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      • KCI등재

        Identification of the Plastic Deformation Characteristics of AL5052-O Sheet Based on the Non-Associated Flow Rule

        Quoc Tuan Pham,김영숙 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.2

        This study aims to determine the plastic deformation characteristics of aluminum 5052-O based on non-associatedflow rule. To achieve this goal, a new strain hardening model named as Kim-Tuan hardening modelis proposed to perfectly describe the stress-strain relation of the studied material in terms of the uniaxial tensiletest and to predict the material’s post-necking behavior. Additionally, the plastic behaviors of AL5052-O sheetare described by two approaches: the associated flow rule with YLD2000-2d yield function and the nonassociatedflow rule with Hill's quadratic function (NAFR-Hill48). The parameters of these functions werederived from the material properties that were obtained from uniaxial tensile tests and bulge test. The flow curvebased on Kim-Tuan model and plastic behaviors obtained from two above-mentioned approaches were importedinto a finite element analysis code to simulate the hydraulic bulge test for this material to confirm the precisionof material characteristics achieved before. The simulation results based on the NAFR-Hill48 match wellwith the experiment results of bulge test while the YLD2000-2d provides highly accurate predictions foranisotropy of this material.

      • KCI등재

        New Stress-Strain Model for Identifying Plastic Deformation Behavior of Sheet Materials

        김영석(Young Suk Kim),팜콕트완(Quoc Tuan Pham),김찬일(Chan Il Kim) Korean Society for Precision Engineering 2017 한국정밀공학회지 Vol.34 No.4

        In sheet metal forming numerical analysis, the strain hardening equation has a significant effect on calculation results, especially in the field of spring-back. This study introduces the Kim-Tuan strain hardening model. This model represents sheet material behavior over the entire strain hardening range. The proposed model is compared to other well known strain hardening models using a series of uniaxial tensile tests. These tests are performed to determine the stress-strain relationship for Al6016-T4, DP980, and CP Ti sheets. In addition, the Kim-Tuan model is used to integrate the CP Ti sheet strain hardening equation in ABAQUS analysis to predict spring-back amount in a bending test. These tests highlight the improved accuracy of the proposed equation in the numerical field. Bending tests to evaluate prediction accuracy are also performed and compared with numerical analysis results.

      • KCI등재

        Determining the Required Vitamin D Level for Bone Health Based on Bone Turnover Markers

        Tuan Salwani Tuan Ismail,Bayani Che Muda,Roznie Aida Mohd Rosdi,Azalina Zainuddin,Salbiah Isa,Zulkarnain Mustapaha 대한임상검사과학회 2017 대한임상검사과학회지(KJCLS) Vol.49 No.4

        To date, no clear threshold that has been established for defining an adequate store of vitamin D for bone health. Therefore, this study aims to determine the required level of vitamin D to maintain a healthy skeleton based on bone remodelling process among healthy adult population. This was a cross sectional study, involving a healthy adult population in Kota Bharu, Malaysia, aged 18∼50 years. We measured serum 25(OH)D (vitamin D), serum parathyroid hormone (PTH), serum C-terminal telopeptide of type 1 collagen (CTX), and Procollagen 1 Intact N-Terminal (P1NP) in 120 healthy adults selected via multi stage sampling (64 males, 56 females) from 6 subdistricts in Kota Bharu. The mean level of 25(OH)D was 23.50 (±8.74) nmol/L. There was a significant difference of the vitamin D level between genders (26.81±8.3 nmol/L vs 19.72±7.68 nmol/L in males and females respectively) (p value<0.001). More than 50% of female subjects had 25(OH)D less than 20 nmol/L, while only 20.3% of male subjects had 25(OH)D below 20 nmol/L. Based on the LOESS plot, the bone turnover markers showed a plateauing result, at the 25(OH)D level of 35 nmol/L for CTX and 20 nmol/L for P1NP. Contrastingly, PTH showed a step rise in the 25(OH)D level of 20 nmol/L. Based on the LOESS plot for CTX, P1NP and PTH versus 25(OH)D, level of vitamin D between 20 to 35 nmol/L is recommended to maintain healthy skeleton.

