Comparison of J Equations for SENT Specimens

Abstract

AbstractA test standard for single edge notched tension (SENT) fracture toughness testing was issued in 2014 by British Standards as BS 8571:2014. Prior to BS 8571, most guidance on SENT test methodology was taken from DNV RP F108:2006 for installation of girth welds under high strain, which is still commonly cited by pipeline design and fabrication standards such as DNV OS F101:2013 for subsea pipelines. The intention of BS 8571 was to maintain some continuity with DNV RP F108 to allow users time to adopt the new Standard, and therefore BS 8571 included the DNV specimen design and J formulae, but also offered a different J approach based on work by Shen & colleagues (2009) from CanmetMaterials, for specimen designs currently beyond those permitted in DNV RP F108 but included in BS 8571. However, recent independent research by Zhu & McGaughy (2015) has identified an error in the K solutions adopted from DNV RP F108 into BS 8571, and therefore, there is a need to review the various equations to calculate J for SENT specimens to ensure that the optimum approach is employed in BS 8571, both in terms of accuracy and ease of application. A review of different published solutions for the elastic K solutions, and plastic eta factor solutions, which comprise parts of the calculation of J has been carried out, to compare the range of possible solutions in relation to those currently used in BS 8571:2014. Furthermore numerical modelling of crack tearing resistance curves was undertaken to compare the two different methods currently given in BS 8571 to determine which would provide the best single approach appropriate for all SENT specimens tested to BS 8571. The analyses determined that the ‘Canmet’ solutions should be used for a single equation for J to cover specimens with W/B ratios from 0.5 to 2 in future versions of BS 8571. This change will improve the accuracy of the determination of J from SENT specimens, with a simpler method, but little difference to the values of J for typical specimens which have been tested using BS 8571 to date