Department of Mechanical Engineering

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In the present investigation, a detailed microstructure and mechanical behaviour study for P91 welded joint were investigated. The welded joint was produced using the Gas Tungsten Arc welding (GTAW) process with dissimilar Ni-based filler IN625 (ERNiCrMo-3). For microstructure characterization of the weld joint, optical microscopy and scanning electron microscopy were utilized. The effort was made to get a relationship between microstructure and mechanical properties variation. The residual stress measurement was also carried out for both the condition by using the hole-drilling method. To evaluate the mechanical properties, tensile testing and Charpy testing was done at room temperature. The weld joint developed with dissimilar Ni-based filler processes the austenitic microstructure having equiaxed dendrites in bulk weld metal and columnar and cellular dendritic structure near the interface. The segregation of the alloying elements like Mo and Nb was also confirmed along the inter-dendritic areas. The welded joint qualified the tensile test and Charpy test with average value of 580 ± 12 MPa and 65 ± 5 J, respectively in as-welded. However, a reduction was observed in tensile strength and Charpy toughness after the PWHT. A significant variation in microhardness was measured across the welds joint, and peak hardness was measured about 344 HV in the coarse-grained heat affected region while in weld metal it was 263 HV. The peak hardness value in HAZ and variation in hardness also get reduced after the PWHT. In the weld metal, a significant variation in the residual stresses was measured along the thickness with peak magnitude 250 MPa and 172 MPa for longitudinal and transverse stress, respectively in the as-welded condition. A significant reduction in peak residual stresses (longitudinal stress and transverse stress) was obtained after the PWHT. © 2021 Elsevier Ltd

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International Journal of Pressure Vessels and Piping

Role of dissimilar Ni-based ERNiCrMo-3 filler on the microstructure, mechanical properties and weld induced residual stresses of the ferritic/martensitic P91 steel welds joint

The objective of the current investigation to carry out a detailed research study on the relationship of microstructure and mechanical properties of the dissimilar Gas Tungsten Arc Weld (GTAW) joint of heat-resistant ferritic/martensitic P91 and austenitic SS304H steel, prepared using the Ni-grade ERNiCrMo-3 filler. The metallographic characterization of the weldments (P91 HAZ, weld metal, SS304H HAZ) was performed by availing the optical microscope and scanning electron microscope equipped with energy dispersive spectroscopy for precipitate size, their distribution in matrix, morphology and chemical composition. Mechanical properties of the weldments were also evaluated and for that, tensile testing, microhardness testing and Charpy testing were conducted. The metallographic and mechanical characterization of the weldments were also performed after the post-weld heat treatment (PWHT) at 775 °C for 60 min and compared with the as-welded condition. The results indicated that a complete heterogeneous microstructure formation across the weldments which led to variation in the mechanical behaviour of the weldments. The tensile strength and Charpy impact toughness (CIT) of the weld metal were measured 631 MPa and 79 J, respectively, in the as-welded condition. The coarse-grained HAZ region of P91 side showed the peak hardness of 412 HV (as-welded), which was higher than the hardness of the weld metal (303 HV). After the PWHT, an improvement in tensile properties was observed and tensile strength and % elongation was measured 666 MPa and 16.14 %, respectively. After the detailed study, it was concluded that the GTAW process with ERNiCrMo-3 filler offered a better combination of the microstructure and mechanical properties in as-welded condition for the dissimilar welded joint of P91 and SS304H. © 2021 The Society of Manufacturing Engineers

Journal of Manufacturing Processes

Role of the Ni-based filler (IN625) and heat-treatment on the mechanical performance of the GTA welded dissimilar joint of P91 and SS304H steel

This paper aims to investigate the effect of different weld groove configurations on the residual stresses dispersed in 40 mm thick multipass high strength low alloy (HSLA) steel butt-welds. Two welded joints having double-V type groove geometry were prepared, one of which had an equal double-V groove, and the other had an unequal double-V groove appearance. The locked-in residual stresses present in the weld zone and heat-affected zone (HAZ) were evaluated using both computational and experimental approaches. Furthermore, the effect of restrained condition on the trend of residual stresses of the equal double-V groove weld was analyzed using computational modeling technique with varying weld pass sequence. Lastly, a feasibility study was conducted on the implementation of mechanical tensioning technique to mitigate the weld-induced residual stresses in thick multipass butt-welded joints. The findings show that using an unequal-V groove joint can effectively reduce residual stress levels in the bottom half of the weld. A restrained welding condition with a single directional weld pass sequence can adversely impact the intensity of residual stresses across the weldment. The transverse residual stress levels can be reduced in the weld zone and its vicinity by an amount equal to the corresponding applied mechanical lateral tensioning load.

