Effect of the notch-component relative size on the notch fatigue limit of AISI 304L specimens under push-pull tests

摘要

Results of a large set of fatigue tests on AISI 304L stainless steel cylindrical round specimens with a circumferential notch of semicircular profile and subjected to uniaxial loading (R = -1) are reported. The outer diameter of the specimens has been kept fixed, whereas the radius of the notch has been increased progressively. A whole range of configurations is studied, from combinations of notch radius and specimen diameter where the remaining ligament is much larger than the notch (semi-infinite problem) to configurations where the ligament is much smaller than the notch (finite problem) and where interaction effects have a noticeable influence on the shape of the stress gradient. An S-N curve has been obtained for each configuration. The experimentally obtained fatigue limits for the different notch radii have been compared with predictions made with several methods. However, a strong divergence between the experimental values and the theoretical predictions, which were extremely conservative, has been found and this has been attributed to work-hardening and residual stress effects connected with the machining process. It has also been suggested that a geometrical notch strengthening effect, possibly connected with stress triaxiality due to the notch, and the accompanying hydrostatic tensile stress, may also be a contributing factor. A simple practical engineering method to account for these effects has been proposed.