Development of Auto-Searching Method of Brittle Fracture Initiation Point Based on River-Pattern and Tear Ridge

This study focused on the determination of fracture toughness by instrumented indentation technique. A theoretical model to estimate the fracture toughness of ductile materials is proposed and used to verify those results. Modeling of IIT to evaluate fracture toughness is based on two main ideas; the energy input up to characteristic fracture initiation point during indentation was correlated with material’s resistance to crack initiation and growth, and this characteristic fracture initiation point was determined by concepts of continuum damage mechanics. The estimated fracture toughness values obtained from the indentation technique showed good agreement with those from conventional fracture toughness tests based on CTOD. In addition, we confirmed that the proposed model can be also applied in the brittle material through modification of void volume fraction.

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On the Characteristics of Brittle Fracture Initiation in a Structurally Stress Concentrated Region (2nd Report)

Journal of the Society of Naval Architects of Japan ◽

10.2534/jjasnaoe1968.1980.148_169 ◽

1980 ◽

Vol 1980 (148) ◽

pp. 169-176 ◽

Cited By ~ 2

Author(s):

Kin-ichi Nagai ◽

Hiroshi Yajima ◽

Katsuya Kajimoto ◽

Takahiro Hino ◽

Nagio Minami

Keyword(s):

Brittle Fracture ◽

Fracture Initiation

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PENETRATION RESISTANCE OF RUBBER VULCANIZATES

Rubber Chemistry and Technology ◽

10.5254/rct.20.79934 ◽

2020 ◽

Vol 93 (4) ◽

pp. 704-728

Author(s):

Anil K. Bhowmick ◽

Subhabrata Saha ◽

Anshul Baral ◽

Kumar Vineet ◽

Arup S. Deuri ◽

...

Keyword(s):

Carbon Black ◽

Young’S Modulus ◽

Young's Modulus ◽

Fracture Initiation ◽

Penetration Resistance ◽

Theoretical Interpretation ◽

Initiation Point ◽

Static Test ◽

Rubber Compounds ◽

The Impact

ABSTRACT Aspects of penetration resistance of rubber compounds have been studied by developing a quasi-static test. The effects of indenter material and design, nature and dosage of fillers, and crosslinking density were investigated. Indenter material was found to have a negligible contribution to the penetration characteristics of the rubber compounds, whereas the conical indenter's shape and size of the tip were important. A change in the slope of the generalized penetration characteristic curve of the developed quasi-static test was considered to be the fracture initiation point. Although fracture initiation was early at higher carbon black loading, the overall penetration resistance was improved due to hysteresis, which was in accord with the impact energy method. This was a unique observation. The carbon black–filled sample was compared with the silica-filled vulcanizate. Surface morphology of the specimens penetrated at different energy levels was examined using scanning electron microscopy. A theoretical interpretation of the forces acting at the tip of the indenter and the energy requirement while penetrating a rubber compound against a conical indenter has been proposed. The initiation energy for penetration has inverse square root dependence on the Young's modulus of the compounds. The energy required for crack propagation in contrast, was directly proportional to the Young's modulus and also correlated with the hysteresis loss and frictional coefficient for the carbon black–filled vulcanizates.

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The thermodynamics of brittle fracture initiation under triaxial stress conditions

International Journal of Fracture Mechanics ◽

10.1007/bf00703878 ◽

1972 ◽

Vol 8 (2) ◽

pp. 167-173 ◽

Cited By ~ 7

Author(s):

S. A. F. Murrell ◽

P. J. Digby

Keyword(s):

Brittle Fracture ◽

Fracture Initiation ◽

Stress Conditions ◽

Triaxial Stress

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Investigation of the Microstructure Factors Affecting the Brittle Fracture Initiation of Pre-Cracked Charpy-Type Samples of VVER-1000 RPV Steel

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.592-593.635 ◽

2013 ◽

Vol 592-593 ◽

pp. 635-638

Author(s):

Evgenia A. Kuleshova ◽

Maxim A. Artamonov ◽

Artem D. Erak

Keyword(s):

Brittle Fracture ◽

Base Metal ◽

Fracture Initiation ◽

Type Specimens ◽

Fracture Origin ◽

Factors Affecting ◽

Three Point Bending ◽

Weld Metals ◽

Rpv Steel ◽

Higher Temperature

The correlation between fracture toughness parameter KJc and cleavage initiation distance (CID) for the three point bending (3PB) pre-crecked Charpy type specimens of VVER-1000 reactor pressure vessel base and weld metals was observed. Two types of brittle fracture origin sites were found: nonmetallic inclusions and grain or subgrain boundaries. It was shown that KJc values are shifted to the higher temperature area for weld metal with respect to base metal data. In case when the initiation origin is grain or subgrain boundary, the KJc values are higher for base metal at the same CID values. This indicates the higher crack resistance of base metal.

