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

The detrimental effect of porosity in cast turbine and compressor blades has been a major issue since long. Though there has been extensive development in casting technology and the incorporation of advanced strategies to reduce the defects, the complete preclusion of porosity in the cast products has not been achieved. The influence of porosity on the path of propagation of a crack has been studied in this work. Quasi-static tensile simulation was performed on polymethyl methacrylate specimens, using Extended Finite Element Method (XFEM). This was done to observe the changes in the crack propagation path due to the presence of macro porosity. The XFEM results were validated by experimental tensile testing on the same specimens. This serves as a pilot study to understand and predict the path of crack propagation in cast components such as turbine/compressor blades with inherent porosity. Â© 2019 Elsevier Ltd.

World University root node

Materials Today: Proceedings

Study on the effect of porosity on crack propagation

Colour adaptation techniques are useful in extending the method of Twelve fringe photoelasticity (TFP) to solve problems in industries as one can minimise the generation of specific calibration tables for each experiment. Image artefacts affect the functioning of existing colour adaptation techniques affecting the fringe order demodulation. Colour transfer is a popular technique in the field of image processing to tackle colour mismatch between images. In this paper, the applicability of two colour transfer strategies in the context of TFP is explored, of which one is selected for implementation. A comparative study on the performance of the novel colour transfer method with the existing colour adaptation techniques is carried out. © 2019 Elsevier Ltd

Optics and Lasers in Engineering

Applicability of colour transfer techniques in Twelve fringe photoelasticity (TFP)

In this article, the effect of charge partitioning in a silicon-on-insulator lateral double-diffused metal-oxide-semiconductor (LDMOS) transistor on its nonlinearity model is investigated. It is found that the prediction of the third-order intermodulation distortion (IM3) depends on the model equivalent circuit (EC) and appropriate charge assignments at various nodes therein. The investigation is carried out using a highly accurate static model of LDMOS along with a couple of different charge-partitioning schemes in order to single out their effects on the nonlinearity model behavior. We observe that charge partitioning in a more flexible EC framework yields an improved IM3 prediction when compared with the TCAD simulated results. © 1963-2012 IEEE.

Department of Electrical Engineering

IEEE Transactions on Electron Devices

Effect of Charge Partitioning on IM3 Prediction in SOI-LDMOS Transistors

This study investigates the behavior of a damped, inelastic, sinusoidally forced impact oscillator which has its barrier placed such that the oscillator always vibrates under compression about its subharmonic resonant frequencies. The Poincaré sections at near subharmonic resonance conditions exhibit finger-shaped chaotic attractors, similar to the strange attractor mapping of Hénon and the ones found by Holmes in his study of chaotic resonances of a buckled beam. The number of such fingers are observed to increase as the barrier distance from the equilibrium is decreased. These chaotic states are interspersed with regimes of periodic behavior, with the periodicity being in accordance with well defined period adding laws. This study also focuses on the ordered behavior of the one-impact period-p orbits around the higher subharmonics of the oscillator. © 2020 World Scientific Publishing Company.

International Journal of Bifurcation and Chaos

Bifurcations in a Pre-Stressed, Harmonically Excited, Vibro-Impact Oscillator at Subharmonic Resonances

Crack growth kinetics in crystalline materials is examined both from the point of continuum mechanics and discrete dislocation dynamics. Kinetics ranging from the Griffith crack to continuous elastic-plastic cracks are analyzed. Initiation and propagation of incipient cracks require very high stresses and appropriate stress gradients. These can be obtained either by pre-existing notches, as is done in a typical American Society of Testing and Materials (ASTM) fatigue and fracture tests, or by in situ generated stress concentrations via dislocation pile-ups. Crack growth kinetics are also examined using the modified Kitagawa–Takahashi diagram to show the role of internal stresses and their gradients needed to sustain continuous crack growth. Incipient crack initiation and growth are also examined using discrete dislocation modeling. The analysis is supported by the experimental data available in the literature. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

Fulltext

Crystals

Analysis of the crack initiation and growth in crystalline materials using discrete dislocations and the modified kitagawa–takahashi diagram

