Factors Influencing the Mechanical Behavior of Raw Unfilled Natural Rubber

1984 ◽  
Vol 57 (1) ◽  
pp. 104-117 ◽  
Author(s):  
D. S. Campbell ◽  
K. N. G. Fuller
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Mechanical Behavior ◽  
Relaxation Behavior ◽  
Complete Dissolution ◽  
Factors Influencing ◽  
Stiffening Effect ◽  
Fraction Comparison

Abstract The influence of gel and soluble nonrubbers on the relaxation behavior of raw, bale NR has been studied by testing fractionated and solvent-extracted rubber. The fractionation was carried out by progressive dissolution, each fraction being recovered by evaporation of the solvent. The tests were performed in tension for extensions up to 70%. Removal of the soluble nonrubbers from the bale was found to decrease the rate of stress relaxation quite markedly, especially at longer times. The fractions fell broadly into three categories: sol rubber, “sol + microgel”, and undissolved macrogel. The last, in the case of the more complete dissolution, was an extremely stiff, almost nonrelaxing material. Despite this, the relaxation behavior of the whole bale rubber was closely reproduced by the “sol / microgel” fraction. Comparison of this fraction with the sol rubber showed that the microgel had predominantly a stiffening effect, though it did also significantly reduce the rate of relaxation.

Effects of accelerator type on stress relaxation behavior and network structure of aged natural rubber/chloroprene rubber vulcanizates

2016 ◽  
Vol 49 (5) ◽  
pp. 381-396 ◽  
Author(s):  
Farzad A Nobari Azar ◽  
Murat Şen
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Network Structure ◽  
Structural Changes ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Rubber Blends ◽  
Chloroprene Rubber ◽  
Weather Changes ◽  
Behavior Network

Natural rubber/chloroprene rubber (NR/CR) blends are among the commonly used rubber blends in industry and continuously are exposed to severe weather changes. To investigate the effects of accelerator type on the network structure and stress relaxation of unaged and aged NR/CE vulcanizates, tetramethyl thiuram disulfide, 2-mercaptobenzothiazole, and diphenyl guanidine accelerators have been chosen to represent fast, moderate, and slow accelerator groups, respectively. Three batches have been prepared with exactly the same components and mixing conditions differing only in accelerator type. Temperatures scanning stress relaxation and pulse nuclear magnetic resonance techniques have been used to reveal the structural changes of differently accelerated rubber blends before and after weathering. Nonoxidative thermal decomposition analyses have been carried out using a thermogravimetric analyzer. Results indicate that there is a strong interdependence between accelerator type and stress relaxation behavior, network structure, cross-linking density, and aging behavior of the blends. Accelerator type also affects decomposition energy of the blends.

Stress-relaxation behavior of natural rubber/polystyrene and natural rubber/polystyrene/natural rubber-graft-polystyrene blends

2008 ◽  
Vol 108 (2) ◽  
pp. 904-913 ◽  
Author(s):  
R. Asaletha ◽  
P. Bindu ◽  
Indose Aravind ◽  
A. P. Meera ◽  
S. V. Valsaraj ◽  
...  
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior

The Stress Relaxation of Sulfur Vulcanizates of Natural Rubber

1957 ◽  
Vol 30 (1) ◽  
pp. 42-53
Author(s):  
J. P. Berry
Keyword(s):  
Experimental Study ◽  
Stress Relaxation ◽  
Natural Rubber ◽  
Oxygen Pressure ◽  
Relaxation Behavior ◽  
Two Stage ◽  
Stress Relaxation Behavior ◽  
Stage Process ◽  
Force Time ◽  
Effect Of Oxygen

Abstract An experimental study is reported of the stress relaxation behavior of sulfur vulcanizates of natural rubber maintained at constant extension. Of particular interest is the effect of oxygen pressure on the shape of the force-time curves, and the relaxation proceeding in absence of oxygen. The results are interpreted according to a two-stage process: (1) oxidation at the crosslinks and (2) scission of oxidized crosslinks.

Stress Relaxation of a Twaron®/Natural Rubber Composite

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
N. V. David ◽  
X.-L. Gao ◽  
J. Q. Zheng
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Rheological Model ◽  
Maxwell Model ◽  
Relaxation Behavior ◽  
Stress Relaxation Behavior ◽  
Generalized Maxwell Model ◽  
Rubber Composite ◽  
Long Time ◽  
Different Levels

The stress relaxation behavior of a Twaron CT709® fabric/natural rubber composite under a uniaxial constant strain is studied using three viscoelasticity models with different levels of complexity and a newly developed para-rheological model. The three viscoelasticity models employed are a one-term generalized Maxwell model (comprising one Maxwell element and an additional spring in parallel), a two-term generalized Maxwell model (including two Maxwell elements and an additional spring in parallel), and a four-parameter Burgers model. The values of the parameters involved in each model are extracted from the experimental data obtained in this study. The stress relaxation tests reveal that the stress starts to decay exponentially for a short duration and then continues to decrease linearly with time. It is found that the initial relaxation response of the composite is predicted fairly well by all of the four models, while the long-time stress relaxation behavior is more accurately predicted by the para-rheological model. The accuracy of each model in describing the stress relaxation behavior of the composite is quantitatively compared.

Understanding the microscopic deformation mechanism and macroscopic mechanical behavior of nanocrystalline Ni by the long-term stress relaxation test

2014 ◽  
Vol 28 (20) ◽  
pp. 1450124 ◽  
Author(s):  
Xixun Shen ◽  
Congcong Zhang ◽  
Tao Zeng ◽  
Danhong Cheng ◽  
Jianshe Lian
Keyword(s):  
Stress Relaxation ◽  
Strain Rate ◽  
Mechanical Behavior ◽  
Deformation Mechanism ◽  
Rate Sensitivity ◽  
Dislocation Motion ◽  
Relaxation Behavior ◽  
Nonlinear Stress ◽  
Two Stages

The long-term stress relaxation tests with a relaxation time of about 7 h are performed on the bulk dense nanocrystalline Ni (with a mean grain size of 27 nm) pre-deformed at strain rate from 4.17 s-1- 4.17 × 10-6 s-1, where a phenomenon that the initial relaxation behavior of nc Ni depends on itself deformation history. That is, the nc Ni s pre-deformed at higher strain rate (not less than 4.17 × 10-3 s-1) exhibit a three-staged relaxation process from the initial near linear rapidly stress delayed (LRSD) stage and the subsequent lumber nonlinear stress delayed (LNSD) one and the final near linear slowly stress delayed (LSSD) one while only the later two stages are observed for the nc Ni s pre-deformed at low strain rate. The three-stage relaxation behavior is attributed to the transition from the initial dislocation-dominated plasticity to the mixture of dislocation motion and diffusion-based GB activity and finally to the entire diffusion-based GB activity including GB sliding or grain rotation in the rate-controlling deformation mechanism, which was illuminated by the attained three-staged strain rate sensitivity and activation volume and the exhaustion of mobile density of deformed nc Ni in the first two stages of relaxation. Such rate-controlling deformation mechanism well interpreted the macroscopic tensile mechanical behavior of nc Ni and simultaneously an optimizing strategy in improving the ductility of nc Ni is also mentioned.

Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates

1959 ◽  
Vol 32 (3) ◽  
pp. 739-747 ◽  
Author(s):  
J. R. Dunn ◽  
J. Scanlan
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Protective Action ◽  
Dicumyl Peroxide ◽  
Vulcanized Rubber ◽  
Aging Properties ◽  
Photochemical Aging ◽  
Natural Rubber Vulcanizates

Abstract The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.

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