Tensile Strain Characteristics of Small-Scale Fracture Toughness Test Specimens and Large-Scale Tests Under Loading

Pipelines are susceptible to significant longitudinal deformation in areas affected by ground movements, including slope movement, frost heave, thaw settlement, and/or erosion. The assessment of tensile strain capacity (TSC) in girth-welded pipes with circumferential cracks, therefore, is of utmost importance when designing pipelines exposed to these geohazards. However, variations in strain calculation and measurement methods can lead to design inaccuracies due to the uneven strain distribution resulting from the inhomogeneous material properties in the weldment region of the pipe containing a crack. This study examines strain characteristics of small-scale single-edge notched tension (SENT) and single-edge notched bend (SENB) specimens under loading, compared to published data from intermediate-scale curved-wide plate test (CWPT) and full-scale (FS) pipe tests from the same pipe material and nominally identical girth welds. The findings in this study reveal that the stress distribution and responses of the SENT specimens closely resemble those of the CWPT and FS tests, exhibiting asymmetrical strains and asymptotic remote strains. It is important to emphasize that the fracture toughness of pipe/weld materials is influenced by the level of constraint at the crack tip. As a result, SENT tests are being used to evaluate the fracture toughness, due to the similarity in constraint between SENT specimens and FS pipes, rather than strain characteristics. The objective of this study is to enhance the understanding and characterization of strain behavior for a girth-welded pipeline.