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Mica Grujicic - One of the best experts on this subject based on the ideXlab platform.
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a comparative discrete dislocation nonlocal crystal plasticity analysis of plane strain mode i fracture
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: D. Columbus, Mica GrujicicAbstract:Abstract Crack growth associated with plane-strain mode I loading is studied computationally using both a discrete-dislocation approach and a nonlocal crystal-plasticity formulation. Within the discrete-dislocation approach, the material is modeled as a Linear Elastic Solid which contains discrete dislocations capable of moving and interacting with each other and with other lattice defects either at a distance through their stress fields, or through direct contact. In the case of nonlocal crystal-plasticity, the effect of the plastic strain gradient on the materials’ behavior is incorporated through the contribution that the geometrically necessary dislocations make to the rate of strain hardening. In both formulations, the behavior of the crack is modeled using a cohesive zone approach. The results show that while both approaches yield comparable stress and strain fields around the crack tip, the global (stress intensity versus crack extension) responses as well as the crack tip profiles can be significantly different in the two cases. These differences are related to the ways crystallographic slip is modeled in the two approaches.
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A comparative discrete-dislocation/nonlocal crystal-plasticity analysis of plane-strain mode I fracture
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: D. Columbus, Mica GrujicicAbstract:Abstract Crack growth associated with plane-strain mode I loading is studied computationally using both a discrete-dislocation approach and a nonlocal crystal-plasticity formulation. Within the discrete-dislocation approach, the material is modeled as a Linear Elastic Solid which contains discrete dislocations capable of moving and interacting with each other and with other lattice defects either at a distance through their stress fields, or through direct contact. In the case of nonlocal crystal-plasticity, the effect of the plastic strain gradient on the materials’ behavior is incorporated through the contribution that the geometrically necessary dislocations make to the rate of strain hardening. In both formulations, the behavior of the crack is modeled using a cohesive zone approach. The results show that while both approaches yield comparable stress and strain fields around the crack tip, the global (stress intensity versus crack extension) responses as well as the crack tip profiles can be significantly different in the two cases. These differences are related to the ways crystallographic slip is modeled in the two approaches.
D. Columbus - One of the best experts on this subject based on the ideXlab platform.
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a comparative discrete dislocation nonlocal crystal plasticity analysis of plane strain mode i fracture
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: D. Columbus, Mica GrujicicAbstract:Abstract Crack growth associated with plane-strain mode I loading is studied computationally using both a discrete-dislocation approach and a nonlocal crystal-plasticity formulation. Within the discrete-dislocation approach, the material is modeled as a Linear Elastic Solid which contains discrete dislocations capable of moving and interacting with each other and with other lattice defects either at a distance through their stress fields, or through direct contact. In the case of nonlocal crystal-plasticity, the effect of the plastic strain gradient on the materials’ behavior is incorporated through the contribution that the geometrically necessary dislocations make to the rate of strain hardening. In both formulations, the behavior of the crack is modeled using a cohesive zone approach. The results show that while both approaches yield comparable stress and strain fields around the crack tip, the global (stress intensity versus crack extension) responses as well as the crack tip profiles can be significantly different in the two cases. These differences are related to the ways crystallographic slip is modeled in the two approaches.
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A comparative discrete-dislocation/nonlocal crystal-plasticity analysis of plane-strain mode I fracture
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2002Co-Authors: D. Columbus, Mica GrujicicAbstract:Abstract Crack growth associated with plane-strain mode I loading is studied computationally using both a discrete-dislocation approach and a nonlocal crystal-plasticity formulation. Within the discrete-dislocation approach, the material is modeled as a Linear Elastic Solid which contains discrete dislocations capable of moving and interacting with each other and with other lattice defects either at a distance through their stress fields, or through direct contact. In the case of nonlocal crystal-plasticity, the effect of the plastic strain gradient on the materials’ behavior is incorporated through the contribution that the geometrically necessary dislocations make to the rate of strain hardening. In both formulations, the behavior of the crack is modeled using a cohesive zone approach. The results show that while both approaches yield comparable stress and strain fields around the crack tip, the global (stress intensity versus crack extension) responses as well as the crack tip profiles can be significantly different in the two cases. These differences are related to the ways crystallographic slip is modeled in the two approaches.
Eric R. Dufresne - One of the best experts on this subject based on the ideXlab platform.
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Surface tension and the mechanics of liquid inclusions in compliant Solids
Soft Matter, 2014Co-Authors: Robert W. Style, John S. Wettlaufer, Eric R. DufresneAbstract:Eshelby's theory of inclusions has wide-reaching implications across the mechanics of materials and structures including the theories of composites, fracture, and plasticity. However, it does not include the effects of surface stress, which has recently been shown to control many processes in soft materials such as gels, elastomers and biological tissue. To extend Eshelby's theory of inclusions to soft materials, we consider liquid inclusions within an isotropic, compressible, Linear-Elastic Solid. We solve for the displacement and stress fields around individual stretched inclusions, accounting for the bulk Elasticity of the Solid and the surface tension (i.e. isotropic strain-independent surface stress) of the Solid–liquid interface. Surface tension significantly alters the inclusion's shape and stiffness as well as its near- and far-field stress fields. These phenomena depend strongly on the ratio of the inclusion radius, R, to an elastocapillary length, L. Surface tension is significant whenever inclusions are smaller than 100L. While Eshelby theory predicts that liquid inclusions generically reduce the stiffness of an Elastic Solid, our results show that liquid inclusions can actually stiffen a Solid when R < 3L/2. Intriguingly, surface tension cloaks the far-field signature of liquid inclusions when R = 3L/2. These results are have far-reaching applications from measuring local stresses in biological tissue, to determining the failure strength of soft composites.
