The effect of constraint on CTOD fracture toughness of API X65 steel

• Published in: Engineering fracture mechanics Vol. 124-125; pp. 167 - 181
• Main Authors: Han, Kejiang, Shuai, Jian, Deng, Xiaomin, Kong, Lingzhen, Zhao, Xing, Sutton, Michael
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2014
• Subjects: API; Crack opening displacement; Crack tips; Criteria; CTOD fracture toughness; Fracture mechanics; Fracture toughness; High strength low alloy steels; Mathematical models; SENB specimens; SENT specimens; Steels; The critical CTOD; The stress constraint; SENT specimens; The stress constraint; Crack tips; The critical CTOD; SENB specimens; CTOD fracture toughness
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2014.04.014

CTOD1mm is obviously influenced by the thickness of the specimen. when Δa>1.5mm, crack growth begins to go into the stable crack growth stage. The value of CTOD in the stable crack growth stage. The constraint Am is seriously effected by the thickness of the specimen and independent of crack growth amount. By averaging CTOD1mm and Am in the stable crack growth stage, (CTOD1mm, Am) data points for SENB specimens with various thicknesses can be obtained, which will allow us to establish a one-to-one correspondence or relationship between CTOD1mm and Am. This is called constraint-based fracture failure criterion. [Display omitted] •The DIC technique is used to measure the true stress–strain curve for the API X65 pipeline steel.•A void-based micromechanics model is established to investigate the effects of the thickness of SENB specimens.•The relationship between the stress constraint and the fracture toughness CTODc is established.•The applicability of the constraint-based fracture failure criterion is proved to be validated.•This work is beneficial to the development of tearing fracture assessment procedure. Constraints ahead of crack tips and the effect of specimen thickness on the critical CTOD (the CTOD fracture toughness) in SENB specimens are studied. The effect of constraint on CTOD fracture toughness is quantified using a Gurson type void model. Based on the effect of the SENB specimen thickness on CTOD fracture toughness and on the stress constraint ahead of the crack tip, a constraint-based fracture failure criterion for API X65 steel is proposed. Compared with the results of finite element simulations of SENT specimens and pipelines, prediction errors of the constraint-based fracture failure criterion are within 10%.