Department of Applied Mechanics

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

Analysis of uterine contractions using electromyography signals is gaining importance due to its capability to measure the dynamics of uterus. Uterine electromyography (uEMG) provides information on the nature of uterine contractions non-invasively. In this study, the fluctuations in uEMG signals associated with Term pregnancies are analyzed. For this, Term uEMG signals corresponding to second (T1) and third (T2) trimesters are considered. The signals are subjected to Adaptive Fractal Analysis (AFA), wherein a global trend is obtained by using overlapping windows of three orders namely, 25%, 50% and 75%. The signals are detrended and the fluctuation function is estimated. Two Hurst exponent features computed at short range (Hs) and long range (Hl) are extracted and statistically analyzed. Results show that AFA is able to characterize variations in the fluctuations of Term delivery signals. The feature values are observed to vary significantly during different weeks of gestation. It is found that features of T2 signals are higher than that of T1 signals for all the considered overlaps, indicating that T2 signals possess smoother characteristics than T1 signals. Further, coefficient of variation is observed to be low, indicating that these features are able to handle the inter-subject variations in Term signals. Therefore, it appears that the proposed approach could aid in investigation of progressive changes in uterine contractions during Term pregnancies. © 2021 IPEM

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Medical Engineering and Physics

Differentiation of fluctuations in uterine contractions associated with Term pregnancies using adaptive fractal features of electromyography signals

In this paper, the potential of superelastic shape memory alloy (SE-SMA) wire embedded architectures to increase the quasi-static indentation properties of a laminated glass/epoxy composite material was evaluated. Three types of SE-SMA configurations namely straight independent, meshed and anchored wires were embedded in the glass/epoxy composite laminates via a vacuum bag resin infusion technique. Throughout this investigation, the changes in the quasi-static indentation behavior and allied damage mechanisms due to these embedments were compared with the homogenous glass/epoxy laminates. Real time acoustic emission (AE) monitoring technique was employed to characterize the damage profile of the different glass/epoxy specimens during the quasi-static indentation tests. The experimental results showed that SE-SMA embedments play a vital role in increasing the penetration resistance by enhancing redistribution of the indentation load all across the laminates. In particular, the meshed specimens restricted penetration of an indenter and delayed the critical fiber fracture unlike homogeneous and straight wired ones, whereas the anchored specimens further restricted extensive SMA/matrix pull-out, unlike meshed ones and provided the most excellent balance among rigidity, rear face fiber breakage, and SMA/matrix pull-out. Straight, meshed and anchored SE-SMA wires increased the load-carrying capacity approximately by 31%, 79%, and 100%, respectively, in comparison to the homogeneous ones. © 2020 The Authors

Department of Engineering Design

Polymer Testing

Evaluation of quasi-static indentation response of superelastic shape memory alloy embedded GFRP laminates using AE monitoring

Non-invasive assessment of tissue perfusion has gained increased interest in the recent past for monitoring various physiological dysfunctions. Laser speckle imaging and associated processing techniques present useful and inexpensive methods of achieving this goal. However, differentiating the effects of static and dynamic scatterers from the captured speckle image is challenging and limits the sensitivity of such techniques. This paper presents a fractal analysis in the temporal domain to assess the various dynamic scattering features of tissue perfusion demonstrated on a perfusion model. We use detrended fluctuation analysis for the quantitative assessment of image fractal dimensions, which reflect the concentration and flow features of the moving scatterers in the perfusion model. © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only.

Progress in Biomedical Optics and Imaging - Proceedings of SPIE

Differential imaging of dynamic scattering from laser speckle images for applications in perfusion monitoring

A stress-state dependent cyclic cohesive model, which accounts for accumulation of plasticity, during both tensile as well as compressive deformations, and incorporates accumulation of irreversible damage due to macroscopic plasticity as well as microstructural mechanisms, is formulated. The model is implemented in mode-I plane strain fatigue crack growth simulations. The model is validated by reproducing the effect of retardation in crack growth rates after different combinations of tensile and compressive overloads. We show accurate description of the elastic–plastic behaviour of the process zone is vital, in particular for negative stress ratios subsequent to a tensile over-load, as considerable plasticity occurs in compression at the crack-tip, significantly reducing retardation effects. © 2020, Springer Nature B.V.

