Journal of Advanced Materials in Engineering (Esteghlal)

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This paper introduces a novel passive suspension system for ground vehicles. This system is based on a flexible Electromagnetic Shock Absorber (EMSA). In the proposed system, efforts are made to a) select a high damping coefficient usable in a car b) determine Physical dimensions and geometry not much different from those of the mechanical shock absorbers and c) seletct EMSA weight and volume low enough for the core not to be saturated. A model is designed and developed followed by determining the dynamic equations for the model. The results from the simulation in a quarter car model are then compared with those from passive and active suspension systems. Keywords: Active Suspension Systems, Electromagnetic damper, Finite Element method

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A new method (thermal spokes) is proposed to simulate the guide rolls in FE analysis of the ring rolling process. So far this method is the only one, capable of calculating guide rolls reaction contact forces related to the stiffness of their adjustment mechanism. The method is simple to use, does not introduce further nonlinearities and could be used in any kind of FE formulations. The method is successfully employed in FE analysis of rectangular and T-section rings. The results of the thermal spokes method, a new analytical method based on lever arm principle with experimental results are in good agreements. This analysis shows that the guide rolls greatly affect the process. Keywords: ring rolling, finite element method, guide rolls, thermal spokes

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It is empirically established that, due to a number of factors involved, a classical (linear) analysis of buckling pressure is impossible. Nonlinear theories of buckling are, therefore, required that involve effective factors such as imperfections and welding effects. In this study, models are developed which are as close to allowable standard deviations as possible. In the next stage, their buckling behavior is investigated both experimentally and numerically using finite element packages ADINA, ANSYS, COSMOS, and MARC based on specific capabilities of each. Results show that reasonable estimates of real buckling pressure will become possible when material and geometrical nonlinearities and initial imperfections are introduced into the analytical system. Finally, in the light of the results obtained, a submarine pressure hull is analyzed.

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Based on classical plate theory, standard and spectral finite element methods are extended for vibration and dynamic stability of axially moving thin plates subjected to in-plane forces. The formulation of the standard method earned through Hamilton’s principle is independent of element type. But for solving numerical examples, an isoparametric quadrilateral element is developed using Lagrange interpolation functions. The spectral method is, in fact, the solution of motion equation for an axially moving plate. Although this method has some limitations concerning boundary condition of plate and in-plane forces, it leads to an exact solution of free vibration and stability of plates travelling on parallel rollers. The method can be used as a benchmark of accuracy of other numerical methods.

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In this paper, properties of slab deformation in sizing press mill as one of the slab reduction processes in hot rolling mills have been evaluated using the elastoviscoplastic finite element method with explicit formulation. Effect of prarameters such as initial slab width and thickness, reduction, feed pitch, and anvil speed on factors such as dogbone formation, head and tail fishtail profile, width necking at the leading end of slab, and slab edge quality have been studied. Furthermore, a comparison has been made between the two common width reduction methods, i.e. Vertical Rolling (Edging) and sizing Press, in order to determine their differences and the efficiency of each process. The amount of width return (back spread), one of the most important factors related to width reduction efficiency and also slab formation after the first horizontal rolling pass, has been evaluated. Also, in order to validate the applied finite element method, the results obtained have been compared with experimental ones found in the literature. The results show that deformation in sizing press is more favourable and that its efficiency is better than that of the vertical rolling mill.

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The mechanical behavior of cold rolled sheets is significantly related to residual stresses that arise from bending and unbending processes. Measurement of residual stresses is mostly limited to surface measurement techniques. Experimental determination of stress variation through thickness is difficult and time-consuming. This paper presents a closed form solution for residual stresses, in which the bending-unbending process is modeled as an elastic-plastic plane strain problem. An anisotropic material is assumed. To validate the analytical solution, finite element simulation is also demonstrated. This study is applicable to analysis of coiling-uncoiling, leveling and straightening processes.

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In this paper, a modification on the fixed grid finite element method is presented and used in the solution of 2D linear elastic problems. This method uses non-boundary-fitted meshes for the numerical solution of partial differential equations. Special techniques are required to apply boundary conditions on the intersection of domain boundaries and non-boundary-fitted elements. Hence, a new method is also presented for the computation of stiffness matrix of boundary intersecting elements and boundary conditions of higher accuracy are applied. In order to examine the applicability of the proposed method, some numerical examples are solved and the results are compared with those obtaioned from both fixed grid finite element and standard finite element methods.

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In this study, a three-dimensional finite element (FE) model for armchair, zigzag and chiral single-walled carbon nanotubes (SWCNTs) is proposed. To create the FE models, nodes are placed at the locations of carbon atoms and the bonds between them are modeled using three-dimensional elastic beam elements. The FE model is used to investigate the influence of chirality and Stone-Wales defects on the ultimate strength (Ultimate stress and ultimate strain) of SWCNTs. Results indicate that Stone-Wales defect significantly reduces the ultimate stress and strain of armchair CNTs. But this defect has a negligible effect on the ultimate strength of zigzag nanotubes. Based on the results, the crack growth path in zigzag and armchair nanotubes have 90 and 45 degree angle to the long axis of the nanotube, respectively.

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Simultaneous application of mechanical pressure and electrical charge on powder samples in spark plasma sintering process, has resulted in a sample with a density close to the theory. In the present study, a thermal-electrical-mechanical coupled finite element model of spark plasma sintering system using multi-objective optimization algorithm is proposed to optimize the mold variable. The simulation performed for Si₃N₄-SiO₂ (1:1 mol) specimen has good agreement with the experimental results. Multi-objective genetic algorithms was used for optimization of mold design in order to maximize the temperature of sample core and minimize the mises stress in the mold. The results show that the optimized dimensions cause 8% increase in sample temperature and about 18% decrease in temperature difference between mold surface and sample core. This leads to better uniformity in the porosity distribution of final sample.