sajjad ebrahimzadeh

In this study the radial-forwad-backward extrusion of axially joint cup shaped AM60 magnesium alloy part is investigatd. In the experimental tests, the cylindrical AM60 alloy samples were prepaed and pressed by a punch into the die cavity. In the next step, the initial and extruded samples were investigated in terms of microstructural evolution and mechanical poperties variation. The microscopic observations showed the significant grain refinement of AM60 is occurred at the end of extrusion proessingwhere the fine grains in size of ~7μm are obtained from the initial value of ~75μm. Also, the Vickers microhardness is increased to 88Hv from the initial value of 56 Hv. The obtained results of uni-axial tensile tests showed the increase in yield and ultimate tensile strength to 142.6 and 290.3 from the initial value of 93 and 230MPa, respectively. The extruded sample elongation is incresead to 13.4% from 10% due to texture evolution, grain refinement and breakage of brittle eutectic phases. The macro and micromechancal based cellular automaton (CA) finite element method were implemented to simulate the process to predict the microstructure evolution of AM60 during extrusion processing. The cellular automaton finite element(CAFÉ) and experimentally obtained results were in good agreement. The effect of some important parameters including friction coefficient, gap thickness and height and die corner radius are studied on the variation of maximum forming load, microhardness values and grain size.

Drought can affects by reduced water resources، agricultural productivity، change in vegetation cover، and accelerate the desertification of areas. In order to drought monitoring، we need to quantify drought effects by using drought indices. These indices based on type of available data are divided into two general categories of ground- and satellite- based indices. The aim of this study was to compare the capability of detection and classification of vegetation changes occurred due to the drought، between one ground-based drought index (Standardized Precipitation Index (SPI)) and four satellite drought indices derived from AVHRR-NOAA (normalized difference vegetation index (NDVI)، temperature condition index (TCI)، ratio vegetation index (RVI)، standardized vegetation index (SVI) in the Kermanshah province. To do this، the change vector (CV) analysis was used as one of the important change detection algorithms. In this method، the change occurred in vegetation has been shown by two components، change magnitude and change direction. The results of implementation of the CVA on the maps of drought indices during the growing season (March to August) in selected years (two normal years، one wet year، and one drought year) showed the best response to the drought in the study years (except the wet year 1992)، obtained by SVI. The lowest similarity was obtained between the SPI and TCI، for wet and normal years. Finally، the study suggests mostly the satellite indices based on the vegetation conditions، rather than the temperature indices، for assessing the effect of drought on vegetation cover.