T-Peel Tearing of a Model Black-Filled Natural Rubber Tread Ply Vulcanizate

2007 ◽  
Vol 80 (5) ◽  
pp. 820-825 ◽  
Author(s):  
B. Adamu ◽  
G. R. Hamed
Keyword(s):  
Natural Rubber ◽  
Fast Growth ◽  
Growth Stages ◽  
Stick Slip ◽  
Fracture Surfaces ◽  
Rough Fracture ◽  
Loading Direction

Abstract T-peel tearing of a model black-filled natural rubber tread ply vulcanizate has been carried out. Tearing alternates between slow (“stick”) and fast growth stages (“slip”). “Stick” fracture involves sideways cracking into the loading direction. This blunts the peel front, slows forward tearing, and results in rough fracture surfaces. “Slip” fracture is the sudden forward growth of a crack, leaving relatively smooth fracture surfaces. “Stick-slip” fracture is characteristic of highly reinforced rubbers; it is also seen in edge-cut tensile specimens and trouser tear specimens of black-filled NR.

Effect of Crosslink Density on Cut Growth in Gum Natural Rubber Vulcanizates

2002 ◽  
Vol 75 (2) ◽  
pp. 323-332 ◽  
Author(s):  
G. R. Hamed ◽  
N. Rattanasom
Keyword(s):  
Natural Rubber ◽  
Crosslink Density ◽  
Rough Fracture ◽  
Test Pieces ◽  
Loading Direction ◽  
Crosslinked Networks ◽  
Cut Depth ◽  
Natural Rubber Vulcanizates ◽  
Crack Contour ◽  
Unusual Increase

Abstract Conventional sulfur-cured, gum natural rubber vulcanizates of various crosslink densities were prepared. Dumbbell test pieces with and without edge precuts were tested in uniaxial tension. Relative strengths of the different vulcanizates depended on cut size. Lightly crosslinked specimens exhibited an abrupt drop in strength at a critical cut size, ccr, which became smaller as crosslink density increased because of reduced strain crystallizability. At all cut depths, crack growth was simply perpendicular to the loading direction and crack surfaces were smooth. A moderately crosslinked composition exhibited crack deviation prior to rupture. This was associated with an unusual increase in strength with increasing cut size. Densely crosslinked networks exhibited lateral fracture, like the lightly crosslinked gums, but produced a jagged crack contour path reflective of a rough fracture surface. Moreover, for the highly crosslinked samples, a critical cut size was not found. Rather, log-log plots of strength versus cut depth were linear and had slopes slightly greater than minus one-half.

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.

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.

Stereological Estimation of Fractal Number of Fracture Planes in Concrete

1995 ◽  
Vol 407 ◽  
Author(s):  
P. Stroeven
Keyword(s):  
Process Zone ◽  
Single Fracture ◽  
Fractal Nature ◽  
Direct Tension ◽  
Fracture Surfaces ◽  
Fracture Planes ◽  
Loading Direction ◽  
Chain Link ◽  
Particulate Filler ◽  
Fractal Number

ABSTRACTConcrete is a man-made material containing a particulate filler designed on the basis of a sieve curve. In case of river aggregate, the particles are approximately spherical and smoothtextured. The particle-matrix interface is mostly the weakest chain link in the mechanical system. This implies damage evolution to start at particle-matrix interfaces. In case of direct tension, these interface cracks will be on average perpendicular to the loading direction. In case of direct compression, they will be parallel to the loading direction. A single fracture surface is formed in tension and a series of fracture surfaces in compression. They are the result of crack concentration within a process zone, in which the engineering crack closely meanders around a dividing plane. This allows to model these fracture surfaces on different resolution levels. It is shown, using stereological notions, that the very phenomenon is of a non-ideal fractal nature. Estimates for fractal dimension of fracture surfaces in concretes based on sieve curves at the border of the practical range are found to closely match experimental data reported in the literature.

Numerical study of heat transfer across rough fracture surfaces

2020 ◽  
Author(s):  
Thomas Heinze
Keyword(s):  
Heat Transfer ◽  
Laboratory Experiments ◽  
Numerical Study ◽  
Three Dimensional ◽  
Fracture Morphology ◽  
Geothermal Systems ◽  
Fracture Surfaces ◽  
Rough Fracture ◽  
Transfer Processes ◽  
Fracture Morphologies

