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

In this study, we computationally corroborate the flow of rock glaciers against borehole measurements, within the context of a model previously developed (2020). The model is, here, tested against the simulation of the sliding motion of the Murtel-Corvatsch alpine glacier, which is characterized in detail in the literature with internal structure description and borehole deformations measurement. The capability of the model to take into account the composition of the rock glacier, as a mixture of ice and rock and sand grains with the local impact of pressure and heat transfer, results in the accurate detection of the internal sliding. With careful calibration of the model parameters, the computed numerical solution of the model reports a relative error of 1.8% and of 0.3% in the reproduction of the measured shear zone velocity and of the ratio of measured shear zone deformation over top surface deformation, respectively. Furthermore a deeper understanding of the role of the model parameters involved in the simulation of such a process is also gained and we discuss the same in detail. © 2021 The Author(s)

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International Journal of Non-Linear Mechanics

Computational corroboration of the flow of rock glaciers against borehole measurements

The most critical component in an aerospace tank pressurisation system is a pneumatic pressure regulator with helium gas as the medium. The current paper focused on dynamic analysis of high pressure, spring-loaded, cryogenic medium pressure regulator. In order to evaluate its dynamic behaviour, a nonlinear model has been developed based on the fundamental equations by considering various forces–pressure forces, spring forces, bellow forces and Coulomb friction forces. The simulation is carried out for nominal operating conditions of the pressure regulator using commercial available AMESIM simulation tool. The effect of damping orifice size and downstream ullage volume are studied and obtained results are presented in the paper. Also experimental tests have been carried out for the same parameters to validate the simulation model using a proto model developed in-house with emphasis on machining of various precise parts of the high pressure regulator. These parts are manufactured in-house using high precision surface grinding, jig boring, electro discharge machining process, etc. The machined parts are realised to achieve precise sliding diametrical clearances between 32 microns and 50 microns, eccentricity within 20 microns and average surface roughness of 0.4 microns. The dimensional parameters of the machined parts are evaluated using the co-ordinate measuring machine (CMM), Talyrond and Talysurf equipments. The simulation results and experimental test results are found to be in good agreement. The developed model serves as a tool for optimisation of the regulator performance parameters. © 2020 Informa UK Limited, trading as Taylor & Francis Group.

Advances in Materials and Processing Technologies

Simulation of cryogenic high pressure regulator dynamics

Microstructural evolution during the strain-induced phase transformation of austenite in an Austempered ductile iron (ADI) under various thermomechanical processing conditions is studied in the present study. An alloyed ductile iron is taken as the base material, and thermomechanical treatment is carried out on a Gleeble 3800 thermomechanical simulator coupled with dilatometry. The effect of deformation on the austempering process has been studied by microstructure characterization using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. The variations in retained austenite volume fraction and its carbon content with respect to different austempering times are analyzed to study the effect of strain-induced transformation of austenite. It has been observed that the thermomechanical treatment significantly influences the phase transformation kinetics during the austempering process. The thermomechanical treatment produced a martensite free ausferritic microstructure for all austempering times with a high volume fraction of carbon enriched retained austenite as compared to the conventional heat treatment. © 2021 Trans Tech Publications Ltd, Switzerland.

Department of Metallurgical and Materials Engineering

Materials Science Forum

Microstructure evolution during strain-induced transformation of austenite in an austempered ductile iron (ADI)

The primary objective of this project is to increase the fatigue life of aluminium wheels and to prevent the fatigue failure of the wheel above the bolt hole region. In the testing and validation of wheels, the cornering fatigue test (CFT) plays an important role in deciding the stiffness of the wheel. In CFT testing, the wheel will be fixed in the bottom flange, and the bending moment will be applied, according to the load rating of the wheel multiplied by its corresponding test factor. CFT testing results of aluminium wheels showed crack above the bolt hole region in most of the cases. To prevent this mode of failure, and also to improve the fatigue life of the wheel further, it has been found that increasing the localized hardness above the bolt hole region will improve the fatigue life in CFT. Laser peening is a surface hardening technique by which the surface hardness of the material will be enhanced, along with which hardness and compressive residual stresses will be imparted on the surface in which the treatment is done. The depth of the high magnitude compressive stresses will greatly improve the material’s resistance to fatigue failure. In aluminium wheels, laser peening was done circumferentially around the bolt hole region to induce localized compressive stress and increase the hardness in that area. The wheel in which laser peening was done was tested on CFT and showed a significant improvement in life. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd 2021.

Department Of Chemical Engineering

Lecture Notes in Mechanical Engineering

An innovative method of preventing bolt hole crack in aluminium wheels by using laser peening technique

In the present investigation, water based multi-walled carbon nanotube (MWCNT) dispersed nanofluid was produced and used as a cutting fluid in small quantity cooling lubrication (SQCL) assisted grinding of hardened AISI52100 steel. The work material was ground by an alumina wheel. The SQCL technology utilizes atomized aerosol of liquid grinding fluid. Use of MWCNT nanofluid aerosol in place of soluble oil was found to be substantially beneficial in reduction of specific energy and development of compressive residual stress on ground surface. The steady and lower value of the force ratio (tangential to normal grinding force, Ft/Fn) was suggestive of the superior lubrication and grit sharpness retention ability of the aerosol of MWCNT nanofluid. Higher compressive residual stress on the ground surface under MWCNT nanofluid environment suggests lesser grinding zone temperature, which can be attributed to its superior wettability, lubricity and heat dissipation ability of the MWCNT nanofluid. The consumption rate of grinding fluid in SQCL was varied. It could be reduced to 200 ml/h for MWCNT nanofluid to obtain an almost similar or better effect to that of 500 ml/h for soluble oil. Lesser surface tension of MWCNT nanofluid, compared to its counterpart, seemed to facilitate wetting, thus improving lubrication and heat transfer capability further. © 2021 Taylor & Francis Group, LLC.

