Development and Calibration of DCPD (Direct Current Potential Difference) Crack Length Measurement Equipment

摘要

The objective of this work has been to investigate the applicability of a switching direct current potential difference (DCPD) method to crack length estimations in ferromagnetic materials. The test materials have been stainless steel (AISI 316) pipes ( diameter 10mm ) and compact tension (CT) specimens of different steel compositions. In creep crack measurements and with slow loading rates the direct current method is suitable. The crack extension can be calculated from the potential readings and the crack extension is in good agreement (error less than 10 percent) with optical measurements and 2-dimensional metal film measurements. The DCPD results seem to be better than the results from the unloading compliance method, which was used simultaneously. The DCPD equipment developed is very stable and is suitable for long term creep crack tests. (Copyright (c) Valtion teknillinen tutkimuskeskus (VTT) 1987.)