Faculty Publications
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Item A Closed-Form Solution for the Effect of Free Edges on Melt Pool Geometry and Solidification Microstructure in Additive Manufacturing of Thin-Wall Geometries(Springer Boston, 2016) Gockel, J.; Klingbeil, N.; Bontha, S.Laser and electron beam-based additive manufacturing of Ti-6Al-4V are under consideration for application to aerospace components. A critical concern for these processes is the ability to obtain a consistent and desirable microstructure and corresponding mechanical properties of the deposit. Based on the Rosenthal solution for a moving point-heat source, recent work has developed simulation-based process maps for the thermal conditions controlling microstructure (grain size and morphology) in beam-based deposition of semi-infinite geometries, where a steady-state melt pool exists away from free edges. In the current study, the Rosenthal solution is modified to include the effects of free edges. This is accomplished by the superposition of two point-heat sources approaching one another, with the line of symmetry representing the free edge. The result is an exact solution for the case of temperature-independent properties. Dimensionless results for melt pool geometry are determined, and plotted as a function of distance from the free edge. Results are plotted on solidification maps to predict trends in microstructure for Ti-6Al-4V. Finite element analysis is used to verify results. Results suggest that melt pool geometry is more sensitive to free edges than solidification microstructure. © 2015, The Minerals, Metals & Materials Society and ASM International.Item Additive manufacturing of an aluminum matrix composite reinforced with nanocrystalline high-entropy alloy particles(Elsevier Ltd, 2017) Karthik, G.M.; Panikar, S.; Janaki Ram, G.D.J.; Kottada, R.S.In the present work, a metal-metal composite consisting of aluminum-magnesium alloy AA5083 matrix and nanocrystalline CoCrFeNi high-entropy alloy reinforcement particles in 12 vol% was successfully friction deposited in multiple layers. The layer interfaces or the reinforcement/matrix interfaces showed no brittle intermetallic formation – thanks to the inert nature as well as the high strength and hardness of the high-entropy alloy reinforcement particles. The composite showed significantly higher tensile and compressive strengths as compared to standard wrought-processed alloy AA5083-H112 and offered a much better combination of strength and ductility when compared to conventional aluminum matrix composites reinforced with ceramic particles. The current study establishes friction deposition as a viable technique for additive manufacturing of novel high-performance composite materials. © 2016 Elsevier B.V.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 Parametric studies on bending stiffness and damping ratio of Sandwich structures(Elsevier B.V., 2018) Rajpal, R.; Lijesh, L.; Gangadharan, K.V.Sandwich structures are extensively used in aviation industries to reduce the overall weight of the system. Although the mechanical behavior of these structures has been widely studied, the performance of core shape in vibration response has been minimally explored. This study focuses on understanding the various influences of sandwich structures considering the following parameters: (i) nature of core shape, (ii) number of infill shapes, and (iii) orientation of cores, which affect the dynamic behavior of sandwich structures. Nine sandwich structures comprising three different core shapes, hexagon, triangle, and square shapes, in three different orientations, namely 0° 45° and 90° were considered for the present study. These structures in the beginning were put by modal analysis using finite element method (FEM). All the nine structures were printed using the fused deposition method to validate the FEM findings, while the DEWE soft data acquisition system was used to estimate the modal parameters (i) natural frequency and (ii) damping ratio. Natural frequency and damping ratio were estimated using FRF and Nyquist circle plot, respectively. This study demonstrates that although the square core orientated at 0° exhibited superior stiffness in bending loads, the hexagonal core orientated at 0° displayed an admirable combination of both stiffness and damping properties. © 2018 Elsevier B.V.Item On the corrosion resistance of some selective laser melted alloys(Elsevier B.V., 2018) Suryawanshi, J.; Baskaran, T.; Prakash, O.; Arya, S.; Ramamurty, U.The electrochemical corrosion resistances of selective laser melted (SLM) 316 L austenitic stainless steel (SS), 18(Ni) 300-grade maraging steel (MS), and Al-12 wt.% Si (AS) alloy in a 0.1 M NaCl solution at room temperature were evaluated. The effects of laser scanning strategy (single melt vs. checker board styles), post-SLM heat treatment, and corroding surface orientation (with respect to the scan and build directions) on the corrosion behavior were examined. In all cases, results were compared with those obtained on samples with the same compositions, but manufactured using conventional means. The experimental results show that, for the particular set of experimental conditions employed in this study, SLM in general improves the corrosion resistances of Al-12 wt.