On the preload attenuation of PTFE bolted joints under temperature loads

Polytetrafluoroethylene (PTFE)-bolted joints are commonly used in equipment, apparatuses, and devices in various industries, including the semiconductors, chemical, biomedicine, food, and pharmaceutical industries. However, owing to their significant viscoelasticity, these joints are prone to preload attenuation during service, which significantly compromises the joint reliability. This study aimed to elucidate the preload attenuation behavior of PTFE bolts and the effects of environmental temperature, initial tightening torque, and bolt geometry on this attenuation. A thermo-viscoelastic constitutive model for PTFE was developed based on material relaxation test data, followed by the construction of a finite element model for the PTFE bolted joints. The simulation and experimental results over 24 h indicated that approximately 90% of the total preload attenuation occurred within the first hour of loading. The model achieved a mean absolute percentage error of less than 15% compared with the experimental results under various environmental temperatures, initial tightening torques, nominal bolt diameters, and cyclic temperature loadings. Using this model, the factors influencing the PTFE bolt preload attenuation were investigated, and a sensitivity analysis was conducted. The findings indicate that the environmental temperature has the greatest influence on preload attenuation, followed by the initial tightening torque and bolt nominal diameter, whereas the bolt effective length has little impact.