MECHANICAL CHARACTERISTICS OF THE RUBBED MAIZE STRAW DURING SCREW CONVEYING

In order to reduce the power consumption of screw conveyor and to improve the productivity, this study investigated such mechanical characteristics of rubbed maize straw as coefficient of sliding friction, angle of repose, internal friction coefficient, cohesion, flow function value and compressible coefficient with respect to its moisture content and density. An experiment was designed and consists of a sliding friction characteristic test-bed, a direct shear apparatus, a self-made device with adjustable density and compression. The results showed that: the coefficient of sliding friction increases with the increase of moisture content and density; the angle of repose and internal friction coefficient each increases with increasing moisture content respectively; there is no significant effect between the moisture content and the cohesion of rubbed maize straw; the flow function value goes up with the increase of the moisture content; also the increase of the moisture content leads to the increased bulk density due to the reduced materials gap and the increased compression coefficient, which makes it hard to compress. The equation of pressure and density was found, and it is suitable for the analysis of compression characteristic of rubbed maize straw. The research results lay a theoretical foundation and a basis for the further study on mechanical properties of maize straw.

Transient Evolution of Rheological Properties of Dense Granular Inertial Flow Under Plane Shear

Exploration on the transient evolution of the rheological properties of dense granular inertial flow is essential for revealing how the balance is established between the boundary drive strength and the internal shear strength. In this paper, discrete element method simulations are performed to study the transient flow characteristics of a dense granular system under plane shear in the inertial regime. To this end, we quantitatively analyze the changes in the system’s flow state, interfacial friction coefficient, internal friction coefficient, and microstructure. Simulation results show that the evolution of the horizontal flow experiences three typical stages, namely transmission, adjustment, and stabilization. Meanwhile, the shear dilatancy caused by the vertical movement of particles, gradually loosens the filling state, weakens the spatial geometric constraint and the system’s tangential load-bearing capacity, thereby decreasing the interfacial friction coefficient and reducing the boundary drive strength. On the other hand, the variations in the anisotropies of both contact orientation and contact forces, increase the internal friction coefficient and improve the internal shear strength. Therefore, the evolution of flow state from initially static to finally stable reduces the boundary drive strength while enhances the internal shear strength, and eventually a balance between them is achieved. Distinguished from the micromechanical behaviors, under different shear velocities the internal shear strength always mainly originates from the anisotropies in contact orientation and in normal contact force. Moreover, the contribution of the anisotropy in contact orientation becomes more predominant with the increase of shear velocity.

Internal Friction and Compressive Deformation in the Primary Zone during the High-Speed Cutting of SiCp/Al Composites

The present work proposes that there is internal friction and compressive deformation in the primary zone. Mathematical model was established, in which the internal friction coefficient and some compressive characteristics of serrated chips were calculated. High-speed orthogonal cutting experiment was performed on SiCp/Al composites at cutting speeds of 10–350 m/min and feed rates of 0.07–0.12 mm/r. The internal friction and compressive deformation in the primary zone were investigated by combing results obtained in the experiments with the mathematical model. The internal friction coefficient (0.21–0.47), compressive stress (185.4 MPa–226.9 MPa), and compressive strain rate (0.013×104 /s–0.554×104 /s) increased with increasing cutting speed. However, the compression value (17.3 µm–50.0 µm) and compressive strain (0.18–0.26) decreased with the cutting speed.

