Browsing by Author "Mohan Kumar, G.C.M."

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Calcium phosphate bioceramics with polyvinyl alcohol hydrogels for biomedical applications
(Institute of Physics Publishing helen.craven@iop.org, 2019) Kumar, B.Y.S.; Isloor, A.M.; Sukumaran, S.; Venkatesan, J.; Mohan Kumar, G.C.M.
Polyvinyl alcohol (PVA) hydrogels show desirable characteristics to use as a biomaterial especially for soft tissue replacement. However, their bio inertness restricts their application in vivo. In this study, polyvinyl alcohol was blended with bi-phasic calcium phosphate and to develop a composite hydrogel by a physical freeze-thawing method, followed by annealing treatment. The synthesized bi-phasic calcium phosphate (BCP) and composite hydrogels were characterized by SEM, XRD and FTIR. The concentration of BCP was optimized and it was found that BCP modifies the hydrogel network by developing the secondary electrostatic bonding between matrix and reinforcement. The highest tensile and compressive strength could reach 5.2 ± 0.6 MPa and 14.9 ± 0.3 MPa respectively for PVA/2.5BCP and they exhibit time-dependent, rapid self-recoverable and fatigue resistant behavior based on the cyclic loading-unloading compression test. Similar observations were found for viscoelastic properties which are relevant for the tissue engineering application. Friction study showed the composite hydrogel had a cartilage-like frictional response, dominated by the interstitial fluid support. Besides composite hydrogel showed excellent antimicrobial activity against bacterial species, Escherichia coli, Staphylococcus aureus and Candida albicans fungi, and the cytocompatibility towards L929 fibroblast cells provides a potential pathway to develop a hydrogel as a promising substitute for tissue engineering scaffold material. © 2019 IOP Publishing Ltd.
Characterization and mechanical properties of sisal fabric reinforced polyvinyl alcohol green composites: Effect of composition and loading direction
(Institute of Physics Publishing helen.craven@iop.org, 2019) Nagamadhu, M.; Jeyaraj, P.; Mohan Kumar, G.C.M.
This research focuses on microstructure characterization and exploring mechanical properties of sisal fabric reinforced Polyvinyl Alcohol composites using conventional vacuum-assisted pressure compression method. Naturally available sisal fiber is used as reinforcement material in this composite because of its abundant availability in Southern India. The sisal fiber, PVA and its composites were characterized using Fourier Transform Infrared Spectroscopy. Initially, Polyvinyl Alcohol polymer was cross-linked with Glutaraldehyde, and mechanical properties were evaluated. It was observed that 20% Glutaraldehyde and 80% Polyvinyl Alcohol polymer combination yielded best mechanical properties. Further, two plain and one weft rib were considered and their textile properties were characterized. The results revealed that fabric crimp and yarn linear density had significant influence on tensile properties of the fabric. Influence of different fabric properties such as weaving pattern, grams per unit area, and loading direction on mechanical properties of composites were analyzed. The woven fabric having least gram per unit area of sisal resulted in best mechanical properties like tensile, bending, and impact. The weft rib fabric composites in weft direction exhibited best mechanical properties. © 2019 IOP Publishing Ltd.
Dynamic impact behavior of syntactic foam core sandwich composites
(DEStech Publications Inc. info@destechpub.com, 2018) Breunig, P.; Damodaran, V.; Shahapurkar, K.; Waddar, S.; Doddamani, M.; Jeyaraj, P.; Mohan Kumar, G.C.M.; Prabhakar, P.
Sandwich composites and syntactic foams have historically been used in many engineering applications to meet the needs of a system. However, there has been minimal effort to take advantage of the weight saving ability of syntactic foams in the cores of sandwich composites, especially with respect to the impact response of the structure. The goal of this experimental study is to investigate the mechanical response and damage mechanisms associated with sandwich composites with syntactic foam cores. The core was manufactured using epoxy resin as the matrix and cenospheres as the reinforcement with varying volume fractions of 0%, 20%, 40%, and 60%. The sandwich composites were manufactured with the vacuum assisted resin transfer molding (VARTM) process. Impact tests were performed on the specimens according to ASTM D7766 at two energy levels: 80J and 160J. The data from the tests was post-processed to gain quantitative understanding of the damage mechanisms present in the specimens. A qualitative understanding was obtained through MicroCT scanning imaging. The analysis showed that increasing the volume fraction of cenospheres in the syntactic foam made the damage mechanism more desirable, even at high energy levels. Â© 2018 by DEStech Publications, Inc. All rights reserved..
