Mechanical Engineering

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Shiv Nadar University

(SoE) School of Engineering

AIP Conference Proceedings

Preface of the "symposium on analysis and design of multi-functional composite structures"

We investigate the role of viscous forces on the wetting of hydrophobic, semi-hydrophobic, and hydrophilic textured surfaces as second-order effects. We show that during the initial contact, the transition from inertia-to viscous-dominant regime occurs regardless of their surface topography and chemistry. Furthermore, we demonstrate the effect of viscosity on the apparent contact angle under quasi-static conditions by modulating the ratio of a water/glycerol mixture and show the effect of viscosity, especially on the semi-hydrophobic and hydrophobic textured substrates. The reason why the viscous force does not affect the apparent contact angle of the hydrophilic surface is explained based on the relationship between the disjoining pressure and surface chemistry. We further propose a wetting model that can predict the apparent contact angle of a liquid drop on a textured substrate by incorporating a viscous force component in the force balance equation. This model can predict apparent contact angles on semi-hydrophobic and hydrophobic textured surfaces exhibiting Wenzel state more accurately than the Wenzel model, indicating the importance of viscous forces in determining the apparent contact angle. The modified model can be applied for estimating the wetting properties of arbitrary engineered surfaces.

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Scientific Reports

Role of Viscous Dissipative Processes on the Wetting of Textured Surfaces

Erosion is a serious concern for machinery dealing with particle-laden fluids. For protection against erosion, coatings are usually recommended. Laboratory experiments are conducted to evaluate the erosion rates of these coatings. Alternatively, one could consider the use of modeling and simulation to predict the erosion rates. Although several models are available in literature for bulk materials, there is limited work reported in this direction for coatings. In present work, several models from literature were evaluated for their ability to predict the slurry erosion of coatings. A model based upon contact-fracture theory (CFT), proposed in present work, was also evaluated. Another variant of this model considered the effect of splat size. It was observed that none of the existing models evaluated in the present work could predict the erosion rates of the coatings. The proposed CFT model was able to predict the erosion rates with reasonable accuracy, whereas another variant of this model based upon splat size was observed to be inappropriate for predicting erosion rates of coatings. Possible reasons for the observed disparity are discussed. © 2014 Springer Science+Business Media.

Tribology Letters

A phenomenological model for slurry erosion prediction of thermal spray coatings

Structural changes in a bulk metallic glass subjected to high-strain plastic deformation was investigated. A zirconium-based bulk metallic glass was friction stir processed at different tool rotational speeds. The alloy retained its fully amorphous structure at lower speed. At higher tool rotational speed there was partial nano-crystallization with nearly three times increase in surface hardness. Changes in the glass transition temperature, relaxation and crystallization enthalpies were analyzed to explain the physics of high-strain deformation in amorphous metals. © 2014 Elsevier B.V.

Materials Science and Engineering A

Structural changes in amorphous metals from high-strain plastic deformation

Friction stir processing (FSP) of Mg based AE42 alloy was performed under single pass as well as double pass conditions. The evolution of microstructure was investigated using electron back scatter diffraction (EBSD) analysis. EBSD revealed that the grain size and texture varies within the nugget zone of friction stir processed region. The variation of mechanical properties across the nugget region was evaluated using nanoindentation. Hardness and Young's modulus was found to increase along the depth of the friction stir processed specimen. This was attributed to a finer grain structure with increasing depth. The friction stir processed specimen showed higher tendency toward strain hardening compared to as-cast alloy. Understanding microstructure-property relationship paves the way for optimization of FSP conditions and development of advanced functional Mg alloys. Friction stir processing (FSP) of Mg based AE42 alloy is investigated. EBSD analysis revealed that the grain size got more refined with increasing depth across the specimen cross-section. Hardness and Young's modulus is also found to increase along the depth of the friction stir processed specimen. The friction stir processed specimen show higher tendency towards strain hardening compared to as-cast alloy which is attributed to the fine in situ precipitates. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Advanced Engineering Materials

