NANOTECHNOLOGY ENABLED MULTIFUNCTIONAL DAMPING FOR AEROSPACE COMPOSITE STRUCTURES

Jonghwan Suhr,Pulickel M. Ajayan,Gopal P. Mathur 한국소음진동공학회 2008 한국소음진동공학회 국제학술대회논문집 Vol.2008 No.7

다중벽 탄소나노튜브의 형상인자에 따른 고분자 복합재료의 탄성계수에 관한 연구

서종환(Jonghwan Suhr) 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.1

탄소나노튜브는 우수한 기계적 특성으로 인해 주목받고 있으며, 다양한 산업 분야로의 잠재적 활용성을 갖는 고강도/고강성의 나노복합재료를 설계/제작하기 위한 다양한 연구가 이루어 지고 있다. 본 논문에서는 다중벽 탄소나노튜브를 이용한 강화 복합재료를 효과적으로 설계하고, 기계적 물성을 예측/평가하기 위한 미시역학적 해석 방법 연구를 수행하였다. 이를 위해 먼저 대표체적요소 모델을 설계하고 이를 이용한 유한요소 해석을 통해서 강화 복합재료의 기계적 물성을 평가하였다. 특히 MWCNT 의각 형상인자에 따른 복합재료의 탄성계수 변화를 예측하고, 각 인자들의 영향을 정성적으로 평가하였다. 더불어 형상인자들의 복합적 조건에서의 탄성계수에 대한 영향 평가도 수행하였다. The high Young"s modulus and tensile strength of carbon nanotubes has attracted great attention from the research community given the potential for developing super-strong, super-stiff composites with carbon nanotube reinforcements. Over the decades, the strength and stiffness of carbon nanotube?reinforced polymer nanocomposites have been researched extensively. However, unfortunately, such strong composite materials have not been developed yet. It has been reported that the efficiency of load transfer in such systems is critically dependent on the quality of adhesion between the nanotubes and the polymer chains. In addition, the waviness and orientation of the nanotubes embedded in a matrix reduce the reinforcement effectiveness. In this study, we carried out performed micromechanicsbased numerical modeling and analysis by varying the geometry of carbon nanotubes including their aspect ratio, orientation, and waviness. The results of this analysis allow for a better understanding of the load transfer capabilities of carbon nanotube?reinforced polymer composites.

Effect of Grafted Biobased Acrylics on the Mechanical Properties of Polylactic Acid (PLA)/Starch Eco-Friendly Composite

( Marcela Godoy ),( Jonghwan Suhr ) 한국복합재료학회 2022 Composites research Vol.35 No.6

Using non-biodegradable polymers is a severe environmental problem as they are not recyclable and generate a large amount of waste. Biopolymers, such as starch-based composites, have been considered one of the most promising replacement materials. These eco-friendly materials have the advantage of being low-cost, biodegradable, and obtained from renewable sources. However, as starch tends to be brittle and hydrophilic, it can make these materials unusable when exposed to water and limit its processability for further applications. In this work, a biobased modified starch was grafted using two bioderived materials, lauryl methacrylate (LMA) and tetrahydrofurfuryl methacrylate (THFMA), by radical polymerization. A polylactic acid (PLA) composite based on the modified starch (m-St) was fabricated to enhance its toughness. These samples were characterized by Fourier transform infrared, ¹H NMR and ¹³C NMR analysis, optical and scanning electron microscopy. The starch was successfully grafted, thus improving the compatibility with the PLA matrix. The mechanical properties of these films were also studied. Results from mechanical tests showed a slight enhancement of the mechanical performance of these composites when m-St was added to the PLA matrix. Such behavior is related to the improved dispersion of m-St 1:2 on PLA, confirmed by SEM images showing enhanced compatibility between modified starch and PLA matrix. This indicated excellent properties of the produced composite film for further eco-friendly applications.

