Sharif Digital Repository

One of the most useful methods in metal forming is Sheet Metal Forming. Use of Forming limit diagrams (FLD) in designing is a conventional method. Therefore many experimental and theoretical efforts have been carried out in order to investigate the FLDs. Many ways to obtain this FLDs and their effective parameters have been studied. But the stress state at these studies is planar which lead to an untrue model for several metal forming process such as incremental sheet forming. With this technique, the forming limit curve (FLC) appears in a different pattern, revealing an enhanced formability, compared to conventional forming techniques. Therefore, in this study, the effect of through... 

In this research, two-layered sheets of copper and stainless steel 316 were produced by roll bonding. These sheets provide a combination of properties of copper and stainless steel; including high strength, thermal conductivity and corrosion resistance, as well as low weight and cost-efficient means of production. The effects of thickness reduction, different preheat temperatures and varying heating conditions after rolling on bond strength were studied. In some specimens, an aluminum sheet was used as a middle-layer, which significantly improved the bonding quality. In order to observe the interface of the bonded specimens, optical microscope images of the cross sections were studied.... 

Sheet metal forming is widely being used in the production fields. Improve of quality, production rate and efficiency of this process are important. Temperature and strain rate are the most effective parameters on the formability of sheet metals. Utilizing forming limit diagram is the most common method of determining the formability. In this study, forming limit diagram of AA3003 aluminum alloy is extracted in different temperatures and velocities using simulation of Nakazima test with Abaqus finite element software. The simulation results, indicate that at 250°C formability is about 3 times more than that at room temperature. increasing the velocity of the punch in low strain rates causes... 

Strain rate dependence of plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. This paper investigates the influence of the strain rate on the forming properties of some industrial sheet metals used in Automotive and Aerospace industries. First, Split Hopkinson Tensile Bar (SHTB) experiments are carried out to determine the influence of the strain rate on the materials’ stress-strain curves. Then, the SHTB results are used to model the constitutive behaviour of the metal sheets using the phenomenological Johnson-Cook (JC) and Voce models. Finally, forming limit diagrams (FLDs) are calculated using... 

These days the usage of welded tailor blanks with sufficient stability and flexibility is accelerating rapidly in order to production of slighter parts and reduction of fuel consumption in transportation means. Therefore, the conjuncture of blanks by welding methods is highly considerable before forming and ultimate production. Friction Stir Welding is greatly appealing to industry as one of the newest methods of solid state welding in production of TWB blanks. In this research, the feasibility study of Friction Stir Welding of thin Al 1100 – H18 alloy blanks with 1.5, 2 and 2.5mm thickness has been evaluated first. After creation of sound welds with same thicknesses, Friction Stir Welding... 

Whenever and wherever there is shipping, there exist risks of marine accidents. Subsequently, such accidents at sea may result in potential economic loss,environmental pollution and fatalities. In fact, ship grounding accident is a type of marine accident that involves the impact of a ship on seabed or waterway side. It may result in the damage of the submerged part of the ship’s hull and in particularly the bottom structure; potentially leading to water ingress, which may at the end compromise the ship's structural integrity, stability, and finally safety. An overall view on groundings categorizes the accidents in two major groups: Soft Grounding and Hard Grounding. A soft grounding does... 

The Tilor welded blank (TWB) two or more sheets with different thickness or strength which are welded together. The automobile designer are searching for new methods to reduce the cars’ weight and producing cost in order to diminish fuel consumption so they can survive in the competitive market. One way to achieve to this seemingly Contradictory demands, is using TWB in cars’ body. One of the most applicable methods to investigate the formability of metals sheets, is Forming Limit Diagrams (FLD). Three ways to determine the FLD are: Analytical Method, Experimental Methods, and Numerical Method. The experimental method to determine FLD, require metal sheets to undergo in different strain... 

In this study, the forming limit stress and strain diagrams have been determined based on the strain gradient plasticity theory. Forming limit stress diagram (FLSD) has been reported as being much less path-dependent and much more favorable than the forming limit diagram (FLD) in representing forming limits in the numerical simulation of sheet metal forming processes. Therefore, the purpose of this study is to develop a methodology for prediction of the forming limits both in strain and stress spaces. All simulations are based on strain gradient theory of plasticity in conjunction with the so-called Marciniak-Kuczynski (M-K) approach. This method introduces an internal length scale into... 

A broad range of plain carbon steels have ferrite-pearlite microstructures, which are used in many industrial applications due to the good strength and formability provided by the typical combination of ferrite grains and pearlite colonies. The mechanical behavior of ferrite-pearlite steels inherently originates from the configurations of ferrite grains and pearlite colonies, which comprised alternating lamellae of cementite with randomly distributed orientations in a ferrite matrix. In this thesis, three different experimental-numerical approaches were employed to investigate the deformation behavior, damage mechanisms, and formability of the ferrite-pearlite steels. At the first step, two... 

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 research, using the crystal plasticity finite element method, the effects of various microstructural features on behavior of spherical steel sheets have been investigated. The cementite phase ratio, the grain sizes of ferrite and cementite, and the percentage of residual pearlite in the steel structure due to incomplete annealing are the major microstructural parameters studied in this work. A grain generator software has been developed to generate ferrite grains as well as cementite particles distributed in the ferrite matrix. A hard coating with special properties as an intermediate layer around the cementite grains has been considered to simulate the contact between ferrite grains... 

One of the common methods of removing blood clots is angioplasty with stents. Due to the fact that the mechanical properties of the stent are directly related to the microtube it is made of. Therefore, investigating the mechanical properties of microtubes is very important. One of the ways used to evaluate the plasticity of microtubes; Drawing a graph is the limit of shaping. The purpose of this research is to extract the forming limit diagram of magnesium microtube by simulating the hydroforming process in Abaqus software. First, in order to confirm the modeling, the hydroforming process for aluminum has been simulated and compared with the existing experimental results. The comparison...