Department of Mechanical engineering
Permanent URI for this collectionhttp://localhost:4000/handle/123456789/1921
Browse
5 results
Search Results
Item Deformation and boundary motion analysis of a faceted twin grain boundary(Elsevier, 2024-05) Mishra, Radha RamanIn this article, molecular dynamics simulations are used to understand how a nickel bicrystal with faceted incoherent Σ3 grain boundaries responds to uniaxial tensile loading. The deformation response is studied over a wide range of temperatures (100 – 900 K) and strain rates (107 – 1010 s−1). The dislocation extraction algorithm and common neighbor analysis are employed to identify the deformation mechanisms. Our results reveal that the yield stress decreases with temperature and increases with strain rate; whereas the elastic modulus decreases with temperature and is independent of strain rate. Furthermore, incipient plasticity is detected ahead of the yield point at lower temperatures and lower strain rates. Interestingly, the incoherent twin grain boundaries are quite mobile under the uniaxial tensile loading at lower temperatures and lower strain rates. But this mobility decreased at higher temperatures and higher strain rates, thereby, confirming this faceted grain boundary's non-Arrhenius (anti-thermal) migration behavior even under mechanical loading. From a deformation perspective, the incoherent twin facet of the grain boundary served as the major source for stacking fault formation at lower temperatures and higher strain rates. However, with the increase in temperature, the stacking faults became shorter and originated from both the incoherent twin facet and the tips of coherent twin facet. These results are in qualitative agreement with the experimental results documented in the literature.Item 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, TribeniHierarchical (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.Item Synergistic effects of temperature and strain rate on tensile properties of simulated Ni-6Cu alloy with Σ3 non-Arrhenius grain boundary(Taylor & Francis, 2023) Mishra, Radha RamanComprehending the mechanical response of materials on an atomic level is pivotal in the optimisation of advanced materials with superior mechanical properties. This research article utilises the atomistic-scale based molecular dynamics simulations to report the uniaxial tensile behaviour of bicrystalline Ni-6Cu (Nickel – 94% and Copper – 6%) alloy incorporated with pre-existing faceted Σ3 [111] 60° {11 8 5} grain boundaries. The primary aim of this investigation is to comprehend the performance of bicrystalline Ni-6Cu alloy under varying thermodynamic conditions and to assess the influence of pre-existing faceted grain boundaries on its tensile behaviour. This work encompasses a range of strain rates (108 to 1010 1/s) and temperatures (spanning from 100 to 900 K) for the uniaxial tensile deformation simulations. The outcomes unveil that the Young’s modulus of Ni-6Cu alloy (with pre-existing faceted grain boundaries embedded in its domain) was inversely proportional to temperature and constant with respect to strain rate. For the same configuration, yield stress was inversely and directly proportional to temperature and strain rate, respectively. Interestingly, incipient plasticity in the tensile stress–strain response was observed at lower temperature and lower strain rate. From the microstructural point of view, at lower temperatures, the incoherent twin boundary served as a source for the nucleation of stacking faults; however, as the temperature increased, both the incoherent twin boundary and the tips of coherent twin boundary function as the source for stacking faults formation. Our simulations also verified the GB’s anti-thermal (or non-Arrhenius) migration behaviour even under tensile load.Item Exploring deformation mechanisms in a refractory high entropy alloy (MoNbTaW)(Elsevier, 2025-02) Mishra, Radha RamanUnderstanding the deformation behaviour of refractory high-entropy alloy (rHEA) at elevated temperatures are crucial due to their potential for high-temperature applications. In this study, molecular dynamics simulations were employed using a highly accurate machine learning- based forcefield to investigate the deformation behaviour of MoNbTaW rHEA under uniaxial tensile and compressive loading. Additionally, the dependency of deformation behaviour on the applied strain rates (5e8, 1e9, 5e9 and 1e10 s−1) and temperatures (300, 800, 1000 and 1200 K) was investigated. The yield strength of MoNbTaW rHEA increased by two-fold during compressive loading when compared to tensile loading. During tensile deformation, the BCC-FCC-other atom transition resulted in the formation of stripe-like twinning along the {112} plane. On the contrary, during compressive loading, BCC directly transitioned into other atoms, forming twinning that later acted as the nucleation sites for dislocations. These findings further demonstrate that the deformation mechanism during tensile loading is governed by the twinning mechanism, whereas during compressive loading, dislocation-induced plasticity plays a vital role.Item 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, TribeniSilicon 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.