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The usual loading rate for impact testing is near 5 m/s. As it will be demonstrated, force-deflection diagrams show strong oscillations, at least at the beginning. Investigations on realistic loading rates showed, however, in most practical cases effective loading rates below 0.1 m/s. Because this is true in nearly every case, a loading rate of 0.1 m/s seems to be sufficient for precracked specimens.
If the loading rate is reduced from about 5 m/s to 0.1 m/s, the force-deflection-diagram can be evaluated without parasitic oscillations. Therefore measurement of fracture toughness, KId, Jd and the calculations of CTOD become easier.
Regarding fracture work and specific fracture work, the steel investigated shows no significant difference if 5 m/s and 0.1 m/s impact velocity is compared. Fracture toughness characteristics will become comparable when transition temperature shifts below 20°C are negligible.
If a transition temperature shift above 15°C is of importance, the experimental results have to be treated differently. A substitution will become not practicable without a function converting the 0.1 m/s results to 5 m/s results and vice versa.
If the steels tested are sufficiently brittle, an extrapolation to the fracture toughness of larger sections will become possible.
precracked Charpy-type specimen, instrumented impact test, influence of impact velocity, oscillations, transition behaviour, fracture toughness
Professor Dr., Head of Laboratory, Institute for Testing and Research in Materials Technology-Vienna University of Technology (TVFA TU Wien),
senior researcher, TVFA TU WIEN,