BITS Faculty Publications

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Author: search.filters.author.Sharma, AnujSubject: search.filters.subject.Mechanical Engineering

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    Atomic scale insights into material removal mechanisms in nanoscale machining of copper beryllium
    (Sage, 2023-12) Kumar, Amit; Sharma, Anuj
    The heterogeneous nature of the copper beryllium (CuBe) workpiece because of the presence of hard particles tends to affect material removal. When machining a CuBe material, it is anticipated that the mechanism of cutting and surface formation may differ from those seen when cutting a homogenous Cu material. Although these mechanisms are popular for the diamond turning of homogeneous materials, they have not been thoroughly studied in relation to CuBe alloys, which contain hard beryllium precipitates. Therefore, the effect of hard particles in the workpiece specimen on the nano-regime diamond turning of CuBe alloy needs to be understood. To explain the influence of Beryllium (Be) particles on the cutting tool and the workpiece surface, a molecular dynamics (MD) simulation was performed. It is revealed that the material removal mechanism in the case of CuBe is phase-dependent. Ductile machining is dominant in the Cu phase, and brittle fracture is dominant in the Be rich phase. It is also observed that the a/r ratio equal to 1 is suitable for cutting in the Cu phase and for ductile regime machining conditions in the Be phase. The a/r ratio higher than 1 causes higher cutting forces, and thus shear plane cutting takes place, which leads to a higher amount of material removal.
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    Effect of porosity on shock propagation behaviour of single crystal aluminium: A molecular dynamics investigation
    (Elsevier, 2023-02) Sharma, Anuj
    Materials' response to shock waves is largely affected not only by their inherent atomic structure but also by their physical structure. Current study involves analysis of shock propagation behaviour of single crystal aluminium (Al) specimens with different levels of porosities at nanoscale under a compressive shock loading using three dimensional molecular dynamics (MD) simulations. Solid, two dimensional array of pores, and three dimensional array of pores in the single crystal Al specimen were considered for detailed analysis of the shock response. It is observed that the porosity causes time delay in the travel of shock wave from front end of the surface to the rear end. The computational results indicate that the porosity results into increase in time of shock wave travel and it is found that the maximum porosity (47% in this simulation) causes 4 times the time of travel taken in solid Al specimen. The shock wave causes various sequential phenomenon in the Al specimen from compression to rarefaction which further leads to spalling of the material. The study also reveals that the pore walls act as a reflecting wall to the shock wave which causes secondary rarefactions and spalling phenomenon. Analyses show that the deformation in the material during shock loading is largely dominated by Shockley partial dislocations.
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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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    A review on applications of molecular dynamics in additive manufacturing
    (Sage, 2024-02) Sharma, Anuj; Kumar, Amit
    Additive manufacturing (AM) is an emerging technology that has significant geometric and material capabilities, because of which it is being used in different fields such as aerospace, healthcare, automotive, architecture, and construction. This process takes the digital data for the three-dimensional model to be made and adds materials accordingly in a layer-by-layer manner. Therefore, the understanding of materials at the atomic level may help in getting optimized output in the AM process, and it can have a significant impact on the final products. Molecular dynamics (MD) studies the dynamic behavior of molecules and materials at the atomic and molecular scales. The main objective of this review article is to briefly discuss how MD simulations may be utilized to examine AM processes. This review also covers the potential benefits of using MD to characterize AM processes, the current literature on using MD to simulate AM processes, the primary obstacles and limitations of MD simulations, and the methodologies utilized in AM simulations using MD. Finally, this article concludes with an in-depth discussion and outlines future research potentials.
