Browsing by Author "Kumar, Amit"

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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.
Characterization of Residual Stresses in Conventional Forming and Hydroforming of Tailor Welded Blanks
(Springer, 2022-05) Kumar, Amit
Residual stresses in sheet metal components depend on the forming technique and the history of load path changes during the process. Characterization of residual stresses in the case of tailor welded blanks (TWBs) is challenging due to the differences in thickness and/or plastic deformation behavior within the blank. In the present work, the forming outcome is evaluated based on the final residual stress distribution in the formed TWB specimens. The methodology is demonstrated by biaxial stretching of TWBs of interstitial-free (IF) steel and draw quality (DC01) steel under two different processing routes (conventional forming and hydroforming). The numerically predicted residual stresses are observed to be lower and more uniformly distributed in the case of hydroforming when compared to conventional forming. The negligible residual stresses (or less tensile near the weld zone) in the hydroformed parts can be advantageous in the automotive industry leading to an improved life. The weld zone properties play an insignificant role in the distribution of predicted residual stress in biaxial stretching of TWBs. The numerically predicted results are validated experimentally using the x-ray diffraction technique. The agreement between numerical and experimental results is better in hydroforming than in the case of conventional forming.
Effect of Cell Geometry on the Out of Plane Response of Aluminium Honeycomb Using Finite Element Method
(Springer, 2021-11) Kumar, Amit
Two-dimensional cellular structures – honeycombs are known to exhibit high compressive strength and energy absorption in out of plane compressive loading. The energy absorption capability of impact crushing of these structures is affected not only by the mechanical properties of the honeycomb but by the geometric structure of the honeycomb cell as well. In present study, a finite element (FE) framework is utilized for the comparison of the peak collapse stress, mean plateau stress, and densification strain for different cell shapes of aluminum honeycomb core under impact loading. Results obtained are correlated with the deformation mechanisms involved with the change in cell shape. Non-linear dynamics software LS-Dyna is used to develop an explicit code framework for the simulation, which is validated using compression test results on a thin-walled hexagonal honeycomb structure of aluminum. The thin-walled core of the honeycomb is modeled as a deformable body with shell elements, while the crosshead is modeled as rigid bodies, which strikes the honeycomb core with a velocity of 5 m/s. The cell shapes which are commonly used in sandwich panels like the regular hexagonal honeycomb-square, triangular, and square are studied for the same cell size. It is observed that the triangular cell shapes are the stiffest, while the hexagonal honeycomb has high energy absorption. Furthermore, the effect of strain rate has also been studied for each cell shape of the honeycomb core.
Experimental and theoretical analyses of material removal in poppet valve magnetorheological finishing
(Sage, 2022-11) Kumar, Amit
Poppet valves used in internal combustion engines have a high risk of failure due to significant temperature and pressure. These poppet valves need surface finishing at the nano-scale level to prolong their life during their working use. In the present research, the chosen poppet valve has narrow ridge profiles, which is difficult to nano-finish by conventional processes due to certain limitations. The magnetorheological fluid-based finishing method can be effectively used for this kind of complicated narrow profile. For the magnetorheological fluid-based finishing processing of the poppet valve, a novel magnet fixture and setup is used. For checking the efficiency of this setup, surface characterization and surface roughness for polished and unpolished surfaces are outlined using a field-emission scanning electron microscope, microscope and optical profilometer. The final surface roughness of Sa = 23.1 nm at poppet profiles were obtained. All manufacturing defects like burrs, dents, scratches and pits are almost removed. The study of finishing forces in the magnetorheological fluid-based finishing method is also carried out using magnetostatic fluid–solid interaction, experimental and theoretical analysis. This force analysis supports the development of the material dislodgement model to anticipate material removal rate while finishing. The gap (error = 12.87%) between the experimental and theoretical material removal rate is marginal. It has high accuracy and reliability for specific applications.
A facile approach for wettability transition to enhance the hydrophobicity of Ti6Al4V alloy using laser surface texturing
(Sage, 2025-04) Kumar, Amit
Ti6Al4V has been widely used in important sectors such as biomedical, automobile, and aerospace engineering. Apart from superior mechanical properties, the Ti6Al4V must also possess self-cleaning ability. The self-cleaning ability of any material can be enhanced by imparting hydrophobic characteristics. In the current research work, laser surface texturing technique has been used to make linear and cross-hatched (CH) structures over the Ti6Al4V samples. Compared to the plain sample, the CH sample significantly enhanced the hydrophobic nature of Ti6Al4V by substantially increasing the water contact angle to the value of 141°. As compared to the plain sample, the contact angle value was found to be 70% more in the CH sample. The formation of rutile TiO2 film in textured samples can be considered the reason for the enhanced hydrophobicity. The increase in the peak of rutile TiO2 film in textured samples has been observed through the XRD analysis. Upon the point EDX analysis, it has been observed that the amount of oxygen increased approximately 10 times in the textured sample as compared to the plain sample. Further, upon droplet impact testing high recoil height and droplet separation height have been observed for the textured sample. The CH sample has provided a recoil height of 5.25 mm. The recoil height for the CH sample has been found to 3.5 times more than that of the plain sample. The CH sample also provided the droplet separation height of 9.3 mm, whereas the droplet separation phenomenon was found to be absent for the plain sample. Overall, high contact angle, formation of rutile TiO2 film, and enhanced droplet recoiling phenomena indicate that the facile method such as laser texturing can successfully impart high hydrophobicity to the Ti6Al4V samples.
