Department of Mechanical Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

The influence of temperature on the tribological performance of alloy 718 is studied in the present work. The alloy 718 samples were used in double aged condition for reciprocating wear test with a ball on flat configurations. The wear tests were conducted at two conditions viz: room temperature and 300 °C temperature. The testing temperature had a significant influence on the coefficient of friction (COF) and wear resistance of alloy 718. The alloy 718 sample, subjected to high-temperature testing environment had a lower COF and higher wear rate compared to samples tested at ambient temperature. The lower COF values of the alloy 718 samples subjected to high wear testing temperature conditions were attributed to the extent and presence of glaze layer formation, which is insignificant in the case of samples subjected to ambient temperature. The higher wear rate values of the alloy 718 samples subjected to high wear testing temperature conditions were attributed to the due to occurrence of tribo-chemical reactions at the contact zone of tribo-pair. © 2021, Springer Nature Singapore Pte Ltd.

Department Of Chemistry

World University root node

Lecture Notes in Mechanical Engineering

Investigation on Elevated Temperature Tribological Performance of Alloy 718

In this work, a finite-difference-based axisymmetric off-lattice Boltzmann solver is developed to simulate blood flow through pathological arteries. The proposed solver handles arterial geometries using a body-fitted curvilinear mesh. The axisymmetric nature of the flow and the non-Newtonian behavior of blood are incorporated using external source terms. The solver is verified for spatially developing pulsatile inflow through an abdominal aortic aneurysm using reference data from literature. Thereafter, the effects of amplitude and frequency of an irregular-shaped stenosed artery are systematically studied. The results are analyzed using the instantaneous vorticity contours, streamlines, cycle-averaged and phase-averaged profiles of wall shear stress (WSS), and oscillatory shear index. Further, the correlation between the luminal surface concentration (LSC) of low-density lipoproteins and the WSS is studied to predict potential disease initiation and progression locations. It is noted that an increase in the amplitude of irregularity of the stenosis increases the magnitudes of maxima and minima of WSS profiles without altering their locations. On the other hand, an increase in the frequency of irregularity increases the magnitudes of WSS extrema while bringing the peaks closer together. Further, a positive correlation is found between the degree of irregularity as well as the number of locations of elevated LSC. The presence of irregularity creates additional vortices in the upstream section of the stenosis. Both the upstream and downstream sections of the stenosis are subjected to the opposing shear-layers with higher magnitudes, which may lead to endothelial damage. Finally, the shear-thinning effect of blood is studied using the power-law model. The magnitudes of the maxima and minima in WSS have a lower value for the shear-thinning model than the Newtonian case. Also, the vortices that were produced in the upstream section because of the irregularity get suppressed by the shear-thinning effect of the blood. © 2021 Author(s).

Physics of Fluids

An off-lattice Boltzmann method for blood flow simulation through a model irregular arterial stenosis: The effects of amplitude and frequency of the irregularity

Wettability patterning of a surface is a passive method to manipulate the flow and heat transport mechanism in many physical processes and industrial applications. This paper proposes a rational wettability pattern comprised of multiple superhydrophilic wedges on a superhydrophobic background, which can continuously remove the impacted spray droplets from the horizontal surface. We observed that the spray droplets falling on the superhydrophilic wedge region spread and form a thin liquid film, which is passively transported away from the surface. However, most of the droplets falling on the superhydrophobic region move towards the wedge without any flooding. The physics of the passive transport of the liquid film on a wedge is also delved into using numerical modelling. In particular, we elucidate the different modes of droplet transport in the superhydrophobic region and the interaction of multiple droplets. The observed droplet dynamics could have profound implications in spray cooling systems and passive removal of liquid from a horizontal surface. This study’s findings will be beneficial for the optimization of efficient wettability patterned surfaces for spray cooling application. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Fulltext

Processes

Droplet dynamics on a wettability patterned surface during spray impact

The flow stress reduction during plastic deformation superposed with electric current, commonly referred as 'electroplasticity' has been actively researched over the past few decades. While the existence of an electron-dislocation interaction, independent of Joule heating is established, the exact rate controlling mechanism of the observed behaviour lacks consensus. Understanding the governing mechanism is complex due to the combined effect of Joule heating and electron-dislocation interaction. The present work attempts to establish the electroplastic mechanism in AA 6063 alloy and its nanocomposites. The role of microstructure on the electron interaction is investigated by preparing four distinct microstructure from the base alloy. All the samples were subjected to constant amplitude direct current during plastic deformation. The Joule heating effect is decoupled using the experimentally measured temperature history. The potential electroplastic mechanism for the alloy is elucidated by analysing the trend of flow stress reduction with strain and strain rate. It is inferred that micro Joule heating and electron wind effect cannot completely explain the observed electroplastic behaviour in AA 6063. The SiC particles in nano-composites suppressed the electroplastic effect. The observed mechanical behaviour under electric current is in agreement with the trend predicted assuming magnetic depinning mechanism. The reduction of dislocation density quantified using X-ray diffraction is found to concur with the inferred mechanism. © 2021 The Author(s).