Printing direction dependence of mechanical behavior of additively manufactured 3D preforms and composites

Quan, Zhenzhen,Suhr, Jonghwan,Yu, Jianyong,Qin, Xiaohong,Cotton, Chase,Mirotznik, Mark,Chou, Tsu-Wei Elsevier 2018 Composite structures Vol.184 No.-

<P><B>Abstract</B></P> <P>Among the processing parameters of additive manufacturing, printing direction is of critical importance. While studies on effects of printing direction have so far mainly focused on mechanical properties of solid specimens, the present research is intended to demonstrate printing direction dependence of mechanical behavior of additively manufactured 3D preforms and their composites. Compressive behavior of additively manufactured 3D braid preforms and composites was investigated for three distinct printing directions (0°, 45° and Z-direction). Fused filament fabrication (FFF) of acrylonitrile-butadiene-styrene (ABS) filament and short carbon fiber/ABS (CF/ABS) filament was adopted. First, solid cube specimens were fabricated; the parts printed along 0° and 45° directions showed more fabrication-induced pores. Then, 3D braid preforms were fabricated and infused with silicone matrix. For preforms printed along 45° direction, inter-yarn adhesion was observed, which enhanced specimen initial modulus. On the other hand, Z-direction specimens showed higher structural ductility, due to inter-yarn slippage.</P>

Super Duplex Stainless Steel Matrix Composites with High Strength and Favorable Ductility Achieved Through Laser Powder Bed Fusion and Powder Mixture

( Yongjian Fang ),( Yali Zhang ),( Jonghwan Suhr ) 한국복합재료학회 2024 Composites research Vol.37 No.2

In order to evade the premature failure of super duplex stainless steels (SDSSs) in some harsh environments, the increase of their mechanical properties is a promising approach. In this study, based on the laser powder bed fusion (LPBF) technique, SDSS matrix composites without post heat treatment were fabricated by using the powder mixture of SDSSs, super austenitic stainless steels (SASSs) and micron-sized TiC particles. Many in-situ TiCxNy nanoparticles were found to be formed by using micron-sized TiC particles in as-built composites, and both fine ferrite and austenite grains were generated. The as-built composites exhibited an excellent combination of high ultimate tensile strength (UTS) (~1066 MPa) and good uniform elongation (UE) (~15.6%), showing a better mechanical property compared with other reported LPBF-fabricated SDSSs, which was mainly attributed to the fine grain, Orowan and dislocation strengthening mechanisms. In particular, the successful fabrication of SDSS matrix composites can set the stage for producing high-performance metallic parts via LPBF technique.

Mechanical behavior of polycarbonate fabricated at different cooling speeds.

Choi, Jong-Hun,Suhr, Jonghwan,Koh, Bong-Hwan American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.10

<P>This comparative study investigates the mechanical properties of polycarbonate in manufacturing conditions of different cooling speed. All experiments were conducted using 0.8 mm thick specimens made of commercial Polycarbonate granule (3 mm), according to the ASTM standard. The test results illustrate that polycarbonate specimens manufactured in fast-cooling (FC) condition exhibit at least five times higher resilience in ambient temperature than those of slow-cooling (SC) condition. However, the resilience of FC polycarbonate specimen quickly deteriorates, as the test temperature reduces to negative 40 degrees C. On the other hand, SC specimens barely changed their tensile properties. Thus, the test reveals that tensile properties of polycarbonate are significantly affected by the cooling speed in the manufacturing stage, and exposed temperature conditions. In this manuscript, the correlations between toughness and yield strength of polycarbonate specimen are summarized and discussed in terms of the cooling conditions and environmental temperature.</P>

Composites with carbon nanotubes and graphene: An outlook

Kinloch, Ian A.,Suhr, Jonghwan,Lou, Jun,Young, Robert J.,Ajayan, Pulickel M. American Association for the Advancement of Scienc 2018 Science Vol.362 No.6414

