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Recent investigations have indicated that fatigue growth of surface flaws cannot be adequately predicted solely by stress-intensity factor (SIF) analysis. This is due to variations in the stress field triaxiality along the flaw border. A fatigue growth analysis of surface cracks is performed accounting for the variation in stress field triaxiality using the concepts of crack closure. Changes in the geometric parameters describing the flaw size and shape are studied for remote tensile load. For an isotropic material where the Paris equation adequately describes the fatigue crack growth rates, it is found that all subcritical flaws, regardless of initial geometry, extend such that they eventually will have identical size and shape, and that the process is independent of stress range and material properties. Experiments were performed to assess the accuracy of the analysis. Accounting for the constraint variation through the use of the concepts of crack closure yields excellent results.
fracture mechanics, fatigue (materials), surface flaw, fatigue crack growth
Head, Fracture Mechanics Section, Naval Research Laboratory, Washington, D.C.,
Captain, Escuela Superior de la Fuerza Aerea Venzzolana, Caracas,