فهرست مطالب hasan ghiasi

The microstructure formation and mechanical properties of coiled tube CT80 grade steel was investigated with different heat treatments. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to evaluate the microstructure. Acicular ferrite, polygonal and quasi-polygonal ferrite, granular bainite, martensite, pearlite, and small Martensite-Austenite (MA) islands with the banding structure were revealed in original and heat treated samples. In order to assess the effect of grain size and microstructure, mechanical properties were evaluated by hardness, charpy impact, tensile, and fatigue life tests. The best mechanical properties by tensile and fatigue test is obtained from the normalized specimen with the grain size of ASTM 13.

The relife valve is a critical part of a device that has great importance to ensure security of related persons life and financial. Use this piece is necessary in the system with possibility of increasing the internal pressure of the system. One of these systems is gas tanks that is such as a mobile bomb and in case of malfunctioning of relife valve, in which place there is a possibility of explosion. In this study, evaluation of valve failure a portable LPG gas cylinder is performed. For this purpose, chemical analysis, metallography, mechanical properties, and in particular the fractography was done on The broken sample. The surface quality of the samples were examined by stereomicroscope and scanning electron microscopy. The results show the fatigue failure. in effect of loss of surface quality due to pitting of the of inappropriate machining. The main factors contributing to this phenomenon was detected reduction of surface quality due to pitting and improper machining.

Both of the exhaust and intake valves are very important components of a diesel engine which are used to control the entrance and exhaust of gases in internal combustion engines. During opening and closing, these valves are subjected to high temperature, spring force and high pressure (up to 15 Mpa) inside the cylinder. Various factors, including mechanical fatigue at high temperatures, thermal fatigue, reduction their mechanical properties such as hardness and yield strength due to heating, wear caused by impacts, especially at the seat and the guide sections, corrosion, excessive heating and accumulation of soot on the valve can be caused to failure of the valve. However, the valves are mainly failured by fatigue. The temperature of internal portions of intake valve and exhust valve are 550 °C and 800-900 °C, respectively. Therefore, these parts are subjected to thermal loading and chemical corrosion at high temperatures. In this research, the failure causes of a bus exhaust valve were studied using chemical analysis, macroscopic and microscopic investigations by optical and scanning electron microscopes and hardness test. The results of chemical analysis and hardness was in accordance with the relevant standard, However, results of macroscopic and microscopic investigations Were indicative of formation of microstructural defects due to increased temperature. Therefore,it was found that the probable cause of failur is the improper performance of the engine which results in excessive rising of temperature and finally causes to failure of valve.

Age hardening behavior and microstructure of superalloy AEREX 350TM in commercially cold-drawn condition were studied. It was found that aging the cold drawn alloy significantly facilitated the formation of major phases of gamma prime and eta, in AEREX 350TM. Interestingly, the minimum temperature of formation of gamma prime and eta phases in the cold drawn alloy was lower by about 30°C and 5°C, respectively, to that previously reported for the solution treated alloy. Cold working, however, did not considerably influence the maximum temperature of stability of these phases. In addition, Widmanstätten morphology of eta phase significantly improved in the cold drawn samples compared to that seen in the solution treated alloy. Diffusion through dislocation network could have facilitated growth of major phases whereas its influence on dissolution temperature of these phases was negligible. In addition, it was suggested that cold working might increase the density of hcp nuclei in the fcc matrix. This may justify the observed enhancement of the Widmanstätten morphology of eta phase in these samples following the aging process.

In this study the factors controlling the software colorimetry (Photoshop), including illumination (direct and indirect), image background (white and black), camera settings (zoom, light, resolution and environmental conditions) and the conversion equations of R, G, B images to L *, a *, b *, compared with the results of the device were investigated and optimized. The results showed that the factors affecting the photography which werw found to be just the background color and light setting of camera would have the most significant effect on software colorimetery and white background and indirect illumination were the best conditions. significant difference was observed between software and instrumentally colorimetry after optimization the effective factors on photography also relationships used in the conversion were not careful enough. Therefore in consideration of the difference between physical characteristics of foods surface with a color chart (used to optimize the imaging conditions) it is necessary for optimization a software colorimetery system to use the regression between software and device colorimetry results of test foods.

Galvanizing kettle is one of the main components of hot dip galvanizing process. Welding is the final stage in galvanizing kettle fabrication. In the persent research the effect of various welding parameters such as bevel pattern and chemical composition of filler metal on mechanical properties, microstructure and corrosion resistance of welded galvanized steel were investigated. Results showed that symmetry bevel pattern is more effective than the non-symmetry one in developing desired properties in welding zone. Although both patterns developed acceptable mechanical properties in welded coupons. NDT results confirmed that welding zone is free from defects such as porosity, inclusion trapping, lack of penetration and etc. Various tests on the electrode type showed Nilsil electrode is more effective than AMA 1531 and 2000 electrodes in producing sound joints. Corrosion tests showed that silicon is the most detrimental element on corrosion resistance of welded coupons.