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The effects of 1.5, 2.5 and 3.5 wt.% Cu additions on the microstructure and creep behavior of the as-cast Al-9Si alloy were investigated by impression tests. The tests were performed at temperature ranging from 493 to 553 K and under punching stresses in the range 300 to 414 MPa for dwell times up to 3000 seconds. The results showed that, for all loads and temperatures, the Al-9Si-3.5Cu alloy had the lowest creep rates and thus, the highest creep resistance among all materials tested. This is attributed to the formation of hard intermetallic compound of Al 2 Cu, and higher amount of α-Al 2 Cu eutectic phase. The stress exponent and activation energy are in the ranges of 5.2-7.2 and 115 -150 kJ/ mol, respectively for all alloys. According to the stress exponent and creep activation energies, the lattice and pipe diffusion-climb controlled dislocation creep were the dominant creep mechanism.

A viscoelastic carbon nanotube (CNT) conveying pulsating fluid is presented which is based on EulerBernoulli beam theory. Runge-Kutta scheme is chosen in order to illustrate the transverse and longitudinal behavior of structure. The effects of surface stress, magnetic field and nonlocal small-scale theory on motion of structure are expressed in this study. Equilibrium equations of CNT conveying pulsating fluid are obtained using energy method. Galerkin, differential quadrature and Runge-Kutta methods are applied to solve equations of motion. In this paper, the effect of pulsating fluid on longitudinal behavior of CNT and transverse displacement of CNT are presented. The static and dynamic transverse distributed loads and their effects on CNT are expressed. In this study, regions of CNT with chaotic, quasi-periodic and periodic behaviors are presented. Also the effects of various parameters such as distributed loads, surface stress and magnetic field on those regions are demonstrated. The results of this work could be helpful in design and manufacturing of nano-/micromechanical system in advanced medical applications such as drug delivery systems with magnetic field as a parametric controller.

The flexural vibration stability of a coupled double-walled viscoelastic carbon nanotube conveying a fluid based on the Timoshenko beam (TB) model is investigated. The coupled system is surrounded by an elastic medium which is simulated as Pasternak foundation. Van der Waals (vdW) forces between the inner and outer CNTs are taken into account based on the Lenard-Jones model. Using small scale theories, Hamilton's principle and applying two dimensional (2D) magnetic field higher order governing equations are derived. The differential quadrature method (DQM) is applied to solve partial differential equations and investigate natural frequency of the system. The effects of viscoelastic constant, magnetic field with variable magnitudes and surface stresses on natural frequency of the structure are demonstrated in this study.