Estimation of residual stress influence on the low-cycle fatigue of threaded parts

The possibility of using the criterion of average integral residual stresses to estimate the cyclic life of threaded parts in the area of low-cycle fatigue is examined in the article. The peculiarities of fracture under high-cycle and low-cycle stresses are pointed out. The problems of using equations and criteria of linear mechanics in the low-cycle fatigue area are specified. These problems are mostly related to the origination of plastic deformation regions; the sizes of the latter may be significantly greater than those of the cracks. Technological factors affecting the origination and distribution of residual stresses are considered. It is noted that the diameter of the workpiece for thread rolling, heat treatment, the force and time of rolling are of the greatest importance.  The connection between the number of cycles prior to fracture and the residual stress value, expressed in terms of the average integral residual stress criterion under the influence of different technological factors is illustrated. According to the results of low-cycle fatigue tests of threaded parts it has been shown that the dependence of the number of cycles prior to fracture on the value of the average integral residual stress criterion is approximated closely by equations of the quadratic form. The appropriate magnitudes of approximation reliability are not lower than 0.9163.