Numerical simulations of vein evolution contribute to a better understanding of processes involve... more Numerical simulations of vein evolution contribute to a better understanding of processes involved in their formation and possess the potential to provide invaluable insights into the rock deformation history and fluid flow pathways. The primary aim of the present article is to investigate the influence of a 'realistic' boundary condition, i.e. an algorithmically generated 'fractal' surface, on the vein evolution in 3-D using a thermodynamically consistent approach, while explaining the benefits of accounting for an extra dimensionality. The 3-D simulation results are supplemented by innovative numerical postprocessing and advanced visualization techniques. The new methodologies to measure the tracking efficiency demonstrate the importance of accounting the temporal evolution; no such information is usually accessible in field studies and notoriously difficult to obtain from laboratory experiments as well. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures explain the pinning mechanism which leads to arrest of grain boundaries/multi-junctions by crack peaks, thereby, enhancing the tracking behavior.
Numerical simulations of vein evolution contribute to a better understanding of processes involve... more Numerical simulations of vein evolution contribute to a better understanding of processes involved in their formation and possess the potential to provide invaluable insights into the rock deformation history and fluid flow pathways. The primary aim of the present article is to investigate the influence of a "realistic" boundary condition, i.e. an algorithmically generated "fractal" surface, on the vein evolution in 3-D using a thermodynamically consistent approach, while explaining the benefits of accounting for an extra dimensionality. The 3-D simulation results are supplemented by innovative numerical post-processing and advanced visualization techniques. The new methodologies to measure the tracking efficiency demonstrate the importance of accounting the temporal evolution; no such information is usually accessible in field studies and notoriously difficult to obtain from laboratory experiments as well. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures explain the pinning mechanism which leads to arrest of grain boundaries/multi-junctions by crack peaks, thereby, enhancing the tracking behavior.
Vein formation in earth’s crust involves a complex interplay of material transport and local prec... more Vein formation in earth’s crust involves a complex interplay of material transport and local precipitation during ongoing deformation. The geological experts try to correlate the different indicators which may vary across length scales, to reconstruct the past events, in order to gain an understanding of vein formation. However, it is difficult to decompose the effect of different processes that might have acted in sequence or simultaneously in such studies. The approximate reconstruction, which determines the final vein morphology could often be misleading and may result in erroneous interpretation of evolution mechanism. On the contrary, numerical methods applied to the study of vein microstructure formation improves the general understanding, as it is possible to decompose the effect of various boundary conditions. Further, computations provide an in-situ look into the temporal evolution of grains. In spite of numerous attempts in the past to simulate the dynamics of vein growth ...
Morphological evolution of eutectoid phases determine the spheroids' size and distribution post s... more Morphological evolution of eutectoid phases determine the spheroids' size and distribution post sub-critical annealing of steel. In this work, the spheroidization of the 3-dimensional cementite plates is investigated via phase-eld modeling to enhance our understanding of the underlying capillary-mediated mechanisms. Since the interfacial energy plays a key role in the spheroidization process, a phase-eld model which e ciently avoids any contribution of the bulk free energy in the interface is employed to recover the sharp interface solutions. It is identi ed that depending on the cementite aspect ratio, the spheroidization mechanism adopted by the plate, varies. In plates of smaller aspect ratios (< 27), the transformation is characterized by the recession of the edges and corners, following which, the entire plate collapses into a single spheroid. However, if the plate aspect ratios are greater than 27, discontinuities set-in due to a curvature-di erence between the receding edges and the at surfaces. Such discontinuities or holes continue to evolve and coalesce during the annealing process. Our phase-eld simulationbased analysis of the cementite spheroidization provides the rst exposure of the spatiotemporal pathways leading to the spheroidization of cementite. A change in the evolution mechanism from the 'edge-migration regime ' to a 'discontinuities-assisted' one, is found to be responsible for the fragmentation of cementite plates. e in uence of the kinetic pathways on the resulting size and spatial distribution of the spheroids are discussed.
