Browsing by Author "Sharma, Anuj"

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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.
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.
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.
Atomistic study on the effect of the size of diamond abrasive particle during polishing of stainless steel
(Sage, 2023-10) Roy, Tribeni; Sharma, Anuj
Prediction of material removal in any machining process is usually based on the input machining parameters. However, apart from controllable parameters, there are various other parameters that needs to be monitored in real time to ensure better prediction of accuracy, especially in random processes. Hence, real time data monitoring using appropriate sensors in machining processes is extremely important as the input parameters cannot predict the output with high efficiency. In Micro EDM (MEDM), real time signal monitoring can yield various time domain features of individual current and voltage pulses that can help to enhance the prediction accuracy of material removal. In this study, an attempt has been made to predict the material removal in single spark MEDM based on two different modelling approaches i.e. multiple linear regression (MLR) and classification and regression tree (CART). A total number of 21 experiments were conducted on a specially designed single spark MEDM machine with input parameters viz. voltage and capacitance. Material removal measurements was carried out using Coherent Correlation Interferometer. Open source software “R-3.4.0” was used for building and prediction of the model. A total of 14 predictors (2-input and 12-time domain extracted predictors) and a single output i.e. material removal was used for prediction. Prediction model by multiple linear regression (MLR) showed root mean square error of 5.82 whereas that by CART showed 12.07. Hence, material removal in single spark MEDM can be predicted by MLR with better accuracy as compared to CART.
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.
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
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.
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.
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.
Investigation of effect of uncut chip thickness to edge radius ratio on nanoscale cutting behavior of single crystal copper: MD simulation approach
(Sage, 2020-09) Sharma, Anuj
Extremely small cutting depths in nanoscale cutting makes it very difficult to measure the thermodynamic properties and understand the underlying mechanism and behavior of workpiece material. Highly precise single-crystal Cu is popularly employed in optical and electronics industries. This study, therefore, implements the molecular dynamics technique to analyze the cutting behavior and surface and subsurface phenomenon in the nanoscale cutting of copper workpieces with a diamond tool. Molecular dynamics simulation is carried out for different ratios of uncut chip thickness (a) to cutting edge radius (r) to investigate material removal mechanism, cutting forces, surface and subsurface defects, material removal rate (MRR), and stresses involved during the nanoscale cutting process. Calculation of forces and amount of plowing indicate that a/r = 0.5 is the critical ratio for which the average values of both increase to maximum. Material deformation mechanism changes from shear slip to shear zone deformation and then to plowing and elastic rubbing as the cutting depth/uncut chip thickness is reduced. The deformation during nano-cutting in terms of dislocation density changes with respect to cutting time. During the cutting process, it is observed that various subsurface defects like point defects, dislocations and dislocation loops, stacking faults, and stair-rod dislocation take place.
Investigation of Nanoscale Scratching on Copper with Conical Tools Using Particle-Based Simulation
(Springer, 2023-03) Sharma, Anuj
In this study, a modeling approach based on smooth particle hydrodynamics (SPH) was implemented to simulate the nanoscale scratching process using conical tools with different negative rake angles. The implemented model enables the study of the topography of groove profiles, scratching forces, and the residual plastic strain beneath the groove. An elastoplastic material model was employed for the workpiece, and the tool–workpiece interaction was defined by a contact model adopted from the Hertz theory. An in-house Lagrangian SPH code was implemented to perform nano-scratching simulations. The SPH simulation results were compared with nanoscale scratching experimental data available in the literature. The simulation results revealed that the normal force was more dominant compared to the cutting force, in agreement with experimental results reported for a conical tip tool with a 60° negative rake angle. In addition, the simulated groove profile was in good agreement with the groove profile produced in the aforementioned experiment. The numerical simulations also showed that the normal and cutting forces increased with the increase in the scratching depth and rake angle. Although the cutting and ploughing mechanisms were noticed in nano-scratching, the ploughing mechanism was more dominant for increased negative rake angles. It was also observed that residual plastic strain exists below the groove surface, and that the plastically deformed layer thickness beneath a scratched groove is larger for more negative values of the tool rake angle and higher scratching depths.
