Athreya, SR, Kalaitzidou, K. and Das, S.(2011), Microstructure, thermomechanical properties, and ... more Athreya, SR, Kalaitzidou, K. and Das, S.(2011), Microstructure, thermomechanical properties, and electrical conductivity of carbon black-filled nylon-12 nanocomposites prepared by selective laser sintering. Polymer Engineering & Science, 51: n/a. doi: ...
ABSTRACT Part I of this study presented a computational model-based approach for enhancing the pe... more ABSTRACT Part I of this study presented a computational model-based approach for enhancing the performance of solid oxide fuel cells (SOFCs) with designed microarchitecture. The performance of such SOFCs was predicted to greatly improve through a systematic computational design and optimization approach. Part II here proves through experimental fabrication and characterization that microarchitectured SOFC performance can be improved as predicted by the model. A real and specific SOFC is chosen, fabricated and characterized to demonstrate the proof-of-concept. Fabrication techniques using sintering and laser ablation are demonstrated. Pore size and geometry are characterized by interferometry-based surface profilometry and scanning electron microscopy. SOFC button cell performance testing including power output performance and electrochemical impedance spectroscopy are performed. The results show that SOFC performance in a microarchitectured cell can be improved over a baseline button cell by 9–17% in current density and by 7–19% in power density.
We present recent results on fabrication of micrometre- and sub-micrometre-scale structures in po... more We present recent results on fabrication of micrometre- and sub-micrometre-scale structures in polyethylene glycol diacrylate (PEG-DA), a biocompatible hydrogel, useful in biomedical applications. The hydrogel structures were fabricated using two laser-based techniques; laser direct-write photopolymerisation, and multiple-beam laser interference photopolymerisation using continuous wave, nanosecond pulsed and femtosecond pulsed lasers, with light wavelengths of 266 nm, 355 nm, 532 nm and 800 nm. Through these techniques, we demonstrated the ability to fabricate fine structures over large areas without the use of templates or masks. Such structures can be useful for a variety of applications including cell biological studies, tissue engineering and drug delivery.
International Journal of Precision Engineering and Manufacturing, 2013
ABSTRACT Electrically conductive polymer nanocomposites were prepared through selective laser sin... more ABSTRACT Electrically conductive polymer nanocomposites were prepared through selective laser sintering (SLS) of polyamide-12 (PA) powder coated with graphite nanoplatelets (GNP) using sonication. The SLS process parameters were optimized in order to maximize the tensile modulus at 3 and 5 wt% GNP. The highest tensile modulus (2.1 GPa) was achieved at 3 wt%. A slight decrease in flexural modulus and strength was observed at 3 and 5 wt% GNP compared with the neat polymer Morphological observation of the graphite-coated PA powder showed fairly homogeneous dispersion. The SLS processed parts were nearly fully dense and the highest density (99.5%) was found at 3 wt% GNP The bulk electrical conductivity of the SLS-processed nanocomposites was found to be 3.8x10(-11) and 6.4x10(-8) S/cm for 3 and 5 wt% GNP respectively.
ABSTRACT Part I [Metall. Mater. Trans. B, 2014, DOI:10.1007/s11663-014-0117-9] presented a compre... more ABSTRACT Part I [Metall. Mater. Trans. B, 2014, DOI:10.1007/s11663-014-0117-9] presented a comprehensive thermal, fluid flow, and solidification model that can predict the temperature distribution and flow characteristics for the processing of CMSX-4 alloy powder through scanning laser epitaxy (SLE). SLE is an additive manufacturing technology aimed at the creation of equiaxed, directionally solidified and single-crystal (SX) deposits of nickel-based superalloys using a fast-scanning laser beam. Part II here further explores the Marangoni convection-based model to predict the solidification microstructure as a function of the conditions at the trailing edge of the melt pool formed during the SLE process. Empirical values for several microstructural characteristics such as the primary dendrite arm spacing (PDAS), the columnar-to-equiaxed transition (CET) criterion and the oriented-to-misoriented transition (OMT) criterion are obtained. Optical microscopy provides visual information on the various microstructural characteristics of the deposited material such as melt depth, CET location, OMT location, PDAS, etc. A quantitative and consistent investigation of this complex set of characteristics is both challenging and unprecedented. A customized image-analysis technique based on active contouring is developed to automatically extract these data from experimental micrographs. Quantitative metallography verifies that even for the raster scan pattern in SLE and the corresponding line heat source assumption, the PDAS follows the growth relation w ~G −0.5V −0.25 (w = PDAS, G = temperature gradient and V = solidification velocity) developed for marginal stability under constrained growth. Models for the CET and OMT are experimentally validated, thereby providing powerful predictive capabilities for controlling the microstructure of SX alloys processed through SLE.
