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Showing papers on "Fracture (geology) published in 2007"


Journal ArticleDOI
TL;DR: In this article, the Vickers indentation fracture toughness test, or VIF, is addressed by considering its origins and the numerous equations that have been applied along with the technique to estimate the fracture resistance, or the KIc of ceramics.
Abstract: The Vickers indentation fracture toughness test, or VIF, is addressed by considering its origins and the numerous equations that have been applied along with the technique to estimate the fracture resistance, or the KIc of ceramics. Initiation and propagation of cracks during the VIF test are described and contrasted with the pre-cracking and crack growth for internationally standardized fracture toughness tests. It is concluded that the VIF test technique is fundamentally different than standard fracture toughness tests. The VIF test has a complex three-dimensional crack system with substantial deformation residual stresses and damage around the cracks. The VIF test relates to an ill-defined crack arrest condition as opposed to the rapid crack propagation of the standardized fracture toughness tests. Previously published fracture toughness results employing the VIF technique are reviewed. These reveal serious discrepancies in reported VIF fracture toughness values. Finally, recent fracture resistance measurements by the VIF technique for the Standard Reference Material SRM 2100 are presented. These are compared with standardized test results for the same material. It is concluded that the VIF technique is not reliable as a fracture toughness test for ceramics or for other brittle materials. What the VIF actually measures in terms of fracture resistance cannot be readily defined. It is recommended that the VIF technique no longer be acceptable for the fracture toughness testing of ceramic materials.

611 citations


Journal ArticleDOI
TL;DR: In this article, a damage plasticity model for ductile fracture is proposed, which is established on the cylindrical coordinate system of principal stress space, and four simulations with emphasis on crack path prediction are presented.

434 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of hydrogen on the fracture behavior of quenched and tempered AISI 4135 steel at 1450 MPa was investigated by means of slow strain rate tests on smooth and circumferentially-notched round-bar specimens.

306 citations


Book
01 Jan 2007
TL;DR: In this paper, the authors present the fundamental concepts behind the basic theories and tools of discrete element methods (DEM), its historical development, and its wide scope of applications in geology, geophysics and rock engineering.
Abstract: This book presents some fundamental concepts behind the basic theories and tools of discrete element methods (DEM), its historical development, and its wide scope of applications in geology, geophysics and rock engineering. Unlike almost all books available on the general subject of DEM, this book includes coverage of both explicit and implicit DEM approaches, namely the Distinct Element Methods and Discontinuous Deformation Analysis (DDA) for both rigid and deformable blocks and particle systems, and also the Discrete Fracture Network (DFN) approach for fluid flow and solute transport simulations. The latter is actually also a discrete approach of importance for rock mechanics and rock engineering. In addition, brief introductions to some alternative approaches are also provided, such as percolation theory and Cosserat micromechanics equivalence to particle systems, which often appear hand-in-hand with the DEM in the literature. Fundamentals of the particle mechanics approach using DEM for granular media is also presented. Presents the fundamental concepts of the discrete models for fractured rocks, including constitutive models of rock fractures and rock masses for stress, deformation and fluid flow Provides a comprehensive presentation on discrete element methods, including distinct elements, discontinuous deformation analysis, discrete fracture networks, particle mechanics and Cosserat representation of granular media Features constitutive models of rock fractures and fracture system characterization methods detaiing their significant impacts on the performance and uncertainty of the DEM models

284 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present the results of biaxial tests performed on physical models of rock with non-persistent joints, and the failure modes and maximum strengths developed were found to depend on, among other variables, the geometry of the joint systems, the orientation of the principal stresses and the ratio between intermediate stress and intact material compressive strength (σ2/σc).

260 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the dynamic fracture mechanism related to blast-induced borehole breakdown and crack propagation in circular rock models containing a single centrally located source of explosive were numerically blasted using the AUTODYN 2D code.

214 citations


Journal ArticleDOI
TL;DR: A finite element-based cohesive zone model was developed using bilinear softening to predict the monotonic load versus crack mouth opening displacement curve of geometrically similar notched concrete specimens as mentioned in this paper.
Abstract: A finite element-based cohesive zone model was developed using bilinear softening to predict the monotonic load versus crack mouth opening displacement curve of geometrically similar notched concrete specimens. The softening parameters for concrete material are based on concrete fracture tests, total fracture energy (GF), initial fracture energy (Gf), and tensile strength ( f t ′ ) , which are obtained from a three-point bending configuration. The features of the finite element model are that bulk material elements are used for the uncracked regions of the concrete, and an intrinsic-based traction-opening constitutive relationship for the cracked region. Size effect estimations were made based on the material dependent properties (Gf and f t ′ ) and the size dependent property (GF). Experiments using the three-point bending configuration were completed to verify that the model predicts the peak load and softening behavior of concrete for multiple specimen depths. The fracture parameters, based on the size effect method or the two-parameter fracture model, were found to adequately characterize the bilinear softening model.

