Recess Drive System with Distributed Torque Capability Maximizes Fastener Installation & Removal Success

The problem of insufficient removal torque for 100 degree countersunk, flush fitting head fasteners persists after concentration on the development of test methods that can be used to measure fastener recess drive systems in the 1970s and the introduction of new drive systems in the 1980s. AF MIL-STD-1761 test procedures allow experiments to detect improved damage tolerance for new designs. We conclude, after a thorough review of both the recess drive and test method prior art, that continued efforts which limit the torque application to the head will not solve the core problem. While some designs may offer an improvement over others, no design offers an acceptable damage tolerant recess drive solution. The SBST approach will solve the problem by distributing the installation and removal torque along the length of the fastener. Fasteners with internal bores and torque carrying features, e.g. splines along with the mating installation/removal tool, will be developed and analyzed in Phase I. This concept has broad commercial applications ranging from high strength, lightweight fasteners for commercial and military aircraft to instrumented fasteners for large fixed structures such as skyscrapers and bridges (internal bores properly instrumented would allow more accurate preloads and checks).