Imperial College London

Dr. Jagjeevan Singh Bhamra

Faculty of EngineeringDepartment of Mechanical Engineering

Casual - Student demonstrator - lower rate
 
 
 
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j.bhamra19

 
 
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564City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

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3 results found

Bhamra JS, Everhard EM, Bomidi JAR, Dini D, Ewen JPet al., 2024, Comparing the tribological performance of water-based and oil-based drilling fluids in diamond–rock contacts, Tribology Letters, Vol: 72, ISSN: 1023-8883

Oil-based drilling fluids are usually assumed to provide lower friction compared to their water-based alternatives. However, clear evidence for this has only been presented for steel–rock and steel–steel contacts, which are representative of the interface between the drillstring and the borehole or casing. Another crucial interface that needs to be lubricated during drilling is that between the cutter (usually diamond) and the rock. Here, we present pin-on-disc tribometer experiments that show higher boundary friction for n-hexadecane-lubricated diamond–granite contacts than air- and water-lubricated contacts. Using nonequilibrium molecular dynamics simulations of a single-crystal diamond tip sliding on α-quartz, we show the same trend as in the experiments of increasing friction in the order: water < air < n-hexadecane. Analysis of the simulation results suggests that the friction differences between these systems are due to two factors: (i) the indentation depth of the diamond tip into the α-quartz substrate and (ii) the amount of interfacial bonding. The n-hexadecane system had the highest indentation depth, followed by air, and finally water. This suggests that n-hexadecane molecules reduce the hardness of α-quartz surfaces compared to water. The amount of interfacial bonding between the tip and the substrate is greatest for the n-hexadecane system, followed by air and water. This is because water molecules passivate terminate potential reactive sites for interfacial bonds on α-quartz by forming surface hydroxyl groups. The rate of interfacial bond formation increases exponentially with normal stress for all the systems. For each system, the mean friction force increases linearly with the mean number of interfacial bonds formed. Our results suggest that the expected tribological benefits of oil-based drilling fluids are not necessarily realised for cutter–rock interfaces. Further e

Journal article

S Bhamra J, P Ewen J, Ayestarán Latorre C, A R Bomidi J, W Bird M, Dini Det al., 2023, Atomic-scale insights into the tribochemical wear of diamond on quartz surfaces, Applied Surface Science, Vol: 639, Pages: 1-13, ISSN: 0169-4332

A detailed understanding of diamond wear is crucial due to its use in high-performance cutting tools. Despite being a much harder material, diamond shows appreciable wear when cutting silicon dioxides due to a tribochemical mechanism. Here, we use nonequilibrium molecular dynamics simulations with a reactive force field to investigate the wear of single-crystal diamond tips sliding on α-quartz surfaces. Atom-by-atom attrition of carbon atoms is initiated by the formation of C-O interfacial bonds, followed by C-C cleavage, and either diffusion into the substrate or further oxidation to form CO2 molecules. Water molecules dissociate to form hydroxyl groups, which passivates the surfaces and reduces interfacial bonding and wear. At low loads, the initial wear rate increases exponentially with temperature and normal stress, consistent with stress-augmented thermally activated wear models. At higher loads, the initial wear rate becomes less sensitive to the normal stress, eventually plateauing towards a constant value. This behaviour can be described using the multibond wear model. After long sliding distances, wear also occurs through cluster detachment via tail fracture. Here, wear becomes approximately proportional to the sliding distance and normal load, consistent with the Archard model. The normalised wear rates from the simulations are within the experimentally-measured range.

Journal article

Bhamra J, Ewen J, Ayestaran Latorre C, Bomidi J, Bird M, Dasgupta N, van Duin A, Dini Det al., 2021, Interfacial bonding controls friction in diamond–rock contacts, The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, Vol: 125, Pages: 18395-18408, ISSN: 1932-7447

Understanding friction at diamond–rock interfaces is crucial to increase the energy efficiencyof drilling operations. Harder rocks usually are usually more difficult to drill; however, poorperformance is often observed for polycrystalline diamond compact (PDC) bits on soft calcitecontaining rocks, such as limestone. Using macroscale tribometer experiments with adiamond tip, we show that soft limestone rock (mostly calcite) gives much higher frictioncoefficients compared to hard granite (mostly quartz) in both humid air and aqueousenvironments. To uncover the physicochemical mechanisms that lead to higher kinetic frictionat the diamond–calcite interface, we employ nonequilibrium molecular dynamics simulations(NEMD) with newly developed Reactive Force Field (ReaxFF) parameters. In the NEMDsimulations, higher friction coefficients are observed for calcite than quartz when watermolecules are included at the diamond–rock interface. We show that the higher friction inwater-lubricated diamond–calcite than diamond–quartz interfaces is due to increasedinterfacial bonding in the former. For diamond–calcite, the interfacial bonds mostly formthrough chemisorbed water molecules trapped between the tip and the substrate, while mainlydirect tip-surface bonds form inside diamond–quartz contacts. For both rock types, the rate ofinterfacial bond formation increases exponentially with pressure, which is indicative of astress-augmented thermally activated process. The mean friction force is shown to be linearlydependant on the mean number of interfacial bonds during steady-state sliding. Theagreement between the friction behaviour observed in the NEMD simulations and tribometerexperiments suggests that interfacial bonding also controls diamond–rock friction at themacroscale. We anticipate that the improved fundamental understanding provided by thisstudy will assist in the development of bit materials and coatings to minimise friction byre

Journal article

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