Sharif Digital Repository

A gating system is network of canals which leads molten metal to mold cavity. Fluid flow during mold filling is highly complex, involving transients, combined and divided flows at junctions, simultaneous heat transfer during fluid flow, turbulence, momentum exchange and energy loss. In case of non-uniform fluid flow at ingates, it causes week mechanical properties, and non-directional solidification. Accordingly, it cause riser insufficiency . In this Work by solving Bernoulli equations, fluid flow at each ingate was obtained and Genetic Algorithm was utilized for fluid flow optimization. Using this optimization method leads to reach to ideal design, simultaneously SUTCAST software was used... 

The pouring basin is a main part in the gating system. The formation of a vortical flow is a big problem occurs during the discharge of melt from the pouring basin. The vortex formation can enter the floating slag and inclusion into the mold. In the case that the vortex is more stronger, a fully air core to the sprue forms and leads to entraining of the air to the mold. These phenomena can decrease the casting quality significantly. Therefore preventing of the vortex is necessary to produce a sound cast. In this study the mechanism of vortex formation is investigated and several solutions are presented to avoid its detrimental effects. For this purpose discharge of a tank is simulated... 

In this research, a computational method based on thermodynamic and physical metallurgy coupled by the d-electron approach was used to design the composition of a high strength and heat resistant (HSHR) stainless steel. Then, three series of the heat resistant 25Cr-35Ni-Nb (HP-Nb) stainless steels with tungsten, nitrogen, and micro alloying elements additions were cast. In these alloys a Nb/(C+ 6/7 N) ratio of ≈ 2.4 to 3.7 was chosen and they were directionally solidified under two cooling rates of 23 Ks-1 and 6 Ks-1. The effects of the alloy chemical composition and solidification cooling rate on the macrostructure, microstructure, microsegregation, and inclusions in the alloys were... 

The aim of this study is numerical simulation of progerasive failure in conical structures that manufactured by tape-winding proceses in various temperatures. For this purpose, flat laminates by tape-winding proceses firstly manufactured using carbon/phenolic prepreg tape. Then tensile, compression, shear and thermal expansion coefficient specimens are cut from these laminates. Tensile and compression test are done on these specemens in fiber and matrix directions in temperature range 23-200℃ and stress-strain and stress-time curves are achavied. Using these curves tensile elastic modulus in fiber and matrix directions and Poisson's ratio are obtained in room temperature. Also tensile and... 

This thesis examines the modal characteristics of the payload after connecting to the carrier via the adapter. Basically, the modal characteristics of a payload change after connection to the carrier due to the different stiffness of the coupling mechanism. In this report, it is attempted to split and model the assembly structural system into two substructures interconnected by the V band clamp mechanism. Then, each of the substructures analyze individually and the modal characteristics of the integrated system are extracted using the infrastructure coupling methods. The coupling method is the "Component Mode synthesis" (CMS) method and input data, dynamic and modal characteristics required... 

The aim of this project is simulation of microstructure and prediction of microstructural length scales in gray cast iron. To attain this, the Fourier heat transfer equations have been solved in a simple domain by FDM (Finite Difference Method), and both thermal distribution and cooling rate were obtained. By coupling experimental results and numerical methods, a model developed for predicting primary and secondary dendrite arm spacing, thickness of eutectoid layers and graphite, and fraction of graphite, cementite and austenite. Besides this model predicts the ultimate tensile strength and Hardness Brinel. Another approach in this project is a new and simple computational method for... 

The present study aimed to investigate the effects of old and young oxide films on the mechanical properties and reliability of Cast Al A356.2 alloy. The results indicate that the presence of oxides within the microstructure of the alloy decreased the tensile properties of the alloy and increased their scattering. Beside this, the presence of the oxides decreased the reliability of the alloy. The results showed that the presence of double oxide films (especially old oxides) decreased the Weibull modulus of tensile properties and resulted in bi-Weibull distribution in tensile properties of the alloy. The results also indicate that using of a clean melt (with high quality), is vital for... 

The Machinable Austempered Ductile Iron (MADI), a new group of Austempered Ductile Iron (ADI), has been developed to remove the problems (hardness and cost) of ADI cast iron. MADI is a special kind of ductile iron which has proper machinabilty properties. This kind of ductile iron can be produced using a specific chemical composition and defined heat treatment process. By providing these conditions, the hardness of the cast iron will be in the range of as-cast cast iron. On the other hand, because of the especial production process, the cost of the final shape casting will be lower than ADI cast iron. In the present work, firstly the effect of heat treatment parameters, including the time... 

Finemet soft magnetic alloys in the form of toroidally winded ribbons are not suitable for industrial applications where a large volume of magnetic materials is required. Production of Finemet bulk alloy by powder metallurgy techniques is an applicable method to produce complex component with isotropic magnetic properties which are the same as ribbons. In this research, Finemet bulk magnetic alloy with composition of has been produced by consolidation of amorphous powders obtained by milling of melt-spun ribbons. At the all stages, the structure and magnetic properties were studied using X-ray diffraction, differential scanning calorimetry, transmission electron microscopy, scanning... 

In many casting experiments, a well is used in the bottom of downsprue, which causes smooth flow in the runner. When the well is not properly designed, sand erosion happens in the runner and some oxide films and gaseous trap within the melt. These oxide films enter into the cast and decrease its strength and fatigue resistance. In addition, the gaseous trapped in the melt turn into solidification voids within the casting part which deteriorate its mechanical properties. The purpose of this research is to enhance casting efficiency by eliminating the mentioned defects. Modified design of sprue-well is proposed by the means of simulation with ProCAST software. Effective variables considered... 

Hadfield’s manganese steel, nominally Fe–1.2%C–13%Mn, is an alloy with inherent toughness, work-hardening characteristics and excellent resistance to some types of adhesive and abrasive wear. However, due to its low yield strength, it may be deformed markedly before its work-hardening become effective. There have been many studies on increasing strenght by alloying manganese steel, but the effects some other alloying additions such as 1 to 2 percent Al, Cr, W, V despite increase strenght and wear resistance at the low stress abrasive condition, decrease work-hardening characteristics and wear resistance at the high stress abrasive condition. The aim of present work, is to modify...