Department of Mechanical Engineering

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In the present work, an alumina–titania (13 %) coating has been deposited by the air plasma spray process on a mild steel substrate by preheating the substrate to different temperatures. Coating thickness was measured by a scanning electron microscope, the hardness of coatings was measured, and morphology was also checked. The crack compliance technique has been used to determine the residual stress, as it is a very simple method, and also, it is compatible with conventional machining equipment and wire electric discharge machining equipment. Specimens were cut by the diamond cutter up to certain depth in microns, and the strain relieved was recorded. For finding out the residual stress, these recorded values of strain have been used by doing a finite element analysis (FEA) using the ANSYS 15.0 (Ansys, Inc., Canonsburg, PA) software. For validation of the model, uniaxial tension was applied on a sample by using the INSTRON universal testing machine (Instron Inc., Norwood, MA), and strain values at both the coating side and the substrate side were recorded and matched with the model under the same value of the load. After verifying the model, an equation has been developed using the Minitab software (Minitab Inc, Bengaluru, India), and the strains previously recorded were used as an input to the equation obtained, and the value of residual stress was calculated. The maximum value of residual stress was found at the coating–substrate interface, and the values of residual stress for sample preheated at 250°C, 200°C, and 150°C were found to be compressive, with the magnitude of −176.28 MPa, −243.54 MPa, and −255.42 MPa, respectively. Copyright © 2019 by ASTM International,

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Journal of Testing and Evaluation

Experimental and numerical investigation of residual stress in coatings on steel

The current work has been performed to characterize the heterogeneous P91 welded joint. The gas tungsten arc welded (GTAW) P91 welds joint has been prepared using the dissimilar Inconel 617 filler. The P91 welded plates have been subjected to post-weld normalizing and tempering (PWNT) heat treatments for varying normalizing temperature in the range of 950–1150 °C. To homogenize the microstructure across the welded joint, tempering has been performed at 760 °C for 2 h for each normalized conditions. The tensile and microhardness tests have been conducted to determine the mechanical properties of the welded joint in as-welded and heat-treated conditions. The microstructure characterization has been performed for the weld fusion zone (WFZ) and efforts have been made to develop a relation between microstructure evolutions and mechanical behavior of the welded joint. Microstructure analysis was carried out with optical and field scanning electron microscope (FESEM). The optimum combination of strength and ductility was obtained for the sample heat-treated at 1050 °C for 40 min (normalized)+760 °C/2 h (tempering). The lower strength was obtained for the Inconel 617 filler as compared to P91 filler, while ductility obtained for Inconel 617 filler was higher than that of P91 filler. © 2020 Elsevier Ltd

International Journal of Pressure Vessels and Piping

A microstructural and mechanical behavior study of heterogeneous P91 welded joint

This article uniquely characterizes the secondary droplets formed during the impingement of a train of ethanol drops, using three-dimensional direct numerical simulations performed under conditions studied experimentally by Yarin and Weiss. Our numerical results have been previously validated against experimental data demonstrating the ability to accurately capture the splashing dynamics. In this work, the predictive ability of the model is leveraged to gain further insight into secondary droplet formation. We present a robust post-processing algorithm, which scrutinizes the liquid volume fraction field in the volume-of-fluid method and quantifies the number, volume and velocity of secondary droplets. The high-resolution computational simulations enable secondary droplet characterization within close proximity of the impingement point at small length and time scales, which is extremely challenging to achieve experimentally. By studying the temporal evolution of secondary droplet formation, direct connections are made between liquid structures seen in the simulation and the instantaneous distribution of secondary droplets, leading to detailed insight into the instability-driven breakup process of lamellae. Time-averaged secondary droplet characteristics are also studied to describe the global distribution of secondary droplets. Such analysis is vital to understanding fuel drop impingement in direct injection engines, facilitating the development of highly accurate spray–wall interaction models for use in Lagrangian solvers. © IMechE 2019.

Fulltext

International Journal of Engine Research

Computational characterization of the secondary droplets formed during the impingement of a train of ethanol drops

This work presents experiments and computational simulations of a single diesel droplet impinging on a dry surface to provide a better understanding of the dynamics of the impingement process. The experimental work was carried out at several substrate surface temperatures where a single diesel droplet was dropped from a precision syringe pump to provide a specific droplet diameter and impact velocity. The effect of the surface temperature on the temporal evolution of the droplet spreading factor, dynamic contact angle, and contact line velocity was studied. The experimental study on the temporal evolution of the droplet-wall interaction was used to develop a dynamic contact angle model for computational simulations. Using an in-house multiphase flow solver, simulations of the single diesel droplet impingement were performed. The simulation results of the spreading factor were compared to the experimental results and the effects of liquid temperature and contact angle model parameters were investigated. The development of a dynamic contact angle model for diesel droplets enhances the ability to study diesel droplet impingement, an important factor in diesel fuel injection. With an accurate dynamic contact angle model, future studies can be performed at scales and velocities representative of the conditions present in internal combustion engines. © 2018 Solar Turbines Incorporated.

