Modeling of relative shear deformation zones before strong earthquakes in Kamchatka from 2018-2021

Представлено сравнительное моделирование зон относительных сдвиговых деформаций для четырех камчатских землетрясений с Mw ≥ 4.8, произошедших в период с декабря 2018 г. по март 2021 г., основанное на статической модели деформационного поля в рамках теории упругости. Земная кора рассмотрена как однородное изотропное упругое полупространство, в котором присутствуют различные источники напряжения, описывающие очаг землетрясения: точечный источник в виде единичной силы, точечный источник в виде комбинации девяти двойных сил, распределенный источник в виде прямоугольной площадки. We present a comparative modeling of the zones of relative shear deformation for four Kamchatka earthquakes Mw≥4.8 that occurred between December 2018 and March 2021. Modeling based on a static model of the deformation field in the framework of the theory of elasticity. The Earth’s crust is considered as a homogeneous isotropic elastic half-space, in which there are different sources of stress describing the source of the earthquake: a point source in the form of a single force, a point source in the form of a combination of nine double forces, a distributed source in the form of a rectangular area.

Strength and fracture mechanism during torsion of ultrafine-grained austenitic steel for medical applications

The article considers evaluation of torsional strength and fracture of austenitic corrosion-resistant steel 08Kh18N9 with an ultrafine-grained (UFG) and coarse-grained (CG) structure, widely used in medicine for the production of plates, screws, rods for bone osteosynthesis and other medical products. The structure of the CG steel was studied using an Axiovert 40 MAT metallographic microscope, and the fine structure of the UFG steel was investigated with a JEM-2100 transmission electron microscope. Torsion tests of the cylindrical samples with a diameter of 10 mm were carried out at a temperature of 20 °C on MK-50 installation. JEOL JCM-6000 scanning electron microscope was used for the microfractographic studies of fracture surfaces. The analysis of the “Torque - torsion angle” diagrams showed that the torsional ultimate strength (τt) and yield strength (τ0.3) of UFG steel increase by 1.3 - 3.8 times, and the relative shear (g) decreases by 2.4 times in comparison with CG steel. High values of torsional strength properties of UFG steel make it possible to provide high torque without destroying the product. Consequently UFG steel 08Kh18N9 in comparison with CG steel is a more promising material for the manufacture of medical screws and other medical products that experience significant loads during the torsion process. Three areas were identified on the surface of all fractures: fibrous central part, transitional (middle) part, and a relatively smooth peripheral part. Fracture begins with the formation of shear pits in the middle and peripheral parts, which, with further rotation of the sample, are completely rubbed out (in case CG steel), or remain (in case of UFG steel). Final failure occurs under the action of normal stresses in the central part of the sample.

Thermomechanical Slip in Elastic Contact Between Identical Materials

The contact problem for interaction between an elastic sphere and an elastic half-space is considered taking into account partial thermomechanical frictional slip induced by thermal expansion of the half-space. The elastic constants of the bodies are assumed to be identical. The Amontons–Coulomb law is used to account for friction. The problem is reduced to non-linear boundary integral equations that correspond to the initial stage of mechanical loading and the subsequent stage of thermal loading. The dependences of the contact stress distribution, relative displacements of the contacting surfaces, dimensions of the stick and slip zones on temperature of the half-space are studied numerically. It was revealed that an increase in temperature causes increases in the shear contact stress and the relative shear displacements of the contacting surfaces. The absolute values of the shear contact stress reach their maximum at the boundaries of the stick zones. The greatest value of the moduli of the relative shear displacements are reached at the boundary of the contact region. The stick zone radius decreases monotonically according to a nonlinear law with increasing temperature.

Dual Properties of Polyvinyl Alcohol-Based Magnetorheological Plastomer with Different Ratio of DMSO/Water

Polyvinyl alcohol (PVA)-based magnetorheological plastomer (MRP) possesses excellent magnetically dependent mechanical properties such as the magnetorheological effect (MR effect) when exposed to an external magnetic field. PVA-based MRP also shows a shear stiffening (ST) effect, which is very beneficial in fabricating pressure sensor. Thus, it can automatically respond to external stimuli such as shear force without the magnetic field. The dual properties of PVA-based MRP mainly on the ST and MR effect are rarely reported. Therefore, this work empirically investigates the dual properties of this smart material under the influence of different solvent compositions (20:80, 40:60, 60:40, and 80:20) by varying the ratios of binary solvent mixture (dimethyl sulfoxide (DMSO) to water). Upon applying a shear stress with excitation frequencies from 0.01 to 10 Hz, the storage modulus (G′) for PVA-based MRP with DMSO to water ratio of 20:40 increases from 6.62 × 10−5 to 0.035 MPa. This result demonstrates an excellent ST effect with the relative shear stiffening effect (RSTE) up to 52,827%. In addition, both the ST and MR effect show a downward trend with increasing DMSO content to water. Notably, the physical state of hydrogel MRP could be changed with different solvent ratios either in the liquid-like or solid-like state. On the other hand, a transient stepwise experiment showed that the solvent’s composition had a positive effect on the arrangement of CIPs within the matrix as a function of the external magnetic field. Therefore, the solvent ratio (DMSO/water) can influence both ST and MR effects of hydrogel MRP, which need to be emphasized in the fabrication of hydrogel MRP for appropriate applications primarily with soft sensors and actuators for dynamic motion control.

