Effects of Strain Rate on the Tensile Behavior of Stainless Steels, Copper, and an Aluminium Alloy at Cryogenic Temperatures

By inserting small thermocouples inside the tensile specimen, temperature rise during straining and its relation to stress-strain behavior have been investigated for SUS304L and 310S stainless steels at various strain rates between 3.3×10-2s-1 and 3.3×10-5s-1, at 4K and 77K. OFHC copper and 2024 duralumin having quite different thermal conductivities have also been tested for comparison. The results obtained at 4K are summarized as follows:(1) At a strain rate of 3.3×10-2s-1, the maximum temperature rise was about 150K for stainless steel and about 30K for OFHC copper and 2024 duralumin.(2) Below a strain rate of 3.3×10-3s-1, serrations were observed in the stress-strain curve and temperature rise occurred only momentarily.(3) Ultimate tensile strength of stainless steel decreased with an increase of strain rate.(4) It is recommended that the tensile test at liquid helium temperature should be conducted below the strain rate of 3.3×10-3s-1.