Browsing by Author "Waddar, S."

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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.
Buckling and free vibrations behaviour through differential quadrature method for foamed composites
(Elsevier B.V., 2023) Duryodhana, D.; Waddar, S.; Bonthu, D.; Jeyaraj, P.; Powar, S.; Doddamani, M.
The current work focuses on predicting the buckling and free vibration frequencies (fn) of cenosphere reinforced epoxy based syntactic foam beam under varying loads. Critical buckling loads (Ncr) and fn are predicted using the differential quadrature method (DQM). Ncr and fn have been calculated for beams of varying cenosphere volume fractions subjected to axial load under clamped-clamped (CC), clamped-simply (CS), simply-simply (SS), and clamped-free (CF) boundary conditions (BC′s). Upon increasing the cenosphere volume fraction, Ncr and fn of syntactic foam composites increases. These numerical outcomes are compared with the theoretical values evaluated through the Euler-Bernoulli hypothesis and further compared with experimental outcomes. Results are observed to be in precise agreement. The results of the DQM numerical analysis are given out for the different BC′s, aspect ratios, cenosphere volume fractions, and varying loads. It is perceived that depending on the BC′s, the type of axial varying loads and aspect ratios has a substantial effect on the Ncr and fn behaviour of the syntactic foam beams. A comparative study of the obtained results showed that the beam subjected to parabolic load under CC boundary conditions exhibited a higher buckling load. © 2023 The Authors
Buckling and vibration behaviour of syntactic foam core sandwich beam with natural fiber composite facings under axial compressive loads
(Elsevier Ltd, 2019) Waddar, S.; Jeyaraj, P.; Doddamani, M.; Barbero, E.
An experimental study of buckling and dynamic response of cenosphere reinforced epoxy composite (syntactic foam) core sandwich beam with sisal fabric/epoxy composite facings under compressive load is presented. Influence of cenosphere loading and surface modification on critical buckling load and natural frequencies of the sandwich beam under compressive load is presented. The critical buckling load is obtained from the experimental load-deflection data while natural frequencies are obtained by performing experimental modal analysis. Results reveal that natural frequencies and critical buckling load increase significantly with fly ash cenosphere content. It is also observed that surface modified cenospheres enhance natural frequencies and critical buckling load of the sandwich beam under compressive load. Vibration frequencies reduce with increase in compressive load. Fundamental frequency increases exponentially in post-buckling regime. Experimentally obtained load-deflection curve and natural frequencies are compared with finite element analysis wherein results are found to be in good agreement. © 2019 Elsevier Ltd
Dynamic impact behavior of syntactic foam core sandwich composites
(2018) Breunig, P.; Damodaran, V.; Shahapurkar, K.; Waddar, S.; Doddamani, M.; Jeyaraj, P.; Mohankumar, G.C.; 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. � 2018 by DEStech Publications, Inc. All rights reserved..
Dynamic impact behavior of syntactic foam core sandwich composites
(SAGE Publications Ltd info@sagepub.co.uk, 2020) Breunig, P.; Damodaran, V.; Shahapurkar, K.; Waddar, S.; Doddamani, M.; Jeyaraj, J.; Prabhakar, P.
Sandwich composites and syntactic foams independently have been used in many engineering applications. However, there has been minimal effort towards taking advantage of the weight saving ability of syntactic foams in the cores of sandwich composites, especially with respect to the impact response of structures. To that end, the goal of this study is to investigate the mechanical response and damage mechanisms associated with syntactic foam core sandwich composites subjected to dynamic impact loading. In particular, this study investigates the influence of varying cenosphere volume fraction in syntactic foam core sandwich composites subjected to varying dynamic impact loading and further elucidates the extent and diversity of corresponding damage mechanisms. The syntactic foam cores are first fabricated using epoxy resin as the matrix and cenospheres as the reinforcement with four cenosphere volume fractions of 0% (pure epoxy), 20%, 40%, and 60%. The sandwich composite panels are then manufactured using the vacuum assisted resin transfer molding process with carbon fiber/vinyl ester facesheets. Dynamic impact tests are performed on the sandwich composite specimens at two energy levels of 80 J and 160 J, upon which the data are post-processed to gain a quantitative understanding of the impact response and damage mechanisms incurred by the specimens. A qualitative understanding is obtained through micro-computed tomography scanning of the impacted specimens. In addition, a finite element model is developed to investigate the causes for different damage mechanisms observed in specimens with different volume fractions. © The Author(s) 2019.
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 axial compression on dynamic response of concurrently printed sandwich
(Elsevier Ltd, 2021) Bharath, H.S.; Waddar, S.; Bekinal, S.I.; Jeyaraj, J.; Doddamani, M.
In this work, the sandwich is concurrently realized using high density polyethylene (HDPE) skins and syntactic foam core through three-dimensional printing (3DP). Syntactic foam core is printed using lightweight feedstock filaments having glass microballoons (GMBs) by 20–60 vol% embedded in HDPE. These lightweight filaments are used as feed material in FFF (fused filament fabrication) based three-dimensional printer. The concurrently printed sandwich is loaded axially in a compressive mode for investigating the influence of GMB loading on buckling and natural frequency. The experimental load–deflection data and modal analysis are utilized for estimating critical buckling load and natural frequencies, respectively, under axial compression. Increasing GMB content enhances load to buckle and frequency of the printed sandwiches. The natural frequency decrease with higher compressive loads. Furthermore, the fundamental natural frequency increases exponentially when these printed sandwiches are subjected to axial compression loads that are higher than the load required for critical buckling. The load–deflection data and frequency obtained experimentally are compared with numerical predictions deduced using finite element analysis (FEA), which are noted to match well. © 2020 Elsevier Ltd
Effect of thermal loading on syntactic foam sandwich composite
(John Wiley and Sons Inc. cs-journals@wiley.com, 2020) Waddar, S.; Jeyaraj, J.; Doddamani, M.
