مجله مهندسی مکانیک امیرکبیر
سال چهل و سوم شماره 2 (زمستان 1390)

In finite deformation analysis¡ the use of constitutive equations in rate form is often required. In a spatial setting¡ elastic modulus tensor relates some objective rate of a spatial stress tensor to the rate of deformation. It is important to know that¡ the spatial elastic modulus tensors of a material in different constitutive equations differ and relation between them may be interest for some researchers. In this paper¡ a general explicit formulation between the spatial elastic modulus tensors of some constitutive equations expressed. This formulation is a function of left Cauchy-Green tensor and its eigenvectors.

Motivation of this paper is presentation of analytical solution for flexible functionally graded beams problem when carry elastic large deflection, with small strains and without concerning plastic region. The formulation of large deflection in curvilinear and Cartesian coordinate systems for the free-clamped flexible functionally graded beam, culminate in the second order non-linear ordinary differential equation that can solve it in the analytical approach. The components of deflection that are derived with analytical solution and ANSYS approach are compared. The influence of the distribution reversing of the material property and the influence of the variable material property in the components of deflection are studied. This analytical approach can be used for verifying the other method results, if any.

In this paper, the problem of low-velocity transverse impact on a sandwich panel with functionally graded core has been considered. The interaction between the impactor and the panel is modeled with the help of a system having two-degrees-of-freedom consisting of springs-masses. In order to determine the contact force history, a numerical procedure is employed based on improved higher-order sandwich plate theory. Shear deformation theory is used for the face sheets while three-dimensional elasticity theory is used for the core. For the first time effect of consideration of in-plane shear stress and normal stress in the core is considered. Displacement components in the core are assumed to vary with a polynomial function with unknown coefficients. Results indicate that use of the FG core can reduce deflections and increase maximum of contact forces.

A new improved high-order theory is presented to investigate the dynamic behavior of sandwich panels with flexible core. Shear deformation theory is used for the face sheets while the three-dimensional elasticity theory is used for the core. Displacements in the core are assumed as polynomial with unknown coefficients. Inertia forces, moments of inertia and shear deformations in the core and the face sheets are taken into consideration. Unlike the previous improved theory, the in-plane normal and shear stresses in the core are considered. The governing equations and the boundary conditions are derived by Hamilton’s principle. Closed form solution is achieved using the Navier method and solving the eigenvalues. The numerical results of present analysis are compared with the available numerical or theoretical results in the literatures. It indicates that the present new modified theory is more accurate than the other developed theories for sandwich panels. The variations of the non-dimensional natural frequency with respect to the various geometrical and material parameters are investigated.

In this paper, robust control of the wheeled mobile robots in presence of external disturbances and parameter uncertainties of the dynamical system violating the nonholonomic kinematic constraint of non-slipping is presented. Despite to the previous works focused on the kinematic control design, a robust torque control developed as a unified approach for both of the tracking and regulation problems based on the tunable dynamic oscillator. The proposed controller guarantees that the tracking error converges exponentially to an arbitrarily small neighborhood of the origin. To demonstrate the performance of the proposed controller, simulation results for typical differential drive and skid steer mobile robots presented.

One of main methods for protecting nature is to use nature as an inspiration source for designing newproducts for human being’s needs. Movement and maneuver in fluids is an important issue in human activity. In this work, by inspiration from knife fish, an undulating fin for producing propulsion force are designed and implemented. This undulating fin is a segmental anal fin, and produce sinusoidal waves which are needed for producing propulsion force. Then, parameters of this sinusoidal wave are discussed. In the fish robot, with using a special mechanical system, the direction of propulsive force is adjustable for controlling of direction and depth of swimming. Then, details of wireless control system for maneuvering and controlling of robot `s speed are presented. Finally, the results of fish robot `s movement is discussed experimentally.

In this study, the effect of pulsating blankholder by using a new system for improving the formability of aluminum alloy has been investigated. By means of this system, in every pulsating cycle, at first the blankholder force has been removed, metal has been flowed into die and then to prevent excessive metal flow and wrinkles, the blankholder force by springs has been used.Deep drawing of cylindrical cup has been simulated by using ABAQUS6.7 software. Cup depth, tearing and thickness distribution of the experimental and numerical results have been compared. The results show that cup depth by using the pulsating blankholder system and select a proper frequence and gap, can be increased and thickness distribution can be improved. It has further been observed that simulation and experimental results are in good agreement together.

In this study, the parameters of PCGTAW process were optimized for the corrosion protection of SDSS weld pipes by Taguchi method. Analysis of variance is performed on the measured data and signal to noise ratios. The optimum conditions were found by this method. Under optimum conditions, pitting potential was predicted as 1.08 VSCE that was very close to the observed value of 1.06 VSCE. Among the four factors and three levels tested, it was concluded that the pulse current had the most significant effect on the pitting potential and the background current had the next most significant effect. The effect of pulse frequency and % on time are less important when compared to the other factors.

This paper considers minimizing makespan (Cmax) on a single batch-processing machine. A batch-processing machine can process a group of jobs simultaneously, as long as the total size of jobs in the batch does not exceed the machine capacity (B). For each job, we assume a specific job size and job processing time. The processing time of a batch is just the longest processing time of all jobs in the batch. We introduce two new procedures for obtaining lower bounds of the optimal makespan, entitled LB2 and LB3, respectively. We prove that both of the new bounds are tighter than the only existing bound called LB1. We also prove that LB3 is at least as tight as LB2.