Department of Mechanical Engineering

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IIT Jodhpur

International Journal of Mechanical and Production Engineering

Graphene nanostructures on electrodeposited Cu by Chemical Vapour Deposition

Here, investigation to explore the effect of generic payload and externally applied asymmetric load on the calculation of modal parameters and dynamic performance of a rotating flexible manipulator under prismatic motion has been established. We thus have developed a dynamic model of a rotating Cartesian manipulator with a payload whose center of gravity doesn’t coincide with the point of attachment, to determine the modal parameters i.e., natural frequency and corresponding mode-shape. These modal parameters are then illustrated graphically upon varying parameters like offset parameters (i.e., offset mass, offset inertia, offset length), mass and stiffness of rotary actuator, and amplitude and frequency of asymmetric load. An investigation into the nonlinear dynamics of the system accounting of geometric nonlinearity has been executed while obtained results have been validated numerically within the permissible error at the assorted critical points in frequency characteristic curves. Current research further investigates the influences of offset parameters, mass and stiffness of the actuator, frequency and amplitude of axial force on the steady state responses for the primary and sub-harmonic resonance conditions to reveal the built-in saddle-node and pitchfork bifurcation due to which the system losses its structural stability. This work enables an insight into the modal characteristics and nonlinear behavior of a rotating-Cartesian manipulator with a generic payload under asymmetric axial force and prismatic motion. © 2019, © 2019 Taylor & Francis Group, LLC.

World University root node

Mechanics Based Design of Structures and Machines

Modal analysis and dynamic responses of a rotating Cartesian manipulator with generic payload and asymmetric load

As far as design safety and operation of heat exchangers with a horizontal flow are concerned, it is necessary to study local heat transfer coefficient, boiling pressure drop, and critical heat flux for flow in a horizontal tube. In the present experimental work, local axial distribution of heat transfer coefficient, two-phase pressure drop, and critical heat flux for the flow boiling in a horizontal straight tube with R-123 as working fluid has been studied. Experiments are performed in horizontal tubes of diameter 11.9 mm and wall thickness 0.4 mm of SS304, having a heated length of 400 mm, 600 mm, and 1000 mm for the mass flux of 180 to 1210 kg/m2s. The local wall temperature is measured using the Infra-Red thermal imaging technique. The local heat transfer coefficients are compared with six different well-known correlations. Also, the two-phase frictional pressure drop is measured and compared with eight different general correlations. In the present study, a sudden rise in wall temperature at any location of a test section is considered as the occurrence of a boiling crisis. The boiling crisis mechanism observed in the present study is of departure from nucleate boiling (DNB). It takes place in the subcooled, or low quality saturated boiling region and in-between the length of the test sections rather than at exit as in the dry-out type of CHF. The critical heat flux is compared with six different predictive correlations. The mechanism of occurrence of CHF in the present work is found to be a departure from nucleate boiling. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.

Heat and Mass Transfer/Waerme- und Stoffuebertragung

Pressure drop, local heat transfer coefficient, and critical heat flux of DNB type for flow boiling in a horizontal straight tube with R-123

The effects of manufacturing defects creates uncertainty on the mechanical response of unidirectional fibre-reinforced composites. These are studied through modelling of three-dimensional Representative Volume Element (RVE). In this study, an algorithm is developed to generate the microstructure of unidirectional fibre reinforced composite with both regular and random fibre distribution and then analyzed using mathematical theory of homogenization to estimate the homogenized or effective material properties. Here, the RVEs are modelled with random fibre distribution but increasing the number of fibres gradually and also randomly varying their positions. This variation in the randomness of the fibre distribution affects the effective properties. Also, the effect of different loading conditions is investigated. The significance of this structural distribution of heterogeneities on the overall effective behaviour is discussed for random structures and uncertainties that occur in composite materials. The variations in the predicted elastic properties for the given volume fraction of the above mentioned scenarios are compared with the experimental values and good agreement is achieved. There is a significant percentage change in transverse shear moduli, G23 and ν23, which are 21.87 and 35.20% with respect to the experimental results. © Springer Nature Singapore Pte Ltd. 2020.

Lecture Notes in Mechanical Engineering

A micromechanical study of fibre-reinforced composites with uncertainty quantification and statically equivalent random fibre distribution

