Non-Stationary Viscoelastic Modeling of Compression Creep Behavior in Composite Bolted Joints

Fiber-reinforced polymer (FRP) composites are widely utilized in aerospace and shipbuilding due to their outstanding mechanical properties and lightweight nature. During prolonged service, the mechanical performance of composite bolted joints has drawn increasing attention. This study integrates experimental, theoretical, and numerical methods to simulate compressive creep and clarify preload relaxation mechanisms in these joints. A non-stationary Burgers model is proposed to describe the compressive creep behavior of FRP composites and metals, implemented in ABAQUS, which improves fitting accuracy by approximately 10% in R2 compared to the classical model. Two types of creep tests were conducted to examine the effects of initial load and material type on creep behavior, with model accuracy validated against experimental data. Finite element analysis (FEA) was further employed to assess the impact of localized loading and structural parameters on strain. The results demonstrate that the viscoelastic behavior of materials is the dominant factor contributing to preload relaxation in composite bolted joints. Under localized loading conditions, the maximum creep strain can be reduced by more than 60%, effectively mitigating preload loss. This study provides a robust framework for predicting preload relaxation, offering valuable insights for composite bolted joint design.