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    Application of mesh-free and finite element methods in modelling nano-scale material removal from copper substrates: a computational approach
    (Elsevier, 2024-08) Sharma, Anuj
    This study explores the modelling methodology using mesh-free smoothed particle hydrodynamics (SPH) and finite element modelling (FE) techniques to simulate the AFM-based nano-scratching processes for advancing precision engineering in nanotechnology. Tip wear in nano machining substantially increases the tip radius, thereby influencing the material removal mechanism and subsequently affecting the quality of machined nanostructures. In this context, this study examines the effects of rake angle (the inclination of the main cutting edge to the plane perpendicular to the scratched surface), tip radius and scratching depth on cutting forces, groove dimensions, and deformed thickness. This was achieved by implementing an in-house SPH method based particle code employing a Lagrangian algorithm, and an FE model incorporating the dynamic explicit algorithm implemented (in ABAQUS) to carry out nano-scratching simulations. The investigation revealed that the cutting mechanism transitioned to ploughing when the scratching depth decreased to 30% of the tip radius for OFHC-Cu workpiece material machined with a diamond tip. The dominance of normal forces over cutting forces during scratching indicated the side flow of material in the vicinity of the tip radius under intense contact pressure. The ploughing mechanism exhibited more sensitivity at a higher negative rake angle of 60°. Increased scratching depth and tip radius led to more significant material deformation owing to the induction of higher cutting forces, with the maximum deformation thickness 3.6 times the tip radius. The simulated results demonstrated favourable concordance with the experimental data.
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    Molecular dynamics modelling of micro/nano manufacturing processes
    (Sage, 2024) Sharma, Anuj; Roy, Tribeni
    Manufacturing processes such as machining, casting, welding, forming including additive manufacturing are essential processes to fabricate various types of components. These manufacturing processes have been developed and are improving with time by optimising process parameters and revealing better insights about the processes. Earlier, research has used various tools like finite element analysis, mathematical modelling, etc., to improve the process understanding and their optimisation. This has brought the significance of computational modelling to support the analysis and optimization of manufacturing processes. In general, any manufacturing process works on two different domains of size scale such as micro scale and macro scale mechanism. Micro scale mechanism is associated with micro/nano manufacturing processes which differs from the macro scale, and conventional tools of modelling do not support it. During the last few decades, there has been an increasing interest in the simulations of micro/nano manufacturing processes. Modelling at nano scale brings out deep insights into the mechanisms and different phenomena. Out of the various modelling approaches, Molecular Dynamics (MD) modelling approach is the most preferred technique to simulate nanoscale manufacturing and investigate the science behind the processes. In general, MD simulation was extensively being used in the field of biology and chemistry towards discovery of novel drugs, chemical, materials, etc. In the last few decades, MD simulation has also been implemented by researchers in the field of manufacturing especially for polishing and thin film technology. Recently there has been a demand to use this tool to discover all possible phenomena at the atomic scale for all types of manufacturing processes. In this special issue of the Journal of Micromanufacturing, recent findings in micro/nano manufacturing through molecular dynamics modelling are aimed. In MD simulation, materials are modelled from atoms by assuming the atoms obey Newton’s second law of motion and will interact using interatomic potential. This concept of modelling brings insight into the manufacturing processes at atomic scale. However, modelling materials at the atomic scale requires reducing the temporal resolution of the order of a few picoseconds. Thus, the computational effort and time become enormous when any process is being modelled at a nanometric scale. Moreover, this approach becomes impossible to model when the space frame is in order of a few microns or more. To overcome this issue, researchers have identified alternate approaches like coarse grain modelling, multi-scale modelling, atom to continuum modelling, etc. All these techniques utilise the MD modelling at the zone of interaction and due to this, the special issue has focussed on MD simulation related novel outcomes for various types of manufacturing processes such as nanofinishing, nanomachining, additive manufacturing, nano-indentation, material’s mechanical characterisation, etc. In addition, this Special Issue will also promote and disseminate the latest works focused on MD modelling and simulation of various micro/nano-manufacturing processes and encourage researchers to adopt this technique to cater the present and future demand of technology. A brief report about the articles accepted under this issue are summarised as follows.
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    MD simulation study to investigate nanocutting process in Cu and CuBe
    (Euspen’s, 2018-06) Sharma, Anuj
    Impurities and inhomogeneity in the metallic materials change the material deformation and removal mechanisms drastically based upon the impurity content in them. Even a small percentage of Be (0.5-2%) addition in Cu alters the mechanism involved in the cutting process significantly. Since it becomes experimentally difficult to observe the mechanisms involved in the nanocutting process due to its length scale, molecular dynamics simulation provides deep insights during cutting process considering the discrete effects of material. Therefore in this study molecular dynamic simulation (MDS) of cutting operation was performed on Cu and CuBe assuming Cu as single crystal in both the cases. Results show that Be particle in Cu affects the material deformation and cutting forces significantly. It is observed that dislocation flow is obstructed by the particle and tool shows wear at the cutting edge in the form of chipping.
