Influence of Strain Gage Position on the Static and Dynamic Performance of Instrumented Impact Strikers

The quality and reliability of impact forces obtained from instrumented Charpy tests have been investigated considerably at SCK•CEN since the 1990’s, in parallel to the development/qualification of advanced methodologies for the surveillance of nuclear reactor pressure vessels. In this framework, careful analysis of the instrumented force/deflection traces from Charpy tests allows the defining of important material parameters. While first efforts at SCK•CEN were concentrated on the optimization of the striker calibration procedure, more recently the focus has been on the in-house development of reliable instrumented strikers with 2 mm (ISO 148) and 8 mm radius (ASTM E23). Evidence was found that the position of the strain gages affects the static and dynamic performance of the strikers. Additional investigations have shown that the linearity of the strikers during static calibration improves as the gages are placed further away from the striking edge. For the ASTM design, moving the strain gages away also reduces the characteristic “tail” that is typically observed just before a ductile specimen is ejected from the anvils. Our research shows that the best striker performance is achieved when the center of the T-rosette is located at about 16 mm from the striking edge, using a top/bottom configuration.