Sharif Digital Repository

In the classical theories of plasticity, plastic deformation of material is modeled with a macro- scopic viewpoint and without considering the existing physical mechanisms at the crystal scale. However, plastic deformation stems from slip phenomena and evolution of crystalline structure. Furthermore the effects of initial texture of material on its mechanical properties, like formability, and also texture evolution of material can only be calculated by considering these physical mecha- nisms.The main purpose of this thesis is to predict forming limit diagrams of sheet metals based on crystal plasticity approach by considering the effect of initial material texture and presentation of... 

In this research it has been attempted to suggest a modified retrogression and re- aging heat treatment on the sheet of AA7075 alloy with a thickness of 2 mm. The main aim of the research is to reduce the required duration of RRA process while maintaining the value of the conventional tensile strength achieving by the RRA process. This was performed by adding an intermediate warm rolling deformation during the RRA process. The rolling temperature was 180 °C and the rolling reductions were 30%, 40%, 50%. Moreover, the temperature of 170°C was selected as the re-aging temperature, for which the aging time of 0.5, 1, 1.5, 2, and 2.5 hours were examined. This temperature and times were chosen to... 

A common heat treatment used for hardenable aluminum alloys is the retrogression process. In this process, by dissolving a specific precipitate in the alloys (η'), the strength of the alloys is reduced and their formability is enhanced. However, by applying the retrogression process and deforming the alloy, followed by an aging cycle, the strength returns to its original state. In this project the microstructural evolution during the retrogression process in 7075-aluminum alloy has been primarily studied experimentally with the help of a transmission electron microscope and the effect of retrogression time on the microstructural evolution has been assessed. In addition, since the simulation... 

In this study, the ST14 low carbon steel sheet was used as a skin layer in the construction of three-layer laminates. The use of this steel was due to its high mechanical properties and excellent formability. A thermoplastic polyurethane sheet was also used as the core layer. The selection criteria of this polymer were no need for adhesive (for bonding metal to polymer) as well as proper mechanical properties (elongation and strength) and physical (density). The perfect process for manufacturing three-layer laminates is the roll bonding process. To manufacturing a laminate with the desired properties of the designer, the rolling parameters (rolling speed and thickness reduction) must be... 

Demand for high performance components has caused a propensity towards high strength alloys, especially 7000 series, having extended applications in aerospace, automotive and medical industries. Due to high strength, heat treatability, and optimum weight, these alloys have been implemented in various conditions, specifically AA7075, being directly used in airframes. Through the years, numerous attempts have been made to improve the corrosion and formability properties of these alloys, resulting in the development of various tempering methods such as retrogression and re-ageing. Despite achiving optimal properties, it has been of less interest through literature to assess the formability of... 

In this study, the mechanical properties of composite sheet polymer matrix reinforced with steel mesh were investigated. This bonding was carried out by rolling of a three layers of steel mesh in between two composite polymer sheets. Then, the effective parameters of process; Sample maintenance temperature inside the furnace, reduction during rolling, rolling speed, rolling direction and Number of rolling passes were investigated to determine the optimized processing conditions. In this way, adding mesh to the polymeric matrix improves the strength and polymer / polymer bond in the sandwich structure. Placing the mesh in the sandwich structure converts the brittle behavior of the polymeric... 

The precipitation hardenable 7075 Aluminum Alloy is one of the most important heat-treated aluminum alloys. The high strength of this alloy has led to its widespread use in the manufacture of various components in the automotive, aerospace, marine, defense and military industries. Although the production costs of this alloy sheet are high, but since the 7075 aluminum alloy has the capacity to be as strong as steels, by reducing the production process and thus reducing production costs, this alloy can be used more widely in various industries. Therefore, in this study, the mechanical properties of the 7075 aluminum sheet are improved by a new quenching method in the die (HFDQ), which is a... 

Low carbon steel sheets have many applications in the automotive industry. The mechanical properties and ductility of the steel change significantly by the aging phenomena. In this study, the effects of temperature and time of quench aging phenomenon on the tensile properties and formability of a low carbon steel sheet has been investigated. Samples with dimensions of 10×10 cm were prepared for the Erichsen test and also samples with geometry in ASTM E8 standard were prepared for the tensile test of the steel sheet. After performing solution treatment on the samples at 650 °C, they were rapidly cooled to room temperature (25 °C) and then placed in water, air and oil at certain temperatures... 

In the roll bonding process, the same and non-homogeneous metals are bonded to each other by rolling deformation, and the sheet produced exhibits multi-properties. Two- and three-layer copper and stainless steel sheets are used for a variety of purposes. Stainless steel-Copper bilayer sheets are not just cost effective in production, but also have mechanical and thermal benefits from the inherent properties of copper and stainless steel. In addition to its increased strength, good ductility, reduced thermal expansion and excellent soldering are other benefits. In the past, some researchers have been studied on the bonding strength and formability of austenitic stainless steel-copper bilayer... 

There is a major interest to manufacturers of automobile and aerospace parts towards the tailor-welded blanks (TWBs) to reduce the weight and cost of the parts and improve their performance. In this work, formability of four groups of TWBs (two groups with similar thicknesses and different steels and two groups with similar steels and different thicknesses) are investigated. To produce the TWBs, DX54, E275 and E335 steel sheets were used. The results indicate that the inclined laser beam causes the sample failure from the weld zone in the tensile test. Setting the focal point on the top surface of the sheets results in enhancement of yield strength in comparison to the other positions. ...