Faculty Publications
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Item 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.Item 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.Item 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.Item 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) 2025Item Predictive modeling of PMMA-based polymer composites reinforced with hydroxyapatite: a machine learning and FEM approach(Gruppo Italiano Frattura, 2025) Singh, R.K.; Verma, K.; Kumar, G.C.This research examines the mechanical characteristics of polymer composites (PMMA) that are reinforced with Hydroxyapatite (HAp), with a particular emphasis on the Elastic Modulus and Compressive Strength. The investigation employs a multifaceted approach that integrates experimental methods, micromechanical analysis, and machine learning techniques. Experimental assessments of Elastic Modulus and Compressive Strength were conducted at various HAp concentrations (5%, 15%, and 30%) and were compared with theoretical predictions derived from Representative Volume Element (RVE) and micromechanical frameworks, including Voigt and Reuss bounds. Various machine learning algorithms, such as Feedforward Neural Network (FFNN), Radial Basis Neural Network (RBNN), and Support Vector Machine (SVM), were used to predict the mechanical properties. The RBNN exhibited high accuracy (R² = 0.92; MAE = 0.05) for intermediate HAp levels (20-30%) but displayed instability at the extremes % of reinforcements values . The FFNN consistently provided lower estimates of the properties, whereas the SVM yielded robust and stable predictions that closely matched both experimental and theoretical results with the error of (2-5) % (Result value). This research highlights the effectiveness of integrating micromechanical modeling with machine learning to improve the prediction and comprehension of composite behavior, thereby offering valuable insights for the design and application of advanced materials. © 2025, Fracture Structural Integr. All rights reserved.Item Experimental and Numerical Investigation of the Performance of Luffa Fiber-Reinforced Natural Rubber Composites with Process Parameter Optimization using DOE(Korean Fiber Society, 2025) Gurjar, A.K.; Kulkarni, S.M.; Joladarashi, S.; Doddamani, S.Composite materials have gained significant attention due to their high strength-to-weight ratio and sustainability. In particular, natural fiber-reinforced composites are increasingly investigated as environmentally friendly alternatives to synthetic counterparts. This study focuses on fabricating lightweight and biodegradable luffa fiber-reinforced natural rubber (LNR) composites using compression molding, emphasizing optimizing key processing parameters—temperature, curing time, and compression pressure. Latex-form natural rubber was selected as the matrix owing to its biodegradability, low cost, and compatibility with natural fibers. In contrast, luffa fiber served as reinforcement due to its favorable mechanical properties. The Design of Experiments (DOE) approach, specifically Taguchi’s method, was employed to systematically analyze the influence of processing parameters on physical and mechanical performance. Experimental evaluation of mechanical properties was conducted according to ASTM standards. The rule of mixture was used to evaluate the mechanical properties analytically. The multiscale material modeling finite element (FEM) methods were used to assess the orthotropic properties using the representative volume element technique. Results showed that density was only marginally affected by processing conditions, with ROM and FEM generally overestimating values; however, FEM provided closer agreement to experimental data. Shore A hardness and longitudinal modulus highly depended on curing temperature and time, with optimal properties obtained at 100 °C for 15 min under 1.0 MPa pressure. Similarly, the maximum ultimate tensile strength (0.40 MPa) was achieved under the same conditions, attributed to enhanced fiber–matrix bonding and crosslinking. Statistical analysis (ANOVA) confirmed temperature as the most influential parameter, followed by pressure and curing time. Optimized processing conditions significantly improved fiber–matrix adhesion, resulting in superior mechanical performance. These findings provide reliable processing guidelines for developing high-performance, environmentally sustainable LNR composites, making them suitable for high-impact applications in defense and consumer sectors. © The Author(s), under exclusive licence to the Korean Fiber Society 2025.