Sharif Digital Repository

In this research, a powder containing magnesium-aluminate spinel particles is prepared based on co-precipitation method and 5% , 10%, 15% and 20% zirconia-contained composites are produced as second phase from the synthesized powder. The raw materials used in the synthesis comprise hexa-hydrated magnesium nitrate, nona-hydrated aluminum nitrate, ammonium bicarbonate, 28% ammonium solution and distilled water. The properties of the powder is then investigated using STA, XRD and SEM tests. Also, XRD and SEM analyses as well as triple point flexural strength and Vickers hardness tests are carried out in order to investigate the effect of adding zirconia to the powders. The variations of the... 

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.... 

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... 

The most failures caused by wear, fatigue and corrosion are very sensitive to surface of material. Since the most failures starts or occurs at the surface of material, so control and improvement of the surface properties can have a significant effect on increasing the service life and improve the overall behavior of the material. Reforming of the structure and grain size is one of the methods to improve elastic properties, hardness, softness, toughness, etc. Also the macroscopic residual stresses in fracture toughness test specimens, can have tremendous effect on fracture toughness measurements. Many methods are used to modify the surface structure and to create a compressive residual stress... 

In this study in-situ Al/Al3Ti was fabricated by mechanical alloying, hot extrusion and subsequent heat treatment. First, initial pure powders of Al and Ti were mechanically alloyed with 5 weight percentages of Ti for 40 hours. The as-hot extruded samples containing 5 wt% of initial Ti particles, were exposed to heating at 600 oC for various time intervals up to 10 hours. Microstructure analysis by OM and SEM proved that in-situ Al3Ti phase was formed as a layer around Ti particles by solid reactive diffusion between Al and Ti particles. After 10 hours of heating, all the Ti particles were consumed and transformed to Al3Ti. Mechanical properties of samples were investigated by Brinell... 

Epoxy resins have good mechanical and thermal properties, high chemical resistance and low shrinkage during cure but in spite of these good properties,they are brittle and this limits the usage of them. Adding a second, soft or rigid, phase has been always an effective strategy to improve the toughness of epoxy. Rigid phase used in resins are divided into organic and inorganic. The aim of this study is to increase epoxy toughness, maintaining mechanical properties and study effect of silica and polycarbonate on fracture toughness simultaneously. Mechanical properties including yield strength and elastic modulus are evaluated by pressure test. Additionally fracture toughness and three... 

The present paper discusses the possibility of adding recycled polymer fibres to high performance concrete (HPC). Fibres used in this study were recovered from discarded car timing belts. To investigate different characteristics of the concrete specimens several destructive and non-destructive tests, such as compressive strength, modulus of rupture, flexural toughness, ultrasonic velocity and electrical resistance tests were carried out. In addition, slump flow tests were conducted on the fresh concrete. Experimental results from the study showed that the use of low percentages (up to 0.5%) of waste fibres improved the modulus of rupture and flexural toughness. Based on ultrasonic and... 

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... 

Zirconia toughened alumina (ZTA) Nanocomposites were prepared using nano sized Zirconia (ZrO2) powders doped with 3% mol of yttria (Y2O3) nanopowders and the sintering behavior at different temperature (1450 °C, 1550 °C and 1650 °C) were studied. The ZTA composite with different amount of partially stabilized Zirconia (PSZ)(5, 10, 15 and 20% mol) were prepared via axial pressing and then sintered to achieve maximum densification. After that phase changes of the samples were monitored. SEM was used for microstructural study and hardness and fracture toughness were determined by means of Vickers indentation. X-ray diffraction pattern showed that at constant composition, tetragonal zirconia... 

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... 

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... 

Particulate ceramic reinforced aluminum matrix composites have high specific strength and stiffness; however, low fracture toughness and deformability have restricted their industrial applications. Among the methods introduced to overcome this shortcoming is fabricating the layered composites which contain alternative layers of aluminum (Al) and discontinuously reinforced aluminum (DRA). In this study, two different routes; i.e., "Powder extrusion - Casting - Rolling" and "Powder extrusion - Roll bonding" were employed to produce layered Al-DRA composites. After production of Al6061/SiCp composites via hot powder extrusion, mentioned processes were utilized to make DRA-Al-DRA laminate. In... 

In this study, standard composite laminate specimens with micro and nano sized particle additives are made to study the effect of the additives on the fracture toughness of the specimens in standard tests. The composite laminates are made from epoxy resin and unidirectional glass fibers. The mode I and mode II fracture toughness of the specimens are measured under various loadings in standard tests. The fracture surface is then, fractogaphed by microscopic instruments. In conclusion, the fracture behavior of laminated composites, toughened by micro and nano particles is discussed. The results show that using rubber particles will improve fracture toughness of neat epoxy resin and laminated... 

Commercially pure titanium (CP-Ti) is an important groups of titanium family and because of high strength, low density, high corrosion resistance and biocompatibility, this group of titanium is a suitable choice for application at chemical, petrochemical and medicine industry. Nowadays surgeons have a tendency toward use of CP-Ti instead of Ti-6Al-4V alloy. Moreover, because of body anatomy limitation, use of thick sheets result in high volume and damage soft tissue. Therefore, for sheet thickness reduction, study of the effects of metallurgical and geometrical parameter on fracture behavior of thin sheets is important. In this study, the fracture behavior of CP-Ti thin sheets investigated....