In the present study, we employ a multiphase-field model based on the grand chemical potential fo... more In the present study, we employ a multiphase-field model based on the grand chemical potential formulation to simulate the morphological evolution of secondary Widmanst€ atten ferrite (a') during isothermal g (austenite) /a' transformation in binary Fe-C steels. We add the stored-energy to the freeenergy data obtained from CALPHAD database to simulate realistic kinetics of a' plates in diffusioncontrolled regime. By implementing an elliptic anisotropy in the interfacial energy, we study the influence of supersaturation on the growth kinetics and stable morphologies of the single plate and colonies while scrutinising the conformity of numerical simulations with theory. For the first time, we elucidate the curvature-driven mechanism by which, a cascade of parallel offspring plates evolve adjacent to the parent sideplate. The present phase-field simulations, while providing significant insights into the curvature-induced mechanism of evolution of a' colony, also close the gap with in-situ observations reported earlier.
In the present work, we study morphologies arising due to competing substrate interaction, electr... more In the present work, we study morphologies arising due to competing substrate interaction, electric field, and confinement effects on a symmetric diblock copolymer. We employ a coarse-grained nonlocal Cahn-Hilliard phenomenological model taking into account the appropriate contributions of substrate interaction and electrostatic field. The proposed model couples the Ohta-Kawasaki functional with Maxwell equation of electrostatics, thus alleviating the need for any approximate solution used in previous studies. We calculate the phase diagram in electric-field-substrate strength space for different film thicknesses. In addition to identifying the presence of parallel, perpendicular, and mixed lamellae phases similar to analytical calculations, we also find a region in the phase diagram where hybrid morphologies (combination of two phases) coexist. These hybrid morphologies arise either solely due to substrate affinity and confinement or are induced due to the applied electric field. T...
Journal of Geophysical Research: Solid Earth, 2015
Bitaxial crack sealing by epitaxial crystal growth is the most common vein-forming process in Ear... more Bitaxial crack sealing by epitaxial crystal growth is the most common vein-forming process in Earth's crust, but the details of the microstructural processes in these are not well understood. Here we model the evolution of bitaxial crack-seal quartz veins in two and three dimensions, using the phase-field method. Our numerical simulations show the influence of different parameters, such as the obliquity of crack opening and crack location, grain size, and orientations on the evolving vein microstructure. We examine the underlying growth competition observed during epitaxial growth of quartz. Results show many similarities with natural microstructures such as stretched crystals and compare well with the previous numerical findings. As the ratio of crack aperture and matrix grain size for the present studies is chosen to be sufficiently large for growth competition to occur before complete sealing, it leads to the formation of crystal fragments along the crack-opening trajectory. We explain how such fragment trails act as potential indicators of the opening of crack-seal veins, if they are confirmed to be common in natural microstructures. Finally, we highlight the importance of accounting for the third dimension in the numerical simulations by analyzing the evolution of fluid connectivity in 2-D and 3-D during the sealing process. There is an extensive literature describing and analyzing natural vein microstructures (
Numerical simulations of fracture cementation contribute to a better understanding of processes i... more Numerical simulations of fracture cementation contribute to a better understanding of processes involved in their formation and possess the potential to provide valuable insights into the rock deformation history and fluid flow pathways. In this study, the influence of an algorithmically generated fracture surface is investigated, which opens-up temporally along a curved trajectory, on the cement mineralization in 3-D. By adopting a thermodynamically consistent and numerically efficient phasefield approach, the benefits of accounting for an extra third dimensionality are explained. The 3-D simulation results are supplemented by innovative numerical post-processing and advanced visualization techniques. The new methodologies to measure the tracking efficiency of fracture cements reflect the incremental fracture opening and demonstrate the importance of accounting the temporal evolution of grains in 3-D; no such information is usually accessible in field studies and difficult to obtain from laboratory experiments. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures show that cement's grain boundaries and multi-junctions are preferentially arrested at fracture peaks, thereby, enhancing the tracking behavior of syntectonic rock microstructures. By analyzing the temporal evolution of the numerically simulated microstructure, it is found that the grain multi-junctions are pinned more strongly at the peaks on the fractured surface, as compared to the grain boundaries.
