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

Current study investigates tribo-phenomena at sliding interface of Al2124-17SiCp disc and WC-6Co pin and explores suitability of nano-oil aerosols as lubricants. They form chip-tool tribo-pair in machining. Ploughing, adhesion, abrasion were predominant under dry sliding. Adhesion and friction-coefficient (COF) were severer with higher normal load and lower sliding velocity. Aerosol of palm-oil arrested adhesion of aluminium on carbide pin and reduced COF by 80–82% through film-lubrication but at low load conditions. Diamond/graphite nanoparticles (1 wt%) suspension helped palm-oil sustain film-lubrication at sliding interface even in extreme conditions, reducing COF further and arresting adhesion phenomenon. Rolling of near-spherical nano-diamonds or basal-plane shearing within graphite nano-platelets caused additional reduction in friction. Graphite nano-aerosol was superior and similarly effective in high-speed milling as SQL-medium. © 2020 Elsevier Ltd

World University root node

Tribology International

Anti-frictional role of diamond and graphite suspended bio-oil based nano-aerosols at sliding interface of Al-SiCp and WC-6Co

In this work, ceramic reinforcement of soft Ag–Cu–Ti filler alloy has been attempted to produce a superior filler alloy to braze cBN to steel in high vacuum conditions without compromising wettability and joint strength. 2 and 5 wt% of micro-alumina (μAl2O3) particles of average particle size (APS) 10 μm were added to Ti-activated (2 wt%) eutectic (72Ag28Cu) filler alloy as reinforcements for brazing Cubic Boron Nitride (cBN) particles (APS: 427 μm) to steel substrate. The alloy-matrix wetted μAl2O3 particles appreciably. Cu3Ti3O phase formed (confirmed through TEM/SAED-pattern analyses) and grew surrounding the μAl2O3 particles with a very thin interlayer of γ-TiO. Nano-hardness of Cu3Ti3O was measured to be 17.6±2.42 GPa. Cu3Ti3O together with μAl2O3 particles resulted in substantially enhanced (63–76%) abrasion-resistance characteristics of the primary alloy. 5 wt% addition of μAl2O3 to Ag–Cu–2Ti alloy displayed superior performance to 2 wt% addition. However, with higher proportion (5 wt%), wettability of the reinforced filler on cBN part got slightly impaired. Few micro-voids also surfaced on cBN-encapsulating bonding layer. Considering joint strength and wettability, 2 wt% of μAl2O3 is recommended to produce brazed cBN tools for high-impact load applications. © 2020 Elsevier Ltd

Vacuum

High vacuum active brazing of cBN with improved composite filler: Microstructure, interfaces and performance evaluation

This two-part article examines the distribution of metallic layers through the thickness of fiber metal laminates (FMLs) on their response and damage when subjected to high-velocity projectile impact. Glass fiber/epoxy and Ti-6Al-4V titanium alloy sheets are used to obtain four different layups of FMLs fabricating by the hand layup process and exhibiting the same thickness of the total metal layer. Part I deals with experimental investigations of fully clamped square FMLs normally impacting at the center by hemispherical steel projectile using compressed air gun set up. Different parameters are considered to evaluate the FMLs’ performance, which includes damage degree, first cracking energy, crack length, deformation profile, and damage developed on the surface and inside the laminate. The results indicate that the highest permanent deformation and cracking are exhibited by FML 4/3-0.3, exhibiting separation of composite layers with different orientations by the metallic layer. The other FMLs exhibit lower and approximately similar permanent deformations. However, lower cracking and a relatively higher lateral delamination spread and opening of the interlayer are exhibited by FML 2/1-0.6 in which composite layers are arranged together than FML 4/3-0.3, signifying that the damage spreading laterally can be reduced by dispensing titanium layers. The ballistic resistance is found to be similar for FMLs. The levels of permanent deformation, cracking, and delamination with their opening and spreading are lesser for titanium-based FMLs than aluminium-based FMLs. The ballistic response of FMLs will be evaluated using analytical modeling in an accompanying study (Part II). © 2021 Elsevier Ltd

Department of Aerospace Engineering

International Journal of Impact Engineering

High-velocity impact response of titanium-based fiber metal laminates. Part I: experimental investigations