JOURNAL OF MANUFACTURING PROCESSES

Residual stress distribution in thick double-V butt welds with varying groove configuration, restraints and mechanical tensioning

Dielectric elastomer minimum energy structure (DEMES) formed by clinging a pre-stretched dielectric elastomer (DE) membrane to the compliant frame possess both material and geometrical nonlinearity. The viscous and hyperelastic nature of the DE membrane and coupling between the compliant frame and membrane forms the basis of these nonlinearities. Practically, DE membrane based DEMES actuator executes the transient motion which is significantly affected by the viscoelastic behavior of the DE membrane. Hence, for an efficient design of such devices, it is very important to analyse the effect of membrane viscoelasticity on the dynamic response of DEMES. In the present work, we have developed an analytical model to analyse the viscoelastic effect of DE membrane on the nonlinear dynamic behavior of the DEMES. In order to incorporate the viscous effect, the Zener rheological model consisting of a spring element connected in parallel to a Maxwell element is employed. The neo-Hookean material model based on the additive decomposition of the isotropic strain energy density into equilibrium and viscous parts is considered. The governing differential equation representing the dynamic behavior of DEMES actuator is derived using Euler–Lagrange equation of motion for non-conservative system. The isotropic viscous stretch is obtained by using the thermodynamically consistent evolution equation. The developed dynamic model predicts the initial shape, DC and AC response, periodicity of the DEMES for different values of viscosity parameter. The result reveals that the onset of equilibrium state delays as viscosity parameter increases. Further, the bending angle of DEMES actuator is significantly affected by the applied electric field and viscoelastic behavior of the DE membrane. Poincaré maps along with phase diagrams are presented to analyse the periodicity of nonlinear oscillation of the system. Further, the structure executes a stability transition (stable-unstable-stable) as the value of viscosity parameter increases. The obtained results can help in robust and efficient designing of DEMES based actuators subjected to dynamic loading. © 2020 Elsevier Ltd

International Journal of Solids and Structures

Effect of viscoelasticity on the nonlinear dynamic behavior of dielectric elastomer minimum energy structures

In view of their unique shape morphing behaviour, dielectric elastomer-based minimum energy structures (DEMES) have received an increasing attention in the technology of electroactive soft transduction. Because several of them undergo a time-dependent motion during their operation, understanding their nonlinear dynamic behaviour is crucial to their effective design. Additionally, in the recent past, there has been a growing scientific interest in imparting anisotropy to the material behaviour of dielectric elastomers in view of ameliorating their actuation performance. Spurred with these ongoing efforts, this paper presents an analytical framework for investigating the nonlinear dynamic behaviour of aniso-visco-hyperelastic DEMES actuator with an elementary rectangular geometry. We use a rheological model comprising two Maxwell elements connected in parallel with two single spring elements for modelling the material behaviour of the DE membrane. The governing equations of motion for the underlying non-conservative system are then derived using the Euler–Lagrange equation. The proposed model is used for building insights into the attainable equilibrium states, periodicity of the response as well as the resonant behaviour of the DEMES actuator over a feasible range of anisotropy and viscosity parameters. Our results reveal that the DEMES with hyperelastic material properties exhibits a supercritical pitchfork bifurcation of equilibrium state which is further accelerated in terms of attained equilibrium angle due to membrane anisotropy. A significant enhancement in the equilibrium angle attained by the structure with the extent of membrane anisotropy parameter is observed, indicating a favourable impact of material anisotropy. Poincare maps and phase-portraits are presented for assessing the periodicity of the nonlinear oscillations. The frequency response of the actuator for a combined DC and AC load indicates an upsurge in the resonant frequency with an increase in anisotropy parameter. The underlying analytical model and the trends presented in this study can find their potential use in the design and development of the futuristic anisotropic DEMES actuators subjected to time-dependent actuation. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.

