SEDL / STP / STP801-EB / STP44807S

Crack Growth by Stress-Assisted Dissolution and Threshold Characteristics in Corrosion Fatigue of a Steel

Endo, K
Professor, Associate Professor, and Graduate Student, Kyoto University, Kyoto,

Komai, K
Professor, Associate Professor, and Graduate Student, Kyoto University, Kyoto,

Shikida, T

Pages: 15    Published: Jan 1983

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Abstract

Corrosion-fatigue crack growth and the threshold characteristics of a high-tension steel HT55 (σ^B = 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 ΔK^eff.

Supposing a linear summation hypothesis in terms of ΔK^eff 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 ΔK^eff 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.