Halbach EMATs can efficiently generate shear horizontal (SH) guided wave modes. Using the Halbach magnet structure, the EMATs can enhance the magnetic flux density within a material forming ultrasonic waves with relatively large amplitude. The paper first presents a comparison analysis of double-row Halbach EMATs with double-row PPM EMATs using Finite Element based simulation models for SH0 ultrasonic wave generation. The study then analyses the wave interference effects created by the staggered double-row Halbach EMAT configurations. This is also performed using numerical Finite Element Models (FEM) and experimentally validated in an Aluminum plate specimen. It is observed that the steering of the ultrasonic guided waves can be associated and predicted for different double-row staggered PPM EMAT configurations. © 2021 Elsevier Ltd

Department of Metallurgical and Materials Engineering

NDT and E International

Characterising the beam formation of SH waves using double-row Staggered Halbach EMAT configurations

In this paper, Artificial Intelligence (AI) algorithms are employed for first, automating the process of creating a large synthetic Total Focusing Method (TFM) imaging dataset using a small set of Finite Element (FE) simulation datasets, and second for the automated defect-recognition (ADR) in butt-welds. In this paper, six types of imaging datasets are created with three approaches. In the first approach, weld TFM images are constructed using ultrasonic A-scan signals obtained from Full Matrix Capture (FMC) performed using FE analysis on models with weld defects (porosity and slag). The second approach generates near real-time weld TFM images by implementing fast deep convolution generative adversarial networks (DCGAN). This second technique permits simulations that are several orders faster when compared to the FE method. In the third approach, noise is extracted from FMC-TFM experimental measurements using the sliding kernel approach, and this noise is supplemented to individual simulated datasets for creating near to realistic scenarios. The first dataset is created using the first approach. The second dataset is created using the second approach, and the third hybrid dataset is a combination of FE and DCGAN weld TFM imaging. The fourth dataset is noise supplemented to FE based dataset. The fifth dataset is generated by adding noise to DCGAN images. The sixth hybrid dataset with noise is a combination of FE and DCGAN weld TFM noise images. AI plays a significant role in object detection and classification through robust feature extraction, reducing human intervention. In this work, for automated weld defect recognition, a convolutional neural network (CNN) is trained using six types of simulation-assisted weld TFM imaging datasets, which improves the reliability and efficiency of welds quality assurance. The mAP value is 85% for the ADR model trained using the hybrid weld TFM dataset with noise. The model prediction on classification on the hybrid dataset for porosity is 0.86 F1-score, and for slag is 0.80 F1-score. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.

Journal of Nondestructive Evaluation

Automated Defect Recognition for Welds Using Simulation Assisted TFM Imaging with Artificial Intelligence

Biofuels, including biodiesel have the potential to partially replace the conventional diesel fuels for low-temperature combustion engine applications to reduce the CO2 emission. Due to the long chain lengths and high molecular weights of the biodiesel components, it is quite challenging to study the biodiesel combustion experimentally and computationally. Methyl crotonate, a short unsaturated fatty acid methyl ester was chosen for the chemical kinetic study as a model biodiesel fuel. Auto-ignition experiments were carried out in a rapid compression machine at pressures of 20 and 40 bar under diluted conditions over a temperature range between 900 K and 1074 K, and at different equivalence ratios (φ = 0.25, 0.5 and 1.0). The updated mechanism showed satisfactory agreement with the ex- perimental data with significant improvements in low-temperature ignition behavior. The key reactions at various combustion conditions and the improved reactivity of the modified mechanism were analyzed by performing sensitivity and path flux analysis. The importance of low-temperature pathways in predicting the ignition behavior of methyl crotonate at intermediate and low temperatures was demonstrated.

