Cut Growth in Vulcanizates of Natural Rubber, cis-Polybutadiene, and a 50/50 Blend: Part II. Cracking Patterns in the Strained State

1999 ◽  
Vol 72 (5) ◽  
pp. 895-909 ◽  
Author(s):  
G. R. Hamed ◽  
H. J. Kim
Keyword(s):  
Natural Rubber ◽  
Strain Energy ◽  
Crack Opening ◽  
Longitudinal Crack ◽  
Butadiene Rubber ◽  
Loading Direction ◽  
Steady Decrease ◽  
Crack Tips ◽  
Catastrophic Fracture ◽  
Simple Growth

Abstract The tensile strengths, σb, and apparent fracture energies, G, of edge-cut strip specimens (28 mm wide) of carbon black-filled vulcanizates of natural rubber (NR), cis-butadiene rubber (cis-BR), and a 50/50 blend have been determined. The BR vulcanizate exhibited a rather steady decrease in σb with increasing cut size, c, and fractured by simple growth of the original cut tip. NR and the NR/BR blend exhibited much higher strengths as well as a drop in σb at a critical cut size, ccr≈2.2 mm. High strengths are attributed, at least in part, to substantial longitudinal cracking prior to catastrophic fracture, especially when c<ccr. When strengths of edge-cut specimens were normalized by the regular (uncut) tensile strength, similar values were found for all three vulcanizates, when c>ccr. Below ccr, normalized strengths of the NR and NR/BR were comparable and exceeded those of BR. For all three vulcanizates, calculated fracture energies depended on cut size. Photographs of a deformed NR/BR specimen, which had developed the auxiliary cracking, revealed that longitudinal crack tips appear as "corners" propagating along the loading direction. As a longitudinal crack progresses, strain energy is released by the retraction of (sheared) material into the unstressed zone at the extremity of crack opening.

The Mechanism of Carbon Black Reinforcement of SBR and NR Vulcanizates

1999 ◽  
Vol 72 (5) ◽  
pp. 946-959 ◽  
Author(s):  
G. R. Hamed ◽  
B. H. Park
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Uniaxial Tension ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Large Drop ◽  
Steady Decrease ◽  
Longitudinal Cracking ◽  
Catastrophic Fracture ◽  
Styrene Butadiene

Abstract Gum and black-filled vulcanizates of styrene-butadiene rubber (SBR) and natural rubber (NR) were prepared. Strengths in uniaxial tension were determined for specimens with and without edge-cuts. Normal tensile strengths (no cut) of the gum NR, filled NR and filled SBR were similar; whereas, with pre-cuts, even as small as 0.1 mm, strengths of these were markedly different. The SBRs exhibit a steady decrease in strength with increased cut size, while the NR vulcanizates show a drop in strength at a critical cut size ccr. With small cuts, when the gum NR substantially crystallizes in bulk, its strength greatly exceeds that of the filled SBR. The opposite is true with large cuts, due to the large drop in strength of gum NR at ccr. Remarkably, above ccr, the gum NR is only about twice as strong as the gum SBR. Rupture in the gum SBR, gum NR and filled SBR all take place by simple lateral cut growth. At all cut sizes, the filled NR is the strongest material by at least a factor of two, and prior to catastrophic fracture it exhibits auxiliary cracking. It is proposed that crystallization and filler act synergistically, resulting in sufficient anisotropy to cause longitudinal cracking. This provides a super-blunting mechanism, which augments resistance to catastrophic cut growth.

Longitudinal Cracking in a Carbon Black Filled Natural Rubber Vulcanizate during Chemical Stress Relaxation

1998 ◽  
Vol 71 (2) ◽  
pp. 157-167 ◽  
Author(s):  
G. R. Hamed ◽  
J. Zhao
Keyword(s):  
Stress Relaxation ◽  
Carbon Black ◽  
Natural Rubber ◽  
Longitudinal Crack ◽  
Chemical Stress ◽  
Loading Direction ◽  
Rubber Vulcanizate ◽  
Edge Cracks ◽  
Forced Air ◽  
Oxidative Attack

Abstract Thin specimens of a black-filled, natural rubber vulcanizate have been held in uniaxial tension at 72°C and 200% elongation in a forced air oven. After substantial oxidative attack (inferred from stress relaxation), small edge cracks formed. Initially, these cracks grew perpendicular to the loading direction, but, upon reaching about 0.1 mm in depth, longitudinal crack growth commenced and fracture progressed by a kind of 0°-peel process with “splitting-off” of successive strands of rubber. This phenomenon is attributed to anisotropy in strength caused both by straining and by oxidative attack.

