INVESTIGATION OF MODE Ⅱ AND MIXED MODE FRACTURE OF SINGLE LAYER GRAPHENE SHEET

Minh-Ky Nguyen,Young Jin Yum 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.4

Mode I fracture toughness analysis of a single-layer grapheme sheet

Minh-Nguyen Ky,염영진 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.9

To predict the fracture toughness of a single-layer graphene sheet (SLGS), analytical formulations were devised for the hexagonalhoneycomb lattice using a linkage equivalent discrete frame structure. Broken bonds were identified by a sharp increase in the position ofthe atoms. As crack propagation progressed, the crack tip position and crack path were updated from broken bonds in the molecular dynamics(MD) model. At each step in the simulation, the atomic model was centered on the crack tip to adaptively follow its path. A newformula was derived analytically from the deformation and bending mechanism of solid-state carbon-carbon bonds so as to describe themode I fracture of SLGS. The fracture toughness of single-layer graphene is governed by a competition between bond breaking and bondrotation at a crack tip. K-field based displacements were applied on the boundary of the micromechanical model, and FEM results wereobtained and compared with theoretical findings. The critical stress intensity factor for a graphene sheet was found to beKIC = 2.63 ~ 3.2MPa m for the case of a zigzag crack.

단층 그래핀시트의 모드 II 및 혼합모드 파괴

웬민키(Minh-Ky Nguyen),염영진(Young-Jin Yum) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.2

중앙에 균열을 갖는 단층 그래핀시트(single layer graphene sheet, SLGS)의 모드 II 파괴 거동을 원자시뮬레이션과 해석 모델에 기초하여 고찰하였다. 지그재그 그래핀 모델의 파괴를 분자동역학(molecular dynamics, MD)에 의해 해석한 결과 모드 II 파괴인성은 2.04MPa√m인 것으로 밝혀졌다. 또한 SLGS 의 이론적인 KIIc 를 유도하기 위해 면내전단하중을 받는 다공체에 대한 파괴역학적 해석도 진행하였고 유한요소해석도 병행하였다. 모드 I 과 모드 II 의 비를 다양하게 변화시켜가면서 SLGS 의 혼합모드 파괴를 검토한 결과 혼합모드 파괴조건식이 얻어졌고 다른 문헌의 결과와 비슷함을 알 수 있었다. The mode II fracture behavior of a single-layer graphene sheet (SLGS) containing a center crack was characterized with the results of an atomistic simulation and an analytical model. The fracture of zigzag graphene models was analyzed with molecular dynamics and the mode II fracture toughness was found to be 2.04 MPa√m. The in-plane shear fracture of a cellular material was analyzed theoretically for deriving the KIIc of SLGS, and FEM results were obtained. Mixed-mode fracture of SLGS was studied for various mode I and mode II ratios. The mixed-mode fracture criterion was determined, and the obtained fracture envelope was in good agreement with that of another study.

분자역학을 사용한 단층 그래핀 시트의 모드 III 파괴인성

웬민키(Minh-Ky Nguyen),염영진(Young-Jin Yum) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.2

단층 그래핀 시트(Single layer graphene sheet, SLGS)의 찢어짐 모드(모드 III) 파괴 예측을 위한 원자기반 미세결합요소모델이 개발되었다. 이 모델은 그래핀 시트의 최대 변형률 관계를 예측하기 위해 수정된 모스포텐셜을 사용한다. 면외 전단하중 조건에서 그래핀의 모드 III 파괴를 광범위한 분자역학(Molecular mechanics, MM) 시뮬레이션으로 조사하였다. 분자역학은 원자의 균열선단 근처 원자의 변위를 설명하기 위해 사용되었고, 선형탄성파괴역학은 이 영역 바깥의 영역을 설명하기 위해 사용되었다. 해석 결과 분자역학 방법이 SLGS 의 전단 물성 계산뿐만 아니라 armchair 및 zigzag 방향 모드 III 파괴인성 연구에도 단순하면서도 신뢰할만하다는 것을 보여준다. SLGS 의 모드 III 파괴인성은 zigzag 방향에 대해, 0.86MPa√m armchair 방향에 대해 0.93 MPa√m 로 예측되었다. An atomistic-based finite bond element model for predicting the tearing mode (mode III) fracture of a singlelayer graphene sheet (SLGS) is developed. The model uses the modified Morse potential for predicting the maximum strain relationship of graphene sheets. The mode III fracture of graphene under out-of-plane shear loading is investigated with extensive molecular mechanics simulations. Molecular mechanics is used for describing the displacements of atoms in the area near a crack tip, and linear elastic fracture mechanics is used outside this area. This work shows that the molecular mechanics method can provide a reliable and yet simple method for determining not only the shear properties of SLGS but also its mode III fracture toughness in the armchair and the zigzag directions; the determined mode III fracture toughness values of SLGS are 0.86MPa√m and 0.93MPa√m, respectively.

