Spandan Maiti's Research Group

Research Objective

Main research interests of our group are in the predictive modeling and large scale simulation of deformation and failure behavior of physical and biological systems.  A general objective of our research is to provide quantitative descriptions of the relationships between the measurable features of the micro- and nano-structures of materials and their macroscopic mechanical behavior. This involves development of advanced numerical techniques for materials modeling and computational frameworks to conduct large scale simulations in a massively parallel environment. The salient features of our research interests can be described as follows:

Micro- and nano-mechanical analysis in a multiphysics environment

Most advanced physical and biological systems are engineered to exhibit a number of functionalities in a multiphysics environment. Detailed continuum/discrete micro- and nano-mechanical models including multiphysics effects are thus essential to understand the underlying physics, manufacturing/evolution process and service response of these systems. Example systems of interest include:

• Artificial bone scaffolds for tissue regeneration;
• Operation of mechanically gated ion channels in cell membranes;
• Failure of MEMS/NEMS incorporating thin film components;
• Role of cytoskeleton in cell motility and adhesion;
• Healing process and scar formation in living organisms;

Multiscale modeling of deformation of materials

A key challenge to the research community in the field of the computational science today is to provide explicit mechanistic description for the evolution of materials ranging from macromolecules to nanocomposites over a wide range of length and time scales. Current spatial and temporal limitations of the computational tools to simulate various material responses at the finest scale calls for novel scale bridging techniques. Identification of universal scaling laws as well as system specific relations along with successful implementation of degree of freedom thinning concepts is the key to construct effective theories applicable at different scales. My objectives in this area are the following:

• Development of atomistically informed quasi-continuum models to study various phenomena such as diffusion of atoms, nucleation and growth of defects, and response of cell membranes due to external stimuli over system length scales;
• Development of structural models decorated with entropic phenomena to simulate response of various macromolecules;
• Identification of failure laws over multiple length scales and prediction of macro level failures from low level mechanisms. 

Optimum design strategies at the materials processing level for improved performance of systems and devices

Uncertainty from various sources is inherent to most of the engineered materials systems and devices, and its effect becomes dominant in various applications involving small volume of materials. For example, statistical variability of the material properties and service conditions becomes significant for reliable operation of thin film components and molecular devices. Uncertainty arises in such systems through various channels: natural or irreducible uncertainty, wherein the physical system being modeled itself is inherently uncertain (example being the presence of voids, precipitates, grain boundaries, nanoparticles, etc.); model uncertainty, which is incorporated through many correlated factors such as model structure and approximations used and model resolution; and parametric and data uncertainty, which includes experimental and data measurement errors. I intend to pursue a systematic analysis to identify key sources of uncertainty along with their sensitivity on the predicted model output which will provide insight into the level of confidence in model estimates. An overall aim of this research is to identify optimum design alternatives and obtain a robust design at the materials processing and system manufacturing level for optimum performance of systems and devices in the presence of inherent variability from different sources, intentional or otherwise.

• More specifically, the uncertainty analysis can be conducted in the following directions:
• Obtain an input-output map of the system under consideration, to define the propagation of input uncertainty to the model output;
• Perform sensitivity analysis to determine the key parameters to be considered for a robust design;
• Device efficient algorithms to determine optimum design alternatives in the uncertain space of the key parameters;
• Develop methodologies to determine a robust materials design which will be valid over entire service life of the systems and devices.

Current and recent research activities

Multiscale characterization and design space exploration for cellular solids

Cellular materials are finding increasing use as engineering materials owing to their excellent strength to weight ratio, high specific energy absorption capability, superior insulation property and thermal stability, and excellent permeability, to name a few. Cellular structure is also abundant in nature: most noteworthy being woods and corks, human bones and tissues and their bioengineered surrogates such as tissue regeneration scaffolds. One interesting feature of these cellular materials is their extremely complex microstructure, from where they derive their continuum level functionalities. In my research group, a synergistic approach combining experiments and multiscale computational modeling has been undertaken to span the material and experimental design space so as to develop comprehensive understanding of multiphysics behavior of cellular structures, to explore defect tolerant designs using these materials and furnish guidelines for their successful deployment. Accomplishments so far are:

Delevelopment of a unified computational framework for the dynamic response of open cell foams;

Incorporation of different failure behaviors to simulate brittle, ductile and elastomeric responses;

Incorporation of hydrodynamic drag and overdamped response to predict the behavior of biological materials.

