ИСТИНА

Delayed fracture of a long thin-walled cylindrical shell is studied during creep, under an unsteady complex stress state, taking into consideration the influence of an active ambient medium. The influence of the ambient medium on creep and delayed fracture of the shell is determined by diffusive penetration of the media elements into the materials of the shell. With the help of Yu.N. Rabotnov’s kinetic theory, times to fracture of such a shell are determined for two unsteady loading programs. One of the programs is implemented by way of an isolated action of the internal pressure and axial tensile force sequential in time, the other – by a combined joint action of the internal pressure and force at the first loading stage, while at the second loading stage, there acts only the tensile force up to the moment of fracture. The time to shell fracture is determined using a fractional linear creep and delayed fracture model where the tensile strength of the material at the appropriate temperature plays the role of ultimate stress. To take into account damage accumulation during creep and determine the criterion, before fracture, scalar and vector damage parameters are used, while the components of the vector damage parameter are associated with the space of principal stresses. To estimate the speed of the diffusion process, an approximate method for solving the diffusion equation based on the introduction of a diffusion front is used. The impact of the ambient medium on the time to fracture is taken into account by introducing a function of the integral average concentration into the determining and kinetic linear-fractional relationships. Comparison of the times to fracture using the scalar and vector damage parameters is carried out. Special features of using a linear-fractional model to describe long-term fracture processes are determined.