ICLASS 2018 - 14th International Conference on Liquid Atomization and Spray Systems

An experimental and computational study of a single diesel droplet impinging on a dry surface

We present a novel methodology for accurate treatment of viscous terms in evaporation problems. The proposed scheme is an extension of the sharp viscous treatment of Kang et al. (2000) [7] to 3D phase change problems. To ensure accuracy and grid converging solutions, a new implicit approach to computing viscous fluxes across the phase interfaces is proposed, which was previously unavailable in fixed grid numerical schemes. Analytical relations were derived for the jump in velocity gradients across the 2D and 3D phase interfaces, an important constituent of the proposed scheme. The relations show a non-vanishing jump in the tangential gradients across the phase interface that are associated with evaporative flux and interfacial curvature. The proposed methodology demonstrated first order accuracy in canonical test cases. It is general and applicable to arbitrarily oriented interfaces, and can be readily implemented in existing evaporation flow solvers. © 2020 Elsevier Inc.

Journal of Computational Physics

An implicit, sharp numerical treatment of viscous terms at arbitrarily shaped liquid-gas interfaces in evaporative flows

Australasian Fluid Mechanics Conference

CFD-Based Boundary Layer Prediction of Axisymmetric Bodies of Revolution

Hand-eye calibration using a single image and robotic picking up using images lacking in contrast

Reactive metal/metal-oxide based nanoenergetic materials find tremendous applications in propellants, explosives, and pyrotechnics. This paper reports on the synthesis of CuO nanobricks (CuOnb) using simple and rapid solid-state methods and investigation of the combustion reactivity (combustion propagation speed, peak pressure and pressurization rate) of as-synthesized copper oxide nanobricks with nano-aluminum and catalytic activity of copper oxide nanobricks in thermal decomposition of lithium perchlorate (LiClO4). The X-ray diffractometry (XRD) and transmission electron microscopy revealed the fabrication of CuO nanobricks (length of sub-150 nm with square cross-section of size of sub-25 nm). The CuOnb based nano-aluminum energetic composites (Al/CuOnb) exhibited excellent combustion characteristics with combustion propagation speed of 1,760 ± 25 m/s, peak pressure of 61.2 MPa, pressurization rate of 1.02 MPa/µs and heat of reaction of 750 J/g respectively. The copper oxide nanobricks expressed high catalytic activity in thermal decomposition of LiClO4 by accelerating the thermal decomposition to start and accomplish at lower temperature than the pure lithium perchlorate. © 2020 Taylor & Francis Group, LLC.

Particulate Science and Technology

Facile synthesis of CuO nanobricks for high combustion characteristics with nanoaluminum and catalytic thermal decomposition of lithium perchlorate

Wall shear stress (WSS) is an important parameter in arterial mechanobiology. Various flow metrics, such as time averaged WSS (TAWSS), oscillatory shear index (OSI), and transWSS, have been used to characterize and relate possible WSS variations in arterial diseases like aneurysms and atherosclerosis. We use a graphical representation of WSS using shear rosettes to map temporal changes in the flow dynamics during a cardiac cycle at any spatial location on the vessel surface. The presence of secondary flows and flow reversals can be interpreted directly from the shape of the shear rosette. The mean WSS is given by the rosette centroid, the OSI by the splay around the rosette origin, and the transWSS by its width. We define a new metric, anisotropy ratio (AR), based on the ratio of the length to width of the shear rosette, to capture flow bi-directionality. We characterized the flow physics in controls and patient specific geometries of the ascending aorta (AA) and internal carotid artery (ICA) that have fundamentally different flow dynamics due to differences in the Reynolds and Womersley numbers. The differences in the flow dynamics are well reflected in the shapes of the WSS rosettes and the corresponding flow metrics. © 2020 Elsevier Ltd

Journal of Biomechanics

Shear stress rosettes capture the complex flow physics in diseased arteries

Stress-Strain relations are graphical measures to determine the mechanical properties and morphology of engineering materials. In engineering universities, stress-strain curves are introduced in the introductory course of materials science for the mechanical, metallurgical and civil engineers. Stress-strain diagrams can be easily plotted from experimental data obtained from the uniaxial tensile testing of specimens made as per standards of engineering material. However, understanding of the metal’s deformation, dislocation behaviour, as well as the microstructure, is considered challenging. Common teaching aids present stress-strain diagrams as a working tool but does not explain how to relate various attributes like microstructural characteristics and mechanical behaviour with its engineering properties. This accumulated difficulty leads to a decreased level of motivation among first-year engineering students. The article presents CC maps an instructional strategy to gain sustainable knowledge on how to read stress-strain characteristics, interpret engineering properties and promote cognitive transfer in learning. The results obtained indicated that intervention of CC maps has improved conceptual understanding, learning interest and performance of students in the class. © The Author(s) 2020.