On the Reason that Passenger Tire Sidewalls are Based on Blends of Natural Rubber and cis-Polybutadiene

2000 ◽  
Vol 73 (4) ◽  
pp. 743-752 ◽  
Author(s):  
H. J. Kim ◽  
G. R. Hamed
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Natural Rubber ◽  
Crack Growth ◽  
Slow Crack Growth ◽  
Longitudinal Crack ◽  
Crack Branching ◽  
Butadiene Rubber ◽  
Good Resistance

Abstract A tire sidewall must have good resistance to fracture over a range of conditions covering rapid as well as slow crack growth. A vulcanizate based on a 50/50 natural rubber (NR)/cis-butadiene rubber (cis-BR) blend seems to meet this requirement. It retains the ability for longitudinal crack branching and has catastrophic rupture resistance near that of a corresponding NR vulcanizate. At the same time, the blend has good resistance to slow fatigue crack growth, much like that of a cis-BR vulcanizate. The combination of desired properties in the blend may result from co-continuity of its NR and BR phases.

COMPARISON OF THE STRENGTH OF NORMAL AND EDGE-CUT TENSILE SPECIMENS OF STYRENE–BUTADIENE RUBBER AND NATURAL RUBBER WITH SIMILAR CROSSLINK DENSITY

2016 ◽  
Vol 89 (4) ◽  
pp. 631-639 ◽  
Author(s):  
G. Rong ◽  
G. R. Hamed ◽  
J. Jiang
Keyword(s):  
Natural Rubber ◽  
Crosslink Density ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Breaking Strain ◽  
Test Pieces ◽  
Steady Decrease ◽  
Order Of Magnitude ◽  
Cut Depth ◽  
Styrene Butadiene

ABSTRACT Edge cuts of various depths, c, were introduced into tensile specimens of similarly crosslinked (ρc ≈ 6 (10−5) moles of crosslinks/mL) gum (unfilled) natural rubber (NR) and gum styrene–butadiene rubber (SBR). When specimens contained no intentional cut (c = 0, i.e., normal tensile strength), the NR is about 10 times as strong as the SBR. This difference is due to the stereoregularity (cis-1,4-polyisoprene) of NR, enabling it to strain crystallize when deformed. On the other hand, SBR has an irregular, amorphous microstructure that renders it incapable of crystallization. However, for test pieces that contain an edge cut, the strength, σbc, of the NR relative to that of the SBR depends strongly on cut depth. When c ≈ 0.2 mm, the strength of both vulcanizates is reduced about 50%, and hence the ratio of strengths remains about an order of magnitude. But, with a further increase in c, the SBR exhibits a steady decrease in σbc, while the strength of the NR drops discontinuously by nearly a factor of four when c ≈ 1.7 mm. Now, the NR is only about two and one half times as strong as the SBR. Extrapolation of σbc to larger c results in a predicted cut depth c ≈ 4.3 mm, at which the strength of the NR and SBR would be similar. At sufficiently large cut depth, it appears that strain rate at the cut tip is high enough and breaking strain low enough that rupture occurs before significant strain crystallization commences.

Pengaruh penambahan natural rubber (NR), epoxidation natural rubber (ENR-46) dan chlorprene rubber (CR) pada sifat kompon termoplastik

2020 ◽  
Vol 26 (2) ◽  
pp. 62-69
Author(s):  
Farida Ali ◽  
Tuti I. Sari ◽  
Andi A. Siahaan ◽  
Al-Kautsar D. Arya ◽  
Tri Susanto
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Vinyl Chloride ◽  
Butadiene Rubber ◽  
Elongation At Break ◽  
Nitrile Butadiene Rubber ◽  
Poly Vinyl Chloride

