Journal of Applied and Computational Sciences in Mechanics
Year:2013 | Volume:24 | Issue:1 (7)|Papers Count:9

In the present paper, an algorithm is presented for reliability analysis of beams with random material properties under static spatially random loads. The randomness may be due to the employed manufacturing process that leads to components with slightly different microstructures. Since the material properties are random, the stiffness matrices and subsequently, the response will be of random natures. On the other hand, majority of the service loads of some structures, e.g. airplanes, vehicles, and machining equipments are random. Therefore, special techniques should be utilized. In the present paper, variability of the response is determined and discussed through various examples. The proposed algorithm is extended to include a stress-based analysis. Finally, reliability of the beam is evaluated in the treated examples.

Determination of the deformation length is one of the first steps in roll forming design. Roll forming industries are very interested in explicit simple relationsfor prediction the deformation length without using trail-and-error methods at workshop or time consuming finite element simulations. In this paper, elastic properties and work-hardening behaviour of the strip are considered in addition to geometric specifications of a channel section in order to study the strip deformation. Some relations are introduced for the deformation work consumed during the longitudinal stretching of the flange and the transverse bending of the bend line for a linear hardening elastic-plastic strip. Finally, a relation are developed for the deformation length. Theoretical results show that the forming angle, the flange length and the Young’s modulus increase the deformation length and the strip thickness, the initial strength and the tangential modulus at the elastic-plastic range decrease the deformation length. The Poisson’s ratio has no effect on the deformation length. However, the bend radius to the strip thickness ratio increases the deformation length. The elastic properties and work-hardening behaviour result in a deformation length which is shorter than the rigid–perfectly plastic deformation length which was proposed by Bhattacharyya.

The aim of this paper is to develop a systematic method to analyze the effects of forming parameters on the quality of part formability and determine the optimal combination of the forming parameters for the sheet hydroforming process. In this paper, the effects of four important process parameters namely fluid pressure, friction coefficient at blank/punch interface, gap between die rim block and blank holder and die entrance radius in the process of hydrodynamic deep drawing assisted by radial pressure (HDDRP) were determined. A Finite Element (FE) model was developed for simulating the HDDRP process. After validation of the developed FE model by experimental results, by combining FE simulation with Taguchi method and using the analysis of variance test, the effect of mentioned parameters on the formability of the hydroformed cups was investigated. The applied materials were pure copper and St14 steel sheets. The results of analysis indicated that for both cases of maximum thinning ratio at the constant value of cup draw depth and maximum accessible draw depth, fluid pressure has the greatest influence on the formability of part in sheet hydroforming process. Moreover, using rough punch, having smaller gap between die rim block and blank holder or increasing the die entrance radius, the formability of sheet will improve.

In recent years, more attention has been paid on intelligent vehicle suspension systems equipped with magneto-rheological dampers. In order to investigate nonlinear vehicle dynamics, in the majority of the researches, a quarter-car model with one or two degrees of freedom is used. In such simple models, one can only study the bounce motion of sprung and unsprung masses. In this paper, in order to consider more realistic model for vehicle suspension system, a nonlinear half car model with four degrees of freedom is employed. Frequency response diagrams of the model have been obtained. In order to identify the region of excitation frequency in which the system has chaotic behavior, the bifurcation and Poincare maps are used. Results show that near the heave and pitch natural frequencies, the system forced response has been changed considerably and new unstable region has been appeared in frequency diagrams. Moreover, results show that in comparison with quarter car model, the resonant frequency of pitch motion intensifies the chaotic response.

Snake robots are hyper-redundant robots that are connected with one or two DOF joints. They offer a number of potential advantages beyond the capabilities of most wheeled and legged robots. In this paper, kinematics and dynamics of a planar multi-link snake robot in worm-like locomotion on an inclined surface is investigated. In this locomotion, Snake robot is able to move in the vertical plane. Body shape and curvature function are used to determine the joint relative angles in accordance with the worm-like locomotion. Next, position, velocity and acceleration of each link as well as center of gravity of the snake body are calculated. Newton principle is used to derive the dynamic equations based on kinematics of the snake robot. Friction forces, as the only driving force is modeled using Coulomb friction. Effects of friction coefficient and angle of inclined surface on the joint torques are investigated. It is shown that by increasing these coefficients the motor torques also increase. Webots software and Lagrangian method are both used to verify the theoretical results. Additionally, kinematics and dynamics equation presented in this paper may be used to generate other locomotions in vertical plane. Effect of link geometrical shape on motor torques is also investigated. Finally, FUM-Snake3 robot and physical experiments are used to further validate the mathematical model.

