Nonlinear thermal buckling analyses of functionally graded circular plates using higher-order shear deformation theory with a new transverse shear function and an enhanced mesh-free method

Van Do, Vuong Nguyen,Lee, Chin-Hyung Springer-Verlag 2018 Acta mechanica Vol.229 No.9

Bending analyses of FG-CNTRC plates using the modified mesh-free radial point interpolation method based on the higher-order shear deformation theory

Do, Vuong Nguyen Van,Lee, Chin-Hyung Elsevier 2017 COMPOSITE STRUCTURES -BARKING THEN OXFORD- Vol.168 No.-

<P><B>Abstract</B></P> <P>This study presents nonlinear bending analyses of functionally graded (FG) carbon nanotube-reinforced composite (CNTRC) plates using the modified mesh-free radial point interpolation method (RPIM). The nonlinear bending formulations of the FG-CNTRC plates are derived from the modified RPIM which employs a new radial basis function able to construct the shape functions without the need for introducing supporting fixing coefficients based on the higher-order shear deformation plate theory. Single-walled carbon nanotubes (SWCNTs) are selected as the reinforcement and the effective material properties of the FG-CNTRC plates are evaluated by an equivalent continuum model based on the rule of mixture. The simulated results by the modified RPIM are compared with the other numerical solutions to verify the effectiveness and the accuracy of the developed mesh-free method. Detailed parametric studies are then performed to explore the effects that the plate width-to-thickness ratio, aspect ratio, load type, boundary condition and initial deflection have on the nonlinear flexural responses of the CNTRC plates, and the results for uniformly distributed (UD) CNTRC plate are provided for comparison. Results demonstrate that the modified mesh-free RPIM can effectively predict the nonlinear bending behavior of the CNTRC plates.</P>

Nonlinear analyses of FGM plates in bending by using a modified radial point interpolation mesh-free method

Van Do, Vuong Nguyen,Lee, Chin-Hyung Butterworths [etc.] 2018 Applied mathematical modelling Vol.57 No.-

<P><B>Abstract</B></P> <P>A modified mesh-free radial point interpolation method (RPIM) which employs a new radial basis function capable of building the shape functions without any supporting fixing parameters is developed for the nonlinear bending analyses of functionally graded material (FGM) plates. The shape functions constructed by the RPIM possess Kronecker delta function property and thus special schemes for imposing boundary conditions are not needed. The nonlinear bending formulations of FGM plates are based on a higher-order shear deformation plate theory considering the von Kármán large deflection assumption. The nonlinear equations are solved by the modified Newton–Raphson iterative technique. The computed results by the modified RPIM are compared with the other numerical solutions reported in the literature to verify the effectiveness and accuracy of the proposed mesh-free method. Detailed parametric studies are then carried out to scrutinize the effects that the volume fraction, plate length-to-thickness ratio, boundary condition and initial deflection have on the nonlinear flexural responses of FGM plates. Results illustrate that the modified mesh-free RPIM can effectively predict the nonlinear bending behavior of FGM plates.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Modified mesh-free radial point interpolation method was presented and verified. </LI> <LI> New normalized radial basis function was introduced to build the shape functions. </LI> <LI> Higher-order shear deformation plate theory was incorporated into the mesh-free method. </LI> <LI> Nonlinear bending analyses of functionally graded material plates were performed. </LI> <LI> The modified mesh-free method can effectively predict the nonlinear bending behavior. </LI> </UL> </P>

Numerical investigation on post-buckling behavior of FGM sandwich plates subjected to in-plane mechanical compression

Do, Vuong Nguyen Van,Lee, Chin-Hyung Elsevier 2018 Ocean engineering Vol.170 No.-

<P><B>Abstract</B></P> <P>This study intends to numerically analyze post-buckling behavior of functionally graded material (FGM) sandwich plates under mechanical edge compression. A simple yet accurate meshless approximation based on the radial point interpolation method (RPIM) and the higher-order shear deformation theory (HSDT) is presented and used to predict the post-buckling responses. The HSDT constructs a von Kármán type nonlinear equation which accounts for both the large deformation and the initial geometric imperfection for imperfect FGM sandwich plate. The field variables are approximated by introducing the radial basis function in a compactly supported form through which the shape functions are constructed without any fitting parameters. A solution procedure which utilizes the modified Newton-Raphson iterative scheme is designed to solve the discretized system equations needed to obtain the post-buckling path. Performance accuracy of the mesh-free approximation is confirmed by the comparative studies, followed by the detailed parametric investigations to elucidate the post-buckling characteristics of FGM sandwich plates subjected to in-plane mechanical compression. Results illustrate that the proposed mesh-free method can be used as a simple and accurate numerical tool for predicting the post-buckling responses of FGM sandwich plates, and the initial geometric imperfection and loading type have significant effects on the post-buckling behavior.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Post-bucking analysis of FGM sandwich plates under in-plane mechanical compression is performed. </LI> <LI> A simple yet accurate mesh-free approximation for the post-buckling analysis is presented. </LI> <LI> An algorithm based on the modified Newton-Raphson iterative scheme for tracing the post-buckling path is developed. </LI> <LI> The proposed mesh-free method can accurately predict the post-buckling responses. </LI> <LI> Initial geometric imperfection and loading type (uniaxial or biaxial) significantly affect the post-buckling behavior. </LI> </UL> </P>

