5532

5192

كارشناسي ارشد

مهندسي مكانيك

اصفهان: دانشگاه صنعتي اصفهان، دانشكده مكانيك

1389

سيزده،93ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

محمود فرزين، محمدرضا فروزان

محمد مشايخي

29/8/89

محمود سليمي، محمود كدخدايي

مهندسي مكانيك

ID5192

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Leak Before Break Assessment and Allowable Crack Size Determination of All Steel CNG Cylinders Aliakbar Taghipour Lahijani a taghipour@me iut ac ir Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Mahmoud Farzin farzin@cc iut ac ir Mohammad Reza Forouzan forouzan@cc iut ac irAdvisor Mohammad Mashayekhi mashayekhi@cc iut ac irAbstractCNG cylinders are under high cyclic pressure as a result of refueling process Surface cracks of the cylindercan grow with corrosion fatigue mechanism during the service life Hence these cylinders are designed for alimited service life and the initial cracks should not exceed an allowable size An excessive number ofpressure cycles will eventually cause fatigue cracks to grow in the cylinder wall The cylinder standardsrequire that the failure mode of designs that suffer the through wall growth of a fatigue crack is by leakage and not by rupture In this research two analytical methods has been developed for the determination of theallowable crack sizes and the evaluation of leak before break LBB performance of the all steel CNGcylinders by using fracture and damage mechanics A simple method for allowable crack sizes determinationand a new model for the evaluation of LBB performance are presented These methods are used in theanalysis of a 60 liter cylinder made by Faber Company of Italy Backward crack growth approach has been taken in the allowable crack sizes determination Backwardgrowth of the critical surface cracks for a fatigue life equal to the service life of the cylinder will result in aspan of initial cracks that ensure the life requirement The KI stress intensity factors of the axial semi elliptical surface cracks have been calculated using Newman and Raju solutions The growth is alsosimulated with the cycle by cycle integration of the crack growth relation Stability analysis of the ductile growth of the critical surface crack in popping through the thickness eventis recommended for the LBB performance evaluation The remaining ligament in the front of the criticalcrack will break in the ductile mode and a through the thickness crack will appear Stability of the resultingcrack can be evaluated as the LBB performance The ductile crack growth is simulated using the well knownmicro mechanically based damage model of Gurson Tevergard Needlman GTN The GTN model isalready implemented in ABAQUS Explicit software In this research the GTN damage model hassuccessfully shown it s capability in the simulation of popping through and the prediction of the canoe shaped surface crack front in ductile growth The initial and critical void volume fraction parameters f0 fc ofthe model are also determined by the simulation of the expremental three point bending test and finiteelement calibration of the J R curve Finally simulation of the ductile crack growth of a simplified one eightmodel of the cracked cylinder has demonstrated the LBB performance Keywords All steel CNG cylinder Corrosion fatigue Allowable crack size Leak Before Break Damage model

محمود فرزين، محمدرضا فروزان

محمد مشايخي

محمود سليمي، محمود كدخدايي