Abstract
<jats:p>Extremely low-cycle fatigue (ELCF) is a process of degradation of steel elements caused by cyclic load leading to plastic deformations significantly above the yield limit. The paper presents an experimental study conducted to identify the failure mechanism under ELCF conditions. As part of the experimental program, ten steel specimens were tested with controlled cyclic deformations with strain ranges between 10 % and 20 %. During the tests, four characteristic damage stages were identified and described. The endurance of the steel elements was assessed using the amount of hysteresis energy dissipated. Experimentally derived curves were drawn, showing the relationship between the plastic strain range and the number of cycles to failure. Through the tests, the parameters of the Coffin-Manson and Tateishi equations were calibrated, and a comparison was made between the experimental curves and the results from analytical models. As a result of the study, a value for the coefficient of cyclic degradation of dissipated energy (αfr) is proposed. It has been found that solid, compact square cross-sections demonstrate good resistance to extremely low-cycle fatigue.</jats:p>