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| Delamination Cracks and Fracture Evaluation in DWTT of X70 Pipeline Steel |
| YANG Zheng1,CHEN Hongda2,ZHAO Xinwei2,GUO Wanlin3,LUO Jinheng2 |
| 1. Department of Civil Engineering, Xi’an Jiaotong University, Xi’an 710049, Shanxi, China; 2. The Key Laboratory for Mechanical and Environmental Behavior of Tubular Goods, CNPC, Xi’an 710065, Shanxi, China; 3. College of Aerospace Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, Jiangsu, China |
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Abstract The delamination crack and its effect on the fracture of pipeline steel were investigated by dropweight tear test （DWTT）at different temperature and micrograph analysis. It was indicated that the delamination cracking is caused by the effect of 3D stress on the weak interfaces during deformation and appears before beginning or acceleration of main crack. New delamination crack can not appear during stabile propagation or deceleration of crack. The quantity, opening degree of delamination cracks and the distance between two delamination cracks are influenced by the stress state at beginning or accelerating point of main crack , but the length of delamination crack is influenced by the stress state of crack tip during the propagation of crack. The surface of delamination crack is of cleavage fracture appearance with large cleavage face. There is no delamination crack in the brittle fracture below ductile and brittle transition temperature or in the brittle fracture region of mixedmode fracture at about ductile and brittle transition temperature. Macro delamination cracks appear only on the ductile fracture or on the ductile part of fracture. The part of fracture with triangular or other shapes delamination cracks ought to be evaluated as ductile fracture.
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Received: 01 January 1900
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2006, Vol. 41 