Abstract This paper focuses on modeling of the scanning laser epitaxy (SLE) process that is curre... more Abstract This paper focuses on modeling of the scanning laser epitaxy (SLE) process that is currently being investigated and developed at the Georgia Institute of Technology. SLE is a laser-based manufacturing process for the creation of equiaxed, directionally solidified and single-crystal deposits of nickel superalloys onto superalloy substrates through melting and resolidifícation of alloy powders using a scanning laser beam. The thermal modeling of the system, done in a commercial CFD software package, simulates a heat source moving ...
Virtual Prototyping & Bio Manufacturing in Medical Applications, 2008
Page 1. Chapter 11 Selective Laser Sintering of Polymers and Polymer-Ceramic Composites Suman Das... more Page 1. Chapter 11 Selective Laser Sintering of Polymers and Polymer-Ceramic Composites Suman Das 11.1 Introduction It is widely accepted that rapid prototyping methods based on solid freeform fabrication (SFF) [15] have ...
ABSTRACTAdvanced and novel fabrication methods are needed to build complex three-dimensional scaf... more ABSTRACTAdvanced and novel fabrication methods are needed to build complex three-dimensional scaffolds that incorporate multiple functionally graded biomaterials with a porous internal architecture that will enable the simultaneous growth of multiple tissues, tissue interfaces and blood vessels. The aim of this research is to develop, demonstrate and characterize techniques for fabricating such scaffolds by combining solid freeform fabrication and computational design methods. When fully developed, such techniques are expected to enable the fabrication of tissue engineering scaffolds endowed with functionally graded material composition and porosity exhibiting sharp or smooth gradients. As a first step towards realizing this goal, scaffolds with periodic cellular and biomimetic architectures were designed and fabricated using selective laser sintering in Nylon-6, a biocompatible polymer. Results of bio-compatibility and in vivo implantation studies conducted on these scaffolds are r...
... machines. Alternatively, these structures can be scaled up and then fabricated to have optima... more ... machines. Alternatively, these structures can be scaled up and then fabricated to have optimal porosity for bone tissue regeneration (typically 300-1,200 μm; Hollister, unpublished data) while retaining biomimetic architecture. Shown ...
In this paper, we present a concept for multi-material solid freeform fabrication of heterogeneou... more In this paper, we present a concept for multi-material solid freeform fabrication of heterogeneous components. This concept features hopper-nozzles designed for depositing thin layers of multiple patterned materials followed by selective laser sintering for consolidation to desired ...
High aspect ratio periodic carbon nanotube arrays were fabricated using direct laser interference... more High aspect ratio periodic carbon nanotube arrays were fabricated using direct laser interference patterning with a frequency tripled Nd:YAG (YAG: yttrium aluminium garnet) laser (lambda = 355 nm) emitting 10 ns laser pulses. The depth of the fabricated arrays could be adjusted by controlling the number of laser pulses. Application of successive laser pulses (10-20) induced pattern distortion, resulting in the formation of conical organized arrays. The number of laser pulses necessary to produce this distortion is proportional to the spatial period of the interference pattern. Raman spectroscopy analyses confirmed that the chemical form of the carbon nanotubes was preserved after patterning.
Scalable fabrication of carbon nanotube (CNT) bundles is essential to future advances in several ... more Scalable fabrication of carbon nanotube (CNT) bundles is essential to future advances in several applications. Here, we report on the development of a simple, two-step method for fabricating vertically aligned and periodically distributed CNT bundles and periodically porous CNT films at the sub-micron scale. The method involves laser interference ablation (LIA) of an iron film followed by CNT growth via iron-catalyzed chemical vapor deposition. CNT bundles with square widths ranging from 0.5 to 1.5 µm in width, and 50-200 µm in length, are grown atop the patterned catalyst over areas spanning 8 cm(2). The CNT bundles exhibit a high degree of control over square width, orientation, uniformity, and periodicity. This simple scalable method of producing well-placed and oriented CNT bundles demonstrates a high application potential for wafer-scale integration of CNT structures into various device applications, including IC interconnects, field emitters, sensors, batteries, and optoelectronics, etc.
