Now showing 1 - 10 of 36
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    Geometry Controlled Oscillations in Liquid Crystal Polymer Films Triggered by Thermal Feedback
    (12-04-2023)
    Jayoti, Divya
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    Peeketi, Akhil Reddy
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    Kumbhar, Pramod Yallappa
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    Light-induced oscillatory behavior of liquid crystal polymer network (LCN) films has been demonstrated by several researchers in the past decade. Similarly, oscillations in LCN films under constant thermal stimulus have been reported recently, although the mechanism and the factors that govern the oscillatory behavior are not well understood. In this work, we study the dynamics of self-sustained oscillations exhibited by LCN films under a constant thermal stimulus through experiments and simulations. Geometrically asymmetric films such as a right triangle and an equilateral triangle are obtained from a twisted nematic square film. A multiphysics computational framework using the finite element method is developed to simulate the oscillatory behavior of the LCN films kept on a hot plate. The framework accounts for a coupling between heat transfer and mechanical deformations during the oscillations. Small temperature fluctuations (≈ 1 °C) coupled with gravity induced torque are shown to drive the oscillatory behavior at a specific plate temperature. We show for the first time that self-sustained oscillations can also be achieved in symmetric shapes, such as square films, by creating a thickness tapering between two opposite edges. The frequency of the oscillations is found to be in the range of 0.5 to 2.5 Hz for different geometries studied. The oscillation temperature depends on the mean thickness, size, and thickness profile of the films. As a possible application, we demonstrate a thermally actuated optical chopper using the oscillatory response of the films.
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    Material identification for improving the strength of silica/SBR interface using MD simulations
    (01-09-2020)
    Joseph, Edwin
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    Comprehensive molecular dynamics simulations are conducted to identify material modifications which can improve strength and reduce hysteresis losses at the nanointerfaces formed between silica, silane coupling agent (SCA) and styrene-butadiene rubber (SBR), all of which are important ingredients of green tyres. Improving strength and reducing hysteresis losses at such interfaces are expected to reduce rolling resistance (RR), consequently lowering greenhouse emissions. Various modifications considered in this work include a variety of SBR blends, several SCA and surface occupancies of SCA on the silica surface. To tackle a large number of combinations possible and identify modifications which may improve the nature of the interfaces, a hierarchical computational framework is developed. The reduced sample space of such material modifications may be more amenable to comprehensive and computationally or experimentally expensive studies. It was found that some amino-based SCA in combination with certain blends of SBR can improve the interfaces strength and lower hysteresis losses, when compared to the commonly used bis[3-(triethoxysilyl)propyl]tetrasulfide (TESPT), which is a sulphur-based SCA.
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    Calla Lily flower inspired morphing of flat films to conical tubes
    (01-06-2023)
    Peeketi, Akhil R.
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    Sol, Jeroen A.H.P.
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    Schenning, Albert P.H.J.
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    Debije, Micheal G.
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    Recently researchers have developed soft actuators capable of morphing into complex shapes taking inspiration from nature. In this paper, we have developed a splay-nematic liquid crystal polymer network tapered actuator that can morph from a flat film to a cone, mimicking the blooming of single petal Calla Lily flower. We have demonstrated the formation of conical tubes through finite element simulations and experiments. The influence of tapering and alignment orientations with respect to the edge of the film on the cones is analyzed through simulations. The design with tapering and splayed alignments oriented at 45° to the edge is found to be the optimal choice for forming conical tubes.
