scholarly journals Kinetic Interpretation of Rheological Behavior of High Polymers

1962 ◽  
Vol 35 (4) ◽  
pp. 1013-1027
Author(s):  
Junji Furukawa
Keyword(s):  
Polymer Chain ◽  
Rheological Behavior ◽  
Maximum Stress ◽  
Life Time ◽  
Polar Groups ◽  
Maximum Value ◽  
Stress Strain Relation ◽  
Constant Rate ◽  
Creep And Stress Relaxation ◽  
High Polymers

Abstract Rheological behavior of high polymers is interpreted in terms of the pseudo crosslinking hypothesis, i.e., polar groups in a polymer form a kind of pseudolink and contribute to the elastic property of the polymer, but such a crossbond as this is not so firm that plastic flow may not occur to some extent. The ratio of real elongation of polymer chain to overall elongation of specimen is demonstrated as the function of slippage of the polymer chain. Creep and stress relaxation are accounted for as the phenomena involving slippage of the chain accompanied by the elongation of the chain and the dissociation of the crossbond. The stress-strain relation in the ease of constant rate drawing is supposed to show the existence of maximum stress according to the hypothesis. Rupture of linear high polymer is also discussed supposing the breakdown of the second crossbond and the breakdown may be concluded when load applied is larger than the maximum value estimated from the equation for the equilibrium crosslinking. The rate of rupture is also discussed and the logarithmic life time in rupture is concluded to be correlated linearly to the load applied.

Assessment of Reliability and Overall Life-Time of the Turbo Generator in the Kamýk Power Station

2015 ◽  
Vol 732 ◽  
pp. 297-300
Author(s):  
Petr Tej ◽  
Alena Tejová ◽  
Jana Marková
Keyword(s):  
Czech Republic ◽  
Maximum Stress ◽  
Steel Structure ◽  
Life Time ◽  
Residual Lifetime ◽  
Stress Range ◽  
Power Station ◽  
The Czech Republic ◽  
Turbo Generator ◽  
Loaded Part

This paper presents the results of measurement of the stress and the theoretical analysis of the steel structure of the Kaplan turbo generator in the Kamýk power station in the Czech Republic. Based on the number of load cycles and the finding of the maximum stress range of critical details of the most loaded part, the lower star, the residual lifetime of the turbo generator was determined.

scholarly journals Derivation of the initial luminosity function and the past rate of star formation

1959 ◽  
Vol 10 ◽  
pp. 99-104
Author(s):  
M. Schmidt
Keyword(s):  
Star Formation ◽  
Luminosity Function ◽  
Main Sequence ◽  
Life Time ◽  
Interstellar Gas ◽  
The Past ◽  
Constant Rate

The initial luminosity function ψ(Mv) was introduced by Salpeter. He assumed uniform formation of stars and derived the initial luminosity function from the observed main-sequence luminosity function and the life time of a star of magnitude Mvon the main sequence. Recently van den Bergh considered the depletion of the interstellar gas by star formation. He found that at a constant rate of star formation the gas in the solar vicinity will be exhausted about 7 × 108years from now.

Correlation between scratch healing and rheological behavior for terpyridine complex based metallopolymers

2015 ◽  
Vol 3 (44) ◽  
pp. 22145-22153 ◽  
Author(s):  
S. Bode ◽  
M. Enke ◽  
R. K. Bose ◽  
F. H. Schacher ◽  
S. J. Garcia ◽  
...  
Keyword(s):  
Rheological Behavior ◽  
Metal Salt ◽  
Life Time

The healing phenomenon of metallopolymers is studied in detail and the dependency of the chosen metal salt is provided. Furthermore, a correlation between the supramolecular bond life time and the healing behavior could be revealed.

Optimization of melting conditions for the analysis of crystallization kinetics of poly(3-hydroxybutyrate)

e-Polymers ◽  
2009 ◽  
Vol 9 (1) ◽  
Author(s):  
Maria Laura Di Lorenzo ◽  
Pawel Sajkiewicz ◽  
Arkadiusz Gradys ◽  
Paola La Pietra
Keyword(s):  
Melting Point ◽  
Polymer Chain ◽  
Crystallization Kinetics ◽  
Crystallization Temperature ◽  
Degree Of Crystallinity ◽  
Thermal Treatments ◽  
Constant Rate ◽  
Kinetics Of ◽  
Final Degree ◽  
Melting Conditions

