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چكيده انگليسي :

Experimental Determination of Ductile Damage Model Parameters Mohamad Khataei mohamadkhataei@gmail com Date of Submission 2010 05 9 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Hasan Khademi zadeh Mehrdad PoursinaAbstractThe simulation of damage propagation and crack initiation in ductile materials is a substantial subject in theforming process in designers point of view One of the most important aspects of Finite Element based softwares is the ability of prediction of the location of damage propagation and crack initiation under differentcondition of loading Subsequently nowadays various damage models are used in FEM based soft wares One of the most common damage models used in ABAQUS software is ductile damage model In the presentresearch the most important damage models are studied and the method of their application in FEM softwares is explained Then the ductile damage model has been investigated and the input parameters for thismodel assisted simulation have been determined Ductile damage take places during loading processes onductile materials and includes three steps void nucleation void coalescence and crack propagation Thespecification of this type of damage is production of a large plastic strain before fracture The triaxialitystress is the most effective parameter on the fracture strain in ductile damage model and the damageparameter is calculated regarding to the values of triaxiality stress and equivalent strain during loading time The damage parameter has a magnitude between zero and one If the magnitude equal to zero it means thatthe element is undamaged or virgin and the rapture of elements is shown by one Therefore the magnitude ofdamage parameter can be predicting damage propagation and crack initiation The material which is used inthis study is St12 steel Some tension tests on notch samples with different notch radius have been done inorder to specify the material s damage constants The effect of the triaxiality stress on the fracture strain hasbeen studied for different notch radiuses through the tests and the equation which specifies the relationbetween the fracture strain and triaxiality stress is obtained and calibrated for St12 Steel Moreover theductile damage model has been applied for related simulations in order to clarification of validity of theresults of previous experiments It is important to investigate the efficiency of ductile damage criteria undervarious ranges of loading and triaxiality stresses Therefore in the first step the specimens applied forcalibration of the equation of fracture strain simulated based on the ductile damage The results of thesimulation have a good compatibility with experimental observation about the prediction of the time andlocation of fracture In the second step a butterfly specimen and a transient specimen have been designed andmanufactured as the tension test sample Then the tension test has been simulated for mentioned specimens In the case of butterfly specimen triaxiality stress on the fracture section approximately equal to zero In thissituation the shear stress has the main role in fracture phenomena In the case of transient specimen triaxiality stress on the fracture section approximately equal to 0 5 and the fracture phenomena is occurred byreason of the shear and tension stress combination In the final the damage propagation has been studied in anindustrial five stand cold rolling mill The prediction of damage propagation in this process is in goodagreement with experimental observation Keywords Ductile damage Damage parameter Triaxiality stress Fracture strain

خطايي، محمد

تعيين پارامترهاي آسيب مواد نرم به روش تجربي

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