Formability prediction of tailor-welded blanks in hydraulic bulging using flow curves from biaxial tensile tests
(Sage, 2020-12) Kumar, Amit
In this work, the formability of laser-welded tailored blanks of low carbon steel of two different thickness combinations in hydraulic bulging has been studied by numerical simulation. For material modeling, flow curves of the parent sheets were obtained in biaxial stress condition by conducting hydraulic bulge tests. These curves were used to extrapolate the uniaxial tensile curves up to large strains using the work equivalence principle. The limiting dome height in conventional forming and hydraulic bulging of tailor-welded blanks has been predicted in finite element simulations using the flow curves obtained directly from the hydraulic bulge tests and the extrapolated uniaxial tensile curves. Hydraulic bulging and conventional forming experiments on tailor-welded blanks have also been conducted to validate the predicted results. It has been found out that the predicted limiting dome height of the tailor-welded blanks in conventional forming and hydraulic bulging using extrapolated uniaxial tensile curves is closer to the experimental values when compared to the results obtained by using stress–strain curves obtained from hydraulic bulge tests. It has also been found that using an extrapolated uniaxial tensile curve it is also possible to predict strain distribution and percentage thinning more accurately. It has been observed that with an increase in thickness ratio, the peak pressure increased but the predicted values of peak pressure using flow curves obtained directly from hydraulic bulge tests are closer to the experimental values.
Maximum Bulge Height and Weld Line Displacement in Hydroforming of Tailor Welded Blanks
(ASME, 2017-12) Kumar, Amit
Tailor welded blank (TWB) has many advantages over a traditional blank for manufacturing automobile sheet metal components, such as significant flexibility in product design, higher structural stiffness, and crash behavior. However, lower formability and weld line movement are some of the problems associated with forming of TWBs. Hydroforming is a potential technique to enhance formability. In this work, the effect of thickness ratio on maximum dome height and weld line movement in hydraulic bulging of laser welded interstitial-free (IF) steel blanks of different thickness combinations has been predicted using finite element (FE) simulations. The results are also validated with hydraulic bulging experiments on TWBs. It has been found that with increase in thickness ratio, the maximum bulge height decreased and weld line displacement toward thicker side increased. These results have been used to relocate the weld line toward the thinner side in the initial blanks and achieve a more uniform bulge profile of the dome. The peak pressure to achieve maximum safe dome height and percentage thinning has also been found out. The results showed huge improvement in uniformity of bulge profile with little reduction in dome height.
Numerical Modelling of V-Shaped Composite Plate Subjected to Blast Loading
(Springer, 2021-11) Kumar, Amit
Improvised explosive devices (IEDs) buried under the soil have become a new threat to the armored personal carriers (APC). It has generated the need to rethink the design or the material of the V-shaped plate placed under the APCs. The V-shaped plate is generally made of steel material. However, composite materials-Dyneema and Kevlar/Epoxy could be one of the potential materials which can replace the steel, as they are also widely used for high strain loading. Dyneema is an ultra-high molecular weight polyethylene (UHMWPE) fiber, has a high strength, low density (0.97 g/cc) and it is 15 times stronger than steel on an equal weight basis. Kevlar is an aramid fiber which is five times stronger than steel (on an equal weight basis) and are used with various matrix materials. Numerically and experimentally determined center point displacement of the V-shaped steel plate has been well reported in the literature. The present work focuses on the validation of the experimental results on the V-shaped steel plate with numerical results and also comparison of the predicted results of steel plates with V-shaped composite plates. Numerical results have shown a good correlation with the experimental results and followed the same progressive deformation as reported in the literature. An effort has been made to study the center point displacement of the V-shaped plate of Dyneema and Kevlar/Epoxy composites. A series of numerical simulations have been carried out on the V-shaped plate subjected under the blast loading using LS-DYNA. Explosives of different weights were considered. The charge location is considered to be below the mid point of V-shaped plate. The analysis showed that the V-shaped plates of Dyneema composite exhibited lesser deformation when compared to the Kevlar/Epoxy and steel plates. Study also showed that the Dyneema is a better material over steel and Kevlar composites for the use in V-shaped plates for APCs.
Prediction of residual stresses in biaxial stretching of tailor welded blanks by finite element analysis
(IOP, 2019) Kumar, Amit
Residual stresses in sheet metal components play an important role in determining the life of parts especially in automotive industry. In this work, residual stresses have been predicted numerically in biaxial stretching of laser welded interstitial free (IF) steel blanks of different thickness combinations. The effective stress-effective strain curves of the parent sheets obtained from uniaxial tensile tests have been used as an input in finite element (FE) simulations to define the flow behavior of the materials. It has been found out that the residual stresses are tensile and similar on both sides of the weld zone in tailor welded blanks (TWB) of same thickness combination. In TWBs of different thickness combinations, the residual stresses on both sides are tensile and almost equal in the central region of the cup and they became compressive as the distance from the pole increases. The effect of thickness ratio on residual stresses has also been predicted in FE simulations of biaxial stretching of TWBs. It has been found out that with increase in the thickness ratio, the residual stress has slightly increased. Residual stresses have also been determined experimentally by using x-ray diffraction technique and it has been found out that the predicted values agreed well with the experimental results.
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.
Stochastic Modeling of Repairable Machining System with Spare Provisioning
(BITS Pilani, 2019) Kumar, Amit