فهرست مطالب بشیر بهجت

Polymer-based adhesives undergo creep deformation under constant loading due to their viscoelastic nature. The aim of this study was Investigating the effect of 2-D defects on tensile and creep behavior of single-lap ceramic-metal joints (SLJs) manufactured with adhesive Aqua-Flex. Static tensile test was performed at three ambient temperatures, 40 and 60 ° C for flawless and defective adhesive joints in ceramics as well as defects in ceramics and aluminum, and then by applying final stress-to-strength ratios equal to 0.40 and 0.60, tensile creep test has been performed. By increasing the final stress-to-strength ratio from 0.40 to 0.60 at ambient temperature, the creep displacement for faultless connection is 36%, for defective connection in ceramic 33% and for connection defective in ceramic and aluminum 40%. Find. At 40 and 60 ° C, this increase is 35% and 18% for defective connection, 54% and 5% for defective connection in ceramic and 39% and 42% for connection with defective connection in ceramic and aluminum, respectively. Also, with increasing temperature from ambient temperature to 60 ° C, the breaking force for the three types of connections is reduced by 46%, 25% and 80%, respectively.

Nano-beam is one of the most important nano-structures with applications in different fields such as NEMS (Nano electromechanical systems) considering their low weight, low energy consumption and high sensitivity for use in medical, computer, bio-sensors and etc. Since the behavior of material in nano scale is different from usual scales, new methods are innovated to study the mechanical behavior of material in nano scale which one of them is nonlocal model. In this paper, nonlocal elasticity theory is used to describe the behavior of beam on the nonlinear elastic foundation. The Euler-Bernoulli beam theory is used to modeling the beam. The governing equations are obtained using principle of virtual displacements and analytical solution is used to solve governing equations. Maximum deflection, critical buckling load and natural frequencies for simply supported boundary condition and different spring constant, and nonlocal parameter is presented. The obtained results show that deflection is increased and critical buckling load and natural frequencies are decreased by considering nonlocal effects. Also elastic foundation decreases deflection and increases critical buckling load and natural frequencies.

In this paper buckling and free vibration behavior of functionally graded nanoplate resting on elastic foundation is investigated. Small scale effects are taken into consideration with employing elasticity nonlocal theory. The governing equations of functionally graded nanoplate are derived based on the Hamilton's principle and solved by using Navier method for boundary conditions simply support. Mechanical properties of the functionally graded nanoplate are assumed to vary continuously along its thickness according to a power law function. The elastic foundation is modeled as two parameter Winkler-Pasternak foundation. To show the accuracy of the present analytical solution, present results are verified with the results available in the literature. The effects of nonlocal parameter, power index, thickness, Winkler and shear module parameters on the critical buckling load and natural frequency of nanoplate are investigated. The results is shown that the natural frequency and critical buckling load decreases with increase in the aspect ratio, nonlocal parameter and index power. Also Winkler and Pasternak foundations lead to incre ase structure stiffness.

In this paper, the Element-Free Galerkin (EFG) method is employed to obtain three dimensional static behavior of thick functionally graded plates. The Poisson’s ratio is taken to be constant and the Young’s modulus is considered to be graded through the thickness of plate by an exponential function. The shape function is calculated using the 3D moving least squares (MLS) approximation. Because the MLS approximation lacks the Kronecker delta function property, therefore the constrained Galerkin weak-form is used. The Lagrange multiplier method is employed to enforce the essential boundary condition. Effects of weight functions, nodal density and the dimensionless size of the support domain are investigated and favorable value for the dimensionless size of the support domain is calculated. Also a new trigonometric weight function is introduced. Effects of functionally grading index, dimensionless thickness and boundary conditions on the stress and deformation of the plate are investigated. Several examples are presented for thick functionally graded plates under static load. Also in order to verify the obtained results, they are compared with the results of other data reported in the literature. Numerical results indicate that the rate of convergence of the proposed method is higher than that of finite element method especially for stress calculation.