<p>Maximizing heat exploitation in geothermal systems is crucial for the economic efficiency of many geothermal systems. As the hydraulic flow in most geothermal systems is primarily due to fracture flow, heat transfer processes along the fracture surfaces are essential. However, while flow and mass transport in a single fracture have been studied experimentally and theoretically to a great extent, heat transfer processes have been rarely investigated. Laboratory experiments show the influence of the fracture surface morphology on flow and heat transfer processes, though a physical interpretation has been missing so far. Further, in many geothermal systems but also in many natural hydrothermal systems, the solid and fluid phases are not in local thermal equilibrium. Parameterization of local thermal non-equilibrium models was originally developed for porous media and adoptions to fractures have been cumbersome. In this work, I present a numerical study on heat transfer processes across rough fracture surfaces. Using a three-dimensional steady-state flow model, heat transfer across the fracture surface is studied for both scenarios: assuming and neglecting a thermal equilibrium across phase boundaries. Also, separate fracture morphologies have been studied using natural sandstone probes as well as synthetically generated fractures. The numerical simulations results are compared to laboratory experiments using artificially generated and 3D-printed fracture surfaces of various fracture morphologies for code validation. The full three-dimensional simulations reveal the role of flow channeling effects on the heat transfer taking place along rough surfaces, which is not captured by simulations with reduced spatial dimensions. The simulations results suggest a re-examination of the effective heat transfer coefficient for fractured reservoirs under local thermal non-equilibrium conditions incorporating characteristics of fracture morphology. The simulations results can also be linked to thermal stress generation and possibly explaining the deformations of fracture surfaces observed in the laboratory. However, parameterization of surface roughness is neither distinct nor trivial. Various parameters exist, such as the joint roughness coefficient, Hurst exponent or statistical descriptions, but none has been successfully linked to flow, transport or transfer characteristics. Relating fracture morphology with results of numerical simulations and laboratory findings regarding transfer and transport processes indicate a shortfall of conventional roughness parameterizations to sufficiently describe the observed variation in heat transfer parameters.</p>

scholarly journals Compressive Fracture of Brittle Geomaterial: Fractal Features of Compression-Induced Fracture Surfaces and Failure Mechanism

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
L. Ren ◽  
L. Z. Xie ◽  
C. B. Li ◽  
J. Wang
Keyword(s):  
Failure Mechanism ◽  
Fractal Dimensions ◽  
Contrastive Analysis ◽  
Mode Fracture ◽  
Compressive Fracture ◽  
Fracture Surfaces ◽  
Failure Patterns ◽  
Rough Fracture ◽  
Fracture Tests ◽  
Tension Fracture

Compressive fracture is one of the most common failure patterns in geotechnical engineering. For better understanding of the local failure mechanism of compressive fractures of brittle geomaterials, three compressive fracture tests were conducted on sandstone. Edge cracked semicircular bend specimens were used and, consequently, fresh and unfilled compressive fracture surfaces were obtained. A laser profilometer was employed to measure the topography of each rough fracture surface, followed by fractal analysis of the irregularities of the obtained compression-induced fracture surfaces using the cubic cover method. To carry out a contrastive analysis with the results of compressive fracture tests, three tension mode fracture tests were also conducted and the fractal features of the obtained fracture surfaces were determined. The obtained average result of the fractal dimensions of the compression-induced surfaces was 2.070, whereas the average result was 2.067 for the tension-induced fracture surfaces. No remarkable differences between the fractal dimensions of the compression-induced and tension-induced fracture surfaces may indicate that compressive fracture may occur, at least on the investigative scale of this work, in a similar manner to tension fracture.

scholarly journals Isobaric Tags for Relative and Absolute Quantitation-Based Proteomics Analysis Provides a New Perspective Into Unsynchronized Growth in Kuruma Shrimp (Marsupenaeus japonicus)

2021 ◽  
Vol 8 ◽  
Author(s):  
Jichen Zhao ◽  
Minze Liao ◽  
Zexu Lin ◽  
Yiyi Huang ◽  
Yunqi Zhong ◽  
...  
Keyword(s):  
Growth Stage ◽  
Fast Growth ◽  
Growth Stages ◽  
Marsupenaeus Japonicus ◽  
Absolute Quantitation ◽  
Crustacean Species ◽  
Steady Growth ◽  
Kuruma Shrimp ◽  
Isobaric Tags ◽  
New Perspective

Unsynchronized growth is a common phenomenon in farmed crustaceans. The underlying molecular mechanism of unsynchronized growth of crustaceans is unclear. In this study, a comparative proteomic analysis focusing on growth differences was performed using kuruma shrimp Marsupenaeus japonicus, an economic crustacean species, as the model. The study analyzed kuruma shrimp at fast growth stage and steady growth stage from both fast growth group and slow growth group by an Isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis method. A total of 1,720 proteins, including 12,291 peptides, were identified. Fifty-two and 70 differentially expressed proteins (DEPs) were identified in the fast growth stage and steady growth stage, respectively. Interestingly, 10 DEPs, including 14-3-3-epsilon-like, GPI, GPD1, MHC-1a, and MHC-1b, were presented in both growth stages. In addition, all these 10 DEPs shared the same expression tendency at these two growth stages. The results indicated that these 10 DEPs are potential growth biomarkers of M. japonicus. Proteins associated with faster growth of M. japonicus may promote cell growth and inhibit cell apoptosis through the Hippo signaling pathway. The fast growth group of M. japonicus may also achieve growth superiority by activating multiple related metabolic pathways, including glycolysis, glycerophospholipid metabolism and Citrate cycle. The present study provides a new perspective to explore the molecular mechanism of unsynchronized growth in crustacean species.

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