Viscoplastic Properties Research Articles

Применение металлофизических методов аттестации материалов роликовинтовой передачи

The paper is devoted to the selection of methods for determining the materials used for the manufacture of roller drive in the framework of import substitution. Modern research methods were used such as optical and scanning electron microscopy, microhardness measurements using an automatic microhardness tester. As a result of measuring the microhardness of the roller drive material, the authors obtained an increase from 779HV in the center to 835HV on the teeth of the part. Based on metallographic studies, the microstructure of fine-needled martensite with well-defined chains of chromium, molybdenum, and vanadium carbides with a microhardness of 1200…1500 HV has been obtained. In case of microrentgenospectral analysis using a TESCAN LYRA 3 scanning electron microscope with the Ultim MAX microanalysis system, information was obtained on the point chemical composition of the sample material, traces of precipitation of carbides from a matrix with low visco-plastic properties were observed. Recommendations are given on suitable domestic analog materials. The research results can be used in constructive solutions for the design and modernization of machines and mechanisms.

Viscoplastic properties of chromium-nickel steel in short-term creep under constant stress. Part 2

Viscoplastic properties of chromium-nickel steel in short-term creep under constant stress. Part 2

Impact of Nanocarbon-Coated Calcium Carbonate on Asphalt Rutting: Experimental and Numerical Analyses

Rutting is a significant form of pavement distress that arises from irreversible strains accumulating along wheel paths, directly impacting pavement safety. This research investigates the effectiveness of nanocarbon-coated micronized calcium carbonate powder as a modified filler to mitigate rutting, utilizing numerical methods via finite element software. The study specifically examines the addition of 5% by weight of this modified filler to the asphalt mix. To validate the numerical results, laboratory wheel-tracking tests were conducted on samples incorporating both conventional and modified fillers. The findings reveal that the modified calcium carbonate filler enhances the asphalt’s resistance to rutting, with the 5% inclusion demonstrating a marked improvement in durability and performance. The study also underscores the necessity of characterizing the elastic and visco-plastic properties of materials through rigorous testing methods, such as elastic modulus and dynamic creep tests, to better understand their behavior under load. Numerical analysis based on linear elastic conditions was prioritized over viscous conditions to effectively compare the results of these specialized materials. The strong correlation between the numerical simulations and laboratory results reinforces the effectiveness of finite element methods in predicting pavement behavior and optimizing asphalt mixtures.

Important Practical Conditions for Getting the High-Quality Foam Concretes

Introduction. The most important reasons justifying the relevance of the research on the practical methods of reducing the consumption of materials in construction industry have been distinguished. The priorities of the Russian Federation referring to the foam concrete technology have been outlined. The level of reliability of the Internet resources describing properties of the dispersedly reinforced foam concretes has been briefly evaluated. The aim of the study is to establish the relationships between the individual properties of fiber, its quantity to the mass of cement ratio, and the most important operational properties of foam concrete manufactured using a single-stage technology.Materials and methods. The types and properties of raw materials used in the experimental research, the methods for controlling the properties of mixes and hardened foam concretes have been defined.Results. The relationship between the speed of phase transition of the viscoplastic properties of the foam concrete mixes into the elastic ones and the possibility of getting a high-quality structure of the hardened foam concrete have been briefly theoretically justified. The physical reasons influencing the direction and speed of forming the raw material dispersed particle clusters in the structure of the interpore partitions of foam concrete mixes have been revealed, which are the important factors to be considered in practice to get the high-strength foam concretes. Depending on the fiber concentration in the concrete mixture composition, the specifics of the fiber physical nature influence on the speed of phase transition from viscoplastic to elastic state have been established. It has been proved that the synergetic effect of dispersed reinforcement is achieved when fiber concentration is enough to provide the significant acceleration of the phase transition. New experimental data on the influence of the individual properties of fiber on the rheological and physico-mechanical properties of D500 foam concrete has been obtained.Discussion and Conclusion. The scientific explanation of the reasons for emergence of the electret effect on the surface of synthetic fiber has been given. It has been revealed that the discovered effect is induced by the specifics of the foam concrete mixture preparation using a single-stage technology. The most important practical conditions due to be met to get the high-strength foam concrete have been determined.

