Influence of striking edge radius (2 vs. 8 mm) on instrumented Charpy data and absorbed energies

The most commonly used test standards for performing Charpy impact tests (ISO 148 and ASTM E 23) envisage the use of strikers having different radii of the striking edge, i.e. 2 mm (ISO) and 8 mm (ASTM). The effect of striker geometry on Charpy results was extensively studied in the past in terms of absorbed energy measured by the machine encoder, but few investigations are available on the influence of striker configuration on the results of instrumented Charpy tests (characteristic forces, displacements and integrated energy). In this paper, these effects are investigated based on the analysis of published results from three interlaboratory studies and some unpublished Charpy data obtained at SCK·CEN. The t-test was used for establishing the statistical significance of the observed effects. The instrumented variables which are the most sensitive to the radius of the striking edge are the maximum force and its corresponding displacement, with 8 mm-strikers providing systematically higher values. The effect on general yield forces, on the other hand, is less consistent and more difficult to rationalize, although 2 mm-strikers generally tend to deliver higher values. Absorbed energies, obtained both from the instrumented trace and from the pendulum encoder, are almost insensitive to the type of striker up to 200 J. For higher energy levels, the values obtained from 8 mm-strikers become progressively larger. Data scatter is generally higher for 2 mm-strikers.