Evaluation of the Effect of Biaxial Loading on the T_o Reference Temperature Using a Cruciform Specimen Geometry

A series of 12 cruciform geometry fracture toughness specimens has recently been tested using A533B base plate obtained from the decommissioned Shoreham plant pressure vessel. Specimens were tested at −100°C, placing them in the lower ductile to brittle transition of this ferritic structural steel. The overall objective of this work is to compare the results of these biaxial cruciform tests to the results of standard and shallow crack fracture toughness tests to assess the effect of biaxial loading on the measured master curve and the T_o reference temperature as defined by ASTM E 1921. Previous work done at Oak Ridge National Laboratory (ORNL) appeared to demonstrate an increase in the T_o reference temperature due to the presence of the biaxial stress field established in the cruciform test geometry. Because of the cost of the ORNL tests, only a few specimens could be run, and full statistical support of the “biaxial effect” could not be demonstrated. A second goal is to demonstrate that smaller size specimens, and hence lower cost tests, can be used to evaluate the magnitude of the biaxial effect in nuclear reactor pressure vessel materials. This report presents a brief overview of the test procedure, presents the test results, and compares the results to the database available on standard and shallow crack fracture toughness results available for the Shoreham plate material.