Year:2009 | Volume:43 | Issue:4 (123 SPECIAL ISSUE ON: MECHANINCAL ENGINEERING)|Papers Count:10

Numerical modeling of machining processes is of significance in the parametric analysis and optimization of their performance. In this paper, a finite element-based model of abrasive waterjet (AWJ) cutting of a ductile material is presented with the help of an explicit, nonlinear finite element method. In this model, both solid-solid interaction and fluid-structure interaction are considered. The water is modeled as an Eulerian volume. The Euler-Lagrange coupling algorithm is employed to simulate the interaction of the waterjet with the abrasive particle and the target material. An elastic-plastic behavior is defined for the target material and the abrasive particle is assumed spherical, which behaves like an elastic material. The erosion of the target due to the AWJ impact is simulated using the element deletion approach. The variation of the depth of cut with respect to the waterjet pressure is estimated and compared with experimental results.

Determination of the optimum loading path (internal pressure- axial feeding) to restrict the Bursting, buckling and wrinkling through tube hydroforming process is necessary to produce an acceptable tube. In this paper, the wrinkling and fracture criteria are implemented to an finite element code devoted to the simulation of tube hydroforming processes. Using the ANSYS parametric design language (APDL), two macros are built to compute the value of bursting and wrinkling indicators through the elements. By determining the indicators values through the step to step solution of the software, it is possible that compares them with critical values and predicts the fracture and wrinkling in tube hydroforming process.

In the present paper, employing a complete model of a passenger car, contribution of various components and assemblies in the frontal crash energy absorption is determined. Thickness of components with more remarkable contribution is increased to improve the occupant safety. Furthermore, effects of substituting the metallic bumper with one fabricated from GMT materials on the frontal crash behavior of the vehicle are investigated. Boundary condition and dynamic parameters are defined in PAM-CRASH software. To increase the accuracy of the results, all subassemblies and their joints are precisely modeled. Finally, components with more remarkable contribution in energy absorption are detected and a comparison is made between the crash results of the original design and the crash results obtained after the mentioned modifications.

Deep drawing of cylindrical shapes with high limiting drawing ratio (LDR) values is relatively difficult. Annealing is a further operation, which in turn adds costs and consumes significantly time to the forming process. In the present work, cylindrical cups from brass sheet were made with only limited anneal during few steps, but having LDR of 9 that is about 2 times higher than previous works. Cups having 4 mm IDs and 70 mm heights were made successfully. The process was simulated by ABAQUS/Explicit finite element (FE) code and experimental tests were carried out based on FEM results. Parameters affecting the process were studied with experimental results, as well as FEM. The wall thickness obtained from the approach were compared for several tests, and verified significantly.

Slab method of analysis has been used for solving metal forming problems for a long time. However it has been restricted to plane strain and axisymmetric problems due to limitations in its formulations. In this paper a new formulation has been proposed so that it could be applied to three dimensional problems in metal forming. A parametric slab has been considered in this analysis and the force balance on the slab was carried to obtain equilibrium equations in terms of these parameters. The parameters in fact are related to the geometry of the final extruded shape, the die and the material flow regime assumed in the formulation. In this way most of the limitations encountered in previous formulations were surpassed. The effect of reduction of area, frictional conditions and other process parameters on the extrusion pressure was investigated. The theoretical results obtained in this paper were compared with the results of finite element method and a good agreement was observed between them.

In this paper the optimal control of boundary heat flux in a 2-D solid body with an arbitrary shape is performed in order to achieve the desired temperature distribution at a given time interval. The boundary of the body is subdivided into a number of components. On each component a time-dependent heat flux is applied which is independent of the others. Since the thermophysical properties are temperature dependent, the problem is treated as a nonlinear inverse heat conduction problem. Conjugate gradient method (CGM) along with adjoint problem is utilized in order to solve the inverse problem. Optimization process is employed for the heat flux imposed on each of the boundary component individually which was previously shown to be more efficient than optimizing the entire heat flux array simultaneously. Three versions of CGM; that is, the Fletcher-Reeves (FR), Polak-Ribiere (PR) and Powell-Beale are utilized for comparison. As a test case, heating of an Aluminum bar with a square cross section and temperature-dependent thermo-physical properties is considered. Results show that for large time-steps the Powell-Beale version with normalized search direction, and for small time-steps the Polak-Ribiere version are the most efficient method with the least error in the estimated temperature field. Moreover, for large time step size results show that addition of regularization term to the Error Function reduces the amplitude of oscillations in the estimated heat flux.

