Department of Mechanical Engineering

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A Nonlinear Energy Sink (NES) having essential nonlinear stiffness, it is nonlinearly attached to a primary system. In contrast to Tuned Mass Damper, the NES could be capable over a wider frequency range and only require a small additional mass. NES have good potential for vibration mitigation and energy harvesting. One of the most common energy sources in an environment is ambient vibration. Some micro electro-mechanical system with magnetostrictive or piezoelectric materials is used to convert ambient vibration into electrical energy. That can be stored and used to power other devices such as wireless sensors, health monitoring sensors or replacing small batteries that have a finite lifespan or would require difficult and expensive maintenance. This study focuses on materials for energy harvesting with NES. Piezoelectric materials have a good capability to convert the mechanical vibration energy into electrical energy and vice versa; therefore, they are more suitable for energy harvesting with NES. A state of the art review of the piezoelectric material frequently used in NES coupled energy harvester with their relative merit is presented. (C) 2019 Elsevier Ltd. All rights reserved.

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MATERIALS TODAY-PROCEEDINGS

Materials for energy harvesting with a nonlinear energy sink: A literature review

In this article physicochemical and thermo-physical properties of slags obtained from CaO–CaF2–SiO2–Al2O3 based shielded metal arc welding electrodes were investigated. The extreme vertices design methodology was used to prepare twenty-one coating compositions. Multi-pass beads were applied on the P22 low alloy steel plate. The welding slag for each weld bead was collected. Experimentation's on welding slags have been performed to estimate the weight loss, density, specific heat, enthalpy, thermal conductivity and diffusivity. X-Ray Diffraction (XRD) and Fourier transformation infrared spectrometry (FTIR) was performed to analyses the different phases present in slag. Thermogravimetric Analyzer (TGA) and hot disc apparatus have been used to characterize the slag's thermal properties. The regression analysis has been used to study the effect of coating constituents on the slag properties. The obtained output of properties has been further optimized using multi-response optimization. © 2019 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

Investigation on slags of CaO-CaF2-SiO2- Al2O3 based electrode coatings developed for power plant welds

In present study, the wettability behaviour of basic submerged arc welding fluxes for the CaO–CaF2–SiO2 &amp; CaO–SiO2–Al2O3 welding flux system was studied by measuring the contact angle between the solid/liquid interfaces. Twenty-one submerged arc welding fluxes were formulated using mixture design approach. Contact angle of twenty-one basic fluxes were measured at 1100 °C at constant heating rate. X-ray fluorescence technique was used to evaluate the purity level of individual flux components. Phase analysis and structural properties of different fluxes were determined using Fourier transform infrared spectroscopy &amp; X-ray diffraction technique. Using Young's &amp; Boni's equations different surface tension values for CaO–CaF2–SiO2 &amp; CaO–SiO2–Al2O3 flux systems were determined from measured contact angle value. Dupre's equation was used to find the adhesion energy of the fluxes. Optimum wetting behaviour was observed for lower compositional range (i.e. for CaO/SiO2 &amp; CaO/CaF2 ratio). Flux number 1, 2, 3, 4, 7, 12, 14, 17, 18, 19, 20 &amp; 21 gives higher wettability and spreading area (mm2) due to lower value of contact angle. With increase of CaO/SiO2 ratio there is significant increase in calculated surface tension. © 2019 Elsevier Ltd and Techna Group S.r.l.

Experimental investigation on surface behaviour of submerged arc welding fluxes using basic flux system

For TiO2–SiO2–MgO and SiO2–MgO–Al2O3flux system, the thermophysical and physicochemical behaviour of submerged arc slags studied. Slag plays an essential role in shielding the weld joint from atmospheric contamination. The mass percentage of each flux ingredient evaluated by the X-ray fluorescence technique. Twenty-one slags developed based on the mixture design approach. Thermogravimetric, DSC, and Hot-disc techniques used to analyze submerged arc slags. Thermogravimetric &amp; DSC analysis was performed from 25 ºC to 900 ºC to find the thermal properties. The density measurement of slag performed at ambient temperature. Bond-behaviour was studied by Fourier transform infrared spectroscopy (FTIR) technique. Regression models for different slag properties developed. The multi-objective technique utilized to optimize different slags. © 2020 CIRP

CIRP Journal of Manufacturing Science and Technology

Investigations of thermophysical properties of submerged arc welding slag using a rutile-acidic flux system

Linepipes above 16″ diameter are often submerged arc welded. Weld mechanical as well as metallurgical properties are widely affected by the flux composition. Flux composition and welding parameters play an important role in determining the good bead quality and mechanical properties of the welded joint. In present study submerged arc welding fluxes were formulated using constrained mixture design approach. Twenty one submerged arc welding flux compositions based on CaF2–CaO–SiO2 and Al2O3–CaO–SiO2 flux system were designed using extreme vertices design approach. Regression models were developed in terms of individual, binary and ternary mixture flux constituents for submerged arc series of bead on plate weld deposits (API 5 L X70 pipeline steel). By using F-test regression mathematical models have been checked for 95% significance level. Effect of formulated fluxes on silicon, copper, molybdenum, titanium and chromium content was studied using a multi-layer weld deposits. All binary mixtures C·Al, S·CF, S·Al and C·Al have significant increasing effect on silicon content in a bead on plate weld deposits while S·Al is the most effective synergistic binary mixture. Individual and binary flux mixtures tend to decrease the copper content in a bead on plate weld deposits. © 2020 Elsevier Ltd and Techna Group S.r.l.

