Full text
| |
| Author(s): |
Lenin Marcelo Paredes Tobar
Total Authors: 1
|
| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Escola Politécnica (EP/BC) |
| Defense date: | 2012-09-17 |
| Examining board members: |
Claudio Ruggieri;
Túlio Nogueira Bittencourt;
Heraldo Silva da Costa Mattos;
Carlos Alexandre de Jesus Miranda;
José Ricardo Tarpani
|
| Advisor: | Claudio Ruggieri |
| Abstract | |
This work focuses on the numerical study of crack driving forces (J and CTOD) on single edge notch in tension (SE(T)) specimens usually extracted from defective structural components, specifically, circumferentially welded cracked pipes. The most efficient procedure to deploy submarine pipes (risers) on the sea floor is the reeling method. This procedure introduces a huge amount of cyclic loading to the girth welded pipe during the installation causing permanent plastic deformation (around ~2 to ~3%), which can affect the structural integrity and safe operation of the pipeline system. Current material fracture toughness procedures rely upon accuracy of proportionality plastic coefficient (also known n factor), which has to be effective for homogeneous condition. For mismatched configurations, where the strength of the weld metal is higher than the strength of base metal (also referred as overmatching), the direct applicability of such procedures remains a key aspect for defect assessment procedures and fitness for service codes, due to the complexity of the univocal relationship between crack driving forces and remote loading and the weld strength mismatch effect. The goal of the present thesis is to develop an estimation procedure of fracture mechanics parameters (J and CTOD) for SE(T) specimens in heterogeneous conditions. Extensive finite element analyses were conducted in order to obtain n factors for mismatched SE(T) specimens with varying crack lengths (a/W), different levels of overmatch (My) and two loading schemes (clamped and pin loading). Three different but related methods are applied to compute the n factor for welded mismatch configurations, namely the plastic work, load separation and limit load method. Also, the 3D effects are systematically analyzed for different thickness (B/W) and different specimen lengths (H/W) in order to prove the robustness of the proposed solutions derived from FE analyses in plane strain conditions. Finally, the results provide strong support for the use of constraint designed SE(T) specimens in fracture assessments of circumferential surface cracks in girth welded pipes subjected to bending moment. (AU) | |