scholarly journals An Analysis of the Time and Temperature Dependence of the Upper Yield Point in Iron

1961 ◽  
Vol 83 (4) ◽  
pp. 557-564 ◽  
Author(s):  
P. E. Bennett ◽  
G. M. Sinclair
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Yield Point ◽  
Strain Rates ◽  
Influence Of Temperature ◽  
State Of Stress ◽  
The Relationship ◽  
Tensile Test Data

The influence of temperature and strain rate on the upper yield point of ingot iron was studied. Torsion tests were conducted using strain rates of 12.5/sec, 0.25/sec, and 0.0001/sec over the temperature range 77 to 525 deg K. The upper yield point showed a rapid increase as the temperature was lowered. An increase in the strain rate also caused an increase in the yield point. An apparent activation energy can be associated with the strain rate and temperature dependence of the yield point. This energy is influenced by stress level, and it appears from the present study that the relationship can be described by an equation of the form ΔH=ΔH¯τ¯−ττ¯b. If this relationship is substituted for ΔH in a modification of the Boltzmann relation, the following result is obtained: logγ˙γ˙1=MΔH¯RT1τ¯−τ1τ¯b1−T1Tτ¯−ττ¯−τ1b. This equation describes the experimental data within ± 3000 psi. The results of this investigation compared with tensile test data from other investigators confirm that state of stress is an important factor in determining whether a material will behave in a ductile or brittle fashion.

A Theory of the Yield Point and the Transition Temperature of Mild Steel

1956 ◽  
Vol 23 (2) ◽  
pp. 219-224
Author(s):  
F. Forscher
Keyword(s):  
Transition Temperature ◽  
Mild Steel ◽  
Strain Rate ◽  
Yield Point ◽  
Structural Model ◽  
Yield Criterion ◽  
State Of Stress ◽  
Yield Point Phenomenon ◽  
Stress And Strain Rate ◽  
Temperature Strain

Abstract Experimental results indicate the dependence of the yield-point phenomenon of mild steel on temperature, strain rate, duration of stress, and stress state. This paper proposes a yield criterion which can account for these variables. The theory is developed on the basis of a “structural” model, by which the behavior of microscopic and submicroscopic elements is idealized. The theory postulates as yield criterion a critical number of relaxation centers (active Frank-Read sources) or, equivalently, a critical size of relaxation centers. The transition-temperature phenomenon is considered to be the result of an inhibition of yielding (upper yield point) by means of geometry, temperature and/or strain rate. A relation is given which expresses its dependence on the state of stress and strain rate.

scholarly journals Hot Compression Deformation and Activation Energy of Nanohybrid-Reinforced AZ80 Magnesium Matrix Composite

Metals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 119 ◽  
Author(s):  
Houyi Li ◽  
Lingling Fan ◽  
Mingyang Zhou ◽  
Youlong Zhou ◽  
Kuan Jiang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Strain Rate ◽  
Matrix Composite ◽  
Hot Deformation ◽  
Strain Rates ◽  
Magnesium Matrix ◽  
Deformation Activation Energy ◽  
Deformation Behaviors ◽  
Carbon Nano Tubes ◽  
Deformation Test

The hot deformation test of the nano silicon carbide (nano-SiC) and carbon nano tubes (CNT) hybrid-reinforced AZ80 matrix composite was performed at compression temperatures of 300–450 °C and strain rates of 0.0001–1 s−1. It could be observed that the flow stress of the nanocomposite rose with the reduction of deformation temperature and the increase of strain rate. The hot deformation behaviors of the composite could be described by the sine-hyperbolic Arrhenius equation, and deformation activation energy (Q) was calculated to be 157.8 kJ/mol. The Q values of the extruded nanohybrid/AZ80 composite in this study and other similar studies on extruded AZ80 alloys were compared in order to analyze the effect of the addition of reinforcement, and the effects of deformation conditions on activation energy were analyzed. Finally, the compression microstructure in an unstable condition was carefully analyzed, and results indicated that the phenomenon of local instability was easy to occur at the compression specimen of the nanohybrid/AZ80 composite under deformation conditions of low temperature with high strain rate (300 °C, 0.1–0.01 s−1), and high temperature with low strain rate (450 °C, 0.0001 s−1).

