شبيه سازي شكست ديناميكي خطوط لوله ي فولادي تحت فشار داخلي ثابت با ترك محوري اوليه

چكيده انگليسي :

Simulation of Dynamic Fracture of Steel Pipelines Under Constant Internal Pressure with Initial Axial Through Thickness Crack Bijan Jamali b jamali@me iut ac ir Date of Submission Jan 23 2013 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Mohamadreza Foruzan forouzan@cc iut ac ir Abstract In this thesis dynamic fracture based on Rapid Crack Propagation RCP of gas transmission steel pipelines with axial through thickness crack is simulated Crack is assumed to be in the center of the pipes and is propagated at constant velocity after a short accelerating time in order to constant internal pressure the gas pressure decompression ahead of the crack tip and an efficiency of a linear decay behind the crack have been used in the computation A one dimensional 1D model that has been established by comparison based on previous full scale pipe fracture data is used fo applying pressure distribution in axial direction of the pipe Cohesive Zone Model CZM due to elastic plastic fracture process and cohesive element in order to propagate crack is used Several specifications of dyanamic crack propagation as crack tip velocity crack driving force and crack tip opening angle were studied Both energy release rate criterion and Crack Tip Opening Angle CTOA criterion employed and compared together Because of material rate dependent due to dynamic fracture the effect of crack tip velocity applied to material behavior for C300 steel pipe For this purpose experimental results were used and coded in Python to apply the change of dynamic fracture toughness in every steps due to velocity changes Various pressures and geometries modeled for API X65 steel pipe and the influence of various parameters were studied An efficient and novel method introduced to predict cohesive property of the cohesive zone in fracture process that is based on cohesive zone model theory results of full scale steel pipe tests that determined the critical pressure to rapid crack propagation and Drop Weight Tearing Test DWTT which is determined the dynamic fracture toughness for API X65 done by other researchers These properties are maximum cohesive stress that damage initiation occurred and critical energy release rate due to damage evolution This method is coded in Python and applied to 8 different models The results are in good agreement with experimental results In this research critical crack tip opening angle is used as dynamic fracture toughness for API X65 steel pipelines due to experimental results and several parameters studied to predict propagate or arrest occurance in these pipelines Dynamic energy release rate is used for C300 steel pipelines as the fracture criterion then the dynamic fracture toughness of these pipe predicted in the case of crack tip opening angle Crack tip opening angle and Energy release rate calculated numericaly in every steps and graphs were plotted and probability of Rapid Crack propagation occurance discussed The parameters that is impress the fracture process and studied in this thesis were dimension ratio of the pipe internal pipe pressure dynamic fracture toughness and Crack tip velocity Keywords Rapid crack propagation Cohesive element Dynamic fracture Gas transmission pipeline Dynamic energy release rate Crack tip opening angle

جمالي، بيژن

شبيه سازي شكست ديناميكي خطوط لوله ي فولادي تحت فشار داخلي ثابت با ترك محوري اوليه

رشد سريع ترك , المان چسبنده , خطوط لوله انتقال گاز , نرخ آزاد سازي انرژي ديناميكي , زاويه بازشدگي نوك ترك