Faculty Publications

Now showing 1 - 3 of 3

Densification mechanics of polymeric syntactic foams
(Elsevier Ltd, 2022) Prabhakar, P.; Feng, H.; P Subramaniyan, S.; Doddamani, M.
In this paper, a fundamental understanding of the densification mechanics of polymeric syntactic foams under compressive loading is established. These syntactic foams are closed cell composite foams with thin-walled microballoons dispersed in a matrix (resin) whose closed cell structure provides excellent mechanical properties, like high strength and low density. There are several parameters that can contribute towards their mechanical properties, including, microballoon volume fraction, microballoon wall thickness, bonding between the microballoons and the matrix, and the crushing strength of microballoons. Conducting purely experimental testing by varying these parameters can be very time sensitive and expensive. Also, identification of densification mechanics is challenging using experiments only. Higher densification stress and energy are favorable properties under foam compression or crushing. Hence, the influence of key structural and material parameters associated with syntactic foams that dictate the mechanics of densification is studied here by implementing micromechanics based computational models and multiple linear regression analysis. Specifically, specific densification stresses and energy, which are densification stresses and energy normalized by weight, are evaluated which are more relevant for a wide variety of weight saving applications. Microballoon crushing strength and volume fraction are identified as the parameters that have the higher influence on densification stress and energy, and their specific counterparts, whereas the interfacial bonding has the least impact. In addition, designing aspects of syntactic foams with specified overall density are discussed by mapping microballoon volume fraction and wall thickness. The regression model allows for establishing wall thicknesses and corresponding volume fractions that result in higher densification properties for a specified overall foam density. © 2022 Elsevier Ltd
Numerical and experimental stress analysis of spur gears for weight reduction using radial holes
(Springer-Verlag Italia s.r.l., 2024) Sutar, S.S.; Kumar, G.C.M.; Doddamani, M.
Geometric optimization for the optimal use of material and the weight reduction of gear is possible by removing material from the gear teeth. The current research focuses on the stress analysis of gear with radial holes drilled through the gear tooth to reduce the weight of standard gear. The radial holes from the tip of the gear tooth for different depths are introduced. A standard gear with holes is analyzed using ANSYS, and the magnitude of stresses near the root of the gears for similar loading and boundary conditions are studied. New efforts have been made to study the stress distribution by photoelastic technique to supplement FEA results and confirm the stress distribution of gear with and without radial holes. This process achieves a volume reduction of up to 6.1% compared to an AGMA standard spur gear without affecting much of the stress distribution. These holes may be helpful for adequate lubrication and cooling of gears by fluid circulation. © The Author(s), under exclusive licence to Springer-Verlag France SAS, part of Springer Nature 2023.
3D printing of functionally graded nanocomposites: An investigation of microstructural, rheological, and mechanical behavior
(John Wiley and Sons Inc, 2024) Kumar, S.; Rajath, S.; Shivakumar, N.D.; Ramesh, M.R.; Doddamani, M.
Manufacturing functionally graded material through 3D printing is challenging owing to the deposition of different materials with different thermal properties in each layer, leading to a higher thermal gradient between deposited and depositing layers, resulting in improper bonding between them and, hence, reduced mechanical properties. This study focuses on 3D printing of functionalized multi-walled carbon nanotubes (MWCNTs)/high-density polyethylene (HDPE)-based lightweight functionally graded nanocomposites (FGNCs) and their investigation for microstructural, rheological, physical, and mechanical properties. Functionalized MWCNTs (0.5% → 5%) are initially compounded with widely utilized HDPE to develop nanocomposites (H0.5→H5 pellets) for extruding filaments for 3D printing. 3D-printed FGNC samples are investigated through scanning electron microscopy (SEM), rheology, density, tensile, and flexural tests. SEM and rheology confirm the homogeneous dispersion of the filler in HDPE and the processing parameters suitability in blending, extrusion, and 3D printing. Complex viscosity (η*), loss modulus (E″), and storage modulus (E′) of FGNCs increase, while the damping decreases with the MWCNTs rise in the graded layers. Density results revealed the highest weight saving potential (~12%) of FGNC-2 (H1–H3–H5), showing great weight saving potential. Tensile and flexural properties rise when the MWCNTs content rises in the graded layer. The FGNC-2 showed the highest tensile strength and moduli, 37.12% and 90.41% higher than HDPE. Flexural strength and moduli are also found to be the highest for FGNC-2, 28.57%, and 26.83% higher than HDPE. The highest specific moduli and strength are found for FGNC-2, 46.16% and 44.14% higher than HDPE, respectively. Experimental findings are found to be strongly in agreement with numerical findings. 3D-printed FGNC-2 demonstrated the best flexural and tensile characteristics with the lowest weight and hence can be used to make practical parts and structures that need variable stiffness. Highlights: FGNCs functionally graded n anocomposites are concurrently 3D printed. FGNC-2 exhibited the highest weight saving potential of 12%. FGNC-2 showed 90.41% and 37.12% enhanced tensile modulus and strength. FGNC-2 displayed 28.57% and 26.83% improved flexural strength and modulus. FGNCs exhibited better mechanical performance than the homogeneous NCs. © 2024 Society of Plastics Engineers.

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