Stress corrosion cracking precracked specimens

J. Sedtiks, Making and using precracked cantilever beam specimens, in Stress Corrosion Cracking Test Methods, National Association of Corrosion Engineers (NACE), Houston, TX, 1990, pp. 37 5. 

Static tests carried out with non-precracked specimens allow us to characterize, for a given environment, the sensitivity of an alloy to stress corrosion cracking and hydrogen embrittlement. TyfpicaUy, the test specimen subjected to a constant load or a constant strain is exposed to a corrosive environment and one measures the time to failure. The test specimens sometimes contain a notch—not to be confused with precracking—that fixes the location where failure will occur. In constant strain tests, the time to failure corresponds to the appearance of the first cracks. This kind of experiment thus indicates the crack initiation time. In constant load tests, on the other hand, the time to failure is the time leading to fracture of the specimen. It corresponds to the sum of the crack initiation and the crack propagation times. 

Here Og represents the yield strength of the metal, and the dimensions a and b are defined in Figure 11.14. The conditions (10.9) and (10.10) indicate the minimum size of precracked specimens. To the extent that these are met, the results of stress corrosion cracking experiments can be interpreted using fracture mechanics. 

Lisagor, W. B., Influence of Precracked Specimen Configuration ind Starting Stress Intensity on the Stress Corrosion Cracking of 4340 Steel, Environment Sensitive Fracture Evaluation and Comparison of Test Methods, ASTM STP 821, S. W. Dean, E. N. Pugh, and G. M. UgiEmslQf, Eds., ASTM International, West Conshohocken, PA, 1984, pp. 80-97. 

III aged sheet (8 h, 510 °C, or 950 °F) in 3.5%NaCl solution showed a total lack of stress-corrosion reaction under stress equal to 80% of the tensile yield stress. (AFML-TR-70-252, Oct 1970). On the other hand, various degrees of immunity or susceptibility have been reported for Beta III materials where precracked specimens were exposed under stress to salt water (see table). In general, the susceptibility of titanium alloys to stress-corrosion cracking in aqueous media is influenced by the type and concentration of species in solution, the pH, temperature, and viscosity of the solution, and the metal potential in the solution. See Techmcal Note 2 Corrosion for general information. 

Stress-corrosion cracking of susceptible high-strength aluminum alloys can occur in moist air, seawater, and potable waters, and it varies with the alloy and temper and the magnitude of sustained tensile stress. Chloride solutions are generally favored for laboratory tests of both smooth and precracked specimens because sodium chloride is widely distribu in nature, and the test results are potentiaily relatable to stress-corrosion behavior in natural environments. 

D.O. Sprowls and J.D. Walsh, Evaluating Stress-Corrosion Crack Propagation Rates in High Strength Aluminum Alloys with Bolt Loaded Precracked Double Cantilever Beam Specimens, Stress-Corrosion—New Approaches, STP 610, H.R Craig, Jr., Ed ASTM, 1976, p 143-156... 

Stress Corrosion Test Manufacturing aids evaluation (lubricants and coolants) Resistance to corrosion crack growth, pitting on precracked, 50 ksi (in.) prestressed specimens immersed for 24 h in test fluid, and in ambient environment for 76 h minimum Conventional fluid... 

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