Volume 34, Issue 3 (May 2006)
Evaluation of the ASTM J Initiation Procedure Using the EURO Fracture Toughness Data Set
The multiple specimen procedure for the evaluation of a JIc value as presently measured using ASTM E 1820 is examined using the large fracture toughness dataset from the EURO round robin. Although a standard test procedure for JIc determination has been in use for more than 20 years, the multiple specimen option has not been regularly reassessed during that time. The EURO dataset was generated to evaluate the transition fracture toughness methods for steels. However, many of the test results produced ductile fracture information in terms of a final J versus ductile crack extension. This is the same information that is measured in a multiple specimen J initiation fracture toughness test. The dataset has more than 300 individual points of J versus crack extension and may be the largest dataset of that type produced for one material. Therefore, it is a useful dataset for evaluating the multiple specimen JIc procedure in ASTM E 1820. This evaluation showed that a value of JIc cannot be determined for a dataset containing more than 300 points, even though these points gave a consistent J-R curve. The criteria that are used for qualification of the data eliminate all of the points as being not qualified. This raises some serious concerns about the usefulness of the method as it is presently written, especially the restrictive nature of the qualification rules. Individual qualification criteria are examined and recommendations made for developing a more reasonable test method, one that can be used in the future to evaluate a multiple specimen fracture toughness for materials typically used in structural applications.