ABSTRACT We numerically investigate the characteristics of concurrent carbon redistribution pathw... more ABSTRACT We numerically investigate the characteristics of concurrent carbon redistribution pathways, as the ferrite-austenite front evolves during an isothermal eutectoid transformation starting from a random distribution of preexisting cementite particle. By analyzing the influence of initial interparticle spacing, arrangement and undercooling (below A 1 temperature) on the curvature-driven coarsening, we generalize the present criteria of non-cooperative eutectoid transformation. We also propose plausible mechanisms that result in mixed cementite morphologies (spherical and non-spherical) in the transformed microstructure. For the chosen set of parameters, the present phase-field simulations suggest a strong competition between the cooperative, non-cooperative and coarsening regimes, as the transformation proceeds. The predominance of one or more of the three regimes during the intermittent stages, which depend on the local conditions, determine the cementite size distribution in the transformed microstructure. Phase patterns ΔT = 7.5 K, λmin = 0.21 μm 0.5 μm Highlights • Extension of the theory for a random distribution of pre-existing cementite. • Numerical studies reveal overlapping eutectoid transformation modes. • Amended theory explains mixed cementite morphologies in transformed microstructure.
Numerical simulations of vein evolution contribute to a better understanding of processes involve... more Numerical simulations of vein evolution contribute to a better understanding of processes involved in their formation and possess the potential to provide invaluable insights into the rock deformation history and fluid flow pathways. The primary aim of the present article is to investigate the influence of a 'realistic' boundary condition, i.e. an algorithmically generated 'fractal' surface, on the vein evolution in 3-D using a thermodynamically consistent approach, while explaining the benefits of accounting for an extra dimensionality. The 3-D simulation results are supplemented by innovative numerical postprocessing and advanced visualization techniques. The new methodologies to measure the tracking efficiency demonstrate the importance of accounting the temporal evolution; no such information is usually accessible in field studies and notoriously difficult to obtain from laboratory experiments as well. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures explain the pinning mechanism which leads to arrest of grain boundaries/multi-junctions by crack peaks, thereby, enhancing the tracking behavior.
The non-cooperative eutectoid transformation relies on the presence of pre-existing cementite par... more The non-cooperative eutectoid transformation relies on the presence of pre-existing cementite particles in the parent austenitic phase and yields a product, popularly known as the divorced eutectoid. In isothermal conditions, two of the important parameters, which influence the transformation mechanism and determine the final morphology are undercooling (below A 1 temperature) and interparticle spacing. Although, the criteria which governs the morphological transition from lamellar to divorced is experimentally well established, numerical studies that give a detailed exposition of the non-cooperative transformation mechanism, have not been reported extensively. In the present work, we employ a multiphase-field model, that uses the thermodynamic information from the CALPHAD database, to numerically simulate the pulling-away of the advancing ferrite-austenite interface from cementite, which results in a transition from lamellar to divorced eutectoid morphology in Fe-C alloy. We also identify the onset of a concurrent growth and coarsening regime at small inter-particle spacing and low undercooling. We analyze the simulation results to unravel the essential physics behind this complex spacial and temporal evolution pathway and amend the existing criteria by constructing a Lamellar-Divorced-Coarsening (LDC) map.
We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid t... more We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid transformation in steel. To begin with, we extend the Jackson-Hunt-type calculation, done previously for eutectic transformation, to eutectoid transformation by accounting for diffusion in all the phases. Our principal finding, is that the growth rates, in the presence of diffusion in all the phases, is different from the situation, where diffusion is absent in ferrite and cementite. The difference in the dynamics is described by a factor which comprises of the ratio of the diffusivities of the bulk and the growing phases, along with the ratios of the slopes of the phase co-existence lines. Thereafter, we perform phase-field simulations, which numerically confirm our analytical predictions. Our phase-field simulations also reveal that diffusion in austenite as well as ferrite leads to the formation of tapered cementite along with an overall increase in the transformation kinetics as compa...