213 citations


01 Jan 2007
TL;DR: In this paper, the authors present the EPFL-CONF-212847 Record created on 2015-10-08, modified on 2016-08-09 and used in the work of this paper.
Abstract: Note: Abstract Reference EPFL-CONF-212847 Record created on 2015-10-08, modified on 2016-08-09

200 citations


Journal ArticleDOI
TL;DR: In this paper, the fracture paths correspond with the lowest hardness distribution profiles in the joints, and the heat indexes cannot be used as parameters to evaluate the thermal input, mechanical properties and fracture mode.

200 citations


Journal ArticleDOI
TL;DR: In this paper, the use of digital image correlation (DIC) as a fracture mechanics tool is described, for two projects currently underway, one of which is to examine the bond between carbon fiber reinforced polymers (CFRP) and concrete substrates.

199 citations


Journal ArticleDOI
TL;DR: In this paper, a modified criterion is used to provide accurate predictions for the reported experimental results, which makes use of a three-parameter model (based on KI, KII and T) for describing the crack tip stresses.

Journal ArticleDOI
TL;DR: In this article, an implicit moving mesh algorithm for the study of the propagation of plane-strain hydraulic fracture in an impermeable medium is presented, where the fluid front is allowed to lag behind the fracture tip.

Journal ArticleDOI
TL;DR: In this article, a discrete element approach was used in the simulation of rock fracture using rigid circular particles or cylinders that have interaction through normal and shear springs and were bonded to each other at the contact points to withstand the applied loads.
Abstract: A discrete element approach was used in the simulation of rock fracture. The numerical synthetic material was made of rigid circular particles or cylinders that have interaction through normal and shear springs. The cylinders were bonded to each other at the contact points to withstand the applied loads. To characterize the microscopic properties of this synthetic material, a dimensional analysis approach was presented. It was shown that the dimensionless parameters and graphs obtained were useful tools for fast and efficient calibration of a synthetic material. This calibration method was employed for finding a numerical model for Pennsylvania Blue Sandstone. The numerical model could mimic many deformational and failure characteristics of the sandstone in both conventional and some non-conventional stress paths.

Journal ArticleDOI
TL;DR: In this paper, a study of nine self-compact concrete (SCC) concrete mixtures was conducted and the results showed that increasing the volume of paste has a restricted effect on strength, unless water content varies.
Abstract: Self-compacting concrete (SCC) mixtures are usually designed with higher volumes of paste than vibrated concrete mixtures. The results reported in this paper come from a study of nine SCC concrete mixtures. Volume of paste was varied between 291 and 457 l/m3. One of the mixtures had already been used in a large scale test, and the others were designed by varying several parameters of the reference concrete mixture. Mechanical properties, shrinkage, fracture parameters and fracture process zone (FPZ) size were measured. Fracture behavior was characterized by means of three-point bending tests and acoustic emission analysis. From the experimental results, increasing the volume of paste has a restricted effect on strength, unless water content varies. Strength, elastic modulus and fracture resistance slightly decrease with an increase in paste content. Volume of paste causes an increase in shrinkage and cracking due to shrinkage. Fracture and acoustic emission analysis show that increasing the volume of paste tends to make SCC more brittle.

Journal ArticleDOI
TL;DR: In this paper, two fracture criteria are proposed and applied to blunt-notched components made of brittle materials loaded under mixed mode; the former is based on the averaged strain energy density over a given control volume, the latter on the cohesive crack zone model.
Abstract: Two fracture criteria are proposed and applied to blunt-notched components made of brittle materials loaded under mixed mode; the former is based on the averaged strain energy density over a given control volume, the latter on the cohesive crack zone model. In both instances use of the equivalent local mode I hypothesis is made. Only two material properties are needed: the ultimate tensile strength and the fracture toughness. Numerical predictions of rupture loads from the two criteria are compared with experimental measurements from more than 160 static tests with notched beams. The samples are made of PMMA and tested at − 60°C to assure a bulk behaviour almost linear elastic up to rupture. Notch root radii range from 0.2 to 4.0 mm and load mixicity varies from pure mode I to a prevailing mode II. The good agreement between theory and experimental results adds further confidence to the proposed fracture criteria.

Journal ArticleDOI
TL;DR: Out-of-plane, nanoscale periodic corrugations are observed in the dynamic fracture surface of brittle bulk metallic glasses with fracture toughness approaching that of silica glasses, and a model based on the meniscus instability and plastic zone theory is used to explain such dynamic crack instability.
Abstract: Out-of-plane, nanoscale periodic corrugations are observed in the dynamic fracture surface of brittle bulk metallic glasses with fracture toughness approaching that of silica glasses. A model based on the meniscus instability and plastic zone theory is used to explain such dynamic crack instability. The results indicate that the local softening mechanism in the fracture is an essential ingredient for controlling the formation of the unique corrugations, and might provide a new insight into the origin of fracture surface roughening in brittle materials.