AbstractStudies of kinetics of polymer crystallization are generally performed by heating the material above the melting point, in order to erase previous thermal and mechanical history, followed by rapid cooling to the desired crystallization temperature or by cooling at a constant rate. For poly(3-hydroxybutyrate) this procedure implies some degradation of the polymer chain, which starts below the onset of melting. In this article the effects of melting conditions on the subsequent crystallization kinetics are discussed. It is shown that in order to sufficiently cancel memories of previous crystalline order of the analyzed PHB, it is necessary to bring the material at a temperature higher than 192 °C. Thermal treatments conducted at lower temperatures are not sufficient to destroy all solid aggregates, and crystallization of PHB has an anticipated onset of crystallization due to nucleation occurring via self-seeding. The chain degradation attained upon exposure at high temperatures has much lesser influence on crystallization kinetics than incomplete melting, with some effects detectable on the spherulitic morphology and on the final degree of crystallinity.

scholarly journals In vivo, chromatin is a fluctuating polymer chain at equilibrium constrained by internal friction

2017 ◽  
Author(s):  
M. Socol ◽  
R. Wang ◽  
D. Jost ◽  
P. Carrivain ◽  
V. Dahirel ◽  
...  
Keyword(s):  
Internal Friction ◽  
Polymer Chain ◽  
Motion Tracking ◽  
Life Time ◽  
Physical Parameters ◽  
Imaging Data ◽  
Chromosome Conformation ◽  
Time Motion

AbstractChromosome mechanical properties determine DNA folding and dynamics, and underlie all major nuclear functions. Here we combine modeling and real-time motion tracking experiments to infer the physical parameters describing chromatin fibers. In vitro, motion of nucleosome arrays can be accurately modeled by assuming a Kuhn length of 35-55 nm. In vivo, the amplitude of chromosome fluctuations is drastically reduced, and depends on transcription. Transcription activation increases chromatin dynamics only if it involves gene relocalization, while global transcriptional inhibition augments the fluctuations, yet without relocalization. Chromatin fiber motion is accounted for by a model of equilibrium fluctuations of a polymer chain, in which random contacts along the chromosome contour induce an excess of internal friction. Simulations that reproduce chromosome conformation capture and imaging data corroborate this hypothesis. This model unravels the transient nature of chromosome contacts, characterized by a life time of ∼2 seconds and a free energy of formation of ∼1 kBT.

scholarly journals Compatibilizer Polarity Parameters as Tools for Predicting Organoclay Dispersion in Polyolefin Nanocomposites

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Marek Weltrowski ◽  
Patricia I. Dolez
Keyword(s):  
Polymer Chain ◽  
Polymer Matrix ◽  
Performance Optimization ◽  
Weight Fraction ◽  
Acid Value ◽  
Published Data ◽  
Polar Group ◽  
Nanoparticle Dispersion ◽  
Polar Groups ◽  
Hydrophilic Lipophilic Balance

Nanocomposites give an innovative method to increase the mechanical, thermal, and barrier performance of polymers. However, properly dispersing the nanoparticles in the polymer matrix is often key in achieving high performance, especially in the case of hydrophilic nanoparticles and hydrophobic polymers. For that purpose, nanoparticles may be functionalized with organic groups to increase their affinity with the polymer matrix. Compatibilizing agents may also be included in the nanocomposite formulation. This paper aims at identifying parameters relative to the compatibilizer polarity that would allow predicting nanoparticle dispersion in the polymer nanocomposite. The analysis used published data on nanocomposite samples combining clay nanoparticles, polyolefins, and various compatibilizing agents. We studied the correlations between the nanoclay exfoliation ratio and five different parameters describing the compatibilizer hydrophilic-lipophilic balance: the acid value, the mole, and weight fraction of polar groups, the number of polymer chain units per polar group, and the number of moles of polar groups per mole of compatibilizer. The best correlation was observed with the number of polymer chain units per polar group in the compatibilizer. This parameter could be used as a tool to predict the dispersion of organoclay nanoparticles in polyolefins. Another important result of the study is that, among the compatibilizers investigated, those with a low acid value provided a better nanoclay exfoliation compared to those with a high acid value. This may indicate the existence of a maximum in the nanoclay exfoliation/compatibilizer polarity curve, which would open new perspectives for nanocomposite performance optimization.

High-speed granular chute flows

2012 ◽  
Vol 710 ◽  
pp. 35-71 ◽  
Author(s):  
Alex J. Holyoake ◽  
Jim N. McElwaine
Keyword(s):  
Granular Flow ◽  
High Speed ◽  
Transverse Velocity ◽  
Multiple Points ◽  
Longitudinal Vortices ◽  
Flow Models ◽  
Maximum Value ◽  
Constant Rate ◽  
Experimental Findings ◽  
Steep Slopes

