نشریه مهندسی مکانیک ایران
سال نوزدهم شماره 1 (پیاپی 46، بهار 1396)

In the last decade, the importance of severe plastic deformation techniques is extensively recognized for all researchers in the materials science field. In this research, one of the severe plastic deformation (SPD) methods known as constrained groove pressing (CGP) has been studied. This method is using to create sheets with ultrafine grain structure. Effects of CGP process have been investigated on mechanical properties and microstructure of Copper sheets. Tensile test, Vickers micro hardness and optical microscopy were used to examine mechanical and microstructure properties. The results show, by the CGP process, strength and hardness increase, significantly. After the first pass, the yield and tensile strength increased %57 and %82, respectively. Hardness results illustrated by increasing CGP passes, uniformity of strain increased. The obtained images from optical microscopy demonstrated that the CGP process is very effective for achieving to ultrafine grain structures. Also, the inhomogeneity factor (I. F) was studied to investigate the homogeneity of the hardness.

In this paper, the behavior of small heat shock protein in the effect of temperature changes is studied based on molecular dynamics (MD) simulation. Conformational changes of one and two chains are investigated at constant temperature (310 K) which is defined as normal condition and variable temperatures. Simulation results indicate that by reducing the ambient temperature, one chain of small heat shock protein is able to capture a nanocargo by changing the configuration of the arm. So the arm of each chain is very flexible. However, when two chains are considered, the behaviors of the arms due to an external force are not similar. When an arm is shrunk, the other one is spread. This opposite behavior can be seen in the displacement of central cavity. So the arm is appropriate place to carrying a nano cargo and temperature can be introduced as a control variable for tuning the displacement of arm.

In this article, stress analysis of an isotropic infinite cylinder weakened by multiple concentric cylindrical cracks subjected to shear and radial loadings on the lateral surface of the cylinder is accomplished. First, relations for stress and displacement components are given in terms of the Galerkin biharmonic vector potential. Next, using these relations, the dislocation solutions for both Somigliana and Volterra dislocation are derived. Using the distributed dislocation technique, integral equations for the infinite cylinder with arbitrary number of the cylindrical cracks are constructed. The numerical solution of resulting integral equations which are of the Cauchy type singular equations leads to evaluation of Somiglianaand Volterra dislocation densities on the crack surfaces. Using related dislocation densities, the stress intensity factors of crack tips for some examples are attained and variations of them with lengths of cracks are discussed. For some special cases, validation of the results of this study with others available in the literature is done.

Because of irrational behavior of the load contours applied to aerospace structures, mapping the output contours of fluid software at text file as input file for structural software with respect to requirements of it is most accurate method to analysis and design of aerospace structures. The most applicable of design's software of those, are Fluent and Abacus, therefor in this research, the FACL algorithm, to create of the comprehensive input file of Abacus, is introduced by mapping of the output contours of fluent software. Induced aerodynamic -heating on the surface of the supersonic and hypersonic vehicles is one of the principal parameters of their design in aerodynamic, structural, and other terms, and Because of the deviation of it and surface temperature with empirical results due to steady state of solution and unspooling of shock layer chemical reactions at Fluent software, the temperature result files of CTCA software which written by these researchers is combined with the aerodynamic pressure results of Fluent during the flight trajectory, and the input file to structural automotive analysis by Abacus is created. Designing the attachment structure of ceramic ray dome of the vehicles which equipped to a radar seeker, using the FACL algorithm is essential. The flight test results of a typical vehicle equipped to ceramic ray dome and the structural analysis results of a controller wing of a typical vehicle show, to design and structural analysis of aerospace structures during flight trajectory, the FACL algorithm results is very accurate in comparison of other methods.

The present study provides the vibrations analysis of a solid circular plate made of porous material. The plate is assumed to be comparatively thin and the porous material properties vary through the thickness direction of the plate following given functions. The governing equations and boundary conditions are obtained based on the classical plate theory and by employing Hamilton’s principle. By using differential quadrature method the governing differential equations are converted to algebraic equations and the natural frequencies are obtained. The obtained results show by increasing the porosity, the natural frequency of the plate increases in poro/nonlinear symmetric distribution but the natural frequency remains constant in poro/monotonous distribution. Also in both of mentioned poro distributions, by increasing the pores compressibility which is shown by Skempton coefficient at constant porosity, the natural frequency of the plate increases too. The numerical results are verified for the simpler state with the known results in the literature.

Analysis of multibody mechanical systems using computational dynamics has been greatly developed recently. When these systems operate at higher speeds and under impact conditions, the assumption that the links behave as rigid bodies does not lead to exact analysis and the energy dissipation due to the internal damping of flexible bodies can make considerable effect on the behavior of the system. This issue becomes more important under impact conditions. In this paper, considering the internal damping of the flexible coupler of a high-speed crank-slider mechanism under impact conditions, the effect of different parameters on the reduction of vibration – which is due to contact forces - is investigated using multibody system dynamics.
The internal damping of the coupler is described by Rayleigh’s proportional damping model. Having derived the constrained equations of motion by Euler-Lagrange augmented method, the effect of flexibility and internal damping is presented for the crank-slider mechanism with the flexible coupler under impact conditions. In addition, the effect of the material type on the internal damping and vibration reduction is carefully investigated.