STP513

    Fatigue Crack Propagation Growth Rates under a Wide Variation of ΔK for an ASTM A517 Grade F (T-1) Steel

    Published: Jan 1972


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    Abstract

    Fatigue crack propagation experiments on an ASTM A517 Grade F (T-1) steel were carried out within the framework of linear-elastic fracture mechanics.

    At low ΔK levels an examination of very slow fatigue crack propagation rates of the order of 10-9 in./cycle revealed the existence of a stress intensity threshold level, ΔKT, below which fatigue crack propagation rates become diminishingly small (order of 10-9 in./cycle). Stress ratio, R (ratio of σminmaxKmin/Kmax), was found to alter the threshold ΔKT with higher R ratios resulting in somewhat depressed threshold values. The influence of stress ratio was also felt at ΔK levels above the threshold with increased growth rate being associated with increased values of R.

    Low ΔK level fatigue crack growth rate tests were conducted at room temperature in air, distilled water, and dry hydrogen gas. These environments did not effect the fatigue threshold. Identical values of ΔKT were recorded in each environment studied. Furthermore, for the range of slow growth rates, order of 10-9 to 10-7 in./cycle, and frequencies, 120 to 180 Hz, considered, these environments seemed to produce little effect on fatigue crack growth rate results.

    For higher cyclic growth rates (> 10-7 in./cycle) and ΔK levels, the effect of material condition and heat treatment was evaluated. Plate material rated as ultrasonically good and poor was evaluated in two heat treated conditions. Examination of fatigue crack growth rates indicated that ultrasonic ratings do not necessarily give good indications of crack growth resistance.

    Keywords:

    fractures (materials), fatigue (materials), crack propagation, stress ratio, tension tests, steels, morphology


    Author Information:

    Bucci, RJ
    Del Research Corporation, Hellertown, Pa.

    Clark, WG
    Westinghouse Research Laboratories, Westinghouse Electric Corp., Pittsburgh, Pa.

    Paris, PC
    Del Research Corporation, Hellertown, Pa.


    Paper ID: STP34120S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP34120S


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