Experimental studies of bearing capacity of pipe steel of sewage systems

The results of experimental studies on the kinetics of crack growth, its relationship with the parameters of crack resistance and long-term strength of pipe steels of different service life and their structural and phase composition are presented. It was found that the value of the critical stress SK for all test steels increases with the increase in the service life, and the impact viscosity decreases, which indicates the structural embrittlement of the pipe steels associated with their sudden flooding. It is shown that the new 06G2BA steel, which is economically modified with a carbide-forming element (vanadium) and has a fine-grained structure and a low content of harmful impurities (sulfur, phosphorus), has the highest visco-plastic properties and resistance to brittle fracture. The microstrain of the α-Fe crystal lattice, as well as the quantitative decay of cementite and the redistribution of carbon between ferrite and pearlite, were evaluated by X-ray structural methods. 06G2BA steel is recommended for use in the construction of pipelines and, for example, bridge structures, which are constantly under cyclic loads with simultaneous contact with a corrosive-aggressive environment. The influence of the service life of water pipes on the hydrogen content and microcracks in pipe steels was determined. A diagram of the relationship between long-term and static strength depending on the hydrogen content in steels is recommended, which can be used by designers to rationally choose the type of steels with high crack resistance in aggressive technological environments. In order to extend the service life of pipe structures, it is necessary to use economically modified steels.

Relaxation tests for the time dependent behavior of pharmaceutical tablets: A revised interpretation

Relaxation tests are often used in the pharmaceutical field to assess the strain rate sensitivity of pharmaceutical powders and tablets. These tests involve applying a constant strain to the powder in the die and then monitoring the stress evolution over time. Interpreting these tests is complicated because different physical phenomena, mainly viscoelasticity and viscoplasticity, occur simultaneously. These two phenomena cannot be distinguished by observing the evolution of the axial pressure alone, as it decreases in both cases. In this work, it was shown that monitoring the evolution of the die-wall pressure during relaxation can help separate the effects of these phenomena. Theoretical considerations revealed that during viscoplasticity, the die-wall pressure also decreases, whereas an increase in the die-wall pressure during relaxation indicates a viscoelastic relaxation. This was confirmed experimentally using specially designed compaction cycles on four different pharmaceutical excipients. Experimental results indicated that at low pressure, viscoplasticity was predominant, whereas at high pressure, viscoelasticity became more prominent. These results suggest that at low pressures, relaxation tests can be used to assess the viscoplastic properties of different products. However, the use of high pressure should always be avoided as viscoelastic phenomena might become more significant, and the combination of both phenomena might compromise the interpretation.

Horizontal buoyant jets into viscoplastic ambient fluids

This study investigates the horizontal injection of a heavy Newtonian fluid into a lighter viscoplastic ambient fluid, in a large reservoir. The flow dynamics is experimentally captured via camera imaging, laser-induced fluorescence, and particle image velocimetry techniques. The flow parameters include various density differences, injection velocities, and ambient fluid viscoplastic properties. Our analysis identifies two key dimensionless numbers, the Froude number (Fr) and the effective viscosity ratio (m), which includes the rheology of the viscoplastic fluid. Our study also examines the effects of these dimensionless numbers on critical jet characteristics, such as bifurcation length, transition length, deviation length, and jet trajectory, and provides correlations using Fr and m, to predict these characteristic lengths. A regime classification based on the bifurcation phenomenon is also presented in the Fr−m plane.

Natural convection of viscoplastic fluids in a triangular enclosure

This study extends the analysis of natural convection in a viscoplastic fluid to flow within a triangular enclosure. The finite-element approach provided a numerical solution to the continuity, momentum, and energy equations. The governing parameters for this problem are the Rayleigh number, (Ra=104−106), yield number, (Y=0−Ymax), aspect ratio, (HL=0.5−2.5), and slope angle, (∅=0−π2). The influence of these parameters on the heat and mass transfer, morphology of yielded/unyielded regions, and fluid flow were thoroughly examined. The results show that two opposing factors influence the flow behavior and heat transmission within the triangular enclosure. The proximity of the walls restricts the convective movement, leading to reduced heat transfer. However, the proximity of hot and cold sources increases the temperature gradient and heat transfer. The unique influence of the viscoplastic material properties, particularly the yield stress, further distinguishes the heat transfer in this triangular enclosure from other geometries. The results indicate that an increase in the Rayleigh number mitigates the effects of yield stress to some extent. However, the accumulation of unyielded material at the triangular apex hinders convection flow. Furthermore, the viscoplastic fluid flow and heat transfer changed significantly with changes in triangle height. In particular, the maximum yield stress increased by more than 100 % as the aspect ratio increased from 0.5 to 2.5. A change in the slope angle causes a continuous transition from subcritical to supercritical bifurcation, significantly affecting the morphology of the yielded and unyielded areas, and the maximum (critical) yield number. Finally, correlations were developed to predict the Nusselt number and maximum yield stress in all cases.

