Department of Mechanical engineering
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Item Analysis of material removal mechanism in nanoscale machining of copper(Sage, 2024-01) Sharma, Anuj; Roy, TribeniIn 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.Item A molecular dynamics simulation of wear mechanism of diamond tool in nanoscale cutting of copper beryllium(Springer, 2019-01) Sharma, AnujIn the present study, molecular dynamics simulation (MDS) is employed to study the wear mechanism of single crystal diamond tool during nanocutting of copper beryllium (CuBe). Two edge configurations, i.e., both sharp and worn out tools, are chosen to study the tool and workpiece interaction during the nanocutting of CuBe. Further, the study involves the experimental characterization techniques viz. scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy to confirm the simulation results. The results of the molecular dynamics simulation (MDS) show that the presence of Be as a hard particle in workpiece material influences the cutting forces which subsequently causes degradation of the sharp edge of the diamond tool. Furthermore, the carbon (C) atoms removed from the tool react with Be particles and as a result, it causes the formation of beryllium carbide (BeC). Beryllium interaction with the blunt edge configuration of the tool causes amorphization at the tool edge. Raman spectroscopy of the used diamond tool on CuBe reveals the similar phenomena of amorphization of the diamond at the tool edge. Moreover, surface generation is dependent on the tool edge condition as blunt edge tool leads to smoother surface compared to the surface generated by sharp edge configuration.Item Molecular dynamics simulation to investigate the orientation effects on nanoscale cutting of single crystal copper(Elsevier, 2018-10) Sharma, AnujThe present study investigates the effect of six different crystal orientations on the nanoscale cutting operation carried out on single crystal copper (Cu) at various ratios of uncut chip thickness (a) to cutting edge radius (r). The study is focused on various aspects of cutting operation which include the material deformation mechanism, subsurface deformation, cutting forces, specific cutting energy, ploughing effect and surface roughness. Molecular dynamics simulation (MDS) was performed for the six orientations at five different a/r ratios varying from 0.1 to 2. The MDS results reveal that the material removal and shear deformation mechanisms are distinct for different crystal orientations. 〈1 1 0〉 is the slip direction along which the dislocations propagate predominantly. Maximum material removal occurs for the (0 0 1)[ 0] orientation which is 45% higher than its minimum counterpart in the (1 1 1)[1 0] crystal orientation at a/r equals to 2. Results of cutting forces as well as specific cutting energy plots show that the crystal orientation {1 1 0}〈0 0 1〉 is difficult to cut whereas crystal orientation {1 1 1}〈1 1 0〉 is easier to cut in nanoscale cutting of Cu. Based on the surface roughness calculation, it is observed that surface quality is highest for the crystal orientation while cutting on (0 0 1)[ 0] and lowest for the crystal orientation ()[1 0 0]. Nanocutting of Cu with larger dimensions used to reduce the size effect shows that there is an increase of ∼275% in the dislocation density for the maximum dislocated crystal orientation (0 0 1)[ 0] when the tool edge sharpness is increased from 2 nm to 5 nm.Item Molecular dynamics simulation of single discharge and dimensionless correlation with actual material removal in micro electrical discharge machining(Taylor & Francis, 2019-06) Roy, Tribeni; Sharma, AnujShorter time pulses and length scales in micro EDM (MEDM) makes it difficult to observe the material removal phenomena taking place at very small zone during discharge. Since numerical or analytical model considers material to be uniform/isotropic, it cannot predict the discrete effects viz. crystal structure distortion due to discharge. Also, little attention has been given to the mechanism of material removal in MEDM at the atomistic level. Therefore, to understand the behaviour of material removal and crystal structure distortion due to single spark in MEDM, MD simulations have been carried out. Based on MD simulations, it was found that the percentage of material removed by vaporisation (∼40%) was higher at spark energies used in this model as compared to spark energies used by Wong et al. (20% at 23.50 µJ). Conversion from FCC crystal structure to amorphous was observed at the top surface of crater in both cases; the one with higher spark energy has marginally higher distortion indicating higher amorphisation. A new method is proposed based on which a dimensionless correlation was obtained between results of MDS and experiments which relates the ratio of specific material removal at higher spark energy to that at lower energy for both MDS and experimentsItem Comparative analysis of mechanical properties for mono and poly-crystalline copper under nanoindentation – Insights from molecular dynamics simulations(Elsevier, 2022-02) Roy, Tribeni; Sharma, AnujCrystallographic 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.