The major problem in material removal process specially grinding is heat generation during the process and thus residual stress on the surface of product. Therefore, optimization of High Efficiency Deep Grinding (HEDG) process is the main goal of this study in order to reduce heat and residual stress and also increase strength and surface hardness of AISI1045 steel by optimization of the process. In other words, the effects of main parameters e.g. depth of cut, wheel speed, workpiece speed and cross feed on surface hardness have been investigated in this study. Operating parameter optimizing through SA method in MATLAB's toolbox is so that the produced tensile residual stress and temperature decrease and meanwhile surface microhardness improves. Beside this, the results are validated by measuring and analyzing surface microhardness, surface temperature and forces. The obtained results reveal a good agreement between the optimization results and experimental observations.

Numerical investigation of 3D electrokinetic mixing through micromixer has performed both qualitatively and quantitatively. In order to reduce numerical expenses of 3D flows, we implement the Helmholtz-Smoluchowski method for the numerical modeling of electroosmotic flows. According to the previous study of electrokinetic mixing inside the heterogeneous microchannels, existence of the vortexes within the flow field always increase the mixing performance for 2D flows. However, investigations of 3D micromixers show that this increase does not happen for all the situations and in some cases, existence of the vortexes does not enhance the mixing performance. Findings of this research indicate that the asymmetry degree of the flow field pattern is the key parameter for the mixing performance. Within the 3D flow field, there are more opportunities to increase the asymmetries. Consequently, mixing performances of the 3D flows are much larger compared to those of 2D flows. Studies of various 3D cases for electroosmotic micromixer show that mixing performance can be improved or deteriorated depending on the arrangement of the heterogeneities over the microchannel walls. These results confirmed that 2D simulation of mixing could not explain the complete benefits of passive micromixers. These results can apply to the simulation of micromixers used in Lab-on-a-chip devises.

In this study the effect of input parameters of the EDM process (pulse on-time, duty cycle and tool polarity), on the material removal rate (MRR), tool wear ratio (TWR) and maximum surface roughness (Rmax) in the machining AISI H13 tool steel has been studied. This study shows that increasing the duty cycle in the two conditions of tool polarity, material removal rate and the maximum surface roughness are increased and the tool wear ratio is reduced. Also in the positive polarity, by increasing pulse on- time, material removal rate and surface roughness are increased and tool wear ratio declines; but in the negative polarity by increasing pulse on time, material removal rate and surface roughness are first increased and then decreased. Furthermore, based on results obtained in the negative polarity mode, on the low pulse on-time, material removal rate is high, and tool wear ratio is lower than positive polarity.

Analysis of the flow passing cylindrical obstacles is one of the basic issues in fluid dynamics and is of great importance. Many surveys have been conducted to investigate the velocity field in potential and viscous flows, as a basis for finding pressure field, and investigation of forces exerted by fluid on obstacles such as uplift and drag forces in different flow regimes. Since the nature of formation of vortexes behind the obstacles is absolutely depended on time, the conventional turbulent models which are based on average time, do not justify, and the use of direct solution of Navier Stocks equations is inevitable. One of the presented models which can solve time-dependent Navier Stocks equations in wide range of Reynolds numbers, is Random Vortex Method (RVM). Since in this method velocity field is instantly calculated, it can be used to simulate turbulent flows with a time-dependent nature. In this paper, vorticity equations gained from Navier Stocks equations are solved in both convection and diffusion phases. In this study, the flow on three cylinders with Re=140000 is investigated and field of average and instant velocity is shown along with streamlines. Also by drawing instant distribution of vortex fields and streamlines, it is possible to provide a revealing presentation of vortex behind cylinders.