% Si and stainless steel alloys and degrades the corrosion resistance of the maraging steel, in comparison to the respective corrosion resistances of their conventionally manufactured counterparts. These results are discussed in terms of microstructural refinement and porosity that are common to the SLM alloys. © 2018 Acta Materialia Inc.Item Experimental investigation of 3D-printed polymer-based MR sandwich beam under discretized magnetic field(Springer Verlag service@springer.de, 2018) Rajpal, R.; Lijesh, K.P.; Gangadharan, K.V.Smart materials are being employed in dynamic systems to tune the stiffness and damping of the structure by using external stimuli. Magnetorheological elastomers (MREs) are considered to be as one of the smart materials because of their characteristics of altering the dynamic properties under the external magnetic field. So far, MRE sandwich beams have been developed by embedding them between two parent structures. In the present work, a novel technique of embedding MR materials is presented to create complex sandwich structures. This technique will replace the conventional embedding technique which uses adhesives to bind the MR materials with the parent structure. The vibration characteristics of the developed sandwich beams are estimated by conducting harmonic analysis to a predefined band of frequency range under the different directions of magnetic field. Sinusoidal signals of desired frequency and amplitude were proffered using NI educational laboratory virtual instrumentation suite to an amplified piezoactuator for exciting the MR sandwich beam. A non-contact-type laser displacement sensor is used in this study to avoid the additional mass of the sensor on the beam. The results indicate that the smart materials can be efficiently embedded with the sandwich beam without using the adhesives. It is also found that by changing the direction of magnetic field, the range of the variation in stiffness of MR sandwich beam can be increased to enhance the isolation effect at fundamental natural frequency. © 2018, The Brazilian Society of Mechanical Sciences and Engineering.Item Additive Manufacturing of Three-Phase Syntactic Foams Containing Glass Microballoons and Air Pores(Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2019) Singh, A.K.; Deptula, A.J.; Anawal, R.; Doddamani, M.; Gupta, N.High-density polyethylene and its syntactic foams reinforced with 20 vol.% and 40 vol.% glass microballoons were 3D printed using the fused filament fabrication method and studied for their compressive response. The three-phase microstructure of syntactic foams fabricated in this work also contained about 10 vol.% matrix porosity for obtaining light weight for buoyancy applications. Filaments for 3D printing were developed using a single screw filament extruder and printed on a commercial 3D printer using settings optimized in this work. Three-dimensional printed blanks were machined to obtain specimens that were tested at 10 ?4 s ?1 , 10 ?3 s ?1 , 10 ?2 s ?1 and 1 s ?1 strain rates. The compression results were compared with those of compression-molded (CM) specimens of the same materials. It was observed that the syntactic foam had a three-phase microstructure: matrix, microballoons and air voids. The air voids made the resulting foam lighter than the CM specimen. The moduli of the 3D-printed specimen were higher than those of the CM specimens at all strain rates. Yield strength was observed to be higher for CM samples than 3D-printed ones. © 2019, The Minerals, Metals & Materials Society.Item Eco-friendly lightweight filament synthesis and mechanical characterization of additively manufactured closed cell foams(Elsevier Ltd, 2019) Patil, B.; Bharath Kumar, B.R.; Bontha, S.; Balla, V.K.; Powar, S.; Hemanth Kumar, V.H.; Suresha, S.N.; Doddamani, M.Environmentally pollutant fly ash cenospheres (hollow microballoons) are utilized with most widely consumed, relatively expensive high density polyethylene (HDPE) for developing lightweight eco-friendly filament for 3D printing of closed cell foams. Cenospheres (20, 40 and 60 by volume %) are blended with HDPE and subsequently extruded in filament to be used for 3D printing. Cenosphere/HDPE blends are studied for melt flow index (MFI) and rheological properties. MFI decreases with cenospheres addition. Complex viscosity, storage and loss modulus increase with filler loading. DSC results on the filament and printed samples reveal increasing crystallization temperature and decreasing crystallinity % with no appreciable change in peak melting temperature. Cooling rate variations exhibit crystallinity differences between the filament and the prints. CTE decreases with increasing cenosphere content resulting in lower thermal stresses and under diffusion of raster leading to non-warped prints. Micrography on freeze fractured filament and prints show cenospheres uniform distribution in HDPE. Intact cenospheres lower the foam density making it lightweight. Tensile tests are carried out on filaments and printed samples while flexural properties are investigated for 3D prints. Cenospheres addition resulted in improved tensile modulus and decreased filament strength. Tensile and flexural modulus of printed foams increases with filler content. Results are also compared with injection molded samples. Printed foams registered comparable tensile strength. Specific tensile modulus is noted to be increased with cenospheres loading implying weight saving potential of 3D printed foams. Property map reveals printed foams advantage over other fillers and HDPE composites synthesized through injection and compression molding. © 2019 Elsevier LtdItem Compressive behavior of fly ash based 3D printed syntactic foam composite(Elsevier B.V., 2019) Patil, B.; Bharath Kumar, B.R.; Doddamani, M.Syntactic foams are widely used in damage tolerance and low-density applications. In present work compressive behavior of 3D printed three-phase syntactic foams under quasi-static strain rates (0.001, 0.01 and 0.1 s?1) are investigated. Extruded filaments of High density polyethylene (HDPE) with environmentally pollutant fly ash cenospheres (0, 20, 40 and 60 vol%) are used for 3D printing. Micrography reveal that syntactic foam filament and 3D printed samples are three phase systems comprising matrix, cenosphere and porosity. Matrix porosity of about 7% makes these foams lightweight and suitable for buoyant applications. The compressive properties are extracted from the stress-strain plots. It is observed that modulus and specific modulus increases with strain rate and cenosphere content. Specific compressive strength increases with strain rate and decrease with cenosphere content. © 2019 Elsevier B.V.