Factors Influencing Propagation of Mode III Fatigue Cracks under Torsional Loading

    Published: Jan 1982

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    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.


    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,

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP28861S

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