Anti-pulling Force and Displacement Deformation Analysis of the Anchor Pulling System of the New Debris Flow Grille Dam

To avoid waste from a large section space structure layout and deep burial to improve the structural strength and stability, anchor technology is introduced, and combined with the advantages of the supporting wall, a new debris flow grille dam is proposed. Starting from the force process and damage mechanism of the new debris flow grille dam, the computation formula for the anti-pulling force and the total displacement is given. The anti-pulling force includes the sidewall frictional resistance of the anchor pier and the positive pressure of the front end face of the anchor pier. The total displacement includes three parts: the elastic deformation of the cable, the relative shear displacement between the anchor pier and the surrounding soil, and the compression deformation of the soil at the front of the anchor pier. Finally, the influence of soil parameters and anchor pier size on the anti-pulling force and displacement deformation of the anchor-pulling system is analyzed by examples, and the results are compared with the numerical results. The results show that the displacement deformation decreases gradually with increasing elastic modulus of the soil around the anchor pier and increases with increasing Poisson's ratio. The change in elastic modulus mainly affects the relative shear displacement of the anchor pier and soil and the compressive deformation of the soil at the front end of the anchor pier. Poisson's ratio has the greatest influence on the relative shear displacement of the anchor pier and soil. A larger anchor pier is not better; thus, it is wise to choose the economic design dimension. Theoretical and numerical simulation results are consistent, showing a linear growth trend. The results of this paper can further improve the theoretical calculation method of the new debris flow grille dam, thus making it widely used in more debris flow control projects.

Investigation of the Rheokinetic Properties and Penetration Depth of Aluminosilicate Adhesive in Pine Wood

Practical work and is devoted to the study of the rheological and deformative properties of Geofip aluminosilicate glue, obtained on the basis of an alkaline aluminosilicate binder composition Na2O Al2O3×6SiO2×20H2O, modified with 5% Cr2O3, when gluing wooden trusses in the field. The rheological and deformative properties of an aluminosilicate adhesive based on an alkaline aluminosilicate binder composition of Na2O×Al2O3×6SiO2×20H2O modified with 5% Cr2O3 have been investigated. It is noted that the dynamic viscosity of the adhesive slurry in the speed range from 0.1 to 0.8 RPM varies from 147600 to 144600 cP, and the average plastic viscosity in the same speed range is 87.39 cP. It was found that at shear rates from 0.021 to 0.168 1/s, an increase in shear force from 31 to 242.9 dyne/cm2 is observed due to the stabilization and uniformity of the dispersion phase particle distribution in the dispersion medium of the adhesive. It is shown that the aluminosilicate adhesive at a surface tension value of 88.1 mN/m is characterized by coefficients of wetting (s = 0.648) and fluidity (f = -62.02 mN/m), which ensures the uniformity of its application to the pine substrate. The average thickness of the adhesive layer was 1.25 mm, and the average depth of penetration of the aluminosilicate adhesive into the wood substrate, respectively, 0.12 mm. The destruction of the adhesive seam occurred at shear stresses of 515 MPa. The relative shear deformations were 162.5×10-5 mm.

DEFORMABILITY OF REINFORCED CONCRETE BEAMS UNDER THE ACTION OF CYCLIC LOADING

The aim of the article is an experimental research of the influence of low-cycle sign-constant loading, as well as the most significant design factors on the deformability of reinforced concrete beam elements. In this regard, for experimental research, the authors developed a four-factor three-level Boxing plan B4. The experimental factors of the plan were varied according to the literature review, which showed that the most significant factors are the following: the value of the relative shear span a/h0, the concrete class C, the value (amount) of transverse reinforcement on the beams support sections ρsw, the level of sign-constant loading η. The samples were tested according to the scheme of a single-span beam, alternately loaded with two centre-point forces. The number of cycles of sign-constant loading was accepted as 10. According to the results of the experiment, using the COMPEX program, adequate mathematical models of the basic parameters of reinforced concrete specimens-beams deformability under the action of low-cycle sign-constant loading were derived, that reflect the influence of these factors both individually and in interaction with each other. Analyzing these models, the features of the development of tensile reinforcement and compressed concrete deformations, as well as beams deflections in the specified conditions, were established. In particular, the factors that have the greatest influence on deformations and deflections are the relative shear span and the level of low-cycle loading. Thus, with their increase, the relative deformations of tensile reinforcement increase by 51% and 52%, the relative deformations of compressed concrete by 40% and 37%, accordingly, by series. The increase of deflections is 43% and 40% with an increase of relative shear span and 38% and 12% with an increase of loading level, accordingly, by series.

