Charpy Specimen Tests at 4 K

This paper describes nonstandard methods of testing Charpy specimens at 4 K. We show that the initial temperature can be achieved using a helium flow method with U-type as well as C-type machines. Unfortunately, heating during impact loading weakens the correlation with quasistatic fracture toughness parameters. Alternative test procedures using fatigue precracked specimens were not fully satisfactory, either: (1) Precracking reduces the impact energy by 35–54%, but the specimen heating is still significant; (2) slow bending curtails the heating most effectively, but then the desired simplicity of a screening test is lost.