A modeling study on composite bolted connections for preload relaxation considering accelerated degradation

Abstract

Composite bolted connections are widely used in aerospace applications with long-term storage requirements, it is essential to analyze and predict their degradation. Existing methods often fail to accurately describe the preload relaxation mechanism under long-term storage conditions, where structural properties and material degradation interact. To address this issue, an accelerated degradation model has been developed to predict the preload relaxation behavior of composite bolted connections. This model considers the variable stress conditions during the relaxation process and the deformation coordination relationship within the structure. By combining accelerated experimental data with optimization algorithms, we can identify acceleration factors, ensure mechanism consistency, and determine model parameters. The model effectively describes the time-varying behavior of preload relaxation under the viscoelastic deformation of composite materials and the accelerated relaxation effects corresponding to different temperatures. It has clear physical significance, reflecting how material and structural parameters influence preload relaxation. Compared with the phenomenon of increasing prediction error over time in other models, the error of the proposed model remained stable within 0.5 % within 500 h, providing a theoretical basis for designing the durability of connections and for conducting accelerated tests.