Department of Mechanical Engineering

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In this paper, an h∕p spectral element method with least-square formulation for parabolic interface problem will be presented. The regularity result of the parabolic interface problem is proven for non-homogeneous interface data. The differentiability estimates and the main stability estimate theorem, using non-conforming spectral element functions, are proven. Error estimates are derived for h and p versions of the proposed method. Specific numerical examples are given to validate the theory. © 2018 Elsevier B.V.

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Computer Methods in Applied Mechanics and Engineering

Spectral element method for parabolic interface problems

This paper presents an analytical error prediction model of a 3PRP planar parallel manipulator using the screw theory. This analytical approach is used to find the effect of mechanical inaccuracies contributing to the end-effector pose errors and their sensitivity coefficients. Finally, parameter sensitivity analysis of non-compensable errors of two different configurations based on their fixed base shape namely ∆-shape and U-shape fixed bases are analysed and compared. © Springer International Publishing AG 2018.

Mechanisms and Machine Science

Error modelling and sensitivity analysis of a planar 3-PRP parallel manipulator

A generalized Weibull model is presented for reliability characterization of single carbon fibres. This generalized distribution gives the probability of tensile failure of fibres as a function of length, surface area and volume of fibres, separately in different models using a statistically significant experimental data set. This model accounts for the unusual variation in the strength of the fibres as the physical parameters capture the severity of the most severe flaws in the ensemble of fibres. The experimental campaign involved analysing the diametric variation in each carbon fibre using photomicrographs. The micro-texture and morphology were further analysed using scanning electron microscopy images. An extensive characterization of the strength dependence on the fibre gage length was performed through “single-fibre uniaxial tensile tests” on several hundred carbon fibres of different grades. The goal of the study is to ensure the reliability of strength characterization of a single fibre, accounting for geometric irregularities and property variation. The present Weibull models are compared to assess their descriptive accuracy, that is, the “goodness-of-fit” in describing the observed statistical data as well their generalizability in predicting future values. The Kolmogorov–Smirnov (KS) test was used to ascertain the goodness of fit for the predicted Weibull plots. It was found that the descriptive adequacy of the models improved with the increase in the number of parameters used in the definition of the Weibull model. The conventional model failed the KS test for the most number of cases and hence was deemed unfit in terms of generalizability. Furthermore, the generalized Weibull model was found to have better descriptive accuracy and predictive power compared to the conventional model. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.

Archive of Applied Mechanics

Generalized Weibull model-based statistical tensile strength of carbon fibres

Before putting in service, the creep strength enhanced ferritic (CSEF) steels are subjected to varying tempering treatment to produce a vast array of mechanical properties and to achieve the optimum combination of microstructure and mechanical properties by controlling normalizing and tempering temperature/time. In the present investigation, P911 steel was subjected to a fixed normalizing temperature of 1040 °C for 1 h and then, subjected to varying tempering temperature (720 °C–800 °C) for 2 h of tempering time. The effect of notch geometry on the tensile properties with respect to the varying tempering temperature was also investigated. The microstructural characterization was studied using optical microscope and field-emission scanning electron microscope (FESEM). A decrease in grain size, hardness and strength were noticed with increase in tempering temperature initially but after 740 °C, the grain size and strength were found to be increased continuously. The area fraction of precipitates was found to be varied inversely with the grain size. For a particular tempering temperature, an increase in notch depth resulted in increase in strength and decrease in ductility. The best combination of hardness, ductility and strength were achieved after normalized at 1040 °C for 1 h and tempered at 760 °C for 2 h. © 2017 Elsevier Ltd

Engineering Failure Analysis

On study of effect of varying tempering temperature and notch geometry on fracture surface morphology of P911 (9Cr-1Mo-1W-V-Nb) steel

