engleski

Fracture Behavior of New Pipe – Ring Specimens for Fracture Toughness Testing of Thin – Wall Pipeline

Structural integrity assessment of the pipelines requires fracture toughness in order to predict the loading capacity of pipeline or resistance to the initiation and crack growth. The thin-walled structures as pipelines are usually unsuitable for the standard testing of fracture toughness. Particularly, it is very difficult to perform the fracture toughness testing in the case of longitudinal surface cracks. In order to find an alternative technique for the measurement of fracture toughness of the already delivered pipeline segment, the new pipe-ring notched bend specimen (PRS) has been proposed. In this paper the differences in fracture behavior between the standard single edge notch bending (SENB) and non- standard pipe-ring notched bend (PRS) specimens are discussed. To avoid the uneven fatigue crack front as a consequence of complex fatigue loading which caused the different fracture behavior, the standard single edge notched bend specimens has been used for comparison to ring specimens. The stress-strain conditions at the crack tip were analyzed by finite element modelling which is not the part of content in this paper. The fracture toughness was measured by testing of both types of specimens. The critical crack tip opening displacement was determined as a crack tip surface strain-relaxation by using stereo- optical grading method and compliance method. The comparison between CTOD-R curves of standard and non-standard specimens shows comparable similarity in fracture behavior, especially in the stable crack initiation, but shows significant difference during ductile tearing. It seems that the use of new pipe-ring notched specimens is promising for low cost and simple testing of fracture toughness.

lomna žilavost; prstenasti ispitni uzorak; cjevovod; uzdužna pukotina

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