Study of weld bead chemical, microhardness &amp; microstructural analysis using submerged arc welding fluxes for linepipe steel applications

We study the morphological evolution of secondary Widmanstätten ferrite plate by using a phase-field model for mixed-mode of growth in austenite. The model also considers anisotropy in the interfacial-energy. During the transformation, offspring-plates form at the both sides of a parent-plate by complex diffusive flow of solute carbon. The composition-dependent lengthening of parent-plate is slow as compared to the experimental observations and offspring-plate. We show that the tip of the offspring-plate shifts laterally away from the parent-plate during the transformation. The tip of the offspring-plate changes its growth-direction in order to move away from the region of accumulated solute. We also analyse the thickening behaviour of offspring and parent-plates. © 2020 Elsevier B.V.

Computational Materials Science

A phase-field study on the evolution of Widmanstätten-ferrite plates under mixed-mode of transformation

We study the transformation of austenite to ferrite under the influence of Grain-Boundary (GB) diffusion. In order to simulate identical level of penetration of solute through GB as predicted by theory, diffusivity gradient at the boundary of a bulk austenitic domain is calibrated by numerical simulations. Applying a phase-field model for mixed-mode of transformation, it has been found that GB allotriomorph has a constant lengthening rate and the sharp tip of the allotriomorph displaces carbon due to its curvature. The accumulated solute has a significant effect on the thickening behaviour in terms of growth coefficient and exponent. We also discuss the morphological evolution of ‘perturbed’ allotriomorphic ferrite. © 2019 Elsevier B.V.

A phase-field investigation of the effect of grain-boundary diffusion on austenite to ferrite transformation

The present work experimentally investigated the Critical Heat Flux (CHF) phenomena in helical coils. Literature on the CHF in helical coils is scarce. The centrifugal force and hence secondary flows of fluid is generated inside the coil due to its curvature. The Secondary flows of fluids may affect the heat transfer mechanism and hence, CHF inside helical coils. In present work, the experimental CHF data is compared with correlation available in literature. Fifteen empirical CHF correlations, that include correlation developed for straight horizontal tubes and helical coils, are compared with the experimental CHF databank. The CHF databank contains 413 CHF data of different helical coils. The data includes two fluids namely refrigerant R123 and water. Data covers the parameter range of tube diameter 5.5–10 mm, coil to tube diameter ratio 14–58, mass flux 92–2062 kg/m2s, heat flux 37–2984 kW/m2, density ratio 31–1352 and exit quality −0.1 to 1.2. The data mainly covers CHF in redeposition zone. The helical coil correlations are working reasonably well for long length helical coils but not working for short length helical coils. The straight tubes correlations are working reasonably well for all helical coils data. A generalised correlation is suggested for CHF in helical coils. The experimental data of CHF is published to contribute to the databank for helical coils. © 2020 Elsevier B.V.

Nuclear Engineering and Design

Experimental correlation for critical heat flux in helical coils

Dielectric elastomers (DEs) are a class of highly deformable electroactive polymers (EAPs) employed for electromechanical transduction technology. When electrostatically actuated dielectric elastomer actuators (DEAs) are subjected to an input signal comprising multiple Heaviside voltage steps, the emerging inherent residual vibrations may limit their motion accuracy in practical applications. In this paper, the systematic development of a command-shaping scheme is proposed for controlling residual vibrations in an electrically driven planar DEA. The proposed scheme relies on invoking the force balance at the point of maximum lateral stretch in an oscillation cycle to bring the actuator to a stagnation state followed by the application of an additional electric input signal of predetermined magnitude at a specific time. The underlying concept of the proposed control scheme is articulated for a single Heaviside step input-driven actuator and further extended to the actuator subjected to the multistep input signal. The equation governing the dynamic motion of the actuator is derived using the principle of virtual work. The devised dynamic model of the actuator incorporates the effects of strain stiffening of elastomer and viscous energy dissipation. The nonlinear dynamic governing equation is solved using matlab ode solver for extracting the dynamic response of the actuator. The applicability of the devised command-shaping control scheme is illustrated by taking a wide range of parameters including variations in the extent of equilibrium state sequences, damping, and polymer chain extensibility. The proposed scheme is found to be adaptable in controlling the vibrations of the actuator for any desired equilibrium state. The results presented in this paper can find its potential application in the design of an open-loop control system for DEAs. © 2020 American Society of Mechanical Engineers (ASME). All rights reserved.

Journal of Applied Mechanics, Transactions ASME

Design of a Command-Shaping Scheme for Mitigating Residual Vibrations in Dielectric Elastomer Actuators

Evaporation from a porous medium goes through three different stages; the physics of drying is completely different in each stage. In the first stage, liquid films maintain high hydraulic conductivity leading to high evaporation rates; it mainly depends on the atmospheric demand. Duration of stage 1 is given in terms of a suitable length scale, Lcap, which originates from the competition between the capillary, gravitational, and viscous forces. It is known that Lcap depends strongly on the particle size and distribution of the pore sizes in a porous medium. We report experiments of evaporation from an initially saturated homogeneous porous medium consisting of nearly mono-disperse (0.70–0.85 mm diameter) glass beads, while heating from above using IR radiation. We found significant changes in Lcap values depending on the incident heat load. We discuss these results based on changes in the fluid properties, such as surface tension and sub-surface temperature gradient. It is expected that such a study would be beneficial not only to the drying industries but also in the agricultural sector and cooling devices. © 2019, © 2019 Taylor & Francis Group, LLC.