The Experts below are selected from a list of 54 Experts worldwide ranked by ideXlab platform
G E Exadaktylos - One of the best experts on this subject based on the ideXlab platform.
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gradient elasticity with surface energy mode i Crack problem
International Journal of Solids and Structures, 1998Co-Authors: G E ExadaktylosAbstract:Abstract The solution of the mode-I Crack problem is given by using an anisotropic strain-gradient elasticity theory with surface energy, extending previous results by Vardoulakis and co-workers, as well as by Aifantis and co-workers. The solution of the problem is derived by applying the Fourier transform technique and the theory of dual integral and Fredholm integral equations. Asymptotic analysis of the solution close to the tip gives a cusping Crack with zero slope of the Crack Displacement at the Crack tip. Cusping of the Crack tips is caused by the action of “cohesive” double forces behind and very close to the tips, that tend to bring the two opposite Crack lips in close contact. Consideration of Griffith's energy balance approach leads to the formulation of a fracture criterion that predicts a linear dependence of the specific fracture surface energy on increment of Crack propagation for such Crack length increments that are comparable with the characteristic size of material's microstructure. This important theoretical result agrees with experimental measurements of the fracture energy dissipation rate during fracturing of polycrystalline, polyphase materials such as rocks and ceramics. The potential of the theory to interpret the size effect, i.e. the dependence of fracture toughness of the material on the size of the Crack, is also presented. Also, the theory predicts an inverse first power relation between the tensile strength and the size of the pre-existing Crack which is in accordance with experimental evidence. Furthermore, it is shown that the effect of the volumetric strain-gradient term is to shield the applied loads leading to Crack stiffening, hence the theory captures the commonly observed phenomenon of high-effective fracture energies of rocks and ceramics; the effect of the surface strain-energy term is to amplify the applied loads leading to Crack compliance and essentially captures the development of the “process zone” or microCracking zone around the main Crack in a brittle material. Thus, the present anisotropic gradient elasticity theory with surface energy provides an effective tool for understanding phenomenologically main Crack-microdefect interaction phenomena in brittle materials.
Baolin Wang - One of the best experts on this subject based on the ideXlab platform.
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fracture mechanics analysis of an anti plane Crack in gradient elastic sandwich composite structures
International Journal of Mechanics and Materials in Design, 2019Co-Authors: Jine Li, Baolin WangAbstract:The strain gradient elasticity theory is applied to the solution of a mode III Crack in an elastic layer sandwiched by two elastic layers of infinite thickness. The model includes volumetric and surface strain gradient characteristic length parameters. Both the near-tip asymptotic stresses and the Crack Displacement are obtained. Due to stain gradient effects, the magnitudes of the stress ahead of the Crack tip are significantly higher than those in the classical linear elastic fracture mechanics. When the gradient parameters reduce to sufficiently small, all results reduce to the conventional linear elastic fracture mechanics results. In addition to the single Crack in the finite layer, the solution and the results for two collinear Cracks are also established and given.
Timothy S Fisher - One of the best experts on this subject based on the ideXlab platform.
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near Crack contour behaviour and extraction of log singular stress terms of the self regular traction boundary integral equation
International Journal for Numerical Methods in Engineering, 2003Co-Authors: Ariosto Bretanha Jorge, T A Cruse, Timothy S FisherAbstract:This work contains an analytical study of the asymptotic near-Crack contour behaviour of stresses obtained from the self-regular traction-boundary integral equation (BIE), both in two and in three dimensions, and for various Crack Displacement modes. The flat Crack case is chosen for detailed analysis of the singular stress for points approaching the Crack contour. By imposing a condition of bounded stresses on the Crack surface, the work shows that the boundary stresses on the Crack are in fact zero for an unloaded Crack, and the interior stresses reproduce the known inverse square root behaviour when the distance from the interior point to the Crack contour approaches zero. The correct order of the stress singularity is obtained after the integrals for the self-regular traction-BIE formulation are evaluated analytically for the assumed Displacement discontinuity model. Based on the analytic results, a new near-Crack contour self-regular traction-BIE is proposed for collocation points near the Crack contour. In this new formulation, the asymptotic log-singular stresses are identified and extracted from the BIE. Log-singular stress terms are revealed for the free integrals written as contour integrals and for the self-regularized integral with the integration region divided into sub-regions. These terms are shown to cancel each other exactly when combined and can therefore be eliminated from the final BIE formulation. This work separates mathematical and physical singularities in a unique manner. Mathematical singularities are identified, and the singular information is all contained in the region near the Crack contour. Copyright © 2003 John Wiley & Sons, Ltd.
