Department of Mechanical Engineering

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IIT Jodhpur

Electrically driven dielectric elastomer actuators (DEAs) are susceptible to an electromechanical instability because of a positive feedback between the applied electric field and the concomitant reduction in thickness of the membrane. This paper investigates the effect of material anisotropy on the dynamic electromechanical instability of a dielectric elastomer actuator when subjected to DC and AC voltage signals. We use a computationally efficient energy based Hamiltonian approach, which relies on the energy balance at the position of maximum overshoot in an oscillation cycle, for extracting the DC dynamic instability parameters of a biaxially prestretched anisotropic DEA. Analytical solutions are obtained for static and DC dynamic instability parameters. The AC dynamic instability fields are extracted by numerically integrating the differential equations of motion devised using the Euler-Lagrange equation. The trends of variation of the thickness stretch and electric field on the onset of static and dynamic pull-in instability with the material anisotropy parameter are presented. The results demonstrate a significant enhancement in the deformation and electric field on the onset of electromechanical instability with increase in the anisotropy parameter. The results of the present investigation can find potential application in the development and design of the dielectric elastomer actuator subjected to transient loading. © 2018 IOP Publishing Ltd.

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Smart Materials and Structures

Effect of anisotropy on the dynamic electromechanical instability of a dielectric elastomer actuator

In the present research work, P91 steel plates of thickness 18 mm were welded using the shielded metal arc welding process. The welded steel plate subjected to different heat treatment condition including post weld heat treatment (760 °C for 2 h, followed by air cooling) and re-austenitizing (1040 °C for 60 min and air cooled) and tempered (760 °C for 2 h, followed by air cooling). The heat treatments were referred as the PWHT and PWNT. The creep sample was prepared to form the welded and heat treated plate. The creep tests were performed at 620 °C for stresses of 150 and 200 MPa. The weld fusion zone and fine-grained heat affected zone of the crept sample were characterized using the field emission scanning electron microscope (FESEM). The fracture surface morphology of crept sample was also studied using the FESEM. The maximum creep exposure time was measured for the PWNT sample as a result of homogeneous microstructure across the weldments. © 2018

Engineering Failure Analysis

Fracture behaviour of crept P91 welded sample for different post weld heat treatments condition

Effect of ‘double austenitizing’ (DN) on microstructure evolution and mechanical properties of martensitic 9Cr–1Mo–V–Nb (P91) steel were studied and compared with the ‘conventional normalizing’ (CN) process. In CN treatment, P91 steel is normalized at 1050 °C for 1 h, finally air cooled. In DN treatment, the first stage of normalizing was performed at 1050 °C/1 h/air cool. The second stage of normalizing was performed in the temperature range of 950–1150 °C for 1 h (950 °C-DN1, 1050 °C-DN2, 1150 °C-DN3), followed by water quenching. The grain size was measured 42 and 35 µm for CN and DN1 treatment, respectively. The double normalizing (DN) produced complete martensitic microstructure as a result of complete dissolution of precipitates. In DN-based heat treatment, optimized microstructure and mechanical properties were obtained for the sample that normalized at 950 °C, followed by water quenching. © 2019, ASM International.

Metallography, Microstructure, and Analysis

Role of Heat Treatment on Grain Refinement and Microhardness of 9Cr–1Mo–V–Nb Steel

APS Division of Fluid Dynamics Meeting Abstracts, G17.

CFD-ready Turbulence Models from Gene Expression Programming: Concepts

University of Melbourne

Turbulence Model Development and Implementation for Low Pressure Turbines Using a Machine Learning Approach

Energetic materials are the reactive materials containing fuels and oxidizers that can liberate chemical energy preserved in their molecular structure. Nano-energetic materials have found to be the potential sources for extremely high heat release rates, tailored burning rate, extraordinary combustion efficiency, and reduced sensitivity. These materials play a vital role in defense applications as a recent advancement in emerging areas such as manufacturing of explosives, solid and liquid propellants, rocket propelling, advanced gun propellant materials. Considering the immense scope of these functional materials, this chapter focuses to cover the fundamental aspect of energetic materials, description of contemporary reported literature on design and synthesis of nano-energetic materials and their significance for microscale applications in the defense sector. © 2019, Springer Nature Singapore Pte Ltd.

