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 dynamic compressive behavior of foams with a non-linear variation in the cross-sectional area profiles is studied. A theoretical model has been developed based on the one-dimensional shock theory and the rigid, perfectly-plastic, and locking (RPPL) material model, to establish the governing equations of motion of an initially stationary foam struck by a rigid projectile. Both decreasing and increasing cross-sectional area profiles with various power-law exponents are considered. The numerical simulations suggest that the decreasing area profiles, referred to as the convergent foams, exhibit a double-shock mode. In contrast, the foams with an increasing area-profile, referred to as the divergent foams, exhibit a single-shock mode. The theoretical predictions of both the double-shock and the single-shock cases are validated against the finite element simulations. Compared to the foam with a uniform cross-sectional area, the convergent foams transmit lower mean forces at the distal end, and the divergent foams transmit higher forces at higher impact velocities. An interesting phenomenon observed is that the mean force at the distal end decreases with an increase in the impact velocity beyond the densification velocity, for the convergent foams. An expression for the plastic energy dissipated by convergent foams has been derived, and we observe that the convergent foams dissipate less energy than the divergent foams. The performance of the foams has been compared through the dissipation performance parameter, defined as the ratio of non-dimensional plastic energy dissipated at the end of the crushing process to the mean non-dimensional force at the distal end. Convergent foams with low gradients and high power-law exponents have the highest dissipation performance. A special case of a decreasing density-gradient combined with an increasing area-gradient is shown (through finite element simulations) to be beneficial for structural protection. © 2021 Elsevier Ltd

World University root node

International Journal of Impact Engineering

Theoretical analysis on the dynamic compressive behavior of cellular solids with non-linear variation in cross-sectional area

Differences in the dynamics and transport of blood make certain regions of the arterial network the preferred sites for initiation and formation of arterial diseases like stenosis and aneurysms. Understanding of such arterial diseases is directly linked to critical hemodynamic parameters such as the wall shear stress (WSS). The present work generalises the influence of WSS on the concentration of LDL that was observed in an earlier study. To this end, a wide variety of simplified flow domain, inspired by the near-wall regions of aneurysms and stenosis, are constructed and analyzed. The effects of pulsatile inflow condition, rheology of blood and curvature of the wall on the correlation between WSS and LDL concentration are investigated. It is demonstrated that the time-scale of variation of lumen-surface-concentration (LSC) of LDL is larger than a single cardiac cycle. As a consequence, the time-average values of WSS are sufficient to locate the regions of higher LSC. This idea is strengthened by making use of simplified flow domain that generates moving stagnation point. Further, it was observed that the rheology of the blood and curvature of the wall does not affect the observed correlation between the WSS and LDL concentration. © 2021 Informa UK Limited, trading as Taylor &amp; Francis Group.

Department of Applied Mechanics

Computer Methods in Biomechanics and Biomedical Engineering

A study on the transport and interaction between blood flow and low-density-lipoprotein in near-wall regions of blood vessels

This paper explores the relationship between financial constraints and firm participation in global value chains (GVC). We use a rich firm-level data belonging to the Indian manufacturing sector for the period 2001–2016. Controlling for endogeneity and sample selection bias, our empirical outcome reveals a negative impact of financial constraint on firm GVC participation. We also find that inter-firm trade credit fosters firm participation in GVCs. Our findings also highlight that firms dependent on external finance find it challenging to participate in GVCs. Further, sub-sample analysis shows a significant effect of financial constraints in the case of small firms. Finally, we find that firms that are relatively more financially constrained are more likely to become a part of GVC (GVC starters) during the study period. Our findings have strong policy implication on the lines of promoting GVC participation for Indian manufacturing firms and hence remains of interest for policymakers. © 2021 Informa UK Limited, trading as Taylor & Francis Group.

