Browsing by Author "Mishra, Radha Raman"

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4D printing: fundamentals and applications
(IOP, 2024-12) Mishra, Radha Raman
This chapter presents a comprehensive overview of 4D printing, including the process fundamentals, materials, techniques, challenges, and applications.
Analysis of Density of Laser Powder Bed Fusion Fabricated Part Using Decision Tree Algorithm
(Springer, 2023-05) Mishra, Radha Raman
Additive manufacturing (AM) enabled manufacturing industries to fabricate metallic components with complex shapes. However, the properties of additively manufactured parts need further improvements to compete with the performance of traditionally manufactured parts. Machine learning (ML) models provide an alternative to study the correlation between the process parameters–properties of the fabricated parts. In the present work, the ML approach has been applied to understand the effect of AM process parameters on the density of additively built parts. The decision tree model was developed for the laser powder bed fusion-processed parts based on the input parameters such as laser power, scan speed, hatching space, energy density, and build rate. The model was trained and tested with experimental data obtained from the relevant literature. The process parameters were optimized to achieve the desired density of the part. A good agreement was indicated between the predicted and experimental data. The study revealed the applicability and potential of the model to determine and predict the density of the additively manufactured parts.
Applications and Drawbacks of Epoxy/Natural Fiber Composites
(Springer, 2022-03) Mishra, Radha Raman
Epoxy is a thermosetting polymer and due to its versatile characteristic it is made useful as matrix material in fabrication of polymer composite. Wide diversity of epoxy composites make its application in different industries such as coating, insulator, electric components, adhesives, sound acquisition, automobile, packaging, construction material, etc. The major application of epoxy composites is in the area of thermal insulation such as electric switch board, decorative article coating, tiles, and other civil constructions works. Another important property of epoxy composite is of good electric insulator as compared to metal matrix composites. But there are also some limitations such as low impact strength, nonbiodegradability, delamination, brittleness, and fracture toughness behavior, which limit its applications. To overcome these limitations, certain measures have been taken by different researchers such as incorporation of natural fibers, modification in chemical structure, particle reinforcement, etc.. Natural fibers come out as one of the prominent sources of reinforcement material for polymer composites due to their high strength and modulus of the fibers, fiber dispersion, fiber-matrix adhesion, and increase in toughness of the matrix. In this chapter overview of natural fibers with their advantages and disadvantages as reinforcement material in polymer composites has been provided. Studies of thermosetting polymer mainly epoxy resin including its thermal, mechanical, and chemical properties also have been done. Comparison of thermosetting resin with thermoplastic resin and curing stages of epoxy composites is discussed. Application of epoxy composites reinforced with natural fiber as thermal and electrical insulator is done in detail.
Casting of materials using microwave energy
(Springer, 2024-08) Mishra, Radha Raman
Microwave 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.
Challenges in Microwave Processing of Bulk Metallic Materials and Recent Developments
(Association for Microwave Power in Europe for Research and Education, 2018-07) Mishra, Radha Raman
In the recent years, microwave energy has been exploited for processing of metallic materials through different heating based processes such as sintering, joining, cladding, casting and drilling. Metallic powders are primarily processed through microwave sintering; whereas, other processes are used to heat/melt/ablate desired portion of the bulk metallic materials. Microwave sintering is the most mature process in terms of the literature and its presence in the industry among these processes. The feasibilities of casting, joining and cladding processes are well documented, though they are yet to become popular in industrial applications as alternatives to the conventional processes. Microwave drilling of non-metals have been demonstrated; however, drilling of the bulk metals using microwave energy is in the investigation stage and needs exhaustive experimentation to get established as an advanced metal machining process. This letter provides an overview of microwave energy based techniques used for processing of bulk metallic materials. The challenges in processing these materials have been identified; processing strategies have been briefly discussed. Future research opportunities in microwave processing of the bulk metallic materials have been outlined.