General hydrodynamic features of elastoviscoplastic fluid flows through randomised porous media

A numerical study of yield-stress fluids flowing in porous media is presented. The porous media is randomly constructed by non-overlapping mono-dispersed circular obstacles. Two class of rheological models are investigated: elastoviscoplastic fluids (i.e. Saramito model) and viscoplastic fluids (i.e. Bingham model). A wide range of practical Weissenberg and Bingham numbers is studied at three different levels of porosities of the media. The emphasis is on revealing some physical transport mechanisms of yield-stress fluids in porous media when the elastic behaviour of this kind of fluids is incorporated. Thus, computations of elastoviscoplastic fluids are performed and are compared with the viscoplastic fluid flow properties. At a constant Weissenberg number, the pressure drop increases both with the Bingham number and the solid volume fraction of obstacles. However, the effect of elasticity is less trivial. At low Bingham numbers, the pressure drop of an elastoviscoplastic fluid increases compared to a viscoplastic fluid, while at high Bingham numbers we observe drag reduction by elasticity. At the yield limit (i.e. infinitely large Bingham numbers), elasticity of the fluid systematically promotes yielding: elastic stresses help the fluid to overcome the yield stress resistance at smaller pressure gradients. We observe that elastic effects increase with both Weissenberg and Bingham numbers. In both cases, elastic effects finally make the elastoviscoplastic flow unsteady, which consequently can result in chaos and turbulence.Graphical abstract

APPLICATION OF HYDROGELS FOR WATER SHUTOFF TREATMENTS. Message 1

Application of gels for well water shutoff has become a part of oilfield practice, and this direction is constantly evolving due to several objective reasons. The main reason is the growing water cut of well production, and repair and isolation operations using hydrogels occupy a worthy place in this segment of technological processes for limiting water inflow. The second reason for oilfield workers’ interest in hydrogels for water shutoff is related to the possibility of smooth regulation of their properties: they are injected with low viscosity, then mature in the required isolation interval, and their viscosity and structural-mechanical properties increase multiple times. The penetration ability of gelants (immature gels) into porous media far exceeds traditional cement slurries and synthetic curing resins. An important reason for the interest of scientists and engineers in the oil industry in hydrogels is the possibility of complexing technology: after injection they are reinforced by cement slurry or curing resins, which synergistically increases the effect of water isolation. Also, gel-forming compositions can be easily transformed into foam-gel compositions by simple manipulations, which increases their isolation efficiency. In terms of rheological characteristics, hydrogels, depending on whether they are based on organic or inorganic materials, have viscoelastic or viscoplastic properties. Organic-inorganic hybrid plugging materials combine both of these important properties, allowing hydrogels of different natures and structures to be used for targeted blocking of the source of water inflow.This article emphasizes the primary importance of determining the source of well watering, depending on which the treatment design is already built, and the appropriate materials are selected.

Structural And Mechanical Properties Of Oils From The Muradkhanly And Sangachal-Deniz Fields Of Azerbaijan

In the range of 278-293 K, the structural-mechanical properties of high-viscosity asphaltene-resinous and highly solidifying paraffinic oils of the Muradkhanly and Sangachal-deniz fields of Azerbaijan, which exhibit abnormal viscosity at various shift rates and are characterized by non-Newtonian, viscoplastic and thixotropic properties, have been studied. According to the Eyring-Frenkel equation, the activation energies of the viscous flow Ea and the change in the entropy ΔS of these oils are calculated for the indicated temperature range. Various algorithms for estimating the thermodynamic parameters of the flow ΔH and ΔS published in the literature are analyzed, and the scatter of the values of the estimates of parallel calculations is shown. It is shown that with a decrease in temperature, phase transitions in oils are activated, in particular, for the highly solidifying paraffin oil Sangachal-deniz, it originates from 297 K. For the oils under consideration for the selected shift rate of 67 s-1, the values of the temperature of the beginning of structure formation, static and limiting dynamic shift stresses were determined: for Muradkhanly oil T = 282.83 K, Sangachal-deniz - T = 297.23 K. The results obtained can be used to predict the behavior of oils

New empirical test method to assess Reynolds dilatancy of concrete under free-surface flow

In this study, a new test method was proposed to evaluate the shear-induced volumetric changes, namely Reynolds dilatancy (RD), of sixteen conventional vibrated concrete (CVC) mixtures under free-surface flow. The RD measurements were carried out using a rheometer set-up and different vane-blade types rotating at different speeds. According to the experimental results, the RD values were found in good agreement with the workability of the investigated mixtures. Moreover, the RD values were well correlated with the coupled effect of the relative solid packing fraction of coarse aggregate (φ/φmax) and viscoplastic properties of the investigated CVC mixtures. Furthermore, a strong correlation was established between the rheological properties of the lubrication layer, RD values, and the φ/φmax of coarse aggregate.

