Faculty Publications

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    Pressure-induced variation of structural, elastic, vibrational, electronic, thermodynamic properties and hardness of Ruthenium Carbides
    (Elsevier Ltd, 2016) Harikrishnan, H.; Ajith, K.M.; Natarajan, S.; Chandra, S.; Mundachali Cheruvalath, V.
    Three of the five structures obtained from the evolutionary algorithm based structure search of Ruthenium Carbide systems in the stoichiometries RuC, Ru2C and Ru3C are relaxed at different pressures in the range 0-200 GPa and the pressure-induced variation of their structural, elastic, dynamical, electronic and thermodynamic properties as well as hardness is investigated in detail. No structural transition is present for these systems in this pressure range. RuC-Zinc blende is mechanically and dynamically unstable close to 100 GPa. RuC-Rhombohedral and Ru3C-Hexagonal retain mechanical and dynamical stability up to 200 GPa. For all three systems the electronic bands and density of states spread out with pressure and the band gap increases with pressure for the semiconducting RuC-Zinc blende. From the computed IR spectrum of RuC-Zinc blende at 50 GPa it is noted that the IR frequency increases with pressure. Using a semi-empirical model for hardness it is estimated that hardness of all three systems consistently increases with pressure. The hardness of RuC-Zinc blende increases towards the superhard regime up to the limiting pressure of its mechanical stability while that of RuC-Rhombohedral becomes 30 GPa at the pressure of 150 GPa. © 2016 Elsevier Ltd. All rights reserved.
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    Determining elastic properties of CSEB masonry using FEA-based homogenization technique
    (Elsevier Ltd, 2023) Shalini, S.; Honnalli, S.; Pavan, G.S.
    The world today is embracing a sustainable approach in all sectors. The construction industry is grappling with the problem of minimizing energy consumption and lowering carbon emissions involved in the manufacture of construction materials. Soil blocks are an alternative to fired clay bricks. Soil bricks are inexpensive, recyclable, environmentally friendly, and provide better thermal comfort. However, masonry walls built with soil blocks have several drawbacks. They are bulky, have poor durability properties and their strength capacity reduces significantly when saturated due to rain. The remedy for this problem is a Cement Stabilized Earth Block (CSEB). An engineered mixture of soil-sand-cement-moisture compacted at predefined levels offers superior strength and durability properties. The percentage of cement added is minimal in comparison to the soil-sand mixture content. In this study, a numerical model to predict the elastic properties of masonry comprised of CSEB and soil–cement mortar is developed. Both the constituents, CSEBs, and soil–cement mortar have different elastic properties. The presence of bed joints and perpends lends orthotropic behavior to masonry. The present study considers the Finite element analysis (FEA)-based homogenization technique to predict the elastic properties of CSEB masonry. A small periodic part of masonry called a repetitive unit cell (RUC) is considered, which is representative of the block-mortar arrangement in masonry. The three-dimensional masonry RUC is modelled using FE-based ABAQUS-CAE software. A user-defined Python script is developed to apply PBCs (Periodic boundary conditions) to RUC. The six far-field unit strains are applied to the RUC model in three normal and three shear directions. Finally, volume-averaged stress components are computed to determine the elastic properties. The modulus of elasticity and Poisson's ratio of CSEB masonry along three directions are determined. The proposed approach is governed by mechanics and not by empirical relationships and provides satisfactory results. © 2023
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    Multiscale Numerical Modeling of 2D C/C Composites Considering Pore Size Distribution
    (American Society of Civil Engineers (ASCE), 2024) Vishnu, O.S.; Pavan, G.S.
    This study proposes a multiscale numerical modeling procedure to evaluate the elastic properties of two-dimensional (2D) eight-harness satin woven carbon/carbon (C/C) composites. The multiscale modeling technique consists of analysis at the microlevel and mesolevel. In microscale analysis, a 3D representative volume element (RVE) of C/C composite with carbon fiber, pyrolytic carbon, and pores is considered. The microstructure of the C/C composite is analyzed using scanning electron microscope (SEM) images. Statistical characterization of pore distribution inside the C/C composite is performed, and different probability density functions are generated for pores' number, area, and aspect ratio inside the C/C composite. Carbon fibers and pores are inserted in the 3D RVE using the RSA algorithm. The size and shape of the pores inserted in 3D RVE are based on the probability density functions generated. Effective elastic properties of C/C composite at the microscale are computed by finite element analysis (FE) based homogenization and taken as input for the next level of homogenization. The RVE at mesoscale is modeled using the information from SEM images, and FE-based homogenization is performed to compute the effective elastic properties of 8HS woven C/C composite. The effective elastic properties obtained from the numerical study are validated with the results of the uniaxial tensile test performed on 2D C/C composite. The effect of fiber volume fraction, yarn volume fraction, and porosity on elastic properties of 2D 8HS woven C/C composite are also assessed and presented in this study. © 2024 American Society of Civil Engineers.
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    Experimental and numerical investigation on the elastic properties of luffa–cenosphere-reinforced epoxy hybrid composite
    (John Wiley and Sons Inc, 2024) Gurjar, A.K.; Kulkarni, S.M.; Joladarashi, S.; Doddamani, S.
