In analytical studies, step (Heaviside) function is used to simulate an impact load. However, in real behaviour of materials, loading and unloading take a short time. The present study discusses analytically the effects of pulse shape and rising time of an impact load on dynamic stress intensity factor. Firstly, a pulse load with positive slip (linear and non-linear) is applied on a cracked plate and the amount of dynamic stress intensity factor on the crack tip is obtained. Then the effects of pulse time are discussed. Results show that increasing the rise time decreases the stress intensity factor because of reduction of inertia effects. Moreover, the duration of rise time plays the main role in dynamic stress intensity factor changes and how the variations are not matter. تفاصيل المقالة

In this paper, the analysis and optimization of the effect of the materials distribution on the behavior of 2D functionally graded media subjected to impacted loading has been investigated. First, it is assumed that there are two cases for distributing the components in the FG material. In the first case, the power law is considered for materials distribution, and in the second case, the volume fractional changes of the components are made by third degree interpolation. Considering the elastodynamic behavior of the FG materials under loading, the general governing equations of the wave propagation are extracted for the case of properties variation in two dimensions and then the equations are solved using the finite difference method. Finally, an optimization has been made using a single objective genetic algorithm. The results show that the materials distribution has a considerable effect of stress wave propagation in FGMs. تفاصيل المقالة

Regarding the necessity of designing high Q-resonators in micro electromechanical systems, this paper investigates the viscoelastic behavior of a rectangular micro-plate subjected to electrical actuation. Equations governing the vibrations of the homogeneous plate were obtained on the basis of classical plate theory (Kirchhoff's model). The Kelvin–Voigt model was also employed to consider the viscoelastic properties. The Galerkin decomposition method was used for decomposition of the governing differential equations. Additionally, the effects of various parameters were investigated on the Q-factor. Furthermore, a Finite Element simulation is carried out using COMSOL Multiphysics. The verification of the proposed model was conducted by comparing the obtained results with those from previous studies which revealed the validity of the proposed approach and the accuracy of the assumptions made The suggested design approach proposed in this this study is expected to design high Q-factor micro resonators and may be used to improve the performance of many MEMS devices. تفاصيل المقالة