Journal ArticleDOI
TL;DR: In this article, the authors reveal the micromechanisms of fatigue damage formation and evolution with respect to particle topology and grain size and orientation in a rolled 7075-T651 Al alloy.

Journal ArticleDOI
TL;DR: A detailed statistical analysis of acoustic emission time series from laboratory rock fracture obtained from different experiments on different materials including acoustic emission controlled triaxial fracture and punch-through tests indicates its general validity for fracture processes independent of time, space, and magnitude scales.
Abstract: We present a detailed statistical analysis of acoustic emission time series from laboratory rock fracture obtained from different experiments on different materials including acoustic emission controlled triaxial fracture and punch-through tests. In all considered cases, the waiting time distribution can be described by a unique scaling function indicating its universality. This scaling function is even indistinguishable from that for earthquakes suggesting its general validity for fracture processes independent of time, space, and magnitude scales.

Journal ArticleDOI
TL;DR: In this paper, an empirical linear relationship between the fracture toughness and tensile strength of the tested clay, which is K IC ǫ = 0.3546 σ t, was suggested.

Patent
16 Oct 2007
TL;DR: In this paper, a method and apparatus for orchestrating multiple fractures at multiple well locations in a region by flowing well treatment fluid from a centralized well-treatment fluid center is disclosed that includes the steps of configuring a well treatment fluids center for fracturing multiple wells, inducing a fracture at a first well location, measuring effects of stress fields from the first fracture, determining a time delay based in part upon the measured stress effects, inducing another fracture after the time delay at a second location based on the measured effects, and measuring the stress effects from the second fracture.
Abstract: A method and apparatus for orchestrating multiple fractures at multiple well locations in a region by flowing well treatment fluid from a centralized well treatment fluid center is disclosed that includes the steps of configuring a well treatment fluid center for fracturing multiple wells, inducing a fracture at a first well location, measuring effects of stress fields from the first fracture, determining a time delay based in part upon the measured stress effects, inducing a second fracture after the time delay at a second location based upon the measured effects, and measuring the stress effects of stress fields from the second fracture. Sensors disposed about the region are adapted to output effects of the stress fields. Location and orientation of subsequent fractures is based on the combined stress effects of the stress fields as a result of the prior fractures which provides for optimal region development.

Journal ArticleDOI
TL;DR: In this article, a review of experimental results that allow one to interpret the essential features of fracture in ferroelectric ceramics under electric and mechanical load is presented. And theoretical fracture mechanical concepts are then introduced.
Abstract: This chapter reviews experimental results that allow one to interpret the essential features of fracture in ferroelectric ceramics under electric and mechanical load. First, crack growth measurements on unpoled and poled ferroelectric ceramics are reviewed, and numerous experiments that demonstrate the existence and relevance of a domain-switching zone are presented. Thereafter the review concentrates on results of fracture experiments with applied electric fields and addresses the controversial outcomes of such experiments. Theoretical fracture mechanical concepts are then introduced. One part of the discussion focuses on electrical boundary conditions used at the crack surface because they decisively determine the predicted energy release rate. The other part of the discussion, which concerns theoretical concepts, discusses the predicted switching zones around cracks and their influence on the stress intensity factor and energy release rate. Finally, this chapter attempts to mirror the tremendou...

Journal ArticleDOI
TL;DR: In this article, the authors developed practical techniques useful for FE modeling to simulate structural crashworthiness of ships in collisions or grounding, which can be applied to existing test structural models, which involve both crushing and fracture behavior, are shown by a comparison with the experimental results and corresponding FE simulations to confirm the validity of the proposed methods.
Abstract: The aim of this paper is to develop practical techniques useful for FE modeling to simulate structural crashworthiness of ships in collisions or grounding. Approaches to define relevant FE mesh size, material stress'strain relationship, and critical fracture strain and also to deal with the dynamic effects related to dynamic yield strength, dynamic fracture strain, inertia, and frictions are addressed so that the crushing and rupture behavior in collisions and grounding can be analyzed efficiently and accurately in the FE simulations. Benchmark studies on material tensile coupon test specimen and a perforated plate under axial tension are undertaken for the simulation of the fracture behavior. In a separate paper, applications on the existing test structural models, which involve both crushing and fracture behavior, are shown by a comparison with the experimental results and the corresponding FE simulations to confirm the validity of the proposed methods.

