Stress-Time-Temperature Relations in Polysulfide Rubbers

1946 ◽  
Vol 19 (4) ◽  
pp. 1178-1192 ◽  
Author(s):  
M. D. Stern ◽  
A. V. Tobolsky
Keyword(s):  
Activation Energy ◽  
Relaxation Time ◽  
High Temperature ◽  
Stress Relaxation ◽  
Relaxation Process ◽  
Network Structure ◽  
Constant Load ◽  
Internal Structures ◽  
Relaxation Measurements ◽  
Temperature Relaxation

Abstract Polysulfide rubbers of various internal structures have been investigated by measurements of continuous and intermittent relaxation of stress and by creep under constant load at temperatures between 35° C and 120° C. Continuous stress relaxation measurements indicate that these rubbers obey approximately the simple Maxwellian law of relaxation of stress, which indicates that one definite type of bond in the network structure is responsible for stress decay. The activation energy for the relaxation process in each of the polysulfide rubbers is nearly the same, indicating that the same type of bond is responsible for the relaxation behavior of all the polysulfides investigated. In contrast to hydrocarbon rubbers, oxygen is not the cause of high temperature relaxation in polysulfide rubbers, nor does heating in air at moderate temperatures for times comparable to the relaxation time produce changes in physical properties as determined by modulus or by appearance of the samples. Several possibilities regarding the mechanism of the relaxation process and the type of bond involved are considered in the light of the experimental results.

scholarly journals Dielectric Properties of Rhombohedral PbNb2O6

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Kriti Ranjan Sahu ◽  
Udayan De
Keyword(s):  
Activation Energy ◽  
Relaxation Time ◽  
High Temperature ◽  
Single Phase ◽  
Rhombohedral Phase ◽  
Orthorhombic Phase ◽  
Dielectric Materials ◽  
Rietveld Analysis ◽  
Bulk Resistance ◽  
Relaxation Time Constant

Dielectric materials are needed in many electrical and electronic applications. So, basic characterizations need to be done for all dielectrics. PbNb2O6 (PN) is ferroelectric and piezoelectric only in its orthorhombic phase, with potential high temperature applications. So, its rhombohedral phase, frequently formed as an undesirable impurity in the preparation of orthorhombic PN, has been ignored with respect to possible dielectric characterizations. Here, essentially single phase rhombohedral PN has been prepared, checking structure from XRD Rietveld Analysis, and the real and imaginary parts of permittivity measured in an Impedance Spectrometer (IS) up to ~700∘C and over 20 Hz to 5.5 MHz range, for heating and some cooling runs. Variations, with temperature, of relaxation time constant (τ), AC and DC conductivity, bulk resistance, activation energy and capacitance have been explored from our IS data.

Stress Relaxation Mechanisms in Rubbers Reinforced with Carbon Blacks

1972 ◽  
Vol 45 (1) ◽  
pp. 82-93 ◽  
Author(s):  
G. M. Bartenev ◽  
N. M. Lyalina
Keyword(s):  
Activation Energy ◽  
Stress Relaxation ◽  
Relaxation Process ◽  
Activation Energies ◽  
Relaxation Processes ◽  
Carbon Blacks ◽  
Multi Stage ◽  
Chemical Relaxation ◽  
Filled Rubbers ◽  
Weight Structures

Abstract 1. In vulcanized rubbers containing blacks a multi-stage mechanism for stress relaxation was observed. It was discovered that the stress relaxation process consists of five fundamental processes: the first three relaxation processes, related to the slow stages of physical relaxation within the bulk of the rubber, have no connection with the fillers (“soft” domains); the fourth process has to do with the relaxation in the black-rubber domain; the fifth process involves the chemical relaxation of vulcanizates. 2. The fundamental mechanisms of the first 3 relaxation processes in the soft domains have the same activation energy values and the same segmental mechanism as the rearranged domains found in supermolecular weight structures, which are also present in unfilled vulcanizates. 3. In the investigated stress range of up to 200% elongation, the activation energy for the first 3 relaxation processes in the soft domains of filled vulcanizates is not a function of the deformation strain, whereas the activation energy of the fourth relaxation process in the black-rubber domains of filled rubbers is a function of the deformation and of the filler content. For these reasons, rubber loaded with carbon blacks, in contrast to unfilled rubbers, possess the typical nonlinearity of viscoelastic materials. 4. The activation energies of the relaxation processes in the black-rubber domains decrease in a linear fashion with the value for the initial tensile stress in filled vulcanizates, and decrease in like manner for vulcanizates containing different proportions of fillers. The kinetic units, determined from the activation energies of these processes, appeared to be segments of chains with activation energies of up to 40% more than the activation energies of the physical relaxation processes in the soft domains. The other kinetic units of the processes proved to be black particles, the dimensions of which were calculated from the values for the coefficients in the formula for relaxation time.