Microstructure-property relationship for friction stir processed magnesium alloy

In the present work, the slurry erosion behavior of friction stir processed (FSPed) hydroturbine steel (CA6NM) was investigated. For comparison, the erosion performance of unprocessed CA6NM steel was evaluated under similar conditions. Friction stir processing (FSP) is a microstructural refinement tool which is useful in enhancing the bulk and surface properties of materials. An in-depth characterization of both steels was done using an optical microscope (OM), a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS), the electron backscatter diffraction (EBSD) technique, and micro- and nano-indentation techniques. The FSP of the steel helped in reducing the erosion rates by 50% to 60%, depending upon the impingement angle. The improved performance of the FSPed steel in comparison to unprocessed steel was attributed to microstructural refinement, which increased the hardness and yield strength. At an oblique impingement angle, plowing, along with microcutting, was observed to be the dominant erosion mechanism. At a normal impingement angle, the material removal process was controlled by the platelet mechanism of erosion. A modified form of the mathematical model for predicting the erosion rates of the ductile materials, proposed by authors earlier, was also presented. This modified model based upon the theory of plasticity was able to predict the erosion rates with an accuracy of ±20%. Copyright © 2014 by ASME.

Journal of Tribology

Improving erosion resistance of hydroturbine steel using friction stir processing

Control of web tension is crucial for maintaining quality of products processed on roll-to-roll (R2R) system. An R2R system can be divided into different tension spans which interact with each other. But converting industries tend to neglect these interactions and use decentralized single-input-single-output (SISO) control approaches to deal with tension control. Multi-input-multi-output approaches have been reported in literatures but are practically not in use. Interaction between the various tension spans is unavoidable as they are all connected by a single web. Disturbances produced in a span tend to travel further downstream along the direction of web travel. When the number of spans is less or the disturbance amplitudes are small, this does not present a big challenge and simple SISO control is sufficient. But when the amplitudes of disturbances produced in processing is large - as is the case with printed electronics - or the number of spans is large or both, then the interactions cannot be neglected. R2R-based offset printers have the potential for mass production of precision-printed electronics. In this paper, a fuzzy logic-based hybrid approach has been followed that specifically targets the printed electronics industry and this method considerably reduces the interactions. The algorithm has been designed such that it takes information from previous span to reduce the propagation of tension disturbances to the given span. This has been achieved through online computation of correlation coefficient and reducing the interaction through fuzzy feedback control. © 2013 Springer-Verlag London.

International Journal of Advanced Manufacturing Technology

Fuzzy decoupling to reduce propagation of tension disturbances in roll-to-roll system

We investigated the influence of nanoscale pattern shapes, contours, and surface chemistry on wetting behavior using a combination of experimental and modeling approaches. Among the investigated topographical shapes, re-entrant geometries showed superior performance owing to their ability to restrain the liquid-air interface in accordance with Gibbs criteria. The wetting state is also controlled by the surface texture in addition to the surface chemistry. Topographies with smaller intrinsic angles are better able to support the liquid droplet. Based on these observations, two geometrical relationships for designing superhydrophobic patterns exhibiting the Cassie-Baxter state are proposed. A detailed analysis of the simulation results showed the presence of viscous forces during the initial transient phase of the droplet interaction with the solid surface even at negligible normal velocity, which was verified experimentally using a high-speed imaging technique. During this transient phase, for a polystyrene surface, the liquid front was observed to be moving with a radial velocity of 0.4 m s-1, which gradually decreased to almost zero after 35 ms. We observed that the viscous energy dissipation density is influenced by the surface material and topography and the wetting state. The viscous energy dissipation density is minimal in the case of the Cassie-Baxter state, while it becomes quite significant for the Wenzel state. The viscous effects are reduced for topographies with smooth geometries and surfaces with high slip length. This journal is © The Royal Society of Chemistry.

Nanoscale

Effect of topography on the wetting of nanoscale patterns: Experimental and modeling studies

An in situ composite coating on pure aluminium substrate was prepared by novel microwave processing of iron based metallic glass powder precursor. The microstructure obtained after processing comprised of a molybdenum rich harder phase uniformly distributed in iron rich softer phase. The hardness and modulus of each phase were obtained by nanoindentation. Scratch test across the substrate coating indicated good interface strength and strong adhesion of the coating with the substrate. © 2014 Institute of Materials, Minerals and Mining.

Surface Engineering

Microwave assisted in situ composite coating using metallic glass precursor

This chapter presents a comprehensive study on the influence of friction stir processing/welding (FSW/FSP) on corrosion behaviour. It briefly discusses the different aspects of corrosion including corrosion types, measurement techniques and data analysis. The corrosion behaviour of a wide range of friction stir processed materials, including light weight metals such as magnesium and aluminum alloys, as well as high strength metals such as steel, has been discussed in detail. The influence of FSP parameters on the microstructural evolution, comprising grain-size and precipitate refinement along with its correlation with the corrosion properties, has been described for different materials. © 2014 The authors and contributors. All rights reserved.