Department of Mechanical Engineering

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Ring core technique is widely used to measure the subsurface residual stresses in components. In the analytical evaluation of residual stresses by ring core technique, the calibration coefficients play the vital role for the correct estimation of residuals stresses. Calibration coefficients needed to evaluate the residual stresses by dry ring core technique have been determined with respect to varying ring core tool dimensions. The effect of the biaxial stress combinations and trepan tool diameters on the calibration coefficients was investigated. The trepanning effect of dry ring core process was also investigated through 3D finite element models. The finite element analysis was done to prepare a database of strains for the different stress combinations with respect to the depth of cut. After that the regression equations were developed to directly calculate the calibration coefficients for the material SS 304L. Furthermore, this finite element data was also used to develop the mathematical relations to calculate the residual stresses from the strain readings obtained in dry ring core process. Error estimation of residual stress calculation was also done for both analytical and regression models. The database of relations between residual stress and strains developed in the present study with respect to a given dimension of ring core tool was found to be adequate in estimating the residual stresses directly from the strain reading during dry ring coring. © IMechE 2017.

World University root node

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

To study the effect of stress magnitude and tool geometry on the calibration coefficients: Ring core technique

This paper aims to investigate the secondary flow characteristics and the associated vacuum generation caused with increase in the primary pressure ramping in zero-secondary flow ejectors. The sudden expansion of the primary jet into the diffuser during the ejector start-up results in flow separation from the shear layer formed between the primary and inducted flows and produces large recirculation bubbles in the top and bottom sides of the jet. These recirculation bubbles cause an induced flow from ambient air into the diffuser duct as well. The fluid supply from the reverse flow due to the shear layer separation and the induced flow from ambient air provide a counter momentum against fluid entrainment from a vacuum chamber. As a result of this, the initial vacuum generation process progresses in a slow rate. Thereafter, the primary jet expansion reaches a critical level and a rapid vacuum generation can be seen. It is found that with the jet expansion reaching a critical level, the fluid supply from the reverse flow is suddenly entrained back into the main jet at the maximum jet expansion point. This suddenly reduces the counter-momentum which has been prohibiting the entrainment of fluid from the vacuum chamber and results in rapid evacuation. This is followed by a stage in which the vacuum chamber pressure is increasing due to the attainment of a constant Mach number at the diffuser inlet and the jet pressure ramping. It is found that the secondary flow dynamics and the vacuum generation processes in rectangular and round ejectors show a close resemblance. © 2018 Author(s).

Fulltext

Physics of Fluids

Physics of vacuum generation in zero-secondary flow ejectors

Mechanical properties and residual stresses of friction stir welded and autogenous tungsten inert gas welded structural steel butt welds have been studied. Friction stir welding (FSW) of structural steel butt joints has been carried out by in-house prepared tungsten carbide tool with 20 mm/ min welding speed and 931 rpm tool rotation. Tungsten inert gas (TIG) welding of the butt joints was carried out with welding current, arc voltage and the welding speed of 140 amp, 12 V and 90 mm/min respectively. Residual stress measurement in the butt welds has been carried out in weld fusion zone and heat affected zone (HAZ) by using blind hole drilling method. The magnitude of longitudinal residual stress along the weld line of TIG welded joints were observed to be higher than friction stir welded joint. In both TIG and FSW joints, the nature of longitudinal stress in the base metal was observed to be compressive whereas in HAZ was observed to be tensile. It can be stated that butt welds produced with FSW process had residual stress much lower than the autogenous TIG welds. © 2018 Polish Academy of Sciences. All Rights Reserved.

Archives of Metallurgy and Materials

A comparative study of residual stress and mechanical properties for fsw and tig weld on structural steel

The welding of nuclear grade P91 and P92 steel plate of thickness 5.2 mm were performed using the autogenous tungsten inert gas (TIG) welding process. The welded joint of P91 and P92 steel plate were subjected to the varying post weld heat-treatment (PWHT) including the post weld heat treatment (PWHT) and re-austenitizing based tempering (PWNT). A comparative study was performed related to the microstructure evolution in fusion zone (FZ) of both the welded joint using the scanning electron microscope and optical microscope in a different condition of heat treatment. The hardness test of the FZ for both joints was also conducted in a different condition of heat treatment. P92 steel welded joint have observed the higher tendency of the δ ferrite formation that led to the great variation in hardness of the P92 FZ. The homogeneous microstructure (absence of δ ferrite) and acceptable hardness was observed after the PWNT treatment for both the welded joint. © 2018 Polish Academy of Sciences. All Rights Reserved.

Characterization of weld fusion zone for TIG welded p91 and P92 steels

A novel numerical framework for conducting linear stability analysis of two-dimensional steady laminar flows is presented. Using two case studies involving analysis of thermal and laminar flows, stability of laminar flows in the numerical sense is addressed. The two-dimensional base flow is computed by using the lattice Boltzmann method for various values of the controlling parameter (Reynolds number for flow past a square cylinder and Rayleigh number for double-glazing problem). Subsequently, the perturbed equations with two-dimensional disturbances are linearized and form a set of partial differential equations that govern the evolution of these perturbations. Using normal mode analysis, the eigenvalues of the resultant equation are used to determine the stablilty of the base flow. © 2018 by the authors of the abstracts.

