A new experimental failure model based on triaxiality factor and Lode angle for X-100 pipeline steel

• Ductile failure of X-100 pipeline steel is studied.
• Experiments are done to extract Hill plasticity parameters and hardening curve.
• Experiments and FE analysis are done on round and flat notched specimens.
• Failure strain is sensitive to triaxiality and is not sensitive to Lode angle.
• A correlation for failure strain is developed.

API X-100 steel is one of the recently developed materials for production of gas transportation pipelines which has high strength and toughness. In order to study the failure of this material, experiments on smooth and notched round bars and flat notched specimens with different notch radius are done. Whereas this material is severely anisotropic in plastic region, Hill׳s 1948 anisotropic plasticity model is used to simulate this material. X-100 steel is highly ductile and necking occurs at early stages of plastic region.Lode angle, which contains the effect of third invariant of deviatoric stress tensor, along with triaxiality factor are studied in the fracture of this material. Based on these experiments and analysis, a correlation is extracted for the failure strain of this material as a function of triaxiality and Lode angle which is very useful in pipeline failure analysis.