Shiv Sharma

Bio: Shiv Sharma is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Calcite & Raman spectroscopy. The author has an hindex of 2, co-authored 2 publications receiving 11 citations.

Microstructure Induced Shear Instability Criterion During High-Speed Machining of Ti–6Al–4V

Abstract: The microstructure attributes are responsible for the deformation mechanism of material which induces shear instability primarily in difficult-to-machine material like Ti6Al4V. Consequently, the dynamic cutting force yields serrations in the chip morphology. Therefore, microstructure induced shear instability has been investigated in the present work using an analytical tool to unveiled the deformation behaviour in correlation with microstructural characteristics (grain sizes, phase fractions and microhardness) and process parameters; temperature, strain and strain rate. The combined effect of feed rate and high cutting speed was found to enhance the strain localization phenomena, which leads to a more pronounced cracking, inducing dynamic cutting force. Segmentation frequency and force-frequency correlation imply that there is a significant transition exhibit from static to dynamic nature of cutting force. The segmentation frequency of the equiaxed microstructure is lowest among the rest at lower cutting speed, which reveals the shear instability dependency on the microstructure. Grain size effect restricts the dislocation movement at the higher cutting speed which led to a larger strain in as-received microstructure followed by equiaxed and fully lamellar microstructure.

Raman analysis of octocoral carbonate ion structural disorder along a natural depth gradient, Kona coast, Hawai‘i

Abstract: Abstract Both environmental and physiological factors cause carbonate ion structural disorder in biogenic Mg-calcites. A major component of this disorder is driven by the incorporation of Mg through environmental forcing and growth rate kinetics although non-Mg factors (e.g., other cation/anion impurities, organic molecules) also contribute. Understanding the drivers of Mg content in biogenic calcite and its effects on disorder has implications for octocoral Mg paleo-proxies and the stability and diagenetic alteration of their calcitic skeletons. However, prior studies of biogenic Mg-calcites have often been complicated by sampling inconsistencies over space and time and potential intra-sample Mg variability. This study aims to analyze the relative contributing factors of octocoral Mg-calcite structural disorder along gradients of both depth and growth rate. Calcitic octocorals (Coralliidae and Keratoisididae, N = 28) were collected from 221–823 m depths across a natural gradient in biogeochemical parameters (pH: 7.4–7.9, T: 5–16 °C) off the Kona coast of Hawai‘i Island and were analyzed using Raman spectroscopy. Samples were collected during the same month, controlling for potential seasonal variability. Raman spectral parameters from the ν1 peak quantified total carbonate ion structural disorder (full-width at half maximum height [FWHM] of ν1) and Mg content (ν1 position, Raman shift). The total structural disorder was then partitioned into Mg-driven and non-Mg driven components (residual ν1 FWHM). The total structural disorder and Mg content decreased significantly with increasing depth, correlating with temperature and carbonate system parameters. The Mg-temperature relationships from this study were also consistent with prior studies. Non-Mg structural disorder did not correlate to any environmental parameters. When measured across an intra-sample gradient of ontogenetic growth rate, total structural disorder, Mg content, and non-Mg structural disorder increased with growth rate for all but one taxon, demonstrating the kinetic effect of growth rate as well as potential taxon-specific physiological effects. These results provide insight into how environmental and growth rate kinetic effects independently afect different components of carbonate ion structural disorder (Mg content and non-Mg factors). These findings also suggest that Raman spectroscopy may be helpful in quantifying solubility within biogenic calcites.

