Faculty Publications
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Item Influences of dielectric and conductive fillers on dielectric and mechanical properties of solid silicone rubber composites(Springer London, 2019) Manohar Shankar, B.S.; Kulkarni, S.M.Dielectric elastomers are materials being used for electromechanical transduction applications. Their electromechanical response depends on permittivity, Young’s modulus and electric breakdown strength. A factor that limits its application is high operating voltages that can be reduced through improvement in permittivity. One of the methods is by incorporating high permittivity fillers into polymer matrix to obtain dielectric–dielectric composites (DDC).These composites show high permittivity at the cost of reduced flexibility. An alternative solution is development of composites by incorporating organic or inorganic conductive fillers into polymer matrix. These composites show high permittivity with high dielectric loss and low breakdown strength. To overcome both the above limitations both dielectric and conductive fillers are incorporated into dielectric polymer matrix to obtain conductor–dielectric composites (CDC). In this study, high temperature vulcanized solid silicone rubber as matrix has been used to prepare DDC composites with barium titanate (BT) filler and CDC composites with both BT as dielectric and ketjenblack as conductive fillers, using Taguchi design of experiments. The effect of factors such as amount of fillers and curing agent, mixing time in roll mill and curing temperature on the dielectric and mechanical properties are reported. Lichtenecker model predicts the permittivity of the DDC composite more accurately. For the CDC composites permittivity increased by 390%, effective resistivity decreased by 80%, Young’s modulus increased by 368% and Shore A hardness increased by 90% as compared to those of reference matrix. Important interaction effects are observed among both the fillers that are uniformly dispersed without any aggregation. © 2019, Iran Polymer and Petrochemical Institute.Item Effect of ketjenblack and barium titanate on the piezoresistive behaviour of silicone rubber particulate composites(IOP Publishing Ltd, 2021) Manohar Shankar, B.S.; Hiremath, H.; Kulkarni, S.M.In the present study, silicone rubber reinforced with ketjenblack and barium titanate were fabricated using high temperature compression molding method. These particulate composites are characterized for piezoresistive sensitivity. Ketjenblack and barium titanate are the conducting and dielectric fillers in the high temperature vulcanized silicone rubber matrix. The effects of ketjenblack and barium titanate fillers, filler loading, amount of curing agent, curing temperature and mixing time on the piezoresistive properties of these composites were investigated. The piezoresistive sensitivity recorded maximum values of 3.7(10-3) (kPa)-1 for dielectric and dielectric-conductive composites. The linear variation of normalized resistance change was observed for change in pressure up to 20 kPa. The dielectric composite sensitivity increases with reduction in dielectric filler and curing agent loadings, increasing with mixing time and curing temperature. The piezoresistive sensitivity for dielectricconductive composites depends on ketjenblack and barium titanate filler loading. These composites demonstrate interaction effects among the factors. © 2021 The Author(s). Published by IOP Publishing Ltd.Item An experimental study on adhesion, flexibility, interlaminar shear strength, and damage mechanism of jute/rubber-based flexible “green” composite(SAGE Publications Ltd, 2022) Mahesh, V.; Joladarashi, S.; Kulkarni, S.M.Determining the interlaminar shear strength (ILSS) of the composite laminates is vital for deciding their usage in any engineering applications. The matrix used and its curing characteristics are vital in deciding the ILSS of the composite. Present work deals with an experimental study on adhesive behavior, degree of flexibility, ILSS, and damage mechanism of the novel jute/rubber-based flexible “green” composite. The proposed flexible composites were prepared in three different stacking sequences, namely jute/rubber/jute (JRJ), jute/rubber/rubber/jute (JRRJ), and jute/rubber/jute/rubber/jute (JRJRJ), using compression molding technique. After determining the optimal curing characteristics of the proposed rubber-based matrix, the constituents are tested for their adhesive strength with the matrix which showed that rubber matrix system is compatible with jute fabric and natural rubber sheet. Composites are prepared and degree of flexibility for each stacking sequence is found out. Results pertaining to ILSS show that JRJRJ has better ILSS compared to JRJ and JRRJ. Fractographic analysis using scanning electron microscope reveals the mode of failure of the composites and the mechanism governing their failure. Fourier transform infrared spectroscopic study reveals the bonding between the constituents is good enough to be used in composites with flexibility. © The Author(s) 2019.Item Effect of fillers on the piezocapacitive behaviour of silicone rubber particulate composites(Institute of Physics, 2024) Manohar Shankar, B.S.M.; Kulkarni, S.M.Robotics and fluid dynamics applications have created demand for development of electronic skins with embedded pressure sensors. These applications require simple and low-cost fabrication processes with large area deployment. Both structured and unstructured material approaches to sensor development have been followed. Among the various sensing mechanisms, piezo capacitive transduction is superior. This paper reports the influence of fillers on the piezo capacitive characteristics of unstructured solid silicone rubber composites. Dielectric, conductive and conductive-dielectric fillers were incorporated into solid silicone rubber and fabricated using high temperature compression moulding to form dielectric-dielectric, conductive-dielectric and conductive-dielectric dielectric composites. The results reveal that piezo capacitive sensitivity varies with filler type, filler loading, curing agent loading, mixing time and curing temperature. The experiments reveal improved normalized capacitance with pressure characteristics of linearity and sensitivity of 3.9 × 10−3 (kPa)−1 in the 0-20 kPa range of pressure. These composites are thus candidate materials for flexible pressure sensing applications. © 2024 IOP Publishing LtdItem 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.