JOURNAL OF MECHANICAL ENGINEERING AMIRKABIR (AMIRKABIR)
Year:2017 | Volume:48 | Issue:4|Papers Count:13

This article deals with the small-scale effect on the nonlinear free vibration of isotropic thin nano-plate using the nonlocal elasticity plate theory. The formulations are based on the Kirchhoff's plate theory, and von Karman-type nonlinearity is considered in strain displacement relations. To include the small scale and the geometrical nonlinearity effects, the governing differential equations are derived based on the nonlocal elasticity theory in conjunction with the von Karman geometrical model in which the effects of rotary inertia and transverse shear are neglected. With cubic non-linearities, Duffing's equation is solved by elliptic integral and natural frequencies are obtained. Also by means of Jacobi elliptic functions, some analytical solutions for deflection of plate are presented. The efficiency and accuracy of the method are demonstrated by comparing the developed result with those available in literature. The effects of various parameters on the nonlinear vibrations of nanoplates are presented. Occurrence probability of internal resonance in rectangular nanoplate is investigated.

Hydraulic engine mounts are used to support powertrain and reducing transmitted vibration from motors to the frame. One important use of hydraulic engine mounts is in the air industry. In turbofans, the maximum amplitude of vibration occurs at the two distinct frequencies. So, by using an engine mount with maximum flexibility at these frequencies (called notch frequency), one can achieved reducing the transmission of the engine induced vibrations to the cabin. Here in this paper, using bond graph method, linear modeling of a double-notch hydraulic engine mount is done. Then, by applying nonlinear terms, nonlinear modeling of the engine mount is carried out using variance method. It has been shown that the dynamic stiffness will be changed by considering nonlinear terms. Finally, sensitivity analysis is applied to show the effect of each parameter on the dynamic behavior of the mount. It has been shown that the diameters of outer and inner inertia tracks are most effective parameters on the first and second notch frequencies, respectively.

In this paper, the behavior of shape memory actuator is evaluated experimentally and theoretically. Actuator is made of shape memory fibers in elastomer compounds. Prior to embed SMA, a strain of low temperature is applied on them and then the outer surface of the beam is embedded, by applying heat to SMA given that the structural beam is embedded and cannot be return strain recovery are free. have released the tension on the outer surface of pressure will return, this has led to the creation of the beam will be deflection. In this paper, first the relationship of stress - strain- temperature for SMA has been studied. Later, the stress of temperature increase in SMA is calculated based on the theory, differential equations and the beam deflection. Afterward, the experimental tests are performed on smart actuators. Voltage is applied to increase the temperature on SMA in beam and that caused the creation of deflection in beam. This has a fast flexibility, and by controlling the input current to SMA the movement of the beam can be managed.

In this research, the effect of agglomeration and dispersion of the Carbon nanotubes (CNTs) on the viscoelastic properties of CNT-reinforced polymeric nanocomposites is investigated, parametrically. The effective properties of the nanocomposite are obtained by Mori-Tanaka micromechanical approach, assuming completely random oriented CNTs. Considering spherical shaped inclusions for CNTs agglomerated region, two parameters are presented and applied to Mori-Tanaka micromechanical method to model the agglomeration and dispersion of the CNTs. The polymeric matrix is assumed to be viscoelastic. The viscoelastic properties of polymer matrix are simulated by standard linear solid model with three structural parameters. Due to time-dependency of constitutive equation of the matrix, direct using of the micromechanical method is not possible. Hence, the constitutive equations of the matrix are transferred to the Laplace domain and algebraic form the mentioned equations are inserted to the Mori-Tanaka relations. To verify the model, predicted results of that are compared with available experimental data for CNT reinforced polymeric nanocomposites. Investigation of agglomeration parameters shows that the overall properties of the composite can be improved by decreasing agglomeration of the CNTs.

This paper deals with the effect of Poisson's ratio on the static response of smart laminated composite beams. The actuation performance of smart beams with extension and shear mode piezoelectric orientation has been investigated. The first order and high order shear deformation beam theory has been implemented for modelling the problem. The piezoelectric stress resultants are expressed in terms of Heaviside discontinuity functions. The state space approach is used to obtain an analytical solution for the response of smart beams with different boundary conditions. The effect of actuator length, location of piezoelectric patches, order of theory, fibre orientation, boundary condition and Poisson's ratio on the beam deflection, has been investigated. Also the response of beam with complete piezoelectric layer has been obtained with the same procedure and compared with the solution for the beams with piezoelectric patch of same length. Results show that neglecting Poisson's effect in calculations causes significant errors in the response of angle ply beam with extension mode actuators.

