An investigation into the behaviour of thick pin-loaded joints under a bearing load

The behaviour of a thick pin-loaded lug was investigated when subjected to a bearing load using the embedded strain gauge technique and finite element analysis. The embedded strain gauge technique was extended to the analysis of strains in a highly-conforming contact. Three embedded strain gauge models were manufactured to measure strains due to contact at multiple angular locations around the bolt hole and multiple depths through the lug. Strains were measured in three orthogonal directions for loading by a steel pin. Three fits of pin were considered representing a neat-fit and two clearances (0.17% and 0.5% of hole diameter). Testing was performed for lubricated and unlubricated contact conditions to examine the effects of friction A gradient in stress was found through the model thickness for the loading cases considered. A smaller bearing stress was present at the outer surfaces than on the lug midplane. Similarly, the maximum tensile hoop stress was diminished at the outer surface. The difference between the surface and internal strains was up to 25% and was most extreme for the case of loading by a clearance-fitting pin. The exact level of pin clearance was not important in the hoop stress case. The experimental measurement of outer surface behaviour may therefore not be representative of internal stress concentrations and the use of a plane stress finite element model may lead to over-simplifications for a thick lug. The effect of friction was to reduce the bearing stress at the centre of the contact, though this effect was diminished at the lug ligament at the edge of the contact arc. A history-dependency was found for the dry friction case where the strains during unloading did not match the corresponding strains during loading. The difference between these values reached 27%. Therefore, it is necessary to consider the loading history in such a lug rather than just the load level of interest. The effects of friction were diminished when moving from a neat fit to clearance fit due to the smaller contact arc.