Research Projects
Modeling the fracture of brittle epoxy nanocomposite
Modeling the fracture of brittle epoxy nanocomposite
Epoxy is an important engineering material with applications ranging from aviation industry to food industry. Experiments show that adding a trace amount of nanofiller (0.1-0.2wt% of Graphene) can drastically enhance the mechanical properties of cured epoxy thermoset polymers (see https://pubs.acs.org/doi/abs/10.1021/nn9010472). Currently literature has significant gap in modeling brittle fracture of epoxy that would help interprete such experiments. We used bump-LJ potential to fracture of model epoxy nanocomposite. Our modeling approach can stabilize the epoxy polymer, and can effectively capture the crosslinking reaction and bond rupture during fracture, yet with a significantly smaller computational cost compared to the trivial reactive force field approaches. We studied the effect of filler/matrix interaction and found that too strong interface interaction can give birth to premature cavitation at the interface leading to a declination in the mechanical properties, whereas a moderately strong interface can concurrently improve the stiffness and toughness of the matrix.
Epoxy is an important engineering material with applications ranging from aviation industry to food industry. Experiments show that adding a trace amount of nanofiller (0.1-0.2wt% of Graphene) can drastically enhance the mechanical properties of cured epoxy thermoset polymers (see https://pubs.acs.org/doi/abs/10.1021/nn9010472). Currently literature has significant gap in modeling brittle fracture of epoxy that would help interprete such experiments. We used bump-LJ potential to fracture of model epoxy nanocomposite. Our modeling approach can stabilize the epoxy polymer, and can effectively capture the crosslinking reaction and bond rupture during fracture, yet with a significantly smaller computational cost compared to the trivial reactive force field approaches. We studied the effect of filler/matrix interaction and found that too strong interface interaction can give birth to premature cavitation at the interface leading to a declination in the mechanical properties, whereas a moderately strong interface can concurrently improve the stiffness and toughness of the matrix.
Giant pyroelectricity in nanomembranes
Giant pyroelectricity in nanomembranes
Pyroelectric materials with a wide range of interlayer characteristics (eg., indium selenide with van der walls, CsBiNb2O7 with quasi van der waals bonds, to ZnO with ionic/covalent bonds) showed augmented pyroelectric coefficient at thin film limit. Experiments shows that this dimensionally effect is stronger for chemically bonded layers. For example for In2S3, pyroelectric coefficient increases from 958 μCmˆ-2Kˆ-1 at thickness 222nm to 5.5x10ˆ3 μCmˆ-2Kˆ-1 at 11nm; for CBNO, from 2 μCmˆ-2Kˆ-1 at thickness 250nm to 110.8 μCmˆ-2Kˆ-1 at 12nm; for ZnO, from 42 μCmˆ-2Kˆ-1 at thickness 1920nm to 8.7x10ˆ3 μCmˆ-2Kˆ-1 at 32nm.
Pyroelectric materials with a wide range of interlayer characteristics (eg., indium selenide with van der walls, CsBiNb2O7 with quasi van der waals bonds, to ZnO with ionic/covalent bonds) showed augmented pyroelectric coefficient at thin film limit. Experiments shows that this dimensionally effect is stronger for chemically bonded layers. For example for In2S3, pyroelectric coefficient increases from 958 μCmˆ-2Kˆ-1 at thickness 222nm to 5.5x10ˆ3 μCmˆ-2Kˆ-1 at 11nm; for CBNO, from 2 μCmˆ-2Kˆ-1 at thickness 250nm to 110.8 μCmˆ-2Kˆ-1 at 12nm; for ZnO, from 42 μCmˆ-2Kˆ-1 at thickness 1920nm to 8.7x10ˆ3 μCmˆ-2Kˆ-1 at 32nm.
Complementing a 1945 theory by Born (10.1103/RevModPhys.17.245), in 1975 Szigeti proposed that pyroelectric coefficient is composed of a first order contribution from the rigid ion displacement and a second order contribution owing to electron-phonon renormalization (10.1103/PhysRevLett.35.1532). This electron-phonon renormalization, or otherwise known as Debye-Waller term is related to the mean square displacement <uˆ2>. In this paper we hypothesize that the dimensionality effect of pronounced on the electron-phonon renormalization, based on the Hohenberg, Mermin and Wagner's theorem.
