Abstract

Corrosion-fatigue crack growth and the threshold characteristics of a high-tension steel HT55 (σB = 580 MPa) have been investigated in 1% NaCl solution by using an automated microcomputer-controlled K-device. Crack growth rates are significantly reduced in 1% NaCl solution at 5 Hz and R = 0.1, with a threshold value above the air values. The corrosion-products-induced wedge effect results in a reduced ΔK-value, thereby reducing growth rates. Therefore crack growth rates in 1% NaCl solution exceed those in air, with a lower threshold value than in air when considered in terms of ΔKeff. Supposing a linear summation hypothesis in terms of ΔKeff given by (da/dN)CF = (da/dN)F + (da/dN)D, the crack growth that proceeds by stress-assisted dissolution (da/dN)D is derived. A proposal to estimate long-term corrosion-fatigue crack growth characteristics is presented, where ΔKeff is assumed to be identical to ΔK since the crack tip is blunted and the crack is much thickened in long-term corrosion fatigue. The long-term corrosion-fatigue crack growth curves are finally derived at various stress cycle frequencies.

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