Grain growth behavior of a nanostructured 5083 Al–Mg alloy

2001 ◽  
Vol 16 (4) ◽  
pp. 938-944 ◽  
Author(s):  
V. L. Tellkamp ◽  
S. Dallek ◽  
D. Cheng ◽  
E. J. Lavernia
Keyword(s):  
Activation Energy ◽  
Stress Relaxation ◽  
Low Temperature ◽  
Grain Boundaries ◽  
Relaxation Process ◽  
Grain Growth ◽  
Alloy Powder ◽  
Growth Behavior ◽  
Mg Alloy ◽  
Grain Growth Behavior

A nanostructured 5083 Al–Mg alloy powder was subjected to various thermal heat treatments in an attempt to understand the fundamental mechanisms of recovery, recrystallization and grain growth as they apply to nanostructured materials. A low-temperature stress relaxation process associated with reordering of the grain boundaries was found to occur at 158 °C. A bimodal restructuring of the grains occurred at 307 °C for the unconstrained grains and 381 °C for the constrained grains. An approximate activation energy of 5.6 kJ/mol was found for the metastable nanostructured grains, while an approximate activation energy of 142 kJ/mol was found above the restructuring temperature.

Relaxation Measurements of the Persistent Photoconductivity in Sulfur-Doped a-Si:H.

1996 ◽  
Vol 420 ◽  
Author(s):  
D. Quicker ◽  
J. Kakalios
Keyword(s):  
Activation Energy ◽  
Relaxation Time ◽  
Sulfur Atom ◽  
Hydrogenated Amorphous Silicon ◽  
Persistent Photoconductivity ◽  
Sulfur Concentration ◽  
Illumination Time ◽  
Thermally Activated ◽  
Relaxation Measurements ◽  
Hydrogenated Amorphous

AbstractThe slow relaxation of the persistent photoconductivity (PPC) effect in sulfur-doped hydrogenated amorphous silicon (a-Si:H) has been measured as a function of temperature and illumination time. The relaxation is found to be thermally activated, with an activation energy which varies with sulfur concentration, while illuminating the film for a longer time leads to a longer relaxation time. A correlation is observed between changes of the photoconductivity during illumination and the magnitude of the PPC effect following illumination. These effects are also observed in compensated a-Si:H, suggesting that the mechanism for the PPC effect is the same in both sulfur-doped a-Si:H and compensated a-Si:H. The presence of donor and compensating acceptor states in sulfur-doped a-Si:H could arise from valence alternation pair sulfur atom defects.

Activation Energy Measurement in Thin Gold Film by MEMS-Based Tensile Testing Device

Materials ◽  
2004 ◽  
Author(s):  
Jong H. Han ◽  
Taher M. Saif
Keyword(s):  
Activation Energy ◽  
Relaxation Time ◽  
Stress Relaxation ◽  
Analytical Model ◽  
Tensile Testing ◽  
Relaxation Times ◽  
Tensile Specimen ◽  
Testing Device ◽  
Free Standing ◽  
Tensile Tester

In this paper, we report a methodology to measure activation energy for time-dependent stress-relaxation in a thin free-standing tensile specimen by utilizing a MEMS-based tensile testing device. An analytical model is developed to investigate its stress-relaxation behavior. Along with this analytical model of the MEMS tensile tester, Arrhenius relation is applied to estimate relaxation times for different temperatures of a free-standing sample beam. From the relation between relaxation time and temperature, the activation energy for the stress-relaxation is obtained. For a 200-nm Au film, we obtained the relaxation time of 250, 67, and 40 seconds for the corresponding temperatures of 295, 312, and 323 K, respectively. The activation energy for stress-relaxation was 0.544 eV. The experimental data is fitted with the analytical model to find the relaxation time. The thin film on the MEMS tensile tester is prepared by sputter-deposition. By optical lithography and ICP DRIE Si etching, the MEMS tensile tester with a free standing beam is fabricated.

Prediction Methodology of Creep Performance from Stress Relaxation Measurements

2013 ◽  
Vol 401-403 ◽  
pp. 920-923 ◽  
Author(s):  
Jin Quan Guo ◽  
Hui Chao Shi ◽  
Wu Zhou Meng
Keyword(s):  
High Temperature ◽  
Stress Relaxation ◽  
Creep Strain ◽  
Estimation Method ◽  
Creep Tests ◽  
High Temperature Materials ◽  
Relaxation Measurements ◽  
Isothermal Creep ◽  
The Relationship ◽  
Good Agreement

An estimation method to predict creep performances of high temperature structural materials has been proposed. The method is to use a simplified and normalized model of stress relaxation to derive creep strain rates and creep strain vs. time curves from stress relaxation measurements through an integrated analytical procedure according to the relationship between stress relaxation and creep. In order to validate the approach, the predicted results are compared to the experimental results of uni-axial isothermal creep tests conducted on 1Cr10NiMoW2VNbN steel with the same temperature of stress relaxation tests. Good agreement between results of relaxation tests and the predicted results indicates that the developed method can be recommended in the creep behavior evaluation of high temperature materials.

