Stress analysis method for a clearance-fit bolt under bearing loads

Mechanically fastened joints are becoming widely used in composite aerospace structures. In most such applications, some bolt-hole clearance exists which may influence the stresses around the hole. In the past, analyses of a clearance-fit bolt have involved complicated iterative-incremental schemes or simplifying assumptions for the stresses or displacements in the contact region. A simple method of analysis has been developed and verified in the present study. It uses an inverse formulation with a finite element analysis. Conditions along the bolt-hole contact arc are specified by displacement constraint equations. The present method is simple to apply and can be implemented with most general-purpose finite element programs. The method was applied to analyze a singlefastener, clearance-fit joint with typical values of clearance. In this analysis, a rigid, frictionless bolt was used with a quasi-isotropic graphite/epoxy laminate. Results showed that the contact arc as well as the peak stresses around the hole and their locations were strongly influenced by the clearance. After a slight initial nonlinearity, the peak stresses varied linearly with applied load. The typical clearance levels were shown to have only a minor influence on the overall joint stiffness.