Sharif Digital Repository

Microstructure and mechanical properties developments of X80 weld metal by addition of different amounts of alloying elements such as: Nickel and Manganese in coated electrodes were investigated. For this reason samples were welded by electrodes that Ni value has been changed between 0.8%- 3.2% in tow critical amounts of Mn: 0.7 and 1.6. The weld quality was evaluated using nondestructive testing methods (NDT), such as visual inspection and radiography. Tensile test, Charpy impact test and microhardness results indicated the suitable range of Ni and Mn for achieving acceptable mechanical properties. In addition, optical microscopy and scanning electron microscopy (SEM) were applied to link... 

Alumina as an engineering ceramic has special characteristics such as hardness, high abrasive, fatigue and corrosion resistance but suffers from low toughness. One effective method in improving toughness is adding second phases such as tetragonal zirconia and carbon nanotubes.
In this research, alumina- zirconia nanopowders has been prepared by solution combustion method and carbon nanotubes was added to it by two different ways: 1) in situ synthesis of CNTs by CVD 2) dispersion of CNTs by heterocoagulation method. In the case of in situ synthesis of CNTs in AZ matrix, the synthesis temperature and flow ratio of N2/C2H2 gases was investigated and optimum conditions were 800̊C and 300/30,... 

Polymer blending has an important role in preparation of materials with suitable properties without synthesizing new polymers. One of these blends is polypropylene (PP)/ polyethylene (PE). PE is added for improving the impact strength and toughness of PP. For improvementof the properties, a compatibilizer is used due to incompatibility of the PP/PE blend. Improving the impact properties is usually related to the reduction in stiffness. Considering the importance of stiffness in many industrial applications, mineral fillers are employed for increasing the stiffness. In this research, the goal has been to manufacture polypropylene-based ternary composite(Polypropylene/ Polyethylene/Nanometric... 

Discontinuously reinforced aluminum matrix composites (DRA) are candidates as a substantial class of materials for improved strength, stiffness, and wear resistance. However, the low fracture resistance of DRA's has restricted the widespread use of these materials as structural components. Consequently, intrinsic and extrinsic mechanisms have been considered in order to enhance the damage tolerance of composite materials based on microstructural and architectural modification, respectively. The intrinsic toughening technique has shown to elevate fracture resistance to some extent; usually at the expense of reducing several other properties such as strength. The more recent approach to... 

Repair welding is one of the important maintenance processes that include build-up welding and surfacing.In this study, investigation of repair welding parameters has been conducted to achieve desired microstructure with the appropriate toughness and minimum residual stress.In this research, local post-weld heat treatment has been performed by Tungsten electrode arc on weld zone. Performing this process with optimum parameters leads to the best heat cycle with the tempered Martensite microstructure. Residual stress of the sample will be reduced. HAZ coarse grains will be refined to finer grains which result in to improved toughness and reduced hardness to the acceptable limit.
Results... 

The purpose of this thesis is the construction of hard and tough Zirconia bodies from economical raw materials using minimum sintering time and temperature.
Stabilizers cause tetragonal particles to be remained in cubic phase. Most additives are Ca, Ce, Mg and Y ions the whole of which are rare earth elements and make solid solutions with Zirconia.
In this project different percents of CaO, MgO, CeO2, and Y2O3 were mixed with ZrO2 and they were sintered after granulation, cold pressing and Cold Isostatic Pressing. Using jar milling and fast milling, the particle size of purchased ZrO2 was reduced to 0.7 um. The whole needed additives were purchased with particle size below 300 nm.... 

Nowadays, we know that many hydrocarbon reservoirs are fractured regarding this, the investigation of the properties of these reservoirs is necessary to predict the storage, production and the drilling methods. To identify fractured reservoirs, the fracture properties and their geometries under different conditions should be investigated. Besides, the evaluation of the behavior of induced fractures in distinct under ground conditions is very important. The Mechanical properties of the drilling bed like crack propagation, layer and mass rock is impactful in planning of drilling process and hydraulic fracturing operation. In this research, at first we introduce natural and induced fractures... 

Polyamide6 has many engineering applications due to its physical, mechanical and processability properties. However, its low impact resistance limits the use of polyamide6. One of the common ways to overcome this problem and extend the range of polyamide6 application is its elasticity with elastomeric materials, which reduces the strength and modulus (tensile and flexure) in comparision with neat polyamide6. To overcome this limitation, various reinforcements, often fiber or particle-shaped, are used. Today, with the development of nanoparticles, this effort is being made to use nanoparticles, especially carbon nanoparticles with unique properties. Recent research has shown that the addition... 

Low tensile strength and also low strain capacity make plain concrete a ‘brittle’ material. To overcome this shortcoming, the addition of fibre as a reinforcing material has proved to be a reasonable solution. One of the crucial factors in deciding to make this type of concrete is the cost of fibre, which varies depending on its type. In this project a special type of fibre which does not cost a lot and at the same time has a high strength has been used. To investigate the effect of the fibre on the tensile strength of concrete, splitting tensile test (Brazilian test) was adopted. Altogether, 30 standard cylindrical specimens with dimensions of 15 × 30 cm2 were made (3 of each type) which... 

Fe-Cr-C hardfacing alloy is the most popular alloy used in severe abrasive condition such as mining and cement industries. One of the limitation of these hardfacing alloys is their low toghness, which reduce the application of these alloys under impact wear conditions. The purpose of this thesis is to investigate the effect of microstructure on the wear and toughness properties of AISI420 hardfaced martensitic stainless steel alloy. For this purpose, after deposition of the hardfaced alloy on a steel substrate, various heat treatments such as quench, quench temper, quench and partitioning and austenite reversion are designed to change the microstructure of the hardfaced alloy from fully... 

One drawback of polypropylene (PP) as a widely-used semicrystalline thermoplastic is its low toughness at sub-zero temperatures. Along with adding elastomers to PP as impact modifiers, modification of PP’s crystalline structure by means of beta-phase nucleating agents —beta being the toughest polymorph of PP —is a standard method of improving PP’s toughness. Nucleation efficiency is highly dependent on the optimum dispersion of the nucleating agent. Therefore, improving the dispersion of the nucleating agents assumes an essential role. The objective of this study is to determine the influence of the incorporation method of calcium pimelate (CaPi), a highly-selective beta nucleating agent, on...