Application of elastoplastic model of the fatigue crack growth to pressure vessel materials

The procedure of using the elastoplastic model of the growth of fatigue cracks for various metals used for vessels operating under pressure is described. The growth rate of fatigue cracks is associated with the fracture at the tip of the fatigue crack due to embrittlement of the metal ahead of the crack front. Using steel 10G2 as an example, it was considered a method for determining the constants of an equation that describes the growth rate of cracks according to the results of standard fatigue tests of samples. To model thick-walled vessels and research the stress state in the crack area, the finite element method performed in the ANSYS software package was used. The cylindrical part of the pressure vessel with the biaxial stress state of the shell in the crack area is considered. For a semielliptical crack, the stress state at the crack tip was studied and average stresses ahead of the crack front were determined when the vessel was loaded to maximum pressure and unloaded to zero pressure. The crack growth rate was determined under biaxial loading of the crack growth zone under the conditions of elastoplastic behavior of the material, taking into account the residual stresses per loading cycle. The proposed method for applying the elastoplastic model of fatigue crack growth makes it possible to control the degree of danger of a registered surface crack in the wall of a pressure vessel under conditions of an variable loading cycle.