Current activities involve:

• Simulation of cytoskeleton deformation in cells;
• Sensitivity analysis in the presence of various defects;
• Characterization of ultrasonic wave propagation in cancellous bones.

Fracture pattern evolution due to static indentation in Boron Carbide

The fracture patterns due to static  indentation boron carbide is transgranular in nature with a zig-zag pattern within each grain. This zig-zag pattern is speculated to be the result of crack deflection along favorably oriented cleavage planes responsible for the formation of intermittent parallel crack facets oriented at an angle to the macroscopic crack direction.  While cleavage plane crack propagation can be conveniently modeled through cohesive element technique, we need special computational technique (such as XFEM) for off cleavage plane crack path. But XFEM techniques can be quite expensive, and difficult to implement. We are developing a novel computational technique, termed as "generalized cohesive element technique", which retains the simplicity of implementation of cohesive elements, can simulate multiple crack initiation, propagation and coalescence, while does not require predefined crack paths within the FE mesh. The method is shown to be robust, mesh insensitive, and a simple extension of conventional cohesive element technique. Accomplishments so far are:

• Simulation of mixed mode crack propagation
• Multiple crack propagation
• Simulation of zigzag crack pattern

Current activities involve:

• Extension of this technique in dynamic regime
• Simulation of discrete dislocations
• Simulation of shear bands

Deformation and failure behavior of multilayer  thin films (In collaboration with Prof. G. Subhash, University of Florida)

Ceramic nanofilms are finding increasing use in many advanced and emerging technologies such as integrated electronic circuits for charge storage, surface coatings and thermal barriers to protect structural components, and as parts for MEMS devices. For improved performance and operational reliability of systems and devices incorporating nanofilms, it is necessary to evaluate their mechanical properties and failure behavior. Objectives for this research are experimental characterization of multilayer films, identification of physical phenomena responsible for deformation and failure behavior of these materials, and development of scale bridging computational techniques to simulate and predict the mechanical response of this class of materials at different length scales. The accomplishment of my research group so far is

• Development of a scale bridging framework to simulate thin film response in continuum scale incorporating nanoscale phenomena;
• Incorporation of interfacial debonding and microcracking of the films.

Research is under way to further develop the computational model to include

• Dislocation dynamics in thin films to quantify creeping;
• Creep and diffusion assisted nucleation and growth of voids;
• Damage accumulation and attendant failure due to void growth, debonding, and microcracking.

Adhesion in nano-sized and biological materials

Interfacial adhesion and friction are important factors in determining the performance of a wide array of systems ranging from cell motility in living organisms to the reliability of microelectromechanical systems (MEMS). Van der Waals dispersion forces among non-contacting surfaces contribute nontrivially towards the adhesion of surfaces which are not considered by standard rough surface adhesion models. Furthermore, recent studies in biological systems have opened up the possibility of manufacturing novel biomimetic adhesives requiring new insight, experiments and modeling paradigms to fully realize their potential. For example, the strong adhesion at gecko feet has been shown to be due to dry adhesion arising from van der Waals interaction between surfaces, while sacrificial bonds and hidden lengths of collagen fibrils between brittle aragonite platelets in nacre shells are responsible for improved energy absorpotion characteristics. Objectives in this research project are

• Characterize adhesion mechanisms between contacting as well as non-contacting surfaces at the nanoscale in the presence of surface impurities;
• Develop scale bridging computational adhesive models;
• Predict the effect of adhesion on cell migration, attachment to substrates, entanglement of nanotubes and performance of MEMS.

