PLASTIC DEFORMATION OF SUS 304 UNDER COMBINED STRESS STATES AT LOW TEMPERATURES.

Equipments and procedures for combined stress testing in a cryogenic state are presented. The combined axial load and torsion are applied to a thin wall tubular specimen in a cryostat. The specimen is cooled by liquid nitrogen and helium. A strain measuring system of a mechanical type is developed and the sensitivity of the system is calibrated. The cryogenic plastic behavior of SUS 304 is experimentally investigated under combined tensile stress and torsional stress. At 77 K, the plastic deformation follows the Mises law under combined stress states of tension and torsion, but the compressive flow-stress is greater than tensile or torsional. An unstable serrated flow by the proportional loading under stress control conditions is observed at 4. 2K.