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Surface tension and the mechanics of liquid inclusions in compliant Solids
arXiv: Soft Condensed Matter, 2014Co-Authors: Robert W. Style, John S. Wettlaufer, Eric R. DufresneAbstract:Eshelby's theory of inclusions has wide-reaching implications across the mechanics of materials and structures including the theories of composites, fracture, and plasticity. However, it does not include the effects of surface stress, which has recently been shown to control many processes in soft materials such as gels, elastomers and biological tissue. To extend Eshelby's theory of inclusions to soft materials, we consider liquid inclusions within an isotropic, compressible, Linear-Elastic Solid. We solve for the displacement and stress fields around individual stretched inclusions, accounting for the bulk Elasticity of the Solid and the surface tension (\textit{i.e.} isotropic strain-independent surface stress) of the Solid-liquid interface. Surface tension significantly alters the inclusion's shape and stiffness as well as its near- and far-field stress fields. These phenomenon depend strongly on the ratio of inclusion radius, $R$, to an elastocapillary length, $L$. Surface tension is significant whenever inclusions are smaller than $100L$. While Eshelby theory predicts that liquid inclusions generically reduce the stiffness of an Elastic Solid, our results show that liquid inclusions can actually stiffen a Solid when $R
P. Burgers - One of the best experts on this subject based on the ideXlab platform.
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Mode-III crack kinking with delay time: An analytical approximation
International Journal of Solids and Structures, 2003Co-Authors: P. BurgersAbstract:Abstract The singular part of the elastodynamic field in the vicinity of a propagating crack tip plays an important role in fracture mechanics considerations. The dynamic solution near a crack tip which branches or kinks is required to understand the observed bifurcation events in brittle materials. We consider a rather general time dependent stress wave loading incident at an arbitrary angle on a semi-infinite crack in a Linear Elastic Solid. To model the kinking of a stationary crack under stress wave loading correctly, a delay time for initiation of the new crack must be included which means the problem loses the property of self-similarity and makes it significantly more difficult. A perturbation method is used to obtain the dynamic stress intensity factor for the kinking crack. The method relies on solving simple problems which can be used with Linear superposition to solve the problem of a kinked crack. The solution is represented in a simple closed form as a function of the incident angle α of the stress wave, the kink angle δ, the kinking crack speed υ c , and the finite delay time t f . This gives more information about the effect of parameters on the solution than the purely numerical results. Finally, the maximum of the energy flux into the propagating kinked crack tip is found as a function of kink angle and crack tip velocity, and some implications of this are discussed.
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Dynamic mode I and mode II crack kinking including delay time effects
International Journal of Solids and Structures, 2003Co-Authors: P. BurgersAbstract:Abstract The dynamic stress intensity factor of an initially stationary semi-infinite crack in an unbounded Linear Elastic Solid which kinks at some time t , after the arrival of a stress wave is obtained as a function of crack tip velocity α c , kink angle δ , time t α and the delay time t 1 . A perturbation method, using the kinking angle δ as the perturbation parameter, is used. The solutions can be compared with numerical results and other approximate results for the case of t α = 0 and give excellent agreement for a large range of kinking angles. The results indicate that if a maximum energy release rate is accepted as a crack propagation criterion, then for both the incident stress wave parallel to the original crack faces and uniform dynamic loading applied to the original crack faces, the crack will propagate straight ahead of the original crack for any delay time.
J. B. Haddow - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional dynamic soil-structure interaction analysis in the time domain
Earthquake Engineering & Structural Dynamics, 1999Co-Authors: Xiong Zhang, J. L. Wegner, J. B. HaddowAbstract:A new numerical procedure is proposed for the analysis of three-dimensional dynamic soil-structure interaction in the time domain. In this study, the soil is modelled as a Linear Elastic Solid, however, the methods developed can be adapted to include the effects of soil non-Linearities and hysteretic damping in the soil. A substructure method, in which the unbounded soil is modelled by the scaled boundary finite-element method, is used and the structure is modelled by 8-21 variable-number-node three-dimensional isoparametric or subparametric hexahedral curviLinear elements. Approximations in both time and space, which lead to efficient schemes for calculation of the acceleration unit-impulse response matrix, are proposed for the scaled boundary finite-element method resulting in significant reduction in computational effort with little loss of accuracy. The approximations also lead to a very efficient scheme for evaluation of convolution integrals in the calculation of soil-structure interaction forces. The approximations proposed in this paper are also applicable to the boundary element method. These approximations result in an improvement over current methods. A three-dimensional Dynamic Soil-Structure Interaction Analysis program (DSSIA-3D) is developed, and seismic excitations (S-waves, P-waves, and surface waves) and externally applied transient loadings can be considered in analysis. The computer program developed can be used in the analysis of three-dimensional dynamic soil-structure interaction as well as in the analysis of wave scattering and diffraction by three-dimensional surface irregularities. The scattering and diffraction of seismic waves (P-, S-, and Rayleigh waves) by various three-dimensional surface irregularities are studied in detail, and the numerical results obtained are in good agreement with those given by other authors. Numerical studies show that thc new procedure is suitable and very efficient for problems which involve low frequencies of interest for earthquake engineering.