Proceedings of the Combustion Institute

Experimental and kinetic modeling studies on the auto-ignition of methyl crotonate at high pressures and intermediate temperatures

This paper reports the simultaneous generation of multiple fundamental ultrasonic guided wave modes L(0,1), T(0,1), and F(1,1) on a thin wire-like waveguide (SS-308L) and its interactions with liquid loading in different attenuation dispersion regimes. An application towards liquid level measurements using these dispersion effects was also demonstrated. The finite element method (FEM) was used to understand the mode behavior and their dispersion effects at different operating frequencies and subsequently validated with experiments. In addition, the ideal configuration for the simultaneous generation of at least two modes (L(0,1), T(0,1), or F(1,1)) is reported. These modes were transmitted/received simultaneously on the waveguide by an ultrasonic shear wave transducer aligned at 0◦/45◦/90◦ to the waveguide axis. Level measurement experiments were performed in deionized water and the flexural mode F(1,1) was observed to have distinct dispersion effects at various frequency ranges (i.e., &gt;250 kHz, &gt;500 kHz, and &gt;1000 kHz). The shift in time of flight (TOF) and the central frequency of F(1,1) was continuously measured/monitored and their attenuation dispersion effects were correlated to the liquid level measurements at these three operating regimes. The behavior of ultrasonic guided wave mode F(1,1) when embedded with fluid at three distinct frequency ranges (i.e., &gt;250 kHz, &gt;500 kHz, and &gt;1000 kHz) were studied and the use of low frequency Regime-I (250 kHz) for high range of liquid level measurements and the Regime-II (500 kHz) for low range of liquid level measurements using the F(1,1) mode with high sensitivity is reported. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Department of Electrical Engineering

Fulltext

Sensors (Switzerland)

Experimental study on dispersion effects of f (1,1) wave mode on thin waveguide when embedded with fluid

An extensive analysis of radiative flux biases in the Climate Forecast System Model Version 2 (CFSv2) is done. Annual mean and seasonal variations of biases at the surface and top of the atmosphere (TOA) are reported in the global domain. Large regional biases in shortwave (SW) and longwave (LW) radiation are observed over convectively active zones in the tropics. The relative contribution of various processes responsible for the reported biases is quantified. The poor simulation of clouds and inadequate representation of surface properties seem to be major contributors. Over certain regions, errors due to different processes add up, whereas, over other regions, errors tend to nullify each other. Surface and atmospheric variables taken as input parameters in the radiative transfer modules are compared with satellite-based observations. The maximum biases in SW and LW radiation are observed over the regions of persistent low clouds. The magnitude of the SW and LW biases at the TOA is in phase with the biases in cloud fraction by and large. However, the error in the radiative fluxes due to errors in surface radiative properties is of equal importance. The cold bias in near-surface air temperature reported in other studies may partly be attributed to an underestimation in the net SW radiation at the surface. In the present study, a plausible prescription is also provided to correct the source of the biases. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

Climate Dynamics

An assessment of radiative flux biases in the climate forecast system model CFSv2

The poor machining characteristics of super duplex stainless steels (SDSS) affect the surface integrity as it induces tensile residual stress in the parts. When this machined part is exposed to hostile chloride conditions, it results in the stress corrosion crack (SCC) formation, thereby impacting their service life. To understand the cracking phenomenon involved, it is important to study the distinct characteristics of cracks formed in compliance with the machining (turning) process. This study focusses on studying the effects of machined surface integrity on the stress corrosion cracking of SDSS. Following machining, the specimens were subjected to SCC examination in the chloride condition at different immersion time of 1 h, 2 h, and 5 h. The testing was done in pursuant with ASTM G36 standard. The result indicated that major cracks generated along both parallel as well as the perpendicular direction of machining marks due to the high magnitude of biaxial tensile residual stress. With the increase in immersion time (5 h), new forms of crack and localized corrosion were noticed on the surface. At 1 h and 2 h, only the major cracks were evident, along with minor pit formation on the surface. But at 5 h, selective attack/selective leaching occurred on the turned surface along with the formation of network of cracks. Analysis of the transition pit/crack behaviour of revealed that different pits merge to form a detrimental crack with more intensity than the major cracks. The crack density continue to grow with immersion time of 5 h and also there is no evidence was observed on reduction of crack density. However, the quantification of crack density was not possible at 5 h due to the complex network of high density crack formation. The microstructure analysis revealed that the ferrite phase was more vulnerable to SCC than the austenite phase in chloride environment. © 2021 Elsevier Ltd

Engineering Failure Analysis

Effect of machined surface integrity on the stress corrosion cracking behaviour of super duplex stainless steel

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