Mechanical Engineering

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There has been tremendous interest in recent years in a new class of multi-component metallic alloys that are referred to as high entropy alloys, or more generally, as complex concentrated alloys. These multi-principal element alloys represent a new paradigm in structural material design, where numerous desirable attributes are achieved simultaneously from multiple elements in equimolar (or near equimolar) proportions. While there are several review articles on alloy development, microstructure, mechanical behavior, and other bulk properties of these alloys, then there is a pressing need for an overview that is focused on their surface properties and surface degradation mechanisms. In this paper, we present a comprehensive view on corrosion, erosion and wear behavior of complex concentrated alloys. The effect of alloying elements, microstructure, and processing methods on the surface degradation behavior are analyzed and discussed in detail. We identify critical knowledge gaps in individual reports and highlight the underlying mechanisms and synergy between the different degradation routes. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

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Metals

Corrosion, erosion andwear behavior of complex concentrated alloys: A review

In the last few years the research activity in multifunctional composite materials and structures (MFCMS) is remarkably increased. This paper is a review of journal publications that are related to multifunctional composite materials and structures. MFCMS are meant for performing a variety of functions apart from the primary structural function which provides structural functions such as strength, stiffness, stability while non-structural functions provides energy harvesting, self-healing capability, sensing and actuation and sometimes acts as a protective layer etc. Many of the recent developments focused on the applications of MFCMS such as High Altitude Airship (HAA), morphing aircraft wings, energy harvesting, nanomaterials & nanostructures, smart structures, coupled field analysis, biomechanical etc. This paper also focused on the nonlinear mechanics of MFCMS because High Altitude Airship type of problems comes under geometrically and materially nonlinear case, so to analyse this type of problems one of the effective method called Variational Asymptotic Method is used. This method solves the problem by splitting the 3-D nonlinear problem into 1-D analysis through the thickness and 2-D nonlinear shell analysis. This paper concludes with a discussion of future scope and difficulties in design and analysis of multifunctional composite structures. © 2017 Elsevier Ltd.

Materials Today: Proceedings

A review of recent research on multifunctional composite materials and structures with their applications

This paper deals with permutation flow shop scheduling problem in which an integrated cost model consisting of work-in-process inventory carrying cost and penalty cost due to batch delay is proposed. The objective is to obtain an optimum production schedule which minimizes the expected total cost per unit time of scheduling. To optimize the objective function, we apply two new metaheuristic optimization techniques namely TLBO (teaching-learning based optimization) and Jaya and two traditional algorithms: PSO (particle swarm optimization) and SA (simulated annealing). The problem is solved for several instances ranging from 8 jobs and 5 machines to 500 jobs and 20 machines. Computational results show that for small instances, all algorithms performed equally good when compared with the exact solution (total enumeration method). However, for medium and large size problems, enumeration method was unable to give the results in a reasonable computation time period. Therefore the results of all four algorithms are compared among themselves and found that Jaya outperforms all algorithms. However, for a few large instances, SA yields better results in less computation time as against other heuristics. The overall performance of all algorithms reveals that TLBO and Jaya have considerable potential to solve discrete combinatorial problems such as permutation flow-shop scheduling problems. © 2018 Elsevier Ltd

Computers and Industrial Engineering

A TLBO and a Jaya heuristics for permutation flow shop scheduling to minimize the sum of inventory holding and batch delay costs

Opportunistic maintenance (OM) models take the opportunity of economic dependencies among components in the system when it stops due to failure or scheduled preventive maintenance (PM) of a certain equipment. Performing maintenance actions simultaneously can substantially bring down the maintenance costs in terms of reduced downtime costs, production losses, service and labor costs, etc. However, maintaining all components together may be uneconomical due to over or underutilization. Secondly, most of the study on opportunistic maintenance consider the system comprising of either multi-machines with the single component or single machine with multi-components. Based on this motivation, the present paper proposes an effective opportunistic grouping policy for multi-component multi-machine system considering time-based imperfect PM actions. The imperfect PM addresses the most practical issue that PM does not always return the component to as-good-as-new status. To the best of our knowledge, this is the first attempt to develop the multi-machine OM policy with multi-components. The objective is to obtain an optimum group of components and PM times in order to minimize the total system maintenance cost per unit time during the mission. The opportunistic grouping model is based on the individual component’s PM intervals. Two grouping strategies viz. grouping within the machines and grouping between the machines are adopted in order to identify the diversity of the proposed model. A recently developed meta-heuristic named Jaya algorithm is applied to optimize the objective function. The effectiveness of the proposed model is analyzed with an illustrative example. Results reveal that the proposed model shows better economic performance as compared from the individual maintenance practices. © 2018, Curran Associates Inc. All rights reserved.

Proceedings of International Conference on Computers and Industrial Engineering, CIE

Opportunistic group maintenance policy for multi-machine system with multi-components

In present research paper, semi-transparent photovoltaic module (SPVM) integrated greenhouse solar drying system has been used for grapes (Vitis vinifera) drying. Based on hourly experimental information namely solar intensity, moisture evaporated, ambient air temperature, grape surface temperatures, relative humidity and greenhouse air temperature etc. heat and mass transfer coefficient for the SPVM drying system have been evaluated. It has been seen that the convective heat transfer coefficients for grapes found between 3.1–0.84 W/m2 K. Also, there is a fair agreement between theoretical and practical mass transfer (moisture evaporated) during drying of grapes with a correlation coefficient (r) and root mean square percentage deviation (e) of 0.88 and 11.56 respectively. Further, nonlinear regression procedure has been used to fit various drying models namely Henderson and Pabis model, Newton’s model, and Page’s model. From the analysis, it was found that Page’s model is best fitted for grapes drying in SPV greenhouse as well as open sun drying. Further, net electrical energy, thermal energy and equivalent thermal energy were found to be 3.61, 17.66 and 27.15 kWh during six days of drying respectively. © 2017, Springer-Verlag GmbH Germany, part of Springer Nature.