Penelitian ini untuk mengetahui pengaruh penambahan Natural Rubber (NR) dan Epoxidation Natural Rubber (ENR-46) dengan kompatibiliser Chlorprene Rubber (CR) pada aplikasi kompon termoplastik Poly Vinyl Chloride (PVC) dan Nitrile Butadiene Rubber (NBR), variabel penelitian meliputi ENR-46/PVC/NBR/CR, NR/PVC/NBR/CR dan CR-NR/PVC/NBR, CR-ENR-46/PVC/NBR. Parameter pengujian sifat fisik-mekanik : Hardness (Shore A), Tensile Strength (Mpa), Elongation at Break (%) dan ketahanan terhadap pelarut minyak (n-Pentane, Toluene, Hexane dan Pertalite). Hasil penelitian didapatkan untuk sifat fisik-mekanik, semakin banyak penambahan NR Kekerasan kompon termoplastik akan menurun, Tensile Strength dan Elongation at Break kompon akan meningkat begitu juga dengan CR-NR. Tetapi berbanding terbalik hasilnya untuk ENR-46 dan CR-ENR-46. Pengujian Ketahanan terhadap pelarut minyak semakin banyak penambahan ENR-46 Ketahanan kompon termoplastik terhadap pelarut akan meningkat, hasil yang sama juga pada CR-ENR-46. Tetapi berbanding terbalik hasilnya dengan penambahan NR dan CR-NR pada kompon termoplastik.

scholarly journals The Influence of Filler Size and Crosslinking Degree of Polymers on Mullins Effect in Filled NR/BR Composites

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2284
Author(s):  
Miaomiao Qian ◽  
Bo Zou ◽  
Zhixiao Chen ◽  
Weimin Huang ◽  
Xiaofeng Wang ◽  
...  
Keyword(s):  
Particle Size ◽  
Strain Energy ◽  
Mathematical Expression ◽  
Rubber Matrix ◽  
Mullins Effect ◽  
Butadiene Rubber ◽  
Crosslinking Degree ◽  
Test Range ◽  
Two Factors ◽  
The Matrix

Two factors, the crosslinking degree of the matrix (ν) and the size of the filler (Sz), have significant impact on the Mullins effect of filled elastomers. Herein, the result. of the two factors on Mullins effect is systematically investigated by adjusting the crosslinking degree of the matrix via adding maleic anhydride into a rubber matrix and controlling the particle size of the filler via ball milling. The dissipation ratios (the ratio of energy dissipation to input strain energy) of different filled natural rubber/butadiene rubber (NR/BR) elastomer composites are evaluated as a function of the maximum strain in cyclic loading (εm). The dissipation ratios show a linear relationship with the increase of εm within the test range, and they depend on the composite composition (ν and Sz). With the increase of ν, the dissipation ratios decrease with similar slope, and this is compared with the dissipation ratios increase which more steeply with the increase in Sz. This is further confirmed through a simulation that composites with larger particle size show a higher strain energy density when the strain level increases from 25% to 35%. The characteristic dependence of the dissipation ratios on ν and Sz is expected to reflect the Mullins effect with mathematical expression to improve engineering performance or prevent failure of rubber products.

Mastication Process of Natural Rubber/Butadiene Rubber Blending: Validation Method on Influence of Peptizer

2020 ◽  
Vol 391 (1) ◽  
pp. 1900175
Author(s):  
Dewi K. Arti ◽  
Ade S. Hidayat ◽  
Ika M. Ulfah ◽  
Herri Susanto ◽  
Lies A. Wisojodharmo ◽  
...  
Keyword(s):  
Natural Rubber ◽  
Butadiene Rubber ◽  
Validation Method

Tensile Behavior after Oxidative Aging of Gum and Black-Filled Vulcanizates of SBR and NR

1999 ◽  
Vol 72 (4) ◽  
pp. 721-730 ◽  
Author(s):  
G. R. Hamed ◽  
J. Zhao
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Tensile Behavior ◽  
Styrene Butadiene Rubber ◽  
Butadiene Rubber ◽  
Oxidative Aging ◽  
Prolonged Aging ◽  
Aging Period ◽  
Early Aging ◽  
Styrene Butadiene

Abstract Typical sulfur-cured vulcanizates of styrene-butadiene rubber (SBR) and natural rubber (NR) were prepared, and subjected to air-oven aging at 100 °C. Gum specimens exhibited an initial aging period in which stiffness was unchanged, while tensile strength and strain-to-break were significantly reduced. In contrast, black-filled vulcanizates stiffened during early aging. After intermediate aging times, NR specimens softened, while SBR stiffened. With prolonged aging, all compositions became hard and inextensible.

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