Abstract in English:Abstract In this study a newly developed thin-walled structure with the combination of circular and square sections is investigated in term of crashworthiness. The results of the experimental tests are utilized to validate the Abaqus/ExplicitTM finite element simulations and analysis of the crush phenomenon. Three polynomial meta-models based on the evolved group method of data handling (GMDH) neural networks are employed to simply represent the specific energy absorption (SEA), the initial peak crushing load (P1) and the secondary peak crushing load (P2) with respect to the geometrical variables. The training and testing data are extracted from the finite element analysis. The modified genetic algorithm NSGA-II, is used in multi-objective optimisation of the specific energy absorption, primary and secondary peak crushing load according to the geometrical variables. Finally, in each optimisation process, the optimal section energy absorptions are compared with the results of the finite element analysis. The nearest to ideal point and TOPSIS optimisation methods are applied to choose the optimal points.
Abstract in English:Abstract The aim of this paper is to analyse two-dimensional linear elastic continuum containing multiple interacting cracks. Both the mechanical model and the numerical approach are addressed throughout the text as key concepts for the computational framework, whose main characteristics will be described. The Splitting Method is a decomposition method considered for mechanical modeling of multiple interacting cracks. Accordingly, the original problem is divided into a set of global and local sub-problems. The Generalized Finite Element Method (GFEM) is adopted aiming at finding accurate numerical solutions for local sub-problems. Such problems are conceived so as to consider the stress concentration and the effects of interaction on the cracks. The main findings are related to the effectiveness of the proposed combination between the Splitting Method and the GFEM to provide accurate results, as well as the versatility of the conceived computational framework for analyzing different scenarios, including cracks of multilinear shapes and mixed mode fractures. Finally, it is possible to verify that the GFEM provides precise results using simpler meshes, in comparison with standard FEM used, for example in Franc2D(r).
Abstract in English:Abstract This paper investigates the numerical modeling of the flexural wave propagation in Euler-Bernoulli beams using the Hermite-type radial point interpolation method (HRPIM) under the damage quantification approach. HRPIM employs radial basis functions (RBFs) and their derivatives for shape function construction as a meshfree technique. The performance of Multiquadric(MQ) RBF to the assessment of the reflection ratio was evaluated. HRPIM signals were compared with the theoretical and finite element responses. Results represent that MQ is a suitable RBF for HRPIM and wave propagation. However, the range of the proper shape parameters is notable. The number of field nodes is the main parameter for accurate wave propagation modeling using HRPIM. The size of support domain should be less thanan upper bound in order to prevent high error. With regard to the number of quadrature points, providing the minimum numbers of points are adequate for the stable solution, but the existence of more points in damage region does not leads to necessarily the accurate responses. It is concluded that the pure HRPIM, without any polynomial terms, is acceptable but considering a few terms will improve the accuracy; even though more terms make the problem unstable and inaccurate.
Abstract in English:Abstract The present paper studies the Propagation of SH waves in a double non-homogeneous crustal layers lying over an isotropic homogeneous half-space, where upper layer ((i.e. rigidity and density varying trigonometrically with depth) and intermediate layer (i.e. rigidity and density varying parabolically with depth). The wave velocity equation has been obtained. Closed form solutions have been derived separately for the displacements in two non-homogeneous crustal layers and lower half-space. The dispersion curves are depicted by means of graphs for different values of non-homogeneity parameters and thickness ratio for layers.
Abstract in English:Abstract In this paper, the problem of vibration suppression of a smart composite plate with bonded piezoelectric patches is considered. A higher order plate model is used for finite element modeling of the plate and the PID controller is used to generate control voltage command to the piezo actuators from the piezo sensors data. Derived formulation and the control algorithm is implemented in a finite element (FE) code and the FE modeling results are verified using available results of previous studies. The effect of control gain on the vibration suppression characteristics is studied. Furthermore, since FE modeling reduces the order of the real problem, the problem of un-modeled residual modes on the so-called spillover effect is investigated.
