Modeling and numerical analysis of multi-bolt elastic interaction with bolt stress relaxation

Abstract

Multi-bolt joint distributed around the connecting members are generally adopted to meet the high-performance assembly requirements in aerospace, energy and power industries. However, the initial preload could be low due to non-optimized preload sequence and bolt stress relaxation, especially at elevated temperature. Thus, it is necessary to take elastic interaction and bolt stress relaxation into account before jointing. In this article, a general multi-bolt elastic interaction with bolt stress relaxation is modelled analytically. First, the multi-bolt joint is characterized by ‘spring-node’ model and elastic interaction stiffness. Second, the bolt residual preload can be estimated according to linear superposition of elastic interaction and bolt stress relaxation under the condition of node displacement equilibrium. Further, the influence of preloading sequence and bolt stress relaxation on residual preload distribution was numerically analyzed using a typical circular ring with 8-bolt joint. Two bolts’ preloading sequences were planned, star sequence and counterclockwise sequence, respectively. The bolt creep simulation time was set as 10 h using the power-model at intermediate temperature. From comparison, the predicted results using the developed model were consistent with the FE simulations both with and without bolt stress relaxation.