ON THE ERRORS IN MEASUREMENT OF RESIDUAL STRESSES AND PREDICTION OF THE ENDURANCE LIMIT OF HARDENED PARTS

The study is devoted to the analysis of discrepancy between the results of prediction and of multi fatigue tests of cylindrical parts with stress concentrator in the form of a semicircular notch, made of construction steels 20, 45, 30ХГСА and 40Х. The surface of the parts was hardened by hydro and pneumatic shot blasting methods. When predicting by the reference specimen method, bushes with a length of 80 mm, with an outer diameter of 51.5 mm and an inner diameter of 45 mm were used to determine residual stresses in the hardened layer. Modeling of the residual strain-stress state in bushes and notched parts was carried out using the Finite Element method in the environment of PATRAN/NASTRAN and ANSYS calculation systems using the thermo elastic method. When predicting the increment in the endurance limit due to hardening for parts with notches, the criterion of average integral residual stresses was adopted, determined at the critical depth of a non-propagating fatigue crack. The discrepancy between the calculated prediction and bending test results in the case of a symmetrical cycle was no more than 11% for pneumatic shot blasting and no more than 8% for hydro shot blasting. The positive results of the study showed that the accepted assumptions in the reference specimen method are completely justified.