Influences of Stress Cycle Frequency on Propagation of Corrosion Fatigue Cracks

概要

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Corrosion fatigue test of a mild steel in salt water has been carried out at various cycle frequencies ranging from 1400 c/min to 0.28 c/min to study corrosion fatigue mechanism. The following results have been obtained from the measurement of crack growth rate and the microscopic observation on the cross section and on the fractured surface of specimens. At the cycle frequencies from 1400 c/min to 100 c/min, the decreases of the wedge action due to the hydrodynamic pressure of corrosion products are predominant for the increase of crack rate, and the crack rate increases at lower cycle frequencies from 100 c/min to several cycles par minute, the wedge effect mentioned above becomes negligibly small, and the growth of crack width due to the corrosion of crack walls increases the crack rate at lower frequencies. At the cycle frequencies lower than several cycles per minute, the dissolution of crack tips increases the crack rate. However, at extremely lower frequencies a decreases of crack rate is sometimes caused by a remarkable branching of crack tips.
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