    Estimating the elastic characteristics of natural fiber-reinforced polymer composites such as luffa fiber reinforced with epoxy is challenging. The structure of luffa cylindrica is complex, like a three-dimensional natural fibrous mat, netting-like structure. The multiscale modeling of such structures is the challenge to be addressed. The prime objective of this work is to determine the specific elastic properties of luffa–cenosphere-reinforced epoxy (LCE) composite, considering the effect of filler volume fractions. Furthermore, multiscale modeling techniques, such as representative volume elements (RVEs) of finite element techniques with chopped, unidirectional, plain, and twill weaving fiber arrangements, were employed. The longitudinal modulus, transverse modulus, shear modulus, and Poisson's ratio were predicted through these modeling approaches. However, experimental and analytical methodologies, including the rule of mixture and Halpin–Tsai, were considered to validate the finite element analysis results. The elastic characteristics of LCE composite were therefore shown to be enhanced by increasing filler volume fraction. However, the cenosphere's 20% volume fraction has the highest elastic properties as determined by analytical, experimental, and computational models. Analytical and finite element simulation results were compared with the experimental results, and based on the findings, the most suitable (unidirectional, chopped, plain, and twill weaving) RVE was identified for finite element modeling of LCE composite for the evaluation of elastic properties. Results from practical approaches and the RVE twill weaving model showed good agreement, with less than 1% error, compared to the other analytical and finite element methods. Highlights: NFCs are gaining ground in polymer composites. Overcoming challenges in modeling of luffa fiber inside epoxy matrix. The study uses multiscale modeling with diverse fiber arrangements. Experimental and analytical methods used to confirm FEA results. Increased cenosphere volume fraction boosts LCE composite properties. © 2024 Society of Plastics Engineers.
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    Numerical studies on modeling heterogeneity in elastic properties of 8HS woven C/C composites
    (Taylor and Francis Ltd., 2025) Vishnu, O.S.; Pavan, G.S.; R, S.; Thomas, A.
    The variation in fiber volume fraction and pores developed at the microscale during the manufacturing process is a source of heterogeneity in the elastic properties of woven Carbon/Carbon (C/C) composites. This study investigates the effect of heterogeneity on the elastic properties of Eight Harness Satin (8HS) woven C/C composites using a two-scale (micro–meso) finite element (FE) homogenization method. At the microscale, variations in fiber volume fraction and porosity are incorporated by generating 25 representative volume elements(RVEs) from the reconstructed CT scan images. The RVEs preserve the shape, size, orientation, and spatial distribution of pores that are present in the microstructure. The carbon fibers are virtually generated inside the 25 micro-RVEs using the random sequential adsorption (RSA) algorithm in accordance with the reconstructed microstructure of actual pores. At the mesoscale, the model incorporates warp and weft yarns embedded in a pyrolytic carbon matrix. Yarn heterogeneity is modeled by subdividing the meso RVE into smaller domains, each assigned elastic properties derived from the microscale RVEs. The degree of heterogeneity was varied using different combinations of the microscale RVEs to assign material properties. This approach effectively incorporates the randomness of the microstructure into the computation of the effective elastic properties of woven composites. The on and off-axis elastic properties of 8HS woven C/C composites are computed, and the results determined from the numerical study are compared with experimental tests conducted on 0° and 45° specimens. This study highlights the importance of fiber volume fraction and pores on material heterogeneity in accurately computing the elastic properties of 8HS woven C/C composites. © 2025 Taylor & Francis Group, LLC.
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    Thermoelastic buckling and vibration analysis of shear and normal deformable three-phase bio-inspired composite beams under axially varying temperature fields
    (Springer, 2025) Patil, H.H.; Pitchaimani, J.
    The thermoelastic buckling and free vibration behaviors of a Three-Phase Composite (TPC) beam subjected to axially varying Non-Uniform Temperature (NUFT) fields is investigated by incorporating Temperature-Dependent (TD) elastic properties of both Carbon Nanotubes (CNTs) and the matrix. The Shear and Normal Deformable Beam Theory (SNDBT) is used to model the kinematics, and the governing equations are formulated through Hamilton’s principle and solved using the Ritz method. TD elastic properties of CNTs are accounted in terms of TD Hill’s constants. Dispersion issue of CNT is accounted in terms of partial and complete agglomeration effects for more realistic material modeling. The results indicate that the area beneath the NUFT distribution profiles serves as a meaningful parameter for interpreting both the critical buckling temperature (?Tcr) and the induced axial membrane force (N). NUFT-induced differential thermal expansion generates localized thermal strain variations, and the strain reverses its sign whenever the temperature at a point exceeds the spatially averaged temperature for the given NUFT. Consideration of thickness-stretching deformation (Wz) produces noticeable changes in ?Tcr and the fundamental frequency (?1), particularly for the beams with lower aspect-ratio, emphasizing its necessity in thick-beam modeling. The findings provide practical guidance for the design of lightweight, thermally stable composite structures deployed in aerospace and other thermal-environment-critical engineering systems. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2025.