An analytical theory is proposed for describing the growth of a small surface “microcrack” under uniaxial fatigue loading. The theory is based upon dimensional analysis and uses the stress-intensity factor and crack extension force concepts of elastic fracture mechanics. Experimental measurements were made of the growth of surface micro-cracks, ranging from 0.0005–0.040 in. long, in polished specimens of 4340 steel. Good correlation was achieved in comparing the test results with the theoretical predictions. Finally, an approach is indicated for extending the analytical model to the prediction of fatigue failure.

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