Stress gradient as a size effect in fatigue life determination for alternating bending

This paper compares the results of experimental fatigue life tests for two types of materials. For each of them, fatigue tests taking into account both the size effect and stress or strain gradient were considered. Two different materials were selected for the analysis: 16Mo3 steel and 6082-T6 aluminum alloy. In the case of 6062-T6 aluminum, both the scale effect and the gradient effect are small, which is probably due to the fact that the material behaves elastically to a very large extent. On the other hand, this effect is noticeable for the tests of 16Mo3 steel, where the material is to a large extent a material in the elastic-plastic state. The analysis shows that the stress gradient obtained in fatigue bending of 16Mo3 steel and 6082-T6 aluminum produces a similar effect as that of small specimens, i.e., an increase of the fatigue life compared to standard tension-compression tests. Therefore, the bending stress gradient of specimens without geometric notch can be considered as a different type of size effect.