Development of a Fastener Structural Element Test for Certifying Navy Fastener Materials

Abstract

New materials intended for use in critical U.S. Navy applications are evaluated by a Fracture Toughness Review Process (FTRP) for acceptability. In addition to developing data on the mechanical properties, fatigue life, and fracture toughness, the FTRP requires that a representative structural element test be performed to verify that the material can withstand plastic deformation at high loading rates in the presence of a detectable flaw. A Fastener Structural Element Test (FSET) has been developed to certify fastener materials such that the results of fracture mechanics testing on candidate alloys can be verified. The testing required the development of a suitable specimen that best represented a fastener, flaw seeding, and pre-cracking techniques, load and displacement measurement techniques suitable for high loading rates, and material performance acceptance criteria. The complete results of the testing on titanium alloy Ti-5AI-1Sn-1Zr-1V-0.8Mo (a.k.a. Ti-5111) and a Co-Ni-Cr-Mo-Al-Fe alloy will be presented along with the test methodology, data acquisition, and analysis details. The challenges encountered and areas that require further refinement will also be discussed.