polyhedral particles whose shapes are randomly generated via Voronoi tessellation. The effect of the aspect ratio of particles is investigated. A novel algorithm to compute repulsive contact force based on the intersecting volume of polyhedrons is presented. Crushing of grains is included via splitting the particles into smaller polyhedrons when a certain stress-based criterion is fulfilled. The results obtained from the model are compared with the published experimental investigations.

Numerical model of crushing of grains inside two-dimensional granular materials

A theoretical model is proposed to define the failure criterion on an individual grain subjected to an arbitrary set of contact forces. The model is implemented in a two-dimensional computer simulation code based on the molecular dynamics method to study the crushing mechanisms of grains inside a granular material under œdometric compression. The simulation results are partially compared with experiments performed on granular packings composed of moulding plaster disks of uniform thickness under an œdometric compression, and a good agreement has been achieved.

A laboratory study of sediment deformation: stress heterogeneity and grain-size evolution

In shearing sediment beneath glaciers, networks of grains may transiently support shear and normal stresses that are larger than spatial averages. Consistent with studies of fault-gouge genesis, we hypothesize that crushing of grains in such networks is responsible for surrounding larger grains with smaller grains. At sufficiently large strains, this should minimize stress heterogeneity, favor intergranular sliding and abrasion rather than crushing, and result in a self-similar grain-size distribution.This hypothesis is tested with a ring-shear device that slowly shears a large annular sediment sample to high strains. Shearing and comminution of weak equigranular (2.0–3.3 mm) sediment resulted in a self-similar grain-size distribution with a fractal dimension that increased with shear strain toward a steady value of 2.85. This value is significantly larger than that of gouges produced purely by crushing, 2.6, but it is comparable to values for tilts thought to be deforming beneath modern glaciers, 2.8 to nearly 3.0. At low strains, under a steady mean normal stress of 84 kPa, variations in normal stress measured locally ranged in amplitude from 50 to 300 kPa with wavelengths that were 100 times larger than the initial grain diameter. Crushing of grains, observed through the transparent walls of the device, apparently caused the failure of grain networks. At shearing displacements ranging from 0.7 to 1.0 m, the amplitude of local stress fluctuations decreased abruptly. This change is attributed to fine sediment that distributed stresses more uniformly and caused grain networks to fail primarily by intergranular sliding rather than by crushing of grains. Sliding between grains apparently produced silt by abrasion and resulted in a fractal dimension that was higher than if there had been only crushing.A size distribution with a fractal dimension greater than 2.6 is probably a necessary but not sufficient condition for determining whether a basal till has been highly deformed. Stress heterogeneity in subglacial sediment that is shearing through its full thickness should contribute to the erosion of underlying rock.

A laboratory study of sediment deformation: stress heterogeneity and grain-size evolution

In shearing sediment beneath glaciers, networks of grains may transiently support shear and normal stresses that are larger than spatial averages. Consistent with studies of fault-gouge genesis, we hypothesize that crushing of grains in such networks is responsible for surrounding larger grains with smaller grains. At sufficiently large strains, this should minimize stress heterogeneity, favor intergranular sliding and abrasion rather than crushing, and result in a self-similar grain-size distribution.This hypothesis is tested with a ring-shear device that slowly shears a large annular sediment sample to high strains. Shearing and comminution of weak equigranular (2.0–3.3 mm) sediment resulted in a self-similar grain-size distribution with a fractal dimension that increased with shear strain toward a steady value of 2.85. This value is significantly larger than that of gouges produced purely by crushing, 2.6, but it is comparable to values for tilts thought to be deforming beneath modern glaciers, 2.8 to nearly 3.0. At low strains, under a steady mean normal stress of 84 kPa, variations in normal stress measured locally ranged in amplitude from 50 to 300 kPa with wavelengths that were 100 times larger than the initial grain diameter. Crushing of grains, observed through the transparent walls of the device, apparently caused the failure of grain networks. At shearing displacements ranging from 0.7 to 1.0 m, the amplitude of local stress fluctuations decreased abruptly. This change is attributed to fine sediment that distributed stresses more uniformly and caused grain networks to fail primarily by intergranular sliding rather than by crushing of grains. Sliding between grains apparently produced silt by abrasion and resulted in a fractal dimension that was higher than if there had been only crushing.A size distribution with a fractal dimension greater than 2.6 is probably a necessary but not sufficient condition for determining whether a basal till has been highly deformed. Stress heterogeneity in subglacial sediment that is shearing through its full thickness should contribute to the erosion of underlying rock.

Strength of cemented grains

We conducted compaction tests (isotropic drained loading) on randomly packed glass beads that were a) uncemented and b) cemented by epoxy at their contacts. In the latter case, the volume of the epoxy accounted for 10 percent of the pore space. Intensive crushing of grains was observed in the first case at about 50 MPa. In the second case, the cemented grains stayed intact, the failure being localized within the epoxy. Therefore, even small amounts of cement at contacts prevent the failure of grains. Theoretically, this effect follows from our theory of cemented granular materials: stress concentration is high at the contacts of uncemented grains, whereas even small amounts of relatively soft cement result in a more uniform stress distribution over a larger contact area.

Variation of the friction angle of granular materials in the high-speed high-stress ring shear apparatus : influence of re-orientation, alignment and crushing of grains during shear

Variation of the friction angle of granular materials in the high-speed high-stress ring shear apparatus : influence of re-orientation, alignment and crushing of grains during shear

ラッピングにおける砥粒破砕過程の解析

It is widely known that the lapping is necessary to work the brittle materials such as Si single crystal. In this paper, the lapping mechanism of Si crystal is investigated by the aid of measuring the diameter of many grains crushed and analysing the variation of the grain size distribution during lapping. A few types of mechanisms about crushing of grains are discussed. The main results obtained are as follows:(1) The large grains are crushed in the beginig period of the lapping time. In this period, the lapping is performed by grains acting the rolling motion and lapping removing rate is large. The mean diameter of grains decreases rapidly in this time.(2) The ratio mean long diameter to mean short diameter of grains crushed is almost constant and its value is about 1.57.(3) The formula calculating the number of grains is derived by using grain size distribution and the shape model of the abrasive grains proposed. This is the shape combined two hexagonal truncated pyramids in its base plane.(4) The theoretical formula expressing the variation of the grain size distribution during lapping is obtained.