Sharif Digital Repository

With the rapid growth of Internet popularity, web applications are growing in usage and complexity, and therefore, are attractive targets for attackers. Increasing number of services and amount of information stored in the Internet, stimulates attackers to focus on these kind of applications. On the other hand, security specialists are deploying different solutions to mitigate such threats. One of these solutions are Honeypot systems. In contrast with other security solutions, honeypots are not designed to defend against attackers directly. Honeypots, rather, are planned to gather data about what attackers do. This information can help security administrators to learn and understand... 

Sponge Iron production is conducted in various methods that one of them is using coal as a reduction agent. Hoganas process is a different coal-based method that has not been investigated in details. Therefore, the heat transfer method in the system is one of the basic steps to a better recognition of this process (with special Hoganas charging). The present paper investigates the temperature distribution method in the Hoganas cylinder through a numerical model using finite elements. The effects of different parameters, namely preheating and porosity were studied on ceramic crucible made from silicon carbide and it was observed that the consumption energy decreases with the increase of... 

Todays, thanks to the positive effects of electric vehicles, (against the vehicles which use patrol as their fuel), reduction of the Earth temperature and its climate change; the manufacturing, sale and use of electric vehicles experience a sharp increase. In addition to decreasing the air pollution, due to their abundant smart implications, they have been dramatically propagated. Massive use of these devices has raised the concern about the loss of the security which is indispensable part of the infrastructure. None of the past publications and works have taken the cyber-attack on the charging price rate and other data into account. In this thesis, charging methods of electric vehicles are... 

The objective of this investigation was obtaining sound Friction Stir Welded (FSWed) Commercially Purity Titanium using suitable Tool’s Materials (for Shoulder and Pin) in order to be able to work in high temperature (>1000 ˚C) with great mechanical properties and minimum wear during process. Consequently, different materials and designs for Tool, such as High Speed Steel tool, Tungsten based tool, Tungsten Carbide (WC-Co) based tool and diverse tool geometry and designs like simple design, threaded design, fixed pin and inserted pin (adjustable pin) was used. The results demonstrated that using simple cylindrical WC-Co for pin and Tungsten for shoulder resulted in joints with the best... 

IC221M is a cast Ni3AI-based intermetallic alloy which chemical composition bases on Ni- 8Al-8Cr-1.5Mo-1Zr-O.OIB %wt. Because of high strength, good high temperature oxidation, carburization and creep resistance as mechanical and physical properties, IC221M has got good attention in aeronautical, military and steel production industries nowadays. The best service temperature range is 600-800°C and melting starts at II 70°C. Since 1993 according to broad range of researches and applications, ASTM standardized it at Al002-99 and from that time researchers try to replace steel with IC221M. %80 volume of microstructure in this alloy consisted of brittle y' and remain are y and low... 

”Self-organized criticality” is a conceptual term that has helped us describe cer- tain critical behaviors in nature over the past approximately thirty years. In systems exhibiting this characteristic, critical behavior emerges without the need for external parameter adjustments. The necessary mechanism to observe such phenomena is for the critical point to be a dynamical attractor. Based on this, other phenomena have been proposed in which the critical point is not an attractor; instead, a stable cycle forms around it. This mechanism has led to the emergence of a new concept known as ”self- organized bistability.” The primary model proposed for such a phenomenon is based on a sandpile... 

The thesis is focused on the process-microstructure-properties relationships in transient liquid phase (TLP) bonded IN718 nickel based superalloy. The bonding was carried out using Ni-B-(Si)-(Cr) interlayers at temperatures of 1273-1448 K with various bonding time to ensure completion of isothermal solidification. Microstructure development mechanism, kinetics of isothermal solidification during bonding process, influence of microstructure gradient induced by bonding process on the aging behavior of the joint and the response of joint region to post-bonded heat treatment were considered. It was shown that the isothermal solidification rate depends on the (1) diffusion flux of B into the... 

In the present study the production of ferrite-martensite dual-phase (DP) Steel was investigated during the bonding process by transient liquid phase method. The effect of martensite morphologies on mechanical properties of bonding zone were also studied. To make the bonding process and DP steel production heat treatment cycle simultaneously, the step in which the isothermal solidification completed, bonding process, was done simultaneously with austenitising of the steel. Homogenizing of the bond zone, was also done with DP steel making at the intercritical temperature. The St52 steel was utilized for producing DP steel and for bonding process, iron base interlayer with melting point of... 

Ferritic stainless steels, despite having a good combination of mechanical properties and corrosion properties and low price, are less used than austenitic stainless steels due to their low weldability. The main challenges of welding ferritic stainless steels are coarse grain formation in the molten area as well as grain growth in the heat affected zone. In this research, in the first phase, an attempt is made to change the shape and size of the grains in the melted zone by changing the GTAW fusion welding parameters, including welding current and welding speed. In the second phase, an attempt is made to prevent the formation of columnar grains by adding micron particles to the molten pool... 

In order to prevent deterioration of metallic interconnects in solid oxide fuel cells (SOFC), while interacting with glass-ceramic sealant, a nickel electroplated ferritic stainless steel (UNS 430) was used. After applying a layer of powdered glass (SiO2-B2O3-Al2O3-Na2O-BaO-K2O) with thickness around 300-450 μm on the ferritic stainless steel sheets with dimansion of 0.5 × 60 × 60 mm and 0.5 × 10 × 10 mm, samples were heated at temperatures between 770-850 °C and durations of 1 to 15 hours. To evaluate the effect of the Ni layer, two types of sample (only sanded and only electropolished) were also submitted to the same process, and their results were compared with the coated samples. XRF,... 

In this work, mathematical models are employed to predict transient temperature field, fluid flow within the melt zone and distribution of thermal and residual stresses during and after GTAW process. At the first step, fluid flow in the weld pool and transient temperature field within the metal being welded are determined by simultaneously solving the equations of conservation of mass, energy and momentum. To do so, a commercial finite volume base-program, FLUENT, is utilized. In the next step, temperature distribution during cooling as well as resulting thermal and residual stresses are predicted by means of a commercial finite element base program, ABAQUS. The employed models are capable... 

The purpose of this research is to monitor the health of structures using the updated finite element model, in which digital images are used to optimize the numerical model. Structural Health Monitoring (SHM) is always an important and significant issue that has attracted the attention of many researchers in recent years. In general, some researches have been conducted in this field using physical sensors that provide discrete data to the system for analysis. Using cameras to monitor the structure makes it possible to extract continuous and integrated data from the structure using digital images, which is a significant advantage compared to physical sensors.In this research, a steel... 

Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium interlayer, has been investigated. Bonding experiments were carried out using two basic methods; Conventional and Temperature gradient TLP bonding. Optimum values of isothermal solidification temperature and time, pressure, surface roughness, heating rate and homogenizing conditions were determined in conventional TLP bonding experiments. Aluminum oxide layer was not removed before TLP bonding to prevent gallium attack.this layer is crashed during bonding. Al2O3 particles are not soluble in the liquid and are pushed into liquid by solidification front progression. These particles are accumulated in grain boundaries and in... 

The purpose of the present study was to investigate the effects of friction stir welding parameters on the fatigue life of friction stir welded sheets of Aluminum 7075 alloy. The welding process was carried out under three different rotational speeds and three different welding speeds and specimens were extracted transversely to be used for rotating-bending fatigue tests. Optical microscope and SEM images were used respectively for studying the microstructure of the weld zone and fractography. It was the indicated that an increase in the welding speed or a decrease in the rotational speed will result in an increase in the fatigue life