MODARES TECHNICAL AND ENGINEERING
Year:2003 | Volume:- | Issue:12|Papers Count:13

In structures, which are free from residual stresses, the stress intensity factor can be evaluated using the displacement extrapolation techniques. These numerical values are often in good agreement with the energy based calculations. In practice, the energy-based J-Integral is used for many structures as the appropriate fracture parameter or for the indirect calculation of the stress intensity factor. If the J-integral is to be evaluated in presence of residual stresses based on its original expression, the obtained integral will not be path independent. In this paper, a modified form of the J-Integral is used and its path independency is verified. The J-integral is evaluated for two different geometries and the effects of various residual plus applied stresses are investigated.

In this paper the turbulent, incompressible and unsteady viscous flow around a circular cylinder is numerically simulated and the imposed fluid forces are calculated. The Random Vortex Method (RVM) with the using of a Large-Eddy Simulation (LES), as a turbulence modelling, is developed to investigate the fluid flow around a circular cylinder. A LES of turbulent flow is applied to account for the effect of turbulence in the wake. The Navier-Stokes equations are filtered by LES and transformed to computational domain by a general conformal transformation. The fil- tered equations are solved by an operator splitting where the velocity is found from Cloud-in-Cell (CIC) method and the diffusion equation is modeled by random walks (RW). The numerical results lift, darg coefficients and Strouhal number are in reasonable agreement with experimental results.

The steady state flow of viscous fluid in two dimensional and axisymmetric nozzles in all regimes has been numerically studied using compressible TLNS equations. Implicit delta form of Roe finite difference is used as the numerical scheme. The numerical simulation of two-dimensional transonic flow through a double throat nozzle is studied as a test problem. In order to show ability of the method flow in a plug nozzle is also studied. Due to the strong interaction of shock, the entropy condition in solution of plug nozzle has been modified. The dependency of the solution upon grid refinement has been also studied and the results are validated using the results of previous investigators.

In this paper, a novel automated method for modeling 2D and 3D planar delamination growth in laminated composites under mode-I, mode II and mixed model-I/II displacement components is introduced. The method is based on minimizing the difference between strain energy release rate value/distribution (G) at/along the crack front and interlaminar fracture toughness. The method consists of the virtual crack closure technique for calculation of G and a moving mesh algorithm embedded in an optimization solution procedure. The standard sequential linear programming (SLP) performs the solution of the optimization problem. It has already been shown that the SLP method has good convergence and stability behavior in general engineering optimization problems. To further increase the performance of the SLP method in G-gradients calculation, a technique based on the difference of elemental stiffness has been developed. This technique enables calculation of G-gradients in the postprocessor part of the solution, without imposing a large amount of numerical calculation efforts. The efficiency and performance of the technique has been investigated by solving three case studies. In all three cases, good performance and acceptable numerical efficiency have been achieved.

Numerical Simulation is one of the most important ways to optimize hot forming processes and to control geometry and mechanical properties of final products. In hot forming, microstructure of the workpiece, changes during and after deformation. These changes affect the mechanical properties of the workpiece. To simulate these processes, the changes of microstructure and flow stress should be taken into account. A new incremental formulation for flow stress prediction is presented. The results of analysis agree well with one experimental data. An accurate simulation of hot forming processes can be obtained by coupling this model with thermo mechanical analysis programs such as FEM.

This paper investigates the software development and experimental evaluation of warpage in injected molded parts. Warpage is one of the primary defects in dimensional instability, which is not easily removed by changing processing parameters, and thus, in most cases imposes mold-rebuilding expenes. Hence, predicting the occurrence of this effect is necessary especially in multi-component parts in assembly. Due to the high cost of special softwares, an appropriate software development was found to be effective using commonly-used software packages. In this research, three important steps, namely solidification, shrinkage, and warpage were analyzed and experimentally verified. The results show that the developed software could predict the final shape and warpage in a reasonable degree. The effect of increasing pressure is to lower the warpage, as expected. When compared with the part without rib, the existence of rib was found to have a considerable effect on increasing warpage.

Genetic Algorithm (GA) and Singular Value Decomposition (SVD) are deployed for optimal domains selection of antecedents and consequents, respectively, of associated fuzzy sets in fuzzy systems which are used for modelling of explosive cutting process of plates by shaped charges. The aim of such modelling is to show how the depth of penetration varies with the variation of important parameters namely, apex angle, standoff, liner thickness, and mass of charge. !t is demonstrated that SVD can be effectively used to fine tuning of such fuzzy models obtained either from direct matching method or designed by GA method. Such application of SVD will highly improve the performance of genetically designed fuzzy systems to model the very complex process of explosive cutting of plates by shaped charges.

Explosive welding is a process to produce bi- metallic cylindrical components. The process is dynamic and for a chosen geometrical configuration and material properties, is completed in 30m Sec. This paper includes the implication of a finite element engineering package and JWL type pressure- time equation to model the contact response between two similar materials at a very high strain rate - which accurse in explosive welding of cylindrical components. The simulation employs the FE ABA QUS/Explicit code and the cylindrical components (tube and plug) are assumed to be made from an aluminum alloy, with isotropic work and hardening characteristics. The aim of present research work is to find the important parameters, such as impact velocity of tube to plug, the dynamic angle, the pressure of the explosion at the point of contact between explosive material and tube, the amount of stress and strain in the tube during the deformation. With use of simulation results, various thickness of Aluminum tube and curve plug were explosively welded. The interfacial zone at the welded interface is composed of a wavy structure by intensive plastic deformation of the Aluminum alloy. The weld ability of Aluminum tube is decided by the change in impact velocity and dynamic angle, which are achieved with the geometry of curve plug. Finally the models are validated by the results from explosive welding experiments.