فهرست مطالب شهاب کاظمی

In this research, the cement base composite reinforced with sand was produced by water and poly-polyurethane. In order to investigate the destructive effect of corrosive environments, the samples produced in different amounts of water, polyurethane polymer and sand were immersed in 10% caustic soda and 10% sulfuric acid electrolytes for 70 days. Next, in order to characterize the samples after immersion, the samples were examined by mechanical and physical evaluations including densitometry test and pressure test. The results of the densitometry test showed that the density of the samples immersed in sulfuric acid is about 10-20% lower than the samples immersed in caustic soda. The results of the pressure test showed that the strength of water produced samples is higher than the samples produced with polyurethane polymer. On the other hand, it was found that if sand is used and composite concrete samples are produced, the strength of the samples increases by 75%. The results of the compressive strength test showed that the strength of samples immersed in sulfuric acid electrolyte is generally 20-30% weaker than the strength of samples immersed in caustic soda electrolyte.

In this study friction stir welding was used to perform butt joint of Al5083 and simultaneous production of Al-ZrO2 nanocomposite in weldment. Welding parameters such as rotational speed, travel speed and tilt angle were varied to obtain optimum weldment with no defect and high tensile strength, and then by adding zirconia nanoparticle to welding zone of optimum sample, the effects of pass number on microstructure, mechanical properties and wear characteristics of welded specimens were investigated. In order to investigate microstructure, optical and scanning electron microscope and atomic force microscope was used. Results showed that by increasing pass number, the distribution of nanoparticles in the matrix become more homogenous and grain size in the stir zone has considerably decreased. The reason of this phenomena could be attributed to the presence of reinforcement nanoparticles which it causes pinning the grain boundary, enhancing nucleation of new recrystallized grains and the effect on breaking of initial grains. The maximum microhardness and tensile strength of weldment were obtained for composite weldment after four pass of 111 Hv and 328.3 MPa, which these values were 24 and 26% higher than weldment without reinforcement. Wear resistance of the weldment was determined by pin on disk test and revealed that by increasing pass number of FSW, the wear resistance increased.

Friction stir processing (FSP) is a method for improvement surface. This process development for refinement of microstructure, improvement of materials mechanicals properties so production of surfsce composite. The aim of article product metal matrix composite (MMC) on surface of copper sheets by means of SiO2 refinement by friction stir processing for improve mechanical properties. In this article travel speed was fixed and56 mm/min and rotationals speed were 500, 710, 1000 rpm to sue. Optimum sample selected due to microstructure resualts and highest mechanical properties. Microstructure resualts reported by optical and scaning electron microscopical. Resualt indicating via increase rotational speed, increase size and decrase hardness. Maximum hardness related to specimen whit rotational speed 500 rpm, and 121 Hv, least size 10µm. so tensile properties statement white standard tensile test. Resualt of mechanichal surface composite were about on 218 to 227 Mpa respectively. At last wear properties of surface composite were investigated. The resualt of wear test exhibiting better wear behaviour of the developed composite.

In this study, A356 aluminum alloy matrixcomposites reinforced with different weight percentages of SiC nano- and microparticles respectively with 50 nm and 5 µm average particle sizes were fabricated by stir casting method. Due to the effect of T6 heat treatment on the strength and hardness of A356alloy, the obtained composites were subjected to the T6 heat treatment. The mechanical properties such as hardness and compressive properties of the composites were investigated. Microstructures of the samples were also investigated by an optical microscope (OM), scanning electron microscope (SEM) and field emission scanning electron microscope (FESEM). Microstructural investigation indicated that T6 heat treatment led to thechange of eutectic silicon morphology and formation of theMg2Si precipitates during age hardening stage, leading to increase the hardness and compressive strength. The results showed that an increase in wt.% of nanoparticles led to an increase in hardness and compressive strength. The results of microstructural investigationshowedthe relatively uniform distribution of reinforcement particles. Also, the strength and hardness of the composites reinforced with nanoparticleswere greater than those of the composite reinforced with microparticles, even with higher weight percent of reinforcement particles. Hardness and compressive strength at 35% strain for the composite reinforced with 1.5 wt.% nanoparticles were respectively obtained 62 HBN and 252MPa, which are improved compared to the base alloy.

Hybrid ratio of each reinforcement phases in hybrid composite can be defined as proportion of its volume to total reinforcement volume of the composite. The hybrid ratio is an important factor which controls the participation extent of each reinforcement phases in overall properties of hybrid composites. Hence, in the present work, surface hybrid nano composites of Al2024, Graphite average particle size of 100 μm and ZrO2 average particle size of 15 with different. For fabrication of nano composite the tool rotation rate was set to be 1000 rpm, and its advancing speed was 20 mm/min and tilt angle of 3 degree were chosen and all samples were subjected to 2 passes of FSP to obtain more homogeneous dispersion of the reinforcements. Subsequently, effect of hybrid ratio on microstructural, mechanical and tribological properties investigated. Optical microscopy and scanning electron microscopy were utilized to perform microstructural observation on the samples showed that reinforcements are well dispersed inside the Nugget Zone. Hardness value measurements and pin on disk dry sliding wear tests were carried out to investigate effect of hybrid ratio on mechanical and tribological properties of the nano composites.

