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L. M. Brock - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional dynamic fracture in a transversely isotropic thermoelastic solid: Framework for study
Journal of Thermal Stresses, 2018Co-Authors: L. M. BrockAbstract:AbstractA semi-infinite plane Crack is at rest in an unbounded, transversely isotropic, thermoelastic solid. Point forces are applied to the Crack faces, and translated with constant, subcritical speed at right angles to the initial Crack Edge. Fracture occurs, and a dynamic steady state is achieved: The Crack Edge is no longer rectilinear, but extension and translation speeds are identical. The Crack plane contains the axis of material symmetry lies in that plane, and the initial Crack Edge is not aligned with that axis. An analytical three-dimensional solution is obtained, and a criterion for fracture based on dynamic energy release rate imposed, with kinetic energy included. A nonlinear differential equation for Crack Edge location and constraint equations result, and together form a framework for study of Crack and contact zone geometry.
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Contours for planar Cracks growing in three dimensions: Coupled thermoelastic solid (planar Crack growth in 3D)
Journal of Thermal Stresses, 2016Co-Authors: L. M. BrockAbstract:ABSTRACTDynamic steady-state growth in 3D of a semi-infinite plane brittle Crack in a coupled thermoelastic solid is considered. Compressive loads cause growth by translating on the Crack surfaces at constant, subcritical speed. An asymptotic solution is obtained in an analytic form and subjected to a criterion of the Griffith type for the case of a compressive point force. The exact solution to a nonlinear differential equation indicates a rectilinear Crack Edge deformed by a bulge near the point force. Temperature change near the Crack Edge is examined in terms of a mathematical norm.
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Contours for Planar Cracks Growing in Three Dimensions: Influence of Kinetic Energy
Journal of Applied Mechanics, 2015Co-Authors: L. M. BrockAbstract:Dynamic steady-state growth in 3D of a semi-infinite plane brittle Crack in isotropic elastic solids is considered. Loads cause growth by translating on the Crack surfaces at constant, subcritical speed. An analytical solution is obtained and subjected to a criterion for brittle Crack growth based on dynamic energy release rate, with kinetic energy included. The result is a nonlinear differential equation for the Crack contour, i.e., the curve formed by the Crack Edge in the Crack plane. The equation is studied for the case of compression loading by translating point forces. At large distances from the forces, the Crack Edge asymptotically approaches the rectilinear and kinetic energy effects can be negligible. A bulge forms around the forces, however, the effect of kinetic energy on its size can be pronounced.
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Dynamic Crack Extension Along the Interface of Materials That Differ in Thermal Properties: Convection and Thermal Relaxation
Journal of Applied Mechanics, 2008Co-Authors: L. M. BrockAbstract:Moving surface loads cause Crack extension at a constant subcritical speed between perfectly bonded materials. The materials differ only in thermal properties and are governed by coupled thermoelastic equations that admit as special cases Fourier heat conduction and thermal relaxation with one or two relaxation times. Convection from the Crack surfaces is allowed and for the latter two models is itself influenced by thermal relaxation. A dynamic steady state of plane strain is assumed. Fourier heat conduction is shown to dominate away from the Crack Edge at low speeds; solution behavior at the Crack Edge at high speeds depends upon the particular thermal model. Thermal mismatch is seen to cause solution behavior similar to that for the isothermal bimaterial, and so insight into the case of general material mismatch is provided.
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Dynamic Crack extension along the interface of materials that differ in their thermal properties: with and without thermal relaxation
Acta Mechanica, 2008Co-Authors: L. M. BrockAbstract:Moving surface stresses cause Crack extension along the interface of perfectly bonded thermoelastic materials at a constant sub-critical speed. The materials differ only in their thermal properties, and are governed by coupled thermoelastic equations that admit as special cases Fourier heat conduction as well as thermal relaxation with one or two relaxation times. A dynamic steady state of plane strain is assumed. The exact transform solution for a propagating displacement and temperature discontinuity is used to find solutions to the interface Crack valid away from the Crack Edge for low extension speeds and solutions valid at the Crack Edge for high speeds. Results show that Fourier heat conduction dominates the former case, but solution behavior in the latter is dependent upon the particular thermal model. Thermal mismatch is seen to by itself cause a solution behavior similar to that for bonded dissimilar isothermal elastic solids. In particular, the two-relaxation time solution exhibits both oscillatory and non-oscillatory terms, and the interface temperature at the Crack Edge is finite.
