Exploring the strengthening mechanisms of Refractory High Entropy Alloy due to the presence of different alloying elements. [2024 to Present]

Objective:

The primary objective is to study the dislocation mobility in chemically concentrated alloys and the effect of different alloying elements on the strengthening mechanism of such alloys. Once the strengthening mechanism is understood, a surrogate model will be developed to search for different alloy compositions for better strength and dislocation mobility-induced ductility at room temperature. At present, the focus is on elements in the group 4(Ti),5(Nb, Ta) and 6(Mo).

Pure BCC
Diluted Soid Solution
High Entropy Alloy

Understanding the Chemical complexity of the crack tip plasticity for refractory complex concentrated alloys(RCCAs). [2024 to Present]

Objective:

In this project, the objective is to explore the effect of different alloying elements on the nucleation events(dislocation, twin) near a crack tip in the RCCAs. Then use this understanding to design optimal alloy compositions for refractory applications with significant ductility at room temperature. 

CrackTipPlasticity_RCCAs_01
CrackTipPlasticity_RCCAs_02
CrackTipPlasticity_RCCAs_03
CrackTipPlasticity_RCCAs_04
CrackTipPlasticity_RCCAs_05

Development of an inter and intra granular dislocation transport based crystal plasticity model, it's implementation within the MOOSE code. (Postdoc work at Los Alamos)

Objective:

Development of a dislocation transport-based crystal plasticity material model and it’s implementation in the open source code MOOSE.

Special features of the model: 
  • Dislocation density evolution has both local and nonlocal terms in it.
  • Nonocal evolution of dislocation density within a grain is achieved by transporting the dislocation density using advection equation(stabilized).
  • A grain-boundary-geometry informed transfer matrix is used to determine the dislocation transfer across the grain boundary. The transfer can happen between two different slip-system as well as from positive to negative dislocation depending on the relative mis-orientation between the two grains.
Applications:
  • Study the effect of the interface (Grain Boundary) on the mechanical properties of polycrystal metallic materials.
Discoflux_SingleCrystal
Discoflux_BiCrystal
Discoflux_GB_InteractionMatrix
Polycrystal sample under shear loading. Local-CP VS Dislocation Transport based CP.
Discoflux_PolyCrystal_Tensile

LANL release code: LA-UR-23-28137

Publications:

  1. Subhendu Chakraborty, Abigail Hunter, Darby Jon Luscher, “Modeling inter-and intra-granular dislocation transport using crystal plasticity” , Int. J. Plasticity, 145, 10422(2025). https://doi.org/10.1016/j.ijplas.2024.104222

  2. Luscher, Darby, Hunter, Abigail, and Chakraborty, Subhendu. DiscoFluxM version 1.x. Computer Software. https://www.osti.gov/doecode/biblio/127424

Coupling MOOSE with LAMMPS to extend the spatial scale of the atomistic model to simulate the additive manufacturing process. [Postdoc work at Los Alamos]

Objective:
  1. Model the additive manufacturing process where the physics of impact of the laser and subsequent melting and recrystallization will come from the  Molecular Dynamics model and the already crystallized region is modeled as a continuum.
Special features of the model: 
  • MOOSE is coupled with LAMMPS in a concurrent fashion where LAMMPS is used as a library and MOOSE as the driver code.
  • Moving the interface boundary to convert the atomistic domain into a continuum as more and more material is deposited, hence keeping the computational cost uniform during the deposition process.
  • Phonon transfer mechanism at the interface.
  • Characterization, quantification and transfer of dislocations from atomistic to continuum during the migration of the interface.
Applications:
  • Study the development of defect microstructure and grain morphology in the additive manufacturing process (SLS and SLM).

**This project is still on-going. Identification of the Grain Boundary in the atomistic domain and transfer of that information while migrating the interface is yet to be achieved.

Grain morphology and defect formation during AM process
AM_ProcessModeling_CouplingScheme-1
AM_ProcessModeling_GrainFormation-3
AM_ProcessModeling_EnergyVsStep
AM_ProcessModeling_LaserImpact
Selective Laser Sintering (Preliminary work)

LANL release code: LA-UR-22-30084

Presentation: https://www.osti.gov/servlets/purl/2350611

Concurrent coupling of Molecular Dynamics(MD) with Crystal Plasticity FE (CPFE)model. (PhD work at Johns Hopkins Uni.)

Objective:

Develop a concurrent model by coupling the Molecular Dynamics(MD) with Crystal plasticity Finite Element (CPFE) to study the brittle and ductile fracture of metallic materials.