New biopolymers as viscosity-modifying admixtures to improve the rheological properties of cement-based materials

The performance of various new biopolymers as viscosity-modifying admixtures (VMAs), including tragacanth, almond, and locust bean gums and giant kelp extract, in addition to two commercial biopolymer-VMAs, welan and guar gums in cement-based materials was evaluated. The effect of the preparation/addition method, type, and dosage of the investigated biopolymers on rheology, hydration kinetics, stability, and compressive strength of various cement paste mixtures was evaluated. The pre-dispersion and pre-dispersion/pre-hydration techniques showed greater influence on the rheology of the investigated mixtures compared to dry addition. Moreover, the investigated biopolymers led to a shear-thinning response with higher viscoplastic properties than the reference. The structural build-up of the mixtures was mainly influenced by the type and dosage of the biopolymers, observing higher performances in mixtures containing guar gum, giant kelp extract, and welan gum. The use of the investigated biopolymers enhanced the stability of the paste mixtures, while negatively influenced the early-age strength development.

Experimental studies of the bearing capacity of pipe steels of sewage systems

It was established that the value of the critical stress SK for all experimental steels increases with the increase in the service life, and the impact viscosity decreases, which indicates structural embrittlement of pipe steels associated with their sudden flooding. It is shown that the new 20FA steel has the highest visco-plastic properties and resistance to brittle fracture, which is economically modified with a carbide-forming element (vanadium) and has a fine-grained structure and a low content of harmful impurities (sulfur, phosphorus). The microstrain of the α-Fe crystal lattice, as well as the quantitative decay of cementite and the redistribution of carbon between ferrite and pearlite, were evaluated by X-ray diffraction methods. The new steel grade 10FA is recommended for use in the construction of underground sewage systems and, for example, bridge structures, which are constantly under cyclic loads with simultaneous contact with a corrosive and aggressive environment. For the first time, the influence of the service life of pipelines on the hydrogen content and microcracks in pipe steels was determined.

Direct measurement and modeling of viscoelastic-viscoplastic properties of freely standing thin polystyrene films.

The demand for applications, such as coatings, separation filters, and electronic packaging, has greatly driven the research of polymer films. At nanometer scale, mechanical properties of thin polymer films can significantly deviate from bulk. Despite outstanding progresses, there still lack deep discussions on nonlinear viscoelastic-viscoplastic response and their interactions under nanoconfinement. In this work, by conducting measurements via the bubble inflation method and modelling using Schapery and Perzyna equations, we demonstrate nonlinear viscoelastic-viscoplastic properties of freely standing thin polystyrene (PS) films. The results show the unchanged glassy compliance and the rubbery stiffening phenomenon for thin PS films, where the lower rubbery plateau in rubbery stiffening may originate from the induced molecular orientation by plastic deformation. With decreasing film thickness, viscosity and yield stress in viscoplasticity increase in an exponential and a linear trend, respectively, indicating the significant role of nanoconfinement effect on viscoplastic properties. These findings may reveal that there are many properties from linear viscoelasticity to nonlinear viscoelasticity-viscoplasticity that need to be explored and unveiled for sufficient understanding of the nanoconfinement effect on altering mechanical behavior of polymers.

A Fractional-Order Creep Model of Water-Immersed Coal

The long-term stability of a coal pillar dam is a serious concern for coal mine underground reservoirs because of the creep behavior of coal in complex water immersion and mechanical environments. In order to investigate the characteristics of creep deformation of water-immersed coal and develop a proper creep model, this paper implemented a series of creep experiments of coal via multistage loading at various water-immersion times. The experiment data were analyzed, in terms of immersion-induced damage, elasto-plastic performance, creep behavior, etc., suggesting obvious mechanical properties’ degradation of coal by water. The elastic modulus and peak strength of water-immersed coal decrease exponentially with the immersion time, while the creep rate of coal shows an upward tendency with the promoted immersion time. According to the remarked relationships of elastic, viscoelastic, and viscoplastic properties versus the stress levels and water-immersion time, a creep model based on conformable fractional derivatives is proposed, considering the influence of the water-immersion time and variable stress level. The proposed model was verified using the experiment data, showing a good capacity of the creep model for reproducing the creep process of water-immersed coal. This paper provides a fundamental model for further studying the stability of coal pillars and their influence on the safety of underground water reservoirs.