In order to address the growth of crystals in veins, a multiphase-field model is used to capture ... more In order to address the growth of crystals in veins, a multiphase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a detailed understanding of the polycrystal growth phenomena in veins, we investigate the influence of various boundary conditions on crystal growth. In particular, we analyze the formation of vein microstructures resulting from the free growth of crystals as well as crack-sealing processes. We define the crystal symmetry by considering the anisotropy in surface energy to simulate crystals with flat facets and sharp corners. The resulting growth competition of crystals with different orientations is studied to deduce a consistent orientation selection rule in the free-growth regime. Using cracksealing simulations, we correlate the grain boundary tracking behavior depending on the relative rate of crack opening, opening trajectory, initial grain size and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in the free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small and crystals touch the wall before the next crack increment starts. Further, we find that within the complete crackseal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack opening velocity is increased and wall roughness is not sufficiently high. Additionally, the overall capability of phase-field method to simulate large-scale polycrystal growth in veins (in 3D) is demonstrated enumerating the main advantages of adopting the novel approach.
We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid t... more We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid transformation in steel. To begin with, we extend the Jackson-Hunt-type calculation (previously used to analyze eutectic transformation) to eutectoid transformation by accounting for diffusion in all the phases. Our principal finding is that the growth rates in presence of diffusion in all the phases is different as compared to the case when diffusion in growing phases is absent. The difference in the dynamics is described by a factor ′ ρ ′ which comprises of the ratio of the diffusivities of the bulk and the growing phases, along with the ratios of the slopes of the phase coexistence lines. Thereafter, we perform phase-field simulations, the results of which are in agreement with analytical predictions. The phase-field simulations also reveal that diffusion in austenite as well as ferrite leads to the formation of tapered cementite along with an overall increase in the transformation kinetics as compared to diffusion in austenite (only). Finally, it is worth noting that the aim of present work is not to consider the pearlitic transformation in totality, rather it is to isolate and thereby investigate the influence of diffusivity in the growing phases on the front velocity.
Abstract Globally, the increasing human population has resulted in land use conversions and cause... more Abstract Globally, the increasing human population has resulted in land use conversions and caused habitat loss to large carnivores leading to their presence in human-dominated landscapes. Because of the shared resources in human-dominated landscape, the interactions between the human and carnivore often becomes negative which becomes a challenging aspect to conservation practitioners. Mitigating these negative interactions has become a priority for wildlife managers to conserve large carnivores, human lives, and livelihoods. Moreover, it poses a challenge to execute effective mitigation measures, especially in areas where these interactions are persistent. Junnar Forest Division in western Maharashtra has a history of livestock damages and attacks on humans by leopard, which may be attributed to change in land use patterns in the past couple of decades assisted by the development of linear infrastructure. In this study we used machine learning to understand the spatio-temporal dynamics of the negative interactions of two decades (1999–2018) using compensation records. We found a significant increase in reporting of cases, especially livestock depredation after the year 2014, with annual depredation cases rising from 66/year to 599/year. A total of 34 human deaths (~1.79/year) and 99 human injuries (~5.21/year) due to leopard attacks were also recorded. Our analysis revealed different categories and clusters of negative human-leopard interactions hot spots in the landscape across the decades. The different categories of hot spots will be crucial for helping in the management interventions and site-specific approaches in the targeted areas for implementing effective mitigation strategies to minimize the chances of negative human leopard interactions in the landscape.