In this study, particulate nanocomposites with A356 aluminum alloy as a matrix reinforced with 1 and 1.5 wt.% SiCnanoparticles with 50 nm average grain size were fabricated by stir casting method and then the obtained composites were subjected to T6 heat treatment. The mechanical properties such as Hardness Test and Tensile Test of composites Samples were investigated. Microstructures of the samples were also investigated by using optical microscope (OM) and scanning electron microscope (SEM). The results show that T6 heat treated nanocomposites have significantly higher Hardness and tensile Strength compared to the nanocomposites without heat treatment. The enhancement in the mechanical propertiecanis due to the formation of Mg2Si phase and globular silicon particles.Also, increasing in the concentration of SiC nanoparticles led to improve the hardness and tensile strength, So that the highest tensile strength and hardness was obtained for the 1.5 wt.%SiCnanocomposite. Tensile strength and hardness of 1.5 wt% SiCnanocompositesbefore and afterT6 heat treatmentachieved 177MPa and 236MPa and 80 HBN and 123 HBN, respectively.Fracture surfaces were studied using SEM show that failureof all samples is brittle fracture.

Friction stir processing (FSP) is a novel process for refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In this investigation via friction stir processing, metal matrix composite (MMC) was fabricated on surface of 5083 aluminum sheets by means of 5 μm SiC particles. First combination of rotational speed and travelling speeds were performed. Optimum condition was selected due to highest tensile strength. It was seen that sample which fabricated by 1000rpm and 28mm/min had improvement in tensile strength in comparison to other conditions. After that the effect of multipass on the optimum sample were investigated. The friction processed surface composite layer was analyzed through optical and scanning electron microscopical studies. Mechanical properties of the friction stir processed surface composites were evaluated through microhardness and universal tensile tests. The results were compared with the properties of the base metal. The surface composite layer resulted in that change of tool rotational direction between FSP four passes exhibited better properties in hardness, tensile behavior and wear resistance compared to the behavior of the base metal. The microhardness and tensile strength of the as-received alloy, and surface composite after that change of tool rotational direction between four passes specimens were about 85Hv and 285 MPa, 118Hv and 316 MPa, respectively.

The fabrication of nano‐composites is quite challenging because uniform dispersion of nano‐sized reinforcements in metallic substrate is difficult to achieve using powder metallurgy or liquid processing methods. Friction stir processing (FSP) is a new solid-state process used to modify the refinement of microstructure, improvement of material’s mechanical properties and production of surface layer composites. In this investigation via friction stir processing, metal matrix composite surface (MMCs) was fabricated on surface of 5083 aluminum sheets by means of 5 μm and 80 nm TiO2 particles. The friction processed surface composite layer was analyzed throughoptical and scanning electron microscopical studies. Effects of reinforcing particle size and FSP pass number on the microstructure, microhardness, on tensile and wear properties of the developed surfaces were investigated. Results show that the created nanocomposite layer by TiO2 particles exhibits a microstructure with smaller grains and higher hardness, strength, and elongation compared to the composite TiO2 layer by particles. Increasing FSP pass number results in improved distribution of particles, finer grains, and higher hardness, strength, elongation, and wear resistance. The surface composite layer resulted in four passes with change in rotation direction with nano particle reinforcement exhibited better properties in hardness, tensile behavior and wear resistance compared tothe behavior of the base metal.

The science of exegesis is a lucrative element to better understand the Quran and obey the divine teachings. To be aware of interpreter's exegetical tendencies and methods plays a key role in apprehension of the exegeses and thus has always attracted the attention of researchers. Ignaz Goldziher, a Hungarian Jew Oriental, is one of those Orientalists who have explored the exegetical tendencies of the Quran amongst the Muslims and have challenged some of the Shiite means of induction. The present paper studies the books written on exegetical tendencies among the Muslims and responds the baseless critiques developed by Goldziher on the Shiite exegesis. The writer has critically treated Goldziher's opinion on the Shiite metaphorical and symbolic styles of exegesis, his accusation that the Shiites do not rely on the Uthmanic Codex of the Quran and that they believe in distortion of the Quran. Finally, the conclusion is drawn that Goldziher has attributed the exegetical styles and theories of the Qur’ānic sciences of many Muslim sects to Shia.

Despite the majority of Quaternary deposits consist of alluvial sediments، an important proportion of deposits (in active tectonic zones) are formed as tufa and travertine. The studied travertine in this research (from seven measured sections) are located in three neighboring provinces (Qazvin، Hamedan and Kurdistan)، situated in the Central Iran and Sanandaj-Sirjan structural zones. Petrographic studies show distinct lamination، microscopic and macroscopic porosity (5-10%) in the samples. Most studied samples are biosparite; plant and algae debris present in some sections. SEM analysis shows mosaic and equant calcite crystals، grows in pore spaces. XRD analysis indicates low-magnesium calcite is present in all studied sections; some clay minerals and quartz are present in few sections. Geochemical analysis (XRF method) indicates that the average CaO and SiO2 in samples are 52. 98% and 1. 98% respectively; Si mainly occurs as quartz veins and sandstone clasts. MgO (0. 062%)، Al2O3 (0. 47%، as clay minerals) and Fe2O3 (0. 41%، as iron oxide) are also exists. Based on the cement type، meteoric and vadose diagenetic environments were recognized.