Simulation of Ductile Crack Propagation in Pipeline Steels Using Cohesive Zone Modeling

Finite element simulations of ductile crack propagation are carried out using cohesive zone modeling. Two sets of materials are modeled. The first material set was defined by Tvergaard and Hutchinson (1992), and has four traction-separation (TS) laws of varying strength and toughness. The second set is modeled after X70 pipeline steel, and is referred to as C2 steel. Three TS laws are used to model this C2 material. The specimens analyzed include small-scale yielding (SSY) and drop-weight tear test (DWTT). The fracture propagation characteristics and CTOA values are obtained. It is shown that cohesive zone models can be successfully used to simulate ductile crack propagation and to numerically measure CTOAs.;From SSY simulations, steady-state CTOAs for the TH materials were measured to range from 2° - 6°. The CTOAs for the C2 materials were higher than those of the TH materials due to higher fracture resistance, but no steady-state values were obtained from the SSY simulations. From simulations of the DWTT specimens, steady-state CTOA values for the TH materials ranged from 2° - 4.5°, and therefore had good agreement with the SSY results. Estimated steady-state CTOA values for the C2 materials ranged from 14° - 26°. The measured CTOAs agree reasonably well between the SSY and DWTT simulations for both the TH and C2 material sets, indicating that these values are transferable among specimens. Direct comparisons of the CTOAs obtained from DWTT simulations to the experimental observations (12.4° - 18.5°) have reasonable agreement as well.