scispace - formally typeset
Author

Anand K. Kanjarla

Bio: Anand K. Kanjarla is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Grain boundary & Crystal twinning. The author has an hindex of 14, co-authored 36 publication(s) receiving 1379 citation(s). Previous affiliations of Anand K. Kanjarla include Los Alamos National Laboratory & Indian Institutes of Technology.

...read more

Papers
More filters

Journal ArticleDOI
Abstract: We present the infinitesimal-strain version of a formulation based on fast Fourier transforms (FFT) for the prediction of micromechanical fields in polycrystals deforming in the elasto-viscoplastic (EVP) regime This EVP extension of the model originally proposed by Moulinec and Suquet to compute the local and effective mechanical behavior of a heterogeneous material directly from an image of its microstructure is based on an implicit time discretization and an augmented Lagrangian iterative procedure The proposed model is first benchmarked, assessing the corresponding elastic and viscoplastic limits, the correct treatment of hardening, rate-sensitivity and boundary conditions, and the rate of convergence of the numerical method In terms of applications, the EVP–FFT model is next used to examine how single crystal elastic and plastic directional properties determine the distribution of local fields at different stages of deformation

...read more

371 citations


Journal ArticleDOI
01 Feb 2015-Acta Materialia
Abstract: We present here a numerical study of the distribution of the local stress state associated with deformation twinning in Mg, both inside the twinned domain and in its immediate neighborhood, due to the accommodation of the twinning transformation shear. A full-field elastoviscoplastic formulation based on fast Fourier transformation is modified to include the shear transformation strain associated with deformation twinning. We have performed two types of twinning transformation simulations with: (i) the twin completely embedded inside a single crystal and (ii) the twin front terminating at a grain boundary. We show that: (a) the resulting stress distribution is more strongly determined by the shear transformation than by the intragranular character of the twin or the orientation of the neighboring grain; (b) the resolved shear stress on the twin plane along the twin direction is inhomogeneous along the twin–parent interface; and (c) there are substantial differences in the average values of the shear stress in the twin and in the parent grain that contains the twin. We discuss the effect of these local stresses on twin propagation and growth, and the implications of our findings for the modeling of deformation twinning.

...read more

156 citations


Journal ArticleDOI
Abstract: Twinning in hexagonal close-packed (hcp) metals is a multi-scale process that depends on the microstructural and mechanical response details at the polycrystalline aggregate, grain, micro, and atomic scales. Twinning can generally be regarded as a two-step process, a nucleation event followed by propagation and growth. This articles presents a stochastic model for the nucleation of deformation twins in hcp polycrystals. Twin nucleation is modeled through its dependence on lower length scale material details, such as the defect configurations at potential nucleation sites within grain boundaries, and mechanical details such as highly localized stress concentrations at the microscale in a probabilistic manner. These two aspects, the material and mechanical, must align for a successful nucleation event. The nucleation process is cast as a survival model parameterized by the local stress at the grain boundary. The model gives an explicit form for the probability distribution for the critical stress values required for twin nucleation. The model is implemented into a viscoplastic self-consistent (VPSC) crystal plasticity framework in order to test its predictive capability against previously reported statistical characterization in deformed zirconium at multiple temperatures. For implementation in VPSC, the stress concentrations are sampled from a distribution calibrated to full-field crystal plasticity simulations and a three-dimensional model of grain neighbors and distribution of grain boundary areas are implemented.

...read more

122 citations


Journal ArticleDOI
Abstract: The response of polycrystals to plastic deformation is studied at the level of variations within individual grains, and comparisons are made to theoretical calculations using crystal plasticity (CP). We provide a brief overview of CP and a review of the literature, which is dominated by surface observations. The motivating question asks how well CP represents the mesoscale behavior of large populations of dislocations (as carriers of plastic strain). The literature shows consistently thatonly moderate agreementis foundbetween experimentandcal

...read more

113 citations


Journal ArticleDOI
Abstract: Micromechanical models aimed at simulating deformation textures and resulting plastic anisotropy need to incorporate local plastic strain heterogeneities arising from grain interactions for better predictions. The ALAMEL model [Van Houtte, P., Li, S., Seefeldt, M., Delannay, L 2005. Deformation texture prediction: from the Taylor model to the advanced Lamel model. Int. J. Plasticity 21, 589-624], is one of the models in which the heterogeneous nature of plastic deformation in metals is introduced by accounting for the influence of a grain boundary on the cooperative deformation of adjacent grains. This is achieved by assuming that neighbouring grains undergo heterogeneous shear rates parallel to the grain boundary. The present article focuses on understanding the plastic deformation fields near the grain boundaries and the influence of grain interaction on intra-grain deformations. Crystal Plasticity Finite Element Method (CPFEM) is employed on a periodic unit cell consisting of four grains discretised into a large number of elements. A refined study of the local variation of strain rates, both along and perpendicular to the grain boundaries permits an assessment of the assumptions made in the ALAMEL model. It is shown that the ALAMEL model imbibes the nature of plastic deformation at the grain boundaries very well. However, near triple junctions, the influence of a third grain induces severe oscillations of the stress tensor, reflecting a singularity. According to CPFEM, such singularity can lead to grain subdivision by the formation of new boundaries originating at the triple junction. (C) 2009 Elsevier Ltd. All rights reserved.

