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    Toward an Understanding of Mode II Fatigue Crack Growth

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    The Mode II crack flank displacement and crack growth responses of three precracked specimens made from structural steel were measured, using plastic replicas and a crack-tip compliance gage. Crack surface interaction was found to dominate behavior: at low stress intensity range (ΔKIInom = 9 MPa √m) the precracks did not suffer reversed slip to their tips and no crack growth occurred, while at high stress intensity range (ΔKIInom = 19 MPa √m) the effective stress intensity range was less than half that nominally applied. Three sources of crack flank frictional attenuation were identified: compressive residual stresses due to precracking, Mode I wedging over asperities, and gross plastic deformation of interlocking asperities. The measured unlocking response was modeled successfully by assuming that crack flank frictional stresses obeyed a constant interfacial shear stress friction law.


    fatigue crack growth, Mode II, shear mode, steels, crack flank locking, crack flank slip, friction

    Author Information:

    Smith, MC
    Lead stress engineer, Mechanical Design and Development Department, British Aerospace PLC, Dynamics Group, Space and Communications Division, Stevenage,

    Smith, RA
    Lecturer, Cambridge University Engineering Department, Cambridge,

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP23220S