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    Corrigendum to “Insights into traction-separation phenomena of graphene-cis-1,4-polyisoprene interface using molecular dynamics†[Polymer 122 (2017) 280–295](S0032386117306080)(10.1016/j.polymer.2017.06.038)
    (16-10-2017)
    Jose, Jeeno
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    Varkey T., Bijo
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    The authors regret that there were errors in the calculation of the values of the work of adhesion. Consequently, the work of adhesion values in tables 2 and 3 have been corrected. These changes do not in any way alter the conclusions of this paper as well as the discussions. The corrections are shown below and have been updated on the online version. 1. Correction in Table 2 [Table presented] 2. Correction in Table 3 [Table presented]. The following values of work of adhesion are also corrected: 3.1. Section 3.2.1 (page 286), paragraph 1, line 20 The value 1.38 ± 0.2 (kcal/molÅ2) has been corrected to 0.138 ± 0.02 (kcal/molÅ2).3.2. Section 3.2.1 (page 287), paragraph 2, line 19 The value 1.99 (kcal/molÅ2) has been corrected to 0.199 (kcal/molÅ2).The authors apologise for any inconvenience caused.
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    Molecular Dynamics Simulation of Primary Damage in β-Li2TiO3
    (01-11-2018)
    Suhail, Mohammed
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    Puliyeri, Baldev
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    Chaudhuri, Paritosh
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    Displacement cascades were conducted on β-Li2TiO3 to determine threshold displacement energies and understand primary damage. Two different PKA energies and three different crystallographic directions were used for the study. Ti seemed to have the lowest threshold displacement energy. The evolution of the damage showed an oscillating behavior suggesting that subcascades form even for the low PKA energies considered in this work. This observation suggested that, either high angle scattering or short range channeling occurs during radiation damage. The primary damage was found to consist mainly of Li Frenkel pairs, OLi and LiO antisites. Almost all the defects showed a strong, identical dependence on the PKA direction, independent of the PKA energy. In particular, PKA directions of [100] produced maximum defects, while [001] the lowest. LiTi and TiLi showed directional dependence only for high energy cascades. The primary damage state had significant fractions of Lii close to O atoms, and Oi close to Li atoms. This observation suggests that Li atoms are trapped by O atoms due to Coulombic interactions. Such a trapping behavior may also be observed for positively charged T, thus reducing T yield. For the PKA energies and the time scales examined in this work, no clusters were found to occur.
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    Mapping of multiphase field model parameters to physical factors in order to simulate desired phase transformations
    (25-06-2023)
    Hussain, Umair
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    The multiphase field modelling is a powerful tool to understand sufficiently complicated material transformation phenomena. The numerical implementation of this modelling technique faced many challenges and finally Ohno and Matsuura (2009) provided a consistent model which overcame some of the numerical artifacts of its predecessors. However, the Ohno and Matsuura model has not had a robust numerical implementation. This difficulty in implementation is due to the complicated nature of equations that arise from the model. Furthermore, fitting the model for the desired problem needs a thorough understanding of the behaviour of the model parameters. Hence, this work uses an FEM based solver to understand the use of parameters in a multiphase field model and their effect on interface characteristics. Finally, it is shown how the parameters of the model can be tuned to simulate common types of phase transformation.
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    A phase-field model for crack growth in electro-mechanically coupled functionally graded piezo ceramics
    (01-01-2020)
    Mohanty, Shaswat
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    Kumbhar, Pramod Yallappa
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    The analysis and design of piezoelectric actuators and sensors require the understanding of their failure due to the coupled electromechanical interactions. We present a phase-field model for damage to capture the brittle fracture associated with piezoelectric ceramics. A homogeneous PZT-4 specimen is used to demonstrate the interaction of various geometric parameters and polarization direction on the growth and arrest of a crack. In addition, the effect of holes and their arrangement on the fracture load is also discussed to assist in topology optimization. It was found that an ordered arrangement of holes could enhance the reliability of these ceramics more than a single hole with a similar amount of material removed. Finally, the functional gradation of material properties is modelled to understand the fracture in a piezoelectric composite containing PZT-4 and BaTiO3. The effect of the relative orientation of the material with respect to the polarization direction, on the fracture load is studied to improve the life of such piezoelectric composites. The resistance of fracture is found to be the maximum when the crack propagates into the tougher region of the domain. Whereas, the field enhances the fracture load irrespective of its magnitude when the gradation of material properties for the PZT-4/BaTiO3 ceramic is along the polarization direction. The aim of the study is to identify the factors that arrest crack propagation by analyzing the coupled system for the better design of piezoelectric sensors and actuators.