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Time-Dependent Initiation of Multiple Hydraulic Fractures in a Formation With Varying Stresses and Strength

SPE Journal ◽

10.2118/171030-pa ◽

2015 ◽

Vol 20 (06) ◽

pp. 1317-1325 ◽

Cited By ~ 2

Author(s):

Andrew P. Bunger ◽

Guanyi Lu

Keyword(s):

Tensile Strength ◽

Hydraulic Fracture ◽

Fracture Initiation ◽

Time Frame ◽

Hydraulic Fractures ◽

Static Fatigue ◽

Breakdown Pressure ◽

Initiation Point ◽

Delayed Failure ◽

Wellbore Pressure

Summary The premise of classical hydraulic-fracture-breakdown models is that hydraulic-fracture growth can only start when the wellbore pressure reaches a critical value that is sufficient to overcome the tensile strength of the rock. However, rocks are well-known to exhibit static fatigue; that is, delayed failure at stresses less than the tensile strength. In this paper, we explore the consequences of delayed failure on axially oriented initiation of multiple hydraulic fractures. Specifically, given a certain breakdown pressure, we investigate the conditions under which subsequent hydraulic fracture(s) can begin within the time frame of a stimulation treatment in regions of higher stress and/or strength because of delayed-failure mechanisms. The results show that wells completed in shallower formations are more sensitive to variations in strength, whereas wells completed in deeper formations are more sensitive to variations in stress. Furthermore, cases in which all hydraulic fractures break down according to the same pressurization regime—that is, all are “fast” (nonfluid-penetrating) pressurization or else all are “slow” (uniformly pressurized fluid-penetrating) pressurization cases—are highly sensitive to small stress/strength variability. On the other hand, if the first hydraulic-fracture initiation is in the “fast”-pressurization regime and subsequent fracture(s) are in the “slow”-pressurization regime, then the system is robust to a much-higher degree of variability in stress/strength. Practically, this work implies that methods aimed at moderately reducing the variability in stress/strength among the possible initiation points (i.e., perforation clusters) within a particular stage can have a strong effect on whether multiple hydraulic fractures will begin. In addition, this analysis implies that pumping strategies that encourage “fast,” nonpenetrative breakdown of the first initiation point followed by the opportunity for fluid-penetrating, “slow” breakdown of subsequent initiation points could be effective at encouraging multiple-hydraulic-fracture initiation.

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Numerical Simulation and Laboratory Experiments of Hydraulic Fracturing of Highly Deviated Well

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.275-277.278 ◽

2013 ◽

Vol 275-277 ◽

pp. 278-281 ◽

Cited By ~ 4

Author(s):

Hai Yan Zhu ◽

Jing Gen Deng ◽

Song Yang Li ◽

Zi Jian Chen ◽

Wei Yan ◽

...

Keyword(s):

Numerical Simulation ◽

Hydraulic Fracturing ◽

Fracture Initiation ◽

Element Model ◽

Simulation Method ◽

Horizontal Stress ◽

Initiation Point ◽

Strength Failure ◽

Fluid Penetration ◽

Maximum Horizontal Stress

Considering the combined action of the fluid penetration and the casing, the seepage coupled deformation finite element model of the highly deviated casing perforation well is established by using the tensile strength failure criterion and applied on the BZ25-1 oil filed. The results show that the increasing of the perforation angle and the well azimuth and the decreasing of the inclination would lead to a higher fracture initiation pressure. The fracture initiation point always locates on the wellbore face when the influence of the casing is considered. When the casing is ignored: when the perforation angle is 0°-45°, the fracture initiation point locates on the root of the tunnel; when the angle is 45°-90°, the fracture initiation point may be on the wellbore face or the perforation biased toward the maximum horizontal stress direction; when the angle is near to 90°, the hydraulic fracturing difficultly fractures the rock through the perforation tunnels. The laboratory hydraulic fracturing simulation experiments of 45° deviated well are carried through 400mm3 cement specimen so as to obtain the fracture initiation point and geometric shape under different perforation angles, the results verify the accuracy of the numerical simulation method.

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