Statistical evaluation of the effects of surface processing on aerospace fastener tested strength

In the aerospace industry, various surface processing or coatings are widely used. It is known that surface processing can affect tested strength values. However, no detailed research on the aerospace fastener tensile and double shear strength variation due to surface processing has been conducted. Thus, the purpose of this study was to systematically evaluate the effect of surface processing on the standard aerospace fastener's tensile and shear properties. We selected three of the most common fastener finishes, including bare, passivation, and dry film processing. We conducted statistical analyses to identify the relationship between surface friction and tested strength. Our results showed that fastener tensile and double shear strength decreased in the groups that received surface processing compared to the bare group. This decrease was likely due to a change in surface characteristics, such as the friction coefficient instead of intrinsic material degradation due to surface processing. This evaluation may provide a solid foundation to gauge the true strength to improve aerospace fastener processing.