Dislocation density-based fatigue approach for structural steel details

Global approaches have been the main procedure for designing structural details and components under fatigue loading. This procedure is easy to apply but it disregards not only the effect of the material type but also the influence of the geometry. On the other hand, local approaches rely on the specific local parameters that can be assessed for each type of material and detail geometry. The parameters derived from low cycle fatigue (LCF) tests are the most common damage parameters used to predict fatigue life and establish fatigue design approaches. Recently, Huffman proposed a fatigue damage model based on strain energy density and dislocation density of the material. In this regard, two structural steels were selected to perform a metallographic and mechanical characterization aiming to determine fatigue life parameters and dislocation density. The fatigue behavior of these materials was evaluated using strain-Morrow, SWT, and strain-Huffman parameters, and the dislocation density values obtained by XRD were analyzed. Additionally, experimental results from fatigue tests on structural details (plate with hole) were compared with fatigue life predictions based on each local model. It was found that the Huffman model based on dislocation density is a reliable approach to predict the fatigue life of structural steel details.