COMPARISON OF SOLUTIONS TO THE BENDING PROBLEMS OF THREE-LAYER PLATES ON THE WINKLER AND PASTERNAK FOUNDATIONS

Solutions of problems on axisymmetric bending of an elastic three-layer circular plate on the Winkler and Pasternak foundations are given. The bearing layers are taken as isotropic, for which Kirchhoff’s hypotheses are fulfilled. In a sufficiently thick lightweight, incompressible in thickness aggregate, the Timoshenko model is valid. The cylindrical coordinate system, in which the statements and solutions of boundary value problems are carried out, is connected with the median plane of the filler. On the plate contour, it is assumed that there is a rigid diaphragm that prevents the relative shear of the layers. The system of differential equations of equilibrium is obtained by the variational method. Three types of boundary conditions are formulated. One- and two-parameter Winkler and Pasternak models are used to describe the reaction of an elastic foundation. The solution to the boundary value problem is reduced to finding three desired functions, plate deflection, shear, and radial displacement in the filler. The general analytical solution to the boundary value problem is written out in the case of the Pasternak model in Bessel functions. At the Winkler foundation, the known solution is given in Kelvin functions. A numerical comparison of the displacements and stresses obtained by both models with a uniformly distributed load and rigid sealing of the plate contour is carried out.

Fibrinogen and Fibrin Differentially Regulate the Local Hydrodynamic Environment in Neutrophil–Tumor Cell–Endothelial Cell Adhesion System

As cancer is one of the major fatal diseases for human beings worldwide, the metastasis of tumor cells (TCs) from a blood vessel to an adjacent organ has become a focus of research. A tumor metastasis theory named the “two-step theory” pointed out that polymorphnuclear neutrophils (PMNs) could facilitate TC adhesion on an endothelial monolayer under flow, which was regulated by shear flow and promoted by fibrinogen and fibrin. In order to further understand the role of hydrodynamics played in the “two-step theory”, we improved our side-view micro-particle imaging velocimetry (PIV) system and successfully measured the flow velocity profiles around adherent PMNs and TCs on an endothelial monolayer in the presence of soluble fibrinogen or fibrin under shear flow. Combined with a computational fluid dynamics simulation, we found that: (1) soluble fibrinogen and fibrin influenced the variations of relative shear rates above an adhered PMN and an adherent TC at different PMN-to-TC position states; (2) compared with soluble fibrinogen, soluble fibrin made the curves of relative shear rates above an adherent cell flatter. Soluble fibrin might increase the collision frequency and affect the contact time and contact area between PMNs, TCs, and endothelium cells, resulting in the enhancement of TC adhesion and retention on an endothelial monolayer.

SUBSTANTIATION OF CHIPPING FRACTURE MECHANICS DURING DRAWING OF CYLINDRICAL SURFACES WITH ALLOWANCE

The mechanics of chip fracture when cutting the allowance of pre-divisible technological grooves was studied for the first time, and the relationship between the profile and depth of the latter and the characteristics of the stress-strain state in the chip formation zone (relative shear, chip shrinkage, shear angle, front angle, contact processes . This article discusses a more complex problem - the longitudinal division of chips or allowance. Most researchers are inclined to believe that this problem should be solved by pre-dividing the allowance by a network of special chip-splitting ring or screw grooves. The depth of these grooves should be 0.6… 0.95 of the amount of rise on a single tooth of the broach. The results of the study of the mechanics of chip destruction are described when the tool meets the process groove in the drawing process. The connection between the structure of the pipe and the intensively deformed state in the zone of chip formation is shown. From the obtained results the following follows. Preliminary deformation hardening by means of deforming drawing allows to increase hardness of OM twice (steel 10), to 60% (steel 35), to 50% (steel 45) and to 25% (aluminum alloy AK6). This significantly reduces the shrinkage coefficient of chips (respectively 2; 1.4; 1.4 and 1.3 times) and the actual previous angle (at a sharpening angle γ = 15⁰, respectively: from 36⁰ to 18⁰; from 25⁰ to 17⁰; from 21⁰ to 16⁰ and from 22⁰ to 17⁰). All this indicates a decrease in the intensity of the cutting process with increasing intensity of the previous HPD The following minimum values of the groove profile angle for the investigated materials 2φmin were determined: 80⁰ (steel10); 60⁰ (steel 35); 50⁰ (steel 45 and alloy AK6). It is established that the minimum depth of the chip-splitting groove hC is determined from the condition of chip destruction when the tangential stresses in the shear zone are exceeded above the shear resistance of the processed material. The following values of the minimum depth of the chip-splitting groove for the studied materials were obtained: hCmin = (0.4… 0.55) Sz - steels 35 and 45; hCmin = (0.55 (0.6) Sz - AK6 alloy.