Volume 19, Issue 2 (March 1991)
Development of Methodology for Qualifying Safety Critical A286 Threaded Fasteners
Nondestructive inspection and proof test are the principal flaw screening methods used to ensure the integrity of fracture critical fasteners. However, because of the limitations of various nondestructive inspection methods and the simplicity of the proof test, the latter method has been identified as a preferred method for flaw screening of fasteners.
A test program was initiated at the Jet Propulsion Laboratory to experimentally determine the cyclic fatigue life of pre-cracked A286 stainless steel fasteners which just survived a proof test to a prescribed fraction of their ultimate tensile strength.
The functional dependency of the cyclic fatigue life of a fastener on the fatigue stress (mean and alternating stresses), fastener size, material tensile strength, and proof load was formulated using the NASA/FLAGRO computer program. It was found that proof load has the strongest effect on fatigue life, while the mean stress has the least effect. The fastener size only has a minor effect, but the alternating stress range has a strong influence on the fatigue life of fasteners. Limited experimental verification of the hypothesized functional relationship is provided in this program for the effect of proof load and fastener size in addition to the analytic verification.