Publications

 

REFEREED JOURNAL PUBLICATIONS

 

2007

1. H. Zhang, S. Maiti, and G. Subhash. Local heating associated with shear band evolution in bulk metallic glass. In press, Journal of Applied Physics, 2007.
2. S. Yao, G. Subhash, and S. Maiti. Nanoindentation response of diatom frustules. In press, Journal of Nanoscience and Nanotechnology, 2007
3. P. G. Nittur, S. Maiti and P. H. Geubelle. Grain-level analysis of dynamic fragmentation of ceramics under multiaxial compression. In press, Journal of the Mechanics and Physics of Solids, 2007.
4. X. Jing, G. Subhash and S. Maiti. A new analytical model for estimation of scratch induced damage in brittle solids. Journal of the American Ceramic Society, 90(3):885-892, 2007.
5. V. Dantuluri, S. Maiti, P. H. Geubelle, R. Patel and H. Kilic. Cohesive modeling of delamination in Z-pin reinforced composite laminates. 67(3-4):616-631, Composites Science and Technology, 2007.

 

2006

6. S. Maiti, C. Shankar, P. H. Geubelle and J. Keiffer. Continuum and molecular-level modeling of fatigue crack retardation in self-healing polymers. Journal of Engineering Materials and Technology, 128(4):595-602, 2006.
7. M. L. Parks, E. de Sturler, G. Mackey, D. D. Johnson, and S. Maiti. Recycling Krylov subspaces for sequences of linear systems. SIAM Journal on Scientific Computing, 28(5):1651-1674, 2006.
8. G. Subhash, M. A. Marszalek, and S. Maiti. Sensitivity of Scratch Resistance to Grinding-Induced Damage Anisotropy in Silicon Nitride. Journal of the American Ceramic Society, 89(8):2528-2536, 2006.
9. S. Maiti and P. H. Geubelle. Cohesive modeling of fatigue crack retardation in polymers: Crack closure effect. Engineering Fracture Mechanics, 73(1):22-41, 2006.

 

2005

10. S. Maiti, K. Rangaswamy, and P. H. Geubelle. Mesoscale analysis of dynamic fragmentation of ceramics under tension. Acta Materialia, 53(3):823-834, 2005.
11. S. Maiti and P. H. Geubelle. A cohesive model for fatigue failure of polymers. Engineering Fracture Mechanics, 72(5):691-708, 2005.

 

2004

12. S. Maiti and P. H. Geubelle. Mesoscale modeling of dynamic fracture of ceramic materials. CMES Computer Modeling in Engineering & Sciences, 5(2):91-102, 2004.

 

 

SUBMITTED PAPERS

 

13. N. C. Das, S. Maiti and H. Wang. Electromagnetic interference shielding effectiveness of single walled carbon nanotube/poly(methyl methacrylate) composites. Under review, Journal of Polymer Science Part B: Polymer Physics, 2006.
14. D. Ghosh, S. Maiti and G. Subhash. A generalized cohesive element technique for arbitrary crack propagation. Engineering Fracture Mechanics, 2007.

 

 

PAPERS IN PREPARATION

 

1. P. Hittepole, G. Subhash, and S. Maiti. Mechanics of deformation of multilayer ceramic thin films. 2007.
2. S. Pal and S. Maiti. Deformation localization of soft cellular materials at high strain rate regime. 2007.
3. S. Pal, S. Maiti and G. Subhash. Computational analysis of experimental and material design space for testing of soft cellular materials in split Hopkinson pressure bar. 2007.
4. H. Zhang, S. Maiti, and G. Subhash. Shear bands evolution in bulk metallic glass under dynamic loading. 2007.
5. S. Maiti and G. H. Paulino. A Novel frictionless contact formulation and implementation using the boundary element method. 2007.

 

 

REFEREED CONFERENCE PROCEEDINGS

 

1. G. Subhash, D. Ghosh, and S. Maiti. Static and dynamic indentation response of fine grained boron carbide. Proceedings of 31^st International Conference on Advanced Ceramic Composites, American Ceramic Society, Daytona Beach, Jan 2007.
2. S. Maiti, P. H. Geubelle, and K. Rangaswamy. Fragmentation of ceramics in rapid expansion mode.Proceedings of 8^th International Symposia of Fracture Mechanics of Ceramics, Houston, Feb 2003.