ISO 6892-4:2015 specifies the method of tensile testing of metallic materials in liquid helium (the boiling point is ?269 °C or 4,2 K, designated as 4 K) and defines the mechanical properties that can be determined.
This part of ISO 6892 may apply also to tensile testing at cryogenic temperatures (less than ?196 °C or 77 K), which requires special apparatus, smaller test pieces, and concern for serrated yielding, adiabatic heating, and strain-rate effects.
To conduct a tensile test according to this part of ISO 6892 at 4 K, the test piece installed in a cryostat is fully submerged in liquid helium (He) and tested using displacement control at a nominal strain rate of 10-3 s-1 or less.
NOTE The boiling point of the rare 3He isotope is 3,2 K. Usually, the tests are performed in 4He or a mixture of 3He and 4He with a high concentration of 4He. Therefore, the temperature is, as designated before, 4 K.