Visual investigation of static contact conditions at bolted joints

Accurate numerical models of physical systems are vital in engineering applications, and those for single components are generally accurate. However, there are significant errors in modelling the dynamics of bolted joints, which is a key source of friction in real-life systems, because existing experimental techniques are still far from offering sufficient understanding of the contact conditions of bolted joints. In the current study, static contact conditions of bolted joints are investigated with at least one component in the assembly being transparent. A novel visual identification method is proposed to (i) measure the clearance between plates in the vicinity of bolted joints and (ii) identify the contact conditions in receding contacts by applying a paste (known as Engineer's blue) to the contact surface. The paste is thinner than most media applied in previous studies. Clearance results obtained by visual inspection are checked against micrometer profile tracing, and the contact regions predicted by the method are used to validate simulation results obtained from two contact mechanics algorithms. Difference between simulation and experiment is as low as 9% in terms of contact region diameters. Last but not least, the reproducibility of the method has been demonstrated, especially if the clearance is in the range of 2 to 5 mu m.