International Conference on Computational Methods for Thermal Problems

A numerical framework for linear stability analysis of two-dimensional steady flows

Urea-formaldehyde microcapsules containing dicyclopentadiene (DCPD) were prepared by in-situ polymerization in an oil-in-water emulsion for self-healing of epoxy polymer. Microencapsulated DCPD healing agent was dispersed into epoxy matrix through ultrasonication to produce a polymer composite capable of self-healing and the effect of weight fraction of microcapsules on fracture properties of the composites was investigated. Composites having 0.5, 1. , and 1.5 wt. % of microcapsules were prepared. The virgin and healed fracture toughness of composite was measured using a single edge notched bending (SENB) specimen. An improvement of 78% in virgin fracture toughness was observed at 1.5 wt %. The fracture toughness of the composite after healing increased by 84%, 75% and 68% for the microcapsules wt.% of 0.5, 1 and 1.5 respectively in comparison to that of neat epoxy. Scanning electron microscopy of the fractured surface of composite was carried out to understand the various mechanisms responsible for the improvement in fracture toughness. © 2018 Elsevier Ltd. All rights reserved.

Materials Today: Proceedings

Effect of Self-Healing Dicyclopentadiene Microcapsules on Fracture Toughness of Epoxy

In this paper, a new family of 3-degree-of-freedom planar parallel manipulators (PPMs), namely U-shape fixed base PPMs starting with an active prismatic joint on each leg, is proposed. In order to identify the best manipulators of this family, comparative kinematic and dynamic performance studies are performed. The kinematic performances are quantified through the local performance index, namely the kinematic isotropy. From the kinematic isotropy analysis results, it is observed that PPR-PRP-PRP, PRP-PRP-PRP and PRR-PRP-PRP configurations have better kinematic design aspects compared to other configurations of this family of U-shape fixed base parallel configurations. Further, from the workspace analysis, it is observed that the PPR-PRP-PRP configuration has a higher value of workspace to the total area required ratio compared to other configurations. This paper also presents a comparative dynamic performance analysis of these top-three U-shape fixed base configurations in terms of dynamic driving performance measures, and energy requirements for three different (fixed base size of the manipulators) aspect ratios under two different loading conditions. From the analyses results, it is perceived that the PRP-PRP-PRP configuration is requiring lower energy and dynamic driving performances than others. These analyses are done with the help of multi-body dynamic software, namely MSC ADAMS, and the results are validated through the help of real-time experiments conducted on in-house fabricated prototypes of these three PPMs. In specific, the energy consumption is measured and compared in this study. Experimental results demonstrated that the PRP-PRP-PRP manipulator displays a considerably better performance in terms of minimum energy requirement. Copyright © Cambridge University Press 2018.

Robotica

Kinematic and dynamic performance investigations of asymmetric (U-shape fixed base) planar parallel manipulators

This paper presents a dual-loop control scheme based on an integral sliding mode control scheme for the task-space pose error correction in trajectory-tracking of a planar 3-PRP parallel manipulator due to mechanical inaccuracies. The proposed dual-loop control scheme uses redundant sensor feedback, i.e., individual active joint displacements, velocities (at the joint-space level) and, end-effector positions and orientation (at the task-space level) are obtained as feedback signals using appropriate sensors. Using the redundant feedback information, the actual pose errors of the end-effector are computed in the outer-loop (kinematic) control and rectified in joint-space inner-loop (dynamic) control to achieve the given desired task-space trajectory. To demonstrate the efficacy and show complete performance of the controllers, real-time experiments are executed on an in-house fabricated planar 3-PRP parallel manipulator. The experimentation results show that the manipulator tracing performance is considerably improved with the proposed dual-loop control scheme. In addition, the controller parameter sensitivity and robustness analyses are also accomplished. © 2017, Springer Science+Business Media Dordrecht.

Journal of Intelligent and Robotic Systems: Theory and Applications

Dual Integral Sliding Mode Control Loop for Mechanical Error Correction in Trajectory-Tracking of a Planar 3-PRP Parallel Manipulator

The existence of geometric errors (misalignment and kinematic errors) and joint clearances is an inherent problem in manipulators. In addition, friction between surfaces and gear backlash errors are unavoidable factors in manipulators using geared motors as their joint actuators. This paper presents a potential solution for the above issues through the application of a dual-loop control scheme. The proposed control scheme uses a redundant feedback strategy, i.e., individual joint displacements (at the joint space level) and, end-effector positions and orientation (at the task space level) are obtained as a feedback signal using appropriate sensors. Using this redundant feedback information, the actual error of the joint displacements are computed and rectified the desired joint space trajectory in joint-space trajectory tracking control to achieve the desired task space trajectory. To demonstrate the effectiveness and show overall performance of the controllers, real-time experiments are performed on an in-house fabricated 2-PRP+1-PPR planar parallel manipulator. The experiment results show that the manipulator tracking performance is significantly improved with the proposed dual-loop control scheme. In addition, the controller parameter sensitivity and robustness analyses are performed. © Springer International Publishing AG 2018.

Mechanisms and Machine Science

Dual-loop motion control for geometric errors and joint clearances compensation of a planar 2-PRP+1-PPR manipulator

The authors present a computational study of drop-train impingement on a smooth, initially dry surface, with the aim of providing a high-quality dataset to develop reliable spray-wall interaction submodels for engine simulations. Such submodels require information at micron scales, which is unfeasible to obtain experimentally under high-pressure engine conditions. However, supercomputing and high-resolution simulations can resolve thin liquid structures and their breakup, yielding accurate datasets for liquid splashing and film deposition. The current study employs an MPI-parallel multiphase flow solver to simulate surface impingement of a train of ethanol drops. Comparing its results to the experiments, the solvers capability in accurately capturing the sharp splashing threshold and splashed mass ratio was demonstrated. Through a computational technique that tags individual drops, further insight into the splashing dynamics postimpingement was gained, which could be used to formulate more sophisticated spray-wall interaction submodels. © 1999-2011 IEEE.