Energy, Environment, and Sustainability

Nano-energetic Materials for Defense Application

We report a simple device that generates synchronized mechanical and electrical pressure waves for carrying out bacterial transformation. The mechanical pressure waves are produced by igniting a confined nanoenergetic composite material that provides ultrahigh pressure. Further, this device has an arrangement through which a synchronized electric field (of a time-varying nature) is initiated at a delay of ≈85 μs at the full width half-maxima point of the pressure pulse. The pressure waves so generated are incident to a thin aluminum-polydimethylsiloxane membrane that partitions the ignition chamber from the column of the mixture containing bacterial cells (Escherichia coli BL21) and 4 kb transforming DNA. A combination of mechanical and electrical pressure pulse created through the above arrangement ensures that the transforming DNA transports across the cell membrane into the cell, leading to a transformation event. This unique device has been successfully operated for efficient gene (∼4 kb) transfer into cells. The transformation efficacy of this device is found comparable to the other standard methods and protocols for carrying out the transformation. © 2019 American Chemical Society.

Fulltext

ACS Omega

Synchronized Electromechanical Shock Wave-Induced Bacterial Transformation

This paper presents a novel image-based path-planning and execution framework for vision-based control of a robot in a human centered environment. The proposed method involves applying Rapidly-exploring Random Tree (RRT) exploration to perform Image-Based Visual Servoing (IBVS) while satisfying multiple task constraints by exploiting robot redundancy. The methodology incorporates data-set of robot's workspace images for path-planning and design a controller based on visual servoing framework. This method is generic enough to include constraints like Field-of-View (FoV) limits, joint limits, obstacles, various singularities, occlusions etc. in the planning stage itself using task function approach and thereby avoiding them during the execution. The use of path-planning eliminates many of the inherent limitations of IBVS with eye-in-hand configuration and makes the use of visual servoing practical for dynamic and complex environments. Several experiments have been performed on a UR5 robotic manipulator to demonstrate that it is an effective and robust way to guide a robot in such environments. © 2019 IEEE.

2019 28th IEEE International Conference on Robot and Human Interactive Communication, RO-MAN 2019

A Novel Image-based Path Planning Algorithm for Eye-in-Hand Visual Servoing of a Redundant Manipulator in a Human Centered Environment

Due to high degrees-of-freedom of humanoids and induced redundancy, there are multiple ways of performing a given manipulation task. Finding optimal ways of performing tasks is one desirable property of any motion planning framework. This includes optimizing both the path with respect to a certain objective function and also the final pre-grasp or goal position. Additionally, a variety of constraints need to be satisfied such as stability, self-collision and collision with objects in the environment and also kinematic loop-closure formed during the task. In this paper, an asymptotically optimal sampling based approach for generating motion plans is presented. A novel constraint solver extension to the bidirectional Fast Marching Trees (BFMT*) algorithm in the form of a way-point generator is proposed such that it can be applied for whole-body motion planning of humanoids. Moreover, a comparison of the performance of the proposed extension of BFMT* and the state-of-art RRT* based motion planner is shown. A gradient based inverse kinematics solver has also been implemented in combination with an optimization technique to generate goal configurations in order to ensure optimality in the pre-grasp position. The efficacy of the proposed approach is evaluated in a simulation environment on Hubo+ robot model. The results show a significant improvement in path costs, as well as overall optimality of given tasks for the proposed approach. Additionally, rigorous analysis over the choice of planning algorithms considered in this paper is present for the considered scenarios. © 2019 Elsevier B.V.

Robotics and Autonomous Systems

Optimal whole-body motion planning of humanoids in cluttered environments

Windless environments are prevalent in greenhouses, where precise temperature control is critical to the health of plants and errors in temperature measurement must be avoided. A mathematical model based on heat balance is used to estimate the error in temperature sensors under different conditions and sensor geometries. The model is then applied to two geometries and solved numerically. The sensors used are a T-type thermocouple and a Sensirion SHT 75. Experiments are carried out in a greenhouse prototype to replicate conditions in a greenhouse and validate the error model. Active ventilation of the sensors is provided by a fan and passive ventilation is provided using a model built on the concept of a ‘solar chimney’. It is shown that even small flow rates can decrease the error shown by unventilated sensors by as much as 10°C. © 2019, Indian Academy of Sciences.