Exadaktylos Georgios(http://users.isc.tuc.gr/~gexadaktylos) - One of the best experts on this subject based on the ideXlab platform.
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Gradient elasticity with surface energy: mode-I Crack problem
'Elsevier BV', 1998Co-Authors: Εξαδακτυλος Γεωργιος(http://users.isc.tuc.gr/~gexadaktylos), Exadaktylos Georgios(http://users.isc.tuc.gr/~gexadaktylos)Abstract:Summarization: The solution of the mode-I Crack problem is given by using an anisotropic strain-gradient elasticity theory with surface energy, extending previous results by Vardoulakis and co-workers, as well as by Aifantis and co-workers. The solution of the problem is derived by applying the Fourier transform technique and the theory of dual integral and Fredholm integral equations. Asymptotic analysis of the solution close to the tip gives a cusping Crack with zero slope of the Crack Displacement at the Crack tip. Cusping of the Crack tips is caused by the action of “cohesive” double forces behind and very close to the tips, that tend to bring the two opposite Crack lips in close contact. Consideration of Griffith's energy balance approach leads to the formulation of a fracture criterion that predicts a linear dependence of the specific fracture surface energy on increment of Crack propagation for such Crack length increments that are comparable with the characteristic size of material's microstructure. This important theoretical result agrees with experimental measurements of the fracture energy dissipation rate during fracturing of polycrystalline, polyphase materials such as rocks and ceramics. The potential of the theory to interpret the size effect, i.e. the dependence of fracture toughness of the material on the size of the Crack, is also presented. Also, the theory predicts an inverse first power relation between the tensile strength and the size of the pre-existing Crack which is in accordance with experimental evidence. Furthermore, it is shown that the effect of the volumetric strain-gradient term is to shield the applied loads leading to Crack stiffening, hence the theory captures the commonly observed phenomenon of high-effective fracture energies of rocks and ceramics; the effect of the surface strain-energy term is to amplify the applied loads leading to Crack compliance and essentially captures the development of the “process zone” or microCracking zone around the main Crack in a brittle material. Thus, the present anisotropic gradient elasticity theory with surface energy provides an effective tool for understanding phenomenologically main Crack-microdefect interaction phenomena in brittle materials.Presented on: International Journal of Solids and Structure
Ferdinand S. Rostásy - One of the best experts on this subject based on the ideXlab platform.
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bond failure of concrete fiber reinforced polymer plates at inclined Cracks experiments and fracture mechanics model
Fourth International Symposium on Fiber Reinforced Polymer Reinforcement for Reinforced Concrete StructuresAmerican Concrete Institute (ACI), 1999Co-Authors: U Neubauer, Ferdinand S. RostásyAbstract:Bond failure is mostly brittle and often occurs a few millimeters deep in the concrete. A fracture mechanics-based engineering model of bond strength for this failure type, derived from pure bond tests exists. In a beam vertical shear Crack, mouth Displacements can reduce bond strength by reducing the total fracture energy required to destroy the local bond. To quantify this effect, the shear Crack mouth Displacements have to be calculated, dependent on the acting forces, the geometry, the reinforcement and the material parameters of the beam. Then a mixed mode fracture mechanics approach is used to quantify the of bond strength due to simultaneous action of bending and shear. In most cases, bond strength reduction due to vertical shear Crack Displacement will range around 5-10%. In CFRP-plates another type of debonding failure, specific to fiber reinforced plastics was observed. Interlaminar failure in the plate, preferably occurring with higher-strength concrete is considered a mixed mode fracture problem and was investigated by simultaneous measurements of the Mode I and mode II Displacements of the bond Crack with electronic speckle pattern interferometry (ESPI). A fracture mechanics approach to a criterion for interlaminar plate failure was derived. According to this, a surface tensile strength of the concrete of more than 3,0 MPa cannot be taken advantage of in design, since interlaminar plate failure will then govern bond failure.
