Bolt Preload Detection Method Based on Connection Interface Porosity

Abstract The bolted connection structure is used in fields such as mechanical equipment, aerospace, and civil engineering. Its preload state directly affects the load-bearing capacity, service reliability, and safety of the connection structure. The existing methods for measuring and evaluating bolt preload mostly focus on the bolt body as the research object, mainly reflecting the variation law of preload through parameters such as bolt length change, strain response, or axial elongation. However, the preload is closely related to the contact state of the connection interface. Especially, changes in the porosity of the connection interface can alter the true contact area and local stress distribution of the interface, thereby affecting the overall mechanical properties of the connection structure. A new method for characterizing the contact state of bolts based on contact mechanics from the perspective of interface porosity and establishing a preload measurement model based on interface porosity is proposed. This method not only enables effective measurement of changes in bolt preload but also further characterizes the contact state of the connection interface, revealing the relationship between interface porosity, real contact area, and interface contact pressure. The results indicate that the measurement error of preload force is less than 10%, and it simultaneously analyzed the contact state of the connection interface. This study expands the analysis object of preload from the bolt body to the connection interface, providing a new research method for health monitoring, reliability evaluation, and anticrushing design of bolt connection structures under complex service conditions.