STP432

    Effects of a 3.5 Per Cent Sodium Chloride Aqueous Saline Environment on the Fatigue Crack Propagation Characteristics of Titanium Alloys

    Published: Jan 1968


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    Abstract

    Fatigue crack propagation studies were conducted on Ti-6Al-4V, Ti-7Al-2Cb-1Ta, Ti-6Al-6V-2Sn-1Cu-0.5Fe, Ti-6Al-3V-1Mo, and Ti-7Al-2.5Mo alloys. These materials possess yield strengths in excess of 100 ksi, combined with favorable levels of fracture toughness, and they are currently under evaluation for application in large welded structures. Where an application involves repetitive loading, a knowledge of fatigue crack propagation characteristics is required for failure-safe design against fracture. Fabrication and nondestructive testing procedures cannot guarantee that crack-like defects which can grow to a critical size will not be present in plate-thickness sections containing welded joints. In addition, the role of an aggressive environment, such as salt water, in this failure mechanism is of the utmost importance. This paper reports on fatigue crack propagation data taken in both ambient room air and 3.5 per cent salt water environments. Surface-notched plate bend specimens were cycled in full-reverse (tension-to-compression) sinusoidal loading. The fatigue crack was observed optically, and the crack growth rate is described as an empirical power-law function of the total (elastic plus plastic) strain range. Fatigue crack growth rate relationships are first developed in an air environment and then employed as baselines for establishing the effect of the salt water environment. Comparisons are made among the fatigue crack propagation characteristics of the several titanium alloys described in this paper and among a broad spectrum of high-strength structural alloys, both ferrous and nonferrous, previously studied.

    Keywords:

    titanium alloys, fatigue, crack propagation, aqueous environment


    Author Information:

    Crooker, TW
    Materials research engineer and headPersonal member, Naval Research LaboratoryASTM, Washington, D. C.,

    Lange, EA
    Materials research engineer and headPersonal member, Naval Research LaboratoryASTM, Washington, D. C.,


    Paper ID: STP33630S

    Committee/Subcommittee: B10.01

    DOI: 10.1520/STP33630S


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