Progressive damage analysis of multi-bolt composite joints with variable bolt-hole clearances

A 3D progressive damage finite element model of multi-bolt, double-lap composite joints is developed in the non-linear finite element code ABAQUS. The model is validated by comparing load-displacement characteristics and surface strains to experimental results. A study is then performed of the effects of variable bolt-hole clearance with results compared to experiments in which bolt loads were measured in joints loaded to ultimate failure. It is shown that clearance can cause major changes in the load distribution and damage mechanisms in the joint. It can also lead to a significant reduction in the load at which initial failure (due to bearing at one of the holes) occurs, making it an important variable to consider in the limit load design of aircraft. Unlike previous methods, the method presented here is capable of correctly accounting for bearing and bypass stresses, in the presence of damaged material properties, as well as the load re-distribution that occurs after bearing failure at one or more holes.