Effect of arctic environment on flexural behavior of fly ash cenosphere reinforced epoxy syntactic foams
(Elsevier Ltd, 2018) Garcia, C.D.; Shahapurkar, K.; Doddamani, M.; Mohan Kumar, G.C.M.; Prabhakar, P.
In this paper, the effect of arctic conditions on the flexural response of cenosphere/epoxy syntactic foams is investigated. Understanding the behavior of such foams under extreme conditions is critical for exploring their suitability for constructing lightweight platforms used in arctic explorations. Such platforms are exposed to subzero temperatures for extended periods of time potentially degrading their mechanical properties. In the research study presented here, samples of cenosphere/epoxy syntactic foams were conditioned under arctic environment at ?60 °C temperature for a period of 57 days. Flexural tests were then conducted at room temperature as well as in-situ ?60 °C on the conditioned samples and compared against unconditioned samples. Combinations of surface modification and cenosphere volume fractions were considered. Experimental findings showed that an increase in flexural modulus can be observed at room temperature with increasing cenosphere volume content for both untreated and treated cenosphere reinforced syntactic foams. In contrast, a decrease in flexural strength was observed as compared to neat resin. For the case of arctic exposed samples, an apparent increase in flexural modulus was recorded between 7-15% as compared to room temperature cenospheres/epoxy syntactic foams. In addition, an apparent increase of 3–80% in the flexural strength was observed under arctic environment. The conditioning of cenosphere/epoxy syntactic foams under low temperatures manifested lower strains to failure as compared to neat epoxy and they exhibit quasi-brittle behavior leading to sudden failure in the post peak regime. © 2018 Elsevier Ltd
Experimental and 3D FE evaluation of crack initiation energy J 1C in Al6061-TiC composites
(IOS Press Nieuwe Hemweg 6B Amsterdam 1013 BG, 2018) Raviraj, M.S.; Sharanaprabhu, C.M.; Mohan Kumar, G.C.M.
The test data crack initiation energy in Mode-I fracture, J 1C is determined experimentally for various compositions of Al6061-TiC composites by using compact tension (CT) specimen with variable aW ratios. Also, 3D nonlinear (elastic-plastic) finite element analysis was carried for Compact Tension (CT) specimen to evaluate J 1C, ahead at the crack-front of several Al6061-TiC composite specimens with various crack lengths. The 3D FEA J 1C results were compared with the experimental results. The J 1C values decrease with increasing crack length of the specimen because of decrease in load carrying capacity of the specimens. Al6061-TiC composites exhibit higher fracture toughness values than their counterparts Al-SiC composites. © 2018 IOS Press and the authors. All rights reserved.
Experimental study on rate of solidification of centrifugal casting
(2010) Madhusudhan; Narendranath, S.; Mohan Kumar, G.C.M.; Mukunda, P.G.
Centrifugal casting is a process of producing casting by causing molten metal to solidify in rotating moulds. The quality of the final casting is mainly depending upon the flow pattern of the molten metal and rate of solidification, which in term depends upon the rotational speeds of the mould. Experiments have been conducted by rotating a partially filled horizontal axis cylinder at different rotational speeds and also at different fluid temperatures. Cooling rates of the liquids were observed at different rotational speeds, which depend upon the relative movement between the inner surface of the rotating mould and the fluid. This study gives us some insight into the effect of rotational speed on solidification rate of centrifugal casting. Micro structures of centrifugally cast Al-12 Si castings are also exhibit the same behavior for different rotational speeds.
Influence of glutaraldehyde on dynamic properties of poly(vinyl alcohol) polymer
(ICE Publishing, 2020) Mohan Kumar, G.C.M.; Jeyaraj, J.; Nagamadhu, M.
This study investigated the dynamic mechanical properties of poly(vinyl alcohol) (PVA; (CH2CH(OH)) n ) cross-linked with glutaraldehyde (GA; OHC(CH2)3CHO).*The cross-linked polymer was prepared by using a conventional casting technique and then treated with sulfuric acid (H2SO4) for 24 h.*The flexural properties during static and dynamic modes were studied using a three-point bending condition.*The static flexural properties are improved with the addition of 30% GA in PVA, with higher value of strain.*It was observed that the dynamic mechanical properties of PVA improved significantly with an increase in cross-linking percentage.*The storage and loss moduli increased drastically with the addition of the cross-linker up to 20%, and marginal changes occurred with further addition of the cross-linker.*The fracture behavior was transformed from ductile to brittle for more than 20% cross-linker.*Shifting of the rubber region and liquid region with higher temperatures was observed in storage and loss modulus plots.*Improvement in the adhesion factor, cross-linking density and effectiveness was observed for GA up to 25%.*The test duration was estimated using the Williams-Landel-Ferry model for different temperatures.*The major changes were in the modulus in the rubbery plateau region.*The cross-linked polymer had much greater storage and loss moduli, indicating a closer network structure and higher stiffness.* © 2020 ICE Publishing: All rights reserved.
