Volume 6, Issue 1 (January 2009)
On the Effectiveness of the Dynamic Force Adjustment for Reducing the Scatter of Instrumented Charpy Results
One of the key factors for obtaining reliable instrumented Charpy results is the calibration of the instrumented striker. An interesting alternative to the conventional static calibration recommended by the standards is the dynamic force adjustment (DFA), in which forces and displacements are iteratively adjusted until equality is achieved between absorbed energies calculated under the test record (Wt) and measured by the machine encoder (KV). In this study, the procedure has been applied to the instrumented data obtained by ten international laboratories using notched and precracked Charpy specimens, in the framework of a Coordinated Research Project (CRP8) of the International Atomic Energy Agency (IAEA). DFA is extremely effective in reducing the between-laboratory scatter for both general yield and maximum forces. The effect is less significant for dynamic reference temperatures measured from precracked Charpy specimens using the Master Curve procedure, but a moderate reduction of the standard deviation is, however, observed. It is shown that striker calibration is a prominent contribution to the interlaboratory variability of instrumented impact forces, particularly in the case of maximum forces.