Helical Spring Stress Relaxometer

1957 ◽  
Vol 30 (3) ◽  
pp. 889-894
Author(s):  
J. P. Berry
Keyword(s):  
Stress Relaxation ◽  
Practical Importance ◽  
Chain Scission ◽  
Routine Test ◽  
Test Procedures ◽  
First Order ◽  
Time Graph ◽  
Aging Conditions ◽  
Force Time ◽  
Random Scission

Abstract Changes in the tensile properties of rubber are obviously of great practical importance. Consequently, measurements of the change in force required to maintain or produce a given extension under controlled conditions of temperature and atmosphere have frequently been made and have advanced our understanding of the physical process of crystallization and of the chemical reactions responsible for thermal aging to the extent that they may become routine test procedures. The decrease in the force required to maintain a constant extension during the period of aging (stress relaxation) has been the most common measurement, in part because rubber elasticity theory predicts an equality between the fractional decrease in force and the fraction of the network chains originally supporting the stress which have become ineffective. Stress-relaxation behavior may characterize the type of scission reaction occurring; for example, the stress relaxation of most vulcanizates can be interpreted as a first-order scission of crosslinks, and not as a random scission of monomeric units in the chains between crosslinks. Stress-relaxation results, however, do not provide all the necessary information on network changes—the final properties of the rubber depend not only on crosslink or chain scission but to a comparable degree on crosslink formation during aging, which does not affect the force at constant extension. To examine this second effect requires measurements on the intermittent stretching of an unstrained sample to a constant extension. Parallel measurements of force at constant and intermittent extension under identical aging conditions are therefore required. The several designs of apparatus already described have usually been rather complicated and require practice and skill in use. A simple apparatus developed in these laboratories, which can readily be used for routine operations, is described in the following paragraphs. The fractional change in force is read directly from a vernier scale on the instrument, and may be immediately plotted on a force-time graph, preferably as log10 (force/forcet=0) vs. time (cf. Reference 3).

Chemorheology of Irradiation-Cured Natural Rubber. I. Stress Relaxation Mechanisms for Various Curing Systems in Natural Rubber at High Temperature

1975 ◽  
Vol 48 (2) ◽  
pp. 141-153 ◽  
Author(s):  
S. Tamura ◽  
K. Murakami
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Main Chain ◽  
Chain Scission ◽  
Chemical Structures ◽  
Carbon Carbon Bonds ◽  
Interchange Reaction ◽  
Thermal Scission ◽  
Physical And Chemical ◽  
Random Scission

Abstract 1. There was no difference of stress relaxation, either in air or in nitrogen, between DCP cures (Sample 1) and irradiation cures (Sample 2). This suggests that these vulcanizates have the same physical and chemical structures. In air Samples 1 and 2 underwent random scission of only the main chain. 2. In the case of irradiation-TMTD cures (Samples 4 and 5), the stress decay was also based on oxidative scission of the main chain. The number of moles of main chain scission, qm(t), was independent of the ratio ρ (of Nc(0)) based on the carbon—carbon bonds to Nm(0) based on the mono- and disulfide links). However, qm(t) was larger than that of Sample 2. The oxidative scission of the main chain seemed to be accelerated by mono- and disulfide. It was found from comparison of Samples 4 and 5 that TMTD cures (Sample 3) underwent random scission on the main chain. The stress relaxation in nitrogen for Samples 3, 4, and 5 was due to thermal scission of the crosslink. 3. The stress relaxation, either in air or in nitrogen, of accelerated-sulfur-cures (Sample 6) and irradiation-sulfur cures (Samples 7 and 8) was expressed by the sum of two exponential terms. The stress relaxation in air of Samples 6, 7, and 8 could be explained by the interchange reaction of polysulfide links and the random scission on the main chain. The stress decay in nitrogen of these vulcanizates was based on both interchange of polysulfide links and thermal scission of crosslinks. The rate of the interchange reaction in air was very closely consistent with that in nitrogen. 4. The apparent activation energy of oxidative scission of the main chain was about 21 kcal/mol for Samples 2, 6, 7, and 8 and 27 kcal/mol for Samples 3, 4, and 5.

