The influence of crack length on stress corrosion crack velocity
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(a)
1. A.N. Niemi and T.H. Courtney: Metall. Trans. A, 1981, vol. 12A, p. 1987. 2. S. Takajo: Kawasaki Steel Corporation, Tokyo, Japan, 1981. 3. A. N. Niemi and T. H. Courtney: J. Mater. Sci., 1981, vol. 16, p. 226. 4. A. N. Niemi, L.E. Baxa, J.K. Lee, and T. H. Courtney: Mod. Dev. PowderMetall., 1981, vol. 12, p. 483. 5. S. Takajo: Ph.D. Thesis, Powder Metallurgy Laboratory, University of Stuttgart, Federal Republic of Germany, 1981.
The Influence of Crack Length on Stress Corrosion Crack Velocity P. DOIG and P. E. J. FLEWITT
(b) Fig. 1--(a) Sample sintered 24 h in HE at 1423 K and then cooled to 1403 K and sintered for 1 h. (b) This same sample after cooling to room temperature and then resintering for 1 h at 1403 K. (Particle diameters are approximately 50/.tm.)
Fig. 2 - - Sample resintered at 1403 K after originally sintering for 24 h at 1523 K and cooled to room temperature. The "deep etched" scanning electron micrograph clearly reveals the penetration of Cu along high angle y / y grain boundaries formed during the thermal cycling. The large number of such boundaries wetted is an indication of the grain refinement occurring during the y-ot-y cycling.
978--VOLUME 14A, MAY 1983
Introduction. The application of fracture mechanics concepts to the phenomenon of stress corrosion cracking has led to the use of crack growth velocity vs stress intensity plots to describe the kinetics of cracking.~-7 Implicit in such a description is the assumption that the crack is singular and the stress intensity operating at its tip is sufficient to define the expected crack growth rate. Any influence of crack length is accommodated by its contribution to the value of the stross intensity. Most mechanisms of stress corrosion cracking in electrolytic solution environments include some consideration of electrochemical control associated with either anodic dissolution or cathodic hydrogen production. 6-~~ Thus, the crack extension process, and therefore its kinetics, is influenced by the distribution of electrode reactions both within the crack and on the surface of the sample. In addition, the distribution of electrode reactions within a crack is dependent on the local solution composition as controlled by chemical equilibria in solution and the flux of corrosion reactants and products from the bulk external solution and crack tip. Thus, in the limit for short cracks, the electrode potential and solution composition distribution in the region of the crack tip will be influenced by those existing at the mouth of the crack, i.e., at the sample surface. As the crack length increases, any influence of the bulk or surface P. DOIG, Research Officer, and P. E.J. FLEWITT, Section Head, are both with Central Electricity Generating Board, South Eastern Region Scientific Services Department, Canal Road, Gravesend, Kent, United Kingdom. Manuscript submitted March 2, 1982.
METALLURGICALTRANSACTIONS A
conditions on the crack tip environment will decrease. Consequently, it may be expected that, where crack tip advance occurs under the elect
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