BITS Faculty Publications
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Item Molecular dynamics study on tensile strength of ni-10cu alloy with pre-existing σ3 grain boundary(Springer, 2024-07) Mishra, Radha RamanThis book presents select proceedings of the International Conference on Mechanical Engineering (INCOME 2023). It includes the topics related to design and functional requirements of components used in mechanical systems. The contents covered include concept design, detailed design, structural design, mechanics, static, and dynamic systems. The book also discusses various methods of software-aided design and analysis. Given the contents, the book is a valuable reference for beginners, researchers, and professionals working in various domains of mechanical engineering.Item Numerical simulation study on microwave joining of Hastelloy C-276 plates using Inconel-718 interface powder(Elsevier, 2024) Mishra, Radha RamanMicrowave joining is an emerging technique for the joining of metallic materials because it can join metals faster and offers uniform heating. The current work studies the multi-physics simulation of a microwave-joined Hastelloy C-276 plate with Inconel 718 interface powder inside a multimode microwave applicator at 2.45 GHz and 900 W. The distribution of electric field, temperature, and thermal stress in the joint were analyzed to understand the microwave-joined Hastelloy C-276 plates. The results revealed that the maximum values of electric field strength and temperature at the central plane of symmetry were 7.4 × 104 V/m and 1.43 × 103 ⁰C, respectively. The maximum thermal stress (1.37 × 109N/m2) was estimated using von-Mises criterion. Resistive losses were found to be maximum i.e., 2.72 × 108 W/m3 at the ends of the graphite plate. The study determined the optimum parameters for microwave joining of Hastelloy C-276 plates.Item Unravelling the atomistic-scale insights into tensile response of equiatomic cupronickel alloy with pre-existing faceted grain boundary interface(Elsevier, 2024-02) Mishra, Radha RamanThe aim of this research work is to investigate the effect of strain rates and temperatures on the mechanical properties of an equiatomic copper-nickel (Cu–Ni) alloy with a pre-existing faceted Σ3 [111] 60° {11 8 5} grain boundary. Molecular dynamics simulations conducted in this scrutiny focuses on understanding the tensile behaviour of bicrystalline equiatomic Cu–Ni alloys (denoted by Cu50Ni50) under various thermodynamic conditions. The uniaxial tensile deformation simulation was carried out at various strain rates (108, 109 and 1010 1/s) in conjunction with different conditions of cryogenic temperature (100 K), room temperature (300 K) and high temperature (500 K). The authors found that the yield stress and Young's modulus of the bicrystalline Cu50Ni50 alloy were highest at the cryogenic temperature, and decreased as the temperature increased. To add on, the yield stress of the bicrystalline Cu50Ni50 alloy increased with an increase in the strain rate value. From the microstructural and dislocation analysis point of view, it was observed that the formation of dislocations was lowest at the cryogenic temperature. Interestingly, at the yield point, the coherent twin boundary tip act as the nucleation site for the dislocations for cryogenic temperature condition. These findings shed light on the relationship between the temperatures, strain rates, and the mechanical properties of Cu–Ni alloys, which will aid in reporting the optimized conditions for their desired engineering applications. It is also proposed that tailoring of the tensile properties is achievable by exposing Cu–Ni alloys to various environmental conditions (cryogenic, ambient, and elevated temperatures with different applied strain rates).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 Casting of materials using microwave energy(Springer, 2024-08) Mishra, Radha RamanMicrowave energy has been widely used in various material processing methods such as drying, sintering, joining, and cladding processes. However, its use has been very limited in the field of casting of materials. Microwave casting has gained significant attention in recent years due to its potential to reduced processing time and energy consumption, improved quality of castings, and reduced porosity over conventional casting methods. This chapter provides a brief idea about the fundamentals associated with the microwave casting process. Major research reported in this area have been highlighted. The role of different process parameters as well as the challenges and opportunities associated with the microwave casting process have been briefly discussed.Item Exploring microwave heating characteristics of polycrystalline 3c-sic using molecular dynamics study(MDPI, 2024-09) Mishra, Radha RamanPolycrystalline silicon carbide (SiC) has been significantly used as a susceptor material during microwave-based material processing owing to its excellent microwave absorption properties. However, the interaction of microwaves with polycrystalline SiC at an atomic level has not been explored experimentally or theoretically. This work investigates the microwave heating characteristics of polycrystalline cubic 3C-SiC through molecular dynamics (MD) simulation using the Vashishta interatomic potential. The effect of change in electric field strength and frequency on the structural evolution and thermo-physical properties of polycrystalline 3C-SiC has been studied. The study revealed that the presence of grain boundaries in polycrystalline 3C-SiC structures plays a critical role in enhancing microwave absorption efficiency. Microwave exposure to polycrystalline 3C-SiC beyond 2830 K significantly increases total energy; consequently, a solid-to-liquid transition occurs in the 3C-SiC structure, initiated from the grain boundaries. Further, an increase in microwave exposure time results in a reduction in grain size due to rapid microwave absorption at grain boundaries. The phase transition temperature of polycrystalline 3C-SiC was observed to be 14% lower than that of the single-crystal 3C-SiC.Item 4D printing: fundamentals and applications(IOP, 2024-12) Mishra, Radha RamanThis chapter presents a comprehensive overview of 4D printing, including the process fundamentals, materials, techniques, challenges, and applications.Item Unraveling atomistic heating behavior of vacancy induced 3C-SiC during microwave exposure(Elsevier, 2025-01) Mishra, Radha Raman; Roy, TribeniThis study explores the impact of pre-existing silicon and carbon vacancies on the microwave heating of 3C-SiC at an atomistic level using molecular dynamics simulations. Microwaves were introduced at different electric field strengths (0.1 and 0.5 V/Å) and different frequencies (100, 150, 200, 250 and 300 GHz) to the vacancy-induced 3C-SiC crystal to understand its heating characteristics. During microwave exposure, the temperature of the 3C-SiC crystal increased rapidly with increasing Si vacancies, electric field strength, and frequency. The results revealed that 3C-SiC crystals having 1.5 % and 2.0 % Si vacancies undergo 40–50 % physical and structural change with the application of microwave for 4.985 ns and 4.49 ns, respectively, at 0.5 V/Å and 300 GHz. Additionally, a comparative analysis was performed to study the microwave heating rate of 3C-SiC with Si and C vacancies (1.5 and 2.0 %). C vacancies at 1.5 % and 2.0 % showed 95.5 % and 142.2 % higher heating rates, respectively, than Si vacancies. Additionally, beyond 1000 K, microwave heating is driven by structural changes induced by vacancies as compared to the thermal conductivity of the 3C-SiC crystal.