Faculty Publications
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Item Compressive and flexural properties of functionally graded fly ash cenosphere-epoxy resin syntactic foams(John Wiley and Sons Inc, 2015) Doddamani, M.; Kishore; Shunmugasamy, V.C.; Gupta, N.; Vijayakumar, H.B.The present study focuses on developing functionally graded syntactic foams (FGSFs) based on a layered co-curing technique. The FGSFs were characterized for compressive and flexural properties and compared with plain syntactic foams. The results showed that the specific compressive modulus was 3-67% higher in FGSFs compared to plain syntactic foams. FGSF exhibited 5-34% and 34-87% higher specific modulus and strength, respectively in flexural mode. The microscopic examinations of comparative responses of the filler and matrix to deformation suggest that the failure is dominated by the matrix. The gradient in the composition of syntactic foams helps in effectively distributing the stress throughout the microstructure and results in improved mechanical performance of syntactic foams. From the microscopy studies, it is evident that, the failure mechanism in the FGSF under flexural loading is governed by a crack that initiated on the tensile side of the specimen and propagated through the thickness to cause complete fracture. The microscopic observations further clearly demonstrate the existence of seamless interfaces between the layers and a clear difference in the cenosphere concentration across the interface, affirming the gradation in the prepared samples. The results show that appropriate compositions of FGSFs can be selected to develop materials with improved mechanical performance. © 2014 Society of Plastics Engineers.Item Dry sliding wear of epoxy/cenosphere syntactic foams(Elsevier Ltd, 2015) Manakari, V.; Parande, G.; Doddamani, M.; Gaitonde, V.N.; Siddhalingeshwar, I.G.; Kishore; Shunmugasamy, V.C.; Gupta, N.Abstract Dry sliding wear behavior of epoxy matrix syntactic foams filled with 20, 40 and 60 wt% fly ash cenosphere is reported based on response surface methodology. Empirical models are constructed and validated based on analysis of variance. Results show that syntactic foams have higher wear resistance than the matrix resin. Among the parameters studied, the applied normal load (F) had a prominent effect on wear rate, specific wear rate (ws) and coefficient of friction (?). With increasing F, the wear rate increased, whereas ws and ? decreased. With increase in filler content, the wear rate and ws decreased, while the ? increased. With increase in sliding velocity as well as sliding distance, the wear rate and ws show decreasing trends. Microscopy revealed broken cenospheres forming debris and extensive deformation marks on the wear surface. © 2015 Elsevier Ltd.Item Additive Manufacturing of Syntactic Foams: Part 2: Specimen Printing and Mechanical Property Characterization(Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2018) Singh, A.K.; Saltonstall, B.; Patil, B.; Hoffmann, N.; Doddamani, M.; Gupta, N.High-density polyethylene (HDPE) and its fly ash cenosphere-filled syntactic foam filaments have been recently developed. These filaments are used for three-dimensional (3D) printing using a commercial printer. The developed syntactic foam filament (HDPE40) contains 40 wt.% cenospheres in the HDPE matrix. Printing parameters for HDPE and HDPE40 were optimized for use in widely available commercial printers, and specimens were three-dimensionally (3D) printed for tensile testing at strain rate of 10?3 s?1. Process optimization resulted in smooth operation of the 3D printer without nozzle clogging or cenosphere fracture during the printing process. Characterization results revealed that the tensile modulus values of 3D-printed HDPE and HDPE40 specimens were higher than those of injection-molded specimens, while the tensile strength was comparable, but the fracture strain and density were lower. © 2018, The Minerals, Metals & Materials Society.Item Additive Manufacturing of Syntactic Foams: Part 1: Development, Properties, and Recycling Potential of Filaments(Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2018) Singh, A.K.; Patil, B.; Hoffmann, N.; Saltonstall, B.; Doddamani, M.; Gupta, N.This work focuses on developing filaments of high-density polyethylene (HDPE) and their hollow particle-filled syntactic foams for commercial three-dimensional (3D) printers based on fused filament fabrication technology. Hollow fly-ash cenospheres were blended by 40 wt.% in a HDPE matrix to produce syntactic foam (HDPE40) filaments. Further, the recycling potential was studied by pelletizing the filaments again to extrude twice (2×) and three times (3×). The filaments were tensile tested at 10?4 s?1, 10?3 s?1, and 10?2 s?1 strain rates. HDPE40 filaments show an increasing trend in modulus and strength with the strain rate. Higher density and modulus were noticed for 2× filaments compared to 1× filaments because of the crushing of some cenospheres in the extrusion cycle. However, 2× and 3× filament densities are nearly the same, showing potential for recycling them. The filaments show better properties than the same materials processed by conventional injection molding. Micro-CT scans show a uniform dispersion of cenospheres in all filaments. © 2018, The Minerals, Metals & Materials Society.Item Influence of axial compressive loads on buckling and free vibration response of surface-modified fly ash cenosphere/epoxy syntactic