Benzyl Glycosides from the Aerial Parts of Gynostemma laxum and Their NF-κB Inhibitory Activity in HepG2 Cells

Pham, Thanh Ky,Pham, Tuan Anh,Phan, Van Kiem,Chau, Van Minh,Nguyen, Xuan Nhiem,Bui, Huu Tai,Nguyen, Thi Thanh Ngan,Tran, Hong Quang,Nguyen, Nguyen Phuong,Kim, Young-Ho Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.10

Removal of nutrients and organic pollutants from domestic wastewater treatment by sponge-based moving bed biofilm reactor

Huynh Tan Nhut,Nguyen Tri Quang Hung,Tran Cong Sac,Nguyen Huynh Khanh Bang,Tran Quang Tri,Nguyen Trung Hiep,Nguyen Minh Ky 대한환경공학회 2020 Environmental Engineering Research Vol.25 No.5

This study evaluates the efficiency of domestic wastewater treatment via Sponge-Based Moving Bed Biofilm Reactor (S-MBBR). The laboratory-based treatment plan uses polyurethane sponge with a specific surface area was 260 ㎡/㎥ as a carrier. The treatment plan operated under four different organic load rate: OLR1 = 0.4 ㎏ BOD/㎥.day; OLR2 = 0.6 ㎏ BOD/㎥.day; OLR3 = 0.8 ㎏ BOD/㎥.day; and OLR4 = 1.0 ㎏ BOD/㎥.day. During 80 d of the experiment, the highest treatment efficiency was at the organic load rate of 0.4 ㎏ BOD/㎥.day, with COD, SS, TN and TP were found to be 85.0 ± 12.9%, 85.7 ± 5.3%, 68.9 ± 1.7%, and 40.3 ± 0.2%, respectively. In which, the influent SS concentration were from 117.3 to 126.0 ㎎/L, the effluent concentration were in ranged 18.0 to 34.22 ㎎/L, respectively. The values of influent and effluent COD were 298.8 ± 12.88 and 44.8 ± 3.78 ㎎/L in turn. The OLR1 influent TN, TP concentrations were respectively 47.9 ± 2.11 and 3.6 ± 0.15 ㎎/L; the effluent TN, TP concentration were 14.9 ± 0.18 and 2.2 ± 0.06 ㎎/L, respectively. The study suggests that the effluent is within the allowable limits of National technical regulation on domestic wastewater (Column B1), indicating the applicability of S-MBBR for the domestic wastewater treatment plant.

Microwave-assisted synthesis of MgFe2O4-decorated UiO-66(Zr)-NH2 compositesfor collaborative adsorption and photocatalytic degradation of tetracycline

The Ky Vo,Minh Tien Nguyen,Van Cuong Nguyen,김진수 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.9

MgFe2O4-decorated UiO-66(Zr)-NH2 composites (MFO@UN) with different blending ratios were efficientlyprepared by microwave-assisted synthesis. The results indicate that the hybrid composite exhibits high surfacearea and magnetic properties. Moreover, combining ferrite into the UiO-66(Zr)-NH2 framework produces a heterojunctionstructure and an interfacial interaction that improves the composite's visible-light absorption. Tetracyclineremoval experiments show that the MFO@UN composites exhibit excellent photodegradation performance comparedwith the pure ferrite and MOF. The optimal 1.5MFO@UN catalyst (molar Zr4+/MgFe2O4=1.5) exhibits the highestremoval efficiency of approximately ca. ~92% after 90 min of pre-adsorption and 160min of visible-light illumination.The photocatalytic mechanism investigation reveals that photo-induced holes (h+) and ·OH radicals predominantlygovern the photodegradation process. Notably, the separation and immigration of the photo-induced holes and electronsimprove due to the heterojunction structures that form between the two semiconductors. In addition, the prepared catalystsare highly recoverable and renewable. These findings suggest that the microwave-derived MgFe2O4@UiO-66(Zr)-NH2 catalyst may be a promising candidate for treating organic contaminants in wastewater.

Synthesis of ternary core-shell carbon sphere@α-Fe2O3@Ag composites and their application for simultaneous voltammetric detection of uric acid, xanthine, and hypoxanthine

Ho Van Minh Hai,Dinh Quang Khieu,The Ky Vo,Van Cuong Nguyen,김진수 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.3

Core-shell carbon sphere (CS)@α-Fe2O3@Ag was synthesized via a multistep hydrothermal method. First, the D-glucose hydrothermal process was employed to synthesize micron-size CSs on which α-Fe2O3 was grown to obtain the composite sphere of CS@α-Fe2O3. Thereafter, Ag+ was reduced on the surface of the CS@α-Fe2O3 sphere using NaBH4 agent to produce the core-shell CS@α-Fe2O3@Ag. Finally, microsphere composite CS@α-Fe2O3@Ag was coated on a glassy carbon electrode (GCE) to enhance its electrochemical performance in the simultaneous determination of uric acid (UA), xanthine (XN), and hypoxanthine (HP). Results indicated that the CS@α-Fe2O3@Ag-coated GCE exhibited improved voltammetric sensitivity toward UA, XN, and HP compared to bare GCE. The oxidation peak currents of the simultaneous detection of UA, XN, and HP increased linearly in the concentration range of 0.5–8.0 µmol L−1. The detection limits of the fabricated electrodes for UA, XN, and HP were −0.042, 0.089, and 0.048 µmol L−1, respectively, being more sensitive than many other modified GCEs. Moreover, the CS@α-Fe2O3@Ag-coated GCE exhibited good stability and repeatability. This study opens a new perspective for developing highly efficient electrodes for electrochemical analysis.