Objectively Measured Physical Activity of Vietnamese Adults With Type 2 Diabetes: Opportunities to Intervene

Do, Vuong Van,Jancey, Jonine,Pham, Ngoc Minh,Nguyen, Chung Thanh,Hoang, Minh Van,Lee, Andy H. The Korean Society for Preventive Medicine 2019 Journal of Preventive Medicine and Public Health Vol.52 No.2

Objectives: To objectively determine and compare the physical activity (PA) levels of adults newly diagnosed with type 2 diabetes (T2D) and adults without T2D in Vietnam using an accelerometer. Methods: A total of 120 participants with newly diagnosed T2D and 120 adults without T2D were recruited from a large hospital in Hanoi, the capital city of Vietnam. All participants wore an ActiGraph GT3X accelerometer for at least 5 days, including 1 weekend day. Freedson cut-off points were used to estimate different intensities of PA. In addition, comparisons between groups were made with respect to achieving the World Health Organization (WHO) and International Diabetes Federation (IDF) recommended PA guidelines. Results: Men with T2D had significantly lower levels of PA than men without T2D. The respective multivariable-adjusted mean values of daily step count, daily light-intensity, moderate-intensity, and moderate-to-vigorous-intensity PA were approximately 14%, 19%, and 22% lower in the men with T2D than in their non-T2D counterparts. However, women with T2D accumulated a greater number of steps per day than women without T2D. Only 59.2% of the adults with T2D met the minimum recommended level of PA (WHO and IDF), compared to 74.2% of adults without T2D (p<0.05). After adjusting for potential confounders, participants with T2D experienced 50.0% significantly lower odds of achieving PA recommendations. Conclusions: Vietnamese men with T2D were less physically active than those without T2D, and adults with T2D were less likely to meet PA guidelines. The results suggest a need for integrating PA into the self-management of this chronic condition.

Determining Ideal Strength and Electronic Properties of Ge/Si Core-Shell Nanowires

Vuong Van Thanh,Nguyen Tuan Hung,Tran The Quang,Do van Truong 한국정밀공학회 2019 한국정밀공학회지 Vol.36 No.8

Core/shell nanowire (NW) is recognized as promising one-dimensional material for nanoelectronic and nanoelectromechanical systems. However, its mechanical properties so important for engineering applications remain largely unexplored. Based on the density functional theory (DFT), we theoretically investigate mechanical and electronic properties of the Ge-core/Si-shell NWs along the [100] direction within the cross sectional size of 1.0 nm and 1.4 nm under the axial strain. Our results show that ideal strength of Ge-core/Si-shell NWs strongly depends on wire cross sectional size compared with that of the Si and Ge NWs. Ideal strength (maximum tensile strength) of Ge-core/Si-shell NWs increases significantly when increasing thickness of the Si-shell. We found that bond lengths around interfaces between the core and the shell play a predominant role in ideal strength of Ge-core/Si-shell NWs. Additionally, band structures of NWs are modififed by applying axial strain. Band gaps of NWs decrease with increasing strain. Our results provide important insight into intrinsic mechanical behavior and electronic properties of Ge-core/Si-shell NWs, useful for the design of nanodevices with Ge-core/Si-shell NWs in future applications.

Quasi-3D isogeometric buckling analysis method for advanced composite plates in thermal environments

Do, Vuong Nguyen Van,Lee, Chin-Hyung Elsevier 2019 Aerospace science and technology Vol.92 No.-

<P><B>Abstract</B></P> <P>A quasi-3D isogeometric thermal buckling analysis method for advanced composite plates such as functionally graded plates is presented. A new quasi-3D plate theory for the numerical analysis, which enables the normal deformations to be considered with only four unknowns, is introduced. A simple trigonometric normal shape function that is able to accurately express the through-thickness displacement while facilitating the numerical computation is developed. The refined quasi-3D theory is combined with the non-uniform rational B-spline (NURBS)-based isogeometric analysis (IGA) which satisfies the <SUP> C 1 </SUP> -continuity of the displacement field required by the proposed theory to resolve the thermal buckling issue. Several numerical examples which entail buckling analysis of diverse types of functionally graded plates including the one with a complex cutout under different temperature gradients through the thickness are simulated to validate the quasi-3D isogeometric approach, and to explore the thermal buckling response of functionally graded plates. The present quasi-3D IGA is concluded to be accurate and effective numerical method, and significance of including the thickness expansion effects in the thermal buckling assessment of functionally graded plates is confirmed.</P>

