Прогнозирование динамического предела текучести металлов с помощью двух структурно-временных параметров

AbstractThe behavior of the yield strength of steel and a number of aluminum alloys is investigated in a wide range of strain rates, based on the incubation time criterion of yield and the empirical models of Johnson-Cook and Cowper-Symonds. In this paper, expressions for the parameters of the empirical models are derived through the characteristics of the incubation time criterion; a satisfactory agreement of these data and experimental results is obtained. The parameters of the empirical models can depend on some strain rate. The independence of the characteristics of the incubation time criterion of yield from the loading history and their connection with the structural and temporal features of the plastic deformation process give advantage of the approach based on the concept of incubation time with respect to empirical models and an effective and convenient equation for determining the yield strength in a wider range of strain rates.

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Studies on the Dynamic Compressive Properties of Open-Celled Aluminum Alloy Foams

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.306-308.905 ◽

2006 ◽

Vol 306-308 ◽

pp. 905-910 ◽

Cited By ~ 1

Author(s):

Zhi Hua Wang ◽

Hong Wei Ma ◽

Long Mao Zhao ◽

Gui Tong Yang

Keyword(s):

Yield Strength ◽

Strain Rate ◽

Split Hopkinson Pressure Bar ◽

Strain Rates ◽

Hopkinson Pressure Bar ◽

Aluminum Foams ◽

Wide Range ◽

Split Hopkinson ◽

Pressure Bar ◽

Dynamic Loading Conditions

The compressive deformation behavior of open-cell aluminum foams with different densities and morphologies was assessed under quasi-static and dynamic loading conditions. High strain rate experiments were conducted using a split Hopkinson pressure bar technique at strain rates ranging from 500 to 1 2000 − s . The experimental results shown that the compressive stress-strain curves of aluminum foams also have the “ three regions” character appeared in general foam materials, namely elastic region, collapse region and densification regions. It is found that density is the primary variable characterizing the modulus and yield strength of foams and the cell appears to have a negligible effect on the strength of foams. It also is found that yield strength and energy absorption is almost insensitive to strain rate and deformation is spatially uniform for the open-celled aluminum foams, over a wide range of strain rates.

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Experimental Study of Internal Variable Evolution in SS304L, at Multiple Rates and Temperatures

Journal of Engineering Materials and Technology ◽

10.1115/1.2812362 ◽

1999 ◽

Vol 121 (2) ◽

pp. 162-171 ◽

Cited By ~ 4

Author(s):

E. J. Harley ◽

M. P. Miller ◽

D. J. Bammann

Keyword(s):

Yield Strength ◽

Kinematic Hardening ◽

Internal Variable ◽

Isotropic Hardening ◽

304L Stainless Steel ◽

Strain Rates ◽

Inelastic Behavior ◽

Model Framework ◽

Wide Range ◽

Strength Asymmetry

Most metals exhibit a deformation-induced uniaxial yield strength asymmetry. Interpreted within the context of macroscale viscoplastic models, it is conventional to describe this yield strength asymmetry with an isotropic hardening variable, κ, and a kinematic hardening variable, α. The focus of this work was to conduct a series of reverse yield experiments to directly measure the evolution of α and κ in 304L stainless steel (SS304L) over large ranges of temperatures and strain rates. We found that the material exhibited inelastic behavior immediately on changing the straining direction. We discussed the ramifications of this behavior on our goal to directly measure α and κ within the context of an isotropic/kinematic hardening model framework. We also explored the capability of the model to simulate the behavior of SS304L under different loading conditions across a wide range of temperatures and strain rates.

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Моделирование временных эффектов необратимого деформирования на основе релаксационной модели пластичности

Физика твердого тела ◽

10.21883/ftt.2019.06.47673.238 ◽

2019 ◽

Vol 61 (6) ◽

pp. 1015

Author(s):

Н.С. Селютина ◽

Ю.В. Петров

Keyword(s):

Plastic Deformation ◽

Yield Strength ◽

High Strength ◽

High Rate ◽

Smooth Transition ◽

Strain History ◽

Strain Rates ◽

Relaxation Model ◽

Yield Drop ◽

Wide Range

The analysis of plastic deformation of metals and polymethylmethacrylate under dynamic loading is carried out using a relaxation model of plastic deformation. The invariance of the parameters of the relaxation model of plasticity to the strain history allows us to obtain any set of deformation curves from a united viewpoint, both monotonic, with varying yield strength, and non-monotonic, with emerging and varying yield drop, as it is observed in experiments. The increase of the yield strength of high-strength 2.3Ni-1.3Cr steel together with the hardening effect both under high-rate and slow deformation is also modeled on the basis of the relaxation model. Using DP600 steel and nanocrystalline nickel as an example it is shown that the relaxation model of plasticity allows one to predict a smooth transition to the plastic deformation stage at slow quasi-static effects of ~ 10–3 s – 1, and also the appearance of a yield drop effect at strain rates of 500–6000 s –1. It is also shown that the developed approach allows one to simulate similar effects under high-rate deformation of polymethylmethacrylate. Thus, it was demonstrated using specific materials as an example that it is possible to effectively predict the deformation dependencies of the materials studied in a wide range of strain rates of 10-4-104 s-1 based on the parameters of the relaxation model of irreversible deformations.