Machining Science and Technology

On grinding force ratio, specific energy, G-ratio and residual stress in SQCL assisted grinding using aerosol of MWCNT nanofluid

In the aero engine rotor-bearing systems, a design modification to move the critical speed away from resonance zone and to improve the unbalance response is a practical problem for designers. The objective functions are selected as amplitude of vibration due to unbalance and second critical speed. The two selected objectives are found to be conflicting, and hence, multi-objective optimisation is used to solve this problem through numerical formulation. Diameters of the stepped shaft and stiffness of the two bearings are selected as design variables. Weight is set as a constraint, and additional constraints based on the initial design are introduced. Objectives resulting from multi-objective optimisation and corresponding design variables are clustered separately using k-means clustering algorithm. The novelty of the work is in empowering the designer to recognise the hugely diverse designs resulting in identical solutions and achieving manufacturing sovereignty in choice of design through clustering in objective and design space and their mapping. © 2021, Springer Nature Singapore Pte Ltd.

Clustering in Pareto Front: Application on an Aero Engine Rotor-Bearing System for Improved Design

A recovery-based error indicator developed to evaluate the quality of polygonal finite element approximations is presented in this paper. Generalisations of the finite element method to arbitrary polygonal meshes have been increasingly investigated in the last years, as they provide flexibility in meshing and improve solution accuracy. As any numerical approximation, they have an induced error which has to be accounted for in order to validate the approximate solution. Here, we propose a recovery type error measure based on a moving least squares fitting of the finite element stress field. The quality of the recovered field is improved by imposing equilibrium conditions and, for singular problems, splitting the stress field into smooth and singular parts. We assess the performance of the error indicator using three problems with exact solution, and we also compared the results with those obtained with standard finite element meshes based on simplexes. The results indicate good values for the local and global effectivities, similar to the values obtained for standard approximations, and are always within the recommended range. © 2021 Elsevier Ltd

Computers and Mathematics with Applications

Error estimation for the polygonal finite element method for smooth and singular linear elasticity

In this paper, we propose a robust framework based on the scaled boundary finite element method to model implicit interfaces in two-dimensional differential equations in nonhomegeneous media. The salient features of the proposed work are: (a) interfaces can be implicitly defined and need not conform to the background mesh; (b) Dirichlet boundary conditions can be imposed directly along the interface; (c) does not require special numerical integration technique to compute the bilinear and the linear forms and (d) can work with an efficient local mesh refinement using hierarchical background meshes. Numerical examples involving straight interface, circular interface and moving interface problems are solved to validate the proposed technique. Further, the presented technique is compared with conforming finite element method in terms of accuracy and convergence. From the numerical studies, it is seen that the proposed framework yields solutions whose error is O(h2) in L2 norm and O(h) in the H1 semi-norm. Further the condition number increases with the mesh size similar to the FEM. © 2021 Elsevier Ltd

Engineering Analysis with Boundary Elements

Robust modelling of implicit interfaces by the scaled boundary finite element method

This work presents a framework to study the quasi-static brittle fracture in functionally graded materials with random material properties using a non-intrusive phase field method. The model accounts for variation in the material and fracture properties. Further, the effective Young’s modulus, the gradient index and the fracture properties of the constituent materials are considered as random input variables. The output randomness is represented by polynomial chaos expansion. Two-dimensional benchmark numerical examples are presented to demonstrate the benefits of the non-intrusive approach to study fracture characteristics. The influence of the randomness in the material properties on the peak load carrying capacity is considered as a primary quantity of interest in this study. A systematic parametric study is carried out to bring out the sensitivity of the input randomness on the stochastic output response using Sobol indices. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.

Acta Mechanica

A non-intrusive stochastic phase field method for crack propagation in functionally graded materials

Performance evaluation of prosthetic feet during their design is typically performed experimentally, which may be time and cost intensive. This work presents a first-of-its-kind application of a numerical procedure for the a priori determination of various stance phase biomechanical parameters of a prosthetic foot, such as its roll-over characteristics, centre of pressure trajectory, ankle flexion moment arm and ankle range of motion, to aid in its design. The numerical procedure is based on finite element analysis, which includes geometric, material and contact non-linearity. Boundary conditions emulating the rocker-based inverted pendulum model were employed to evaluate the biomechanical parameters. The finite element model was validated by employing an inverted pendulum-based apparatus using the structurally complex Ottobock Solid Ankle Cushioned Heel (SACH) prosthetic foot as the test device. A comparison of the numerical and experimental results showed low magnitude of errors. For example, the percentage error of the radius of curvature of the roll-over shape was  0.1%. The differences found appear to be clinically insignificant, which substantiates the reliability of the model. The proposed numerical model can be employed to obtain detailed a priori insights into the biomechanical parameters influencing a prosthetic foot's characteristics during gait, which can better inform the design, analysis and prescription of prosthetic feet. © 2021