Quasi-3D higher-order shear deformation theory for thermal buckling analysis of FGM plates based on a meshless method

Do, Vuong Nguyen Van,Lee, Chin-Hyung Elsevier 2018 AEROSPACE SCIENCE AND TECHNOLOGY Vol.82 No.-

<P><B>Abstract</B></P> <P>This study introduces a new quasi-3D (three-dimensional) higher-order shear deformation theory (HSDT) capable of accounting for the through-thickness deformations with only four unknowns, which is suited to the numerical method for buckling analysis of functionally graded material (FGM) plates in thermal environments. The refined quasi-3D HSDT is incorporated into the improved meshless radial point interpolation method (RPIM) in order to scrutinize the thermal buckling responses of FGM plates. In the improved RPIM, the radial basis function is presented in a compactly supported form to build the shape functions without any fitting parameters. Parametric studies on the buckling behavior of FGM plates under various types of through-thickness temperature changes are conducted and the effects of temperature distribution on the plate surface are investigated. Results illustrate the accuracy of the proposed meshless method based on the refined quasi-3D HSDT and the improved RPIM for predicting the thermal buckling behavior of FGM plates.</P>

Objectively Measured Physical Activity of Vietnamese Adults With Type 2 Diabetes: Opportunities to Intervene

Vuong Van Do,Jonine Jancey,Ngoc Minh Pham,Chung Thanh Nguyen,Minh Van Hoang,Andy H. Lee 대한예방의학회 2019 Journal of Preventive Medicine and Public Health Vol.52 No.2

Objectives: To objectively determine and compare the physical activity (PA) levels of adults newly diagnosed with type 2 diabetes (T2D) and adults without T2D in Vietnam using an accelerometer. Methods: A total of 120 participants with newly diagnosed T2D and 120 adults without T2D were recruited from a large hospital in Hanoi, the capital city of Vietnam. All participants wore an ActiGraph GT3X accelerometer for at least 5 days, including 1 weekend day. Freedson cut-off points were used to estimate different intensities of PA. In addition, comparisons between groups were made with respect to achieving the World Health Organization (WHO) and International Diabetes Federation (IDF) recommended PA guidelines. Results: Men with T2D had significantly lower levels of PA than men without T2D. The respective multivariable-adjusted mean values of daily step count, daily light-intensity, moderate-intensity, and moderate-to-vigorous-intensity PA were approximately 14%, 19%, and 22% lower in the men with T2D than in their non-T2D counterparts. However, women with T2D accumulated a greater number of steps per day than women without T2D. Only 59.2% of the adults with T2D met the minimum recommended level of PA (WHO and IDF), compared to 74.2% of adults without T2D (p<0.05). After adjusting for potential confounders, participants with T2D experienced 50.0% significantly lower odds of achieving PA recommendations. Conclusions: Vietnamese men with T2D were less physically active than those without T2D, and adults with T2D were less likely to meet PA guidelines. The results suggest a need for integrating PA into the self-management of this chronic condition.

Relaxor characteristics of PSLZT-BMT-based ferroelectric material ceramics

Nguyen Van Thinh,Le Dai Vuong,Do Viet On,Truong Van Chuong,Le Vu Truong Son,Trinh Ngoc Dat,Le Van Thanh Son,Vo Thanh Tung 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.3

(1-x)[(Pb0.94Sr0.05La0.01)(Zr0.54Ti0.46)0.9975O3]-x[Bi(Mn1/2Ti1/2)O3] (PSLZT-BMT) ferroelectric material ceramics with x in therange of 0-0.05 mol were successfully synthesized following the conventional solid-phase route. The materials were thoroughlyinvestigated to study their structural phase, microstructure, ferro-piezoelectric characteristics, and dielectric behavior. Theexperimental results show that the density of the samples decreased from 7.75 to 7.58 g/cm3, and the relative density decreasedin the range of 98.48%-96.28%. However, with increasing contents of BMT, the dielectric and ferroelectric properties ofPSLZT-BMT ceramics tend to decrease, specifically the maximum dielectric constant (εmax) of PSLZT-BMT decreased in therange of 23579-9991 and the residual polarization (Pr) decreases in the range of 22.54-7.87 μC/cm2 when the doping contentincreased in the range of 0.0-0.05 mol. The diffusivity values (γ) of the PSLZT-BMT material are 1.74, 1.78, 1.82, 1.84, 1.79,and 1.77 when the doping content x varies as 0.0, 0.01, 0.02, 0.03, 0.04, and 0.05 mol, respectively, which is characteristic ofrelaxor ferroelectric materials. Besides, the Tm, TB, TC-W, and C values depend on BMT concentration, and the trend decreases.