Department of Metallurgical and Materials Engineering

Journal of Materials Research and Technology

Microstructure dependent electroplastic effect in AA 6063 alloy and its nanocomposites

Context: Numerous minor bodies of our solar system are covered by loosely bound dust particles; these layers are called regolith. Light scattered by regolith surfaces is a function of their bulk porosity, of the sizes, shapes, structures and compositions of the constituent particles. Aims: To increase our data base, the present work is an extension of our previous work by Kar et al. (2016), where we reported light scattering data for regolith surfaces with different porosities, sizes, and composition of the particles (from very low to moderate absorption). The new samples have larger particles with moderate to high absorption, three originate from industry, and three are natural (among them a mixture of two previously studied samples). Methods: The samples were prepared with different bulk porosities. Photometric phase curves were built for two different geometrical configurations. The light source was a He–Ne laser at 632.8 nm. The phase angle (g) covered for the first configuration is from 45 to 126° and for the second configuration it is from 45 to 108°, in steps of 9 and 4.5° respectively. We maintained incident angle (i)= emergent angle (e) for the first configuration and i=45°, while e varying for the second configuration. The experimental data were fitted successfully to the semi-empirical model proposed by Hapke (2008) and interpreted in terms of the porosities and sizes of the particles. The albedo values obtained from the model for two samples are compared to those calculated directly from Mie theory. Results: The successful fit by the model is confirmed just as the increase of reflectivity with the decrease of porosities for a given composition and particle size. Further, it was observed that reflectivity increases with the decrease in particle size for a given composition. Finally, we have tested that for corundum and silicon carbide samples with a 22μm and 15μm particle sizes ( respectively), the best fitted albedo (ω) values that can be obtained from Hapke model, match very well with those calculated directly by Mie Theory. This also re-validated our approach adopted in the present work. © 2020 Elsevier Inc.

Icarus

Laboratory photometry of regolith analogues: Effect of porosity-II

Background and Aim: The proposed work was planned to evaluate the potential protective role of aqueous Aloe vera (AV) concentrate and/or Omega-3 fatty acids (O3FAs) against GM -initiated renal toxicity in rats. Materials and Methods: Thirty female Wistar-albino rats were distributed into five equivalent groups as follows: Normal control group, GM control group, GM + AV group (200 mg/kg, p.o.), GM + O3FAs group (100 mg/kg, p.o.), GM + AV + O3FAs group. All the treatments were administered for 10 days. Renal toxicity was initiated by intraperitoneal administration of GM (80 mg/kg/day) for last 5 days of test duration. Results: Noticeable rise in the levels of serum creatinine, urea, MDA, TNF-α, TGF-β1, Fibronectin and NGAL was seen alongside a significant decrese in the levels of serum albumin, total protein content and antioxidant enzymes, SOD, GSH, catalase in GM control group. Treatment with AV or O3FAs or AV + O3FAs exhibited a considerable reduction in serum creatinine, urea, MDA, TNF-α, TGF-β1, Fibronectin and NGAL levels and a rise in the levels of serum albumin, total protein and antioxidant enzymes. Conclusion: The study concluded the importance of AV and Omgea-3 fatty acids as effective nephroprotective agents. However, the combined treatment with AV and O3FAs showed similar beneficial effects as compared to monotherapy in mitigating adverse effects of GM-initiated renal toxicity. There was no significant difference observed in monotherapy as well as combination therapy. © 2021, Association of Pharmaceutical Teachers of India. All rights reserved.

Indian Journal of Pharmaceutical Education and Research

Therapeutic interventions using monotherapy versus combination therapy of aloe Vera and omega-3 fatty acids on gentamicin-initiated renal toxicity via attenuation of renal biomarkers

