Influence and evaluation of constraint on fracture toughness in pipeline research

Accessing nowadays fossil fuel reserves requires a strain-based design approach. Within such design, the ductile tearing resistance is a key parameter in assessing the defect tolerance. To determine this tearing resistance, full scale (pressurized) tests can be performed. However, such approach would be costly and time consuming. Consequently, effort is made to select appropriate small scale test specimens. Most research has focused so far on the single edge notch bend (SENB) and tensile (SENT) specimen. To evaluate the suitability of these test specimens, the crack tip stress fields can be examined or the resistance curves compared with full scale structures. This paper aims at comparing the trends observed using these techniques. Furthermore, the suitability of the small scale test specimens is evaluated. It is concluded that sufficiently long (length-to-width ratio equal to ten) clamped SENT specimens have the potential to predict the tearing resistance of full scale pipes. In addition, the internal pressure does not significantly affect the fracture toughness. These conclusions are stated by both experimental results and finite element simulations