To confirm the experimental findings, we designed a simple molecular model of HCP material using bump-LJ potential (see https://www.nature.com/articles/s41586-022-04850-7). We measured the mean square displacements of HCP films between 10 and 32 layers and varied strength of interlayer bonds. Our simulation reveals that mean square displacement grows we decrease the film thickness. We clearly showed that sheets with stronger out-of-place bonding strength has more pronounced dimensionality effect on the mean square displacement, and hence on the Debye-Waller factor, which in turn proves the dimensionality effect on electron-phonon renormalization and thus pyroelectricity.
Complementing a 1945 theory by Born (10.1103/RevModPhys.17.245), in 1975 Szigeti proposed that pyroelectric coefficient is composed of a first order contribution from the rigid ion displacement and a second order contribution owing to electron-phonon renormalization (10.1103/PhysRevLett.35.1532). This electron-phonon renormalization, or otherwise known as Debye-Waller term is related to the mean square displacement <uˆ2>. In this paper we hypothesize that the dimensionality effect of pronounced on the electron-phonon renormalization, based on the Hohenberg, Mermin and Wagner's theorem.
To confirm the experimental findings, we designed a simple molecular model of HCP material using bump-LJ potential (see https://www.nature.com/articles/s41586-022-04850-7). We measured the mean square displacements of HCP films between 10 and 32 layers and varied strength of interlayer bonds. Our simulation reveals that mean square displacement grows we decrease the film thickness. We clearly showed that sheets with stronger out-of-place bonding strength has more pronounced dimensionality effect on the mean square displacement, and hence on the Debye-Waller factor, which in turn proves the dimensionality effect on electron-phonon renormalization and thus pyroelectricity.
Molecular Modeling of Bio-Polymers
Molecular Modeling of Bio-Polymers
We are modeling Biopolymers at the nanoscale. We use Moltemplate package for structure generation. Straight Chains from Moltemplate packages are formed into self avoiding randomly oriented curves within the scheme of codes developed by me. Currently we are working with all-atom modeling of Polycaplatone (PCL) sample with OPLSAA force field and measuring the strength of polymer for different morphologies and looking for deriving techniques for increasing the strength with metal nano-fragments.
We are modeling Biopolymers at the nanoscale. We use Moltemplate package for structure generation. Straight Chains from Moltemplate packages are formed into self avoiding randomly oriented curves within the scheme of codes developed by me. Currently we are working with all-atom modeling of Polycaplatone (PCL) sample with OPLSAA force field and measuring the strength of polymer for different morphologies and looking for deriving techniques for increasing the strength with metal nano-fragments.
Graphene - Water Hetero system
Graphene - Water Hetero system
We are exploring the interfacial physics of Graphene-Water (Gr-W) contact system. Graphene's hydrophobicity has been previously observed to be largely dependent on the substrate underneath, and shown to have contact angles in the range of 40° to as much as 130° . In this project we are checking if Graphene's hydrophobicity can be tailored by controlling the dimensions of the Gr ripples placed on a plane Gr sheet
We are exploring the interfacial physics of Graphene-Water (Gr-W) contact system. Graphene's hydrophobicity has been previously observed to be largely dependent on the substrate underneath, and shown to have contact angles in the range of 40° to as much as 130° . In this project we are checking if Graphene's hydrophobicity can be tailored by controlling the dimensions of the Gr ripples placed on a plane Gr sheet
Thermal and Mechanical properties of defected Silicon Carbide Nanotube
Thermal and Mechanical properties of defected Silicon Carbide Nanotube
Silicon Carbide nanostructures are known to be highly resistant to heat and corroding environment, are often regarded as the next generation materials for harsh environmental use, including spacr. Atomic level defects are often inevitable and associated with the production route and operation temperature. So properties calculated for pristine structures are of limited in practice. In this project we are studying the effect of defect concentration on the thermal and mechanical properties of SiC nanotubes.
Silicon Carbide nanostructures are known to be highly resistant to heat and corroding environment, are often regarded as the next generation materials for harsh environmental use, including spacr. Atomic level defects are often inevitable and associated with the production route and operation temperature. So properties calculated for pristine structures are of limited in practice. In this project we are studying the effect of defect concentration on the thermal and mechanical properties of SiC nanotubes.
Thermal Rectification of InP Nanocones
Thermal Rectification of InP Nanocones
Indium Phosphides is a very promising materials for semiconductor industry and often regarded as one of the suitable replacements for Si at the chip level. InP crystals are grown as conic structures. Conic nanostructures have been previously observed to show thermal rectification property. We are looking for such effects in InP nanocones, which might help to design efficient thermal management devices at the nanoscale.