Inhomogeneous co-flowing fluids inside a microchannel exposed to an acoustic standing wave can lead to the relocation of the fluids. Here we investigate the use of combined acoustic relocation and acoustophoretic migration for the transfer of particles between co-flowing fluids inside a microchannel exposed to a standing pressure half-wave with a pressure nodal plane along the channel center line and antinodal planes along the walls. We show that under the influence of the applied field, particles suspended in a carrier fluid of low acoustic impedance flowing along the channel center are initially dragged toward the walls along with the relocating fluid and later migrate into the target fluid that relocates from the walls to the channel center. We found that the particle motion is initially controlled by the dominant fluid relocation-induced Stokes drag force and later governed by the primary acoustic radiation force as stable fluid configuration is reached. Experimentally we unraveled that depending on the operating parameters-particle size, flow rates, and acoustic energy density-the final locations of the particles at the end of the channel leads to three distinct regimes-complete medium exchange, partial medium exchange, and no medium exchange. Our study reveals that the relocation and migration dynamics of the particles is underpinned by the relevant timescales â advection timescale, acoustophoretic timescale, and the relocation timescale, which in turn govern the different regimes observed. Numerical simulations predicted the complete migration and nonmigration of particles of two different sizes, in agreement with the experimental observations. We also demonstrate the medium exchange and size-based sorting of biological cells, which shows the potential application of the study in biochemical assays. © 2021 American Physical Society.

Physical Review Fluids

Combined acoustic relocation and acoustophoretic migration for particle transfer between co-flowing fluids in a microchannel

Ladder frame structures are used as models for multistorey buildings. These periodic structures exhibit alternating propagating and attenuating frequency bands. Of the six different wave modes of propagation, two modes strongly attenuate at all frequencies. The other four modes have nonoverlapping stop band characteristics. Thus, it is challenging to isolate such structures when subjected to broadband, multimodal base excitation. In this study, we seek to synthesize a periodic ladder frame structure that has attenuation characteristics over the maximal range of frequencies for all the modes of wave propagation. We synthesize a unit cell of the periodic structure, which comprises two distinct regions having different inertial, stiffness, and geometric properties. The eigenvalues of the transfer matrix of the unit cell determines the attenuating or the nonattenuating characteristics of the structure. A novel pictorial presentation in the form of eigenvalue map is developed. This is used to synthesize the optimal unit cell. Also, design guidelines for suitable selection of the design parameters are presented. It is shown that a large finite periodic structure comprising a unit cell synthesized using the present approach has significantly better isolation characteristics in comparison to the homogeneous or any other arbitrarily chosen periodic structure. © 2021 American Society of Mechanical Engineers (ASME). All rights reserved.

Journal of Vibration and Acoustics, Transactions of the ASME

Broadband Seismic Isolation of Periodic Ladder Frame Structure

In vitro, cellular processing on polymeric surfaces is fundamental to the development of biosensors, scaffolds for tissue engineering and transplantation. However, the effect of surface energy and roughness on the cell-surface interaction remains inconclusive, indicating a lack of complete understanding of the phenomenon. Here, we study the effect of surface energy (Es) and roughness ratio (r) of a polydimethylsiloxane (PDMS) substrate on cell attachment, growth, and proliferation. We considered two different cell lines, HeLa and MDA MB 231, and rough PDMS surfaces of different surface energy in the range Es = 21-100 mJ m-2, corresponding to WCA 161°-1°, and roughness ratio in the range r = 1.05-3, corresponding to roughness 5-150 nm. We find that the cell attachment process proceeds through three different stages marked by an increase in the number of attached cells with time (stage I), flattening of cells (stage II), and elongation of cells (III) on the surface. Our study reveals that moderate surface energy (Es ≈ 70 mJ m-2) and intermediate roughness ratio (r ≈ 2) constitute the most favourable conditions for efficient cell adhesion, growth, and proliferation. A theoretical model based on the minimization of the total free energy of the cell-substrate system is presented and is used to predict the spread length of cells that compares well with the corresponding experimental data within 10%. The performance and reusability of the rough PDMS surface of moderate energy and roughness prepared via facile surface modification are compared with standard T-25 cell culture plates for cell growth and proliferation, which shows that the proposed surface is an attractive choice for efficient cell culture. © The Royal Society of Chemistry.

RSC Advances

Effect of surface energy and roughness on cell adhesion and growth-facile surface modification for enhanced cell culture

Multi-layer graphene nanoplatelet (mGNP)/poly(methyl methacrylate) (PMMA) nanocomposite flexible thin films were prepared at various GNP loadings (1–5 wt%) and their optical properties were investigated in the UV, visible, and near IR region (200–850 nm). The transmittance and reflectance of the films reduced with an increase in the GNP loading. Although it is known that the transmittance of pure graphene is independent of wavelength, it was observed that in the UV region, the optical properties of mGNP/PMMA are wavelength-dependent. However, at higher GNP loadings (3–5%), these films have shown optical properties with less wavelength dependency. This may be attributed to diverse types of attenuation mechanisms in the nanocomposite films when graphene is incorporated as filler in the polymer matrix. In the visible region (400–700 nm), no such wavelength-dependent optical properties were observed. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.

Journal of Materials Science: Materials in Electronics

Optical properties of multilayer graphene nanoplatelet (mGNP)/poly(methyl methacrylate) (PMMA) composite flexible thin films prepared by solvent casting