Effect of Hot Extrusion on the Flow Behaviour of a Nickel-Based P/M Superalloy

2019 ◽  
Vol 298 ◽  
pp. 43-51
Author(s):  
Jia Yong Si ◽  
Song Hao Liu ◽  
Long Chen
Keyword(s):  
Activation Energy ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Work Hardening ◽  
Rate Sensitivity ◽  
Hot Extrusion ◽  
Turbine Disk ◽  
Flow Behaviour ◽  
Strain Rates ◽  
Work Hardening Rate

This research investigated the effect of hot extrusion on the flow behaviour of nickel-based superalloy FGH4096 by hot compression experiments in the temperature range from 1020 to 1110 °C and strain rates ranging from 0.1 to 0.001 s-1. The influence of the hot extrusion on the initial microstructures, work hardening rate, strain rate sensitivity, and activation energy of deformation were discussed. The results show that the extruded microstructure is constituted by the fine dynamic recrystallisation of grains. The true strain-true stress curves show that the as-HIPed and as-HEXed FGH4096 superalloy present double flow stress peaks and discontinuous flow softening. The as-HEXed FGH4096 is easily dynamically softened at high temperatures and high strain rates compared with as-HIPed microstructures. As for the work hardening rate, the as-HEXed FGH4096 exhibits higher θ values than that of as-HIPed. It is beneficial to the homogenous deformation and grain refinement during subsequent turbine disk forging. Comparing to as-HIPed FGH4096, the highest strain rate sensitivity value of as-HEXed is 0.306 at 1110 °C. The isothermal superplastic forging of a P/M turbine disk may be carried out at this temperature. The deformation activation energy value of the as-HIPed FGH4096 is lower which means that dislocation sliding and climbing can be easily initiated in the as-HIPed alloy.

Time and Temperature Dependence of the Ultimate Properties of an SBR Rubber at Constant Elongations

1961 ◽  
Vol 34 (3) ◽  
pp. 897-909
Author(s):  
Thor L. Smith ◽  
Paul J. Stedry
Keyword(s):  
Tensile Strength ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Rate Dependence ◽  
Strain Rates ◽  
Type Specimens ◽  
Stress Strain ◽  
Ultimate Elongation ◽  
Tensile Tester ◽  
Ultimate Properties

Abstract A study was made previously of the temperature and strain rate dependence of the stress at break (tensile strength) and the ultimate elongation of an unfilled SBR rubber. In that study, stress-strain curves to the point of rupture were measured with an Instron tensile tester on ring type specimens at 14 temperatures between −67.8° and 93.3° C, and at 11 strain rates between 0.158×10−3 and 0.158 sec−1 at most temperatures. The tensile strength was found to increase with both increasing strain rate and decreasing temperature. At all temperatures above −34.4° C, the ultimate elongation was likewise found to increase with increasing strain rate and decreasing temperature but at lower temperatures the opposite dependence on rate was observed; at −34.4° C, the ultimate elongation passed through a maximum with increasing rate.

The Rate (Time)-Dependent Mechanical Behavior of the PMR-15 Thermoset Polymer at 316°C: Experiments and Modeling

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
M. B. Ruggles-Wrenn ◽  
O. Ozmen
Keyword(s):  
Experimental Data ◽  
Strain Rate ◽  
Deformation Behavior ◽  
Inelastic Deformation ◽  
Rate Sensitivity ◽  
Experimental Program ◽  
Strain Rates ◽  
Neat Resin ◽  
Strain Behavior ◽  
Thermoset Polymer

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at 316°C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior following strain-controlled loading were examined. Positive, nonlinear strain rate sensitivity is observed in monotonic loading. The material exhibits nonlinear, “curved” stress-strain behavior during unloading at all strain rates. The recovery of strain at zero stress is strongly influenced by the prior strain rate. The prior strain rate also has a profound effect on relaxation behavior. Likewise, creep response is significantly influenced by the prior strain rate. The experimental data are modeled with the viscoplasticity theory based on overstress (VBO). The comparison with experimental data demonstrates that the VBO successfully predicts the inelastic deformation behavior of the PMR-15 polymer under various test histories at 316°C.

scholarly journals INFLUENCE OF TEMPERATURE AND STRAIN RATE ON SUPERPLASTICITY KINETICS OF COMPOSITE AZ61-F MAGNESIUM MATERIALS

2018 ◽  
Vol 24 (3) ◽  
pp. 200
Author(s):  
Michal Besterci ◽  
Song-Jeng Huang ◽  
Katarína Sülleiová ◽  
Beáta Ballóková
Keyword(s):  
Plastic Deformation ◽  
Strain Rate ◽  
Superplastic Deformation ◽  
Strain Rates ◽  
Maximum Strain ◽  
Influence Of Temperature ◽  
Angular Pressing ◽  
Micromechanisms Of Fracture ◽  
The Mean ◽  
Kinetics Of

