THE INFLUENCE OF CUT’S DEPTH ON RESIDUAL STRESSES DISTRIBUTION AND AN ENDURANCE LIMIT OF SPECIMENS UNDER SURFACE HARDENING

Abstract

The influence of cuts depth on residual stresses distribution and an endurance limit under bending of hollow cylindrical specimens made of steel 20 with external diameter 50 mm and interior diameter 40 mm after outstripping superficial plastic deforming by roller strengthening of two regimes has been examined. Its been stated that the value of compressive residual stresses in a dangerous section of specimens decreases on cuts depth increase. As a result, an endurance limit increment of hardened specimens with cuts diminishes. In order to preserve the effect of hardening by increasing the endurance limit under outstripping superficial plastic deforming with an increase in a cuts depth, it is necessary to increase the thickness of a smooth part with compressive residual stresses layer. Its been shown that in order to estimate the increase in the endurance limit of hardened specimens, one should use not residual stresses at the bottom of a cut, but average integral residual stresses through the parts dangerous section surface layer thickness that equal a critical depth of a non-propagating fatigue crack.