Multifractality and randomness in the unstable plastic flow near the lower strain-rate boundary of instability

2008 ◽  
Vol 77 (2) ◽  
Author(s):  
M. A. Lebyodkin ◽  
T. A. Lebedkina
Keyword(s):  
Strain Rate ◽  
Plastic Flow ◽  
Lower Strain Rate ◽  
Lower Strain

scholarly journals Hot Workability of 300M Steel Investigated by In Situ and Ex Situ Compression Tests

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 880 ◽  
Author(s):  
Rongchuang Chen ◽  
Haifeng Xiao ◽  
Min Wang ◽  
Jianjun Li
Keyword(s):  
Flow Stress ◽  
Strain Rate ◽  
Hot Working ◽  
Ex Situ ◽  
Lower Strain Rate ◽  
Hot Workability ◽  
Compression Tests ◽  
300M Steel ◽  
Lower Strain

In this work, hot compression experiments of 300M steel were performed at 900–1150 °C and 0.01–10 s−1. The relation of flow stress and microstructure evolution was analyzed. The intriguing finding was that at a lower strain rate (0.01 s−1), the flow stress curves were single-peaked, while at a higher strain rate (10 s−1), no peak occurred. Metallographic observation results revealed the phenomenon was because dynamic recrystallization was more complete at a lower strain rate. In situ compression tests were carried out to compare with the results by ex situ compression tests. Hot working maps representing the influences of strains, strain rates, and temperatures were established. It was found that the power dissipation coefficient was not only related to the recrystallized grain size but was also related to the volume fraction of recrystallized grains. The optimal hot working parameters were suggested. This work provides comprehensive understanding of the hot workability of 300M steel in thermal compression.

Influence of Mg Content, Grain Size and Strain Rate on Mechanical Properties and DSA Behavior of Al-Mg Alloys Processed by ECAP and Annealing

2014 ◽  
Vol 794-796 ◽  
pp. 870-875 ◽  
Author(s):  
Min Zha ◽  
Yan Jun Li ◽  
Ragnvald H. Mathiesen ◽  
Christine Baumgart ◽  
Hans J. Roven
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Strain Rate ◽  
Room Temperature ◽  
Uniform Elongation ◽  
Mg Alloys ◽  
Lower Strain Rate ◽  
Lower Strain ◽  
Mg Content ◽  
Al Mg Alloys

Ultrafine-grained (UFG) binary Al-xMg (x=1, 5 and 7 wt %) alloys were processed by equal channel angular pressing (ECAP) at room temperature via route Bccombined with inter-pass annealing. The effects of Mg content, grain size and strain rate on mechanical properties and dynamic strain aging (DSA) behaviour of the Al-Mg alloys upon tensile testing at room temperature were studied. An increase in Mg content from 5 to 7 wt % leads to a pronounced increase in strength and uniform elongation in both the as-homogenized and as-ECAP Al-Mg alloys. Thereby, the Al-7Mg alloy, either prior to or after ECAP processing, possess significantly higher strength and comparable or even higher uniform elongation than the more dilute Al-Mg alloys. However, the as-ECAP Al-Mg alloys exhibit significantly higher strength but little work hardening and hence rather limited uniform elongation. In general, decreasing grain size leads to significant increase in strength while dramatic decrease in ductility. Moreover, DSA serration amplitudes increase with reducing grain size in the micrometer range. However, the UFG Al-Mg alloys exhibit much less DSA effect than the micrometer scaled grain size counterparts, i.e. probably due to the high dislocation densities and special grain boundary features in the UFG materials. Also, the Al-Mg alloys, especially those with a UFG structure, exhibit higher strength and ductility at lower strain rate than at higher strain rate, due mainly to enhanced DSA effect and hence work hardening at a lower strain rate.

scholarly journals Impact of arterio–ventricular interaction on first-phase ejection fraction in aortic stenosis