The present article treats the nonlinear dynamic analysis of a lightweight flexible rotor–disk–bearing system with geometric eccentricity and mass unbalance. A large deflection model has been derived to represent a nonlinear flexible rotor–bearing system to study the bifurcation, stability, and route to chaos. This mathematical model includes a bidirectional flexible shaft characterized by nonlinear curvature and gyroscopic effect, geometric eccentricity, a rigid disk crooked with unbalance mass, and nonlinear flexible bearings. A perturbation technique has been used to obtain a set of nonlinear algebraic equations that govern the overall dynamics of the system. The system stability has been studied by investigating the bifurcation and route to chaos upon changing the design parameters such as geometric eccentricity, mass unbalance, and disk parameters under the resonance conditions. The present system exhibits a complex behavior traveling with periodic, quasi-periodic, period doubling and chaotic behavior on a gradual change in design variables. The system loses its stability due to S–N bifurcation, which leads to a sudden jump in the response amplitude. These complex behaviors have been studied in detail with the illustration of time history, phase trajectories, bifurcation diagrams, and Poincaré’s map for each category. Qualitative assessment of bifurcation diagrams has been studied to explore the boundaries of the stable and unstable behaviors and essential dynamics of the systems. Special attention to predict its rich dynamics to highlight the route to chaos as a future diagnostic tool has been explored. The presented results offer significant understanding of the dynamic performances and its critical operating conditions of a rotor system subjected to geometric eccentricity and mass imbalance. © 2019, Springer-Verlag GmbH Austria, part of Springer Nature.

Acta Mechanica

Nonlinear modeling, dynamics, and chaos in a large deflection model of a rotor–disk–bearing system under geometric eccentricity and mass unbalance

Thermal barrier ceramic coatings (TBCs) formed using detonation gun was characterized in this paper. The coating consisted of nickel chromium (Ni-Cr) as bond coat and aluminum oxide (Al2O3) as the top coat. The microstructure at interfaces of thermal barrier coating was characterized using the scanning electron microscope (SEM). Thermal cycling have been done for performance evaluation and hot corrosion behaviour of the coatings. Thermally grown oxide layer was developed after few thermal cycles and the thickness of the layer was analysed using SEM. Energy dispersive analysis was used to analyse the elements present in coatings after thermal cycles. © 2020 Elsevier Ltd. All rights reserved.

Fulltext

Materials Today: Proceedings

Characterization of damage in thermal barrier coating under different thermal cycle

This work was performed to characterize the dissimilar austenitic grade SS304 L and martensitic grade creep strength of an enhanced P92 steel welded joint. The welded joint was prepared using the autogenous gas tungsten arc welding process. The welded joint was subjected to conventional heat treatment consisting of tempering at 760 °C for 2 hours, followed by air cooling and unconventional heat treatment (UHT) consisting of normalizing (1040 °C/40 min), further followed by air cooling and, finally, stabilized tempering at 760 °C for 2 hours. The heat-treated welded joint was subjected to the microstructural characterization and mechanical testing. The room temperature Charpy toughness (CT) testing for both the weld fusion zone (WFZ) and heat-affected zone, tensile testing, and hardness testing were performed to characterize the dissimilar welded joint. Stabilized microstructure associated with improved mechanical properties were observed for UHT. The CT and tensile strength were optimum for the UHT. © 2020, The Minerals, Metals & Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Mechanical and Metallurgical Characterization of Dissimilar P92/SS304 L Welded Joints Under Varying Heat Treatment Regimes

The martensitic 10CrMoVNb 91 (P91) steel welded joint is subjected to reaustenitizing-based post-weld heating, referred to as post-weld normalizing and tempering (PWNT). The various zones of P91 weldments in PWNT treatment and after creep exposure at 620 °C for 150 MPa are studied. The evolution of intermetallic Laves phase in the various zones of P91 weldments is observed after the creep rupture tests. The evolution of Laves phase is characterized using field-emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Steel Research International

The Characterization of Soft Fine-Grained Heat-Affected Zones in P91 Weldments under Creep Exposure Conditions

In this present study, a novel approach of measuring through-thickness residual stresses based on the general strain relaxation methodologies has been described. This new method is an amalgam of the conventional deep hole drilling technique and the contour method with a reduced degree of damage to the component made during measurements. The annular deformation of a reference hole made at the measurement location has been interpreted as the displacement boundary conditions in a two-dimensional finite element model. In this regard, a thick, partially plastic four-point bent bar specimen was used to validate the proposed method. Through-thickness axial residual stresses induced in the bar were measured using the proposed technique and were observed to be in a reasonably close match with the theoretical and DHD results. © 2020 Elsevier B.V.

Materials Letters

Novel residual stress measurement technique to evaluate through thickness residual stress fields

For any type of machining process, surface integrity and dimensional accuracy is a critical examination for machined material. Electro-discharge machining (EDM) process is the most effective method for surface integrity and dimensional accuracy evaluation of the machined surface. The present research work focused to investigate the influencing of machining parameters (pulse current, pulse on time and duty cycle) on machining of P91 tool steel. During the machining process, quantitively measurement of surface roughness (SR) and surface crack density (SCD) has been considered as surface integrity. Dimensional accuracy is characterized by over cut (OC) in this process of machining. In this study EDM parameters arranged using RSM-based design of experiment, on SCD, SR, and OC and study their individual impact on these response parameters. Pulse current is the most significant factor as compared to other parameters for the machining in EDM. The current work also recommends an optimum setting of system parameters for obtained good dimensional accuracy and surface integrity after P91 tool steel machining with EDM. © 2019 Elsevier Ltd. All rights reserved.