Numerical simulations of vein evolution contribute to a better understanding of processes involve... more Numerical simulations of vein evolution contribute to a better understanding of processes involved in their formation and possess the potential to provide invaluable insights into the rock deformation history and fluid flow pathways. The primary aim of the present article is to investigate the influence of a 'realistic' boundary condition, i.e. an algorithmically generated 'fractal' surface, on the vein evolution in 3-D using a thermodynamically consistent approach, while explaining the benefits of accounting for an extra dimensionality. The 3-D simulation results are supplemented by innovative numerical postprocessing and advanced visualization techniques. The new methodologies to measure the tracking efficiency demonstrate the importance of accounting the temporal evolution; no such information is usually accessible in field studies and notoriously difficult to obtain from laboratory experiments as well. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures explain the pinning mechanism which leads to arrest of grain boundaries/multi-junctions by crack peaks, thereby, enhancing the tracking behavior.
Numerical simulations of vein evolution contribute to a better understanding of processes involve... more Numerical simulations of vein evolution contribute to a better understanding of processes involved in their formation and possess the potential to provide invaluable insights into the rock deformation history and fluid flow pathways. The primary aim of the present article is to investigate the influence of a "realistic" boundary condition, i.e. an algorithmically generated "fractal" surface, on the vein evolution in 3-D using a thermodynamically consistent approach, while explaining the benefits of accounting for an extra dimensionality. The 3-D simulation results are supplemented by innovative numerical post-processing and advanced visualization techniques. The new methodologies to measure the tracking efficiency demonstrate the importance of accounting the temporal evolution; no such information is usually accessible in field studies and notoriously difficult to obtain from laboratory experiments as well. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures explain the pinning mechanism which leads to arrest of grain boundaries/multi-junctions by crack peaks, thereby, enhancing the tracking behavior.
Vein formation in earth’s crust involves a complex interplay of material transport and local prec... more Vein formation in earth’s crust involves a complex interplay of material transport and local precipitation during ongoing deformation. The geological experts try to correlate the different indicators which may vary across length scales, to reconstruct the past events, in order to gain an understanding of vein formation. However, it is difficult to decompose the effect of different processes that might have acted in sequence or simultaneously in such studies. The approximate reconstruction, which determines the final vein morphology could often be misleading and may result in erroneous interpretation of evolution mechanism. On the contrary, numerical methods applied to the study of vein microstructure formation improves the general understanding, as it is possible to decompose the effect of various boundary conditions. Further, computations provide an in-situ look into the temporal evolution of grains. In spite of numerous attempts in the past to simulate the dynamics of vein growth ...
Morphological evolution of eutectoid phases determine the spheroids' size and distribution post s... more Morphological evolution of eutectoid phases determine the spheroids' size and distribution post sub-critical annealing of steel. In this work, the spheroidization of the 3-dimensional cementite plates is investigated via phase-eld modeling to enhance our understanding of the underlying capillary-mediated mechanisms. Since the interfacial energy plays a key role in the spheroidization process, a phase-eld model which e ciently avoids any contribution of the bulk free energy in the interface is employed to recover the sharp interface solutions. It is identi ed that depending on the cementite aspect ratio, the spheroidization mechanism adopted by the plate, varies. In plates of smaller aspect ratios (< 27), the transformation is characterized by the recession of the edges and corners, following which, the entire plate collapses into a single spheroid. However, if the plate aspect ratios are greater than 27, discontinuities set-in due to a curvature-di erence between the receding edges and the at surfaces. Such discontinuities or holes continue to evolve and coalesce during the annealing process. Our phase-eld simulationbased analysis of the cementite spheroidization provides the rst exposure of the spatiotemporal pathways leading to the spheroidization of cementite. A change in the evolution mechanism from the 'edge-migration regime ' to a 'discontinuities-assisted' one, is found to be responsible for the fragmentation of cementite plates. e in uence of the kinetic pathways on the resulting size and spatial distribution of the spheroids are discussed.
