Browsing by Author "Vishnu, O.S."

Now showing 1 - 7 of 7

Insights into the influence of microstructure on strength and damage progression in carbon/carbon composites
(SAGE Publications Ltd, 2025) Vishnu, O.S.; Pavan, G.S.
Microstructural features influence the mechanical properties and damage progression in advanced materials like Carbon/Carbon (C/C) composites. This study proposes a finite element-based framework to analyze the damage mechanism in unidirectional C/C composites incorporating the effects of fiber arrangement, microstructural defects, and fiber-matrix interface. A 3D Representative Volume Element (RVE) is developed, which consists of carbon matrix, randomly distributed carbon fibers, and pores. The pores in the microstructure are modeled as ellipsoids of varying size, shape, and orientation. Separate stress-based failure criteria and fracture energy-based evolution laws are prescribed for fiber, matrix, and fiber-matrix interface. A user-defined material subroutine (UMAT) is developed in the finite element software Abaqus to implement the initiation and progression of damage in the composite constituents. The homogenized stress-strain response is computed under different loading conditions, namely longitudinal, transverse, in-plane shear, and out-of-plane shear loading. The variation of transverse tensile strength with porosity is also examined, highlighting the influence of pore volume fraction on the mechanical performance of the material. The proposed numerical model is validated through comparison with the Chamis analytical model and with numerical and experimental results from the literature. The proposed framework adopts detailed modeling strategies harnessing the power of computation and individual failure criterion-evolution laws for reliable simulation of damage and strength evaluation of composite materials, which are extensively used in advanced aerospace and engineering applications. © The Author(s) 2025
Micromechanical Analysis of Carbon/Carbon Composites with Pore Characterization
(Springer Science and Business Media Deutschland GmbH, 2025) Vishnu, O.S.; Paul, J.; Pavan, G.S.
In this study, the elastic properties of carbon/carbon (C/C) composite are computed by incorporating the presence of pores. Microstructure of C/C composites is analysed using scanning electron microscope (SEM) images. The pores inside the C/C composite are characterized based on area, shape and dimensions. Thirty-six SEM images are analysed. Based on this analysis, a three-dimensional RVE of C/C composite is constructed. The number of pores, their size and spatial distribution in the RVE is given by the analysis. Carbon fibres inside the representative volume element (RVE) are generated using the random sequential adsorption algorithm (RSA). Once the model is generated, periodic boundary conditions are imposed on the RVE model using Python script in Abaqus CAE. Effective elastic properties of C/C composites are computed using the finite element analysis (FEA)-based homogenization method. The effect of pore size distribution on the elastic properties of C/C composite can be understood from this study. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Microstructure Characterization and Effective Elastic Properties of Carbon/Carbon Composites
(Springer Science and Business Media Deutschland GmbH, 2024) Vishnu, O.S.; Pavan, G.S.
In this research, the effective elastic properties of C/C composites are evaluated using FEA-based homogenization technique. The FEA-based homogenization procedure is carried out by generating a Representative Volume Element (RVE). The features in the microstructure are observed with the help of Scanning Electron Microscopy (SEM) images. A detailed study on the SEM images of C/C composites is carried out. The microstructure of C/C composite consists of carbon fibers and carbon matrix. The details obtained from the microstructure are used to generate the RVE of the C/C composite. Random Sequential Adsorption (RSA) algorithm is employed to insert the carbon fibers inside the RVE model. Periodic boundary conditions are imposed on the RVE model, and six different far-field strains are applied on the RVE. For each case of far-field strains, the effective response of the RVE model is evaluated. The effective elastic properties of C/C composites are obtained by combining the volume-averaged stresses of the RVE for each case of far-field strains. The results from the numerical study are compared with those from the Moriâ€“Tanaka method. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
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.
Multiscale numerical modeling of clay brick masonry under compressive loading
(Springer Science and Business Media Deutschland GmbH, 2024) Honnalli, S.; Vishnu, O.S.; Pavan, G.S.
Masonry is generally comprised of periodic arrangement of masonry unit bonded together with mortar. Masonry is a heterogenous material and exhibits orthotropic behavior. In this study, the elastic-inelastic behavior of brick masonry under compressive loading is predicted using Finite Element Analysis (FEA) based homogenization approach. A three-dimensional repetitive unit cell representing English bond brick masonry is adopted for the homogenization procedure. The proposed approach requires elastic properties, peak compressive and tensile stress, and strain at peak stress values of brick and mortar as the inputs. Material non-linearity in brick and mortar is modeled using concrete damage plasticity model present in ABAQUS software. Using the FEA-based homogenization approach, homogenized stress–strain response of brick masonry subjected to compressive loading (both, normal and parallel to bed joint) and shear loading are obtained. Failure of masonry due to progressive damage development in bricks and mortar joints when subjected to compressive loading is studied. A user-defined material (UMAT) code is developed based on homogenized stress–strain curves. This UMAT can be adopted as constitutive relationship for macro scale modeling of brick masonry using ABAQUS software. The performance of the UMAT is assessed by simulating compression test experiments performed on masonry assemblages found in the literature. The UMAT is found to be satisfactory in predicting the behavior of masonry under compression. © Springer Nature Switzerland AG 2024.
Numerical Modeling of Damage Behavior in Unidirectional Carbon/Carbon Composites
(Springer, 2025) Vishnu, O.S.; Pavan, G.S.
Carbon/carbon (C/C) composites are frequently employed in aerospace industries because of their outstanding mechanical properties at high temperatures. This study proposes a progressive damage development model for unidirectional C/C composites. C/C composite consists of carbon fibers and pyrolytic carbon matrix. A Representative Volume Element (RVE) incorporating the microstructural features is generated based on the Scanning Electron Microscopy (SEM) images of the C/C composite samples. The composite constituents, namely carbon fiber and pyrolytic carbon matrix, are modeled explicitly inside the RVE, and failure criteria are provided for the individual constituents. The damage model used in this study comprises damage initiation and evolution criteria. The carbon fibers are inserted inside the RVE using the Random Sequential Adsorption algorithm (RSA). The carbon fiber is modeled as a transversely isotropic material, and the damage initiation is based on the maximum stress criteria. The carbon matrix is considered as an isotropic material, and damage initiation inside the carbon matrix is based on modified von Mises stress criteria. The damage evolution criteria, which depend on the fracture energy of the material, are used to predict the post-peak behavior of the components following the onset of damage. The non-linear damage behavior of unidirectional C/C composite is studied under axial tensile loading conditions. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
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.