foams(SAGE Publications Ltd info@sagepub.co.uk, 2018) Waddar, S.; Jeyaraj, P.; Doddamani, M.This work deals with experimental buckling and free vibration behavior of silane-treated cenosphere/epoxy syntactic foams subjected to axial compression. Critical buckling loads are computed from compressive load–deflection plots deduced using universal testing machine. Further, compressive loads are applied in the fixed intervals until critical loading point on different set of samples having similar filler loadings to estimate natural frequency associated with the first three transverse bending modes. Increasing filler content increases critical buckling load and natural frequency of syntactic foam composites. Increasing axial compressive load reduce structural stiffness of all the samples under investigation. Syntactic foams registered higher stiffness compared to neat epoxy for all the test loads. Similar observations are noted in case of untreated cenosphere/epoxy foam composites. Silane-modified cenosphere embedded in epoxy matrix registered superior performance (rise in critical buckling load and natural frequencies to the tune of 23.75% and 11.46%, respectively) as compared to untreated ones. Experimental results are compared with the analytical solutions that are derived based on Euler–Bernoulli hypothesis and results are found to be in good agreement. Finally, property map of buckling load as a function of density is presented by extracting values from the available literature. © The Author(s) 2018.Item Snap-through buckling of fly ash cenosphere/epoxy syntactic foams under thermal environment(Elsevier Ltd, 2018) Waddar, S.; Jeyaraj, P.; Doddamani, M.Experimental investigation on deflection behaviour of fly ash cenosphere/epoxy syntactic foam at room temperature and under thermal environment (three different heating conditions) is investigated. Influence of fly ash cenosphere volume fraction and nature of temperature variation on deflection behaviour of syntactic foam beam is discussed elaborately. Results reveal that the syntactic foam beam experience snap-through buckling under thermal environment and is reflected by two bifurcation points in temperature-deflection plot. It is observed that the time duration for which the foam beam stays in the first buckled position increases with increase in cenosphere content. Thermal environment induces compressive stresses in the samples causing such snap-through buckling. However, such phenomenon is not observed when mechanical compressive loads are applied under room temperature conditions. Temperature variation across the beam strongly influences snap-through buckling in syntactic foams in addition to volume fraction of filler content. © 2018 Elsevier LtdItem 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 LtdItem 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.Item Buckling and free vibration behavior of cenosphere/epoxy syntactic foams under axial compressive loading(ASTM International, 2018) Waddar, S.; Jeyaraj, P.; Doddamani, M.; Gupta, N.The buckling and free vibration behavior of cenosphere/epoxy syntactic foams under axial compressive loading are investigated experimentally in this work. The buckling load is obtained from the load-deflection curve based on the Double Tangent Method (DTM) and Modified Budiansky Criteria (MBC). Furthermore, the influence of an axial compression load on the natural frequencies associated with the first three transverse bending modes is analyzed. Finally, the buckling loads predicted using DTM and MBC are compared to the buckling load calculated based on the vibration correlation technique. It is observed that the buckling loads predicted through the three different methods are in close agreement. The experimental results revealed that the buckling load and natural frequency of the syntactic foams increase with the cenosphere volume fraction. It is observed that the natural frequencies reduce with increases in the axial compression load for all the modes. However, a rapid increase in the fundamental frequency is observed when the compressive load is near and beyond the critical buckling load. © © 2018 by ASTM International.Item Effect of cenosphere filler surface treatment on the erosion behavior of epoxy matrix syntactic foams(John Wiley and Sons Inc. cs-journals@wiley.com, 2019) Shahapurkar, K.; Doddamani, M.; Mohan Kumar, G.C.; Gupta, N.Influence of cenosphere surface modification and volume fraction on the solid particle erosion of cenosphere/epoxy syntactic foams is investigated. Fly ash cenospheres are used as filler in both as received and silane surface modified configurations. Erosion behavior is studied at room temperature for different impact angles (30, 45, 60, and 90°) and velocities (30, 45, and 60 m/s). Neat epoxy shows the highest erosion rate compared with that of the syntactic foams. Results show a strong dependence of impact angle and velocity on erosion rate of syntactic foams. With increasing cenosphere content erosion rate decreases for all impact angles. Erosion rate decreases with increasing impact angle and with decreasing velocity. Good interfacial bonding of treated cenospheres enhances the erosion resistance. All the samples exhibit ductile erosive behavior, with maximum erosion at 30°. The velocity exponent and erosion efficiency parameters confirm the ductile behavior of syntactic foams. POLYM. COMPOS., 40:2109–2118, 2019. © 2018 Society of Plastics Engineers. © 2018 Society of Plastics Engineers