Power-Law Creep from Discrete Dislocation Dynamics

Keralavarma, Shyam M.; Çağın, Tahir; Arsenlis, A.; Benzerga, A. Amine

doi:10.1103/physrevlett.109.265504

Cited by 101 publications

(66 citation statements)

References 20 publications

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“…In the sought framework, the continuum theories of elasticity and stress-affected diffusion are used as a basis, and both glide and climb motion of dislocations are accounted for. Climb-enabled dislocation plasticity has known increasing interest in the past few years (Mordehai et al, 2008;Keralavarma et al, 2012;Davoudi et al, 2012;Ayas et al, 2014;Po and Ghoniem, 2014;Geslin et al, 2014); also see Raabe (1998); Gao et al (2010); Arsenlis et al (2012) and Geers et al (2014). This paper contains the theoretical foundations of the creep simulations reported by Keralavarma (2011) and Keralavarma et al (2012) and reports additional simulations.…”

Section: Introductionmentioning

confidence: 93%

“…Mordehai et al (2008) developed an analytical climb kinetic model that takes explicit account of the osmotic force contribution using equilibrium solutions for the climb rate of dislocations in a prescribed uniform vacancy field. Their kinetic law was used in 3D DD simulations of diffusion-controlled dislocation loop coarsening (Bakó et al, 2011) and irradiation hardening in BCC iron as well as in 2D DD simulations of thin films (Davoudi et al, 2012) and creep (Keralavarma et al, 2012). Gao et al (2010) included the effect of pipe diffusion in a 3D DD simulation, but neglecting bulk diffusion.…”

Section: Introductionmentioning

confidence: 99%

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High-temperature discrete dislocation plasticity

Keralavarma

Benzerga

2015

Journal of the Mechanics and Physics of Solids

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A framework for solving problems of dislocation-mediated plasticity coupled with point-defect diffusion is presented. The dislocations are modeled as line singularities embedded in a linear elastic medium while the point defects are represented by a concentration field as in continuum diffusion theory. Plastic flow arises due to the collective motion of a large number of dislocations. Both conservative (glide) and nonconservative (diffusion-mediated climb) motions are accounted for. Time scale separation is contingent upon the existence of quasi-equilibrium dislocation configurations. A variational principle is used to derive the coupled governing equations for point-defect diffusion and dislocation climb. Superposition is used to obtain the mechanical fields in terms of the infinite-medium discrete dislocation fields and an image field that enforces the boundary conditions while the point-defect concentration is obtained by solving the stress-dependent diffusion equations on the same finite-element grid. Core-level boundary conditions for the concentration field are avoided by invoking an approximate, yet robust kinetic law. Aspects of the formulation are general but its implementation in a simple plane strain model enables the modeling of high-temperature phenomena such as creep, recovery and relaxation in crystalline materials. With emphasis laid on lattice vacancies, the creep response of planar single crystals in simple tension emerges as a natural outcome in the simulations. A large number of boundary-value problem solutions are obtained which depict transitions from diffusional to power-law creep, in keeping with long-standing phenomenological theories of creep. In addition, some unique experimental aspects of creep in small scale specimens are also reproduced in the simulations.

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

High-temperature discrete dislocation plasticity

Keralavarma

Benzerga

2015

Journal of the Mechanics and Physics of Solids

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“…Recent discrete dislocation dynamics (DDD) simulations that incorporate both glide and climb have reproduced responses consistent with both diffusional and power law creep in fcc metals 19 . It therefore appears that the length scales, dislocation den-sities, and underlying mechanisms relevant to some forms of power law creep may be accessible with this type of coarse grained description.…”

