Abstract: In this study, a scale-dependent model is employed to investigate the size effects of copper on the behavior of the crack-tip. This model includes the homogeneous and non-homogeneous strain hardening based on the wavelet interpretation of size effect. Introducing additional micro/nano structural considerations together with decreasing grain size, different size effects can be obtained. As the size dependency is not taken into account in conventional plasticity, an enhanced theory which is related to the strain gradient introduces a length scale will give more realistic representations of state variables near the crack-tip. Accordingly, the contribution of geometrically necessary dislocations (GNDs) activity on strengthening and stress concentration factor is identified in the crack-tip. Finally, the affected zone which is dominated by presence of GNDs is identified
Abstract: Mechanical alloying (MA) is a potential processing method for various equilibrium and non-equilibrium alloy phases such as supersaturated solid solution, metastable crystalline, amorphous, quasi-crystalline phases, nanostructures. Compared to conventional high temperature material processing such as melting and casting, improvement of solid solubility limit results from mechanical alloying at room temperature. The solid solubility increases with increase in milling time due to enhanced stress assisted atomic diffusion during particle refinement and reaches a saturation level at higher milling time. The extension of solid solubility is attributed to thermodynamic, dynamic or kinetic factors such as high dislocation density due to severe plastic deformation during particle refinement and enhanced diffusivity during MA. The review aims to discuss the insight of MA than other non-equilibrium processing in terms of achieving higher solubility, reasoning and mechanism of solubility improvement during MA of different alloy systems.
Abstract: The slag bath accelerated formation technological processes in the "solid" start of mono-and bifilar process schemes are worked out. The melted electroslag steel 5ХНМ (5HNM) and 34ХН1М (34HN1M) properties satisfy to the requirements that apply to the open wrought metal smelting mechanical properties. It is found that an effective way to enhance productivity is the electroslag processes exothermic flux (slag, ferroalloys, and aluminum powder in amounts sufficient to exothermic reactions) use. It is experimentally proved that an electrically conductive layer exothermic flux presence allows electroslag process, both in mono and bifilar schemes in "solid" start. The 34ХН1М (34HN1M) steel in non-heat treated condition tend to hairline cracks formation. The heat treatment provides the required mechanical properties and the hairline cracks absence in electroslag molten metal.
Abstract: Ni-Ti foams of varying relative densities have been made by varying the size and volume fraction of NH4(HCO3), which was used as space holder. The green compacted pellets, after evaporation of NH4(HCO3), were sintered at 1100°C for 2 hrs. The XRD and EDX analysis confirms that there is no residual space holder. The extent of openness of cell walls increases with increase in porosity. The compressive stress-strain behavior of these foams varies with the relative density. The peak stress and energy absorption of these foam increases with relative density following power law and linear relationships respectively, and the densification strain decreases with relative density following a linear relationship. The pseudo elastic recovery strain and shape recovery strain decrease with increase in porosity. The overall recovery increases with decrease in degree of deformation. This phenomenological behavior indicates that these foams can be used for their shape memory effect.
Abstract: Electroless Nickel-Phosphorus (ENi-P) coating is well-known in surface engineering techniques and is preferred in various mechanical, chemical and electronic industries view its extraordinary resistance to wear and corrosion. The paper summerizes the effect of surfactant on the mechanical properties of electroless Nickel-Phosphorus (Ni-P) alloy coating obtained from an acidic bath. The endeavor of this study is to analyse the influence of surfactant Ammonium Lauryl Sulfate (ALS) concentration on the microhardness, surface roughness and wettability of ENi-P deposit on AZ91 Mg alloy substrate. It was observed that there was significant improvement in the rate of deposition, microhardness and wettability, along with reduction in surface roughness (Ra) by addition of ALS surfactant in the chemical bath.
Abstract: In the design of the rolling mill plants, it is fundamental to study the behaviour of the deformation process to assess the main process variables (such as torque and rolling force) in all operating conditions.In this paper, a finite element model is developed and the numerical simulations of the plastic deformation process, in the hot rolling mill of AISI 304 stainless steel, are shown. In the proposed model a Multilinear Isotropic Hardening behaviour of material has been assumed and true stress-true strain curves have been found, taking into account temperature and strain rate. Numerical results are compared with experimental measures regarding an existing hot rolling mill plant.
Abstract: This paper presents the roller hemming operation of FEE220BH sheet metal with convex edge-convex surface geometry. The investigation is focused on process parameters of bending angle and roller geometry whose effects have not been investigated in previous studies. A set of numerical simulations is designed to observe the multi response of the process parameters. The objective of the study is to determine the influences of these parameters on deformation, undesired wrinkling formation and hemming force which are directly related to the material reliability and the visual quality in the operation. The results are discussed to improve the outputs of the operation.
Abstract: Tomatoes (Lycopersicon esculentum), is a fleshy berry regarded as very popular perishable fruit as well as vegetable grown throughout the tropical and temperate regions of the world. This research work investigated the effect of tomato juice on the electrochemical properties of brass, galvanized and stainless steel using potentiostatic polarization method and weight loss technique at room temperature. The samples were cut into sizes, 2 cm by 2 cm for galvanized and stainless steel, while brass a cylindrical shape of 2.5 mm diameter was cut into 5 cm height, the cut metallic samples was weighed using a sensitive weighing balance and recorded. The pH of the tomato juice was measured and the cut metallic samples were immersed into the containers filled with tomato juice and exposed for a period of 30 days. Weight losses of samples and pH of the tomato juice were determined at an interval of 5 days and the corrosion rates were evaluated. The results showed that brass and stainless steel had very low corrosion rates which decreased with time. High corrosion attack was observed on the galvanized steel and this is shown by the high corrosion current density and corrosion rate obtained on the polarization curve showing active corrosion reaction properties. The pH of the tomato progressed to neutrality within five days and to alkalinity at the end of the thirty days test for galvanized steel while the pH of the tomato juice was less acidic at the end of the thirty days test for both brass and stainless steel. Stainless steel was confirmed as best storage material for tomato juice in this study.Keywords: Corrosion, electrochemical, potentiostatic polarization, weight loss, tomato, metal
Abstract: For any space mission to be successful it is necessary to guide the satellite to revolve in the right orbit and gather all the required data without any flaws. Among the many spacecraft subsystems contributing in this regard, Star sensors are the attitude estimation sensors installed in the satellites in order to determine the exact location of the satellite. It helps to bring back the satellite to the required position if there is any deviation from its path. Star sensor captures the image of any of the predetermined reference star. This image is compared with that of the image of the same star captured from the Earth. By this comparison and with the help of star catalogs, digitizers and microprocessors, the attitude and inclination of the satellite is determined.