Characterization of SiC-Reinforced AZ91 Magnesium Alloy Composites Produced Using In situ Microwave Casting
(Springer, 2021-02) Mishra, Radha Raman
Magnesium-alloys-based metal matrix composites (MMCs) are one of the most researched materials for producing industrial components due to their high specific strength. In recent years, microwave energy has been used for processing of various materials including polymers, ceramics, metals, and composites owing to significant saving of energy and time as compared to the conventional processes. In the present work, microwave energy at 2.45 GHz was used to fabricate AZ91 magnesium-alloy-based MMCs. The AZ91 magnesium alloy (bulk) pieces were hybrid heated inside a microwave applicator at 1400 W. The melt was processed with silicon carbide (SiC) and allowed to pour into a graphite mold. The produced composites were characterized to study their microstructural properties. The microstructural characterization of the composites revealed that distribution of SiC particles is uniform. Finer grains were achieved in the composite as compared to as-received alloy. The presence of SiC, Mg2Si, Mg2C, Mg2C3, Mg17(Al, Zn)12, and α-Mg phases was confirmed in the composite through energy-dispersive X-ray spectroscopy analysis. The micro-indentation hardness of the composite was found as 206 ± 28 HV which is higher than as received alloy.
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.
Deformation and boundary motion analysis of a faceted twin grain boundary
(Elsevier, 2024-05) Mishra, Radha Raman
In 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.
Design of a Customized Fixture for Joining Jute Fiber-Based Composites Using Microwave Energy
(Springer, 2021-02) Mishra, Radha Raman
Polymer matrix composites (PMCs) fabricated using natural fibers as reinforcement are preferred in many engineering applications including marine, automotive and aerospace industry due to their eco-friendly nature. The components fabricated using natural fiber-based PMCs often need the joining of different sections to fabricate an industrial component. Usually, adhesive joining is used to join the thermoplastic-based composite parts. However, achieving adequate mechanical strength is challenging due to moisture entrapment in between the joining adherents and uneven transfer of heat, which causes the burning of matrix material and damage to the natural fibers. In the present work, PMCs were developed through the compression molding technique using jute fibers as reinforcement and polypropylene (PP) as matrix material. Subsequently, developed composite samples were lap joined using microwave energy at 2.45 GHz and 900 W. A special fixture was designed and developed to concentrate microwave energy around the joining area. The study demonstrates that microwave energy provides rapid heating (75 s) for joining on the samples. Using the developed fixture, the tensile test results for fabricated composite joints revealed that the maximum joint efficiency was 81% with the maximum tensile strength of 21 MPa. The present study indicates that microwave energy can be further exploited as a potential rapid joining process for polymers in the future.
Designing porous electrode structures for supercapacitors using quenched MD simulations
(Elsevier, 2022) Mishra, Radha Raman; Belgamwar, Sachin U.; Roy, Tribeni
Recently, supercapacitors with hierarchical porous structured electrodes are gaining a lot of research interest due to their unique qualities such as high power, durability and eco-friendly nature. In this study, porous structured electrodes were generated using quenched molecular dynamics (QMD) simulations, that can provide high energy density by virtue of high porosity. Here, three different quench rates (16, 8 and 4 K/ps) were applied on liquid carbon system to generate different porous structures. It was observed that at 4000 K, the carbon atoms become disorderly bonded and arranges themselves in an ordered hexagonal ring sheets after the completion of quenching process at 300 K. The porous carbon structures were visualized by contour surface mesh. The pore size distribution showed an increase of 62% on decreasing the quench rate from 16 K/ps to 4 K/ps. These light-weight porous carbon structures may also be tested for mechanical and electrical performances, which can have future implications as electrodes for supercapacitor.
Effect of carbon-vacancy on microwave heating characteristics of 3C-SIC
(Springer, 2025-08) Mishra, Radha Raman
Understanding the thermal response of materials with defects under microwave irradiation is critical for various applications, including electronics, materials science, and energy conversion. This study investigates microwave energy interaction with carbon defect-induced 3C-SiC by employing non-equilibrium molecular dynamics to gain insights into the molecular level heating of 3C-SiC in the presence of carbon defects. Simulation studies were conducted to explore the effects of microwave irradiation at varying electric field strengths and frequencies. The results demonstrated that introducing C-vacancies within the 3C-SiC system significantly improved microwave absorption, enabling the material to reach the melting point more rapidly than pure 3C-SiC. Moreover, this simulation study revealed that C-vacancies facilitated higher atomic diffusivity within the system. At 2.0% C-vacancy concentration, the 3C-SiC system exhibits 492, 260, and 77.8% higher diffusivity than 0.5, 1.5, and 1.5% C-vacancy concentration, respectively, at an electric field strength of 0.5 V/Å and frequency of 300 GHz. Pair correlation function study revealed a reduction in crystallinity by approximately 60 for 0.5% C-vacancy concentration during microwave irradiation. Pair correlation function analysis further confirmed that the accelerated solid-to-liquid phase transition occurred with increasing C-vacancy concentration and microwave exposure time.
