Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
14 results
Search Results
Item Bending strength of cenosphere foam cored jute/glass skin sandwiches(2004) Kulkarni, S.M.; Sandesh, S.; SharnappaSandwich construction is widely used in structural application because of its high bending stiffness coupled with lightweight. In design of sandwiches, skin made of high modulus of elasticity is used with core of high shear modulus. This balance is important so that neither material fails long before the other is stressed to accepted level. In the present study, experiments have been carried out on polymeric foam core sandwich beams with jute/epoxy faces. Syntactic polymeric foam cores, which have high compressive strength compared to open cell foams are made by mixing hollow fly-ash particles called cenospheres in a matrix material. The variable considered is the density of the core varied by differing the volume fraction of cenospheres. Cenospheres used in the present study are obtained from flyash, a waste byproduct of thermal power plants using a low cost separation process. Cores with four different volume fractions are prepared and sandwiched between a set of jute fabric layers. It is noticed that as volume fraction of cenospheres increased density is decreasing (1.12 to 0.98 g/cm3). The sandwich beams cut from the samples are tested using standard three-point bending procedure and the results obtained are compared with the results of glass skin sandwich with similar cores. Results showed a large difference in specific strengths of glass and jute skin sandwiches, which could be attributed to high tensile strength of glass fiber compared to jute fiber. There is a decrease of about 13% and 8% from the maximum specific strength for glass skin and jute skin sandwiches respectively at higher volume fractions of cenospheres. This could be traced to the failure of core well before the skin is stressed to accepted level in case of glass skin sandwiches. The jute skin sandwiches exhibited a little flatter specific strength response with respect to volume fraction of cenospheres indicating matching of the features pertaining to jute skin and the core properties. As the specific strength per unit cost of jute approaches that of glass, jute may be used to replace glass fiber with a significant cost advantage for less demanding applications.Item Analytical study of the effects of delamination in glare fiber-metal laminate using modified virtual crack closure technique (MVCCT)(Elsevier B.V., 2019) Shashidhar Naik, H.G.; Javagal, S.Progression in the field of materials used in an aircraft, has seen resurgence in a relatively successful Fiber-Metal Laminate called GLARE, which is composed of several layers of very thin metal (often aluminium), along with layers of uni-directional Glass Fiber pre-pregs. All the layers are bonded to each other with the use of matrix such as epoxy-resin system. The major advantage of this material is that it can be tailored to fit the stress condition by varying the orientation of the Glass Fiber layers. Furthermore, other advantages include better damage tolerance, corrosion resistance, fire resistance and low specific weight. Although GLARE is a composite material, its material properties and fabrication techniques are considered to be homogeneous aluminium like. In this paper, we try to approach this material as a composite, and determine the effect of delamination that occurs due to various reasons. To achieve this, a finite element model of size of 200 mm x 200 mm plate is generated and a compressive load in terms of initial displacement is applied. Various crack sizes at the centre of the plate along the stacking sequence is modelled and analysed. The corresponding Strain Energy Release Rates (SERR) are computed along with various other parameters such as Elemental Stress, Displacement and Contact Stresses. Modified Virtual Crack Closure Technique (MVCCT) is used to obtain the SERR values in all three modes of failure, and their direct effect on the structural integrity of the model is studied and reported. © 2019 The Authors. Published by Elsevier B.V.Item A comparative study of the behavior of CFRP and GFRP laminates in a plate specimen using modified virtual crack closure technique (MVCCT)(Elsevier B.V., 2019) Javagal, S.; Raju, J.; Venkataramana, K.The applications of polymer composites in aircraft industry have exponentially increased in the recent years due to their high strength to weight ratio. Presence of delaminations in composites is inevitable which affects the structural stability due to reduction in structural stiffness and strength. The degradation of a structural component depends on the geometric characteristics of delamination, nature of loading and material characteristics. Damage tolerance study is thus essential to determine the extent of degradation of the structure due to the presence of delamination. The present paper brings about a comparision between the behaviour of a standard plate specimen made up of Carbon Fibre Reinforced Polymer (CFRP) and Glass Fibre Reinforced Polymer (GFRP) laminates with circular delaminations of varying diameters and subject to compressive load. A constant compressive load in terms of initial displacements was applied on a quasi-isotropic square plate specimen of dimensions 200 mm x 200 mm with a thickness of 2.88 mm of both CFRP and GFRP configurations. A circular delamination was introduced at the centre of the plate and its diameter and position along the thickness direction were varied and studied. Using ABAQUS codes of practice, Strain Energy Release Rate (SERR) was computed. The principles of Modified Virtual Crack Closure Technique (MVCCT) was used to compute SERR. Delamination propagates when the computed mixed mode energy release rate exceeds the critical value, GC. Depending on the external loading and material properties, Total strain energy release rate, GT (GT=GI+GII+GIII) was