7. A Preliminary Study on Surface Crack Growth in a Combined Tensile and Bending Fatigue Process

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Fatigue tests have been carried out under combined tensile and bending loading on plate specimens containing a surface flaw. The characteristics of fatigue crack growth are studied by a crack-morphological approach. Surface crack growth exhibits two different modes "equilibrated growth" and "non-equilibrated growth". Experimental results are well characterized by the following formulas, a/(b^n-b_0^n)^<1/n> = (0.98 + 0.07R_B)-(0.06 + 0.94R_B)・a/h db/dN = C[(Δ_<σT> +Δ_<σB>/2)・(πb)^<1/2>]^m The direct application of Paris' formula using numerical solutions of stress intensity factor in semi-elliptical surface crack has not much advantage in precision nor in simplification of analysis.
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