Effect of input microwave power and insulation on microstructure and tensile properties of cast Al 7039 alloy produced at 2.45 GHz
(Taylor & Francis, 2020-10) Mishra, Radha Raman
In the present work, microwave energy was used for casting Al 7039 alloy at 2.45 GHz in the ambient cavity environment. Effects of input power and insulation of the mould assembly during irradiation on charge melting and mould preheating were studied. Five different casts were produced at 1000 W, 1200 W, 1400 W, 1400 W with an insulated pouring basin and 1400 W with insulated mould assembly. Melting time of the charge was the least while using 1400 W with insulated mould assembly, whereas preheating of the mould was observed minimum during casting at 1400 W inside an insulated pouring basin. Cast microstructures revealed that less preheating of the mould resulted in finer grains and intermetallics, which improve tensile properties of the cast. Fractographic analyses showed the presence of coarse intermetallics in the casts produced with insulated mould assembly, which resulted in significant reduction of tensile properties.
Effect of Solidification Environment on Microstructure and Indentation Hardness of Al–Zn–Mg Alloy Casts Developed Using Microwave Heating
(Springer, 2017-09) Mishra, Radha Raman
In the present work, microwave casting of Al 7039 was carried out using microwave energy at 2.45 GHz and 1400 W. A set of casts were developed through the in situ microwave casting process inside the applicator cavity applying three different solidification conditions, i.e., closed cavity cooling (cast C1), open cavity cooling (cast C2) and water-cooled cavity cooling (cast C3), whereas another cast was developed through conventional microwave casting (cast C4). Microstructure and microindentation hardness studies of the developed casts revealed that dense cast with smaller equiaxed grains could be obtained in the cast C3. Presence of the intermetallic phases, MgZn2, Mg2Si, Al3Fe and Al8Fe2Si, was observed in the in situ casts, whereas the cast C4 contains intermetallic phases: MgZn2, Mg2Si, Al2Cu, Al2CuMg and Al7Cu2Fe. It was found that the grain structure and major attributes of the intermetallic precipitates (size, shape and distribution) in the casts significantly depend on the solidification conditions. Average microindentation hardness of the cast C4 was found to be 191 ± 32 HV which is higher than other casts. The study showed that microindentation characteristics of the casts depend more on attributes of the precipitated intermetallic phases during solidification than the grain size
Effect of SS-316L and nickel-based interface powders on joint characteristics of microwave welded SS-316L plates
(Sage, 2024-05) Mishra, Radha Raman
Microwave energy has been exploited as a rapid and volumetric heating source in various manufacturing applications, such as microwave joining. This study used stainless steel (SS-316L) plates to be microwave-joined at 2.45 GHz. The microwave hybrid heating (MHH) technique was used to prepare joints inside a microwave applicator using nickel-based (EWAC 1004EN) and SS-316L interfacing powders at 900 W. Microstructural and mechanical characterizations of the developed joints were performed to understand the effect of the interface powder on weld quality. Microstructural observations revealed adequate metallurgical bonding between interfacing powders and bulk metal with columnar and dendritic grains (EWAC-based joint) and equiaxed grains (SS-316L-based joint). The phase analysis revealed the presence of intermetallic phases such as iron-nickel, chromium carbide, and chromium iron carbide in EWAC-based joint and iron-nickel, nickel-chromium, and chromium carbide in SS-316L-based joint, which contribute to enhanced joint microhardness compared to base alloys. A larger grain size, more low-angle boundaries, and higher misorientation angles were found in the EWAC-based joint. Furthermore, the average ultimate tensile strength of SS-316L-based joints was 26% higher, with a 6.9% enhanced elongation, than that of EWAC-based joints. The EWAC-based joint exhibited better corrosion resistance than that of SS-316L-based joint.