An experimental investigation carried out on the deflection behavior of sandwich composites with a fly ash cenosphere/epoxy syntactic foam core and plain-woven sisal fiber fabric/epoxy skin subjected to nonuniform heating is presented. The influence of cenosphere volume fraction in the syntactic foam core, three different heating cases (increase-decrease, decrease, and decrease-increase), and cenospheres’ surface treatment effect is analyzed. The temperature deflection is acquired with the help of a LabVIEW program. The critical buckling and snap-initiation temperatures are found from the temperature-deflection plots. It is observed that the sandwich beam undergoes snap-through buckling behavior due to viscoelastic forces associated with the syntactic foam core. The critical buckling temperature increases with the filler content, and the surface treatment enhances the buckling behavior marginally. Results also demonstrate that the sandwiching of the syntactic foam core between the natural fiber skin enhances critical buckling temperatures compared to the syntactic foam core. © 2020 Society of Plastics Engineers
Experimental investigation on stability and dynamic behaviour of laminated composite beam
(2018) Waddar, S.; Jeyaraj, P.; Doddamani, M.
Experimental investigations carried out to analyze the effect of axial compression on buckling and dynamic behaviour of laminated composite beam is presented. Typical load vs deflection curve for the composite beam under axial compression load is used to evaluate the critical buckling load. Followed by this, the axial compression load is varied in fraction of critical buckling load and corresponding variation in first three transverse bending natural frequencies are analyzed. Influence of uni-directional, bi-directional and pre-preg reinforcement on buckling and natural frequencies also studied. It is found that buckling strength of the pre-preg composite beam is significantly higher than the other two types of beam studied. It is also observed that increase in axial compression load reduces natural frequencies of the beam and the effect is significant for the fundamental mode. � 2018 Author(s).
Experimental investigation on stability and dynamic behaviour of laminated composite beam
(American Institute of Physics Inc. subs@aip.org, 2018) Waddar, S.; Jeyaraj, P.; Doddamani, M.
Experimental investigations carried out to analyze the effect of axial compression on buckling and dynamic behaviour of laminated composite beam is presented. Typical load vs deflection curve for the composite beam under axial compression load is used to evaluate the critical buckling load. Followed by this, the axial compression load is varied in fraction of critical buckling load and corresponding variation in first three transverse bending natural frequencies are analyzed. Influence of uni-directional, bi-directional and pre-preg reinforcement on buckling and natural frequencies also studied. It is found that buckling strength of the pre-preg composite beam is significantly higher than the other two types of beam studied. It is also observed that increase in axial compression load reduces natural frequencies of the beam and the effect is significant for the fundamental mode. Â© 2018 Author(s).
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.
Mechanical behavior of 3D printed syntactic foam composites
(Elsevier Ltd, 2020) Bharath, H.S.; Sawardekar, A.; Waddar, S.; Jeyaraj, J.; Doddamani, M.
A three-dimensional printed (3DP), polymer based syntactic foams are developed using hollow glass micro balloons (GMB) dispersed in high density polyethylene (HDPE). This work presents the buckling and vibration response of 3D printed foams subjected to axial compression. The buckling load is estimated using Modified Budiansky Criteria (MBC) and Double Tangent Method (DTM) through the load–deflection plots. The first three natural frequencies and their mode shapes are computed as a function of axial compressive load. It is noted that the natural frequency reduces with an increase in axial compressive load. It is also observed that with an increase in GMB %, the natural frequencies and critical buckling load increases. In mode-1, the natural frequency decreases in pre-buckling regimes and increases exponentially in post-critical loading conditions. Analytical solutions obtained from the Euler-Bernoulli-beam theory are compared with experimental results. It is noted that the fundamental frequency approaches zero when the axial load is equal to the critical load. The critical buckling load is estimated through the vibration correlation technique and compared with the results obtained using DTM and MBC methods. The property map is plotted for buckling load against the density of various composites. © 2020 Elsevier Ltd
Mechanical behavior of 3D printed syntactic foam composites
(Elsevier Ltd, 2020) Bharath, H.S.; Sawardekar, A.; Waddar, S.; Jeyaraj, P.; Doddamani, M.
A three-dimensional printed (3DP), polymer based syntactic foams are developed using hollow glass micro balloons (GMB) dispersed in high density polyethylene (HDPE). This work presents the buckling and vibration response of 3D printed foams subjected to axial compression. The buckling load is estimated using Modified Budiansky Criteria (MBC) and Double Tangent Method (DTM) through the loadâ€“deflection plots. The first three natural frequencies and their mode shapes are computed as a function of axial compressive load. It is noted that the natural frequency reduces with an increase in axial compressive load. It is also observed that with an increase in GMB %, the natural frequencies and critical buckling load increases. In mode-1, the natural frequency decreases in pre-buckling regimes and increases exponentially in post-critical loading conditions. Analytical solutions obtained from the Euler-Bernoulli-beam theory are compared with experimental results. It is noted that the fundamental frequency approaches zero when the axial load is equal to the critical load. The critical buckling load is estimated through the vibration correlation technique and compared with the results obtained using DTM and MBC methods. The property map is plotted for buckling load against the density of various composites. Â© 2020 Elsevier Ltd
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 Ltd