Journal of Advanced Materials in Engineering (Esteghlal)

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This paper is concerned with investigations into the effect of tension between the stands of the finishing mill on width control in a hot rolling process. An analysis is given to predict satisfactorily the variation in width due to spreading and also due to strip tension between the stands. Wusatowski's model which is developed to give an account of spreading is specified and a similar model to give an account of width reduction due to strip tension between the stands is developed. It is shown that the theoretical values of the model are in good agreement with the experimental results obtained from a hot rolling line of steel strip.

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In this paper, collapse behavior of simple and reinforced thin-walled channel- section beams, subjected to three- point bending, is investigated. Many simple channel- section beams of different geometry and some reinforced ones were tested, and their strengths after collapse were obtained thoroughly. Since the available theories in this area are complicated and little attention has been paid to the case of reinforced thin-walled beams, simple models were used and further developed to give an account of the collapse load and the deformation energy of such beams. The method proposed in this paper is valuable both to the further studies of the symmetric thin-walled beams with arbitrary cross-section and to its practical application of such beams as energy absorbers.

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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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In this paper an analytical model for cold rolling of strip has been described. This model is developed based on the slab method of analysis and the hydrodynamic lubrication. The characteristics of rolling are obtained from the equations of equilibrium and the plate was allowed to strain harden assuming that the lubricant behaves as a Newtonian fluid. The shear stress to the plate is obtained by calculating the thickness of the lubricant film by employing a viscosity-pressure-temperature relation. The governing equations are obtained by composing these relations and the final differential equations have been solved. From the solution of the final equation, the rolling force، torque and shear stress to the plate are calculated. To verify the validity of the proposed model, these values are compared with experimental and analytical results of other investigators. It was also noted that by employing the proposed analytical model, a large amount of computation time and costs are saved

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In this paper, an analytical method based on Modified Slab Method of analysis is presented to study the asymmetrical rolling process due to difference in work rolls radii, rolls speeds and interface frictions. The shear force imposed on material along the contact region is considered to be a function of the frictional factor and the roll gap geometry. Elastic-plastic with linear work hardening constitutive law was assumed. Asymmetric factors considered are roll diameter ratio, roll speed mismatch and differential interface friction conditions. Neutral points’ location along the contact region in relation to the variations on thickness reduction, roll speed ratios, roll diameters ratio and front and back tensions are investigated. Predicted values for rolling force and torque from the present analytical model are compared with those of other workers, which are shown to be in good agreement

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In this paper, an analytical model based on Modified Slab Method is presented for rolling of clad sheet or double-layers in which the two layers are bounded prior to rolling. This model considers the general case of asymmetrical rolling due to unequal surface speed, different contact friction, roll diameters, flow stress, and thickness ratios of the two layers. Using this model, rolling parameters such as pressure distribution along the arc of contact of the rolls and the clad sheet, rolling force, and torque with respect to reduction in thickness can be easily calculated. The analytical rolling force and torque computed by the proposed model were compared with the analytical results of other researchers and were shown to be in good agreement. The proposed model is very suitable for online control application due to its completeness and its capability of predicting the rolling parameters

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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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Open pore metallic foams can be used for high temperature, high performance heat exchanger due to their high gas permeability and heat conductivity provided that skins properly attach to the foam’s struts on the surface. In the current study, a novel process was successfully developed to fill pores on the surface of the foam sheet in order to deposit skin on the foam specimens by thermal spraying. Nickel based superalloy (Inconel 625) skins were deposited on each side of a sheet of nickel metal foam with different pore densities of 10 and 20 pores per inch by high velocity oxy-fuel (HVOF), atmospheric plasma spraying (APS), and twin wire arc spraying to form a sandwich structure. The sandwich structure can be used in high temperature heat exchanger applications. The penetration of the coating materials into the foam struts can be controlled through the filling process before spraying. The microstructure of the skins and the adhesion at the interface between the nickel foam’s struts and skins were characterized. Results showed dense skins with good adhesion to the surfaces of the foam. The foam’s struts were imbedded into the coatings deposited by HVOF more deeply than the coatings deposited by APS and wire arc spraying. Skins deposited by HVOF and wire arc spraying showed higher bending strength than the skin deposited by APS due to lower porosity and oxide content in the coating.

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Due to their superior properties such as high specific strength, high creep resistance and high strength at elevated temperatures, aluminum composites reinforced with alumina nano particles are widely used for advanced purposes such as aerospace and auto industries. Lack of an appropriate welding process limits their applications. Transient liquid phase (TLP) bonding is one of the state-of-the-art joining processes. It is used for welding composites and advanced materials. Microstructure and mechanical properties of TLP bonding depend on the bonding time and temperature. In the current study, the effect of bonding time on the microstructure and bonding strength of the TLP diffusion bonded of Al2O3p/Al nanocomposite was investigated. A thin layer of copper deposited by electroplating was used as an interlayer. The bonding times of 20 and 40 min were not sufficient for completing the isothermal solidification, and the bonding strengths were not satisfactory. By increasing the bonding time to 60 min at constant bonding temperature of 580 ºC, the isothermal solidification was completed and the final joint microstructure consisted of soft α-Al phase with dispersed CuAl2 precipitated particles. Decreasing the amount of brittle eutectic structures in the joint seam by increasing the bonding time was the main reason for improvement of the joint shear strength. The maximum joint shear strength was achieved at 580 ºC for 60 min which was about 85% of the shear strength of the base material.

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Today, along with the advances in circuit printing technology it has become possible to fabricate band lines integrated with circuit elements. The band lines are known as microstrip lines and the whole packages are called microstrip antennas. The microstrip antennas have three layers, including conductive patch layer, dielectric sub layer, and ground conductive layer. One of the most important problems of prevalent antennas is their inflexibility, which was addressed in the current paper using textile based structure with proper flexibility and flexural stiffness. This was done using ink jet printing techniques followed by electrolytic plating to provide diverse antenna patterns based on nickel particles. The coated surface was characterized by scanning electron microscope, elemental analysis and optical microscope. Moreover, the washing fastness and the other physical and mechanical specifications were measured using standard techniques. The elemental analysis of metal-coated fabric clearly indicated a high level of nickel. Furthermore, the morphological investigation proved the formation of homogenous nickel nanoparticle in a diameter range of 100-500 nm with an evident boundary and semi-spherical shape. In addition, the cumulative presence of particles in a sequence followed a cabbage-like structure originating from metallic crystals. The washing fastness tests revealed a high stability in electrical resistance after several washing steps. In the meantime, the antenna gain and the corresponding bandwidth were measured using spectrum analyzer. The results indicated a 1 kHz increase in bandwidth and 11 dB decrease in antenna gain for a large size compared to a small one. Meanwhile, the bandwidth of rectangular pattern showed a 0.2 kHz increase and 2.5 kHz decrease compared to spiral pattern. Finally, the four-probe electrical conductivity test demonstrated a high level of conductivity around 2632 S/cm.

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In the present investigation, spherical nanoparticles of nickel ferrite with uniform structure were successfully produced by hydrothermal method in the presence of polyethylene glycol (PEG) as a polymeric surfactant at 180°C for 12 hour aging time and the effects of the synthesis time, temperature and surfactant were investigated. According to the X-ray analysis, conversion of nickel oxide and hematite to nickel ferrite was a way to produce NiFe2O4. At 140‌°C, agglomerated particles without specific shape were formed, but at 180°C particles were homogenous with spherical shape. Saturation magnetization increased by increasing the hydrothermal process aging time.

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