SEDL / STP / STP924-EB / STP23220S

Toward an Understanding of Mode II Fatigue Crack Growth

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,

Pages: 21    Published: Jan 1988

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Abstract

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 (ΔK^IInom = 9 MPa √m) the precracks did not suffer reversed slip to their tips and no crack growth occurred, while at high stress intensity range (ΔK^IInom = 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.