used to predict growth of delamination. The onset of delamination growth was determined by plotting the values of (GT/GC) across various delamination sizes along the thickness of the plate and reported. © 2019 The Authors. Published by Elsevier B.V.Item Experimental investigations on hole quality in drilling of cenosphere reinforced epoxy composite(Institute of Physics Publishing helen.craven@iop.org, 2019) Angadi, S.B.; Ashrith, H.S.; Gaitonde, V.N.; Karnik, S.R.; Doddamani, M.Cenosphere reinforced epoxy composites are steadily replacing the conventional materials in marine, aerospace and automobile structuresowing to their lightweight properties.Drilling is an important conventional machining process essential for assemblyof polymer composites using rivets and bolts. Drilling induces damage around the hole which significantly deteriorates composite performance. In the present study, hole quality characteristicssuch as cylindricity and delamination in drilling of fly ash cenosphere filled epoxy composites are investigated using coated tungsten carbide drill bits.Feed, cutting speed, filler content and drill diameter are considered as the drilling process variables.Samples are fabricated by varying cenosphere content from 10to 60by volume %inepoxy resin.Full factorial design (FFD) based experiments are conducted on CNC vertical machining center. Response surface methodology (RSM) based mathematical models are proposed to estimate the characteristics of the hole quality in developed composites. Analysis of variance is used to validate the developed mathematical models.Present study reveals that the cylindricity and delamination decreases with increasing feed. Increasing cutting speed decreases the cylindricity, however delamination is found to be increasing.Results also shows the importance of using high cenosphere content for producing sound quality holes, which is also beneficial from weight savingperspective. © 2019 IOP Publishing Ltd. All rights reserved.Item Experimental investigation of mode I interlaminar fracture toughness in T300/914 composite(Elsevier Ltd, 2020) Sachin, S.; Nayaka, S.H.; Santhosh, B.; Krishna, P.An aerospace structural material T300/914 has been studied to understand the Mode I interlaminar fracture toughness. For experimental analysis a Double Cantilever Beam (DCB) test is conducted on the laminate to estimate the Mode I interlaminar fracture toughness of the sample. A 48-layer laminate was prepared by hand layup process and an insert included at the mid plane to produce the artificial initial crack required for the test. All the tests are conducted in accordance to the ASTM standards. Pulse-Echo test results and C-Scan images of the laminate were analyzed to find the defects in the laminate. The data from DCB test were analyzed by Modified Beam theory, Compliance calibration method and modified compliance calibration methods to find the interlaminar fracture toughness. A crack length correction method is implemented for data reduction. Numerical analysis of the data derives results in accordance with the experimental analysis. © 2019 Elsevier Ltd. All rights reserved.Item Multiple response optimisation of process parameters during drilling of GFRP composite with a solid carbide twist drill(Elsevier Ltd, 2020) Bhat, R.; Mohan, N.; Sharma, S.; Dayananda Pai, D.; Kulkarni, S.M.The article focuses on investigating the effect of operational parameters like feed and speed along with the composite material thickness on the damages caused in the glass fibre reinforced polymer (GFRP) composites during the drilling process. The GFRP composite studied in the presented work comprises E-glass fibre as the reinforcing material and the marine-grade isophthalic polyester as the binding matrix. Multiple responses considered in work comprises Peel-up delamination, push-down delamination and surface roughness. The technique for order of preference by similarity to ideal solution (TOPSIS) is used to develop the performance index and optimise the multiple response problem. Stepwise analysis of variance (S-ANOVA) is used to investigate the significance of each input parameter. The interaction effects of the variables are investigated using the response surface plots. The results indicate that the composite thickness contributes maximum towards the variance in the overall performance index (21.30%) and the optimum combination obtained using TOPSIS approach within the experimental limits for the selected GFRP is N3f1t1 with the maximum value of Pi (0.888). The regression model developed proves to have high goodness of fit with just 6.01% average error between predicted and experimental values. © 2019 Elsevier Ltd.Item Burnishing of ultra high molecular weight poly ethylene(Elsevier Ltd, 2021) Ashish, V.; Prasanna Kumar Reddy, S.; Kannan, C.; Oyyaravelu, R.; Balan, A.S.S.Ultra-high molecular weight polyethylene (UHMWPE) has been a choice for knee and hip implants since a very long time due to its outstanding tribological properties. UHMWPE has many applications other than biomedical implants like hydrodynamic bearings and marine applications. The main objective of this research work is to enhance the surface properties of UHMWPE and eventually increase its life expectancy for the implants. For this purpose, the UHMWPE sheet has been milled to give it a required shape and then ball burnished with a carbide ball of 6mm diameter under two different environments viz. room and cryogenic with three different burnishing strategic patterns. A constant load of 150N is maintained by the tool on UHMWPE sample with a burnishing feed of 4000mm/min along with a step over a distance of 0.06mm after every pass for three different carefully chosen burnishing patterns. To understand the wear behaviour of the material, wear test has been performed on reciprocating wear testing machine with a stainless-steel ball as a pin for 6500 cycles in the medium of Hank's balanced salt solution (HBSS) as a lubricating agent and to maintain the pH value which is same as in the human body. The lowest average surface roughness (Ra=0.52μm) is reported for the second strategy pattern which gets burnished under the cryogenic environment. This sample also exhibited better wear resistance than other samples burnished under different environments and using different strategic patterns. © 2021 Elsevier Ltd. All rights reserved.Item Analysis of piezoelectric composite beams and plates with multiple delaminations(2006) Raja, S.; Prathima Adya, H.P.; Viswanath, S.In the present work, the effect of delamination or debonding on the static and dynamic characteristics of laminated piezoelectric beams and plates is studied. A four-noded quadrilateral shear flexible plate element is developed to model the damages in composite substrate and in piezoelectric layers. The elastic stiffness and electro-elastic stiffness degradations are introduced at the elemental level through coupled constitutive relations. The undamaged structure is modeled as a single laminate while the delaminated region is modeled as sublaminates whose interface contains the desired delamination or debonding. The continuity of displacement is maintained across the delaminated edge by imposing the strain-based multipoint constraints. Numerical studies are conducted on composite specimens with surface bonded active layers. The results are presented to evaluate the performance of these smart structures in the presence of delamination. For actuators, the performance is measured in terms of the achievable deflection control and in sensors as a measurable output voltage. It is observed that actuator and sensor debonding degrade the capabilities of active materials significantly. Therefore, the study concludes that a damage tolerant approach is essential for the design of smart structural systems to account for damage-induced uncertainty in the functional properties of smart actuators and sensors. Copyright © 2006 SAGE Publications.Item Delamination analysis in drilling process of glass fiber reinforced plastic (GFRP) composite materials(2007) Mohan, N.S.; Kulkarni, S.M.; Ramachandra, A.Machining processes are generally used to cut; drill, or contour composite laminates for building products. In fact, drilling is one of the most commonly used manufacturing processes to install fasteners for assembly of laminate composites. The material anisotropy resulting from fiber reinforcement heavily influences the machinability during machining. Machining of fiber reinforced plastic (FRP) components is often needed in spite of the fact that most FRP structures can be made to near-net shape and drilling is the most frequently employed secondary machining process for fiber reinforced materials. Therefore, the precise machining needs to perform to ensure dimensional stability and to obtain a better productivity of the component. The drilling parameters and specimen parameters evaluated were speed, feed rate, drill size and specimen thickness. A series of experiments were conducted using TRIAC VMC CNC machining center to machine the composite laminate specimens at various cutting parameters and material parameters. The measured results of delamination at the entry and exit side of the specimen were measured and analyzed using commercial statistical software MINITAB14. The experimental results indicated that the specimen thickness, feed rate and cutting speed are reckoned to be the most significant factors contributing to the delamination. A signal-to-noise ratio is employed to analyze the influence of various parameters on peel up and push down delamination factor in drilling of glass fibre reinforced plastic (GFRP) composite laminates. The main objective of this study is to determine factors and combination of factors that influence the delamination using Taguchi and response surface methodology and to achieve the optimization machining conditions that would result in minimum delamination. From the analysis it is evident that among the all significant parameters, specimen thickness and cutting speed have significant influence on peel up delamination and the specimen thickness and feed have more significant influence on push down delamination. Confirmation experiments were conducted to verify the predicted optimal parameters with the experimental results, good agreement between the predicted and experimental results obtained to be of the order of 99%. © 2007 Elsevier B.V. All rights reserved.Item Predictive analysis of peel up delamination in glass fibre reinforced polyester composite drilling(Transstellar Journal Publications and Research Consultancy Private Limited (TJPRC) editor@tjprc.org, 2019) Bhat, R.; Mohan, N.; Kulkarni, S.M.; Sharma, S.Composites are the engineering materials, comprising two constituents: reinforcing and the matrix or binder material. the composite machining, particularly, drilling is a complex process in comparison to the machining of traditionally employed engineering structural materials. Delamination is the most prevalent integrity issue in composite drilling. In the present work, the independent variables are categorized as continuous and categorical variables. Speed and feed are chosen as the continuous variables, whereas, the drill tool diameter and material thickness are considered as categorical variables. The peel up delamination is chosen as the response. The central composite design form of RSM is employed to develop the experimental design and develop the response regression model. The developed model is then validated using an additional set of small number of experiments and the degree of affirmation is determined. The standard error obtained analytically is 5.91%. The experimental mean standard error for the randomly conducted validating experiment obtained is 4.23%. The validation shows a high degree of agreement (99.75%) between the theoretical and analytical values. © TJPRC Pvt. Ltd.