Abstract in English:Abstract In the present paper, a simplified homogenized beam theory is used in the context of a numerical investigation regarding the dynamic behavior of a rotating composite hollow shaft. For this aim, a horizontal flexible composite shaft and a rigid disc form the considered simple supported rotating system. The mathematical model of the rotor is derived from the Lagrange’s equation and the Rayleigh-Ritz method, which is obtained from the strain and kinetic energies of the disc and shaft, and the mass unbalance. In this case, a convergence procedure is carried out in terms of the vibration modes to obtain a representative model for the rotor system. Therefore, the proposed analysis is performed in both frequency and time domains, in which the frequency response functions, the unbalance responses, the Campbell diagram, and the orbits are numerically determined. Additionally, the instability threshold of the rotor system is obtained. This study illustrates the convenience of the composite hollow shafts for rotor dynamics applications.
Abstract in English:Abstract In this work, the modal characteristics, including modal damping, of FRP composite skin, honeycomb core sandwich panels with arbitrary geometries are computed using a mixed finite element-meshless method. By using the meshless node distribution scheme in conjunction with the lagrangian quadrilateral interpolating functions, the continuity of inter-elemental displacements is assured. Since the distribution of the elements is not limited to the geometry of the problem, any arbitrary geometry can be readily analysed by using the same node and element distributions. Using the first order shear deformation plate theory, together with a structural damping model, modal response results are produced for a number of sandwich panel geometries, including triangular, trapezoidal, circular as well as rectangular plates with different combinations of free and clamped edges. Results are compared with those reported in the literature, showing the viability and the accuracy of the method.
Abstract in English:Abstract This paper proposed an integrated algorithm of neuro-fuzzy techniques to examine the complex impact of socio-technical influencing factors on road fatalities. The proposed algorithm could handle complexity, non-linearity and fuzziness in the modeling environment due to its mechanism. The Neuro-fuzzy algorithm for determination of the potential influencing factors on road fatalities consisted of two phases. In the first phase, intelligent techniques are compared for their improved accuracy in predicting fatality rate with respect to some socio-technical influencing factors. Then in the second phase, sensitivity analysis is performed to calculate the pure effect on fatality rate of the potential influencing factors. The applicability and usefulness of the proposed algorithm is illustrated using the data in Iran provincial road transportation systems in the time period 2012-2014. Results show that road design improvement, number of trips, and number of passengers are the most influencing factors on provincial road fatality rate.
Abstract in English:Abstract This paper presents a two-dimensional frame finite element methodology to deal with flexible multi-body dynamic systems and applies it to building progressive collapse analysis. The proposed methodology employs a frame element with Timoshenko kinematics and the dynamic governing equation is solved based on the stationary potential energy theorem written regarding nodal positions and generalized vectors components instead of displacements and rotations. The bodies are discretized by lose finite elements, which are assembled by Lagrange multipliers in order to make possible dynamical detachment. Due to the absence of rotation, the time integration is carried by classical Newmark algorithm, which reveals to be stable to the position based formulation. The accuracy of the proposed formulation is verified by simple examples and its capabilities regarding progressive collapse analysis is demonstrated in a more complete building analysis.
Abstract in English:Abstract In this paper, non-linear dynamics analysis of functionally graded material (FGM) shell structures is investigated using the higher order solid-shell element based on the Enhanced Assumed Strain (EAS). With this element, a quadratic distribution of the shear stress through the thickness is considered in an enhancing part. Material properties of the shell structure are varied continuously in the thickness direction according to the general four-parameter power-law distribution in terms of the volume fractions of the constituents. Performance and accuracy of the present higher order solid-shell element are confirmed by comparing the numerical results obtained from finite element analyses with results from the literature.
Abstract in English:Abstract A new C1 element is proposed to model Euler-Bernoulli beams in one and two-dimensional problems. The proposed formulation assures C1 continuity requirement without the use of rotational degrees of freedom, used in traditional elements, through the use of an Overhauser interpolation scheme for bending displacements. The principle of virtual displacements is used to determine the equilibrium equations and boundary conditions for one and two-dimensional Euler-Bernoulli beams. The Overhauser interpolation is introduced and the new bending interpolation functions are defined. Finally, beam and frame problems are solved with the new formulation and the results are compared to the traditional Euler-Bernoulli element and exact solutions.