An investigation of tool and hard particle interaction in nanoscale cutting of copper beryllium
(Elsevier, 2018-04) Sharma, Anuj
The present study adopts molecular dynamics simulation to analyze tool and hard particle interaction in the nano-cutting of copper beryllium (CuBe). The presence of hard particles in workpiece materials affects the cutting process in terms of surface generation, material deformation, and tool wear mechanisms. Therefore, in this simulation study, three cases are considered based on the distinct size and location of hard particle in the base material. Results show that Be particle, when encountered by a diamond tool at the cutting plane, is suppressed and subsequently is projected from the generated surface with a dig left behind the particle. Furthermore, particle removal or suppression depends on its size and location with respect to the cutting plane. Shockley partial dislocations are noticed to be dominant in plastically deforming the workpiece material. Moreover, it is not only the workpiece surface which gets affected; hard particle also deteriorates the tool by causing wear to its cutting edge. The cutting process – in terms of surface generation, material deformation, and tool edge condition – is found to be dependent on the crystallographic planes of the base material.
Investigation of Tool and Workpiece Interaction on Surface Quality While Diamond Turning of Copper Beryllium Alloy
(ASME, 2020-02) Sharma, Anuj
Among all the materials, diamond turning of heterogeneous materials like copper beryllium (CuBe) poses serious machining challenges as the heterogeneity in the workpiece affects the quality of generated surface. Therefore, the present study is aimed to understand the effect of tool–workpiece interactions on the surface characteristics of heterogeneous CuBe workpiece material. Experiments and molecular dynamics simulation (MDS) were carried out to analyze the various surface and subsurface interactions during cutting. Results from the experiments on both the materials for whole cutting length show that the average roughness values on CuBe-machined surface are found to be ∼48% higher than those of copper (Cu). Scanning electron microscopy (SEM) results show that while deterministic lay pattern is obtained in the case of Cu, the CuBe-machined surface possesses near-random lay pattern, which is also reflected by the fast Fourier transform (FFT) spectrum of surface roughness profiles. Experimental and MDS results reveal that the hard precipitate suffers cracks which propagate vertically as well as radially and as the tool travels from Cu-rich phase to Be-rich phase, ductile to brittle transition in cutting mechanism is observed. Furthermore, it is observed that diamond-turned Cu and CuBe surfaces are contaminated by the oxides of C and Cu. MDS results verify the mechanisms involved in the surface and subsurface interactions during diamond turning.
Investigation of tool-workpiece interaction in nanoscale cutting: a molecular dynamics study
(Inder Science, 2019) Roy, Tribeni; Sharma, Anuj
Ductile and brittle materials differ in their physical and mechanical properties and pose distinct interaction with the cutting tool while nano-machining. It is thus imperative to analyse the mechanism of material removal and tool-workpiece interaction. Towards this, molecular dynamics simulation (MDS) is carried out to study the diamond tool and workpiece interaction in the nanoscale cutting of Cu (ductile material) and Si (brittle material). Results show that material removal in Cu takes place through shear deformation by dislocations formation and their propagation while in case of Si, it takes place through phase transformation of the material in cutting zone. Force analysis of both the materials shows that machinability of Cu in nanoscale cutting is better compared to Si. Furthermore, tool wear while machining of Si with sharp edge tool is due to chipping whereas radial distribution function reveals that graphitisation of the round edge tool occurs during machining of Si.
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.