Nonlinear Dynamics

Nonlinear oscillations of electrically driven aniso-visco-hyperelastic dielectric elastomer minimum energy structures

This paper proposes a lying/sitting type lower-limb rehabilitation robot based on a three degrees of freedom spatial parallel kinematic manipulator namely “The Orthoglide” along with an actuated rotational degree of freedom at the end-effector for the purpose of lower-limb rehabilitation treatments. This rehabilitation robot is an end-effector/foot-plate based mechanism which controls the ankle-joint movements to assist physiotherapists in performing therapeutic treatments along with a passive orthosis (supporting system). The conceptual and detail design of the rehabilitation device is presented along with its kinematics. Further, the functional validation of the proposed robot in terms of the kinematic motion capabilities to provide physiological motions like knee flexion-extension, hip adduction-abduction and hip flexion-extension are also investigated. The required safety features for the proposed rehabilitation robot in terms of mechanical constraints and non-actuated joints are also discussed. © 2021, Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

A New Sitting-Type Lower-Limb Rehabilitation Robot Based on a Spatial Parallel Kinematic Machine

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Resonance

Editorial

Latent heat, undoubtedly the most important component of the Earths’ energy cycle, serves two major purposes, cools the natural bodies and controls weather. Timely and accurate measurement of the evaporation rate is, therefore, of paramount interest. Unfortunately, the time needed to measure such a slow process is an hour at the least. In this era of real-time data analysis, there is a need for quick measurement of this parameter. Here we present a unique way to quickly measure the evaporation rate of water. The time duration of the measurement varied between 2.5 and 6 min; this temporal resolution opens new opportunities in the area of plant sciences. The effect of varying atmospheric conditions, including wind speed and Sun-like radiation, were also studied. We also proposed a reduced-order mathematical model for evaporation, whose results agreed reasonably well with those measured in the experiments. The device is easy-to-use, simple to construct, and portable. Considering these benefits, the proposed device can become an integral part of the weather stations and will improve the analysis of the real-time energy distribution at the earths’ surface. © 2020 Elsevier B.V.

Journal of Hydrology

A fast method to measure the evaporation rate

Micro pressure sensors generally employ diaphragm as the sensing element which converts the applied pressure into appropriate displacement. The displacement can be further used for sensing the actual physical phenomena viz., pressure or force with different transduction techniques. The transduction mechanism could be piezoresistive, capacitive, piezoelectric or resonant, etc. It is utmost essential to comprehend the behaviour of the structural element before its design with respect to transduction technique. The parameter optimization of diaphragm is the prime challenge in order to achieve the unsurpassed performance of the device. In this work, three of the diaphragm geometries namely a square diaphragm, a rectangular diaphragm and a circular diaphragm are considered for structural analysis. The displacement and stress analysis of the structures are carried out and investigated with the help of finite element-based simulation. The performed analysis will be useful in the selection of pressure sensor which provides optimized sensor geometry for required sensitivity, linearity, output range and area. © 2021 Elsevier Ltd. All rights reserved.

Materials Today: Proceedings

Mathematical modeling of different diaphragm geometries in MEMS pressure sensor

Micro-EDM (electro-discharge machining) is a derived form of EDM process especially evolved for micro-machining. The machining and removal of nonconducting materials are performed in EDM by providing an auxiliary conductive layer (assisting electrode), which is recreated after every spark discharge. Hence, an assisting conductive layer is formed on the workpiece surface to begin the spark erosion process. A robust model deducing the spark gap in a single discharge in μ-EDM needs to be designed to evaluate various phenomena in the pre-breakdown period. It is to be understood that the gap phenomenon in EDM involves various variables and is highly complicated. Numerous improved simulations have been performed to further discover and contribute towards modifications in EDM technology. Recent work provides new insights and challenges based on existing theories on the interelectrode gap as well as the spark discharge associated with the EDM phenomenon. © 2021 Elsevier Ltd. All rights reserved.