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 undergoi ng corrosion-fatigue in an elevated temperature aqueous environment. W ater-enhanced crack growth behavior is influenced by the concentration of hydrogen sulfide at the crack tip, and the sulfide concentration i s in turn influenced by mass-transport considerations. The mass-transp ort characteristics of surface cracks may be different from those of m ore 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' surfa ce cracks because of differences in the mass-transport paths. It is al so 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 rat es. (C) 1997 Elsevier Science S.A.