Session: CS-20-01 Master Curve Method and Applications

Paper Number: 120918

120918 - Impact of Interrupting Master Curve Fracture Toughness Tests for the Material Exhibiting Ductile Crack Growth at the Kjc Between Kjclimit and the Final Kjc at the Test Termination 

Master Curve evaluation by 4mm thickness Mini-C(T) is an option to extend the operable lifetime of light water reactor surveillance programs.  However, when using such small specimens and/or with relatively lower yield stress materials, ductile crack growth can occur at KJc values lower than that at test termination, but still above the KJclimit. Since the test method cannot resolve the moment of ductile crack initiation the experimentalist risks conducting tests in a manner that the specimen may discover after test termination that both the KJclimit and ductile crack growth limit were violated.  In most cases the E1921 standard requires that such KJc data is censored by KJcΔa, which it defines as the maximum of uncensored valid KJc in the dataset. Unfortunately using the maximum uncensored KJc as a censoring value may introduce large uncertainty in the estimated T0 value, especially if the number of specimens is limited.

Because of the uncertainty introduced by censoring using KJcΔa, censoring using KJclimit is preferable. Within the current requirements of E1921, this can be achieved by interrupting a test just above KJclimit but below the onset of ductile crack growth initiation. If no ductile crack growth occurs in such interrupted specimens, we can use KJclimit according to the current E1921 requirements.

The present work compares T0 values between two cases: (a) all tests will be continued to the final specimen separation, and (b) tests exceeding KJclimit will be interrupted at just above KJclimit, in a series of sensitivity analyses with ductile initiation KJc set as a parameter.  The impact of the interrupting tests at KJclimit on the estimated T0 values will be discussed in detail.

Presenting Author: Masato Yamamoto CRIEPI

Presenting Author Biography: Dr. Masato Yamamoto has been working for CRIEPI for 30 years. A half of his entire CRIEPI carrier is dedicated to the fracture toughness investigations for utilization of miniature C(T) specimens to the Master Curve evaluation of RPV materials. With successfully established concensus of using such small C(T) specimens, he is now working active to develop and revise the Japanese codes and standards for Master Curve evaluation and for the RPV structural integrity assessment methodologies.

Authors:

Masato Yamamoto CRIEPI
Mark Kirk CRIEPI