Mechanism of material removal on stainless steel through diamond abrasion: a molecular dynamics simulation study
(MTT, 2023) Roy, Tribeni; Sharma, Anuj
A rough surface of any engineering material exhibits high surface energy which results in higher potential energy or cohesive energy of the material, and it affects both optical as well as chemical properties. In this paper, stainless steel 304 (or SS304) is selected for nano-finishing through diamond abrasive using MD simulations. It is found that the diamond abrasive creates new bonds with Cr and Fe atoms by rise in local temperature and stresses. Moreover, Ni atom diffuses inside the abrasive as it does not chemically bond with C atom. The abrasion on steel due to diamond also leads to phase transformation on both abrasive as well as the workpiece. Subsequently, the transformed phase is removed from the workpiece due to the newly formed chemical bonds, however, in the process, the abrasive particle deteriorates by phase transformation and materials loading. Thus, the present study is useful in optimising
Mechanism of surface modification on monocrystalline silicon during diamond polishing at nanometric scale
(Sage, 2023-11) Sharma, Anuj; Roy, Tribeni
The demand for polished silicon wafers has increased significantly in recent years to cater to the development of the semiconductor industry. For example, polished silicon wafer has direct applications in integrated circuits, radio frequency amplifiers, micro-processors, micro-electromechanical systems, etc. To carry out mechanical polishing, lapping, grinding, or single-point diamond turning of silicon, diamond abrasives were extensively used before the implementation of chemo-mechanical polishing. During the diamond-based polishing, a few problems have already been identified, such as the formation of an amorphous phase, heat-affected zones, low material removal, etc. Some research work has also reported that nano-structured abrasives lead to a thin layer of the amorphous phase and a better material removal rate. In the same direction, a molecular dynamics simulation is carried out in this paper to investigate the mechanism of material removal from monocrystalline silicon during the diamond-abrasive-based polishing process. The present work is mainly focused on the dynamics of material removal phenomena near the abrasive particles at the nanometric scale by considering stress, lattice, cohesive energy, etc. This reveals that a higher value of indentation force results in surface buckling, which creates a zone of both compressive and tensile stresses, which increases the coordination number and forms β-silicon just ahead of the abrasive particle. This mechanism happens by developing a β-silicon phase on the surface with a thickness beyond a certain value of indentation force on the zone of compression. Buckling on this phase happens due to stress localisation in compression, as the flow stress of this phase is less than that of diamond cubic lattices. To avoid the mechanism of surface buckling and process silicon material on the surface, the indentation force needs to be maintained below a critical value. In the present case, it was found that the indentation force of less than or equal to 190 nN for the abrasive size of ϕ8 nm does the material removal by surface processing only without surface buckling. It was also found that surface processing helps to reduce the depth of the amorphous layer significantly without compromising the material removal rate or the generation of a wavy surface. Thus, the present mechanism will help in the polishing of silicon with minimum defects and reduce processing time for the final stage of polishing towards manufacturing ultra-smooth and planer surfaces.
Mechnism of the pathogenesis of venezuelan equine encephalitis virus infection
(BITS Pilani, 2007) Sharma, Anuj
Micromachining: An overview (Part I)
(sage, 2020-03) Sharma, Anuj
This article gives classification of micromanufacturing in general and micromachining processes in particular. For different micromachining processes, one can have different kinds of operations through which different features, shapes, accuracy, precision, and dimensions can be achieved. This article as Part I reports an overview of only three processes as diamond turn machining (a class of traditional micromachining processes), electrochemical micromachining, and focused-ion-beam micromachining (a class of advanced micromachining processes). About all these three processes, a brief introduction to the mechanisms of material removal is reported followed by the new developments in each process which are discussed independently. In various sections, some areas where research work needs to be done are identified and very briefly discussed.
Modeling and analysis of tool wear mechanisms in diamond turning of copper beryllium alloy
(Elsevier, 2020-08) Sharma, Anuj
The interaction of hard Be particles in CuBe alloy with cutting tool, during diamond turning of CuBe contributes significantly to the tool wear. However, the mechanism of this interaction and its effect on tool wear have not been explored adequately thus far. Therefore, to understand the role of Be particles, diamond turning (facing) experiments were performed on Cu as well as CuBe alloys. The flank wear was assessed by SEM and Raman spectroscopy, the machined surfaces on the other hand, were assessed by EDS. MD simulations were also carried out to support the experimental findings. The experimental and simulation results show that the amorphization of diamond is the dominant tool wear mechanism, which indicates the transformation of sp3 phase of diamond structure while machining of CuBe. EDS analysis reveals that there are 15–20 % C atoms present on the location of hard particles on the machined surface which signifies that the Be particles are mainly responsible for tool wear. Forces recorded by dynamometer during cutting show that thrust forces are approximately one order higher for CuBe as compared to that of Cu. Furthermore, MDS results reveal that the principal cause of phase transformation in the diamond tool is high atomic stress in conjunction with the occurrence of high interface temperature.