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    A comparative study on the reflectivity of metallic mirrors finished by deterministic and random processes
    (AIMTDR, 2014) Sharma, Anuj
    Manufacturing has reached the level of finishing the metallic& non-metallic surfaces to nanoand sub- nanoregimes. Metallic mirrors finished in this regime are finding their application in visible range and near infra-red optics. There are basically two types of methods by which the metallic mirrors are finished viz. deterministic nano- regime machining and random finishing. The present study investigates the behaviour of reflectivity pattern for various wavelengths of incident light on two surfaces generated by these methods and discusses about the range of wavelength for which the surface can be used as a reflective mirror. This paper also explains the difference in reflectivity pattern caused due to nano-irregularities present on the two surfaces due to the process characteristics. One simple model has also been used to confirm the experimental results. Alternatively, this study also expects the scope of predicting the surface characteristics by using the reflectivity spectrum
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    Improvement in surface quality of diamond-turned aluminium substrate by using hydrogen peroxide: a molecular dynamics simulation study
    (Sage, 2020-11) Sharma, Anuj
    In this work, the atomic mechanism of chemical treatment on diamond-turned aluminium surface due to aqueous H2O2 is investigated using a reactive molecular dynamics simulation (R-MDS). This study is carried out to understand the mechanism of surface quality improvement of a diamond-turned aluminium workpiece due to chemical treatment. Surface quality improvement is focused to analyse the effect of chemical treatment process for improving surface finish, reflectance and chemical stability of the workpiece. It is observed that the diamond-turned surface contains a higher cohesive energy as compared to atomically smooth surfaces. Chemical treatment does more material removal on nano-peaks with respect to the smooth surface, and this helps to reduce the cohesive energy as low as naturally possible. By applying this treatment, the optical quality of the workpiece gets enhanced drastically. R-MDS also reveals that the nano-peaks of diamond turn machining (DTM) surface can further improve surface finish by using the chemical treatment process, and the same is validated by experiments. Experimental data also support that due to the reduction of surface roughness, reflectance increases in a broad band of wavelength. The present work shows that material removal from the nano-peaks of workpiece occurs due to the oxygen radicals generated from H2O2, which raise the local temperature, followed by temperature-assisted chemical reaction. When most of the nano-peak atoms are removed, further material removal stops. Experimental results also support the mechanism of such process of chemical treatment. Hence, the diamond turned surface can be further improved beyond the capability of the diamond turning process to cater the need for optics and astronomical mirror at-least one step ahead in the domain of ultra-precision manufacturing.
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    Effect of porosity on shock propagation behaviour of single crystal aluminium: A molecular dynamics investigation
    (Elsevier, 2023-02) Sharma, Anuj
    Materials' response to shock waves is largely affected not only by their inherent atomic structure but also by their physical structure. Current study involves analysis of shock propagation behaviour of single crystal aluminium (Al) specimens with different levels of porosities at nanoscale under a compressive shock loading using three dimensional molecular dynamics (MD) simulations. Solid, two dimensional array of pores, and three dimensional array of pores in the single crystal Al specimen were considered for detailed analysis of the shock response. It is observed that the porosity causes time delay in the travel of shock wave from front end of the surface to the rear end. The computational results indicate that the porosity results into increase in time of shock wave travel and it is found that the maximum porosity (47% in this simulation) causes 4 times the time of travel taken in solid Al specimen. The shock wave causes various sequential phenomenon in the Al specimen from compression to rarefaction which further leads to spalling of the material. The study also reveals that the pore walls act as a reflecting wall to the shock wave which causes secondary rarefactions and spalling phenomenon. Analyses show that the deformation in the material during shock loading is largely dominated by Shockley partial dislocations.