Method of determining endurance limit stress of cylindrical specimens made of structural steels by residual stresses of “check test piece”

We consider the criteria of the estimation of surface strengthening influence on the endurance limit stress increase of the solid and hollow cylindrical specimens with cuts under the bend for the symmetrical cycle of loading. We check the possibility of “check test piece” method using forecasting of the tested standard specimens endurance limit stress. The “check test piece” method allows preventing the destruction of standard specimens when the residual stresses are determined experimentally. In this case the endurance limit stress of the standard specimens can be calculated by the residual stresses of “check test piece” that is strengthened simultaneously with the standard specimens by the same technology. We assume the standard specimens and the “check test piece” having the equal isotropic initial strain, the shear strains are small and we do not take them into account for the initial strain determination. We explore the solid and hollow cylindrical specimens of different diameters made of steel 20 and steel 45. The circular cuts of the specimens were strengthened by the anticipatory surface plastic deformation technology using the air/hydraulic shot blasting. The obtained results make it possible to conclude that the compressive residual stresses, calculated for smooth cylindrical specimens by the initial strains of “check test piece”, do not differ much from those that have been determined experimentally (up to 7 %). We compute the increment of the endurance limit stress of the strengthened specimens with cuts by the developed procedure using the mean integral residual stresses criterion. The difference between the calculated increase of the endurance limit stress of cylindrical specimens with cuts under the bend for the symmetrical cycle of loading and the experimental data is not more then 11 %.