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    Effect of Spherical Discontinuities on Fatigue Crack Growth Rate Performance

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    Room temperature, air environment fatigue crack growth rate data were generated with 2.540 cm (1 in.) thick hot-isostatically pressed and heat-treated low carbon steel powder metal toughness specimens containing artificial defects (alumina ceramic spheres) ranging from 0.317 to 1.270 cm (0.125 in. to 0.500 in.) in diameter. The procedure used to fabricate the test material and the subsequent evaluation of the effect of the defects on the localized rate of crack growth are discussed. Results show that the effect of unbonded spherical defects on fatigue crack growth rate behavior depends upon both the effect of the defect on localized net section stresses and the crack “blunting” influence of the defect. In addition, the specific influence of the defect on the rate of crack growth depends upon the applied stress intensity level. It is also shown that relatively large isolated spherical defects are required to yield a significant effect on fatigue crack growth rate performance. A preliminary evaluation of the effect of multiple defects is also included. Recommendations for further work and additional uses for powder metal materials containing controlled artificial defects are discussed.


    fatigue (materials), steels, crack growth, fracture (materials), defects, failure, structure, life, cycles, powders, crack propagation

    Author Information:

    Clark, WG
    Manager, Westinghouse Research and Development Center, Pittsburgh, Pa.

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP34920S