Stress Relaxation of Natural Rubber During Irradiation

1970 ◽  
Vol 43 (2) ◽  
pp. 262-269
Author(s):  
D. Evans ◽  
J. T. Morgan ◽  
R. Sheldon ◽  
G. B. Stapleton
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Crosslink Density ◽  
Chain Scission ◽  
Crosslinking Reaction ◽  
Small Contribution ◽  
Relaxation Data ◽  
Strain Measurements ◽  
Random Scission ◽  
Crosslink Densities

Abstract The site of chain scission and crosslinking in vulcanized natural rubber irradiated with 4 MeV electrons has been determined by analysis of stress relaxation data. Sulfur and peroxide vulcanizates of different crosslink densities were prepared and the crosslink densities determined from stress—strain measurements. Stress relaxation was measured during irradiation using modified commercial relaxometers. The specimens were maintained in an atmosphere of nitrogen to minimize oxidative side effects. Scission is deduced to take place in the vicinity of crosslinks, since the rate of continuous stress relaxation is independent of crosslink density. Scission may be associated both with crosslinks initially present and with those subsequently introduced by irradiation. Crosslinking by radiation is largely a random process. However, there is a crosslinking reaction dependent to a slight extent on crosslink density as well as a small contribution from random scission reactions. G values for the random reactions are given.

A Direct Experimental Determination of the Elastic Contribution of Chain Entangling in a Tightly Crosslinked Elastomer

1982 ◽  
Vol 55 (1) ◽  
pp. 62-65
Author(s):  
W. Batsberg ◽  
O. Kramer
Keyword(s):  
Stress Relaxation ◽  
Elastic Equilibrium ◽  
Relaxation Modulus ◽  
Chain Scission ◽  
Experimental Result ◽  
Strained State ◽  
Equilibrium Stress ◽  
Linear Chains ◽  
Network Methods

Abstract The experimental result, that the equilibrium force is nearly equal to the pseudoequilibrium force immediately prior to quenching and irradiation, allows the following conclusions: (1) Chain scission during crosslinking is not a serious problem. (2) The network of highly entangled linear chains is effectively at elastic equilibrium immediately prior to crosslinking in the strained state. This would not be the case if the entangled structure remained untrapped. (3) The effect of chain entangling in tightly crosslinked elastomers is large, also at elastic equilibrium. In fact, it is almost quantitatively equal to the pseudo-equilibrium stress relaxation modulus of the uncrosslinked linear polymer. This result is in agreement with the results from the Langley and the two-network methods.

The Effect of Aging Conditions on the Stress Relaxation Behavior of 17-7PH Stainless Steel

2021 ◽  
Vol 1016 ◽  
pp. 1664-1669
Author(s):  
Shota Yamasaki ◽  
K. Takano
Keyword(s):  
Stainless Steel ◽  
Stress Relaxation ◽  
Dislocation Density ◽  
Cold Working ◽  
Relaxation Behavior ◽  
Age Hardening ◽  
Stress Relaxation Behavior ◽  
Long Time ◽  
Aging Conditions ◽  
High Age

17-7PH stainless steel is high age-hardening property due to precipitate NiAl intermetallics by aging heat treatment after the deformation induced martensitic transformation by cold working. In this study, the effect of aging conditions on stress relaxation behavior of 17-7PH stainless steel was investigated, and the mechanism of the stress relaxation was discussed. The 0.2% proof stress after aging at 753K for 180s-18ks is about 450MPa, and then decreases after 18ks. On the other hand, the stress relaxation ratio decreases by long time aging at 753K. The dislocation density of 17-7PH decreases by long time aging at 753K. The formation of NiAl clusters around 5nm by 3D-AP analysis is observed in 17-7PH aged at 753K for 1.8ks. It is suggested that the reduction of the stress relaxation ratio after long time aging at 753K is caused by NiAl clusters and decreasing mobile dislocation density.

Stress Relaxation of Sugi (Cryptomeria japonica D.Don) Wood in Radial Compression under High Temperature Steam

Holzforschung ◽  
1999 ◽  
Vol 53 (5) ◽  
pp. 541-546 ◽  
Author(s):  
W. Dwianto ◽  
T. Morooka ◽  
M. Norimoto ◽  
T. Kitajima
Keyword(s):  
High Temperature ◽  
Stress Relaxation ◽  
Cryptomeria Japonica ◽  
Chain Scission ◽  
Strain Recovery ◽  
Crystalline Lattice ◽  
Compressive Deformation ◽  
Radial Compression ◽  
Stress Strain ◽  
Permanent Fixation

Summary To clarify the mechanism of the permanent fixation of compressive deformation of wood by high temperature steaming, stress relaxation and stress-strain relationships in the radial compression for Sugi (Cryptomeria japonica D.Don) wood were measured under steam at temperatures up to 200°C. The stress relaxation curves above 100°C were quite different in shape from those below 100°C, showing a rapid decrease in stress with increasing temperature. In the stress-strain relationships measured above 140°C, the stress reduced as pre-steaming time increased when compared at the same strain. The recovery of compressive deformation (strain recovery) was decreased with steaming time and reached almost 0 in 10 min at 200°C. The relationship between the residual stress and the strain recovery at the end of relaxation measurements could be expressed by a single curve regardless of time and temperature. The permanent fixation of deformation by steaming below 200°C was considered to be due to chain scission of hemicelluloses accompanying a slight cleavage of lignin. In some cases, the increase in regularity of the crystalline lattice space of microfibrils or the formation of crosslinks between the cell wall polymers seemed to play an important role in the permanent fixation of compressive deformation.

