Volume 33, Issue 6 (November 2005)
Corrected Procedure for Crack Length Calculation by the Unloading Compliance Technique for Charpy-sized Specimens
The problems with crack length determination by the unloading compliance method are well known for Charpy-sized specimens. The final crack lengths calculated for bend specimens do not fulfill ASTM E 1820 accuracy requirements. Some investigations have been performed to resolve this problem by correcting the compliance value, but satisfactory results were not obtained. In the present work the measured specimen compliance was taken as a correct value and the calculation procedure was modified. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths, a calculation procedure enabling accurate crack length calculation up to 5 mm of plastic deflection was developed. Applying the new procedure to a sample of 238 measured crack lengths, more than 80 % of the values fulfilled the ASTM E 1820 accuracy requirement, while the presently used procedure provided only about 30 % valid results. The newly proposed procedure also can be used prospectively in modified form for specimens other than Charpy-sized.