The Experts below are selected from a list of 37845 Experts worldwide ranked by ideXlab platform
J W Hutchinson - One of the best experts on this subject based on the ideXlab platform.
-
Crack Tip fields in strain gradient plasticity
Journal of the Mechanics and Physics of Solids, 1996Co-Authors: Z. Cedric Xia, J W HutchinsonAbstract:Solutions are presented for mode I and mode II Crack Tip fields for plane strain deformations of an elastic-plastic solid whose constitutive behavior depends on both strains and strain gradients. The constitutive law is the simplest generalization of the J2 deformation theory of plasticity to include strain gradient effects. Only one new constitutive parameter enters, a length parameter characterizing the scale over which gradient effects become important. The formulation is cast within the framework of coupled stress theory. Crack Tip solutions are obtained which display the transition from the HRR fields, governing behavior in an intermediate region with the plastic zone, to the dominant fields at the Tip. The dominant fields are obtained in closed form, and finite element methods have been used to produce the solution over the entire field. Some of the difficulties encountered in arriving at an accurate numerical scheme are detailed. Implications of the solutions for fracture are discussed, as are avenues for further research.
K. C. Hwang - One of the best experts on this subject based on the ideXlab platform.
-
Non-existence of separable Crack Tip field in mechanism-based strain gradient plasticity
International Journal of Solids and Structures, 2000Co-Authors: M.x. Shi, Yonggang Huang, Huajian Gao, K. C. HwangAbstract:We investigate the structure of asymptotic Crack Tip fields associated with the recently developed theory of mechanism-based strain gradient (MSG) plasticity. The MSG plasticity theory directly connects micron scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor’s dislocation hardening model to strain gradient plasticity. We show that the Crack Tip field in MSG plasticity does not have a separable form of solution. In contrast, all previously known asymptotic fields around stationary Crack Tips have separable form of solutions such as the classical K field, HRR field, Crack Tip field in the couple stress theory of strain gradient plasticity, and the Crack Tip field in the Fleck–Hutchinson phenomenological theory of strain gradient plasticity. The physical significance of this lack of separable solution of the Crack Tip field in MSG plasticity is that stresses at a distance on the order of dislocation spacing from a Crack Tip can no longer be characterized by a single parameter as in classical J-controlled Crack Tip fields. This difficulty can be overcome by combining MSG plasticity theory with a cohesive model of fracture.
Stephan Schonecker - One of the best experts on this subject based on the ideXlab platform.
-
ductile and brittle Crack Tip response in equimolar refractory high entropy alloys
Acta Materialia, 2020Co-Authors: Douglas L Irving, L K Varga, Levente Vitos, Stephan SchoneckerAbstract:Abstract Understanding the strengthening and deformation mechanisms in refractory high-entropy alloys (HEAs), proposed as new high-temperature material, is required for improving their typically insufficient room-temperature ductility. Here, density-functional theory simulations and a continuum mechanics analysis were conducted to systematically investigate the competition between cleavage decohesion and dislocation emission from a Crack Tip in the body-centered cubic refractory HEAs HfNbTiZr, MoNbTaVW, MoNbTaW, MoNbTiV, and NbTiVZr. This Crack-Tip competition is evaluated for tensile loading and a totality of 15 Crack configurations and slip systems. Our results predict that dislocation plasticity at the Crack Tip is generally unfavorable – although the competition is close for some Crack orientations, suggesting intrinsic brittleness and low Crack-Tip fracture toughness in these five HEAs at zero temperature. Fluctuations in local alloy composition, investigated for HfNbTiZr, can locally reduce the resistance to dislocation emission for a slip system relative to the configuration average of that slip system, but do not change the dominant Crack-Tip response. In the case of single-crystal MoNbTaW, where an experimental, room-temperature fracture-toughness value is available for a Crack on a {100} plane, theoretical and experimental results agree favorably. Factors that may limit the agreement are discussed. We survey the effect of material anisotropy on preferred Crack Tip orientations, which are found to be alloy specific. Mixed-mode loadings are found to shift the competition in favor of cleavage or dislocation nucleation, depending on Crack configuration and amplified by the effect of material anisotropy on Crack Tip stresses.
N A Fleck - One of the best experts on this subject based on the ideXlab platform.