K. B. Broberg - One of the best experts on this subject based on the ideXlab platform.
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Significance of morphology changes at a propagating Crack Edge
International Journal of Fracture, 2004Co-Authors: K. B. BrobergAbstract:During dynamic Crack propagation, several distinct changes in the morphology of the dissipative region near the Crack Edge occur, and they have a pronounced influence on the main propagation mechanism. There are also distinct morphological differences between mode I and mode II. For mode I Crack expansion, four successive generations of localization may be observed: micro-separations coalescing with the main Crack, protruding clusters of micro-separations, micro-branches, and finally (macro-)branches. The region of localizations is increasing laterally from the main Crack plane with Crack growth and velocity, as it appears, because of high normal stresses in planes normal to the Crack direction. If sufficient space is available, an expanding mode I Crack accelerates to a constant velocity, which appears to prevail even after branching and multiple-branching. This indicates an amazing self-similarity over the four generations of localization. The morphology changes during Crack propagation depend both on the magnitude of the applied load and on the travelled length of the Crack Edge. For mode II, the energy dissipation seems generally to be much more concentrated to the Crack plane than for mode I. A main reason appears to be that normal stresses in planes normal to the Crack direction are comparatively small in front of the Crack. Therefore, strong micro-separation localizations seem to appear mainly in shear planes parallel with the Crack plane. The appearance of such localizations may be analogous to the remarkable flow velocity gradient discontinuity discovered in turbulent shear flow near a wall.As a consequence of the apparently stronger concentration of the dissipative region to the Crack plane, a mode II Crack can reach higher velocities than a mode I Crack, and it may even reach intersonic velocities.
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Constant velocity Crack propagation––dependence on remote load
International Journal of Solids and Structures, 2002Co-Authors: K. B. BrobergAbstract:It is argued that continuum scaling applies for the dissipative region at a fast running Crack Edge. Then, a self-similar solution is possible for an expanding Crack in a large plate. Analysis of this solution not only shows that a constant terminal velocity is reached, but also that this velocity is dependent on the remote load. However, the magnitude of this velocity may not be uniquely related to the remote load, but also dependent on features of the acceleration phase.
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Intersonic Crack Propagation in an Orthotropic Material
International Journal of Fracture, 1999Co-Authors: K. B. BrobergAbstract:Intersonic Crack propagation is found to exhibit essentially the same features in orthotropic and isotropic materials, provided that the Crack propagates along a plane of elastic symmetry. Thus the stress and strain singularity at the Crack Edge is weaker than the inverse square root singularity in the sub-Rayleigh case, except at one distinct velocity. The energy flux into the process region is determined by using the Barenblatt model. It depends on the Crack velocity and on the size of the process region, approaching zero with this size.
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Cracks and fracture
1999Co-Authors: K. B. BrobergAbstract:"Cracks and Fracture" consists of nine chapters in logical sequence. In two introductory chapters, physical processes in the vicinity of the Crack Edge are discussed and the fracture process is described. Chapter 3 develops general basic concepts and relations in Crack mechanics, such as path independent integrals, stress intensity factors and energy flux into the Crack Edge region. Chapters 4-7 deal with elastostatic Cracks, stationary or slowly moving elastic-plastic Cracks, elastodynamic Crack mechanics and elastoplastic aspects of fracture, including dynamic fracture mechanics. Appendices include general formulae, the basic theory of analytic functions, introduction to Laplace and Hankel transforms and description of certain basic relations, for instance for stress waves in solids. There is an extensive bibliography, containing references to both classical and recent work, and a comprehensive index. It presents an extensive bibliography containing references to both classical and recent works and a comprehensive index. Appendices include general formulas, the basic theory of analytic functions, introduction to Laplace and Hankel transforms, and descriptions of certain basic relations, for instance for stress waves in solids.
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Crack expanding with constant velocity in an anisotropic solid under anti-plane strain
International Journal of Fracture, 1998Co-Authors: K. B. BrobergAbstract:An analytic solution is given for a Crack expanding with constant velocity from zero length in an anisotropic material under anti-plane strain. Not all anisotropic materials can support anti-plane strain, and the study is therefore by necessity limited to a certain class of materials, including monoclinic materials. A double Laplace transform is used and the inversion technique is based on the self-similarity of the problem. The result shows that the Crack shape is elliptic, as in the corresponding isotropic case. The displacement on the Crack plane outside the Crack is found to be zero. Expressions are given for the stresses, the stress intensity factor and the energy flux into the Crack Edge. In contrast to the isotropic case a transverse normal stress may appear, singular at the Crack Edge.
