(SoE) School of Engineering

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Shiv Nadar University

The combination of high strength and good ductility are very desirable for advanced structural and functional applications. However, measures to enhance strength typically lead to ductility reduction due to their inverse correlation, nano-grained structures for an instance. Bi-modal grain structure is promising in this regard, but its realization is limited by multiple complex processing steps. Here, we demonstrate a facile single-step processing route for the development of bimodal grain structure in austenitic stainless steel, SS316L. The bimodal structure comprised of fine martensite grains (<500 nm) sandwiched between coarse austenite grains (~10 µm). The dual-phase bimodal structure demonstrated higher yield strength (~620 MPa) compared to ultra-fine grain structure (~450 MPa) concurrent with high uniform tensile ductility (~35\%). These exceptional properties are attributed to unique dual-phase, bimodal grain structure which delayed the onset of plastic instability resulting in higher strength as well as larger uniform elongation and work-hardening rate. Our approach may be easily extended to a wide range of material systems to engineer superior performance. © 2019, The Author(s).

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Mechanical Engineering

Fulltext

Scientific Reports

High Tensile Ductility and Strength in Dual-phase Bimodal Steel through Stationary Friction Stir Processing

Hydration of concrete is a very complicated and multiphase process, where the cement gel transforms into a hardened state from plastic/semiplastic phase. Proper progression of the hydration process ensures the development of targeted mechanical properties such as the elastic modulus, the coefficient of thermal expansion, the Poisson’s ratio, and finally, the characteristic strength of concrete. Concrete experiences large thermal variations during the early phase of hydration due to the heat generated during the formation of cement hydration compounds, which contributes to shrinkage and cracking, somewhat making ground for the ultimate failure in the long run. Therefore, it is utmost important to monitor the progression of hydration for enhancing performance during the curing and the early service life. This article presents a new reusable external configuration of piezo-impedance transducers to monitor the hydration process in concrete structures using the electro-mechanical impedance technique. The proposed configuration consists of a thin metal foil instrumented with piezoelectric ceramic patch at the free end with the other end of the foil embedded inside the concrete. This configuration is compared against a piezoelectric ceramic patch directly bonded on the rebar used for reinforcement and another one embedded in the concrete surrounding the rebar. The sensing capability of the proposed metal foil configuration is clearly evident from the coupled admittance signature quantitatively vis-à-vis the other configurations. As a preliminary analysis, root mean square deviation values are employed to monitor the hydration process quantitatively. A piezo-equivalent mechanical model is also developed wherein the piezo-identified mass, stiffness and damping parameters are investigated for the cement hydration process so as to chalk out rigorous quantifiers of hydration progression. The employability of the proposed configuration is further proven by explanation of the physio-chemical products developed during various stage of hydration with step-by-step explanation along with corelation of the piezo-identified mass, stiffness and damping parameters. Overall, the proposed reusable configuration carries a high potential for field deployment in concrete industry for early detection of physio-chemical changes. © The Author(s) 2019.

Civil Engineering

Journal of Intelligent Material Systems and Structures

Development and evaluation of an external reusable piezo-based concrete hydration-monitoring sensor

Bimodal microstructures in metals are attractive because they help in achieving high strength and good ductility simultaneously thereby circumventing the strength-ductility paradox. However, there are few reports and limited understanding of the surface degradation behavior of bimodal alloys. Here, the authors report on the exceptional corrosion resistance of bimodal stainless steel developed using a simple single-step processing route. The microstructure of bimodal steel comprises of fine martensite (≈200–400 nm) in a matrix of coarse austenitic grains (≈10 μm). The bimodal steel shows significantly lower corrosion rate of 0.001 mm/year in 3.5 wt\% NaCl solution compared to 0.088 mm/year for commercially available SS316L stainless steel. The exceptional corrosion behavior of bimodal steel is attributed to favorable electronic properties of its passive layer. Formation of a depletion zone in the passive layer and higher chromium fraction limits the charge transport across metal-oxide-solution interface. The current microstructural design strategy is potentially transformative for developing high-performance structural materials with superior corrosion resistance. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Steel Research International

Excellent Corrosion Resistance of Dual-Phase Bimodal Stainless Steel

In applications where heavy metal welding is performed, the short circuit welding current is very high. During these conditions, manual welding is difficult. Hence, using an automated welding system enhances the productivity and quality of welds, thus reducing dependency on skilled work force. In this manuscript one such mechanism of DC welding, where the welding electrode is automated with a voltage control algorithm is discussed. This algorithm is implemented by sensing the voltage across the electrodes and controls the welding action based on the logic implemented. Implementation of this automated system ensures, monitored time of contact between the job and electrode. © 2019 IEEE.

Electrical Engineering

2019 Global Conference for Advancement in Technology, GCAT 2019

Design and Implementation of Automatic Welding Machine

This abstract reports very high (&gt;1014 cm−2) sheet carrier density (ns)in Zinc Oxide (ZnO) based heterostructure for low Magnesium (Mg) compositions (&lt;0.15) in barrier layer, achieved by alloying Cadmium (Cd) in buffer layer ZnO, grown by Dual Ion Beam Sputtering (DIBS) deposition technique. © Springer Nature Switzerland AG 2019.

