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Anand K. Kanjarla

Bio: Anand K. Kanjarla is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Materials science & Grain boundary. The author has an hindex of 14, co-authored 36 publications receiving 1379 citations. Previous affiliations of Anand K. Kanjarla include Los Alamos National Laboratory & Indian Institutes of Technology.

Papers
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Journal ArticleDOI
24 Jan 2013-JOM
TL;DR: In this paper, the authors present a stochastic constitutive law for twin nucleation in hexagonal close-packed (hcp) materials and describe its implementation into a homogenized crystal plasticity simulation.
Abstract: Twinning is an important deformation mechanism in hexagonal close-packed (hcp) metals such as Mg, Zr, Ti, and Be. Twinning in hcp materials is a multiscale process that depends on microstructural and mechanical response details at the mesoscale, microscale, and atomic scales. Twinning can generally be understood as a two-step process, a nucleation step followed by propagation. The nucleation of twins is governed by both material details such as the defect configurations at potential nucleation sites within grain boundaries, as well as the highly local mechanical field near grain boundaries. These two factors, the material and mechanical, must align for a successful nucleation event. In this article, we present a stochastic constitutive law for nucleation of twins and describe its implementation into a homogenized crystal plasticity simulation. Twin nucleation relies on the dissociation of grain boundary defects under stress into the required twinning partials. This dissociation is considered to follow a Poisson process where the parameters of the Poisson distribution are related to the properties of the grain boundaries. The rate of the process is a direct function of the local stress concentration at the grain boundary. These stress concentrations are randomly sampled from a distribution calibrated to full-field crystal plasticity simulations.

15 citations

Journal ArticleDOI
TL;DR: In this paper, the role of local interactions at the grain boundaries and of the initial orientation of the grain is investigated, and it is shown that a hard grain surrounded by relatively softer grains is prone to subdivide when subjected to opposing shears.
Abstract: In plastically deforming polycrystals, grains interact with their surroundings resulting in heterogeneous deformation fields both at inter- and intragrain level. When the crystal plasticity finite element method (CPFEM) is employed to predict such heterogeneity, splitting of grains is occasionally observed. In the present study, detailed local strain analysis is performed in such subdivided grain and its neighbors. The role of local interactions at the grain boundaries and of the initial orientation of the grain is investigated. It is shown that a hard grain surrounded by relatively softer grains is prone to subdivide when subjected to opposing shears.

15 citations

Journal ArticleDOI
TL;DR: In this article, a combination of experiments and modelling are used to address their effects on texture evolution in duplex stainless steels and conclude that only by accounting for the strong local interactions between the phases, the correct textures are predicted.
Abstract: Deformation twinning is known to be one of the reasons that cause texture transition (copper type to brass type) in single phase fcc materials and is studied extensively. The role of deformation twinning in two phase materials is an area yet to be explored. Similarly in two phase materials, the effect of one phase on the texture evolution of the other phase is not well understood. In this work, a combination of experiments and modelling are used to address their effects on texture evolution in duplex stainless steels. The material is cold rolled to 80% thickness reduction and texture evolution is studied at various strain levels. These are compared with a series of crystal plasticity simulations using the Taylor model and grain interaction based LAMEL model which was extended to a two phase material. Deformation twinning in austenite is incorporated by predominant twin reorientation (PTR) scheme. It is observed that only by accounting for the strong local interactions between the phases, the correct textures are predicted. The texture transition from { 001 } 〈 110 〉 to { 112 } 〈 110 〉 orientation observed in ferrite at higher strain levels is attributed to deformation twinning in austenite. A number of simulations with ideal orientations observed in fcc and bcc materials are performed to assess the role of one phase on texture evolution of the other. It is concluded that experimental observations are also required to comment on the dominant phase during texture evolution.

15 citations

Journal ArticleDOI
TL;DR: In this paper, a commercial magnesium alloy was processed through multi-pass and multi-directional (unidirectional, reverse, and transverse tool movements) friction stir processing (FSP).
Abstract: A commercial magnesium alloy was processed through multi-pass and multi-directional (unidirectional, reverse, and transverse tool movements) friction stir processing (FSP). Based on the FSP location, the dominant prior-deformation basal texture was shifted along the arc of a hypothetical ellipse. The patterns of deformation texture developments were captured by viscoplastic self-consistent modeling with appropriate velocity gradients. The simulated textures, however, had two clear deficiencies. The simulations involved shear strains of 0.8 to 1.0, significantly lower than those expected in the FSP. Even at such low shear, the simulated textures were significantly stronger. Microstructural observations also revealed the presence of ultra-fine grains with relatively weak crystallographic texture. Combinations of ultra-fine grain superplasticity followed by grain coarsening were proposed as the possible mechanism for the microstructural evolution during FSP.

13 citations

Journal ArticleDOI
TL;DR: A β-solidified nearly lamellar γ-TiAl (α 2 + γ ) based alloy was investigated to understand the evolution of microstructure during hot isothermal compression test at 1050 °C (below eutectoid) as discussed by the authors.
Abstract: A β-solidified nearly lamellar γ-TiAl ( α 2 + γ ) based alloy was investigated to understand the evolution of microstructure during hot isothermal compression test at 1050 °C (below eutectoid). Cylindrical samples were compressed to different true strains up to 60%. The deformed samples were then characterized using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) to understand the active deformation mechanisms. Dynamic flow softening behavior, i.e., dynamic recrystallization (DRX) type flow was observed. While no new strain induced phases were observed, there were minor changes in the phase fractions as a function of strain. Kinking and bending of lamellae at certain areas in the microstructure of compressed samples were predominant. Preliminary analysis by TEM indicated the presence of twinning in both γ and β phases.

13 citations


Cited by
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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.
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.

29,323 citations

Journal ArticleDOI
TL;DR: In this paper, a review of continuum-based variational formulations for describing the elastic-plastic deformation of anisotropic heterogeneous crystalline matter is presented and compared with experiments.

1,573 citations

Journal ArticleDOI
TL;DR: In this paper, the authors presented an 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.

441 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).
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.

368 citations