Multiple cracks in VTI rocks: Effective properties and fracture characterization

2007 ◽  
Author(s):  
Vladimir Grechka
Keyword(s):  
Effective Properties ◽  
Multiple Cracks ◽  
Fracture Characterization

Multiple cracks in VTI rocks: Effective properties and fracture characterization

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. D81-D91 ◽  
Author(s):  
Vladimir Grechka
Keyword(s):  
Host Rock ◽  
Effective Properties ◽  
Crack Density ◽  
Transversely Isotropic ◽  
Multiple Cracks ◽  
Multiple Fracture ◽  
Fracture Characterization ◽  
Effective Media ◽  
Important Exception ◽  
Sonic Logs

The existing fracture-characterization techniques are based on assuming the unfractured host rock either to be isotropic or the magnitudes of both the background and crack-induced anisotropies to be small. I relax both assumptions and examine the effective media caused by fractures with realistic (not small) crack densities in a strongly anisotropic, primarily transversely isotropic (TI) host rock. The analysis of penny-shaped cracks in the noninteraction approximation (NIA) reveals the dependence of their excess fracture compliance tensors on the orientation of the background symmetry axis. As a result of this dependence, the excess fracture compliance tensor generally becomes rotationally noninvariant even when the cracks are circular. One of the consequences of this complication (compared to the background isotropy) is a reduction of symmetry from TI to monoclinic resulting from the presence of a single oriented fracture set. Verti–cal dry cracks in a vertically transversely isotropic (VTI) host constitute an important exception to this general rule.The effective symmetry for this arrangement is approximately orthorhombic (or orthotropic) even in the presence of multiple fracture sets that have arbitrary azimuths. I perform finite-element simulations on the so-called digital rocks to verify both the proximity of effective symmetry to orthotropy and the accuracy of the NIA up to the crack density of 0.15. Multiple sets of dry vertical cracks in a VTI host not only result in nearly orthorhombic effective symmetry but also their cumulative influence is equivalent to that of just two orthogonal (or principal) fracture sets. The possibility of replacing multiple fracture sets with two orthogonal ones paves the way for their characterization. The inverse problem of estimating the parameters of two orthogonal crack systems in a VTI background from the effective elasticity, however, is known to be nonunique. I suggest overcoming its ambiguity by combining 3D, wide-azimuth, multicomponent seismic data with sonic logs.

Unconventional Play Fracture Characterization Through Orthorhombic Depth Model Building

2018 ◽  
Author(s):  
Guy Hilburn ◽  
Amit Pendharkar ◽  
William Keller ◽  
René Mott ◽  
Jorge Peinado ◽  
...  
Keyword(s):  
Model Building ◽  
Fracture Characterization

Rubber Fracture Characterization Using J-Integral

1988 ◽  
Vol 16 (1) ◽  
pp. 44-60 ◽  
Author(s):  
C. L. Chow ◽  
J. Wang ◽  
P. N. Tse
Keyword(s):  
Crack Initiation ◽  
Carbon Black ◽  
Natural Rubber ◽  
Fracture Parameter ◽  
J Integral ◽  
Specimen Length ◽  
Fracture Characterization ◽  
Premature Failure ◽  
Testing Procedures ◽  
Material Evaluation

Abstract The use of the J-integral to investigate fracture characterization in a carbon black reinforced natural rubber is described. Three applications to crack initiation are included: two based on the use of a hypothetical zero specimen length and one on conventional testing procedures for metals. While the validity of the zero-length methods is questionable, the conventional method yielded a consistent Jc value of 1.01 N/mm for a typical tire compound. This value was obtained from 24 combinations of varying specimen geometries and pre-crack lengths. The J-integral is revealed as a valid fracture parameter that is applicable not only for material evaluation but also for designing tire structures to resist premature failure. These conclusions disagree with those from an earlier investigation, so the causes for the discrepancies are examined and discussed.

Mathematical Model of the Effective Properties of a Fiber Reinforced Composite with a Linearly Graded Transition Zone

2010 ◽  
Vol 38 (4) ◽  
pp. 286-307
Author(s):  
Carey F. Childers
Keyword(s):  
Mathematical Model ◽  
Transition Zone ◽  
Effective Properties ◽  
Local Stress ◽  
Stress And Strain ◽  
Fiber Reinforced ◽  
Strain Fields ◽  
Shear Moduli ◽  
Fiber Reinforced Composite ◽  
Reinforced Composite

Abstract Tires are fabricated using single ply fiber reinforced composite materials, which consist of a set of aligned stiff fibers of steel material embedded in a softer matrix of rubber material. The main goal is to develop a mathematical model to determine the local stress and strain fields for this isotropic fiber and matrix separated by a linearly graded transition zone. This model will then yield expressions for the internal stress and strain fields surrounding a single fiber. The fields will be obtained when radial, axial, and shear loads are applied. The composite is then homogenized to determine its effective mechanical properties—elastic moduli, Poisson ratios, and shear moduli. The model allows for analysis of how composites interact in order to design composites which gain full advantage of their properties.

Reconstruction of multiple cracks in an ECT round-robin test

2004 ◽  
Vol 19 (1-4) ◽  
pp. 399-404 ◽  
Author(s):  
Mihai Rebican ◽  
Noritaka Yusa ◽  
Zhenmao Chen ◽  
Kenzo Miya ◽  
Tetsuya Uchimoto ◽  
...  
Keyword(s):  
Round Robin ◽  
Multiple Cracks ◽  
Round Robin Test
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