Surface-crack aspect ratio development during corrosion-fatigue crack growth in low-alloy steels

The development of aspect ratios (crack depth/half-crack length), was studied for semi-elliptical surface cracks in low-alloy steel undergoing corrosion-fatigue in an elevated temperature aqueous environment. Water-enhanced crack growth behavior is influenced by the concentration of hydrogen sulfide at the crack tip, and the sulfide concentration is in turn influenced by mass-transport considerations. The mass-transport characteristics of surface cracks may be different from those of more common test specimens; e.g. compact tension specimens. It is also shown that the method of preparing surface-cracked specimens can have an influence upon the crack growth behavior; surface cracks emanating from crack-starter notches may behave differently than 'natural' surface cracks because of differences in the mass-transport paths. It is also shown in that the rate of water flow along the length of a surface crack can affect the resulting crack aspect ratio and crack growth rates. (C) 1997 Elsevier Science S.A.