-
Mode I Crack Tip fields: strain gradient plasticity theory versus J2 flow theory
2019Co-Authors: Martinez-paneda E, N A FleckAbstract:The mode I Crack Tip asymptotic response of a solid characterised by strain gradient plasticity is investigated. It is found that elastic strains dominate plastic strains near the Crack Tip, and thus the Cauchy stress and the strain state are given asymptotically by the elastic K-field. This Crack Tip elastic zone is embedded within an annular elasto-plastic zone. This feature is predicted by both a Crack Tip asymptotic analysis and a finite element computation. When small scale yielding applies, three distinct regimes exist: an outer elastic K field, an intermediate elasto-plastic field, and an inner elastic K field. The inner elastic core significantly influences the Crack opening profile. Crack Tip plasticity is suppressed when the material length scale $\ell$ of the gradient theory is on the order of the plastic zone size estimation, as dictated by the remote stress intensity factor. A generalized J-integral for strain gradient plasticity is stated and used to characterise the asymptotic response ahead of a short Crack. Finite element analysis of a Cracked three point bend specimen reveals that the Crack Tip elastic zone persists in the presence of bulk plasticity and an outer J-field
-
Mode I Crack Tip fields: Strain gradient plasticity theory versus J2 flow theory
'Elsevier BV', 2019Co-Authors: Martinez-paneda E, N A FleckAbstract:The mode I Crack Tip asymptotic response of a solid characterised by strain gradient plasticity is investigated. It is found that elastic strains dominate plastic strains near the Crack Tip, and thus the Cauchy stress and the strain state are given asymptotically by the elastic K-field. This Crack Tip elastic zone is embedded within an annular elasto-plastic zone. This feature is predicted by both a Crack Tip asymptotic analysis and a finite element computation. When small scale yielding applies, three distinct regimes exist: an outer elastic K field, an intermediate elasto-plastic field, and an inner elastic K field. The inner elastic core significantly influences the Crack opening profile. Crack Tip plasticity is suppressed when the material length scale of the gradient theory is on the order of the plastic zone size estimation, as dictated by the remote stress intensity factor. A generalized J-integral for strain gradient plasticity is stated and used to characterise the asymptotic response ahead of a short Crack. Finite element analysis of a Cracked three point bend specimen reveals that the Crack Tip elastic zone persists in the presence of bulk plasticity and an outer J-field
-
Gradient effects on Crack Tip mechanics
2017Co-Authors: Martinez-paneda E, Cf Niordson, Vs Deshpande, N A FleckAbstract:In this work a general framework for damage and fracture assessment accounting for the role of geometrically necessary dislocations (GNDs) is provided. Crack Tip fields are characterized, within both infinitesimal and finite deformation theories, by means of different strain gradient plasticity (SGP) formulations and their finite element implementation. Moreover, the impact of SGP theories on fracture and damage problems is further assessed by modeling Crack growth initiation and subsequent resistance. Results show a strong influence of GNDs, revealing the need to incorporate its influence in continuum models in order to adequately characterize behavior at the small scales involved in Crack Tip deformation
Huajian Gao - One of the best experts on this subject based on the ideXlab platform.
-
Non-existence of separable Crack Tip field in mechanism-based strain gradient plasticity
International Journal of Solids and Structures, 2000Co-Authors: M.x. Shi, Yonggang Huang, Huajian Gao, K. C. HwangAbstract:We investigate the structure of asymptotic Crack Tip fields associated with the recently developed theory of mechanism-based strain gradient (MSG) plasticity. The MSG plasticity theory directly connects micron scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor’s dislocation hardening model to strain gradient plasticity. We show that the Crack Tip field in MSG plasticity does not have a separable form of solution. In contrast, all previously known asymptotic fields around stationary Crack Tips have separable form of solutions such as the classical K field, HRR field, Crack Tip field in the couple stress theory of strain gradient plasticity, and the Crack Tip field in the Fleck–Hutchinson phenomenological theory of strain gradient plasticity. The physical significance of this lack of separable solution of the Crack Tip field in MSG plasticity is that stresses at a distance on the order of dislocation spacing from a Crack Tip can no longer be characterized by a single parameter as in classical J-controlled Crack Tip fields. This difficulty can be overcome by combining MSG plasticity theory with a cohesive model of fracture.
-
Interfacial Crack-Tip field in anisotropic elastic solids
Journal of the Mechanics and Physics of Solids, 1992Co-Authors: Huajian Gao, M. Abbudi, David M. BarnettAbstract:Abstract For interfacial Cracks in anisotropic elastic solids, controversies exist in that several different definitions for the Crack-Tip field have been proposed in the literature. In this paper, we first devise a novel and convenient scheme for constructing the interfacial Crack fields and then carry out a mismatch analysis for understanding the oscillatory structure of the Crack-Tip stress singularity. It is hoped that the mismatch analysis can shed some light on the controversial issues from a different perspective. Among different definitions for the stress intensity factors, it is found that the solution proposed by Wu [Int. J. Solids Struct. 27, 455 (1991)] , which conforms to a general definition suggested by Rice [J. appl. Mech. 55, 98 (1988)] , is consistent with the analysis of local interface mismatch near the Crack Tip. Critical quantities governing the oscillation and mismatch are numerically evaluated for a number of materials including two fiber-reinforced composites and a group of crystals of cubic symmetry.