AbstractThis paper reports experimental findings on the flow of sand down a steep chute. Nearly all granular flow models have a maximum value for the friction and therefore predict that flows on steep slopes will accelerate at a constant rate until the interaction with the ambient fluid becomes important. This prediction has not been tested by previous work, which has focused on relatively low slope angles where steady, fully developed flows occur after short distances. We test this by investigating flows over a much greater range of slope angles (30–50${}^{\ensuremath{\circ} } $) and flow depths (4–130 particle diameters). We examine flows with two basal conditions, one flat and frictional, the other bumpy. The latter imposes a no-slip condition for slow, deep flows, but permits some degree of slip for high flow velocities. The data suggests that friction can be much larger than theories such as the $\ensuremath{\mu} (I)$ rheology proposed by Jop, Forterre & Pouliquen (Nature, vol. 441, 2006) suggest and that there may be constant velocity states above the angle of vanishing ${h}_{\mathit{stop}} $. Although these flows do not vary in time, all but the flows on the bumpy base at low inclinations accelerate down the slope. A recirculation mechanism sustains flows with a maximum mass flux of $20~\mathrm{kg} ~{\mathrm{s} }^{\ensuremath{-} 1} $, allowing observations to be made at multiple points for each flow for an indefinite period. Flows with Froude number in the range 0.1–25 and bulk inertial number 0.1–2.7 were observed in the dense regime, with surface velocities in the range 0.2–5.6 $\mathrm{m} ~{\mathrm{s} }^{\ensuremath{-} 1} $. Previous studies have focused on $I\lessapprox 0. 5$. We show that a numerical implementation of the $\ensuremath{\mu} (I)$ rheology does not fully capture the accelerating dynamics or the transverse velocity profile on the bumpy base. We also observe the transverse separation of the flow into a dense core flanked by dilute regions and the formation of longitudinal vortices.

The effect of seismic-like induced cyclic loading on damage response of sandstone and granite

2020 ◽  
Author(s):  
Rashid Geranmayeh Vaneghi ◽  
Arcady V. Dyskin ◽  
Klaus Thoeni ◽  
Mostafa Sharifzadeh ◽  
Mohammad Sarmadivaleh
Keyword(s):  
Fatigue Life ◽  
Cyclic Loading ◽  
Stress Level ◽  
Maximum Stress ◽  
Low Frequency ◽  
Life Time ◽  
Rock Types ◽  
Axial Tensile ◽  
Stress Cycles ◽  
Level Loading

<p>The detailed study of rock response to cyclic loading induced by natural phenomena, such as seismic and volcanic activities, and man-made explosions and excavation is necessary for failure prediction and hazard mitigation. The effect of the maximum stress level, loading amplitude, and frequency of stress cycles on the fatigue life and failure mechanisms of two microstructurally different rocks of granite/granodiorite and sandstone is investigated. Test data obtained from comprehensive experiments conducted on these rock types incorporated with the results of previous studies show that the fatigue life time of both rock types increases with a decrease in either maximum stress level or stress amplitude. Nevertheless, the fatigue strength threshold of hard rocks like granite is generally lower than that of soft rocks like sandstone. The study also shows that the low-frequency cyclic loading has more damaging effect on both rock types than the high frequency loading. This investigation demonstrates that the failure mechanism of rocks under cyclic loading is characterized by the development of more tensile microcracks compared to the monotonic loading and the opening and extension of the axial tensile microfractures are more evident at higher maximum stresses or loading amplitudes or at lower loading frequencies. The results presented in this study will contribute to a deeper understanding of the fatigue responses of sandstone and granite to seismic-generated loading–unloading processes under different conditions of stress cycles.</p>

The Effects of Surface Irregularities on the Elastohydrodynamic Lubrication of Sliding Line Contacts. Part I—Single Irregularities

1984 ◽  
Vol 106 (1) ◽  
pp. 104-112 ◽  
Author(s):  
P. R. Goglia ◽  
T. F. Conry ◽  
C. Cusano
Keyword(s):  
Shear Stress ◽  
Film Thickness ◽  
Smooth Surface ◽  
Maximum Stress ◽  
Elastohydrodynamic Lubrication ◽  
Maximum Value ◽  
Ehd Lubrication ◽  
Line Contacts ◽  
Surface Irregularities ◽  
Octahedral Shear Stress

A full line contact solution, under isothermal conditions, is obtained in which the effects of single stationary surface irregularities on the EHD lubrication process are studied under pure sliding conditions. The irregularities studied are furrows, furrows with built-up edges, and asperities. The effects of these irregularities on film thickness, pressure, and subsurface octahedral shear stress are presented. The pressure and film thickness resulting from such surface irregularities are significantly changed from their smooth surface values. These changes alter the state of stress in the subsurface region by increasing the maximum value of octahedral shear stress and bringing the location of this maximum stress closer to the surface. The film thickness in the contact is significantly changed from the smooth surface value only when the irregularities are located in the inlet region while the maximum value of the octahedral shear stress increases to the greatest extent when the irregularities are located in the outlet half of the contact.

Sign in / Sign up

Export Citation Format

Share Document