      • KCI등재

        Determining the Required Vitamin D Level for Bone Health Based on Bone Turnover Markers

        Ismail, Tuan Salwani Tuan,Muda, Bayani Che,Rosdi, Roznie Aida Mohd,Zainuddin, Azalina,Isa, Salbiah,Mustapaha, Zulkarnain Korean Society for Clinical Laboratory Science 2017 대한임상검사과학회지(KJCLS) Vol.49 No.4

        To date, no clear threshold that has been established for defining an adequate store of vitamin D for bone health. Therefore, this study aims to determine the required level of vitamin D to maintain a healthy skeleton based on bone remodelling process among healthy adult population. This was a cross sectional study, involving a healthy adult population in Kota Bharu, Malaysia, aged 18~50 years. We measured serum 25(OH)D (vitamin D), serum parathyroid hormone (PTH), serum C-terminal telopeptide of type 1 collagen (CTX), and Procollagen 1 Intact N-Terminal (P1NP) in 120 healthy adults selected via multi stage sampling (64 males, 56 females) from 6 subdistricts in Kota Bharu. The mean level of 25(OH)D was 23.50 (${\pm}8.74$) nmol/L. There was a significant difference of the vitamin D level between genders ($26.81{\pm}8.3nmol/L$ vs $19.72{\pm}7.68nmol/L$ in males and females respectively) (p value<0.001). More than 50% of female subjects had 25(OH)D less than 20 nmol/L, while only 20.3% of male subjects had 25(OH)D below 20 nmol/L. Based on the LOESS plot, the bone turnover markers showed a plateauing result, at the 25(OH)D level of 35 nmol/L for CTX and 20 nmol/L for P1NP. Contrastingly, PTH showed a step rise in the 25(OH)D level of 20 nmol/L. Based on the LOESS plot for CTX, P1NP and PTH versus 25(OH)D, level of vitamin D between 20 to 35 nmol/L is recommended to maintain healthy skeleton.

      • SCOPUS

        Evaluation of Press Formability of Pure Titanium Sheets

        Pham, Quoc Tuan,Kim, Young Suk Trans Tech Publications, Ltd. 2016 Key Engineering Materials Vol.716 No.-

        <P>Commercially pure titanium (CP Ti) has been actively used in plate heat exchangers due to its light weight, high specific strength, and excellent corrosion resistance. However compared with automotive steels and aluminum alloys, only limited research has been conducted on the plastic deformation characteristics and press formability of CP Ti sheets. In this study, the mechanical properties, including the anisotropic property and the stress-strain relation, of the CP Ti sheet are clarified in relation to press formability. A new proposed strain hardening model, Kim-Tuan equation, is successful in perfectly describing the stress evaluation for strain increment of this material during strain path. The forming limit curve (FLC) of the CP Ti sheet as a criterion for press formability was experimentally evaluated by punch stretching testing and analytically predicted via Hora’s modified maximum force criterion. The predicted FLC based on the Kim-Tuan strain hardening equation and the appropriate yield function correlates well with the experimental results of the punch stretching test.</P>

      • SCISCIESCOPUS

        Characterization of the isotropic-distortional hardening model and its application to commercially pure titanium sheets

        Pham, Quoc Tuan,Lee, Myoung Gyu,Kim, Young Suk Pergamon Press 2019 International journal of mechanical sciences Vol.160 No.-

        <P><B>Abstract</B></P> <P>Commercially pure titanium sheets have been widely used in various industrial applications owing to their lightweight nature, superior formability, and excellent corrosion resistance. Previous studies showed that accurate modelling of material characteristics, such as anisotropic yield function and hardening, is essential for the simulation of sheet metal forming with titanium sheets. For example, the non-quadratic anisotropic yield function Yld2000-2d and the modified Kim–Tuan hardening model were used to model initial anisotropy and reproduce flow stress curves at large strains. However, even with these advanced constitutive models for describing the anisotropic behavior of sheet metals, further improvement is necessary to simulate anisotropy evolution, or distortional hardening, in pure titanium sheets. In this study, distortional hardening was experimentally measured under both uniaxial and balanced biaxial loading conditions. Moreover, the evolution of the Yld2000-2d function was modelled as a function of equivalent plastic work. For validation, the developed material models were applied in finite element simulations to analyse deformation behavior in uniaxial tension, hydraulic bulge, and punch-stretching tests. It was confirmed that this approach accurately described material response during these three tests.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Experimental observation of distortional hardening behaviour and three-stage deformation behavior for a pure titanium sheet. </LI> <LI> A procedure to reproduce these material behaviours for the tested material by using an evolutionary yld2000-2d yield function and modified Kim–Tuan hardening law. </LI> <LI> Simulation results of uniaxial tensile tests, hydraulic bulge test, and punch-stretching tests match well with experimental data. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

      • SCISCIESCOPUS

        Influence of the post-necking prediction of hardening law on the theoretical forming limit curve of aluminium sheets

        Pham, Quoc-Tuan,Lee, Bong-Hyun,Park, Kee-Cheol,Kim, Young-Suk Elsevier 2018 International journal of mechanical sciences Vol.140 No.-

