STP761

    Factors Influencing Propagation of Mode III Fatigue Cracks under Torsional Loading

    Published: Jan 1982


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    Abstract

    Mode III fatigue crack growth rates have been measured in a quenched and tempered low-alloy steel heat treated to a range of strength levels. When compared with Mode I crack growth rates, it is found that Mode III rates are slower than the Mode I by a factor of between 10 and 50. ΔKT-values in Mode III are believed to be much larger than those of Mode I.

    The stability of Mode III cracks compared with those in Mode I is shown to be related to applied ΔK, R-ratio, and the strength level of the steel. Mode III cracks are most stable in tests at R = −1, at high values of ΔK, and in the softest material. These conclusions are in part related to the differences between Mode III and Mode I crack growth rates. The results are considered in the light of surface hardening treatments applied to shafts loaded in torsion.

    Keywords:

    torsion, Mode III, Mode I, crack growth, fatigue, thresholds, plasticity, R, -ratio


    Author Information:

    Hurd, NJ
    Metallurgist and Section Head, GKN Technology Ltd., Wolverhampton,

    Irving, PE
    Metallurgist and Section Head, GKN Technology Ltd., Wolverhampton,


    Paper ID: STP28861S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP28861S


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