Effect of susceptor and mold material on microstructure of in-situ microwave casts of Al-Zn-Mg alloy
(Elsevier, 2017-10) Mishra, Radha Raman
In-situ microwave casting is a novel technique; it is based on the principles of microwave hybrid heating. The dynamics of the process and the cast quality are significantly influenced by the materials used in the microwave irradiation. In the present work, role of susceptor and mold on exposure time, melting time, mold preheating and cast properties is studied. Physics of the process in the context of exposure time and mold materials is discussed. The aluminum alloy 7039 casts were developed in ambient atmosphere inside an applicator using microwaves at 2.45 GHz and 1400 W. Charge was hybrid heated using susceptors – SiC and ceramic crucible to melt and cast in-situ in the preplaced alumina and graphite molds. Characterization reveals that grain structures of the casts were influenced by mold preheating and mold material. Finer grains with higher micro-pores were observed in the casts developed in alumina mold with SiC susceptor. The casts contain MgZn2, Mg2Si, Al3Fe and Al8Fe2Si as intermetallics; however, their distribution and size depend upon the cooling pattern of the melt. Microindentation hardness of the casts developed in alumina mold with SiC susceptor was observed to be the highest (146 ± 10 HV) among the developed casts.
Effective parameters of electrochemical discharge machining–a review
(International Journal of Mechanical And Production Engineering, 2014-05) Mishra, Radha Raman
The specific requirements of Advanced materials in Advanced industries like nuclear reactor, Automobiles, Aeronautic have raise the need of Advance machining processes which are able to machine such materials with high material removal rate as well as desired surface quality. Electrochemical discharge machining (ECDM) is one of the hybrid advance machining processes which have potential to machine advance materials with good surface quality desired by Industries. The selection of parameter for higher Material removal rate, higher Surface finish and minimum Tool wear Rate is very essential during ECDM. In this present review Paper, a study of the effective Parameters of ECDM has been carried out with their specific role in Material removal; Surface Finish and Tool wear Rate. The optimized range of parameters by different optimizing techniques has been summarized.
Experimental investigation on in-situ microwave casting of copper
(IOP, 2018) Mishra, Radha Raman
The in-situ microwave casting of metallic materials is a recently developed casting process. The process works on the principles of hybrid microwave heating and is accomplished inside the applicator cavity. The process involves – melting of the charge, in-situ pouring and solidification of the melt. The electromagnetic and thermal properties of the charge affects microwave-material interaction and hence melting of the charge. On the other hand, cooling conditions inside the applicator controls solidification process. The present work reports on in-situ casting of copper developed inside a multimode cavity at 2.45 GHz using 1400 W. The molten metal was allowed to get poured in-situ inside a graphite mold and solidification was carried out in the same mold inside the applicator cavity. The interaction of microwave with the charge during exposure was studied and the role of oxide layer during meltingthe copper blocks has been presented. The developed in-situ cast was characterized to access the cast quality. Microstructural study revealed the homogeneous and dense structure of the cast. The X-ray diffraction pattern indicated presence of copper in different orientations with (1 1 1) as the dominant orientation. The average micro indentation hardness of the casts was found 93±20 HV.
Exploring deformation mechanisms in a refractory high entropy alloy (MoNbTaW)
(Elsevier, 2025-02) Mishra, Radha Raman
Understanding 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.
Exploring microwave heating characteristics of polycrystalline 3c-sic using molecular dynamics study
(MDPI, 2024-09) Mishra, Radha Raman
Polycrystalline 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.
Introduction to Molecular Dynamics Simulations
(Springer, 2022-08) Mishra, Radha Raman
The invention of novel functional materials and their investigation at the molecular level are vital in today’s nanotechnology era. Atomistic modelling approaches are cost-effective and time-consuming alternatives to expensive and time-consuming experimental methods, and they are precise enough to predict the mechanical characteristics of materials. The current chapter goes through the many steps involved in a molecular dynamic’s investigation. The various types of interatomic potentials and their applicability to various materials have been thoroughly examined. Following that, the integration algorithm for solving a set of Newton’s equations, as well as the radius cut-off distance and temperature control, was addressed. Afterwards, many types of ensembles and boundary conditions were addressed, which helped in simulating real-world experimental settings. The approaches for minimizing energy have also been briefly explored. Finally, the limitations of molecular dynamics have been examined, as well as their applicability.