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    Primary radiation damages in Li2TiO3 and Li4SiO4: a comparison study using molecular dynamics simulation
    (01-01-2022)
    Sahoo, Deepak Ranjan
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    Chaudhuri, Paritosh
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    Molecular dynamics simulations are conducted on β-Li (Formula presented.) TiO (Formula presented.) and Li (Formula presented.) SiO (Formula presented.) to compare several of their radiation damage-related properties at 0 K. Overall, Li (Formula presented.) TiO (Formula presented.) was found to be more tolerant to irradiation damage than Li (Formula presented.) SiO (Formula presented.), which is in qualitative agreement with recent experiments. For instance, Li (Formula presented.) TiO (Formula presented.) was found to amorphize at 0.55 dpa, while Li (Formula presented.) SiO (Formula presented.) amorphized at 0.25 dpa itself. Including the polarization of the O atom while modeling cascades in Li (Formula presented.) TiO (Formula presented.) was found to predict a more realistic cascade behavior and defect production. The threshold displacement energies and diffusion coefficients of atoms were calculated for both the materials. Li diffusion was found to be highest when compared to other atoms. For Li (Formula presented.) SiO (Formula presented.), the existing interatomic potential predicted an Li diffusion coefficient which is nearly two orders of magnitude higher than what is seen for Li (Formula presented.) TiO (Formula presented.). Moreover, this potential predicted Li diffusion at temperatures as low as 583K, making it impossible to compare finite temperature primary damage with Li (Formula presented.) TiO (Formula presented.).
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    Role of recombination kinetics and grain size in radiation-induced amorphization
    (27-12-2012) ;
    Morgan, Dane
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    Szlufarska, Izabela
    Using a rate theory model for a generic one-component material, we investigated interactions between grain size and recombination kinetics of radiation-induced defects. Specifically, by varying parametrically nondimensional kinetic barriers for defect diffusion and recombination, we determined the effect of these parameters on the shape of the dose to amorphization versus temperature curves. We found that whether grain refinement to the nanometer regime improves or deteriorates radiation resistance of a material depends on the barriers to defect migration and recombination, as well as on the temperature for the intended use of the material. We show that the effects of recombination barriers and of grain refinement can be coupled to each other to produce a phenomenon of interstitial starvation. In interstitial starvation, a significant number of interstitials annihilate at the grain boundary, leaving behind unrecombined vacancies, which in turn amorphize the material. The same rate theory model with material-specific parameters was used to predict the grain-size dependence of the critical amorphization temperature in SiC. Parameters for the SiC model were taken from ab initio calculations. We find that the fine-grained SiC has a lower radiation resistance when compared to the polycrystalline SiC due to the presence of high-energy barrier for recombination of carbon Frenkel pairs and due to the interstitial starvation phenomenon. © 2012 American Physical Society.
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    Development of User Element Routine (UEL) for Cell-Based Smoothed Finite Element Method (CSFEM) in Abaqus
    (01-03-2020)
    Kumbhar, Pramod Y.
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    Francis, A.
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    In this paper, we discuss the implementation of a cell-based smoothed finite element method (CSFEM) within the commercial finite element software Abaqus. The salient feature of the CSFEM is that it does not require an explicit form of the derivative of the shape functions and there is no need for isoparametric mapping. This implementation is accomplished by employing the user element subroutine (UEL) feature in Abaqus. The details on the input data format together with the proposed user element subroutine, which forms the core of the finite element analysis are given. A few benchmark problems from linear elastostatics in both two and three dimensions are solved to validate the proposed implementation. The developed UELs and the associated input files can be downloaded from https://github.com/nsundar/SFEM-in-Abaqus.