In the present study, we employ a multiphase-field model based on the grand chemical potential fo... more In the present study, we employ a multiphase-field model based on the grand chemical potential formulation to simulate the morphological evolution of secondary Widmanst€ atten ferrite (a') during isothermal g (austenite) /a' transformation in binary Fe-C steels. We add the stored-energy to the freeenergy data obtained from CALPHAD database to simulate realistic kinetics of a' plates in diffusioncontrolled regime. By implementing an elliptic anisotropy in the interfacial energy, we study the influence of supersaturation on the growth kinetics and stable morphologies of the single plate and colonies while scrutinising the conformity of numerical simulations with theory. For the first time, we elucidate the curvature-driven mechanism by which, a cascade of parallel offspring plates evolve adjacent to the parent sideplate. The present phase-field simulations, while providing significant insights into the curvature-induced mechanism of evolution of a' colony, also close the gap with in-situ observations reported earlier.
In the present work, we study morphologies arising due to competing substrate interaction, electr... more In the present work, we study morphologies arising due to competing substrate interaction, electric field, and confinement effects on a symmetric diblock copolymer. We employ a coarse-grained nonlocal Cahn-Hilliard phenomenological model taking into account the appropriate contributions of substrate interaction and electrostatic field. The proposed model couples the Ohta-Kawasaki functional with Maxwell equation of electrostatics, thus alleviating the need for any approximate solution used in previous studies. We calculate the phase diagram in electric-field-substrate strength space for different film thicknesses. In addition to identifying the presence of parallel, perpendicular, and mixed lamellae phases similar to analytical calculations, we also find a region in the phase diagram where hybrid morphologies (combination of two phases) coexist. These hybrid morphologies arise either solely due to substrate affinity and confinement or are induced due to the applied electric field. T...
Journal of Geophysical Research: Solid Earth, 2015
Bitaxial crack sealing by epitaxial crystal growth is the most common vein-forming process in Ear... more Bitaxial crack sealing by epitaxial crystal growth is the most common vein-forming process in Earth's crust, but the details of the microstructural processes in these are not well understood. Here we model the evolution of bitaxial crack-seal quartz veins in two and three dimensions, using the phase-field method. Our numerical simulations show the influence of different parameters, such as the obliquity of crack opening and crack location, grain size, and orientations on the evolving vein microstructure. We examine the underlying growth competition observed during epitaxial growth of quartz. Results show many similarities with natural microstructures such as stretched crystals and compare well with the previous numerical findings. As the ratio of crack aperture and matrix grain size for the present studies is chosen to be sufficiently large for growth competition to occur before complete sealing, it leads to the formation of crystal fragments along the crack-opening trajectory. We explain how such fragment trails act as potential indicators of the opening of crack-seal veins, if they are confirmed to be common in natural microstructures. Finally, we highlight the importance of accounting for the third dimension in the numerical simulations by analyzing the evolution of fluid connectivity in 2-D and 3-D during the sealing process. There is an extensive literature describing and analyzing natural vein microstructures (
Numerical simulations of fracture cementation contribute to a better understanding of processes i... more Numerical simulations of fracture cementation contribute to a better understanding of processes involved in their formation and possess the potential to provide valuable insights into the rock deformation history and fluid flow pathways. In this study, the influence of an algorithmically generated fracture surface is investigated, which opens-up temporally along a curved trajectory, on the cement mineralization in 3-D. By adopting a thermodynamically consistent and numerically efficient phasefield approach, the benefits of accounting for an extra third dimensionality are explained. The 3-D simulation results are supplemented by innovative numerical post-processing and advanced visualization techniques. The new methodologies to measure the tracking efficiency of fracture cements reflect the incremental fracture opening and demonstrate the importance of accounting the temporal evolution of grains in 3-D; no such information is usually accessible in field studies and difficult to obtain from laboratory experiments. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures show that cement's grain boundaries and multi-junctions are preferentially arrested at fracture peaks, thereby, enhancing the tracking behavior of syntectonic rock microstructures. By analyzing the temporal evolution of the numerically simulated microstructure, it is found that the grain multi-junctions are pinned more strongly at the peaks on the fractured surface, as compared to the grain boundaries.