2020 ◽  
Author(s):  
Eigir Einarsen ◽  
Johannes J Hjertaas ◽  
Haotian Gu ◽  
Knut Matre ◽  
Philip J Chowienczyk ◽  
...  
Keyword(s):  
Linear Regression ◽  
Aortic Stenosis ◽  
Ejection Fraction ◽  
Strain Rate ◽  
Myocardial Contractility ◽  
Volume Index ◽  
Lower Strain Rate ◽  
Lower Strain ◽  
Arterial Load ◽  
Jet Velocity

Abstract Aims  First-phase ejection fraction (EF1), the EF at the time to peak aortic jet velocity, has been proposed as a novel marker of peak systolic function in aortic stenosis (AS). This study aimed to explore the association of myocardial contractility and arterial load with EF1 in AS patients. Methods and results  Data from a prospective, cross-sectional study of 114 patients with mild, moderate, and severe AS with preserved left ventricular EF (>50%) were analysed. EF1 was measured as the volume change from end-diastole to the time that corresponded to peak aortic jet velocity. Myocardial contractility was assessed by strain rate measured by speckle tracking echocardiography. Arterial stiffness was assessed by central pulse pressure/stroke volume index ratio (PP/SVi). The total study population included 48% women, median age was 73 years, and mean peak aortic jet velocity was 3.47 m/s. In univariable linear regression analyses, lower EF1 was associated with higher age, higher peak aortic jet velocity, lower global EF, lower global longitudinal strain, lower strain rate, and higher PP/SVi. There was no significant association between EF1 and heart rate or sex. In multivariable linear regression analysis, EF1 was associated with lower strain rate and higher PP/SVi, independent of AS severity. Replacing PP/SVi by valvular impedance did not change the results. Conclusion  In patients with AS, reduced myocardial contractility and increased arterial load were associated with lower EF1 independent of the severity of valve stenosis.

scholarly journals Behavior of Elastic Therapeutic Tapes under Dynamic and Static Conditions

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Hermela Ejegu ◽  
Bipin Kumar ◽  
Priyanka Gupta
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Internal Stress ◽  
Dynamic Condition ◽  
Physical And Mechanical Properties ◽  
Static Condition ◽  
Strain Rates ◽  
Lower Strain Rate ◽  
Lower Strain ◽  
Static Conditions

The aim of this paper is to determine the relaxation behavior of the therapeutic tape under different thermomechanical conditions over different time spans and to analyze the physical and mechanical properties of selected kinesiology tapes. The relaxation test was conducted under a static condition with two extended levels (25% and 50%) for one hour and a dynamic condition for 300 cycles with different loading-unloading values, strain rates, and temperatures. For both static and dynamic conditions, at a lower strain rate and higher load and temperature, the therapeutic tapes showed higher loss of internal stress and faster losses of efficiency. Under all selected conditions, the tape’s stress has decreased rapidly.

Study on Deformation-Induced Pearlite Transformation in Vanadium Microalloyed Eutectoid Steel

2019 ◽  
Vol 1156 ◽  
pp. 17-24
Author(s):  
Cai Zhen ◽  
Xin Ping Mao ◽  
Si Qian Bao ◽  
Zhao Gang
Keyword(s):  
Strain Rate ◽  
Volume Fraction ◽  
Microalloyed Steel ◽  
Hot Compression ◽  
Lower Strain Rate ◽  
Compression Tests ◽  
Eutectoid Steel ◽  
Lower Strain ◽  
Vanadium Carbides

In this paper, the hot compression tests were performed to study on deformation-induced pearlite transformation in vanadium microalloyed eutectoid steel. The results showed that volume fraction of deformation -induced pearlite were higher and the pearlite were spheroidized better under lower strain rate and higher strain in vanadium microalloyed steel. Ferrite grains and granular cementites were further refined through vanadium microalloying combined with deformation-induced pearlite transformation .Vanadium dissolved in γmatrix could retard deformation-induced pearlite transformation under low strain, vanadium carbides precipitated due to strain-induced precipitation eliminate the retardation when the strain was increased to a certain extent. Under heavy deformation, ferrite grains and granular cementites in vanadium microalloyed steel were finer compared with vanadium free steel.

