Sharif Digital Repository

Due to the wide application of lightweight concretes, there have been a lot of research activities in this field. The objectives of these activities have been mainly to increase the strength and endurance, and to reduce the weight and the cost of production of such concretes.
Lightweight concretes, in general, have the following advantages: relatively high strength to density ratio, high thermal and acoustic insulation, and fire resistance. However, foam concretes, as a particular type of lightweight concretes, compared with other types, has the advantage of ease of production. Therefore, in this work various aspects of foam concretes were studied. In this project, using a particular... 

n the present study, the optimal design of feeding system in steel sand-mold castings is considered. The first part of this research includes fundamental studies on the physics of shrinkage defect formation during the casting process. The results of these studies lead to new findings on the mechanism of shrinkage defect formation, effect of melt quality on the distribution of defects within the castings and the connection between shrinkage and gases defects. The theoretical analysis of thermal criterion functions for the prediction of shrinkage defects in castings and introducing new criterion function with fewer shortcomings can be accounted as the other finding of this part. A new model... 

Friction Stir Spot Welding as a solid state process is able to solve some of the disadvantages of fusion welding processes. On the other hand, this welding method has disadvantages such as low connection surface due to the hole left by the pin and poor resistance to fatigue loading. In this study, a method called friction stir spot welding via consumable pin was used so that the hole caused by the pin no longer remains at the welding site. The process is done in such a way that first a hole is made in the center of the overlap of the sheets. The rotating tool, in which the consumable pin is made of 6061 aluminum alloy with a diameter equal to the diameter of the hole is lowered at a... 

Al-4.5% Cu alloy, an age-hardenable alloy, is an important alloy in industry due to such unique characteristics as high strength-to-weight ratio and considerable strength at elevated temperatures. In this study, the aim was to evaluate the combined effect of cooling rate and heat treatment on an A206 alloy having more impurities—especially iron—than the nominal specifications. To this end, the melt was poured in a five-step mold. Afterwards, each step was subjected to T4 and T6 treatments in order to study the changes compared to the as-cast samples. Ultimate tensile strength, yield strength, elongation, and grain size were determined by using tensile tests and optical microscopy,... 

New materials as hybrid materials or laminate composites, due to combination of many properties, can be used in many industries. The aim of this research is bonding of three-layered St/AZ31/St composite by roll-bonding process. The roll-bonding process was performed at three preheating temperatures, 340, 400 and 450 ⁰C, with thickness reduction of 30 to 68% and different thicknesses of intermediate layer (AZ31). In order to improve the bonding strength, the as-rolled specimens were annealed at constant temperature of 375 ⁰C. For evaluation of bond strength and investigating the formation of a diffusion layer, the results of peel test and microscopic images were studied. Tensile specimens... 

By employing first principles density functional theory-based (DFT) molecular dynamics (MD), the influences of dangling and floating bonds as well as distorted tetrahedral bonds are studied on the mechanical, physical, and electronic properties of amorphous Si (a-Si). For further examination of the effects of these geometrical defects, two distinct amorphous samples, namely as-quenched and annealed are generated and examined. To verify the validity of the representative cells, the obtained radial distribution function, pair correlation function, and cohesive energy are compared with those corresponding results presented in the literature. Moreover, the surface energy is calculated at final... 

The new generation of advanced high-strength steels use in the automotive industry cause resistance spot welding study and their failure characteristics during static and dynamic loading are important. In this study, the relationship among microstructure, failure mode and mechanical properties are investigate during similar and dissimilar DP980 and MS1400 jointing advanced high-strength steels resistance spot welding. To search for micro and macro structural changes, the optical microscope, stereographic microscope and scanning electron microscope were used. Micro-hardness test, tensile shear test and Cross tension test to evaluate the mechanical properties were conducted. As well as... 

Development of electronic industries, compression of electronic equipment, and removing lead from electronic circuits for environmental reasons, a significant challenge was created in the design and development of tin-based lead-free solders with physical and mechanical properties close to old tin-lead alloys. In this regard, the set of Sn-Ag-Cu alloys with eutectic composition and related compounds have been proposed as alloys to replace Sn-Pb solders. As a lead-free solder alloy, low melting point (≈217℃), high reliability of joints, and compatibility with various fluxes are among the properties of this category of alloys. In order to improve the mechanical properties of the joint... 

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... 

Friction drilling or flow drilling is a method of making holes in metal sheets, in which the material is pushed with the aid of heat from friction. This procedure allows making holes in sheet metal, with a sleeve formed as the hole is created. This sleeve is then threaded and used as the nut, thus eliminating the need for access to the interior faces of hollow steel sections. On the other hand, with the development of advanced manufacturing techniques, larger and thicker hollow structural sections are becoming more popular in mid-rise and multistory structures. onsequently, flow drilling can be considered as a viable alternative for traditional drilling techniques, where the material is... 

This study aims to investigate the mechanical properties and performance of cold recycled asphalt mixtures (CRM). So far, several methods have been proposed for designing CRMs, which are mostly based on the volumetric and mechanical properties of the mixtures. In the meantime, few researches have considered performance of those mixes. The main approach of current research is to evaluate and enhance performance characteristics of CRMs regarding common distresses including early-raveling, moisture damage, fatigue cracking by an appropriate additive.Raveling and Cantabro tests were employed to evaluate the resistance of CRM against abrasion and semicircular bending test (SCB) and crack tolerate... 

Nowadays, Food generation has gained great importance, not only in economic view but also in political. Food reservation is as important as food generation. Synthetic polymer films has widespread use in packaging industries, that is because of its features like easily forming, low price, lightness, etc. The increase of oil resources prices and severe environmental pollution by synthetic polymers, are notable cases which led researchers to find ways in using bio polymers. Starch is one of the bio polymers which is cheap and totally degradable. Using starch in bio degradable leads to high decrease in the mix features. Nano particles are used to solve the problem.
In this study, the effect... 

Use of materials with both high strength and good formability in car structure is a serious approach in the automotive industry to reduce weight as well as maintain the security of occupants. Stainless steels such as duplex steels are one of the most attractive candidates. Thus, metallurgical and mechanical behavior during resistance spot is important. The aim of this work is to study the microstructure-property relationships in resistance spot welding of duplex stainless steel. Austenite-ferrite phase balance and weld nugget size are two key factors determining the mechanical properties of these steels. High cooling rate of resistance spot welding can have a significant impact on the... 

In this research the effect of Si, Cu and Ni alloying elements on the structure and mechanical properties of the A336 alloy is investigated. Expriments were done in two situations, casting and heat treated and the results for all samples with different amount of alloying elements are compared and the effect of heat treating is also investigated. Results show that with increasing the amount of Si and Cu and decreasing the amount of Ni strength and hardness of the cast alloy are 134 MPa and 65 HB and they increase to 187 MPa and 89 HB in heat treated alloy. The elongation and coefficient of linear expansion are decreased from 2.3% and 21.94 μm/m.K to 1.1% and 21.62 μm/m.K. Also the T6 heat... 

Since mechanical properties of cast Al-Si-Mg alloys are directly influenced by microstructural defects, understanding the characteristics of these defects and any interaction between them is important for improving the properties of castings. This study investigated the effect of the most common defects normally found in cast aluminium alloys namely, double oxide films, Fe-rich phases and prosity. A different level of each defect was introduced into castings to investigate their effects on tensile properties of A356 Alloy. Differents casting condition experiment produced different entrained oxide film, Fe-rich phases and porosity caused by shrinkage content, from low to high, were tested...