Abstract in English:Abstract In this paper, weldability of magnesium alloys by friction stir welding (FSW) method which is difficult to join by the fusion welding have been investigated experimentally and numerically. To this end, the connection of magnesium alloys was performed using different welding parameters. AZ31 Mg-alloy plates were friction stir welded at rotation speed of 1200 rev/min and translational speeds of 80,100,120,140 mm/min. Temperature evolution in the weld zone during welding was measured by using embedded K-type thermocouples. The temperature measurements on both advancing and retreading sides were performed by ten thermocouples. Tensile and Vickers hardness tests were conducted to evaluate the mechanical properties and the hardness distribution on the weld, respectively. During FSW, heat is generated by the friction and plastic deformation. Knowledge of the temperature distribution is requisite since mechanical properties and microstructure are substantially affected by the heat generation. It was observed that the heat generated during the FSW process was increasing and the grain structure was refined as the translational speed was decreasing. In the finite element analyses, modeling of the FSW process were carried out by ANSYS software to determine the temperature and stress distributions in the welded joint during FSW. An APDL (ANSYS Parametric Design Language) code was developed to simulate FSW process. Transient nonlinear finite element analyses were performed at two stages which the first step is thermal analysis which heat transfer from the pin and shoulder to the plates was modeled and the second is the structural analysis which the temperature data obtained from the thermal analysis in the first stage is used.
Abstract in English:Abstract The present paper aims at presenting a methodology for characterizing viscoelastic materials in time domain, taking into account the fractional Zener constitutive model and the influence of temperature through Williams, Landel, and Ferry’s model. To that effect, a set of points obtained experimentally through uniaxial tensile tests with different constant strain rates is considered. The approach is based on the minimization of the quadratic relative distance between the experimental stress-strain curves and the corresponding ones given by the theoretical model. In order to avoid the local minima in the process of optimization, a hybrid technique based on genetic algorithms and non-linear programming techniques is used. The methodology is applied in the characterization of two different commercial viscoelastic materials. The results indicate that the proposed methodology is effective in identifying thermorheologically simple viscoelastic materials.
Abstract in English:Abstract A broad class of engineering systems can be satisfactory modeled under the assumptions of small deformations and linear material properties. However, many mechanical systems used in modern applications, like structural elements typical of aerospace and petroleum industries, have been characterized by increased slenderness and high static and dynamic loads. In such situations, it becomes indispensable to consider the nonlinear geometric effects and/or material nonlinear behavior. At the same time, in many cases involving dynamic loads, there comes the need for attenuation of vibration levels. In this context, this paper describes the development and validation of numerical models of viscoelastic slender beam-like structures undergoing large displacements. The numerical approach is based on the combination of the nonlinear Cosserat beam theory and a viscoelastic model based on Fractional Derivatives. Such combination enables to derive nonlinear equations of motion that, upon finite element discretization, can be used for predicting the dynamic behavior of the structure in the time domain, accounting for geometric nonlinearity and viscoelastic damping. The modeling methodology is illustrated and validated by numerical simulations, the results of which are compared to others available in the literature.
Abstract in English:Abstract The present work focuses on the effects of water degradation on the fatigue behaviour of adhesive joints bonded with aluminium adherends. The objective of this study is to measure the influence that humidity has on the fatigue crack growth velocity of two distinct adhesives characterized using the Paris Law, using double cantilever beam (DCB) specimens in unaged and various aged conditions loaded in mode I in order to understand the influence that water content has on the Paris Law constants. It was found that the slope of the Paris Law curve is not heavily changed with the presence of water, but a shift in the curves does occur, generally resulting in a crack initiating at a lower threshold than in the unaged adhesive. Based on this behaviour, it can be concluded that an increase in water content reduces the fatigue joint strength and lifespan of adhesive joints bonded with the studied adhesives.