Heat and Mass Transfer/Waerme- und Stoffuebertragung

Grapes (Vitis vinifera) drying by semitransparent photovoltaic module (SPVM) integrated solar dryer: an experimental study

Aeroelastic systems with hardening nonlinearity exhibit supercritical Hopf bifurcation when the flow velocity exceeds a critical velocity leading to self-sustaining large amplitude limit cycle oscillations known as flutter. This study investigates the effects of irregular fluctuations in the flow on the dynamical stability characteristics of a two-degree-of-freedom pitch-plunge aeroelastic system with hardening nonlinearity. Dynamical or D-bifurcations are investigated through the computation of the largest Lyapunov exponent, while phenomenological or P-bifurcation analysis is carried out by examining the structure of the joint probability density function of the response quantities and their instantaneous time derivatives. The qualitative nature of P-bifurcation analysis makes it difficult to pinpoint the regimes of different response dynamics. In the light of this difficulty, a quantitative analysis using the Shannon entropy measure has been undertaken to quantify the P-bifurcation regime. This regime is shown to be coincident with the intermittency regime observed in the response time histories prior to flutter oscillations in fluctuating flows. © 2018, Springer Science+Business Media B.V., part of Springer Nature.

Nonlinear Dynamics

Intermittency in pitch-plunge aeroelastic systems explained through stochastic bifurcations

Tribo-corrosion is an issue of concern for marine and other fluid machinery. High entropy alloys (HEAs) represent a new category of materials possessing exceptional properties. We investigated the erosion-corrosion behavior of Al0.1CoCrFeNi HEA. For comparison, stainless steel SS316L is also evaluated. Results indicate that despite low hardness and yield strength, HEA exhibits high erosion-corrosion resistance compared to steel. The HEA also shows high pitting and passive potentials compared to steel. The superior erosion-corrosion resistance of HEA is due to high corrosion resistance, and work hardenability. The degradation mechanism investigated using SEM show ploughing as the primary material removal mode (MRM) for HEA at an oblique angle compared to micro-cutting for SS316L steel. At normal impingement, platelet mechanism is observed to be the dominant MRM. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Advanced Engineering Materials

High Entropy Alloys: Prospective Materials for Tribo-Corrosion Applications

Bimodal composite structures conjugating both high hardness and fracture toughness can effectively counter erosion induced degradation. The present work successfully develops bimodal metal matrix composite claddings using facile and cost-effective microwave technique, exploiting the direct and effective coupling phenomenon of reinforcement with microwave irradiation. For comprehensiveness, unimodal micro-/nano-reinforced clads were also developed. Interestingly, unimodal micro-composite clad showed refined structure compared to nano counterpart which is due to the effective coupling of later with microwave irradiation causing particle dissociation into the matrix. Compared to unimodal claddings, bimodal showed the highest hardness and indentation fracture toughness. In addition to ex-situ reinforcements, intrinsically evolved secondary phases also effectively contributed towards improved mechanical properties. The better performance of the bimodal clad is related to reduced agglomeration and dissociation of the nanoparticles, refined microstructure and constructive interaction between micro and nano-reinforcements. The phenomenal mechanical properties of bimodal composite clad resulted in improved durability compared to unimodal composite claddings under different tribological test conditions. © 2018 Elsevier B.V.

Civil Engineering

Surface and Coatings Technology

Towards highly durable bimodal composite claddings using microwave processing

We investigated the structure–property correlation for the complex concentrated alloy (CCA) coatings prepared using different precursor powders. Al3CoCrFeNi CCA precursor powders were prepared through mechanical alloying (MA) (ball milling) and direct mixing (DM). CCA coatings were developed using microwave technique through hybrid heating approach. Coatings showed good metallurgical bonding with substrate exhibiting cellular growth structure. Microstructure for both coatings was primarily composed of A2 phase segregated with B2 phase at intercellular region. CCA coatings with different precursors showed insignificant influence on hardness, elastic modulus and cavitation erosion. Nonetheless, coating developed with MA precursor showed slightly lower fracture toughness compared to DM, mainly attributed to inherently higher fraction of intermetallic B2 phase. We showed that direct mixing is an efficient and effective route for developing CCA coatings. © 2018 Elsevier B.V.

Materials Letters

Complex concentrated coatings: Effect of processing route on microstructural and mechanical properties

<p>The authors report the development of AlxCoCrFeNi (x = 0.1 to 3) high entropy alloy (HEA) coatings using a simple and straightforward microwave technique. The microstructure of the developed coatings is composed of a cellular structure and diffused interface with the substrate. The microstructure of the HEA coatings varies as a direct function of Al content. An increase in Al fraction shows structural transformation from FCC to BCC along with the evolution of σ and B2 as the major secondary phases. The diffusion of Mo from the substrate enhances the mixing entropy and promotes σ-phase formation. The HEA coatings show significantly high hardness compared to SS316L substrate steel (227 HV) with a maximum value of 726 HV observed for three-molar composition. The fracture toughness exhibits an inverse correlation with the Al fraction with the highest value of around 49 MPa m1/2 observed for Al0.1CoCrFeNi coating. The equimolar coating composition shows lowest erosion rates among all the tested samples due to optimum combination of the mechanical properties. The erosion resistance of the equimolar coating is 2 to 5 times higher than steel substrate and around 1.5 times higher than the non-equimolar counterparts depending upon the impingement angles. © 2018 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim</p>