...read more

96 citations


Cited by
More filters

Steven J. Plimpton1Institutions (1)
01 May 1993-
TL;DR: Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems.

...read more

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

...read more

24,496 citations


Journal ArticleDOI
Franz Roters1, Philip Eisenlohr1, L. Hantcherli1, D. D. Tjahjanto1  +2 moreInstitutions (2)
01 Feb 2010-Acta Materialia
Abstract: This article reviews continuum-based variational formulations for describing the elastic–plastic deformation of anisotropic heterogeneous crystalline matter. These approaches, commonly referred to as crystal plasticity finite-element models, are important both for basic microstructure-based mechanical predictions as well as for engineering design and performance simulations involving anisotropic media. Besides the discussion of the constitutive laws, kinematics, homogenization schemes and multiscale approaches behind these methods, we also present some examples, including, in particular, comparisons of the predictions with experiments. The applications stem from such diverse fields as orientation stability, microbeam bending, single-crystal and bicrystal deformation, nanoindentation, recrystallization, multiphase steel (TRIP) deformation, and damage prediction for the microscopic and mesoscopic scales and multiscale predictions of rolling textures, cup drawing, Lankfort ( r ) values and stamping simulations for the macroscopic scale.

...read more

1,288 citations


Journal ArticleDOI
Abstract: We present the infinitesimal-strain version of a formulation based on fast Fourier transforms (FFT) for the prediction of micromechanical fields in polycrystals deforming in the elasto-viscoplastic (EVP) regime This EVP extension of the model originally proposed by Moulinec and Suquet to compute the local and effective mechanical behavior of a heterogeneous material directly from an image of its microstructure is based on an implicit time discretization and an augmented Lagrangian iterative procedure The proposed model is first benchmarked, assessing the corresponding elastic and viscoplastic limits, the correct treatment of hardening, rate-sensitivity and boundary conditions, and the rate of convergence of the numerical method In terms of applications, the EVP–FFT model is next used to examine how single crystal elastic and plastic directional properties determine the distribution of local fields at different stages of deformation

...read more

371 citations


Journal Article
Abstract: A theory is developed which allows one to discuss the stability of multiply-twinned particles and to calculate critical sizes for stable and quasi-stable states. An icosahedral particle is essentially stable for r ≦ r i w * , quasi-stable for r i w * r i t 0 where r is an edge length of the particle, while a decahedral particle is not essentially stable but quasi-stable for r ≦ r d t 0 and unstable for r > r d t 0 . The critical sizes r i w * , r i t 0 and r d t 0 are formulated as functions of the specific surface energy γ h k l , the twin boundary energy γ t , the elastic strain energy W and the adhesive energy γ a to the substrate. Calculated critical diameters 2 r i w * ,2 r i t 0 and 2 r d t 0 for the particles grown in free space for several elements range between 15.5A and 106.8A, between 109.8A and 486.1A and between 725A and 3961A, respectively. These values are in good agreement with experimental results.

...read more

361 citations


Book
09 Oct 2012-
TL;DR: This review presents the MSD framework in the context of both the engineering advances that have led to its creation, and those that complement or provide alternative methods for design of materials (meaning ‘optimization of material structure’ in this context).

...read more

Abstract: The accelerating rate at which new materials are appearing, and transforming the engineering world, only serves to emphasize the vast potential for novel material structure, and related performance. Microstructure-sensitive design (MSD) aims at providing inverse design methodologies that facilitate design of material internal structure for performance optimization. Spectral methods are applied across the structure, property and processing design spaces in order to compress the computational requirements for linkages between the spaces and enable inverse design. Research has focused mainly on anisotropic, polycrystalline materials, where control of local crystal orientation can result in a broad range of property combinations. This review presents the MSD framework in the context of both the engineering advances that have led to its creation, and those that complement or provide alternative methods for design of materials (meaning ‘optimization of material structure’ in this context). A variety of definitions for the structure of materials are presented, with an emphasis on correlation functions; and spectral methods are introduced for compact descriptions and efficient computations. The microstructure hull is defined as the design space for structure in the spectral framework. Reconstruction methods provide invertible links between statistical descriptions of structure, and deterministic instantiations. Subsequently, structure–property relations are reviewed, and again subjected to representation via spectral methods. The concept of a property closure is introduced as the design space for performance optimization, and methods for moving between the closures and hulls are presented as the basis for the subsequent discussion on microstructure design. Finally, the spectral framework is applied to deformation processes, and methodologies that facilitate process design are reviewed.

...read more

324 citations


Network Information
Related Authors (5)
Manoj Settem

7 papers, 23 citations

84% related
Ricardo A. Lebensohn

214 papers, 10.9K citations

64% related
Laurent Delannay

118 papers, 2.9K citations

63% related
Carlos N. Tomé

244 papers, 20.2K citations

61% related
Rohit Kumar Gupta

3 papers, 17 citations

60% related
Performance
Metrics

Author's H-index: 14

No. of papers from the Author in previous years
YearPapers
20221
20216
20204
20194
20183
20162

Top Attributes

Show by:

Author's top 5 most impactful journals