Experimental Investigation on Net-Section-Collapse Criterion for Circumferentially Cracked Cylinders Subjected to Torsional Moment

When a flaw is detected in piping during in-service inspection, the limit load criterion given in the codes such as JSME Rules on Fitness-for-Service for Nuclear Power Plants or ASME Boiler and Pressure Vessel Code Section XI can be applied to evaluate the structural integrity of the piping. Actual piping is generally subjected to combined tensile, bending, and torsional loading, however, a methodology to evaluate limit moment for torsion is not established due to the inadequacy of experimental validation. In this study, fracture tests for circumferentially cracked cylinders subjected to torsional moment were conducted. Experimental maximum moments were compared with the limit moments, which were evaluated based on the concept of the net-section-collapse criterion for torsional moment. The maximum moments could be conservatively predicted by the net-section-collapse criterion. In addition, innovative tests subjected to torsional moments were conducted using a pair of Charpy V-notch specimens and a conventional test machine. The applicability of the net-section-collapse criterion for torsional moment was experimentally validated. The adequacy of the replacement of cracks with machined notches for ductile materials under torsional loading was also investigated through the comparison of the fracture behavior obtained from notched and precracked Charpy specimens. The developed method could be an alternative test method for torsional moment.