Abstract in English:Abstract Experiments and modeling aimed at assessing the mechanical response of latex balloons in the inflation test are presented. To this end, the hyperelastic Yeoh material model is firstly characterized via tensile test and, then, used to numerically simulate via finite elements the stress-strain evolution during the inflation test. The numerical pressure-displacement curves are validated with those obtained experimentally. Moreover, this analysis is extended to a biomedical problem of an eyeball under glaucoma conditions.
Abstract in English:Abstract In this research work, an exact analytical solution for frequency characteristics of the free vibration of rotating functionally graded material (FGM) truncated conical shells reinforced by eccentric FGM stringers and rings has been investigated by the displacement function method. Material properties of shell and stiffeners are assumed to be graded in the thickness direction according to a simple power law distribution. The change of spacing between stringers is considered. Using the Donnell shell theory, Leckhnisky smeared stiffeners technique and taking into account the influences of centrifugal force and Coriolis acceleration the governing equations are derived. For stiffened FGM conical shells, it is difficult that free vibration equations are a couple set of three variable coefficient partial differential equations. By suitable transformations and applying Galerkin method, this difficulty is overcome in the paper. The sixth order polynomial equation for w is obtained and it is used to analyze the frequency characteristics of rotating ES-FGM conical shells. Effects of stiffener, geometrics parameters, cone angle, vibration modes and rotating speed on frequency characteristics of the shell forward and backward wave are discussed in detail. The present approach proves to be reliable and accurate by comparing with published results available in the literature.
Abstract in English:Abstract In this paper, a micromechanical extension of the finite-volume direct averaging micromechanics theory (FVDAM) is presented for evaluation of the homogenized relaxation moduli of linear viscoelastic unidirectional fiber reinforced composites with periodic microstructures. Such materials are assumed as composed of repeating unit cell with arbitrary internal architectural arrangements of fibers coated by thin flexible interphases. These interphases are replaced by equivalent imperfect interface elements with imposed continuity in tractions and discontinuity in displacements. Indeed, the proposed computational procedure allows an easy and efficient treatment of the displacement discontinuity condition across the interfaces. The viscoelastic behavior of the constituent phases is modeled using the generalized Maxwell model. The formulation is particularly derived for the range of small strains, operating directly in the time domain using a numerical incremental time-stepping procedure based on the concept of internal stress variables. The performance of the proposed approach is demonstrated through homogenization of viscoelastic fiber reinforced composites and periodic multilayer materials with flat and wavy architectures.
Abstract in English:Abstract Using GDQ method, the radial and circumferential stresses in an annular FGM plate with a uniform thickness under a transverse axisymmetric load is investigated. It is assumed that a uniform radial magnetic field acts on the top surface of the plate. The modulus of elasticity E and the magnetic permeability coefficient μ of the plate along its thickness are assumed to vary according to the volume distribution function. The Poisson's ratio ν is considered to be constant. Based on the classical plate theory (CPT), equilibrium equations are deduced and the displacement fields are determined. The radial and circumferential stresses as well as transverse and radial displacements are obtained accordingly. The effect of volume fraction function power m on the maximum deflection in the absence and presence of the magnetic field is also investigated. Moreover, the effect of t/a and b/a ratios on displacements, stresses, induction magnetic field intensity and the resulting Lorentz force are also investigated. According to the results, for different points along the radial direction, the application of radial magnetic field to the top surface of the plate completely changes the state of stress in both tangential and radial directions, resulting in tensile and compressive stresses in these two directions. The results also indicate that in presence of magnetic field, the plate displacement and stress components are lowered considerably.
Abstract in English:Abstract Control of time delay integrating systems is a challenging and on-going research. In this paper a new structure for control of stable and integrating time delay systems is presented. The control design process is as simple as selection of some constant gains, for which simple formulae are introduced. The design methods are derived analytically, while no fractional approximation for the time delay term of the plant transfer function is used. Simulation, as well as, experimental studies reveal the exceptional effectiveness of the proposed methods in achieving a robust and well-performing tracking, even when the plant pure time delay is very large.