Section: Creep Phenomenologymentioning

confidence: 99%

Atomistic study of diffusion-mediated plasticity and creep using phase field crystal methods

et al. 2015

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The nonequilibrium dynamics of diffusion-mediated plasticity and creep in materials subjected to constant load at high homologous temperatures is studied atomistically using Phase Field Crystal (PFC) methods. Creep stress and grain size exponents obtained for nanopolycrystalline systems, m 1.02 and p 1.98, respectively, closely match those expected for idealized diffusional NabarroHerring creep. These exponents are observed in the presence of significant stress-assisted diffusive grain boundary migration, indicating that Nabarro-Herring creep and stress-assisted boundary migration contribute in the same manner to the macroscopic constitutive relation. When plastic response is dislocation-mediated, power law stress exponents inferred from dislocation climb rates are found to increase monotonically from m 3, as expected for generic climb-mediated natural creep, to m 5.8 as the dislocation density ρ d is increased beyond typical experimental values. Stress exponents m 3 directly measured from simulations that include dislocation nucleation, climb, glide, and annihilation are attributed primarily to these large ρ d effects. Extrapolation to lower ρ d suggests that m 4 − 4.5 should be obtained from our PFC description at typical experimental ρ d values, which is consistent with expectations for power law creep via mixed climb and glide. The anomalously large stress exponents observed in our atomistic simulations at large ρ d may nonetheless be relevant to systems in which comparable densities are obtained locally within heterogeneous defect domains such as dislocation cell walls or tangles. The tendency of a solid material to gradually and irreversibly deform or even flow under low loads at high temperatures is termed creep deformation 1-6 . Low loads and high temperatures in this context are σ σ y and T T m /2, respectively, where σ y is the yield stress and T m is the equilibrium melting temperature of the material. This type of slow plasticity not only alters material microstructure, shape, and properties over extended time periods, but is also a primary cause of mechanical failure in materials such as gas turbine blades that operate in high temperature load bearing environments 1-3 .The plastic flow that occurs during creep can involve conservative defect evolution mechanisms, such as dislocation glide and grain boundary sliding, but is generally facilitated by thermally activated defect motion along local stress and/or chemical potential gradients, and is therefore inherently diffusive in nature. Vacancy diffusion in particular tends to be a central facilitator of deformation, either directly during diffusional creep or indirectly during dislocation or power law creep, as discussed further in the following. Moreover, it is the collective evolution of different defect populations over multiple length and time scales that leads to the observed diverse macroscopic phenomenology of creep. If the characteristic time scales associated with the diffusion of individual defects are almost entirely inaccessible to most at...

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“…Numerical analysis of the phenomenon is challenging due to the complexity of incorporating both vacancies and dislocations in a single computational framework. Only recently two-dimensional DD simulations are performed illustrating dislocation glide and climb such that power law creep phenomenon can be reproduced (Keralavarma et al 2012).…”

Section: Modeling Approachesmentioning

confidence: 99%

Analysis of Inelastic Behavior for High Temperature Materials and Structures

Naumenko

Altenbach

2015

Advanced Structured Materials

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This review provides a current status in modeling and analysis of structures for high-temperature applications. Basic features of inelastic behavior of heat resistant alloys are discussed. Typical responses for stationary and varying loading and temperature are presented and classified. Microstructural features and microstructural changes in the course of inelastic deformation at high temperature are discussed. The state of the art on material modeling and structural analysis in the inelastic range at high temperature is resented.Keywords Creep · Low cycle fatigue · Damage mechanics · Length scales · Temporal scales · Structural analysis IntroductionThe aim of this contribution is to give an overview of experimental and theoretical approaches to analyze the behavior of materials and structures subjected to mechanical loading and "high-temperature" environment. The definition of "hightemperature" materials and "high-temperature" structures can be related to the value of the homologous temperature, that is T /T m , where T is the absolute temperature and T m is the melting point of the considered material. Materials that can be efficiently used within the temperature range 0.3 < T /T m < 0.7 are called hightemperature materials. Examples include heat resistant steels, nickel-bases alloys, age-hardened aluminum alloys, cast iron materials and metal matrix composites. Structures that operate in the temperature range 0.3 < T /T m < 0.7 over a long period of time are called high-temperature structures. Examples include turbine

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Power-Law Creep from Discrete Dislocation Dynamics

Cited by 101 publications

References 20 publications

High-temperature discrete dislocation plasticity

High-temperature discrete dislocation plasticity

Atomistic study of diffusion-mediated plasticity and creep using phase field crystal methods

Analysis of Inelastic Behavior for High Temperature Materials and Structures

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