Athreya, SR, Kalaitzidou, K. and Das, S.(2011), Microstructure, thermomechanical properties, and ... more Athreya, SR, Kalaitzidou, K. and Das, S.(2011), Microstructure, thermomechanical properties, and electrical conductivity of carbon black-filled nylon-12 nanocomposites prepared by selective laser sintering. Polymer Engineering & Science, 51: n/a. doi: ...
ABSTRACT Part I of this study presented a computational model-based approach for enhancing the pe... more ABSTRACT Part I of this study presented a computational model-based approach for enhancing the performance of solid oxide fuel cells (SOFCs) with designed microarchitecture. The performance of such SOFCs was predicted to greatly improve through a systematic computational design and optimization approach. Part II here proves through experimental fabrication and characterization that microarchitectured SOFC performance can be improved as predicted by the model. A real and specific SOFC is chosen, fabricated and characterized to demonstrate the proof-of-concept. Fabrication techniques using sintering and laser ablation are demonstrated. Pore size and geometry are characterized by interferometry-based surface profilometry and scanning electron microscopy. SOFC button cell performance testing including power output performance and electrochemical impedance spectroscopy are performed. The results show that SOFC performance in a microarchitectured cell can be improved over a baseline button cell by 9–17% in current density and by 7–19% in power density.
We present recent results on fabrication of micrometre- and sub-micrometre-scale structures in po... more We present recent results on fabrication of micrometre- and sub-micrometre-scale structures in polyethylene glycol diacrylate (PEG-DA), a biocompatible hydrogel, useful in biomedical applications. The hydrogel structures were fabricated using two laser-based techniques; laser direct-write photopolymerisation, and multiple-beam laser interference photopolymerisation using continuous wave, nanosecond pulsed and femtosecond pulsed lasers, with light wavelengths of 266 nm, 355 nm, 532 nm and 800 nm. Through these techniques, we demonstrated the ability to fabricate fine structures over large areas without the use of templates or masks. Such structures can be useful for a variety of applications including cell biological studies, tissue engineering and drug delivery.
International Journal of Precision Engineering and Manufacturing, 2013
ABSTRACT Electrically conductive polymer nanocomposites were prepared through selective laser sin... more ABSTRACT Electrically conductive polymer nanocomposites were prepared through selective laser sintering (SLS) of polyamide-12 (PA) powder coated with graphite nanoplatelets (GNP) using sonication. The SLS process parameters were optimized in order to maximize the tensile modulus at 3 and 5 wt% GNP. The highest tensile modulus (2.1 GPa) was achieved at 3 wt%. A slight decrease in flexural modulus and strength was observed at 3 and 5 wt% GNP compared with the neat polymer Morphological observation of the graphite-coated PA powder showed fairly homogeneous dispersion. The SLS processed parts were nearly fully dense and the highest density (99.5%) was found at 3 wt% GNP The bulk electrical conductivity of the SLS-processed nanocomposites was found to be 3.8x10(-11) and 6.4x10(-8) S/cm for 3 and 5 wt% GNP respectively.
ABSTRACT Part I [Metall. Mater. Trans. B, 2014, DOI:10.1007/s11663-014-0117-9] presented a compre... more ABSTRACT Part I [Metall. Mater. Trans. B, 2014, DOI:10.1007/s11663-014-0117-9] presented a comprehensive thermal, fluid flow, and solidification model that can predict the temperature distribution and flow characteristics for the processing of CMSX-4 alloy powder through scanning laser epitaxy (SLE). SLE is an additive manufacturing technology aimed at the creation of equiaxed, directionally solidified and single-crystal (SX) deposits of nickel-based superalloys using a fast-scanning laser beam. Part II here further explores the Marangoni convection-based model to predict the solidification microstructure as a function of the conditions at the trailing edge of the melt pool formed during the SLE process. Empirical values for several microstructural characteristics such as the primary dendrite arm spacing (PDAS), the columnar-to-equiaxed transition (CET) criterion and the oriented-to-misoriented transition (OMT) criterion are obtained. Optical microscopy provides visual information on the various microstructural characteristics of the deposited material such as melt depth, CET location, OMT location, PDAS, etc. A quantitative and consistent investigation of this complex set of characteristics is both challenging and unprecedented. A customized image-analysis technique based on active contouring is developed to automatically extract these data from experimental micrographs. Quantitative metallography verifies that even for the raster scan pattern in SLE and the corresponding line heat source assumption, the PDAS follows the growth relation w ~G −0.5V −0.25 (w = PDAS, G = temperature gradient and V = solidification velocity) developed for marginal stability under constrained growth. Models for the CET and OMT are experimentally validated, thereby providing powerful predictive capabilities for controlling the microstructure of SX alloys processed through SLE.
