Elastic-Plastic Finite Element Analysis For Piping Elbow With Circumferential Part-Throughwall Cracks

The accidents of pressure vessels often occurred and they destroy seriously. Therefore, the interrelated departments in our country attach importance to the safety evaluation of the pressure vessels and pressure pipes all the times. As the researches go on, the fracture mechanics theories developed. Fracture mechanics has been used widely in practice with the combination of computer science and finite element method. The engineers use the elastic and elastic-plastic coefficients to make the evaluation of the pressure vessel being used by fracture mechanics is an effective method. But the scarce of fracture parameters of the structures with crack(Tee Joint, Elbow), especially with surface crack, cause the safety evaluation not convenience. A model of the piping elbow with annular inside surface crack has been built in this study, and the results of elastic and elastic-plastic have been analyzed by the model. The stress intensity factors K₁ in elastic and J-integral in elastic-plastic in different dimension have been calculated. Based on the K₁ and J-integral results, the shape coefficients and full-plastic coefficients have been obtained. The study including:1. Study the fracture mechanics theories and have a conclusion of the research methods of cracked structure. All of these are in order to provide a reference to the next work.2. Demonstrate the rationality of the element chosen by comparing the finite element results with the results provide by EPRI. Proof the method used to build the model is scientific and practicable.3. Build the crack model in different types of elbow, in different crack dimensions and in different forms of load by the program which compile by the APDL provided by ANSYS. The the program can use to built the piping elbow with annular inside surface crack convenient.4. Calculate the stress intensity factors K₁ in different dimensions in elastic condition using SOLU-linear, and then the transform to shape coefficients F.5. The nonlinear material properties of ANSYS are defined in terms of Voce stiffen theory, using the stiffen-exponent n, The full-plastic results are compiled by the method which is based on the full-plastic J integral of EPRI estimation.6. The J-integral of piping elbow with annular inside surface crack is calculated under different properties of internal pressure and bending moment, and then the tables of full-plastic coefficients h₁ are done.