Influence of surface modification on wear behavior of fly ash cenosphere/epoxy syntactic foam
(Elsevier Ltd, 2018) Shahapurkar, K.; Chavan, V.B.; Doddamani, M.; Mohan Kumar, G.C.M.
The present study deals with investigating the surface modification effect of fly ash cenosphere (as received and surface treated) on the friction and wear response of epoxy syntactic foams. Such lightweight syntactic foams have the potential in using them as tribo-materials for friction applications like in brake pad composites. This study also addresses the environmental linked disposal issues of fly ash cenospheres by incorporating them (up to 60 vol%) in the epoxy matrix. Cenosphere content and surface modification influence on the friction and wear response of cenosphere/epoxy syntactic foams is investigated against EN31 steel disc under dry sliding conditions. Wear behavior is studied at room temperature for different velocities (2 and 5 m/s), applied loads (30 and 50 N) and sliding distances (3, 5 and 7 km). Neat epoxy exhibits maximum wear rate as compared to foams. Wear rate decreases with increasing sliding distance and cenosphere content at all tested conditions. With the increase in the applied load and the sliding velocity, higher wear rate is noted for neat epoxy samples while it decreases with increasing filler loading. Surface modified cenosphere reinforced foams exhibit better wear resistance compared to as received cenosphere dispersed foams and neat epoxy for all the operating conditions owing to the good interfacial bonding of treated cenospheres with epoxy matrix. Specific wear rate decreases significantly with an increase in applied load. Further, the coefficient of friction decreases with higher filler loading and surface modifications. Scanning electron microscopy is used to study the wear mechanisms. Wear debris is analyzed and disc temperature is also reported. Finally, wear rate results are summarised and compared with the data available from literature and are presented in a property map. © 2018 Elsevier B.V.
Mechanical and acoustic properties of areca fiber reinforced phenol formaldehyde composites
(2010) Mohan Kumar, G.C.M.
In this paper, mechanical and acoustic properties of natural areca fiber reinforced phenol formaldehyde composite are studied. Areca fiber composites were prepared using phenol formaldehyde with randomly distributed fibers. Strength of the composite is determined and other tests like adhesion tensile test, moisture absorption test, and biodegradable were also carried out. Acoustic tests are carried out to measure the sound transmission loss (STL) of the cured composite and compared with wood based particle board. The results show that the fully developed material has higher STL for frequencies up to 3 kHz compared to wood-based particle boards.
Nanohydroxyapatite Reinforced Chitosan Composite Hydrogel with Tunable Mechanical and Biological Properties for Cartilage Regeneration
(Nature Publishing Group Houndmills Basingstoke, Hampshire RG21 6XS, 2019) Kumar, B.Y.S.; Isloor, A.M.; Mohan Kumar, G.C.M.; Siddique, I.; Asiri, A.M.
With the continuous quest of developing hydrogel for cartilage regeneration with superior mechanobiological properties are still becoming a challenge. Chitosan (CS) hydrogels are the promising implant materials due to an analogous character of the soft tissue; however, their low mechanical strength and durability together with its lack of integrity with surrounding tissues hinder the load-bearing application. This can be solved by developing a composite chitosan hydrogel reinforced with Hydroxyapatite Nanorods (HANr). The objective of this work is to develop and characterize (physically, chemically, mechanically and biologically) the composite hydrogels loaded with different concentration of hydroxyapatite nanorod. The concentration of hydroxyapatite in the composite hydrogel was optimized and it was found that, reinforcement modifies the hydrogel network by promoting the secondary crosslinking. The compression strength could reach 1.62 ± 0.02 MPa with a significant deformation of 32% and exhibits time-dependent, rapid self-recoverable and fatigue resistant behavior based on the cyclic loading-unloading compression test. The storage modulus value can reach nearly 10 kPa which is needed for the proposed application. Besides, composite hydrogels show an excellent antimicrobial activity against Escherichia coli, Staphylococcus aureus bacteria’s and Candida albicans fungi and their cytocompatibility towards L929 mouse fibroblasts provide a potential pathway to developing a composite hydrogel for cartilage regeneration. © 2019, The Author(s).
Potential use of natural fiber composite materials in India
(2010) Saravana Bavan, D.; Mohan Kumar, G.C.M.
This study focuses on the potential use of natural fibers in composite materials, their availability, processing features, mechanical and physical properties, and some of their applications in India. © 2010 The Author(s).