AMIRKABIR
Year:2003 | Volume:14 | Issue:55-B|Papers Count:8

This paper presents analytical static and dynamic models of a rigid work piece held in a machining fixture in contact with locators and clamps (in a 3-2-1 scheme) and three supports (in three locating planes) influenced by machining forces and moments. The models are used to predict effects of support parameters including support position, rigidity, and preload on improving machining accuracies. Milling and creep feed grinding experiments are performed to verify the model. The model can be used to develop present computer aided fixture design systems that consider only locators and clamps in a force analysis module.

The paper discusses all different types of folding mechanism in honycomb structures. A new folding mechanism named Mixed Mechanism is introduced for determining the crashing strength of hexagonal cell honeycombs subjected to axial quasi-static loading. The theoretical solution has been compared with experimental results published in literatures and an excellent correlation has been obtained. This solution can replace the less accurate earlier analysis of the same problem due to Wierzbicki.

Acoustic design of exhaust system for Internal Combustion Engines normally has been based on trial and error, such that even most muffler producers are mainly dependent on practical experience of their designers. The primary reason for this is the complex process of exhaust system acoustic analysis design. The basic design goals are: I) Optimum and compact exhaust system geometry II) Acceptable reduction of exhaust noise III) Enforcement minimum back pressure with proper acoustic performance. The primary object of present article is to employ the linear acoustic filter theory based on the method of transmission loss for optimum design of reactive acoustic silencers in the exhaust system of internal combustion engine. The numerical results examine the effect of internal geometry of various reactive elements on acoustic performance of the exhaust system.

Cone-shaped explosion forming of cone was investigated by new analytical, experimental and numerical approach. In the analytical modeling, it is supposed that deformation profile of plate is a truncated cone during process that will be deformed to a fully formed cone at the end of process. The variation of plate thickness was also neglected. Analysis of the required equations for determining the distribution of hoop strain during the process and the required charge mass are also given in this model.ABAQUS/Explicit package was used for the FEM simulation. The results of the analytical model given in this paper are in agreement with the experimental and the numerical (FEM) results.

In this work, the effects of manufacturing parameters on the microstructure and densification of iron powders processed by direct laser sintering were investigated. A specific energy parameter E, which expresses the energy input per volume of tire sintered layer, was defined and used to evaluate the impact of the parameters on the densification and the attendant micro structural features. The results show that the sintered density is an exponential function of the defined Specific energy. With increasing the energy input up to 2kj/mm3, the densification rate is relatively high. Here, the microstructure consists of bin pores (.5-1mm) and elongated ferrite grains. The densification rate will be decreased if the energy input exceeds 0.2 kJ/mm3 With intensifying the energy over 0.8 kJ/mm3, the formation of horizontally oriented cracks is likely to occur while the deflsit1 remains almost constant.

In this paper impact of rigid cylindrical projectiles on aluminum honeycomb panels is studied. Considering various failure modes of target structure (including cell walls tearing and their folding and shearing of plug) by applying energy balance the ballistic limit velocity of panel is determined analytically. It is assumed that the honeycomb behaviour is rigid, perfectly plastic and the projectile diameter is greater than the cell size. The results show that the ballistic limit velocity is increased by increasing the panel thickness, the compressive and shear strength of honeycomb material and the walls thickness. However increasing the cell size, density, and the length of projectile the velocity decneases. The results of this analysis is in good agreement with experimental data.

The oscillations of cylinders are due to formation of vortices in the make region, which has come to attention of researches in the last decades. The calculation of aerodynamics forces acting on the cylinderical shape bedies is of prime interest in the industry and especially the indestanding of the nature of these farces ourll be helpful to design the off-shose structures, the electrical transport lines and other industrial applications. On the other hand in the flows with high Reynalds numbers the experimental values o the aerodynamics Forces coefficients are very expensive and therefore the theoretical calculations of the coefficients will be of prime interest.It is the aim of this paper to calculate the airedynamic forces coefficients using the numerical methods combining the large Eddy Simulation (LES) and the Random Vortex Method (RVM). The comparison of the calculated values with the experemantal results shows good agreement.