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TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

HUE UNIVERSITY JOURNAL OF SCIENCE TECHNIQUES AND TECHNOLOGY ◽

10.26459/hueuni-jtt.v128i2b.5424 ◽

2019 ◽

Vol 128 (2B) ◽

pp. 29-41

Author(s):

Trần Thanh Nhàn

Keyword(s):

Cyclic Loading ◽

Pore Water ◽

Pore Water Pressure ◽

Water Pressure ◽

Clayey Soils ◽

Loading History ◽

Cyclic Shear ◽

Wide Range ◽

Primary Consolidation ◽

Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

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Research of the activity and viability of spermatozoa at different concentrations and proportions of diluents after incubation

Pig breeding the interdepartmental subject scientific digest ◽

10.37143/0371-4365-2020-74-11 ◽

2020 ◽

pp. 88-95

Author(s):

Svitlana Lobchenko ◽

Tetiana Husar ◽

Viktor Lobchenko

Keyword(s):

Plasma Concentration ◽

Incubation Time ◽

Coefficient Of Variation ◽

Incubation Medium ◽

Wide Range ◽

Series Of Experiments ◽

The Subject ◽

Boar Spermatozoa ◽

Native Plasma ◽

Better Than

The results of studies of the viability of spermatozoa with different incubation time at different concentrations and using different diluents are highlighted in the article. (Un) concentrated spermatozoa were diluented: 1) with their native plasma; 2) medium 199; 3) a mixture of equal volumes of plasma and medium 199. The experiment was designed to generate experimental samples with spermatozoa concentrations prepared according to the method, namely: 0.2; 0.1; 0.05; 0.025 billion / ml. The sperm was evaluated after 2, 4, 6 and 8 hours. The perspective of such a study is significant and makes it possible to research various aspects of the subject in a wide range. In this regard, a series of experiments were conducted in this area. The data obtained are statistically processed and allow us to highlight the results that relate to each stage of the study. In particular, in this article it was found out some regularities between the viability of sperm, the type of diluent and the rate of rarefaction, as evidenced by the data presented in the tables. As a result of sperm incubation, the viability of spermatozoa remains at least the highest trend when sperm are diluted to a concentration of 0.1 billion / ml, regardless of the type of diluent used. To maintain the viability of sperm using this concentration of medium 199 is not better than its native plasma, and its mixture with an equal volume of plasma through any length of time incubation of such sperm. Most often it is at this concentration of sperm that their viability is characterized by the lowest coefficient of variation, regardless of the type of diluent used, which may indicate the greatest stability of the result under these conditions. The viability of spermatozoa with a concentration of 0.1 billion / ml is statistically significantly reduced only after 6 or even 8 hours of incubation. If the sperm are incubated for only 2 hours, regardless of the type of diluent used, the sperm concentrations tested do not affect the viability of the sperm. Key words: boar, spermatozoa, sperm plasma, concentration, incubation, medium 199, activity, viability, rarefaction.

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An Analysis of Acoustic Cavitation Thresholds of Water Based on the Incubation Time Criterion Approach

Fluids ◽

10.3390/fluids6040134 ◽

2021 ◽

Vol 6 (4) ◽

pp. 134

Author(s):

Ivan Smirnov ◽

Natalia Mikhailova

Keyword(s):

Incubation Time ◽

Dynamic Strength ◽

Acoustic Cavitation ◽

Nucleation Theory ◽

Classical Nucleation Theory ◽

Accurate Estimation ◽

Ultrasound Frequency ◽

Time Criterion ◽

Good Potential ◽

Cavitation Threshold

Researchers are still working on the development of models that facilitate the accurate estimation of acoustic cavitation threshold. In this paper, we have analyzed the possibility of using the incubation time criterion to calculate the threshold of the onset of acoustic cavitation depending on the ultrasound frequency, hydrostatic pressure, and temperature of a liquid. This criterion has been successfully used by earlier studies to calculate the dynamic strength of solids and has recently been proposed in an adapted version for calculating the cavitation threshold. The analysis is carried out for various experimental data for water presented in the literature. Although the criterion assumes the use of macroparameters of a liquid, we also considered the possibility of taking into account the size of cavitation nuclei and its influence on the calculation result. We compared the results of cavitation threshold calculations done using the incubation time criterion of cavitation and the classical nucleation theory. Our results showed that the incubation time criterion more qualitatively models the results of experiments using only three parameters of the liquid. We then discussed a possible relationship between the parameters of the two approaches. The results of our study showed that the criterion under consideration has a good potential and can be conveniently used for applications where there are special requirements for ultrasound parameters, maximum negative pressure, and liquid temperature.

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