Creep and long-term strength of metals under unsteady complex stress states (Review)

This article is an analytical review of experimental and theoretical studies of creep and creep rupture strength of metals under unsteady complex stress states published over the past 60 years.
The first systematic studies of the creep of metals under complex stress conditions were published in the late 50s and early 60s of the 20th century in the Soviet Union (L. M. Kachanov and Yu. N. Rabotnov) and Great Britain (A. E. Johnson). Pioneering work on creep rupture strength first appeared in the USSR (L. M. Kachanov and Yu. N. Rabotnov). Subsequently, Yu. N. Rabotnov developed the kinetic theory of creep and creep rupture strength, with the help of which it is possible to efficiently describe various features of the creep process of metals up to fracture under various loading programs. Different versions of the kinetic theory use either a scalar damage parameter, or a vector parameter, or a tensor parameter, or a combination of them. Following the work of M. Kachanov and Yu. N. Rabotnov mechanics of continuum destruction began to develop in Europe, in Asia, and then in the USA.
The hypothesis of proportionality of stress deviators and deviators of creep strain rates is accepted as the main connection between the components of stress tensors and creep strains. When modeling experimental data, the proportionality coefficient in this dependence takes different forms. The main problem in the development of this direction is the difficulty in obtaining experimental data with arbitrary loading programs.
This review provides the main results of studies conducted by scientists from different countries. Except Yu. N. Rabotnov and L. M. Kachanov, also a significant contribution to the development of the direction of science made by Russian scientists N. N. Malinin, A. A. Ilyushin, V. S. Namestnikov, S. A. Shesterikov, A. M. Lokoshchenko, Yu. P. Samarin, O. V. Sosnin, A. F. Nikitenko, et al.