پيش بيني عمر خزشي پره توربين تعمير شده به روش اجزاي محدود

چكيده انگليسي :

Creep life assessment of repaired turbine blade by FEM method Esmaeil Barzkar e barzkar@me iut ac ir May 15 2010 Department of Mechanical Engineering Isfahan University of technology Isfahan 84156 83111 Iran Degree M Sc language Farsi Supervisor Dr Mohammad Reza Forouzan Abstract Gas Turbines have a wide application in power plant electrical gas and aerospace industry Nowadays based on welding of two different materials some economical methods for repairing turbine blades have been developed Creep is slow irreversible strain of materials at above 40 of their absolute melt temperature Super alloys which are used for turbine blades operate at temperatures about 70 percent of their absolute melting temperatures Therefore creep fracture and creep damage is very important in turbine blades Creep is founded as a damage which must be considered to design of mechanical elements which will work in temperatures above their 40 of melt temperatures even in loadings below their yield strength Creep leads to initiate crack in parts and cause degraded mechanical strength In this dissertation for assessing life of a repaired turbine blade made of INCONEL718 and GH4049 super alloys a method has presented based of FEM method This is done by writing a sequence of macros in ANSYS APDL commercial software Data needed for this analisys was collected from references and extracted and formulated in desired format to give them to software These data were creep time stress temperature and stress rupture numerical data A repaired model based on literature was created so that a circular section near root of blade which is criticalest position was created and meshed by softer metal in creep After building a proper model a transient analysis performed and in each material 0 5 strain criteria were checked Then a stress rupture analisys after stress analysis of structure based on Larson miller parameter was performed Having reviewed results concluded that a combination of stress rupture and transient analysis is required and done In transient analysis had seen that maximum stress is obviously a function of time and varies in location in alloy GH4049 base material If RPM and temperature were higher this phenomenon becomes more obvious In all load cases the criticalest element was in softer material and in position of 180 degree with respect of triangular circle These results introduced us to perform a combination of transient and stress rupture analysis which results in shorter life than stress rupture life using time fraction damage rule by numerical integration over time Results shows maximum stress occurs in GH4049 and in tiniest region aside filler metal In all simulations softer material had smaller life than other material Life versus rotational shaft speed curves in semi log axis is provided for various temperatures To see level of reliability an experiment was designed and a same method used to predict life time of a two specimen set of pure lead and tin70 lead30 and their creep behavior under a proper load was studied FEM method had a good agreement with life assessment compared with experiment result and has only 6 difference with experiment result in compare with 20 by Larson miller method From experimental analysis it was concluded that damage fraction rule has better life prediction Then It is concluded that for repaired metals in case of creep simulation using damage fraction rule has more precise answers to predicting life of them Keywords 1 creep 2 life assessment 3 repaired blade 4 transient analysis 5 larson miller 6 Monkam Grant parameter 7 damage fraction summation rule

برزكار، اسماعيل

پيش بيني عمر خزشي پره توربين تعمير شده به روش اجزاي محدود

تحليل گذرا , لارسن ميلر , مونكام گرانت , قانون كسري جمع آسيب