analysis of octocoral carbonate ion structural disorder along a natural depth 3

Abstract: Both environmental and physiological factors cause carbonate ion structural disorder in 15 biogenic Mg-calcites. A major component of this disorder is driven by the incorporation of Mg 16 through environmental forcing and growth rate kinetics although non-Mg factors (e.g., other cation/anion impurities, organic molecules) also contribute. Understanding the drivers of Mg content in biogenic calcite and its effects on disorder has implications for octocoral Mg paleo- proxies and the stability and diagenetic alteration of their calcitic skeletons. However, prior 20 studies of biogenic Mg-calcites have often been complicated by sampling inconsistencies over 21 space and time and potential intra-sample Mg variability. This study aims to analyze the relative 22 contributing factors of octocoral Mg-calcite structural disorder along gradients of both depth and growth rate. Calcitic octocorals (Corallidae and Isididae, N = 28) were collected from 221–823 24 m depths across a natural gradient in biogeochemical parameters (pH: 7.4–7.9, T: 5–16°C) off 25 the Kona coast of Hawai‘i Island and analyzed using Raman spectroscopy. Samples were 26 collected during the same month, controlling for potential seasonal variability. Raman spectral 27 parameters from the ν 1 peak quantified total carbonate ion structural disorder (full width at half 28 maximum height [FWHM] of ν 1 ) and Mg content (ν 1 position, Raman shift). The total structural 29 disorder was then partitioned into Mg-driven and non-Mg driven components (residual ν 1 30 FWHM). The total structural disorder and Mg content decreased significantly with increasing 31 depth, correlating with temperature and carbonate system parameters. The Mg-temperature 32 relationships from this study were also consistent with prior studies. Non-Mg structural disorder 33 did not correlate to any environmental parameters. When measured across an intra-sample 34 gradient of ontogenetic growth rate, total structural disorder, Mg content, and non-Mg structural 35 disorder increased with growth rate for all but one taxon, demonstrating the kinetic effect of 36 growth rate as well as potential taxon-specific physiological effects. These results provide insight 37 into how environmental and growth rate kinetic effects independently affect different 38 components of carbonate ion structural disorder (Mg content and non-Mg factors). These 39 findings also suggest that Raman spectroscopy may be helpful in quantifying solubility within 40 biogenic calcites. strong correlation with residual ν 1 FWHM (R = 0.95) and a strong correlation with Mg-based ν 1 FWHM (R = 0.82) within C. tortuosum from 280 m. ν 1 FWHM values measured from Acanella spp. at 823 m are weakly correlated with Mg-based ν 1 FWHM (R = 0.33) but strongly correlated 413 with residual ν 1 FWHM (R = 0.86).

Advancements in material removal mechanism and surface integrity of high speed metal cutting: A review

Abstract: The research and application of high speed metal cutting (HSMC) is aimed at achieving higher productivity and improved surface quality. This paper reviews the advancements in HSMC with a focus on the material removal mechanism and machined surface integrity without considering the effect of cutting dynamics on the machining process. In addition, the variation of cutting force and cutting temperature as well as the tool wear behavior during HSMC are summarized. Through comparing with conventional machining (or called as normal speed machining), the advantages of HSMC are elaborated from the aspects of high material removal rate, good finished surface quality (except surface residual stress), low cutting force, and low cutting temperature. Meanwhile, the shortcomings of HSMC are presented from the aspects of high tool wear rate and tensile residual stress on finished surface. The variation of material dynamic properties at high cutting speeds is the underlying mechanism responsible for the transition of chip morphology and material removal mechanism. Less surface defects and lower surface roughness can be obtained at a specific range of high cutting speeds, which depends on the workpiece material and cutting conditions. The thorough review on pros and cons of HSMC can help to effectively utilize its advantages and circumvent its shortcomings. Furthermore, the challenges for advancing and future research directions of HSMC are highlighted. Particularly, to reveal the relationships among inherent attributes of workpiece materials, processing parameters during HSMC, and evolution of machined surface properties will be a potential breakthrough direction. Although the influence of cutting speed on the material removal mechanism and surface integrity has been studied extensively, it still requires more detailed investigations in the future with continuous increase in cutting speed and emergence of new engineering materials in industries.

Fundamental Investigation into Tool Wear and Surface Quality in High-Speed Machining of Ti6Al4V Alloy

Abstract: This paper reports a fundamental investigation consisting of systematic trials into the response of Ti6Al4V alloy to high-speed machining using carbide inserts. It is a useful extension to work previously published, and aims at assessing the impact of the process parameters, depth of cut, cutting speed and feed rate in addition to cutting length, and their interrelations, on observed crater and flank wear and roughness of the machined surface. The results showed that abrasion was the most important flank wear mechanism at high speed. It also showed that increased cutting length accelerated crater wear more than exhibited flank wear and had considerable effect on surface roughness. In particular, crater wear increased by over 150% (on average), and flank wear increased by 40% (on average) when increasing cutting length from 40 to 120 mm. However, cutting the same length increased surface roughness by 50%, which helps explain how progression of tool wear leads to deteriorated surface quality. ANOVA was used to perform statistical analyses of the measured data and revealed that cutting length and depth of cut had the greatest effect on both crater and flank wear of the cutting tool. These results confirm that high-speed machining of Ti6Al4V alloy is a reliable process, with cutting speed identified as having a relatively small influence on the tool wear and resultant roughness of the machined surface relative to other parameters.