Department of Mechanical Engineering

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A process geometry model determines engagement angle and instantaneous uncut chip thickness which forms basis in predicting cutting forces and surface quality in micro-end milling operation. This paper presents a process geometry model incorporating cutter runout, elastic recovery of work material and minimum chip thickness. These characteristics are incorporated effectively by realizing different engagement cases that are likely to occur during micro-milling. The model considers interactions of tooth trajectory under consideration with surfaces generated by previous teeth to develop a realistic process geometry model. It has been demonstrated that the inclusion of tooth trajectory interactions has significant effect on prediction accuracy of a model. The results are also substantiated by conducting machining experiments at various cutting conditions. © 2016 The Authors

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Procedia Manufacturing

Improved Process Geometry Model with Cutter Runout and Elastic Recovery in Micro-end Milling

A study presents a method that can be used to capture the target at the specified time while avoiding algorithmic as well as Jacobian singularities for a system that starts from rest. This method can alternatively be used to find a suitable initial configuration for a given desired motion state. It defines initial configuration for a given desired motion state, and the motion state of the robot as the position and velocity of a point on the base along with the joint positions and velocities of the arms. It allows additional constraints such as limits on angles, acceleration, and jerk to be satisfied while avoiding collisions.

Journal of Guidance, Control, and Dynamics

Reactionless maneuvering of a space robot in precapture phase

A new method of silane treatment of nanoclays is reported where in the clay is nanodispersed in hydrolyzed silanes. The surface functionalization of Cloisite® 15A nanoclay has been carried out using two different silane coupling agents: 3-aminopropyltriethoxy silane and 3-glycidyloxypropyltrimethoxy silane using varied amounts of silane coupling agents, e.g. 10, 50, 200, and 400 wt% of clay. The surface modification of Cloisite® 15A has been confirmed by Fourier transform infrared spectroscopy. The modified clays were then dispersed in epoxy resin, and glass fiber-reinforced epoxy clay laminates were manufactured using vacuum bagging technique. The fiber-reinforced epoxy clay nanocomposites containing silane modified clays have been characterized using small angle X-ray scattering, transmission electron spectroscopy and differential scanning calorimetry. The results indicate that the silane treatment of nanoclay aided the exfoliation of nanoclay and also led to an increase in mechanical properties. The optimized amount of silane coupling agents was 200 wt%. The nanocomposites containing clay modified in 200 wt% of silanes exhibited an exfoliated morphology, improved tensile strength, flexural modulus, and flexural strength. The improved interfacial bonding between silane modified nanoclays and epoxy matrix was also evident from significant increase in elongation at break. © 2016 Informa UK Limited, trading as Taylor & Francis Group.

Composite Interfaces

Effect of surface treatment of nanoclay on the mechanical properties of epoxy/glass fiber/clay nanocomposites

The use of nickel base alloy as filler metal is no longer considered as the final solution for unexpected failures due to incidences of hot cracking of bimetallic welds under cyclically shifted temperature environment. The present paper is a novel attempt to study the development of austenitic stainless steel filler material for bimetallic weld joint. The present work aims at the design and development of shielded metal arc welding (SMAW) electrode coatings using extreme vertices design methodology to study the effect of electrode coating ingredients on the mechanical properties such as tensile strength, percentage elongation, impact toughness, micro-hardness of the weld metal. The work also attempts to study the weld metal chemistry along with the control of ferrite number and microstructural evolution to prevent hot cracking in stainless steel welds with variation in coating ingredients. It has been found from the study that the addition of SiO2 content in the coating tends to increase the weld metal silicon content whereas the effect of CaO content is to decrease it. The ultimate tensile strength of welds is increased with the TiO2, SiO2 and CaF2 content in the electrode coating while higher SiO2 content shows decreasing effect on impact toughness and microhardness values of the weld. The microstructures of welds comprise of austenite with varying amount of delta ferrite and inclusions which are further responsible for varying mechanical properties in welds. © 2016 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.

Journal of Manufacturing Processes

Investigation of TiO2-SiO2-CaO-CaF2 based electrode coatings on weld metal chemistry and mechanical behaviour of bimetallic welds

To achieve high thermal efficiency, modern day thermal power plants operate at higher operating temperature and pressure which necessitates use of steels with high creep rupture strength such as modified 9Cr-1Mo steels. In the present study, the evolution of phases in modified 9Cr-1Mo P91 steel and their effects on microstructural stability and mechanical properties have been studied for specimens that were subjected to different thermal heat treatment conditions. The main focus has been to study the effect of heat treatment temperature ranging from 623 K to 1033 K (350-760 °C) on P91 steel. Further, the effect of furnace cooling, water quenching, tempering at 1273 K (1000 °C) and austenitizing on the mechanical properties and microstructure has been studied. The techniques used for material characterization were scanning electron microscopy (SEM), optical microscopy (OM) and X-ray diffraction. For low tempering temperature, i.e. 623 K (350 °C), M23C6, M3C, M7C3, and MX precipitates have been observed with high yield strength (YS), tensile strength (UTS), hardness and low toughness. In the high temperature range, 923-1033 K (650-760 °C), fine MX, M7C3, M23C6, M2X, and M3C precipitates have been observed with low YS, UTS, hardness and high toughness. The steel tempered at 1033 K (760 °C) was observed to be having best combination of YS, UTS, hardness, toughness and ductility. © 2016 Elsevier B.V.