This paper describes the multiresponse optimization of tungsten inert gas welding for an optimal parametric combination to predict the weld characteristics of thin cold rolled steel sheets. The interaction effects of tungsten inert gas welding process parameters such as welding current, arc length, and traverse speed have been observed on the weld characteristic responses such as weld width, heat-affected zone width, and under-bead depression. Full factorial design of experiment was followed for determining the combinations of the experimental runs. Regression analysis was carried out to develop the mathematical models for the welding control factors and responses. Analysis of variance was used to check the adequacy of the developed mathematical model. The confirmatory tests were conducted to validate the accuracy of mathematical model. Sensitivity analysis was also done to analyze the effect of each individual process parameter on the weld responses. The full factorial experimental data was further utilized for multi-response optimization of the tungsten inert gas process parameters. It was observed that weld responses like weld width and heat-affected zone width could be optimized by regression modeling technique while the under-bead depression showed uncertain behavior. The under-bead depression ranged from 0.0 to 0.15 mm and was observed only when the arc traverse speed was at the lowest level (4 cm/min) for all values of the welding current and arc length. The experimental data were also modeled using the artificial neural network technique for the prediction of weld responses and the results were compared with that from the regression analysis. © IMechE 2017.

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

Achieving optimized tungsten inert gas butt welding conditions of thin cold rolled steel sheets by response surface methodology and artificial neural networks

Creep strength enhanced ferritic/martensitic P91 steel is considered as a candidate material for the reactor pressure vessels and reactor internals of Very High Temperature Reactor (VHTR). Heterogeneous microstructure formation across the P91 weldments lead to premature Type IV cracking and makes the weldability of P91 steel a serious issue. The present research work describes the effect of normalizing and tempering (N&T) treatment on microstructure evolution in various zones of gas tungsten arc welded (GTAW) P91 pipe weldments. For N&T treatment, P91 pipe weldments were subjected to various normalizing (950–1150 °C) and tempering (730–800 °C) temperature. The effect of varying heat treatment on tensile properties and hardness of P91 pipe weldments were studied for V-groove and narrow-groove weld designs. The effect of increase in normalizing temperature (fixed tempering temperature) resulted in increase in strength and hardness, while increase in tempering temperature (fixed normalizing temperature) resulted in the decrease in strength and hardness of P91 steel weldments. The better combination of strength, ductility and microstructure were obtained for the maximum normalizing temperature of 1050 °C and tempering temperature of 760 °C. © 2017 Elsevier B.V.

Materials Science and Engineering A

Homogenization of P91 weldments using varying normalizing and tempering treatment

In this paper, we present the fabrication of an efficient thin film temperature sensor utilizing chemical vapor deposited carbon nanotube (CNT) film as the sensing element on Si substrates, with diamond-like carbon (DLC):Ni as a catalyst in assisting CNT growth. The fabricated sensor showed good electrical response with change in temperature. Relative linear change in resistance of 18.4% for an increase in temperature from 22 °C to 200 °C was achieved. Various characterizing techniques, such as scanning electron microscopy (SEM) and Raman spectroscopy, were used to characterize the films. In an effort to study device performance, van der Pauw and Hall measurements were carried out to study the dependence of resistance on temperature and magnetic fields. Temperature coefficient of resistance of the sensor was calculated as 1.03 × 10-3/°C. All implications arising from the study are presented. The results establish the aptness of the as-grown CNT film to be used as an active sensing material in thin film temperature sensors. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.

Sensors (Switzerland)

Developing efficient thin film temperature sensors utilizing layered carbon nanotube films

This paper reports an energy-based method for the dynamic pull-in instability analysis of a spherical dielectric elastomer (DE) balloon subjected to a quasi-statically applied inflation pressure and a Heaviside step voltage across the balloon wall. The proposed technique relies on establishing the energy balance at the point of maximum stretch in an oscillation cycle, followed by the imposition of an instability condition for extracting the threshold parameters. The material models of the Ogden family are employed for describing the hyperelasticity of the balloon. The accuracy of the critical dynamic pull-in parameters is established by examining the saddle-node bifurcation in the transient response of the balloon obtained by integrating numerically the equation of motion, derived using the Euler-Lagrange equation. The parametric study brings out the effect of inflation pressure on the onset of the pull-in instability in the DE balloon. A quantitative comparison between the static and dynamic pull-in parameters at four different levels of the inflation pressure is presented. The results indicate that the dynamic pull-in instability gets triggered at electric fields that are lower than those corresponding to the static instability. The results of the present investigation can find potential use in the design and development of the balloon actuators subjected to transient loading. The method developed is versatile and can be used in the dynamic instability analysis of other conservative systems of interest. © 2018 The Author(s) Published by the Royal Society. All rights reserved.

Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences

DC dynamic pull-in instability of a dielectric elastomer balloon: An energy-based approach

The demand of clean decontaminated water supply is increasing with the increase in the population of the world. As a result, the global need for more economic and efficient technologies for water remediation is also rising. The entry of nanotechnology into the wastewater treatment engineering exemplified a noteworthy advancement, and nanoparticles (NPs) have been exhaustively studied for possible remediation applications. However, the wastewater treatment with dispersed NP suspensions is still inadequate and to some extent antagonistic on the grounds of health and environmental safety, even as NP reaction mechanisms, ecotoxicity, and their transport properties are quiet under exploration. Theoretically, the development of porous nanocomposites containing nanoparticles to overcome these concerns offers the next logical step for developing functional nanomaterials and nanocomposites that are better investigated in the wastewater industry. This purpose of this review is to provide an overview of the range of carbon nanocomposites containing NP of semiconductor photocatalysts being technologically advanced, at the same time highlighting their limitations in practical uses. The review also briefly covers what further improvements are needed to optimize existing nanocomposite-mediated water remediation processes to successively accomplish viable maturity. © 2018, Springer Nature Singapore Pte Ltd.

Energy, Environment, and Sustainability

Recent Advances in Carbon–Semiconductor Nanocomposites for Water Remediation

The present work studies the effect of passive exit flexibility on a two-dimensional starting jet. The exit flexibility is introduced by attaching two flexible (deformable) flaps at the jet exit of a high aspect ratio rectangular duct with the flaps initially being parallel to the channel walls. A controlled piston motion is used to generate the starting jet, which is composed of a rapid acceleration to a constant velocity (Up) that is maintained for a given duration of time, after which it is brought to rest impulsively. The parameters which are varied include the flexural rigidity (EI) of the flaps, flap length (Lf) and piston speed (Up), with measurements of the flap kinematics and flow field in each case. The flaps initially bulge due to the acceleration of the piston from rest, with this bulge growing in size and moving downstream as the flow develops, culminating in a large opening at the flap exit. Subsequently, the flaps return to their initial parallel position and remain there as long as the piston is in motion. Once the piston stops, the flaps collapse inwards due to fluid deceleration causing additional flow out of the flap region in the form of a jet that adds to the net amount of fluid pushed by the piston. We find that the flap kinematics is affected by the flap EI and Lf besides Up. We define a non-dimensional flexural rigidity EI° = EIeq/(1/2ρU2pL2fd), where EIeq is an equivalent flexural rigidity which takes the self-weight of the flaps into account (d = channel width; ρ = fluid density). We find that across different EIeq, Lf, and piston speeds, the maximum opening of the flap tip and the time taken to reach this maximum opening in terms of L/Lf (where L = fluid slug length) fall on a single curve for all the cases studied, when plotted with EI∗. Particle image velocimetry measurements show that the motion of the flaps results in the formation of additional pairs of vortices when compared to the single vortex pair formed in the absence of flaps. The total final circulation coming out of the flap region remains nearly the same as that of the rigid exit case. However, the final fluid impulse is always found to be higher in the flap cases, with the fluid impulse in most flap cases being approximately two times the fluid impulse of the rigid exit case. This increase in impulse is shown to be linked to the fact that the centroids of vorticity get spread out more in the lateral direction due to the opening of the flaps. The increased impulse and the higher time rate of change of impulse, which is linked with force, suggest that introduction of flexible flaps can help improve thrust performance when looked at from a propulsion point of view. © 2018 Cambridge University Press.