Development of stress-modified fracture strain for ductile failure of API X65 steel

Chang Kyun Oh, Yun Jae Kim, Jong Hyun Baek, Woo Sik Kim

Research output: Contribution to journalArticlepeer-review

99 Citations (Scopus)


The present paper proposes ductile failure criteria in terms of true fracture strain (the equivalent strain to fracture) as a function of the stress triaxiality (defined by the ratio of the hydrostatic stress to the equivalent stress) for the API X65 steel. To determine the stress-modified fracture strain, smooth and notched tensile bars with four different notch radii are tested, from which true fracture strains are determined as a function of the notch radius. Then detailed elastic-plastic, large strain finite element analyses are performed to estimate variations of stress triaxiality in the tensile bars, which leads to true fracture strains as a function of the stress triaxiality, by combining them with experimental results. Two different failure criteria are proposed, one based on local stress and strain information at the site where failure initiation is likely to take place, and the other based on averaged stress and strain information over the ligament where ductile fracture is expected. As a case study, ligament failures of API X65 pipes with a gouge are predicted and compared with experimental data.

Original languageEnglish
Pages (from-to)119-133
Number of pages15
JournalInternational Journal of Fracture
Issue number2
Publication statusPublished - 2007 Jan


  • APIX65 steel
  • Ductile fracture
  • Fracture strain
  • Stress triaxiality

ASJC Scopus subject areas

  • Computational Mechanics
  • Modelling and Simulation
  • Mechanics of Materials


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