The Study Of Fracture Parameters Of The Inboard Crack On Mitered Elbow

Along with the development of the production and technology,the fracture mechanics is rising knowledge since the 1950s.Since the 1970s,the fracture mechanics theories and practical applications have been widely developed.However,it is very scarce of the fracture parameters to make safe estimation for some structures with cracks in engineering.Based on fracture mechanics,applying the FEM software ANSYS,the article has built the model of mitered elbow with the inboard circumferential part-thoughwall crack and calculated the stress intensity factor K₁ in elasticity and J-integral in elasticity-plasticity with different dimension and load,then converted to the shape factors F and full-plasticity coefficients h₁. All of these append the database of the fracture parameters.The following missions are included in this article:1.The article has briefly given the using status of in-service pressure pipelines in china, listed some universal safety assessment methods of pressure pipelines with defects and studied the fracture mechanic theories,which are the bases of the subject and repertories of theories.2.ANSYS is applied to analyze the stress of the mitered elbow with no defect under pressure and moment,and then we can know the stress field on the place of crack,which can provide some bases in the farther analysis.3.According to the results provided by EPRI,the article can proof the method used to build the model with crack is correct,which are the bases and foundations of farther studies.4.The article has built the model of mitered elbow with the inboard circumferential part-thoughwall crack.Through the module of the postprocessor of ANSYS,the stress intensity factor K₁ has been calculated in elasticity,and then convert to the shape factors F. Using the results in elasticity,the article has modified the crack tip of the model and discussed the applicability of modification.5.In terms of Voce stiffen theory which can describe the isotropy hardening,the elasticity-plasticity FEA for the crack starts.On the bases of EPRI plastic J-integral estimation,the full-plasticity analysis has been established.6.With differentdimensions of crack,different pressure and different ratio for pressure to moment,the J-integral and full-plasticity h₁ has been calculated,then the tables of h₁ has been done. 7.Using the parameters calculated to protract the failure assessment diagram(FAD),and then the article has compared the failure assessment curve(FAC) with the universal curve in state criterion to investigate.8.The article has calculated and studied the plastic limit load of the model,which has established the foundation of further study of safety assessment of pressure piping.