In sheet forming processes, using Forming Limit Diagrams (FLDs) in study of formability and designi die is very important. One method to achieve the curves of FLDs that has validate and appropriate results is Marciniak-Kuczynski model. This model is a way to predict the local necking. In the present study, FLDs were achieved by imposing the theoretical Marciniak–Kuczynski model in two different finite element model and using Abaqus. In the first model, the theory of Marciniak–Kuczynski was imposed to finite element of Nakazima test and in second one (Flat), the theory of Marciniak–Kuczynski was simulated. The input data for these simulations was obtained from tension tests in three different directions. After comparing the results of Flat and Nakazima finite element model with empirical results, the FLD obtained from the finite element of Nakazima test was valid and less than 10 percent below the empirical FLD. Bending is the reason of difference between FLD obtained from Flat model and empirical one.

Internal pressure and axial feeding are the most important factors in tube hydroforming process. The internal fluid pressure and the material feeding that is produced by punch axial loading form the tube. How to apply these two parameters simultaneously in combination has effects on the quality, thickness and forming limit of the final piece. In this paper, the effects of internal pressure and axial feeding paths were investigated to improve the thickness distribution of stepped cylindrical tubes and the wrinkles in the loading path were used to create a new method for removing the wrinkles. Firstly, the constant pressure loading paths with various pressure levels were investigated. Then, the pressure levels in which the parts weren’t burst and formed perfectly or formed with wrinkles were chosen and the effect of axial feeding on these paths were examined separately. The results showed that the axial feeding in the initial step of increasing pressure improves the part thickness distribution in final step. In addition, through using this new method, the wrinkles on tube body were eliminated at the end of the process by changing the direction of axial feeding, and consequently the sound part with better thickness was obtained. Furthermore, using stepped loading path improved thickness distribution uniformity through applying this new method of wrinkle elimination.

In Fracture phenomenon of orthotropic materials, generally in crack tip vicinity, an area called damaged zone appears that in quasi-brittle materials, is known as fracture process zone. This area contains a multitude of micro cracks which due to various reasons, failure analysis and fracture process of these materials has been difficult. Determination of Mechanical properties in this region can help to predict the value or even the direction of crack growth in orthotropic materials. So far, several models have been proposed to determine the mechanical properties of this region, but due to the immense complexity of this region, the results have not been expressed the behavior of this region properly. Moreover, the existence methods have not been verified with new experimental and numerical data, yet. the present paper, it was attempted to present a new numerical model based on viscoelastic theory (the linear springs and damping) and, according to Perony series, the mechanical properties of the damaged zone simulated. In new approach, that is based on experimenal and FEM results, the mechanical behavior of damaged zone can accurately simulated.

In order to access the reliable structures, detection of the damages initiation and evolution in materials is necessary. Delamination is the most common failure mode in laminated composites. The present study is concerned with an investigation of initiation and propagation behavior of delamination using Acoustic Emission (AE) method. In this work, various lay-ups of glass/epoxy composite laminates have been fabricated and subjected to mode I quasi-static loading condition. The behavior of delamination is investigated in two sections. In the first section, the main focus is on the initiation of damage. In this section, initiation of various damage mechanisms are determined using AE method. In the second section, evolution of delamination is investigated using AE. In order to determine the instantaneous crack tip position during the propagation of delamination, at first, AE wave velocity in the specimens is specified. Then, using the proposed method, unwanted signals are eliminated. The obtained results indicate that AE method has a good performance to detect initiation stage of interlaminar damage and also to determine the delamination propagation in the laminated composite structures.

Flexible roll forming is a modern process to produce products with variable cross section that can be used in construction and automotive industries. The portion which connects the slim section to the wide one is called transition zone. In this paper, effect of different bend curves on the web warping has been studied in the transition zone. Considering the geometrical boundary conditions of the transition zone, five different curves including circular, quadratic, cubic, quartic, and quintic curves were studied numerically and experimentally. According to the finite element results, longitudinal strains on profile edge which are less than the desirable strain increase the web warping defect. Product with circular bend curve showed the maximum amount of web warping while the quartic bend curve led to the lowest web warping. In order to verify the finite element analysis, the longitudinal edge strain and the web warping were measured in products with Circular bend curve experimentally. A good agreement between the experimental and finite element results confirmed the accuracy of the finite element model.