Mechanically fastened joints: Critical testing of single overlap joints

The structural integrity of critical aircraft metal structures, which include bolted joints, has to be validated according to the certification requirements. The objective of the present work is to improve the understanding of the static and fatigue behaviour of single overlap aluminium bolted joints. Three joints were loaded in static with three different pretensions in the bolts. Strain gauges were used to measure strain distributions between the bolt rows and calculate secondary bending at different joint locations. Two instrumented bolts were employed to measure their axial and shear response during loading. An optical measurement method, Digital Speckle Photography (DSP), was applied to measure bolt movement at different fastener locations. After the static programme, the same joints were tested in spectrum until a different number of blocks. The same measurement procedure was carried during spectrum testing. The load transfer between the bolt rows was calculated using the measured strain distribution. The achieved results were then compared with those ones obtained from measurements done on the instrumented bolts. The overall test results indicated that the friction forces between the joint parts affected significantly the load-transfer distribution in the joints. The initial level of pretension in the bolts was a very important issue influencing the load transfer as well as secondary bending. The obtained experimental results could be implemented in finite element modeling of mechanically fastened joints.