ABSTRACT We numerically investigate the characteristics of concurrent carbon redistribution pathw... more ABSTRACT We numerically investigate the characteristics of concurrent carbon redistribution pathways, as the ferrite-austenite front evolves during an isothermal eutectoid transformation starting from a random distribution of preexisting cementite particle. By analyzing the influence of initial interparticle spacing, arrangement and undercooling (below A 1 temperature) on the curvature-driven coarsening, we generalize the present criteria of non-cooperative eutectoid transformation. We also propose plausible mechanisms that result in mixed cementite morphologies (spherical and non-spherical) in the transformed microstructure. For the chosen set of parameters, the present phase-field simulations suggest a strong competition between the cooperative, non-cooperative and coarsening regimes, as the transformation proceeds. The predominance of one or more of the three regimes during the intermittent stages, which depend on the local conditions, determine the cementite size distribution in the transformed microstructure. Phase patterns ΔT = 7.5 K, λmin = 0.21 μm 0.5 μm Highlights • Extension of the theory for a random distribution of pre-existing cementite. • Numerical studies reveal overlapping eutectoid transformation modes. • Amended theory explains mixed cementite morphologies in transformed microstructure.
Numerical simulations of vein evolution contribute to a better understanding of processes involve... more Numerical simulations of vein evolution contribute to a better understanding of processes involved in their formation and possess the potential to provide invaluable insights into the rock deformation history and fluid flow pathways. The primary aim of the present article is to investigate the influence of a 'realistic' boundary condition, i.e. an algorithmically generated 'fractal' surface, on the vein evolution in 3-D using a thermodynamically consistent approach, while explaining the benefits of accounting for an extra dimensionality. The 3-D simulation results are supplemented by innovative numerical postprocessing and advanced visualization techniques. The new methodologies to measure the tracking efficiency demonstrate the importance of accounting the temporal evolution; no such information is usually accessible in field studies and notoriously difficult to obtain from laboratory experiments as well. The grain growth statistics obtained by numerically post-processing the 3-D computational microstructures explain the pinning mechanism which leads to arrest of grain boundaries/multi-junctions by crack peaks, thereby, enhancing the tracking behavior.
The non-cooperative eutectoid transformation relies on the presence of pre-existing cementite par... more The non-cooperative eutectoid transformation relies on the presence of pre-existing cementite particles in the parent austenitic phase and yields a product, popularly known as the divorced eutectoid. In isothermal conditions, two of the important parameters, which influence the transformation mechanism and determine the final morphology are undercooling (below A 1 temperature) and interparticle spacing. Although, the criteria which governs the morphological transition from lamellar to divorced is experimentally well established, numerical studies that give a detailed exposition of the non-cooperative transformation mechanism, have not been reported extensively. In the present work, we employ a multiphase-field model, that uses the thermodynamic information from the CALPHAD database, to numerically simulate the pulling-away of the advancing ferrite-austenite interface from cementite, which results in a transition from lamellar to divorced eutectoid morphology in Fe-C alloy. We also identify the onset of a concurrent growth and coarsening regime at small inter-particle spacing and low undercooling. We analyze the simulation results to unravel the essential physics behind this complex spacial and temporal evolution pathway and amend the existing criteria by constructing a Lamellar-Divorced-Coarsening (LDC) map.
We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid t... more We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid transformation in steel. To begin with, we extend the Jackson-Hunt-type calculation, done previously for eutectic transformation, to eutectoid transformation by accounting for diffusion in all the phases. Our principal finding, is that the growth rates, in the presence of diffusion in all the phases, is different from the situation, where diffusion is absent in ferrite and cementite. The difference in the dynamics is described by a factor which comprises of the ratio of the diffusivities of the bulk and the growing phases, along with the ratios of the slopes of the phase co-existence lines. Thereafter, we perform phase-field simulations, which numerically confirm our analytical predictions. Our phase-field simulations also reveal that diffusion in austenite as well as ferrite leads to the formation of tapered cementite along with an overall increase in the transformation kinetics as compa...
