Model of discontinuous plastic flow at temperature close to absolute zero

In the present study cryogenic tensile tests performed on different materials (316LN, JK2LB) were used. The discontinuous plastic flow phenomenon was analysed, in order to develop a constitutive model of serrated yielding as a support for analysis of structural materials at low temperatures. Devices and structures, cooled be means of liquid helium, operate at the temperatures equal or lower than 4.2 K, which for the examined materials is below the transition threshold between screw and edge dislocations. It is considered a threshold for the appearance of DPF consisting in cyclic drop of load followed by deformation jumps and generation of heat. Temperature oscillations resulting from the thermodynamic instability in stainless steel can be of the order of dT = 40 K, which is exceptionally dangerous for superconducting cables. Suitably calibrated numerical algorithm allows prediction of the behaviour of the material subjected to deformation at low temperatures. The issues presented in the present study are currently of particular interest for accelerator centres, which operate structures at cryogenic temperatures such as superconducting magnets and liquid helium transfer lines. The use of constitutive modelling in the design of structural elements, including physical processes at low temperatures, allows us to obtain structures with desired properties and reliability. There is a good prospect that in the future the cryogenic technologies will be widely used in the industry, and consequently, the correct mathematical models of materials used at extremely low temperatures will become essential tools for the engineers.