Volume 8, Issue 10 (November 2011)
The Use of the Normalization Data Reduction Technique for Measuring Upper Shelf Toughness Under Impact Loading Rates
The multiple-specimen method (low-blow or stop-block tests) is the conventional approach for measuring the upper shelf fracture toughness of steels under impact loading rates, using fatigue precracked Charpy (PCC) specimens tested with an instrumented pendulum machine. The method is fairly simple but requires a relatively large number of specimens. As an alternative, the single-specimen method denominated normalization data reduction (NDR) is based on the analysis of the instrumented force/displacement trace and does not need dedicated instrumentation for the measurement of crack extension during the test. In this study, the NDR technique was applied to low-blow tests performed at different temperatures on two reactor pressure vessel (RPV) steels, 20MnMoNi55 and A553B Cl. 1. Analyses were performed after applying a double fitting approach to the raw test data, which allows selecting a limited set of force/displacement data which are representative of the whole instrumented trace. Results show that the NDR technique provides acceptable accuracy in terms of both ductile crack initiation and resistance to crack propagation (tearing modulus).