Abstract This paper focuses on modeling of the scanning laser epitaxy (SLE) process that is curre... more Abstract This paper focuses on modeling of the scanning laser epitaxy (SLE) process that is currently being investigated and developed at the Georgia Institute of Technology. SLE is a laser-based manufacturing process for the creation of equiaxed, directionally solidified and single-crystal deposits of nickel superalloys onto superalloy substrates through melting and resolidifícation of alloy powders using a scanning laser beam. The thermal modeling of the system, done in a commercial CFD software package, simulates a heat source moving ...
Virtual Prototyping & Bio Manufacturing in Medical Applications, 2008
Page 1. Chapter 11 Selective Laser Sintering of Polymers and Polymer-Ceramic Composites Suman Das... more Page 1. Chapter 11 Selective Laser Sintering of Polymers and Polymer-Ceramic Composites Suman Das 11.1 Introduction It is widely accepted that rapid prototyping methods based on solid freeform fabrication (SFF) [15] have ...
ABSTRACTAdvanced and novel fabrication methods are needed to build complex three-dimensional scaf... more ABSTRACTAdvanced and novel fabrication methods are needed to build complex three-dimensional scaffolds that incorporate multiple functionally graded biomaterials with a porous internal architecture that will enable the simultaneous growth of multiple tissues, tissue interfaces and blood vessels. The aim of this research is to develop, demonstrate and characterize techniques for fabricating such scaffolds by combining solid freeform fabrication and computational design methods. When fully developed, such techniques are expected to enable the fabrication of tissue engineering scaffolds endowed with functionally graded material composition and porosity exhibiting sharp or smooth gradients. As a first step towards realizing this goal, scaffolds with periodic cellular and biomimetic architectures were designed and fabricated using selective laser sintering in Nylon-6, a biocompatible polymer. Results of bio-compatibility and in vivo implantation studies conducted on these scaffolds are r...
... machines. Alternatively, these structures can be scaled up and then fabricated to have optima... more ... machines. Alternatively, these structures can be scaled up and then fabricated to have optimal porosity for bone tissue regeneration (typically 300-1,200 μm; Hollister, unpublished data) while retaining biomimetic architecture. Shown ...
In this paper, we present a concept for multi-material solid freeform fabrication of heterogeneou... more In this paper, we present a concept for multi-material solid freeform fabrication of heterogeneous components. This concept features hopper-nozzles designed for depositing thin layers of multiple patterned materials followed by selective laser sintering for consolidation to desired ...
High aspect ratio periodic carbon nanotube arrays were fabricated using direct laser interference... more High aspect ratio periodic carbon nanotube arrays were fabricated using direct laser interference patterning with a frequency tripled Nd:YAG (YAG: yttrium aluminium garnet) laser (lambda = 355 nm) emitting 10 ns laser pulses. The depth of the fabricated arrays could be adjusted by controlling the number of laser pulses. Application of successive laser pulses (10-20) induced pattern distortion, resulting in the formation of conical organized arrays. The number of laser pulses necessary to produce this distortion is proportional to the spatial period of the interference pattern. Raman spectroscopy analyses confirmed that the chemical form of the carbon nanotubes was preserved after patterning.
Scalable fabrication of carbon nanotube (CNT) bundles is essential to future advances in several ... more Scalable fabrication of carbon nanotube (CNT) bundles is essential to future advances in several applications. Here, we report on the development of a simple, two-step method for fabricating vertically aligned and periodically distributed CNT bundles and periodically porous CNT films at the sub-micron scale. The method involves laser interference ablation (LIA) of an iron film followed by CNT growth via iron-catalyzed chemical vapor deposition. CNT bundles with square widths ranging from 0.5 to 1.5 µm in width, and 50-200 µm in length, are grown atop the patterned catalyst over areas spanning 8 cm(2). The CNT bundles exhibit a high degree of control over square width, orientation, uniformity, and periodicity. This simple scalable method of producing well-placed and oriented CNT bundles demonstrates a high application potential for wafer-scale integration of CNT structures into various device applications, including IC interconnects, field emitters, sensors, batteries, and optoelectronics, etc.
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