Probabilistic bolt load distribution analysis of composite single-lap multi-bolt joints considering random bolt-hole clearances and tightening torques

This paper presents a stochastic bolt load distribution analysis method of composite single-lap multi-bolt joints by using an improved three-stage spring-based method and Monte Carlo simulation. In the proposed method, the random properties of tightening torque, bolt-hole clearance, lamina properties and geometric parameters were involved. The allowable manufacturing tolerance band of parameters and clearance fit were considered, and a combining distribution function consisting of binomial distribution and normal distribution function was adopted for modeling the random tightening torque relaxation. To validate the proposed method, a set of composite single-lap three-bolt joints were designed and tested to achieve the stochastic bolt load distribution of the joint. Good agreements between the numerical and experimental stochastic bolt load distribution validated the proposed method. Furthermore, the probabilistic bolt load distributions of the three-bolt joints in four tightening torque conditions, including finger-tight, wrench torque, standard tightening torque and relaxation tightening torque, were investigated. It is found that tightening torque conditions and bolt-hole clearances have significant influences on the variation of the bolt load distribution, while the effects of other random parameters on the variation of the bolt load distribution are slight.