Corrosion Fatigue Crack Growth of a Martensitic Stainless Steel in NaCl Solution

概要

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Corrosion fatigue crack growth rate of a martensitic stainless steel has been measured at various stress cycle frequencies and stress ratios to elucidate crack growth and crack closure behaviors. Crack closure behavior is affected by plasticity-induced crack closure (PCC), corrosion products-induced crack closure as solid properties (ECC) and as viscoelastic properties (VCC). The load sharing capacity of the wedge effect as VCC is negligibly small, though crack closure behavior is varied by VCC. Meanwhile the wedge effect of ECC is exclusively effective resulting in a raised stress intensity to close the crack, thereby reducing growth rate. The wedge effect of ECC is much affected by stress cycle frequency, stress ratio and cathodic protection. The influence of stress ratios is diminished in da/dN-ΔK_<eff> diagram, and a single curve is obtained at both frequencies. da/dN at f=0.1 Hz is considerably greater than that at f=10Hz. da/dN under cathodic protection is less great than that under free corrosion at low ΔK_<eff>. da/dN is enhanced through stress-assisted dissolution and hydrogen embrittlement.
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