        <P><B>Abstract</B></P> <P>This study clarified the influence of the post-necking prediction of the hardening law on the theoretical forming limit curve (FLC) of aluminium sheets subjected to punch-stretching tests. A procedure was developed to identify the parameters of a recently developed hardening model (Kim–Tuan hardening model) based on the curve fitting method. Subsequently, this model was used to capture the post-necking behaviours of two aluminium alloy sheets (AL5052-O and AL6016-T4), which were compared with those of various other hardening models, including the Swift model, Voce model, Hockett–Sherby model, Ghosh model, and a linear combination of the Swift and Voce models. These hardening models, with their extrapolations for post-necking prediction, were employed to analytically calculate the FLCs of the tested materials based on the modified maximum force criterion (MMFC). Furthermore, a simple and effective method was found to estimate the level of limited strain in the plane strain mode, namely FLC<SUB>0</SUB>. The proposed method was used to clarify the influence of the hardening law and yield function on the level of the computed FLC. The results indicated that the flow curves predicted by the Kim–Tuan hardening model effectively matched the experimental data obtained from uniaxial tensile tests, while their extrapolations provided intermediate predictions of the post-necking behaviour between the flow curves of the Swift and Voce models. In addition, the proposed hardening model improved the accuracy of the computed FLC for the studied materials.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New formulation for strain hardening function is presented. </LI> <LI> A procedure for identifying parameters of proposed hardening model is developed based on curve fitting method. In this procedure, stress and strain data obtained from standard uniaxial tensile test were utilized. </LI> <LI> New method is presented for estimating the level of limited strain in the plane strain mode, FLC<SUB>0</SUB>. Based on this method, influence of post-necking prediction of hardening law on forming limit curve of aluminium sheet is discussed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

      • SCIESCOPUSKCI등재

        QUADRUPLY-IMAGED QUASARS: SOME GENERAL FEATURES

        Tuan-Anh, P.,Thai, T.T.,Tuan, N.A.,Darriulat, P.,Diep, P.N.,Hoai, D.T.,Ngoc, N.B.,Nhung, P.T.,Phuong, N.T. The Korean Astronomical Society 2020 Journal of The Korean Astronomical Society Vol.53 No.6

        Gravitational lensing of point sources located inside the lens caustic is known to produce four images in a configuration closely related to the source position. We study this relation in the particular case of a sample of quadruply-imaged quasars observed by the Hubble Space Telescope. Strong correlations between the parameters defining the image configuration are revealed. The relation between the image configuration and the source position is studied. Some simple features of the selected data sample are exposed and commented upon. In particular, evidence is found for the selected sample to be biased in favor of large magnification systems. While having no direct impact on practical analyses of specific systems, our results have pedagogical value and deepen our understanding of the mechanism of gravitational lensing.

      • Development and Evaluation of Artesunate-Loaded Chitosan-Coated Lipid Nanocapsule as a potential Drug Delivery System Against Breast Cancer

        ( Tuan Hiep Tran ),( Tuan Duc Nguyen ),( Bijay Kumar Poudel ),( Hanh Thuy Nguyeon ),( Jong Oh Kim ),( Chul Soon Yong ),( Chien Ngoc Nguyen ) 영남대학교 약품개발연구소 2016 영남대학교 약품개발연구소 연구업적집 Vol.26 No.-

        Artesunate (ART)-a well-known hydrophobic anti-malarial agent was incorporated in a polymer-lipid hybrid nanocolloidal system for anti-cancer therapeulic, The lipid negatively charged nanocmulsion was formulated by modified hot homogenization method then covered with positively charged chitosan via clectroslatic interaction to obtain chitosan-coated lipid nanocapsule (ART-CLN). Physical properties of the system were characterized in terms of size, charge morphology, drug loading capacity, and physicca stale, In addition, anti-cancer activities were confirmed by conductiong MTT assay for ART and ART-CLN, on different cancer cell lines. Obtained ART_CLN after coating chilosan revelated positive charge (13.2±0.87 mV), small particle size (160.9±3.5 nm), and spherical shape. High drug entrapment cfficiency (95.49±1.13%) and sustaubed rekease pattern were obscrved. Moreover, the good cellular uptake was recorded by flow cytomctry as well as confocal image. Finally, ART-CLN Exhibited stronger anti-cancer activity than free ART on breast cancer cell lines (MCF-7, MDA-MB-231). These results suggested that by lading ART into lipid core of polymer lipid hybrid carrier, the activity and physical stability of ART can be significantly increased for cancer chemotherapy.

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