A Phenomenological Model for Bolt Loosening Characteristics in Bolted Joints Under Cyclic Loading

This paper discusses the bolt-loosening response subject to transverse cyclic loading and its analogy to metal fatigue behavior. A quantitative model accounting for the response was proposed, and the loosening life characteristics were examined. Junker tests were performed on two types of bolts, M6 and M8, along with supplementary FE analysis. Displacement amplitudes ranging from 0.18 to 0.65 mm were applied to each bolt type, and clamping forces with respect to the number of cycles were measured. From the result, a few distinctive stages were found to occur in the bolt-loosening process, and all the normalized clamping force curves were represented by a single mathematical equation, that is, a phenomenological model. In addition, the loosening lives were successfully modeled using a power law relation, as employed in the S–N curves. Consequently, the similarities between bolt-loosening and fatigue processes were verified, providing a valuable reference for future reliability evaluations of bolted structures.