Low-cycle fatigue performance of solid cylindrical steel components subjected to torsion at very large strains

In this research, low-cycle fatigue performance of cylindrical specimens produced from different ductile steel grades subjected to torsion is investigated. The primary motivation behind this research is the need for data on low-cycle fatigue in solid cylindrical specimens of S355 structural steel to use in a new steel Multi-Directional Torsional Hysteretic Damper (MTHD). This steel damper is intended to be used for seismic protection of buildings and bridges. In the newly developed steel damper the energy dissipaters are in the shape of a cylinder with enlarged ends and can undergo cyclic shear strain as large as 13%. Such large strains are not encountered under service conditions in structural or mechanical components but are common in earthquake engineering in those components which are designed to plasticize and dissipate energy, e.g., plastic hinge regions, and in the case of the specific application presented in this paper, in the energy dissipaters of the steel damper. A total of 61 solid cylindrical specimens made of S355J2 + AR and C45E steel grades are tested using a special test setup capable of twisting the specimens up to ± 50°. The steel specimens are tested under different levels of torsional shear strain ranging between 0.044 and 0.130 and the data is used to calibrate the Coffin-Manson model for low-cycle fatigue life prediction of specimens. Also, the impact of various other relevant factors on low-cycle fatigue behavior of specimens are looked into, including loading pattern and sequence, low temperature, surface finishing and aspect ratio (height/diameter).