Materials Science and Engineering A

Evolution of phases in P91 steel in various heat treatment conditions and their effect on microstructure stability and mechanical properties

The present paper is the third of a series of papers devoted to the study of h-p spectral element methods for three dimensional elliptic problems on non-smooth domains using parallel computers. In this paper we provide error estimates, preconditioners and numerical results. The spectral element functions are fully non-conforming. We propose preconditioners on non-smooth domains which can be diagonalized using separation of variables technique. Optimal error estimates in terms of number of layers in the geometrical mesh and in terms of number of degrees of freedom are obtained. The method is easy to implement on a parallel computer and we briefly outline computational techniques. We give results of numerical simulations to confirm the theoretical estimates. Theoretical results have been also validated by computational experiments which are published independently in Dutt et al. (2014). © 2016 Elsevier Ltd. All rights reserved.

Computers and Mathematics with Applications

H-p spectral element methods for three dimensional elliptic problems on non-smooth domains, Part-III: Error estimates, preconditioners, computational techniques and numerical results

Present work aims to investigate the significance of thermal contact area between fins and tubes in a heat exchanger. The heat exchanger type selected for the study is a liquid-gas fin and tube heat exchanger. Four different cases namely I, II, III, and IV, based on a variable degree of thermal contact between fins and tubes are investigated. Case-I with 100% thermal contact area between the fin and tube is set as a reference to cases-II, III, and IV with a thermal contact area of approximately 70%, 50%, and 35%, respectively. Three-dimensional (3D) steady-state numerical models based on finite element method (FEM) are developed for the different cases studied. Conjugate heat transfer mechanism coupled with turbulent flow is simulated to elucidate temperature and velocity profiles. In order to develop a simplified model with desired physical phenomena, only gas-side flow over the fin is simulated in the present study. The performance of the heat exchanger is characterized in terms of overall heat transfer coefficient, Colburn j-factor, flow resistance factor, and efficiency index. Results obtained from numerical modeling are useful to examine the impact of the degree of thermal contact and to compare the performance of heat exchanger design in different cases. Comparative analysis indicates a significant influence of the degree of the thermal contact area between fin and tube on the overall performance. Case-I is found to have higher overall heat transfer coefficient of 47.332 W/(m2 K), higher efficiency index of 9.131 and lower flow resistance factor of 0.123 among the cases investigated and highlights the need for perfect thermal contact between fin and tubes to meet the application based requirements. © 2016 Elsevier Ltd

Applied Thermal Engineering

Influence of the degree of thermal contact in fin and tube heat exchanger: A numerical analysis

The aim of the present study is to characterize the flow patterns, propulsion efficiency and power requirements associated with a self-propelled-heaving thin flat plate in a quiescent medium. In this regard, a numerical model using a shifting discontinuous-grid and based upon multi-relaxation-time lattice Boltzmann method is developed to probe the resulting aerodynamics. The influence of kinematic parameters namely flapping Reynolds number Ref (20−100) and plunging amplitude β (0.2–1), and the density ratio ρ* (101−102) on forward flight is pursued. Depending on the kinematics, various periodic vortex shedding characteristics of the plunging plate are observed that lead to modification of the angle of attack as a result of wing-wake interaction and downward jet. The presence of strong vortex dipole at the trailing edge with an attached leading edge vortex are factors responsible for maximum thrust generation. A wing-wake interaction which occurs at low β and high Ref due to weak vortex dissipation and presence of vortex dipole at the trailing edge acting in tandem can lead to achieving high propulsion efficiency. Through surrogate modelling, a set of Pareto-optimal solutions that describe the tradeoff between efficiency and input power for forward flight is presented and offers insight into the design and development of next generation flapping wing micro-air vehicles. © 2016 Elsevier Ltd

Journal of Fluids and Structures

Flow patterns and efficiency-power characteristics of a self-propelled, heaving rigid flat plate

A translating discontinuous-grid-block model for moving boundaries of finite thickness based on multi-relaxation time version of lattice Boltzmann method has been developed. The implementation of this model to simulate moving boundary flows has been demonstrated for the cases of a cylinder in simple shear flow, a single rigid wing executing 'clap and fling' motion, and the propulsion of a plunging flat plate. A number of interpolation schemes of linear, quadratic and cubic natures are assessed around the discontinuous grid interface. It is shown that the implementation of a body-fitted refined mesh that moves along with the object reduces the spurious oscillations registered in the force and velocity measurements compared to a single coarse grid block. Moreover, use of multiple relaxation times helps overcome stability issues at high Reynolds number, normally encountered in the single-relaxation time model. Significantly, in the former model the same base grid could handle flows with good accuracy for 10 ≤ Re ≤ 1000. The proposed technique offers significant advantage in terms of capturing flow around moving solids at lower computational cost and simulation time as compared to the stationary discontinuous-grid-block method. © 2015 Elsevier Ltd.

Computers and Fluids

A shifting discontinuous-grid-block lattice Boltzmann method for moving boundary simulations

This paper proposes two dynamic modelling approaches for a planar parallel manipulator with a 3-PPR configuration. The planar configuration has three legs each with a Prismatic-Prismatic-Revolute [PPR] configuration where the first joint is actuated. These three legs are joined by an end-effector which is in the form of an equilateral triangle. The dynamics of the manipulator was derived using an energy based Euler-Lagrangian approach and the DeNOC (Decoupled Natural Orthogonal Complement) matrices. Both the formulations are elucidated and the resulting formulation are compared under similar conditions to validate them. © Springer Nature Singapore Pte Ltd. 2016.