Research

Multiscale Computational Mechanics

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.

Atomistic Simulations

Nanomaterials show significant deviation from larger grain polycrystals because of change in dislocation interactions. Dislocation activity in bulk aluminum and titanium were studied using various boundary conditions of deformation. Multilayered Al-Ti representative volume elements (RVE) are created using LAMMPS. Dislocation-interface interaction plays a critical role in driving the mechanical behavior of such multilayer. Effect of layer thickness and orientation on recrystallization, phase transformation, and the deformation mechanism is the prime objective of the work.

Crystal Plasticity

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.

Irradiation Defects During Nuclear Reactor Service

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.

Damage Analysis in TBC

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

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.

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.