سال:1392 | دوره: | شماره: |تعداد مقالات:9

It was with great sadness that we learned of the passing of Professor Mohammad H. Kargarnovin. He was a Professor of Mechanical Engineering at the Sharif University of Technology (Iran). It is 5 years since he was appointed to the Editor-in-Chief of JSM. He proved to be the ideal person to undertake challenges of the journal.He received a bachelor's degree in Mechanical Engineering from the Tehran Polytechnic (Iran) in 1976. After receiving two master's degrees in Mechanical Engineering and Nuclear Engineering from the Massachusetts Institute of Technology (MIT) in 1979, he joined the Rensselaer Polytechnic Institute (USA) to do a PhD in Mechanical Engineering (1979-1983). Professor Kargarnovin will be remembered for the contribution he made to the understanding of smart structures behavior under dynamic loads. His legacy is evident in the students he supervised. In cognition of his research achievements, he received a Distinguished Researcher Award from the Sharif University of Technology (2005) and appeared in Who's Who in Computational Science and Engineering, Saxe-Coburg Publications, UK (2005-2006).To continue succeeding with the journal, as of this issue Professor Mohammad Shariyat from the Faculty of Mechanical Engineering of the K.N. Toosi University of Technology (Iran) will take over the role of Editor-in-Chief. All the members of the Editorial Board and journal staff wish him the best in his new position. Moreover, I am delighted to announce that Professor Ali Ghorbanpour Arani from the Faculty of Mechanical Engineering of the University of Kashan (Iran) will join the Editorial Board from this issue.

In the present study, plasticity induced crack closure (PICC) concept and three dimensional (3D) finite element methods (FEM) are used to study the effect of compressive residual stress field on the fatigue crack growth from a hole. To investigate the effect of compressive residual stress on crack opening levels and crack shape evolution, Carlson’s experiments were simulated. Crack shape evolution is investigated by employing an automatic remeshing technique using MATLAB-ABAQUS code. The effect of mesh element size is considered by using element sizes of 0.025mm and 0.0125mm. Crack opening level results indicate that the applied residual stress increases the opening levels with an average of 45%. The higher opening levels results in higher number of fatigue cycles by a ratio of 3.07 for 1.9mm surface crack growth increment. Comparing the result obtained with Carlson’s experiments indicates that the crack closure method employed in the present analysis is in good agreement. Comparing the results with Jones’ supeposition method, moreover, illustrates that present paper method is more accurate.

In this paper, vibration analysis of multiple-stepped Bernoulli-Euler and Timoshenko beams carrying point masses is presented analytically for various boundary conditions. Each attached element is considered to have both translational and rotational inertias. The method of solution is “transfer matrix method” which is based on the changes in the vibration modes at the vicinity of any discontinuity in geometrical and natural parameters; these changes are shown by transfer matrices depended on the geometry of each step or value of the translational and rotational inertias of each attached element. First, natural frequencies and corresponding normal mode shapes are obtained by implementation of the compatibility conditions and external boundary conditions; Then, the precision of the proposed method is checked by comparison of the results with other exact solutions; Finally, the effect of the translational and rotational inertias and position of the attached elements on the natural frequencies of multi-stepped beams are investigated for various boundary conditions.

This paper presents an analytical solution for response of a piezoelectric hollow cylinder under two-dimensional electro thermo mechanical fields. The solution is based on a direct method and the Navier equations were solved using the complex Fourier series. The advantage of this method is its generality and from mathematical point of view, any type of the thermo mechanical and electrical boundary conditions can be considered without any restrictions. The thermo mechanical and electrical displacements are assumed that vary in radial and circumferential directions. Finally, three examples were considered to confirm the results and investigate the effect of in-phase and opposite-phase electro thermo mechanical boundary loads on two-dimensional electro thermo mechanical behavior of piezoelectric hollow cylinder. The results are compared with the previous work and FEM analysis. The main result of this study is that, by applying a proper distribution of thermal, electrical and mechanical fields, the distributions of electric and mechanical displacement, thermal and mechanical stresses can be controlled.

Study of permeability of Fibrous Composites is important in several natural and industrial processes in mechanical engineering. In this study, a comprehensive mathematical model is presented for calculation of normal permeability of ordered elliptical fibrous media. An innovative scale-analysis technique is employed for determining the normal permeability of elliptical fibrous media. In this technique, the permeability is related to the porosity, elliptical fiber diameters, and tortuosity of the medium. In other word, the normal permeability of the circular fibrous structures, which presented in the literature, is extended to the general case of elliptical fibrous media. The composite material is represented by a “unit cell” which is assumed to be repeated throughout the media. A closed-form relation is obtained for non-dimensional permeability using scale analysis approach. Due to lack of experimental data for permeability of fibrous porous media (composite media), with elliptical cross section, a numerical analysis is also employed. The governing equations are solved numerically in the unit cells using finite volume method. The results obtained by numerical solution are compared with those presented by scale analysis method. The presented relation for normal permeability can suitably cover the case of fibrous media with circular cross section. The results are also compared with those presented in the literature for the case of cylindrical fibers. The developed compact relationships are successfully verified through comparison with the present experimental results and the data reported by others.

Analysis of the laminated composite plates under transverse loading is considered using the new method of Is geometric Analysis (IGA). Non-Uniform Rational B-Splines (NURBS) are used as shape functions for modeling the geometry of the structure and also are used as shape functions in the analysis process. To show robustness of the new technique, some examples are represented and are compared with the theoretical method at the end. The obtained results show the efficiency of the method.

In the presented paper, the governing equations of a vibratory beam with moderately large deflection are derived using the first order shear deformation theory. The beam is homogenous, isotropic and it is subjected to the dynamic transverse and axial loads. The kinematic of the problem is according to the Von-Karman strain-displacement relations and the Hook's law is used as the constitutive equation. These equations which are a system of nonlinear partial differential equations with constant coefficients are derived by using the Hamilton’s principle. The Eigen function expansion method and the perturbation technique are applied to obtain the response. The results are compared with the finite elements method.

In this paper, an analytical solution for computing the plastic & linear plastic stresses and critical angular velocity in a FGM hollow & solid rotating disk is developed. It has been assumed that the modulus of elasticity and yield strength were varying through thickness of the FGM material according to a power law relationship. The Poisson's ratios were considered constant throughout the thickness. In the analysis presented here the effect of non-homogeneity in FGM rotating disk was implemented by choosing a dimensionless parameter, named m, which could be assigned an arbitrary value affecting the stresses in the rotating disk. Distribution of stresses in radial and circumferential directions for FGM rotating disk under the influence of angular velocity were obtained. Graphs of variations of stress, critical angular velocity versus radius of the rotating disk were plotted. The direct method is used to solve the Navier equations.

The plane strain deformation of an isotropic, homogeneous, poroelastic medium caused by an inclined line-load is studied using the Biot linearized theory for fluid saturated porous materials. The analytical expressions for the displacements and stresses in the medium are obtained by applying suitable boundary conditions. The solutions are obtained analytically for the limiting case of undrained conditions in high frequency limit. The undrained displacements, stresses and pore pressure in poroelastic medium are plotted and discussed to draw the conclusions.