Springer Proceedings in Physics

Enhanced sheet carrier density in zno based heterostructure by alloying cadmium in buffer layer zno

Solar colletors of Flat Plate type is a thermal transfer device that absorbs solar radiation and converts it into heat, which is mainly used to increase the water temperature, heat and dryness, dryness of crops in the region, space heating and in industries where this hot fluid is required for many chemical reactions, and for applications requiring the temperature of the fluid to be less than 100°C. As non-renewable sources of energy are becoming depleted and will soon have the power crisis. So, referring to fatigue rates, we should use our entire renewable resources so that we can control the rate of decline. The main components of the flat plate air collector are, absorbing plate, top covering plate (glass cover), insulating material and channel pipes covered with insulating material. Absorber plates are covered with a high absorbent coating. The top cover should be made of a maximum transmittance. The effectiveness of the flat plate air collector is highly affected by the losses through the top covering material and also due to the low heat transfer coefficient between the absorber plate and the air flowing through it. Most of the experiments and studies have shown that efficiency can be increased by using different types of solar collector which include double pass, a single pass with fins etc. Based on the literature survey it has been found that most of the studies on the solar collector are done to increase its thermal efficiency by enhancing the rate heat transfer between air and the absorber plate by using rough surface on the absorber plate. © Published under licence by IOP Publishing Ltd.

IOP Conference Series: Materials Science and Engineering

Heat Transfer Analysis of Flat Plate Air Collector

Air pollution monitoring systems with energy-intensive sensors cannot afford to sample frequently in order to maximize time between successive recharges. In this paper, we propose an energy-efficient machine learning based sensor duty-cycling method for a sensor hub receiving data from the air-pollution sensors. In particular, we demonstrate that temporal correlation of pollutant concentration can be exploited to select optimum sampling period of an energy-intensive sensor to reduce sensing energy consumption without losing much information. Support Vector Regression is used to predict the missing samples during the period sensor is turned off. © 2018 IEEE.

2018 24th National Conference on Communications, NCC 2018

Energy-Efficient Air Pollution Monitoring with Optimum Duty-Cycling on a Sensor Hub

A computational study on active and passive evacuated tube solar collector system is examined in this paper. The paper gives us an understanding of the performance of the ETC system under natural flow as well as forced circulation. Major parameters for useful solar thermal energy gain by evacuated tube solar collector are tilt angle, mass flow rate and specific heat capacity of working fluid. To make sure that the system receives maximum useful heat gain, the optimum mass flow rate has been analyzed using ANSYS Fluent CFD. Thermal efficiency of active evacuated tube solar collector at optimum mass flow rate is compared with thermal efficiency of passive evacuated tube solar collector. It is observed from the numerical modeling of the evacuated tube solar collector that passive system is more efficient than active system. © Springer Nature Singapore Pte Ltd. 2019.

Lecture Notes in Mechanical Engineering

Computational analysis of active and passive evacuated tube solar collector

Surface phenomenon such as cavitation erosion-corrosion limits the working life and durability of the fluid machines through significantly altering the efficiency. Surface modification is an apparent and economical route for improving the sustainability of these components. Recently developed complex concentrated alloys (CCAs) or high entropy alloys (HEAs) possess exceptional properties owing to high configurational entropy. We developed CCA coatings on the stainless steel using a facial and effective microwave processing technique. The effect of Al molar fraction in AlxCoCrFeNi (x = 0.1–3) CCAs on ultrasonic cavitation erosion-corrosion was investigated in 3.5\% NaCl solution. For comparison, cavitation erosion and electrochemical corrosion behavior of the pre- and post-tested samples was also performed. Detailed microstructure and mechanical characterization of the developed coatings were also preformed using different analytical techniques. The equimolar CCA coating showed apical degradation resistance under both pure erosion and erosion-corrosion conditions. The observed behavior is attributed to high strain hardening, optimal hardness, fracture toughness, and utmost stability of the passive layer. The phenomenal conjugation of these properties was associated with highest configurational entropy for equimolar composition resulting in sluggish diffusion, and severe lattice straining. Compared to pits, striations and cracks characterizing the morphology of the degraded stainless steel, the equimolar and Al0.1CoCrFeNi CCAs showed TTS (tearing topograph surface) as the dominant failure mode characterized by presence of microplastic deformation. The degradation of the Al3CoCrFeNi CCA occurred mainly through brittle failure mode. The difference in failure mechanism is related to the mechanical properties and underlying microstructure. © 2018 Elsevier B.V.

Ultrasonics Sonochemistry

Microwave synthesized complex concentrated alloy coatings: Plausible solution to cavitation induced erosion-corrosion

Tailored multifunctional capabilities, demanded in domains ranging from aerospace to biomedical fields, are achieved through judicious combinations of structural/nonstructural fibers, matrices, and coatings. Multifunctional composite structures are thus designed to perform a variety of secondary functions (sensing, actuation, energy storage/harvesting, etc.) apart from their primary structural functions (strengthening, stiffening, and stabilizing). In realizing such multifunctional capabilities, complex stress-prone assemblies of low-length-scale components/coatings of materials with distinct properties are essential. Fortunately, additive manufacturing has demonstrated the potential to efficiently and effectively enable such robust assemblages. Apart from such three-dimensional (3D)-printed spatial nonuniformity, four-dimensional (4D) printing renders time-dependent properties to be triggered by various stimuli; 3D/4D printing of multifunctional composites possesses advantages over conventional manufacturing (where even feasible!) in term of time, mass, volume, overall cost, and efficiency. This chapter reviews various printing methods, candidate materials, and characterization of multifunctional printed components. The emphasis is on structural members integrated with electronic components, photovoltaic solar cells, piezoelectric materials, and battery fiber composites. A short review of 4D structures due to various stimuli is also carried out. Such 3D/4D printed flexible/wearable electronics, smart devices, and adaptive structures could find applications all the way from household appliances to satellites. © 2020 Elsevier Inc. All rights reserved.