Design and Dynamic Force Verification of Instrumented Charpy Strikers for the Tinius Olsen Pendulum Impact Tester

摘要

The reliable measurement of characteristic force values from instrumented Charpy impact tests is considered of high importance at SCK·CEN in view of the “Enhanced Surveillance” of nuclear reactor pressure vessels. The previous development of instrumented strikers for the Toni MFL pendulum impact tester at SCK·CEN demonstrated that the static and dynamic performance of instrumented strikers is influenced by their design, especially the location of the strain gauges.To further improve our design know-how, instrumented ASTM (8 mm radius) and ISO (2 mm radius) strikers are developed for a Tinius Olsen pendulum impact tester. The dynamic performance of these strikers is greatly improved by incorporating new insights in the design. The strikers are extensively tested and meet the requirements of the current ISO 14556 and ASTM E2298-15 standard on the permissible error for the static force calibration of the striker and the limitations on the difference between the absorbed energy and the energy computed from the force-time curve. The ASTM strikers even meet the more stringent requirement on the permissible energy difference of the ISO 14556 standard of ±5 J. The verification of the dynamically measured maximum force value using NIST reference material failed for SRM 2112 but succeeded for SRM 2113 specimens. Because the dynamic force verification using standard reference material is not always reliable, an alternative verification method was evaluated. The comparison of the general yield stress inferred from instrumented Charpy impact tests, using Server’s equation, with the yield stress obtained from dynamic tensile testing of the same material at an equivalent strain rate, demonstrated to be a good method for the verification of the dynamically measured force. This method proved to be independent of the striker radius for our design.