A New Shear Strength Criterion for Rock Masses with Non-Persistent Discontinuities Considering the Nonlinear Progressive Failure Process

The shear strength characteristics of rock masses containing non-persistent discontinuities are strongly affected by discontinuities and rock bridges. The linear Jennings criterion cannot reflect the nonlinear mechanical behavior during progressive failure of rock masses with non-persistent discontinuities. In this study, a new nonlinear shear strength criterion was developed. First of all, a series of shear test data about artificial rock mass samples were collected on the basis of the published literatures, and five types of samples were differentiated according to the positions of discontinuities. After that, a new nonlinear shear strength criterion was proposed by introducing two correction coefficients A and B into the basic form of the Jennings criterion, which could correct the weight of the cohesion and the internal friction coefficient of rock bridges respectively. Then, the new criterion was determined by fitting the basic form of the Jennings criterion with the laboratory data. It was found that the parameters A and B had a nonlinear exponential and negative exponential relation with the connectivity rate respectively. It indicated that both the cohesion and the internal friction coefficient estimated by the new criterion were superior to those estimated by the Jennings criterion. Compared with the linear Jennings criterion, the new nonlinear shear strength criterion had a better applicability.

ENGINEERING MANAGEMENT OF MACHINE FOR FORMATION OF ARTIFICIAL SHELL ON SEED VEGETABLE CULTURES

The article analyses the universalization of the seed material by its physical and mechanical properties by means of pre-sowing treatment, resulting in the formation of an artificial shell. As a result of the generalization, a technological scheme of obtaining an encapsulated seed and a design of a seed coating machine was proposed. A simulation model of the sowing accuracy process from the internal friction coefficient of seeds at different root mean square deviations of seed sizes is proposed. The regression equation for the influence of the dynamic mode of operation of the developed experimental sample of seed coating machine is established. According to the experimental studies’ results, the static and dynamic friction coefficients of the encapsulated vegetable seeds on the steel and plastic working surfaces of seed coating machine were established. Under the production conditions, experimental tests were conducted to compare the seedlings of untreated, coated, branded and encapsulated seeds of vegetables by the quality of prepared seed material and sowing time.

How serpentine peridotites can leak through subduction channels

<p>Serpentinized peridotites are weaker than other mantle rocks, with an internal friction coefficient μ<sub>i</sub>~0.3 vs. ~0.6. Therefore they often promote strain localization. Serpentinite is also considerably lower in density (r=2.5-2.6 g/cm<sup>3</sup>) than most rocks. In the presence of denser material, its buoyancy can mobilize upwelling masses and aid exhumation. Serpentinized peridotites can therefore influence the evolution of tectonic plate boundaries: their presence enhances shear processes, and serpentinite-hosted faults can evolve into zones of permanent lithospheric weakness that can be reactivated during different tectonic phases. Fault reactivation also provides paths for fluid infiltration and upward remobilization of serpentinized peridotites that can also interact diapirically with overlying rocks.</p><p>We have compiled observations that document the near-surface journey of serpentinized peridotites that are exhumed during rifting and continental break-up, reactivated as buoyant material during subduction, and ultimately emplaced as ‘ophiolite-like’ fragments within orogenic belts. This lifecycle is particularly well documented in former Tethys margins that now subduct beneath the Calabrian Arc. Here recent studies describe serpentinized peridotites that diapirically rose from a subducting lithospheric slab to be emplaced into the accretionary prism in front of the continental arc. We show that this newly recognized mode of subduction-linked serpentine diapirism from the downgoing lithospheric slab is consistent with the origin of some exhumed mantle rocks in the Apennines, with these assemblages having been ultimately emplaced into their present locations during Alpine Orogenesis. Transfer of serpentinized peridotites from the mantle lithosphere of the subducting slab to the overriding plate motivates the concept of a potentially “leaky” subduction channel.  In addition to passing vertically through a shallow subduction channel, weak serpentine bodies may also rise into and preferentially migrate within the intraplate shear zone, leading to strong lateral heterogeneities in its composition, mechanical strength and seismic characteristics.</p>

Study of Performance Characteristics of the Gravitational Guide Curve of Feeder Unit