Special features of the model: 
  • This is a surface coupled model, i.e, one layer of FE nodes at the interface region is connected with the corresponding clusters of atoms.
  • A staggered solution technique is used to obtain the updated configuration at the end of each load increment.
  • Kinematic compatibility and the traction reciprocity at the interface is enforced explicitly.
  • Once the nucleated dislocations from the crack reach the interface, those dislocations are characterized and quantified to transfer to the continuum.
  • Dislocation propagation is modeled by using the advection equation.
  • An RKPM based meshless method is used to solve the dislocation propagation PDE on a fine distribution of particles.
Applications:
  • Quantification of the evolution of a crack during brittle fracture.    
  • Quantification of the nucleated dislocations from a crack tip.
  • Using the coupled model as a guiding tool to construct the phase-field energy functional for ductile fracture.
Perfect crystal
Perfect crystal
Crystal with preexisting dislocations
Crystal with preexisting dislocations
Crystal with preexisting dislocations
Crystal with preexisting dislocations
Phase field defect and fracture energy from the coupled model
Phase field defect and fracture energy from the coupled model

**If the above slide show is stuck in one image, click here

Publications:
  1. S. Chakraborty and S. Ghosh, “A Physics based Phase Field Energy Functional for Fracture Derived from Atomistic-Continuum Coupled Concurrent Model”, Journal of the Mechanics and Physics of Solids, 104563 (2021).  https://doi.org/10.1016/j.jmps.2021.104563.
  2. S. Chakraborty and S. Ghosh. “A Concurrent Atomistic-Crystal Plasticity Multiscale Model for Crack Propagation in Crystalline Metallic Materials”, Computer Methods in Applied Mechanics and Engineering, 379,113748 (2021). https://doi.org/10.1016/j.cma.2021.113748
  3. S. Chakraborty. “Development of a self-consistent coupled atomistic-continuum model to study the brittle and ductile fracture in metallic materials”, Ph.D. thesis, Johns Hopkins University, 2020. URL http://jhir.library.jhu.edu/handle/1774.2/62541
  4. S. Chakraborty and S. Ghosh. “Hyperdynamics accelerated concurrent atomistic-continuum model for developing crack propagation models in elastic crystalline materials”, Computational Materials Science, 154:212-224 (2018). https://doi.org/10.1016/j.commatsci.2018.07.064 [Editor’s Choice]

Investigation of the Deformation Mechanisms using Time Accelerated Molecular Dynamics Model. (PhD work at Johns Hopkins Uni.)

Objective: 

Molecular Dynamics is one of the most appropriate models to investigate the deformation mechanisms at the atomic scale. But MD has a severe limitation in the time scale. This time scale limitation demands a very high strain rate based loading for investigating the load-induced deformation mechanisms.

Special features of the model: 
  1. Time-acceleration up to a factor of 10^4 at 300K is achieved.
  2. Model is successful in capturing the change in deformation mechanism from twin domination at high strain rate to dislocation domination at low strain rate for fcc nickel.
Publications: 
  1. S. Chakraborty, J. Zhang and S. Ghosh. “Accelerated molecular dynamics simulations for characterizing plastic deformation in crystalline materials with cracks”, Computational Material Science, 121, 23-34 (2016). http://dx.doi.org/10.1016/j.commatsci.2016.04.026 [Editor’s Choice]
Modeling Al-Al2Cu eutactic alloy using Molecular Dynamics.

Objective: 

Special features of the project: 

Publications: 
  1. C.S.Tiwary, S. Chakraborty, D RoyMahaPatra, K Chattopadhyay. “Length-scale dependent mechanical properties of Al-Cu eutectic alloy: Molecular dynamics based model and its experimental verification”, Journal of Applied Physics, 115, 203502, 2014. http://dx.doi.org/10.1063/1.4879249
  2. C. S. Tiwary, J. Prakash, S. Chakraborty, D. R. Mahapatra & K.Chattopadhyay.  “Subsurface deformation studies of aluminium during wear and its theoretical understanding using molecular dynamics”, Philosophical Magazine, 98:29, 2680-2700 (2018),  https://doi.org/10.1080/14786435.2018.1502481

Optimal Numerical Integration Scheme for Polygonal FEM and Polygonal XFEM.

Objective: 
Special features of the project: 
Publications: 
  1. S. Chakraborty, S. Natarajan, S. Singh, D. Roy Mahapatra & S.P.A. Bordas, “Optimal Numerical Integration Schemes for a Family of Polygonal Finite Elements with Schwarz–Christoffel Conformal Mapping”, International Journal for Computational Methods in Engineering Science and Mechanics, 19:4, 283-304, (2018). https://doi.org/10.1080/15502287.2018.150221
  2. S. Chakraborty, “Optimal Integration Schemes for Polygonal Finite Element Method and eXtended Finite Element Method with Isotropic Homogenious and Polycrystaline Material”, ME Thesis, Indian Institute of Science, Bangalore(India), 2011. url: Thesis_ME_Subhendu
Short term projects, mostly part of some course work
Using the acoustic wave for NDT to detect the internal defect in a Shape Memory Alloy(SMA) wire

Year of work:2010

Building a co-axial contra-rotating RC helicopter capable of carrying a minimum payload of 20gm.

Year of work:2011