Properties of high-strength complex-alloy steel for casing pipes in cold-resistant and corrosion-resistant versions

The influence of alloying on the properties of high-tempered steels used for the production of casing pipes has been studied. It has been shown that an increase of molybdenum content from 0.15 to 0.53% provides a noticeable increase of the mechanical characteristics in chromium-molybdenum steels after tempering at 600‒690 °C. Alloying with vanadium and niobium contributes to an additional increase in strength properties. The influence of vanadium on the highly viscoplastic properties of steels is shown. It has been established that the greatest strengthening of steel with 0.32% molybdenum in a highly tempered state is provided by complex alloying with niobium and vanadium. The influence of austenitization and tempering temperature on the structure and properties, including resistance to cracking in an environment saturated with hydrogen sulfide, of chromium-molybdenum steel grade 26CrMoVNb-2 with micro-alloying additives of vanadium and niobium was determined. Alloying with molybdenum, vanadium and niobium makes it possible to obtain steels for high-strength casing pipes that are resistant to brittle fracture and sulfide stress corrosion cracking, subject to comprehensive consideration of the main factors such as austenitization temperature, tempering temperature and duration, dispersion and homogeneity of microstructure

Estimation of the Viscoplastic Properties of 38G2F Steel Using the Results of Tensile and Impact Bending Tests

Estimation of the Viscoplastic Properties of 38G2F Steel Using the Results of Tensile and Impact Bending Tests

1D elastic viscoplastic consolidation analysis of bi‐layered soft ground under time‐dependent drainage boundary and ramp load

AbstractThe elastic viscoplastic properties are non‐negligible factors of clays that cause the deviation between the theoretical and the measured values, which were rarely incorporated in layered consolidation problems. Thus, this paper extended a generalized bi‐layered one‐dimensional (1D) consolidation model for soft ground under ramp load, simultaneously incorporating elastic viscoplastic deformation, non‐Darcy flow (NDF), and time‐dependent drainage boundary (TDB) condition. The finite volume technique was employed to numerically solve the control equation. Then, the proposed method solutions were verified by comparing with degenerated cases, including oedometer experimental results, analytical and semi‐analytical solutions with different boundary conditions. Furthermore, parametric studies were conducted on the bi‐layered clay creep consolidation characteristics by investigating the effect of the loading rate, interface and flow parameters, and the relative soil layer properties. The results demonstrate that the entire dissipation rate of the excess pore‐water pressure (EPWP) and settlement rate in the bi‐layered ground become faster as the soil thickness with high permeability or low compressibility increases. When considering the viscosity of soft clay, the EPWP exceeding the overlying construction load value can occur in poorly drained locations. Neglecting loading rate, time‐dependent drainage boundary (TDB), and NDF can result in a significant overestimation of consolidation and settlement proceedings.

QSPR study of viscoplastic properties of peptide-based hydrogels

In this study, the power of machine learning was harnessed to probe the link between molecular structures of peptide-based hydrogels and their viscoplastic properties. The selection of compounds was attempted in accordance with the prescribed full list of peptide-based materials exhibiting hydrogel functionality in the literature. In this pursuit, a complete set of molecular descriptors and fingerprints was considered – accounting for an entry of size 17,968 for each peptide-based structure analyzed. The elastic and viscous moduli response of materials were mapped over a wide frequency spectrum in the range [0.1–100] (rad/s). In general, the results indicate that the frequency-dependent mechanical response of peptide-based hydrogels is statistically correlated with its (inter)molecular attributes, such as charge, first ionization potential (or equivalently electronegativity), surface area, number of chemical substrates, bond type, and intermolecular interactions. The performance of several (supervised) soft computing techniques was measured, for our quantitative structure property relationships model. In addition, the hypothesis of mapping our databank to a new system of principal components was tested, by using an unsupervised methodology, which resulted in enhancement of the prediction accuracy. In terms of significance, the present article provides the first report of frequency-dependent elastic and viscous moduli, for a set of 70 peptide-based formulations with hydrogel functionality. Communicated by Ramaswamy H. Sarma