Simulation of Low-Temperature Localized Serrated Deformation of Structural Materials in Liquid Helium Under Different Loading Modes and Potential Energy Accumulation

Numerical results are presented for the low-temperature serrated deformation process in tension induced by a suspended load of 03Kh20N16AG6 austenitic steel and AMg5 aluminum alloy specimens in liquid helium at 4 K. In practice, large loads at cryogenic temperatures are met with liquefied gas tanks, in particular in hydrogen tanks of launch vehicles. The local one-dimensional multiparametric nonlinear mathematical model of the low-temperature serrated metal deformation process was constructed, with its adequate display and quantitative estimates based on mechanical material properties and loading system characteristics. This effect manifests the local thermomechanical metal deformation instability under adiabatic conditions. The mathematical problem was formulated as a nonlinear differential equation of second order with certain initial and other conditions. It represents the dynamic equilibrium of the specimen-loading device system and describes the process of serrated specimen deformation as the system motion. The model is specified for 03Kh20N16AG6 steel and AMg5 aluminum alloy specimens creep-tested in liquid helium. The numerical experiment demonstrated adequate accuracy with the computational method. The qualitative similarity of the process was revealed for the materials of different classes, with the strain levels achieved differing markedly. Comparative computations established that potential energy of the gravitational field induced a much larger localized deformation of the specimen than potential elastic energy, even in combination with additional factors, viz operation of an electric or hydraulic drive, when the deformation rate is two orders of magnitude higher than the standard one for static metal tests in tension. A very large strain arising and localized under slow loading relaxation inevitably fails before the serrated process is complete.