Department of Mechanical engineering

Permanent URI for this collectionhttp://localhost:4000/handle/123456789/1921

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Author: search.filters.author.Roy, TribeniSubject: search.filters.subject.Molecular dynamics

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    A close-packed sphere model for characterising porous networks in atomistic simulations and its application in energy storage and conversion
    (Elsevier, 2024-05) Belgamwar, Sachin U.; Mishra, Radha Raman; Roy, Tribeni
    Hierarchical (micro, meso & macro) porosity in materials plays a crucial role in influencing the movement of ions which governs the energy and power density during energy storage and conversion. The extant available methods to characterise porosity across scales (nano to meso to macro) lacks rigour and accuracy. Having accurate assessment of the porosity in materials can unlock new designs of electrodes for energy efficient energy storage and conversion devices such as batteries, supercapacitors and fuel cells. Through this work, we report the systematic development of a method to fully characterise the carbon porous networks using a molecular dynamics simulation testbed. Our work entails modelling and simulation of porous carbon structures using quenched molecular dynamics (QMD) simulations using Gaussian Approximation potential (GAP) and benchmarking the results with prior literature. This modelling technique can reliably be used for quantitative characterisation of the interconnectivity in porous structures to study ionic movements and charge transfer mechanisms. A new parameter, namely nearest neighbour search (NNS) coefficient was introduced to quantify homogeneity and networking in the porous structures. NNS coefficient increased from 1.62 to 1.92 with decrease of the annealing temperature from 8000 K to 4000 K in carbon. The procedure outlined was although tested on porous carbon networks, but adaptable to study any other material system at multi-length scales.
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    Analysis of material removal mechanism in nanoscale machining of copper
    (Sage, 2024-01) Sharma, Anuj; Roy, Tribeni
    In the current study, molecular dynamics modeling and simulation are carried out to analyse mechanisms in tool-workpiece interaction in nanoscale cutting. Various combinations of a/r ratios for constant r (r = tool edge radius and a = uncut chip thickness) are considered and different crystal orientations of the workpiece specimen are employed in the nanoscale cutting model. From the simulation, material anisotropy behavior is observed during the nanoscale cutting of copper material. Analysis at the molecular scale reveals that the crystal orientations family {1 1 0}<1 0 0> is hard to machine and the family of crystal planes {1 1 1}<1 1 0> is easiest to cut. While comparing in different crystal planes and directions, it was noticed that the material deformation in nanoscale machining takes place only in slip directions, that is, <1 1 0> family of directions. It is also found that as the uncut chip thickness is decreased, the cutting mechanism changes from shear plane cutting to plowing to sliding in Cu.
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    Molecular dynamics simulation of single discharge and dimensionless correlation with actual material removal in micro electrical discharge machining
    (Taylor & Francis, 2019-06) Roy, Tribeni; Sharma, Anuj
    Shorter time pulses and length scales in micro EDM (MEDM) makes it difficult to observe the material removal phenomena taking place at very small zone during discharge. Since numerical or analytical model considers material to be uniform/isotropic, it cannot predict the discrete effects viz. crystal structure distortion due to discharge. Also, little attention has been given to the mechanism of material removal in MEDM at the atomistic level. Therefore, to understand the behaviour of material removal and crystal structure distortion due to single spark in MEDM, MD simulations have been carried out. Based on MD simulations, it was found that the percentage of material removed by vaporisation (∼40%) was higher at spark energies used in this model as compared to spark energies used by Wong et al. (20% at 23.50 µJ). Conversion from FCC crystal structure to amorphous was observed at the top surface of crater in both cases; the one with higher spark energy has marginally higher distortion indicating higher amorphisation. A new method is proposed based on which a dimensionless correlation was obtained between results of MDS and experiments which relates the ratio of specific material removal at higher spark energy to that at lower energy for both MDS and experiments
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    Comparative analysis of mechanical properties for mono and poly-crystalline copper under nanoindentation – Insights from molecular dynamics simulations
    (Elsevier, 2022-02) Roy, Tribeni; Sharma, Anuj
    Crystallographic orientation and grain size for monocrystalline and polycrystalline materials respectively play a critical role in defining their mechanical behaviour under nanoindentation. To understand their effects on mechanical properties, molecular dynamics (MD) simulations help in revealing the underlying physical phenomena governing the nanoindentation behaviour. This paper attempts to comparatively analyse and study the effects of crystallographic orientations of monocrystalline copper {(100), (110) and (111)} and critical grain size of polycrystalline copper on the nanoindentation response using MD simulations. The results obtained for indentation load vs. depth curve, hardness, dislocations, and elastic recovery were analysed for comparison. Cu(111) exhibited an average hardness of 12.62 GPa, which is 18.27% more than that of Cupoly. The pile-ups of 8 Å size were observed in Cupoly; and this was higher than any of copper system studied here. The dislocation extraction algorithm (DXA) analysis revealed that the total dislocations in Cu(111) was 34.23% and 153.8% lower than that of Cu(110) and Cupoly, respectively. Cu(111) comprised of highest Stair-rod dislocation along with LC and Hirth locks. Furthermore, a prismatic loop comprised of sessile dislocations also appeared in Cu(111). The elastic depth recovery rate for Cu(100) was 52.75%, 41.60% and 40.66% higher than that of Cu(110), Cu(111) and Cupoly, respectively. This study revealed that the nanoindentation based mechanical performances of monocrystalline copper systems, specifically Cu(111) were superior to any other copper systems.
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    Thermo-physical characteristics of 3C‐SiC structure subjected to microwave exposure: A molecular dynamics study
    (Elsevier, 2023-06) Mishra, Radha Raman; Belgamwar, Sachin U.; Roy, Tribeni
    Silicon carbide (SiC) is widely used as a susceptor for microwave hybrid heating applications owing to its exceptional microwave absorbing characteristics. In practice, it is challenging to characterize the thermo-physical behaviour of the microwave irradiated SiC-based targets experimentally due to interference of integrated measurement devices with microwaves. In this article, molecular dynamics simulations were performed to understand the atomistic response of a bulk 3C‐SiC model during microwave heating. Atomistic simulations were performed at different electric field strengths (ranging from 0.1 to 0.5 V/Å) and frequencies (ranging from 100 to 500 GHz) to develop a numerical relationship between temperature and time in order to predict the thermal response of bulk 3C‐SiC. On the other hand, the physical characteristics of the bulk 3C‐SiC were determined by the plots between mean square displacement (MSD), time and diffusion coefficients. The results showed that at 0.5 V/Å electric field strength and 500 GHz frequency, the diffusion coefficient increased up to 88% as compared to the electric field strength of 0.1 V/Å at 500 GHz. A change of 75% in the physical phase of 3C‐SiC structure with respect to the initial structure was confirmed by the distorted density distribution profile.