scholarly journals Strain-Rate and Grain‒Size Effects in Ice

1987 ◽  
Vol 33 (115) ◽  
pp. 274-280 ◽  
Author(s):  
David M. Cole
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Transition Point ◽  
Boundary Migration ◽  
Peak Stress ◽  
Strain Rates ◽  
Thin Sections ◽  
Fine Grained ◽  
Lower Strain ◽  
Polycrystalline Ice

AbstractThis paper presents and discusses the results of constant deformation-rate tests on laboratory-prepared polycrystalline ice. Strain-rates ranged from 10−7to 10−1s−1, grain–size ranged from 1.5 to 5.8 mm, and the test temperature was −5°C.At strain-rates between 10−7and 10−3s−1, the stress-strain-rate relationship followed a power law with an exponent ofn= 4.3 calculated without regard to grain-size. However, a reversal in the grain-size effect was observed: below a transition point near 4 × 10−6s−1the peak stress increased with increasing grain-size, while above the transition point the peak stress decreased with increasing grain-size. This latter trend persisted to the highest strain-rates observed. At strain-rates above 10−3s−1the peak stress became independent of strain-rate.The unusual trends exhibited at the lower strain-rates are attributed to the influence of the grain-size on the balance of the operative deformation mechanisms. Dynamic recrystallization appears to intervene in the case of the finer-grained material and serves to lower the peak stress. At comparable strain-rates, however, the large-grained material still experiences internal micro-fracturing, and thin sections reveal extensive deformation in the grain-boundary regions that is quite unlike the appearance of the strain-induced boundary migration characteristic of the fine-grained material.

A State Variable Modeling of Plasticity and Necking Under Uniaxial Tension

1992 ◽  
Vol 114 (4) ◽  
pp. 378-383 ◽  
Author(s):  
G. Ferron ◽  
H. Karmaoui Idrissi ◽  
A. Zeghloul
Keyword(s):  
Strain Rate ◽  
Uniaxial Tension ◽  
Plastic Flow ◽  
Constitutive Equations ◽  
Growth Process ◽  
Constant Strain Rate ◽  
Uniaxial Tensile ◽  
Long Wavelength ◽  
State Variable ◽  
Diffusion Controlled

Constitutive equations based on a state variable modeling of the thermo-viscoplastic behavior of metals are discussed, and incorporated in an exact, long-wavelength analysis of the neck-growth process in uniaxial tension. The general formalism is specialized to the case of f.c.c. metals in the range of intragranular, diffusion controlled plastic flow. The model is shown to provide a consistent account of aluminum behavior both under constant strain-rate and creep. Calculated uniaxial tensile ductilities and rupture lives in creep are also compared with experiments.

scholarly journals Mechanical properties of wrought magnesium alloys

2021 ◽  
Author(s):  
Sanjida Begum
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Magnesium Alloys ◽  
Bauschinger Effect ◽  
Fatigue Crack Initiation ◽  
Hysteresis Loops ◽  
Cyclic Hardening ◽  
Strain Ratio ◽  
Strain Hardening Exponent ◽  
Lower Strain

Lightweight magnesium alloys are being increasingly used in automotive and other transportation industries to achieve energy efficiency. The objective of this thesis was to study the mechanical properties of two wrought alloys AZ31 and AM30. With increasing strain rate the yield strength and ultimate tensile strength increased and the strain hardening exponent decreased for AM30 and increased for AZ31. Both alloys exhibited stable cyclic characteristics at lower strain amplitudes and cyclic hardening characteristics at higher strain amplitudes. The Bauschinger effect was pronounced at higher strain amplitudes, resulting in asymmetric hysteresis loops in both alloys. The influence of strain ratio (Rs), strain rate, and initial straining direction on the cyclic deformation characteristics and fatigue life was evaluated. At low Rs, both alloys exhibited strong cyclic hardening, which decreased as Rs increased. Fatigue crack initiation was observed to occur from the specimen surface and crack propagation was basically characterized by striation-like features.

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