The rate of the feed velocity and specific load in the air separator are interrelated and require a rational approach to their choice, because reducing the rate of velocity increases grain flow thickness, which adversely affects the efficiency of grain separation in the separation zone, but limits separator performance. Based on the research of many authors, it was concluded that the feed velocity of grain material into the pneumatic separation channel should be in the range of 0.4… 0.6 m/s. Taking into account that using a feeder unit for multilevel grain input, the total thickness of grain flow is divided by the number of the involved levels of input. The main condition is to ensure a single layer of grain feed at the velocity at which the most intense release of light impurities. Therefore, the purpose of the study is to identify rational parameters of the guide gravitational surface of the feeder unit with the provision of appropriate performance characteristics of the grain flow during its multilevel feeding into the pneumatic separating channel. As a result of experimental research, the dependences of the modes of movement of grain material on the gravitational guide curve on its main parameters, namely, the length of the acceleration section Lp, its angle α and the radius of the arcuate section r. On the basis of the carried-out research parameters of a gravitational guide surface at which a single-layer mode of movement of grain material for a range of specific loadings is reached are established qB = 250 – 500 kg/hour. Accordingly, for the conditions of movement of grain material with a thickness of one grain with the velocity of feeding into the pneumatic separation channel vв = 0.5…0.6 m/s, the rational parameters of the guide gravity curve for cereals with the internal friction coefficient φтер = 0.47…0.73 there are: the length of the acceleration section Lp = 0.2 m, the angle of its inclination α = 33° and the radius of the arcuate section r = 0.15 m.

Internal friction can be measured with the Jarzynski equality

A simple protocol for the extraction of the internal friction coefficient of polymers is presented. The proposed scheme necessitates repeatedly stretching the polymer molecule, and measuring the average work dissipated in the process by applying the Jarzynski equality. The internal friction coefficient is then estimated from the average dissipated work in the hypothetical limit of zero solvent viscosity. The validity of the protocol is established through Brownian dynamics simulations of a single-mode spring-dashpot model for a polymer. Well-established single-molecule manipulation techniques, such as optical tweezer-based pulling, can be used to implement the suggested protocol experimentally.

Study of the nature of the dynamic coefficient of internal friction of grainmaterials

The article highlights the issues related to the study of physical and mechanical characteristics of bulk materials, namely internal friction coefficients in static and dynamic modes. An innovative device of the carousel type for determining the frictional characteristics of bulk materials is described, which allows to implement the tasks of practical determination of dynamic coefficients of internal friction. Presented the program, methodology and results of research on the practical study of the internal friction coefficient of typical bulk products of agricultural production in the range of linear velocities of displacement of layers from 0 to 2.79 m/s, the reliability of which is not lower than 0.878.

MAPPROXIMATING STRESSES IN THE VICINITY OF A CAVITY EXPANDING AT A CONSTANT VELOCITY IN A MEDIUM WITH THE MOHR - COULOMB PLASTICITY CONDITION

A one-dimensional problem of a spherical cavity expanding at a constant velocity from a point in an infinite elastoplastic medium is considered. The problem has a first-kind self-similar solution. Elastoplastic deformation of the soil is described based on Hooke's law and the Mohr-Coulomb yield criterion. An analytical solution of the problem in the elastic region contacting with the plastic yield region has been obtained. To determine stress and velocity fields in the plastic region, a known algorithm, based on the shooting method, of analyzing a boundary-value problem for a system of two first-order ordinary differential equations, including the fourth-order Runge - Kutta method, has been realized. An effective algorithm of numerically analyzing an expanding cavity problem, earlier proposed in the works by М. Forrestal et al., makes it possible to solve the problem accurately enough for practical applications. A formula for determining the critical pressure - the minimal pressure required for the nucleation, accounting for internal pressure of a cavity in the framework of the Mohr - Coulomb yield criterion, has been derived, which is a generalization of the earlier published solution for an elastic ideally plastic medium with Tresca's criterion. The obtained critical value was compared with a numerical solution in a full formulation at the cavity expansion velocities close to zero in a wide range of variation of the parameters of the Mohr - Coulomb yield criterion. It is shown that the inaccuracy of the approximation of the proposed formula does not exceed 6% for the variation of the internal friction coefficient all over the admissible range, and for the initial value of the yield strength increasing by three orders of magnitude.