Journal ArticleDOI
TL;DR: In this article, a 3D digital image correlation (3D-DIC) system was used to acquire full-field deformations during the loading and stable tearing processes of an aluminum alloy undergoing quasistatic and dynamic mixed-mode I/III loading.
Abstract: Fractures in ductile thin-sheet structures, such as a fuselage or automobile panels, often occur under complex loading conditions. In particular, under remote mixed-mode I/III loading conditions, a cracked structure is subjected to a combination of in-plane tension and large out-of-plane tearing deformation, which may lead to crack tip fields consisting of all three fracture modes (modes I, II, and III). Understanding such fracture events in ductile materials is an important component of the structural integrity analysis of load-bearing structures containing ductile, thin sheets. Due to the complex nature of mixed-mode I/III fracture in ductile thin-sheet materials, reports of experimental investigations are very limited in the literature. We configure three-dimensional digital image correlation (3D-DIC) systems to acquire full-field deformations during the loading and stable tearing processes. The full-field deformation measurements are used to characterize the stable crack extension behavior of an aluminum alloy undergoing quasistatic and dynamic mixed-mode I/III loading. Results confirm that 3D-DIC is an excellent methodology for measuring 3-D deformations in the presence of large out-of-plane warping and motion, both dynamically and statically. Data obtained during the fracture process indicate that the introduction of a mode III component into the loading process alters the crack tip displacement and strain fields relative to those measured in the nominally mode I loading. Furthermore, the measured crack-opening displacement (COD) values during quasistatic and impact mixed-mode I/III fracture show that (1) COD is nearly constant for crack extension beyond 2 mm and (2) COD under combined-mode I/III loading is four times larger than observed during mixed-mode I/II or mode I fracture of the same material, indicating that the magnitude of the critical COD is a function of loading mode in highly ductile, thin-sheet materials.

Journal ArticleDOI
Yoo-Sung Ko1, JS Lee1, Hoon Huh1, Hong-ki Kim2, S. H. Park2 
TL;DR: In this article, a modified ductile fracture criterion is proposed to consider the deformation characteristics of a material accurately in a hole expansion process, which can predict the fracture mode and the hole expanding ratio accurately.

Journal ArticleDOI
TL;DR: In this article, two-dimensional Navier-Stokes flow and transport simulations are conducted for a 15-cm long fracture mapped via X-ray computed tomography, where the actual fracture with irregular aperture, truncated fracture with further thinning of other large aperture areas, and a fracture with uniform vertical aperture equal to actual fracture's mean aperture, are subjected to the same pressure gradient.
Abstract: [1] Two-dimensional Navier-Stokes flow and transport simulations are conducted for a 15-cm long fracture mapped via X-ray computed tomography. (1) The actual fracture with irregular aperture, (2) a truncated fracture where the largest aperture area is excluded from the domain, (3) the truncated fracture with further thinning of other large aperture areas, and (4) a fracture with uniform vertical aperture equal to the actual fracture's mean aperture, are subjected to the same pressure gradient. Slight variations in fracture characteristics result in significantly different flow and transport behavior. Flux is much larger for the uniform-aperture fracture compared to the actual fracture. A pronounced eddy is present at the largest aperture zone of the actual fracture resulting in a power-law tail absent in other cases. The uniform aperture fracture has the largest effective dispersion coefficient estimated via inversion of a 1D analytical model. The analytical model fit to the other cases is not as robust as in the uniform aperture case.

Journal Article
TL;DR: An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is presented in this paper, where the key experimentally detected facts on ductile and brittle fracture processes are discussed.
Abstract: An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is presented. The key experimentally detected facts on ductile and brittle fracture processes are discussed. Special attention is paid to computer simulations and theoretical models of nucleation and growth of nanocracks and nanopores in deformed nanocrystalline materials. Also, we discuss mechanisms for fracture suppression in such materials showing good ductility or superplasticity.

Journal ArticleDOI
TL;DR: It was concluded that to exploit the high strength of the zirconia cores the strength ofThe veneering ceramic has to improve as delamination and cone cracking of the veneer are the most expected failure modes.

Journal ArticleDOI
TL;DR: An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is presented in this paper, where the key experimentally detected facts on ductile and brittle fracture processes are discussed.
Abstract: An overview of experimental study, computer simulations and theoretical models of fracture of nanocrystalline materials is presented. The key experimentally detected facts on ductile and brittle fracture processes are discussed. Special attention is paid to computer simulations and theoretical models of nucleation and growth of nanocracks and nanopores in deformed nanocrystalline materials. Also, we discuss mechanisms for fracture suppression in such materials showing good ductility or superplasticity.

Journal ArticleDOI
TL;DR: In this paper, an experimental investigation into the fracture properties of 160-μm-thick edge-cracked specimens of austenitic nickel-titanium (nitinol) under uniaxial tension is presented.

Journal ArticleDOI
Ahmed Brara, J.R. Klepaczko1
TL;DR: The effect of high loading rates in tension on the failure energy and strength of concrete is reported in this article, where it is shown that at high loading rate, or strain rates, the failure energies of micro-concrete, as well as the strength, substantially increase.