Fatigue Crack Growth Data for Various Materials Deduced from the Fatigue Lives of Precracked Plates

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Abstract
Data previously obtained for a wide range of metallic materials, using thin plates containing edge cracks between 0.3 and 7.5 mm (0.01 and 0.3 in.) long, have shown for both zero mean load and the general tensile stress cycle σm±σa where σm > σa that whether a crack grows or remains dormant can be predicted from the value of ΔK, the range of stress intensity factor during the fatigue cycle: a critical value ΔKc is necessary for crack growth, its value in general depends on the ratio σm/σa. Fatigue crack growth data for many materials can conveniently be represented by the equation da/dΝ = Β(ΔK)m, where Β and m are material constants. If this equation is integrated the initial rate of crack growth can be calculated from the total fatigue life of a cracked specimen. Data for low crack growth rates, obtained in this way from the broken plate specimens, are in good agreement with data obtained from conventional crack growth tests. The method has the advantage that no crack growth monitoring instrumentation is necessary, so that data on crack growth in difficult environments can readily be obtained.