Indium Phosphides is a very promising materials for semiconductor industry and often regarded as one of the suitable replacements for Si at the chip level. InP crystals are grown as conic structures. Conic nanostructures have been previously observed to show thermal rectification property. We are looking for such effects in InP nanocones, which might help to design efficient thermal management devices at the nanoscale.
Mechanical Properties of Cu-Ni and Al-Ni FGM Nanowire
Mechanical Properties of Cu-Ni and Al-Ni FGM Nanowire
In this project, we are exploring the mechanical properties of Functionally Graded Nanowires. Functionally Graded Materials are a comparatively recent practice of material design, often used to achieve multifunctionality without creating phase interfaes. Bulk FGMs are still fledging through commercialization, however, FGMs at nanoscale are a yet to be explored field of research. At nanoscale, such functionalizations offers immense possibilities, since, motions of dislocations can be tailored through design factors and plasticity of materials can be largely be controlled to the desired direction.
In this project, we are exploring the mechanical properties of Functionally Graded Nanowires. Functionally Graded Materials are a comparatively recent practice of material design, often used to achieve multifunctionality without creating phase interfaes. Bulk FGMs are still fledging through commercialization, however, FGMs at nanoscale are a yet to be explored field of research. At nanoscale, such functionalizations offers immense possibilities, since, motions of dislocations can be tailored through design factors and plasticity of materials can be largely be controlled to the desired direction.
Thermal Properties of Graphene-MoS2 Heterostructures
Thermal Properties of Graphene-MoS2 Heterostructures
Graphene is a wonder material, perplexing the researchers for quite a few years now. MoS2 is one of the transition metal dichalcogenides (TMD). Single layer MoS2, an direct bandgap semiconductor, shown quite remarkable mechanical, thermal and optical properties. Gr-MoS2 heterostructures are a field of very recent interest. Such structures showed properties like superlubricity, high photoresponsivity and offer prominent possibility to be used as a Li-ion anode material,
Graphene is a wonder material, perplexing the researchers for quite a few years now. MoS2 is one of the transition metal dichalcogenides (TMD). Single layer MoS2, an direct bandgap semiconductor, shown quite remarkable mechanical, thermal and optical properties. Gr-MoS2 heterostructures are a field of very recent interest. Such structures showed properties like superlubricity, high photoresponsivity and offer prominent possibility to be used as a Li-ion anode material,
Predicting Maximum Allowable Current through a Functionally Graded metal line with Solder Joint
Predicting Maximum Allowable Current through a Functionally Graded metal line with Solder Joint
To tackle the immense heat generated in modern electronics circuits, heat management at the microscale is a necessity. Advanced materials like a FGMs are a prominent candidate for designing next generation thermal devices. In this paper we studied the current carrying capacity of FGM metal lines. Along with two configurations of FGM, namely FGM-I and FGM-II, we used pure Cu line and Cu-Al bimetallic lines in our study. The solution of our problem is approached by solving a highly nonlinear Electro-Thermo-Mechanical system.
To tackle the immense heat generated in modern electronics circuits, heat management at the microscale is a necessity. Advanced materials like a FGMs are a prominent candidate for designing next generation thermal devices. In this paper we studied the current carrying capacity of FGM metal lines. Along with two configurations of FGM, namely FGM-I and FGM-II, we used pure Cu line and Cu-Al bimetallic lines in our study. The solution of our problem is approached by solving a highly nonlinear Electro-Thermo-Mechanical system.
Effect of CNN based image superresolution algorithm on the Landcover Classification of Sundarbans from LANDSAT-7 Images
Effect of CNN based image superresolution algorithm on the Landcover Classification of Sundarbans from LANDSAT-7 Images
In the modern world, satellite images play a key role in forest management and degradation monitoring. For a precise quantification of forest land cover changes, availability of spatially fine resolution data is a necessity. Since 1972, NASA’s LANDSAT Satellites are providing terrestrial images covering every corner of the earth. However, freely accessible satellite images are, generally, of medium to low resolution which is a major hindrance for the precision of the analysis. Hence, we performed a comprehensive study to prove our point that, enhancement of resolution and quality of image will lessen the chance of misclassification of pixels for the enhanced images than the original images, under same classification method. We tested the method on original LANDSAT-7 images of different regions of Sundarbans and their upscaled versions which were produced by bicubic interpolation and SRCNN respectively. It is discovered that for moderate level of upscaling, SRCNN outperforms Bicubic interpolation by many folds. However, at very high upscaling both of their performance matches.
