Integrated multiphysics modeling, testing and optimization of friction stir welding of aluminum alloys

The main objective of this work is the development of a novel integrated multiphysics modeling, testing, and optimization of friction stir welding (FSW) for aluminum alloys, and thereby facilitating a better understating of processing-microstructure-properties relationships in this relatively new welding technique. To this end, in this paper-based dissertation, first we review various models and optimization methods used in the field of FSW. Next, based on the current state-of-the-art and a validated 3D thermal model for aluminum 6061 along with a Taguchi design of experiments approach, we make a proposition that hot welds (with maximum temperature during FSW) have the lowest mechanical properties as opposed to cold welds. Using further experimental studies we also propose that another determining parameter in the resulting mechanical properties of FSW welds is the material flow around the tool which in very cold weld conditions may cause low mechanical properties due to low mechanical bonding. Next, we develop and validate a novel two-dimensional Eulerian steady-state “integrated multiphysics” model of FSW of aluminum 6061 which did not exist earlier in the literature and can simultaneously predict temperature, shear strain rate, shear stress and strain fields over the entire workpiece. The model can additionally predict microstructural changes during and after FSW as well as residual stresses. In order to investigate the effect of different material constitutive equations on this integrated multiphysics model, we implement and compare most commonly used CFD (Computational Fluid Dynamics) and CSM (Computational Solid Mechanics) constitutive equations and show their similarities and differences. Using the same integrated multiphysics model, for the first time we also present a new semi-experimental approach to measure strain during FSW using visioplasticity. Finally, we perform a comprehensive experimental study (tensile testing, Electron Back Scatter Diffraction, Scanning Electron Microscopy, and micro-hardness testing) on FSW of aluminum 6061 samples in order to further validate the developed numerical model and optimize the welding process parameters (tool rotation speed, weld speed and axial force). The experimental study also prove the above mentioned preposition on a correlation among the processing-microstructure-mechanical properties during FSW, especially when comparing the UTS of samples from cold and hot weld conditions.Applied Science, Faculty ofEngineering, School of (Okanagan)Graduat

Policy Analysis the Impact of GDP, the Ratio of Prices and Exchange Rates in Neighboring Countries on the Development of Agricultural Exports

Today, due to International changes regarding the sharp decline in oil revenues, the negative impact of diseases such as Corona-virus on many parts of the country and International trade, change in patterns of development of national income is inevitable. In the current situation, changing the main variables of the country's development, the importance of exporting agricultural products to the national economy and the growth and development of the country is undeniable. Despite numerous studies that support the export of non-oil products for the growth of the country's exports, the effect of price ratios, exchange rates and the GDP of neighboring countries on the country's exports have not been studied. In this article, with the approach of econometric approach and using data panel method, the test of export of Iranian agricultural products to neighboring countries has been tested.               According to the research findings, the effects of GDP on the export of Iran's agricultural products are positive and significant, and the effects of price-to-price ratios between Iran and neighboring countries, as well as the effects of exchange rate ratios between Iran and neighboring countries on Iran's agricultural exports, are negative and significant. Therefore, the increase in gross domestic product of neighboring countries increases the export of Iranian agricultural products to these countries and by increasing domestic prices compared to the prices of neighboring countries and increasing the domestic exchange rate compared to the exchange rate of neighboring countries reduces Iran's agricultural exports