ICME Research Lab
Multiscale
Computational Mechanics for Linking Material Genome to Performance
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This is research group of Prof. Alankar Alankar at Department
of Mechanical Engineering, IIT Bombay. Alankar graduated with a B.Tech (Metallurgical
Engineering) degree at IIT Roorkee, India, MASc (Materials Engineering)
degree at The University of British Columbia, Canada and PhD (Mechanical
Engineering) at Washington State University, USA under the supervision of
Prof. David Field. After doctoral degree, he did postdoctoral research at
Max-Planck Institut fur Eisenforshung, Germany under mentorship of Prof.
Dierk Raabe and Prof. Philip Eisenlohr. His second post-doc stint was at Los
Alamos National Laboratory, USA under the mentorship of Dr. Ricardo
Lebensohn, Dr. Carlos Tome and Dr. Alfredo Caro. Subsequently he joined
Modumetal, Inc. in Seattle, USA where he was responsible for design and
architecture of metal nanolayered coatings. His area of research consists of
dislocation theory, crystal plasticity modeling, multiscale modeling of
microstructure evolution, nanolayered materials, creep, irradiation damage,
wear and degradation of materials and other regime of structure-property
relationship. |
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We work
in the area of development of improved methods of multiscale modeling of
deformation and length scale bridging. The key areas of interests are Crystal
Plasticity, Multiscale and Multi-physics problems, Dislocation Dynamics,
Atomistic Simulations relevant to plasticity and deformation. Our major
effort is in open-source code development or development of new modules for
existing codes.
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Crystal Plasticity |
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Deformation Microstructure Plastic deformation in metals is caused by movement of dislocations
the line defects present in metals. Crystal lattice remains invariant after
the crystallographic slip, as compared to the elastic distortion which changes
both, the crystallographic orientation and the spacing of a crystal lattice.
Apart from accounting for the plastic deformation in crystalline materials,
dislocations are associated with work hardening behavior by means of their
multiplication activity due to mutual interactions that hinders the motion of
gliding dislocations. To model the plastic deformation, crystal plasticity
(CP) is used. The crystal plasticity formulations have successfully addressed
the problems like rotations of individual grains in a polycrystal, evolution
of crystallographic texture using classical hardening models e.g. power laws
defining crystallographic slip. A CP model assumes material as continuum body
and maps the elastic and plastic deformation using crystal kinematics. To get
the stress-strain response of polycrystals, mean-field and full field
approach can be used which may need Finite Element or Fourier Transform based
numerical methods. In the example, the CP model is run for polycrystal of
ferritic-austenitic and ferritic-martensitic dual-phase (DP) steel with
microstructure having 50 grains. The grain reorientation during deformation
is also shown for the above two cases. |
Microstructure
of 50 grains polycrystals
Stress
distribution for ferritic-austenitic DP steel
Stress
distribution for ferritic-martensitic DP steel |
Grain re-orientation and fragmentation in
ferritic-austenitic DP steel
Grain re-orientation and fragmentation in
ferritic-martensitic DP steel |
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Understanding Bulk Metal Deformation Most of the materials are polycrystalline in nature. The difference
between a single crystal and a polycrystal material are the grain boundaries.
Grain boundaries play a major role in strengthening the material. To
understand the behavior of a polycrystalline material completely we need to
track the orientations of grains during deformation. Crystallographic texture displays the anisotropic nature of the
material and is used as a nob for designing mechanical properties. |
Understanding Single Crystals
Understanding Single Crystal Behavior |
Crystallographic Texture Evolution |
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Understanding Dislocations at Small
Scales |
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Dislocation Dynamics The mechanical response of materials alters drastically as the size
of specimen becomes less than a few microns. As such small structures are
getting attention in modern technologies, there is rising need to model and
understand elastic, plastic and fracture behavior. Plastic deformation in
crystalline materials occurs due to glide of dislocations. Work-hardening in
metals occur due to dislocation multiplication and interaction between them.