Kinetics of Chain Scission of Natural Rubber

1989 ◽  
Vol 62 (5) ◽  
pp. 779-787
Author(s):  
M. S. Sambhi
Keyword(s):  
Oxidative Degradation ◽  
Oxidation Mechanism ◽  
Chain Scission ◽  
Bimolecular Reaction ◽  
Zero Order ◽  
Order Kinetic ◽  
Peroxy Radicals ◽  
Order Process ◽  
First Order ◽  
Kinetics Of

Abstract The first-order and zero-order kinetic models of chain scission, based on random chain scission processes, are critically examined. It is likely that for many practical situations, the first-order chain scission kinetics can be represented by pseudozero-order kinetic types of equations. The kinetic results indicate that chain scission of NR occurs either by a pseudofirst-order or a pseudozero-order process. The pseudozero-order chain scission kinetics of NR are in consonance with the result that chain scission involves the bimolecular reaction of peroxy radicals in the termination step of the oxidation mechanism. However, this does not preclude unambiguously other chain scission reactions. The chain scission activation energy of NR is determined with the use of expressions derived for the oxidative degradation of NR as measured in terms of Wallace plasticities.

HEAT AGING OF A BROMOBUTYL TIRE INNER LINER UNDER AEROBIC AND ANAEROBIC CONDITIONS

2021 ◽  
Author(s):  
M. Yerxa ◽  
C. Porter ◽  
R. J. Pazur
Keyword(s):  
Crosslink Density ◽  
Chain Scission ◽  
Double Quantum ◽  
Elongation At Break ◽  
Small Areas ◽  
Diffusion Limited ◽  
Low Field ◽  
Aging Conditions ◽  
Crosslinking Reactions ◽  
Aerobic And Anaerobic

ABSTRACT A bromobutyl tire inner liner compound was prepared and subjected to aerobic and anaerobic heat aging at a temperature of 100 °C for seven aging times up to 8 weeks. Hardness and mechanical properties were monitored, and the evolution of the crosslink density was followed using equilibrium solvent swell and low field double quantum (DQ) nuclear magnetic resonance (NMR). The hardness and the 300% tensile stress increased with heat aging, while both tensile strength and elongation at break dropped. Both chain scission and crosslinking reactions were taking place. Equilibrium swelling and DQ NMR results confirmed that a larger crosslink density increase was seen under aerobic versus anaerobic aging conditions. The network distribution consisting of a dominant low crosslinking zone and small areas of higher crosslinking slowly broadened and shifted toward higher crosslink densities upon heat aging. The compounds aged heterogeneously. Attenuated total reflectance–Fourier transform infrared spectroscopy confirmed the presence of an oxidized surface layer, and therefore diffusion-limited oxidation effects, but only under aerobic aging conditions. Reaction mechanisms are proposed to explain the net crosslink rise with heat aging.

IMPROVEMENTS IN THE TISSUE CULTURE SAFETY TESTING OF SALK VACCINES

1959 ◽  
Vol 5 (5) ◽  
pp. 453-459 ◽  
Author(s):  
R. C. French ◽  
R. E. Armstrong ◽  
W. Yarosh
Keyword(s):  
Tissue Culture ◽  
Volume Of Fluid ◽  
Monkey Kidney ◽  
Kidney Cells ◽  
Routine Test ◽  
Test Volume ◽  
Polio Virus ◽  
Safety Testing ◽  
First Order ◽  
Modified Test

Under the conditions of the official Canadian test, it was found that two simultaneous first-order reactions were in competition. Thus, after 4 hours, while 15% of any initial live MEF1 poliovirus present was adsorbed to the monkey kidney cells, 9% of the virus was destroyed by spontaneous inactivation. When the adsorption rate was increased by decreasing the volume of fluid, it was found that significantly more isolations of virus were obtained. Utilizing the method of Baron for the concentration of polio virus it was found possible to maintain a low test volume without making the routine test unduly cumbersome. The modified test is simpler and more sensitive and may be used with undialyzed vaccines.

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