In the modern world, satellite images play a key role in forest management and degradation monitoring. For a precise quantification of forest land cover changes, availability of spatially fine resolution data is a necessity. Since 1972, NASA’s LANDSAT Satellites are providing terrestrial images covering every corner of the earth. However, freely accessible satellite images are, generally, of medium to low resolution which is a major hindrance for the precision of the analysis. Hence, we performed a comprehensive study to prove our point that, enhancement of resolution and quality of image will lessen the chance of misclassification of pixels for the enhanced images than the original images, under same classification method. We tested the method on original LANDSAT-7 images of different regions of Sundarbans and their upscaled versions which were produced by bicubic interpolation and SRCNN respectively. It is discovered that for moderate level of upscaling, SRCNN outperforms Bicubic interpolation by many folds. However, at very high upscaling both of their performance matches.
Atomistic study on the mechanical properties of polycrystalline SAC solder
Atomistic study on the mechanical properties of polycrystalline SAC solder
In this work, impact of grain size, temperature and strain rate on the uniaxial tensile properties of nc-SAC305 material have been discussed in the light of a polycrystal model with coherent twin boundary. Uniaxial tensile test is performed by varying the average grain size from 3.19 nm to 7.13 nm keeping strain rate and temperature constant at 109 s-1 and 298K accordingly to find out the impact of grain size on the elastic properties. To study the effect of strain rate, strain rate is varied from 108 to 1010 s-1 keeping the average grain size and temperature constant at 5.04 nm and 298 K accordingly. Finally, temperature is changed from 273 K to 398 K maintaining fixed grain size 5.04 nm and strain rate 109 s-1. The fracture mechanism is also discussed in detail.
In this work, impact of grain size, temperature and strain rate on the uniaxial tensile properties of nc-SAC305 material have been discussed in the light of a polycrystal model with coherent twin boundary. Uniaxial tensile test is performed by varying the average grain size from 3.19 nm to 7.13 nm keeping strain rate and temperature constant at 109 s-1 and 298K accordingly to find out the impact of grain size on the elastic properties. To study the effect of strain rate, strain rate is varied from 108 to 1010 s-1 keeping the average grain size and temperature constant at 5.04 nm and 298 K accordingly. Finally, temperature is changed from 273 K to 398 K maintaining fixed grain size 5.04 nm and strain rate 109 s-1. The fracture mechanism is also discussed in detail.
Mechanical Properties of Single and Polycrystal GaAs Nanowires : an atomstic study
Mechanical Properties of Single and Polycrystal GaAs Nanowires : an atomstic study
GaAs is a well known semi conductor material, well known for their high carrier mobility. Despite of their remarkable electrical and optical properties, the understanding of the mechanism of GaAs failure under mechanical failure is still lacking. In this project, we are exploring the Mechanical properties of GaAs nanowire in single crystal and polycrystal form. We are studying the effect of NW dimension, temperature and grain size on the strength of GaAs NW.
GaAs is a well known semi conductor material, well known for their high carrier mobility. Despite of their remarkable electrical and optical properties, the understanding of the mechanism of GaAs failure under mechanical failure is still lacking. In this project, we are exploring the Mechanical properties of GaAs nanowire in single crystal and polycrystal form. We are studying the effect of NW dimension, temperature and grain size on the strength of GaAs NW.
Mechanical Properties of Nickel wafer with a punched hole under shear deformation: Atomstic Study
Mechanical Properties of Nickel wafer with a punched hole under shear deformation: Atomstic Study
Molecular Dynamics Simulations were performed on Ni nano-plate subjected to shear loading to study the effect of voids in the structure using embedded atom method (EAM) potential. The shear stress-strain behavior was observed for Ni nano-plate with voids of 1.0 nm, 1.5 nm, and 2.0 nm radius. Snapshots taken at different strains show the formation of slip planes, crack propagation, and dislocation activity. Simulation results show that the modulus of rupture decreases with the increase of void radius due to more dislocation activity for larger void. Lastly, the effect of different void size on the shear modulus of rigidity is also incorporated.
Molecular Dynamics Simulations were performed on Ni nano-plate subjected to shear loading to study the effect of voids in the structure using embedded atom method (EAM) potential. The shear stress-strain behavior was observed for Ni nano-plate with voids of 1.0 nm, 1.5 nm, and 2.0 nm radius. Snapshots taken at different strains show the formation of slip planes, crack propagation, and dislocation activity. Simulation results show that the modulus of rupture decreases with the increase of void radius due to more dislocation activity for larger void. Lastly, the effect of different void size on the shear modulus of rigidity is also incorporated.