Department of Humanities and Social Sciences

Journal of International Trade and Economic Development

Financial constraints and global value chain participation: Firm-level evidence from India

Longitudinal vortices generated by winglet type vortex generators mounted on fin surface improve fluid mixing with disruption of boundary layer growth, which results in convective heat transfer enhancement. The present study reports the three-dimensional numerical investigation of airflow through heated fin-tube heat exchangers in presence of common flow down configured rectangular winglet pairs (RWPs) for staggered arrangements of circular tubes. It is well known that the thermal performance of a fin-tube heat exchanger is majorly influenced by various locations of winglets corresponding to tube centre. Henceforth, fluid flow and heat transfer characteristics of different possible RWP locations concerning each tube are examined. Further, for higher performance, a search for an effective angle of attack ranging from 15° to 60° is also performed for optimized locations. The effect of different inlet flow conditions is also investigated for Reynolds number ranges from 2000 to 10,000. Thermohydraulic performance is studied by considering Nusselt number, friction factor, secondary flow intensity and thermal performance factor. Irreversibilities due to RWPs are analysed by calculating the entropy generation rate due to viscous and heat transfer effects. Obtained results illustrate that the selection of promising RWP locations plays a vital role in improving thermal performance. The relationship between heat transfer, secondary flow and irreversibility parameters are also reported. © 2020 Elsevier Masson SAS

International Journal of Thermal Sciences

Thermal performance analysis of fin-tube heat exchanger with staggered tube arrangement in presence of rectangular winglet pairs

Microcrystalline cellulose (MCC) and sawdust (SD) green fillers have great potential to act as moisture reservoirs and reactive fillers. In the present study, a one-component moisture curable polyurethane (PU) adhesive was reinforced with MCC and SD fillers. The durability of aluminum/steel joints produced using unreinforced and reinforced PU adhesives was studied using dynamic mechanical analysis (DMA), fatigue, and hygrothermal aging experiments. Lap-shear tests were conducted to evaluate the effects of aging on joints strength. Fourier-transform infrared spectroscopy (FTIR) experiments were performed on adhesive joints after hygrothermal aging to understand the changes in chemical structure due to aging, and the influence of cellulosic fillers on the aging phenomena. DMA results showed that the glass transition temperature of the reinforced PU was similar to that of the unreinforced PU. Fatigue performance of MCC and SD reinforced PU adhesive joints was found to be better than unreinforced PU joints. Further, MCC reinforced PU adhesive joints were found to be more resistant to hygrothermal aging than SD reinforced and unreinforced PU joints. Overall, MCC reinforced PU adhesive joints exhibited good fatigue and superior long-term properties. © 2020 Elsevier Ltd

Department Of Chemical Engineering

Department of Metallurgical and Materials Engineering

International Journal of Adhesion and Adhesives

Hygrothermal aging, fatigue and dynamic mechanical behavior of cellulosic particles reinforced one-component moisture curable polyurethane adhesive joints

The aim of this embodiment is to present an analytical analysis of a functionally graded piezoelectric energy harvester consisting of a flexible functionally graded piezoelectric layers carrying magnetic mass at the free end. The magnetic tip mass is in interaction with a permanent magnet which is located at a distance from the top of the tip mass. The oscillation of the harvester happens via excitation of the base. Using Rayleigh’s beam theory and Hamilton’s principle and considering geometric nonlinearity, the coupled electromechanical governing equations have been developed. The nonlinear frequency response of the piezoelectric energy harvester beam has also been studied under base excitation. A parametric study has been carried out to investigate the effect of grading index and magnetic force on responses of both free vibration and induced excitation cases. The results were compared with those obtained using three-dimensional finite element model developed in COMSOL Multiphysics 5.5 commercial software and good agreement has been observed. The results from both the analytical method and simulation confirm that tuning the design parameters of grading index and magnetic gap to the optimal value results in a considerable change in the performance of the energy harvester. © The Author(s) 2021.

Journal of Intelligent Material Systems and Structures

Dynamic analysis of a functionally graded piezoelectric energy harvester under magnetic interaction

The defect frequency amplitude of the High-Frequency Resonance Technique spectrum is a useful feature for bearing diagnosis. However, it is dependent on the accuracy of the resonance frequency band selection. The vibration data are filtered, with the resonance frequency band being the passband. An alternative approach based on Empirical Mode Decomposition and Instantaneous Energy is proposed to obtain the filtered signal without the need of identifying the resonance frequency band. The objective is to maximize the defect frequency amplitude of the High-Frequency Resonance Technique spectrum. The proposed approach is compared with various optimization techniques and the frequently used Fast Kurtogram approach. These approaches are compared for the simulated and experimental data (seeded and natural defects). The comparison reveals that the proposed approach performs superior to the Fast Kurtogram approach and close to optimization algorithms (the best possible) in a fraction of the time taken by these techniques. © 2021 Elsevier Ltd

