Use of instrumented Charpy tests to determine onset of upper-shelf energy

Identifying the onset of C/sub v/ upper-shelf toughness is of paramount importance to the continued integrity of a pressure vessel. Most in-service surveillance programs require that the C/sub v/ upper-shelf toughness be determined. This is particularly true for the surveillance programs for nuclear pressure vessels. In the nuclear systems the change in C/sub v/ upper-shelf energy due to irradiation must frequently be determined with a limited number of surveillance specimens. Currently, fracture appearance is the criterion used to assure that the tests are being conducted in the C/sub v/ upper-shelf temperature range. This procedure is satisfactory when a number of specimens are available and accessible for interpretation. This is not always the case; irradiated specimens must be remotely tested and interpreted. Examining a specimen remotely may result in an erroneous interpretation of the fracture surface. To avoid this possibility we have developed a procedure, using an instrumented Charpy impact tester, that by linear extrapolation can identify the onset of the C/sub v/ upper-shelf toughness regime with as few as two specimens. This paper discusses the development of the procedure and its application.