<P>Composite materials with carbon nanotube and graphene additives have long been considered as exciting prospects among nanotechnology applications. However, after nearly two decades of work in the area, questions remain about the practical impact of nanotube and graphene composites. This uncertainty stems from factors that include poor load transfer, interfacial engineering, dispersion, and viscosity-related issues that lead to processing challenges in such nanocomposites. Moreover, there has been little effort to identify selection rules for the use of nanotubes or graphene in composite matrices for specific applications. This review is a critical look at the status of composites for developing high-strength, low-density, high-conductivity materials with nanotubes or graphene. An outlook of the different approaches that can lead to practically useful nanotube and graphene composites is presented, pointing out the challenges and opportunities that exist in the field.</P>

Spatial strain variation of graphene films for stretchable electrodes

Xu, Ping,Kang, Junmo,Suhr, Jonghwan,Smith, Joseph P.,Booksh, Karl S.,Wei, Bingqing,Yu, Jianyong,Li, Faxue,Byun, Joon-Hyung,Oh, Youngseok,Chou, Tsu-Wei Elsevier 2015 Carbon Vol.93 No.-

<P><B>Abstract</B></P> <P>Graphene films fabricated by chemical vapor deposition are promising electrode materials for stretchable energy storage devices. The buckled four-layer graphene on a polydimethylsiloxane film substrate subject to various applied tensile strains has been characterized by atomic force microscopy and micro-Raman mapping. The small redshift of 2D band and the indiscernible D band demonstrated that the tensile strains of up to 40% only induced a strain variation of less than 0.2% and did not cause any observable damage in the graphene film. This study has confirmed that the graphene film in the buckled state is suitable for its application as a stretchable electrode.</P>

A flexible supercapacitor based on vertically oriented ‘Graphene Forest’ electrodes

Ma, Yifei,Wang, Mei,Kim, Namhun,Suhr, Jonghwan,Chae, Heeyeop The Royal Society of Chemistry 2015 Journal of Materials Chemistry A Vol.3 No.43

<▼1><P>A flexible supercapacitor was demonstrated with ‘graphene forest’ as electrodes. No capacitance loss was observed even with 100 000 times of bending.</P></▼1><▼2><P>Vertically-grown graphene electrodes are developed for flexible electric double-layer capacitors (EDLC). Solid-state electrolytes and large area flexible electrodes are essential parts for wearable applications. In this work, the vertically-grown graphene electrodes were fabricated by a plasma-enhanced chemical vapor deposition process and applied to flexible electrodes of EDLC. The areal capacitance of the capacitor based on vertical graphene is 2.45 mF cm<SUP>−2</SUP>, which is much better even with solid electrolytes when compared to other reported vertical graphene capacitors. The capacitance also shows good flexibility and it remains unaltered even after 100 000 times of bending or 180 degree folding. These unique features of the capacitor could be ascribed to a discrete ‘tree-like’ morphology of the vertical graphene, which has not been known before.</P></▼2>

High Flame Retardancy and High-strength of Polymer Composites with Synergistically Reinforced MOSw and EG

Kim, Chowon,Lee, Jinwoo,Yoon, Hyejeong,Suhr, Jonghwan The Korean Society for Composite Materials 2022 Composites research Vol.35 No.5

Polymers are inherently vulnerable to flame, which limits their application to various high-tech industries. In addition, environmental regulations restrict the use of halogen-based flame retardants which has best flame-retardant effect. There are inorganic flame retardants and phosphorous flame retardants as representative non-halogen-based flame retardants. However, high content of flame retardants is required to impart high flame retardancy of the polymers, and this leads to a decrease in mechanical properties. In this research, a new approach for inorganic flame retardant-based polymer composites with high mechanical properties and flame retardancy was suggested. Inorganic flame retardants called as magnesium oxysulfate whisker (MOSw) were used in this research. MOSw can extinguish fire by releasing water and non-combustible gases when exposed to flame. In addition, they have reinforcing effect when added into the polymer with its high aspect ratio. Expandable graphite (EG) was used as a flame-retardant supplement by helping to form a more dense char layer. Through this research, it is expected that it can be applied to various industries requiring flame retardancy such as automobile, and architecture by replacing halogen-based flame polymer composites.