Vietnam Journal of Mechanics
http://vjs.ac.vn/index.php/vjmech
Publishing House for Science and Technologyen-USVietnam Journal of Mechanics0866-7136<span>1. We hereby assign copyright of our article (the Work) in all forms of media, whether now known or hereafter developed, to the Vietnam Journal of Mechanics (VJMech). We understand that the VJMech will act on my/our behalf to publish, reproduce, distribute and transmit the Work.</span><br /><span>2. This assignment of copyright to the VJMech is done so on the understanding that permission from the VJMech is not required for me/us to reproduce, republish or distribute copies of the Work in whole or in part. We will ensure that all such copies carry a notice of copyright ownership and reference to the original journal publication.</span><br /><span>3. We warrant that the Work is our results and has not been published before in its current or a substantially similar form and is not under consideration for another publication, does not contain any unlawful statements and does not infringe any existing copyright. </span><br /><span>4. We also warrant that We have obtained the necessary permission from the copyright holder/s to reproduce in the article any materials including tables, diagrams or photographs not owned by me/us.</span>Optimal design for eigen-frequencies of a longitudinal bar using Pontryagin's maximum principle considering the influence of concentrated mass
http://vjs.ac.vn/index.php/vjmech/article/view/6058
In this paper, the problem of optimal design for eigen-frequencies of a longitudinal bar using Pontryagin's maximum principle (PMP) considering the influence of concentrated mass is presented. The necessary optimality condition when simultaneously maximizing system's eigen frequencies and minimizing system's weight considering the influence of concentrated mass is established by using Maier objective functional in order to control the final state of the objective functional. By considering eigen frequencies as state variables, the analogy coefficient <em>k</em> in the necessary optimality condition is explicitly determined. Numerical results obtained in this paper include: (1) the bar's optimal configurations as well as frequency responses in different cases of objective functions; (2) the Pareto front for the system's first eigen frequency and weight; (3) the influence of concentrated mass on the bar's optimal configuration.Bui Hai LeTran Minh Thuy2017-03-282017-03-2839Elasto-plastic analysis of functionally graded metal-ceramic beams under mechanical loading
http://vjs.ac.vn/index.php/vjmech/article/view/7481
The elasto-plastic analysis of functionally graded (FG) metal-ceramic beams under mechanical loading by using the finite element method is presented. A bilinear stress-strain relation with isotropic hardening is assumed for elasto-plastic behaviour of metal, and the effective elasto-plastic properties of the functionally graded material are evaluated by using Tamura-Tomota-Ozawa (TTO) model. A nonlinear beam element based on the classical beam theory is formulated and employed in the analysis. The element employed nonlinear von K\'am\'an strain-displacement relationship is derived by using the neutral surface as reference plane. The layer beam approach, in which the plastic rate equation is solved at Gauss points, is adopted in updating the stress and evaluating the element nodal force vector and tangent stiffness matrix. Numerical examples are given to show the accuracy of the derived formulation and to illustrate the effect of the material distribution and plastic deformation on the behavior of the beams. The formation and propagation of plastic zone during the loading process is also examined and highlighted.Nguyen Dinh KienTran Thi ThomSergey Alexandrov2017-03-302017-03-3039Modal analysis of functionally graded Timoshenko beam
http://vjs.ac.vn/index.php/vjmech/article/view/7582
Dynamic analysis of FGM Timoshenko beam is formulated in the frequency domain taking into account the actual position of neutral plane. The problem formulation enables to obtain explicit expressions for frequency equation, natural modes and frequency response of the beam subjected to external load. The representations are straightforward not only to modal analysis and modal testing of FGM Timoshenko beam with general end conditions but also to study coupling of axial and flexural vibration modes. Numerical study is carried out to investigate effect of true neutral axis position and material properties on the modal parameters.Nguyen Ngoc HuyenNguyen Tien Khiem2017-03-302017-03-3039Isogeometric analysis of linear isotropic and kinematic hardening elastoplasticity
http://vjs.ac.vn/index.php/vjmech/article/view/7817
Material nonlinearity is of great importance in many engineering problems. In this paper, we exploit NURBS-based isogeometric approach in solving materially nonlinear problems, i.e. elastoplastic problems. The von Mises model with linear isotropic hardening and kinematic hardening is presented, and furthermore the method can also be applied to other elastoplastic models without any loss of generality. The NURBS basis functions allow us to describe exactly the curved geometry of underlying problems and control efficiently the accuracy of approximation solution. Once the discretized system of non-linear equilibrium equation is obtained, the Newton-Raphson iterative scheme is used. Several numerical examples are tested. The accuracy and reliability of the proposed method are verified by comparing with results from ANSYS Workbench software.Khuong D. NguyenMinh N. NguyenHoa V. CongH. Nguyen-Xuan2017-03-302017-03-3039XFEM/Level-set for modelling\ of coated inclusion composites
http://vjs.ac.vn/index.php/vjmech/article/view/8561
In this paper, Extended Finite Element method (XFEM) is used to model the embedded coated inclusion composite. The coated inclusion with finite thickness is associated with two level-set functions, which describe its inside and outside interfaces. A simple integration rule is employed for numerical quadrature in elements cut by two interfaces. Accuracy and efficiency of the proposed approach are demonstrated through 3D numerical examples and applied to homogenization of such materials.Tran Anh Binh2017-03-302017-03-3039A numerical study of ultrasonic response of random cortical bone plates
http://vjs.ac.vn/index.php/vjmech/article/view/9342
A probabilistic study on ultrasound wave reflection and transmission from cortical bone plates is proposed. The cortical bone is modeled by an anisotropic and heterogeneous elastic plate sandwiched between two fluids and has randomly varied elastic properties in the thickness direction. A parametric stochastic model is proposed to describe the elastic heterogeneity in the plate. Reflection and transmission coefficients are computed <em>via</em> the semi-analytical finite element (SAFE) method. The effect of material heterogeneity on reflected and transmitted waves is investigated from a probabilistic point of view. The parametric study highlights effects of the uncertainty of material properties on the reflection and transmission coefficients by varying the frequency, angle of incidence and bone thickness. <br />A. AbdoulatufV-H. NguyenC. DesceliersS. Naili2017-03-302017-03-3039