In order to address the growth of crystals in veins, a multiphase-field model is used to capture ... more In order to address the growth of crystals in veins, a multiphase-field model is used to capture the dynamics of crystals precipitating from a super-saturated solution. To gain a detailed understanding of the polycrystal growth phenomena in veins, we investigate the influence of various boundary conditions on crystal growth. In particular, we analyze the formation of vein microstructures resulting from the free growth of crystals as well as crack-sealing processes. We define the crystal symmetry by considering the anisotropy in surface energy to simulate crystals with flat facets and sharp corners. The resulting growth competition of crystals with different orientations is studied to deduce a consistent orientation selection rule in the free-growth regime. Using cracksealing simulations, we correlate the grain boundary tracking behavior depending on the relative rate of crack opening, opening trajectory, initial grain size and wall roughness. Further, we illustrate how these parameters induce the microstructural transition between blocky (crystals growing anisotropically) to fibrous morphology (isotropic) and formation of grain boundaries. The phase-field simulations of crystals in the free-growth regime (in 2D and 3D) indicate that the growth or consumption of a crystal is dependent on the orientation difference with neighboring crystals. The crack-sealing simulation results (in 2D and 3D) reveal that crystals grow isotropically and grain boundaries track the opening trajectory if the wall roughness is high, opening increments are small and crystals touch the wall before the next crack increment starts. Further, we find that within the complete crackseal regime, anisotropy in surface energy results in the formation of curved/oscillating grain boundaries (instead of straight) when the crack opening velocity is increased and wall roughness is not sufficiently high. Additionally, the overall capability of phase-field method to simulate large-scale polycrystal growth in veins (in 3D) is demonstrated enumerating the main advantages of adopting the novel approach.
We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid t... more We investigate the lamellar growth of pearlite at the expense of austenite during the eutectoid transformation in steel. To begin with, we extend the Jackson-Hunt-type calculation (previously used to analyze eutectic transformation) to eutectoid transformation by accounting for diffusion in all the phases. Our principal finding is that the growth rates in presence of diffusion in all the phases is different as compared to the case when diffusion in growing phases is absent. The difference in the dynamics is described by a factor ′ ρ ′ which comprises of the ratio of the diffusivities of the bulk and the growing phases, along with the ratios of the slopes of the phase coexistence lines. Thereafter, we perform phase-field simulations, the results of which are in agreement with analytical predictions. The phase-field simulations also reveal that diffusion in austenite as well as ferrite leads to the formation of tapered cementite along with an overall increase in the transformation kinetics as compared to diffusion in austenite (only). Finally, it is worth noting that the aim of present work is not to consider the pearlitic transformation in totality, rather it is to isolate and thereby investigate the influence of diffusivity in the growing phases on the front velocity.
Abstract Globally, the increasing human population has resulted in land use conversions and cause... more Abstract Globally, the increasing human population has resulted in land use conversions and caused habitat loss to large carnivores leading to their presence in human-dominated landscapes. Because of the shared resources in human-dominated landscape, the interactions between the human and carnivore often becomes negative which becomes a challenging aspect to conservation practitioners. Mitigating these negative interactions has become a priority for wildlife managers to conserve large carnivores, human lives, and livelihoods. Moreover, it poses a challenge to execute effective mitigation measures, especially in areas where these interactions are persistent. Junnar Forest Division in western Maharashtra has a history of livestock damages and attacks on humans by leopard, which may be attributed to change in land use patterns in the past couple of decades assisted by the development of linear infrastructure. In this study we used machine learning to understand the spatio-temporal dynamics of the negative interactions of two decades (1999–2018) using compensation records. We found a significant increase in reporting of cases, especially livestock depredation after the year 2014, with annual depredation cases rising from 66/year to 599/year. A total of 34 human deaths (~1.79/year) and 99 human injuries (~5.21/year) due to leopard attacks were also recorded. Our analysis revealed different categories and clusters of negative human-leopard interactions hot spots in the landscape across the decades. The different categories of hot spots will be crucial for helping in the management interventions and site-specific approaches in the targeted areas for implementing effective mitigation strategies to minimize the chances of negative human leopard interactions in the landscape.
Uploads
Papers by Kumar Ankit