In order to model the dislocation activity and interaction between them,
dislocation dynamics (DD) is often used. In DD, the dislocation sources are
represented by discrete line segments gliding due to numerous driving forces
such as externally applied forces, dislocation line tension and interacting
forces between dislocations. DD simulates behavior of dislocations
individually and interaction between them and supplies mechanical response
and detailed analysis of evolution of microstructure. |
Undeformed
Configuration
Deformed
Configuration |
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Advanced Computational Methods |
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Bridging Length Scales Dislocations in a
crystal influence heavily as the size of the specimen decreases to micron
level. There is an absolute indication of size effect through indentation
experiments, micron beam bending tests and torsion tests. New dislocations
arise due to inhomogeneous deformation which is purely geometrical in nature.
These geometrically necessary dislocations add to the already existing
dislocations creating size effect i.e., smaller is stronger. GNDs contribute
to strengthening of composites as well. |
Cantilever
Beam
Pure
Bending |
Simple
Shear |
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Irradiation Effects: Hardening,
Creep and Growth Reactivity
initiated accident (RIA) or loss of coolant accident (LOCA) in a nuclear
reactor may lead to sudden temperature rise. Accidents caused by LOCA
condition or RIA condition may lead to a dynamic expansion of fuel pallets.
This results into a multiaxial state of deformation caused by high thermal
loading (1000 s-1) in presence of extreme conditions of
irradiation. |
Effect of
Temperature and Irradiation Dose on Yield Stress
Yield
stress as a function of dose |
Residual
Stress in a Zr polycrystal due to Growth |
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Mechanical Performance Analysis |
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Thermal Barrier Coating This study aims at to improve thermal efficiency of IC
engines by reducing heat loss
from the gases inside the combustion chamber to coolant. One promising
technology to reduce heat transfer to coolant is application of thermal
insulation, often referred as thermal barrier coatings (TBC), on the inner
walls of the combustion chamber and on the top surface of the piston. Damage modeling in TBC The modelling of damage in TBC is carried out by using
commercial finite element analysis software ABAQUSTM. A
thermomechanical model is developed with material properties as a function of
temperature. A
more realistic microscopic model is created with preferred orientations of
crystallites. Dynamic Deformation Wear is defined as unwanted removal of material on application
of mechanical load. In the present work we study the micro-plowing mechanism
of wear in which material is not removed but displaced to the sides. Finite Element Model for Wear Analysis The large deformation problem is often difficult to solve by
classical Lagrangian finite element approach. The test block is taken to be a
rectangular block of size 20 mm X 10 mm X 80 mm. The model is composed of two
parts: indenter and the workpiece. The indenter is assumed to be cylindrical
with a hemispherical tip in shape. The indenter is discretized under a
Lagrangian frame while workpiece as an Eulerian frame. The Eulerian region
was divided into two sections, filled elements, and the other was set with
void elements to visualize the material flow. In second case the material
work-piece is modeled with simple rectangular block (20 mm X 20 mm X 10 mm)
and block with 20 grains of which material properties varies from factor 0.1
to 2 of the base aluminum material. |
Damage induced
in TBC for a) 0.1 mm and b) 0.3 mm and c) 0.5 mm TBC thickness
Stress
Distribution in polycrystalline model
Development of Coupled Model
Microwear of a Polycrystal |
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Computational The
group is supported by the following computational facility: 1. Small
HPC Linux cluster with 8 nodes with 170 cores total 2. 32
Core Windows Workstation with GPU 3. 20
Core Unix Workstation with GPU 4. 24 TB
Data Cloud 5. Small
Workstations for Students PS:
Please feel free to contact for usage of resources. Experimental 1.
Calowear Test for Microwear and Coating Thickness up to 200 nm 2. Taber
wear test for Abrasion Test 3.
Pin-on-disk test |
Taber Wear Test
Calowear
Test |
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Current
BTech students / interns who are good at Applied Mathematics, Numerical Integration,
C++, C, MATLAB scripting, FORTRAN, Python / python based tools or are willing
to learn the above on Unix based environment, are welcome to contact. 1
Position for MTech student is available. The project is in collaboration with
DMRL, Hyderabad. 1 BTech
/ MTech project available. The project is in collaboration with BARC. 1
position for a PhD student is available. |
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Contact |
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Please feel free to contact us at the following for collaborative
research work, projects or consultancy for multiscale modeling. Alankar Alankar, Ph.D. Assistant Professor,
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