Micromechanisms of fracture of AZ61-F composites in the zone of quasi-superplastic deformation were analyzed and quantified in this work. Deformation of AZ61-F magnesium alloys with 1 wt.% of Al<sub>2</sub>O<sub>3</sub> phase was tested at a temperature of 473 K and different strain rates. It was shown that at the temperature of 473 K and the highest strain rate applied from 1<em>× </em>10<em><sup>−</sup></em><sup>2</sup> to 1 <em>× </em>10<em><sup>−</sup></em><sup>4</sup> s<em><sup>−</sup></em><sup>1</sup>, a significant growth of ductility was observed. The mean dimples diameter of the ductile fracture decreased with the decreasing strain rate. The grain size of 0.7 μm was reached by severe plastic deformation using equal channel angular pressing (ECAP). Secondary Mg<sub>17</sub>Al<sub>12</sub> and Al<sub>2</sub>O<sub>3</sub> phases were identified. The maximum strain was reached at the temperature of 473 K and strain rate of 1 <em>× </em>10<em><sup>−</sup></em><sup>4</sup> s<em><sup>−</sup></em><sup>1</sup>.

scholarly journals Kinetics of barite reduction from refractory barite-sulphide ore

10.30544/237 ◽  
2016 ◽  
Vol 22 (4) ◽  
pp. 261-268 ◽  
Author(s):  
Miroslav D Sokić ◽  
Vladislav Matković ◽  
Jovica Stojanović ◽  
Branislav Marković ◽  
Vaso Manojlović
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Kinetic Model ◽  
Copper Sulphide ◽  
Influence Of Temperature ◽  
Sulphide Ore ◽  
Lead Zinc ◽  
Complex Structural ◽  
Kinetics Of ◽  
Maximum Removal

Refractory sulphide–barite ore was reduced with carbon in order to release lead, zinc, and copper sulphide from barite-pyrite base. Mineralogical investigations showed that due to the complex structural-textural relationships of lead, copper and zinc minerals with gangue minerals, it is not possible to enrich the ore using the conventional methods of mineral processing. The influence of temperature and time was studied to optimize the conditions, and to determine the kinetics of the barite reduction. The maximum removal of barite from ore was 96.7% at 900oC after 180 min. Chemically controlled kinetic model showed the best compliance with the experimental data. An activation energy of 142 kJ/mol was found.

Diffusion von In und Cu in ZnS-Einkristallen

1969 ◽  
Vol 24 (9) ◽  
pp. 1301-1306 ◽  
Author(s):  
H. Nelkowski ◽  
G. Bollmann
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Diffusion Equation ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Diffusion Constant ◽  
Pair Formation ◽  
Concentration Profiles ◽  
Radioactive Tracers ◽  
Calculated Concentration

Abstract The diffusion of In and Cu in ZnS single crystals was investigated by means of radioactive tracers. The diffusion constant Do and the activation energy EA of the diffusion equation D = D0 · exp(- EA/kT) were determined by analysing the temperature dependence of the concentration profiles. The result for ln EA = 2,2 eV, D0 = 30cm2 s-1) is interpreted as a diffusion via Zn vacancies and that for Cu (EA - 0,79 eV, D0 = 2,6 · 10-3 cm2 s-1) as a diffusion via interstitial sites which probably is influenced by Zn vacancies. - Preceding doping with In significantly retards the Cu diffusion, consistent with the model of Cu-In pair formation. The reasons for some deviations of the experimental data from the calculated concentration profiles are discussed. - Diffusion measurements with high Cu-concentrations yield a Cu-solubility of 300 ppm at 840 K and 1000 ppm at 950 K.

scholarly journals Activation Energies and Temperature Dependencies of the Rates of Crystallization and Melting of Polymers

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1070 ◽  
Author(s):  
Sergey Vyazovkin
Keyword(s):  
Experimental Data ◽  
Phase Transition ◽  
Activation Energy ◽  
Temperature Dependence ◽  
Kinetic Analysis ◽  
Review Paper ◽  
Isoconversional Methods ◽  
Activation Energies ◽  
Phase Transition Kinetics ◽  
Kinetic Treatment

The objective of this review paper is to survey the phase transition kinetics with a focus on the temperature dependence of the rates of crystallization and melting, as well as on the activation energies of these processes obtained via the Arrhenius kinetic treatment, including the treatment by isoconversional methods. The literature is analyzed to track the development of the basic models and their underlying concepts. The review presents both theoretical and practical considerations regarding the kinetic analysis of crystallization and melting. Both processes are demonstrated to be kinetically complex, and this is revealed in the form of nonlinear Arrhenius plots and/or the variation of the activation energy with temperature. Principles which aid one to understand and interpret such results are discussed. An emphasis is also put on identifying proper computational methods and experimental data that can lead to meaningful kinetic interpretation.

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