Evaluating the Suitability of the Gurson—Tvergaard—Needleman Plasticity Model for Crack Resistance Curve Analysis

Abstract

The operational safety of oil and gas storage units is crucial, as any potential imperfections or cracks in a container wall could result in fracture. The key parameter in ensuring the integrity of oil and gas storage units is their fracture toughness. For its determination, compact tension (CT) and single-edge notched bend (SENB) specimens are commonly used. However, these specimens may lead to unnecessary conservatism in safety assessments. Single-edge notched tension (SENT) specimens, on the other hand, could be a more acceptable substitute, as they are shown to lead to less conservatism. The aim of this study was to determine the J-R curve for SENT specimens from pipe steel X65 using an experimentally determined J-R curve for CT specimens. This study was motivated by the fact that the use of the Gurson—Twergaard—Needleman (GTN) model for R-curve determination can significantly reduce the number of physical tests. Calculations were performed using the GTN constitutive model, calibrated on a CT specimen of width w = 50 mm, thickness B = 8.7 mm, and initial crack length a = 25.15 mm, used for the determination of the R-curve. The width and thickness of the SENT specimens considered in the calculations were similar to those for the CT specimens. Ideal clamping of the SENT specimens in the jaws was considered. A comparison of the SENT R-curve with the experimental CT R-curve showed that these curves were practically equidistant, with the former R-curve being superior to the latter one. The SENT R-curve has not been verified experimentally, because the physical specimens that match the models used for calculation do not meet the requirements of the related standards on specimen thickness. However, a comparison of this SENT R-curve with another SENT R-curve, published in the literature and obtained on the basis of the results of a two-parameter fracture mechanics approach, showed a very good agreement between the two R-curves.