Using Stress Relaxation Data to Predict Creep Behavior

2013 ◽  
Vol 842 ◽  
pp. 382-385
Author(s):  
Jin Quan Guo ◽  
Long Tian ◽  
Hui Chao Shi ◽  
Wu Zhou Meng
Keyword(s):  
High Temperature ◽  
Stress Relaxation ◽  
Creep Strain ◽  
Creep Behavior ◽  
Estimation Method ◽  
Prediction Equation ◽  
Relaxation Equation ◽  
Creep Tests ◽  
Relaxation Measurements ◽  
Isothermal Creep

An estimation method to predict creep performances of high temperature structural materials has been proposed. A Stress relaxation equation is obtained by fitting stress relaxation testing curves and modifying Tanaka-Ohba reloading stress relaxation constitutive equation. Based on the relationship between stress relaxation and creep, a unified prediction equation of creep is deduced. The method is to use the unified equation to derive creep strain rates or creep strain vs. time curves from stress relaxation measurements through some specified time increments. In order to validate the approach, the predicted results are compared to the experimental results of uni-axial isothermal creep tests conducted on 1Cr10NiMoW2VNbN steel. Good agreement between results of creep tests and the predicted results indicates that the developed method can be recommended in the creep behavior evaluation of high temperature materials.

scholarly journals The Electronic Transport Mechanism in Amorphous Tetrahedrally-Coordinated Carbon Films

1997 ◽  
Vol 498 ◽  
Author(s):  
J. P. Sullivan ◽  
T. A. Friedmann ◽  
R. G. Dunn ◽  
E. B. Stechel ◽  
P. A. Schultz ◽  
...  
Keyword(s):  
Activation Energy ◽  
Electrical Conductivity ◽  
Stress Relaxation ◽  
Electronic Transport ◽  
Transport Mechanism ◽  
Thermal Evolution ◽  
Carbon Films ◽  
Temperature Dependent ◽  
Thermally Activated ◽  
Relaxation Measurements

ABSTRACTThe electronic transport mechanism in tetrahedrally-coordinated amorphous carbon was investigated using measurements of stress relaxation, thermal evolution of electrical conductivity, and temperature-dependent conductivity measurements. Stress relaxation measurements were used to determine the change in 3-fold coordinated carbon concentration, and the electrical conductivity was correlated to this change. It was found that the conductivity was exponentially proportional to the change in 3-fold concentration, indicating a tunneling or hopping transport mechanism. It was also found that the activation energy for transport decreased with increasing anneal temperature. The decrease in activation energy was responsible for the observed increase in electrical conductivity. A model is described wherein the transport in this material is described by thermally activated conduction along 3-fold linkages or chains with variable range and variable orientation hopping. Thermal annealing leads to chain ripening and a reduction in the activation energy for transport.

Effect of Defects on Dielectric Properties in KTiOPO4, KTiOAsO4, RbTiOAsO4 and CsTiOAsO4 Single Crystals

1996 ◽  
Vol 453 ◽  
Author(s):  
A. R. Guo ◽  
Z. -Y. Cheng ◽  
R. S. Katiyar ◽  
Ruyan Guo ◽  
A. S. Bhalla
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Dielectric Relaxation ◽  
Relaxation Process ◽  
Single Crystals ◽  
Cage Structure ◽  
Dielectric Relaxation Process ◽  
Alkali Ions ◽  
Temperature Range ◽  
Temperature Relaxation

AbstractDielectric measurements were carried out in single crystals of KTiOPO4, KTiOAsO4, RbTiOAsO4 and CsTiOAsO4. All of the materials exhibit a clear dielectric relaxation process in the low temperature range and a conductance mechanism in the high temperature range. The dielectric relaxation process can be well described by the Debye dielectric model with an activation energies of 0.8 eV, 0.5 eV and 0.4 eV respectively. The relaxation process is associated with the deviation of the alkali ions from its ideal lattice positions. The high temperature conductance is associated with the motion of the alkali ions from one lattice site to another. Therefore, both the low temperature relaxation process and the high temperature conductance originate from different features of defect behavior of alkali ions in the cage structure of these materials.

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