International Journal of Fracture

An incremental elastic–plastic triaxiality dependent fatigue model

Deep CO2 storage reservoirs show a wide range of heterogeneous structures across different scales. Here, we show how high-resolution heterogeneity in both permeability and capillary entry pressure control dissolution and local capillary trapping of supercritical CO2 (ScCO2). Prior works mainly considered homogeneous reservoirs or simplified heterogeneity with horizontal and fixed capillary transition zones. Most of those studies ignored simultaneous free-phase ScCO2 spreading and solutal fingering. To advance understanding of heterogeneity effects, we have performed two-dimensional numerical simulations for ScCO2 injection into the middle of a storage reservoir. We have computed metrics including the spatial plume moments to compare the dissolution trapping and spreading of ScCO2 during the injection and post-injection period for different variances and correlation lengths of log-normal permeability and capillary entry pressure fields. The results show that the second-order spatial moment of the ScCO2 saturation field in the horizontal direction decreases by 10% as the permeability variance increases from 0.1 to 3.0. But it decreases by 50% as the capillary entry pressure variance becomes 1.1. For higher capillary entry pressure variance, the ratio of dissolved CO2 mass to free-phase ScCO2 mass decreases, showing higher local capillary trapping. The vertical distance between the centers of mass of the ScCO2 and dissolved CO2 plumes (representing the downward flow of dissolved CO2 through solutal fingering) is greater for heterogeneous reservoirs. © 2021

International Journal of Greenhouse Gas Control

Coupled multiphase flow and transport simulation to model CO2 dissolution and local capillary trapping in permeability and capillary heterogeneous reservoir

Pulsed laser diodes (PLDs) promise to be an attractive alternative to solid-state laser sources in photoacoustic tomography (PAT) due to their portability, high-pulse repetition frequency (PRF), and cost effectiveness. However, due to their lower energy per pulse, which, in turn, results in lower fluence required per photoacoustic signal generation, PLD-based photoacoustic systems generally have maximum imaging depth that is lower in comparison to solid-state lasers. Averaging of multiple frames is usually employed as a common practice in high PRF PLD systems to improve the signal-to-noise ratio of the PAT images. In this work, we demonstrate that by combining the recently described approach of subpitch translation on the receive-side ultrasound transducer alongside averaging of multiple frames, it is feasible to increase the depth sensitivity in a PLD-based PAT imaging system. Here, experiments on phantom containing diluted India ink targets were performed at two different laser energy level settings, that is, 21 and 27 μ \textJ. Results obtained showed that the imaging depth improves by 38.5% from 9.1 to 12.6 mm for 21- μ \textJ energy level setting and by 33.3% from 10.8 to 14.4 mm for 27- μ \textJ energy level setting by using λ /4-pitch translation and average of 128 frames in comparison to λ -pitch data acquired with the average of 128 frames. However, the achievable frame rate is reduced by a factor of 2 and 4 for λ /2 and λ /4 subpitch translation, respectively. © 1986-2012 IEEE.

IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control

Extending Imaging Depth in PLD-Based Photoacoustic Imaging: Moving beyond Averaging

A dislocation density based crystal plasticity model is developed to account for the precipitate induced cyclic softening in IN718. The new model treats the interaction between the precipitates and the dislocations using a probabilistic approach. It is also capable of capturing the reduction in the effective size of the precipitates due to reversible dislocations shearing through them. Further, the phenomenological model accounts for the heterogeneous accumulation of dislocations in the microstructure (i) as a function of distance to the nearest grain boundary and (ii) the interparticle spacing within a grain. The developed model is used to simulate the macroscopic mechanical response of IN718 under a series of monotonic and cyclic loads at different strain rates and alternating strain levels, respectively. Model predictions of macroscopic behavior are shown to be in good agreement with experimental data. They can capture the initial hardening and subsequent softening during cyclic loading for several strain amplitudes. Sensitivity analyses have been performed to understand the influence of grain size, reversible dislocations, and the size of the precipitates. © 2021 Elsevier Ltd.

