Journal of Applied and Computational Sciences in Mechanics
Year:2014 | Volume:25 | Issue:2 (10)|Papers Count:9

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 nonhomogeneous 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 0o and 90o respectively, and for E2/E1<1, vice versa.

In this paper, in order to analyze the transverse vibration of a uniform Bernoulli-Euler beam containing one single edge crack, a new continuous model is proposed for the cracked section. To this end, by using the fracture mechanics, the crack is modeled as a continuous disturbance in the stress and strain fields. By applying the Hamilton’s principle, the equation of motion and the corresponding boundary conditions of the system are derived. The resulting equation is solved by the Galerkin method, and the natural frequencies and mode shapes are obtained. In order to consider the opening and closing effects of the crack, the stiffness at the crack location is modeled by a bilinear function. The results show that the changes in vibration frequencies for a breathing crack are smaller than ones caused by an open crack. The results have been validated by the experimental and theoretical data reported in the previous studies. There is a good agreement between the results obtained through the proposed method and those obtained from the reported experimental data. This agreement shows that present model is more accurate than the previous ones, and it can predict the vibration behavior of beams more precisely.

In this paper, a new kind of gripper is designed which passively conforms to the shape of an object. This universal gripper is proposed when some of the adaptability of a human hand is needed or situations where very different objects need to be gripped easily, reliably within rapid succession without any feedback. By adding an annular balloon around the granular bag, a lateral force pushes the main membrane and increases the friction force between the bag and the load. According to the acquired test results reported in this paper, the modification on this new robotic gripping mechanism is effective and the the successful gripping is formulated. This new complete formulation can provide a good estimation for a successful gripper design.

The present research simulates time-periodic unsteady transonic flow around pitching airfoils via the solution of unsteady Euler and Navier-Stokes equations, using Time Spectral Method (TSM) and compares it with the traditional methods such as BDF and Explicit Structured Adaptive Grid Method. The TSM uses a Fourier representation in time and hence solves for the periodic state directly according to physics of flow. Mathematical tools used here are discrete Fourier transformations. The TSM has been validated with 2D external aerodynamics test cases. These test cases are NACA 64A010 (CT6) and NACA 0012 (CT1 and CT5) pitching airfoils. Because of turbulence nature of flow, Baldwin-Lomax turbulence model has been used in viscous flow analysis with large oscillation amplitude (CT5 type). The results presented by the TSM are compared with experimental data and the two other methods. By enforcing periodicity and using Fourier representation in time that has a spectral accuracy, tremendous reduction of computational cost has been obtained compared to the conventional time-accurate methods. Results verify the small number of time intervals per pitching cycle (just four time intervals) required to capture the flow physics with small oscillation amplitude (CT6) and large oscillation amplitude (CT5) as compared to two other methods.

In this paper, formation of wrinkling in bimetal deep drawing process has been investigated by the analytical, numerical and experimental methods. The effects of width of flange, fillet radii of matrix and punch, clearance of blank holder, contact conditions and relative thickness of two sheets on the number and height of wrinkle waves are studied. Clearance and contact conditions have the greatest impact on the number of waves while only clearance has significant effects on the height of waves. Increasing of the mandrel edge radius and relative thickness of tougher metal increase significantly the forming force. Variation of holder’s clearance and matrix edge radius have a little effects on the punching force.

The evaporation of liquid droplets is of fundamental importance in a large number of practical situations ranging from technological applications such as ink-jet printing, spray cooling and various coating processes, to a variety of biological and geophysical contexts. In this study, the behavior of the surfaces of Glass, Plexiglas, Aluminum and Copper in the evaporation of water droplets is studied experimentally. It is assumed that the transport of vapour in the atmosphere is dominated by diffusion and other effects are ignored. Experimental observations show that the surface evaporation on the surfaces of Aluminum and Copper are generally carried out in a constant contact area while the water droplets on the surfaces of Glass and Plexiglas usually experience the sliding behavior in certain timescales. Furthermore the changes of surface energy during the process of evaporation of water droplets on the surface are also discussed.

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.

In this paper, the capabilities of modeling linear viscoelasticty in a finite element method software package (COMSOL Multiphysics) are investigated. The governing equations of linear viscoelasticity have been developed for 2D cases of plane stress and plane strain. These equations have been verified by solving a related engineering example. Since the developed equations are suitable for modeling of multiphysics mechanisms, the presented model can also be used for modeling of the linear viscoleasticity coupled with other multiphysics phenomena.