These tests confirmed the fuselage would not be susceptible to fatigue degradation for these conservative gap conditions
What are “fit-up forces”?
Fit-up forces are applied to parts to ensure they mate up properly prior to any shimming or assembly. These small forces are used to fit the general shape of the structure.
Gap tests and results
Boeing conducted conservative configured element testing to understand the effects of gaps on static and fatigue performance. The forces induced in these tests were more than 10 times the maximum fit-up force that has been allowed in production. This testing considers a more severe condition than anything induced by the application of the comparatively small fit-up forces. The report for these tests was finalized Nov. 10, 2020.
Findings
These tests also confirmed the static load carrying capability of the structure met requirements