Foreign object damage (FOD) occurs when hard, millimeter-sized objects such as gravel or sand and even the pieces of the engine components are ingested into aircraft jet engines. Particles impacting blades produce small indentation craters which can become sites for fatigue crack initiation, severely limiting the lifetime of the blade. In this study, the impact on the edge of a thin plate is investigated by using the finite element method. Then residual stresses are compared between the quasi-static indentation and fully dynamic impact for three critical locations where the residual hoop stresses are tensile. At the end, experimental stress analysis is performed for investigating the stress concentration factor at the crater base and comparing with data from the finite element method. The comparison shows that the finite element method result agrees well with experimental data at the crater base.

An autonomous underwater vehicle (AUV) with less noise and vortices as well as efficient power consumption, is pursued in this research by inspiration of shark swimming. Design, hydrodynamic analysis, modeling, fabrication, navigation, and control of this novel AUV is the main goal of this research. Detailed explanation of the test and experiment with a brief overview on fabrication are provided. The transfer function of the system has been extracted from the experimental data. The transfer function is then employed for dynamic analysis and control system development. Zigler-Nickols method is used to predetermine the PID control coefficients. Consequently, small modifications have been done by trial and error. Trajectory control in a 10 cm off the wall and in a 20 cm band in a large swimming pool has been examined by a 3 DOF AUV.

The Levy-type analytical solution is employed for the problem of bending of cross-ply and antisymmetric angle-ply piezoelectric hybrid laminated plates with at least two simply supported opposite edges. The governing equations of equilibrium are derived in the framework of the first-order shear deformation plate theory. The equations are classified according to the crystallography type of piezoelectric layers and a comprehensive discussion on limitations of the method for the analysis of this kind of structures is performs. Finally, the governing equations of equilibrium are solved analytically with the aid of the state-space approach. We concluded that during the analysis of piezoelectric hybrid laminated plates with Levy-type method, simultaneous applying of all electrical forces and moments is not possible (depending on type of lay-up, crystallography of piezoelectric layers, and expansion of electrical potential, some of electrical forces and moments may not be considered). In order to study the accuracy and several numerical examples are examined. The numerical results are compared with those obtained by the Navier method and those presented in the other published articles. It is found that the present results have very good agreements with those obtained by other methods.

The built up layer thickness in secondary deformation zone is one of the important parameters in metal cutting process. The built up layer (BUL) is formed in second deformation zone near the tool-chip interface in the back of the chip. This parameter influences the tool life and machined surface quality. This BUL should not be confused with the built up edge (BUE). The deformation of the BUL in the secondary shear zone is a stable and continues process; leading to an uniform thickness of the BUL along the chip's back but the deformation of the BUE is an unstable process in front of the tool edge. Numerical simulation is a suitable method for determination of temperature, stress and strain distribution in metal cutting since it dose not suffer the analytical methods limitations and experimental methods cost. In this paper a new method is presented to calculate the built up layer thickness in secondary deformation zone using finite element simulation of orthogonal metal cutting process. There are two main concepts about chip separation mechanisms from work piece, i.e. crack propagation and pour deformation without crack. In the present work chip formation process is assumed as a pour plastic deformation, considering second chip separation mechanism. There is no separation criterion in the simulations based on pour deformation, but Adaptive remeshing is performed during simulation to avoid the difficulties associated with deformation induced element distortion. An updated Lagrangian finite element model of two dimensional orthogonal cutting process is developed. This model is meshed using 4-node plain strain elements. Thermo-mechanical coupled analysis, with adaptive remeshing is performed by LS-DYNA finite element code. Johnson-Cook material model is used for determination of the work piece material flow stress and the cutting tool is assumed as a rigid body. An updated coulomb friction law is used to describe friction condition in tool-chip interface. The temperature and equivalent strain distribution diagrams in cutting zone are shown at various cutting speeds. The built up layer thickness in various cutting speed are also calculated by equivalent strain gradient in second deformation zone. The numerical calculated tool average temperatures and the built up layer thicknesses in various cutting speeds are compared with the experimental data given in literature and good agreement is observed between them.