Xiaohua Zhao - One of the best experts on this subject based on the ideXlab platform.
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Exact solutions of stress intensity factor histories for a half plane Crack in a transversely isotropic solid under transient point shear loading on the Crack faces
International Journal of Solids and Structures, 2004Co-Authors: Xiaohua ZhaoAbstract:Abstract Three-dimensional analysis is performed for a transversely isotropic solid containing a half plane Crack subjected to point shear forces varying with time as a Heaviside function on the Crack faces at a finite distance from the Crack Edge. The solution of this problem is treated as the superposition of two sub-problems. One considers the transient waves in an elastic half space due to the point shear loading on the surface, while the other concerns the half space with its surface subjected to such distributed shear forces that the tangential surface displacements ahead of the Crack Edge induced by sub-problem 1 can be canceled out. A half space subjected to a distributed dislocation on the surface is constructed as the fundamental problem, which is solved by the use of integral transforms, the Wiener–Hopf technique and the Cagniard-de Hoop method. Exact expressions are derived for the modes II and III stress intensity factors as functions of time and position along the Crack Edge. Some features of the solutions are discussed through numerical results.
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The stress-intensity factor history for a half plane Crack in a transversely isotropic solid due to impact point loading on the Crack faces
International Journal of Solids and Structures, 2001Co-Authors: Xiaohua ZhaoAbstract:Abstract Three-dimensional analysis is performed for a transversely isotropic solid containing a half plane Crack subjected to suddenly applied concentrated point forces acting at a finite distance from the Crack Edge. The solution of this problem is treated as the superposition of two simpler problems. One considers the transient wave in an elastic half space generated by an impact point loading on the surface, the other problem is that which cancels out the surface displacement ahead of the Crack Edge induced by problem 1. A half space subjected to a distributed dislocation on the surface is constructed as the fundamental problem and solved by the use of integral transforms, the Wiener–Hopf technique and the Cagniard-de Hoop method. An exact expression is derived for the mode I stress-intensity factor as a function of time and position along the Crack Edge. Some features of the solution are discussed through numerical results.
Wangtongqing - One of the best experts on this subject based on the ideXlab platform.
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The Crack Edge enhancement of straddle-type monorail track beam surface based on non-subsampled contourlet transform
Journal of Computer Applications in Technology, 2012Co-Authors: Guochunhua, WangtongqingAbstract:This article introduces a new algorithm of Crack Edge enhancement of straddle-type monorail track beam surface based on non-subsampled contourlet transform (NSCT). According to the characteristics ...
N. Eliaz - One of the best experts on this subject based on the ideXlab platform.
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Study of fracture evolution in copper sheets by in situ tensile test and EBSD analysis
Journal of Materials Science, 2010Co-Authors: S. Ifergane, Z. Barkay, O. Beeri, N. EliazAbstract:Microstructural changes during plastic deformation and fracture evolution play an important role in the understanding of fracture mechanisms. However, most publications have focused on the initial stages of deformation where the latter is uniform. The current study was focused on the last stages of fracture, the necking, and Crack propagation. Tensile specimens were examined by in situ scanning electron microscope equipped with a tensile module and electron backscatter diffraction. It was demonstrated that the fracture evolution consists of scanty diffuse necking followed by pronounced localized necking, in which the deformation band spread through the width of the specimen in two combined mechanisms—shearing and dimpling. The microstructural changes inside the deformation band adjacent to Crack Edge were compared to those in the uniform deformation zone. In the deformed areas, the grains became elongated and preferentially orientated in the loading direction. The relative frequency of twin boundaries at 60° was reduced in the deformed areas compared to non-deformed areas, while the misorientations at low angles of 3°–15°, which imply on a dislocation pileups subgrained structure, were increased to greater extent at the Crack Edge. Inside the deformation band, the amount of deformation was increased compared to the uniformly deformed region with grain fragments as a result of the complexity of stresses, although similar deformation mechanisms were identified.
