Assessing the influence of surface hardening on the endurance limit of specimens made of steel 40X using residual stresses of reference specimen

The possibility of the employment of reference specimens hardened simultaneously with the parts has been examined for the hydroblasting influence estimation on the parts with concentrators endurance limit on the example of hollow cylindrical parts made of steel 40 with circular cuts of semicircular profile with the radius 0,3 mm. The investigation has shown that the difference between residual stresses values found by calculating and experimental methods doesn’t exceed 8% in smooth specimens, in specimens with cuts – 6%. Under the hydroblasting influence on the endurance limit estimation in conditions of bending in the case of symmetric cycle for hollow cylindrical specimens made of steel 40Х with cut of radius 0,3 mm it’s been established that the employment of residual stresses distribution calculated by the initial deformations of reference specimen let predict the specimens endurance limit increase under stress concentration conditions to an approximation of 8%. It has been shown that it’s reasonable to use the average integral residual stresses criterion calculated through the dangerous section surface layer thickness equal the non-propagating fatigue crack critical depth for the prediction of the endurance limit increase of hardened by hydroblasting specimens made of steel 40 with stress concentrators.