Background. The human hand plays a crucial role in accomplishing activities of daily living. The contribution of each finger in the human hand is remarkably unique in establishing object stabilization. According to the mechanical advantage hypothesis, the little finger tends to exert a greater normal force than the ring finger during a supination moment production task to stabilize the object. Similarly, during pronation, the index finger produces more normal force when compared with the middle finger. Hence, the central nervous system employs the peripheral fingers for torque generation to establish the equilibrium as they have a mechanical advantage of longer moment arms for normal force. In our study, we tested whether the mechanical advantage hypothesis is supported in a task in which the contribution of thumb was artificially reduced. We also computed the safety margin of the individual fingers and thumb. Methodology. Fifteen participants used five-finger prismatic precision grip to hold a custom-built handle with a vertical railing on the thumb side. A slider platform was placed on the railing such that the thumb sensor could move either up or down. There were two experimental conditions. In the "Fixed"condition, the slider was mechanically fixed, and hence the thumb sensor could not move. In the "Free"condition, the slider platform on which the thumb sensor was placed could freely move. In both conditions, the instruction was to grasp and hold the handle (and the platform) in static equilibrium. We recorded tangential and normal forces of all the fingers. Results. The distribution of fingertip forces and moments changed depending on whether the thumb platform was movable (or not). In the free condition, the drop in the tangential force of thumb was counteracted by an increase in the normal force of the ring and little finger. Critically, the normal forces of the ring and little finger were statistically equivalent. The safety margin of the index and middle finger did not show a significant drop in the free condition when compared to fixed condition. Conclusion. We conclude that our results does not support the mechanical advantage hypothesis at least for the specific mechanical task considered in our study. In the free condition, the normal force of little finger was comparable to the normal force of the ring finger. Also, the safety margin of the thumb and ring finger increased to prevent slipping of the thumb platform and to maintain the handle in static equilibrium during the free condition. However, the rise in the safety margin of the ring finger was not compensated by a drop in the safety margin of the index and middle finger. Copyright 2020 Rajakumar and SKM.

Department Of Chemistry

PeerJ

Comparable behaviour of ring and little fingers due to an artificial reduction in thumb contribution to hold objects

Resin Film Infusion (RFI) process is used for manufacturing large and thick unidirectional fiber reinforced polymer (UD FRP) composite structures for load bearing applications. Designing these load bearing structures requires the knowledge of effective elastic and strength characteristics of these composites. In this study, strength and stiffness properties of UD FRP manufactured through RFI process are predicted using a micromechanical modeling approach. A 3D representative volume element (3DRVE) with hexagonal array of fibers is used and all nine elastic constants of UD FRP composite are predicted. Failure models for fiber and resin are used to predict longitudinal tension/compression, transverse tension/compression and longitudinal shear strengths. Experiments were conducted on UD FRP composite manufactured through RFI process to obtain strength and stiffness properties. Results of experiment and simulations are compared and results validated.

Department of Engineering Design

Characterization of unidirectional fiber reinforced polymer composites manufactured through resin film infusion process using micromechanical modeling

Magnetorheological (MR) gels belong to a group of smart materials whose attributes can be altered when it is exposed to an external magnetic field. In this paper, the investigation on the creep behavior of MR gels under constant stress is performed. MR gels are prepared by dispersing carbonyl iron (CI) microparticles of different volume percentages (10%, 20%, 30%) in a polymer gel. Using a free decay test apparatus built in-house, the effect of the magnetic field on the creep behavior of MR gels with various volume percentages of CI particles is studied, and the results are compared. From the results, a clear increasing trend is noticed in the creep resistance of the magnetic gel with the increase in the volume percentage of the particles under the same magnitudes of the magnetic field. The obtained experimental creep data are fitted suitably using a three-parameter model. © 2020, © 2020 Taylor & Francis Group, LLC.

Mechanics of Advanced Materials and Structures

Creep behavior of magnetorheological gels

Different body postures that can be maintained for a certain duration with awareness are called yogaasanas. These asanas matter flexibility, coordination, and strength, while the breathing practices and meditation sharpens the mind for better awareness and reduce anxiety and thus adds quality into life. Other beneficial effects might involve a reduction of stress, blood pressure, and improvements in resilience, mood, and metabolic regulation. The asanas performed regularly for a short duration in hours is well studied in the literature. However, when performed for a long duration continuously for several hours (40-hour yogathon), without food and sleep has a significant effect in regulating homeostasis. The homeostasis is accessed through cardio-respiratory and galvanic skin response changes. The study shows the physiological changes after the yogathon and compares it with effects on physiology due to short term yoga. It also emphasizes on the reduction of dependency on food, because of energy compensation through yoga-asanas. © 2021 by IGI Global. All rights reserved.

Handbook of Research on Evidence-Based Perspectives on the Psychophysiology of Yoga and Its Applications

An exploration of influence of duration on physiological effects of asanas

The primary aim of the research reported in this paper was to understand the effect of change of gusty simple shear inflow’s gradient on the force and moment patterns of a flapping wing in the 3D reference frame. A wing undergoing one degree of freedom asymmetric flapping and rectangular planform shape was considered. The gradient of the gusty simple shear inflow profile, Vgrad, was varied from –10 to +10 in steps of 5 and corresponding vertical and horizontal forces and moment about the flapping axis were computed. Time series of these forces and moment were used to plot the global recurrence plots and were compared. Quantitative analysis of the findings was carried out by the windowed recurrence quantification analysis of the force and moment patterns. Eight recurrence parameters, viz. recurrence rate, determinism, laminarity, trapping time, ratio, entropy, maximum line and trend were calculated and compared. Numerical investigations revealed that negative gusty shear gradient induced a considerable increase in vertical force and moment and marginally decreased the horizontal forces. Positive gusty shear gradient induced a marginal increase in horizontal forces but caused a substantial decrement in vertical force and moment. © 2020, Springer Nature Singapore Pte Ltd.