Measurement: Journal of the International Measurement Confederation

An approach to improve high-frequency resonance technique for bearing fault diagnosis

A novel piecewise circular interface construction (PCIC) method for accurate reconstruction of interface in a two-phase flow problem is proposed. This is under the framework of a fixed grid, volume of fluid approach applied on a two-dimensional semistaggered structured grid. Fluid interface in each mixed cell is represented using a geometric template of piecewise circular arc. Data corresponding to arc center coordinates and radius are first predicted using curve fitting methods and corrected with the help of volume fraction constraints. Further corrections are carried out to achieve function (c0) continuity at cell boundaries. The proposed method does not require additional calculations for the determination of curvature (for calculation of surface tension force), since it is obtained as part of reconstruction process itself. For dynamic interface construction, simple analytical expressions are derived to construct edge matched flux polygons. Area of intersection of flux polygons with area covered by primary fluid is determined to effect geometric advection across a PCIC interface. Accuracy of this method is demonstrated by the reconstruction of standard static and dynamically evolving interface problems. Accuracy levels superior to most interface reconstruction methods using PLIC and schemes using higher order curves are established. Finally, the capability to handle a complex two-phase flow problem simulation viz the four-vortex flow field, where interface undergoes breakage and coalescence, is also demonstrated. © 2020 John Wiley & Sons, Ltd.

International Journal for Numerical Methods in Fluids

An accurate interface reconstruction method using piecewise circular arcs

Transdermal drug delivery using hollow microneedle enables creating small, wearable and minimally invasive closed-loop system. Polymer hollow microneedles are preferable because they are cost-effective and easy to manufacture. SU-8 is chosen for creating the hollow microneedles as it is a biocompatible photopolymer with robust mechanical properties. Previously reported SU-8 microneedles either use melt casting process for coating SU-8 which is laborious or do not have monolithic structures, thereby making these mechanically weak and difficult to integrate. To the best of our knowledge, for the first time, we report the use of a single-step spin coating process to achieve the desired thickness of SU-8 while using UV lithography to create a monolithic microneedle array. Three types of microneedles were fabricated with outer dimensions varying from 90 to 180 μm, and lumen dimensions ranging from 60 to 80 μm and needle height of 600 μm. These needles are fabricated in a 10×10 array with a platform thickness of 300 μm. Geometrical, mechanical and fluid flow characterisations are carried out for the fabricated arrays. We report the use of a non-destructive evaluation method to characterise the lumen of the fabricated microneedles. The fabricated needles are robust and offer low resistance to fluid flow. The triangular needles can withstand a bending load of 0.2 N and an axial load of 0.7 N. The needles with circular lumen offer least resistance to fluid flow of 0.2 Pa-min μL−1. © 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.

Department of Electrical Engineering

International Journal of Advanced Manufacturing Technology

Fabrication of monolithic SU-8 microneedle arrays having different needle geometries using a simplified process

The current study explores the combustion behavior of methyl crotonate (CH3CH=CHC(=O)OCH3), which is a short ester representative of large unsaturated methyl esters. Starting with a detailed kinetic model for methyl butanoate (CH3CH2CH2C(=O)OCH3) oxidation, revisions are introduced to the C0-C4 chemistry based on the recent Aramco mechanism 3.0. The resulting mechanism is combined with a short model for methyl crotonate, derived from a suitable reference mechanism. Several new classes of reactions are included and the rate constants of the existing reactions are revised based on various theoretical studies and analogies to reactions of similar species. Furthermore, the low-temperature chemistry of methyl crotonate has been implemented in the current study to extend the validity of the mechanism to lower temperatures. The resulting methyl crotonate combustion mechanism has been comprehensively validated using various experiments in the literature. In addition, experiments are performed using a heat flux burner at atmospheric conditions to measure the laminar burning velocities of methyl crotonate at different unburnt mixture temperatures (318, 338, and 358 K). The mechanism is found to reproduce the experimental data for high-temperature combustion of methyl crotonate satisfactorily. The mechanism is also found to predict the low-temperature ignition delays accurately. Sensitivity and path flux analysis are performed to delineate the importance of the different reaction classes in methyl crotonate chemistry. The current study presents a comprehensive mechanism for methyl crotonate combustion, along with a new set of experimental results complementing the existing experimental database in the literature. © 2021