نشریه علوم کاربردی و محاسباتی در مکانیک
سال بیست و پنجم شماره 2 (بهار و تابستان 1393)

In this paper، the mixed-Mode dynamic fracture analysis of a FGM plate is performed using MLPG method also the effect of changes in value and angle of material gradation on the dynamic Stress Intensity Fctor (SIF) of Mode I، II، and effective are investigated. To solve time dependent equations that discretized by MLPG method، the Central Difference Method (CDM) and the Newmark method are used. Although the J integral is one of the most common methods to calculate the SIF، but in general، it is not applicable for FGMs. So، in this paper the path independent integral، J*، which is formulated for the non-homogeneous material is used to calculate stress intensity factor. Results show that the present method has good agreement with the exact and other existent solutions. Results also، show the maximum and minimum values of effective stress intensity factor for E2/E1>1 are occurred at material gradation angle equal to 0 and 90 respectively، and for E2/E1

In this paper، numerical investigation of a flat passive micromixer with heterogeneous surface properties that the flow through it، is driven by the electroosmotic flow have been presented. The governing equations، which consist of a Laplace equation for the distribution of external electric potential، a Poisson equation for the distribution of electric double layer potential، modified Navier-Stokes equations for the flow field، the Nernst-Planck equation for the distribution of ions concentration have been solved numerically for an incompressible steady flow of a Newtonian fluid using the finite-volume method. The key features of an ideal electro-osmotic flow with uniform zeta potential has been compared with analytical solutions for the ionic concentration and velocity fields for the validation of the numerical scheme. Results show that the arrangement of the heterogeneous surface properties has a significant impact on the efficiency of mixing. Maximum mixing efficiency is related to the condition that the asymmetry in the wall of the heterogeneous arrangement loads increase. The increase in intensity of the electric charge with constant power load of the electroosmotic micropump enhances the efficiency of mixing.

In this paper، two API X70 steel pipes (with spiral seam weld) of 56 inch outside diameter and 0. 780 inch wall thickness were girth welded first. Next، hole drilling tests were conducted for strain measurement on the surfaces of the pipes. The values of residual stresses on the internal and external surfaces of the pipe were determined، from strain data using ASTM 837 standard. The experimental data showed that the maximum tensile residual stress (318MPa) was located on the centre line of the weld gap on the pipe outer surface alongside with the pipe hoop direction. Moreover، the maximum compressive (hoop and axial) residual stresses (137MPa) occurred on the pipe inner surface at 30mm from the centre line of the weld gap.