Department of Metallurgical and Materials Engineering

International Journal of Plasticity

Dislocation density based crystal plasticity model incorporating the effect of precipitates in IN718 under monotonic and cyclic deformation

Introduction: Accelerometry-based activity counting for measuring arm use is prone to overestimation due to nonfunctional movements. In this paper, we used an inertial measurement unit (IMU)-based gross movement (GM) score to quantify arm use. Methods: In this two-part study, we first characterized the GM by comparing it to annotated video recordings of 5 hemiparetic patients and 10 control subjects performing a set of activities. In the second part, we tracked the arm use of 5 patients and 5 controls using two wrist-worn IMUs for 7 and 3 days, respectively. The IMU data was used to develop quantitative measures (total and relative arm use) and a visualization method for arm use. Results: From the characterization study, we found that GM detects functional activities with 50–60% accuracy and eliminates non-functional activities with &gt;90% accuracy. Continuous monitoring of arm use showed that the arm use was biased towards the dominant limb and less paretic limb for controls and patients, respectively. Conclusions: The gross movement score has good specificity but low sensitivity in identifying functional activity. The at-home study showed that it is feasible to use two IMU-watches to monitor relative arm use and provided design considerations for improving the assessment method. Clinical trial registry number: CTRI/2018/09/015648

Fulltext

Journal of Rehabilitation and Assistive Technologies Engineering

Quantification of the relative arm use in patients with hemiparesis using inertial measurement units

This study presents a novel plasmonic fiber optic sandwich immunobiosensor for the detection of chikungunya, an infectious mosquito-borne disease with chronic musculoskeletal pain and acute febrile illness, by exploiting non-structural protein 3 (CHIKV-nsP3) as a biomarker. A plasmonic sandwich immunoassay for CHIKV-nsP3 was realized on the surface of a compact U-bent plastic optical fiber (POF, 0.5 mm core diameter) with gold nanoparticles (AuNPs) as labels. The high evanescent wave absorbance (EWA) sensitivity of the U-bent probes allows the absorption of the light passing through the fiber by the AuNP labels, upon the formation of a sandwich immunocomplex of CHIKV-nsP3 on the core surface of the U-bent probe region. A simple optical set-up with a low-cost green LED and a photodetector on either end of the U-bent probe gave rise to a detection limit of 0.52 ng mL-1 (8.6 pM), and a linear range of 1-104 ng mL-1 with a sensitivity of 0.1043A530 nm/log(CnsP3). In addition, the plasmonic POF biosensor shows strong specificity towards the CHIKV-nsP3 analyte in comparison with Pf-HRP2, HIgG, and dengue whole virus. The results illustrate the potential of plasmonic POF biosensors for direct and sensitive point-of-care detection of the chikungunya viral disease. © 2021 The Royal Society of Chemistry.

Analyst

Development of a U-bent plastic optical fiber biosensor with plasmonic labels for the detection of chikungunya non-structural protein 3

We develop a passive control strategy for suppressing thermoacoustic instability in a bluff-body stabilized premixed turbulent combustor. When the equivalence ratio is varied, there is a transition from combustion noise to thermoacoustic instability via intermittency in the combustor. We perform simultaneous acoustic pressure, 2D-PIV, and CH* chemiluminescence measurements to capture the pressure fluctuations, the velocity field, and the heat release rate (HRR) field during the transition. We measure the spatial distribution of the amplitude of turbulent velocity at the acoustic frequency, time-averaged vorticity, time-averaged HRR, and Rayleigh index and identify various regions of significance. We implement a passive control strategy by targeting these regions with a steady injection of secondary micro-jet of air to optimize the injection location and determine the critical region. Targeting the critical region with secondary air leads to greater than 20 dB suppression of the dominant thermoacoustic mode. We observe that the coherent structure forming from the shear layer following the dump plane gets suppressed, leading to an incoherent spatial distribution of HRR fluctuations. We find that the turbulent velocity amplitude correctly identifies the critical region for optimized passive control during thermoacoustic instability. In contrast, the Rayleigh index identifies the region of the most significant acoustic driving; however, it does not identify the region most sensitive to control. Finally, we extend our analysis by determining the spatial distribution of the Hurst exponent measured from the turbulent velocity field. We show that the Hurst exponent identifies the critical region during thermoacoustic instability and intermittency, unlike the other physical measures. Thus, we develop a smart passive control method by combining the need for finding critical regions in the combustor with the predictive capabilities of the Hurst exponent. © 2020 The Combustion Institute