Stress corrosion cracking test specimens

Figure 4-442. Specimen extension as a function of time during constant-load stress-corrosion cracking test. (From Ref. [183].)...

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. 

F ure 11.14 Pre-cracked probe shapes for stress corrosion cracking tests (a) compact tension specimen (CT) and (b) double cantilever beam specimen (DCB). 

G 44 can be used for both stressed and unstressed specimens. Historically, it has been used for stress corrosion cracking testing, but often is used for other forms of corrosion, such as uniform, pitting, intergranular, and galvanic. It uses a 1-h cycle that includes a 10-min period in a aqueous solution of 3.5 % sodium chloride (NaCl) followed by a 50-min period out of the solution, during which the specimens are allowed to dry. This 1-h cycle is continued 24 h/day for the total number of days for the particular alloy being tested. 

Therefore, a new stress corrosion cracking test method was developed (Creviced Bent Beam CBB test), which considers the crevice effect as well as factors B, C and D above. Bend test specimens with an artificial crevice made from graphite wool (more sensitive than those made from PETE and especially metal-metal) were tested (both welded and non-welded but sensitised at 600 C/2 h) in high purity water with 0.2 pS/cm, oxygen saturated, chloride < 0.1 mg/1, pH S.8-6.2 at 250 C. For more than 20 steel specimens with different carbon contents (which are responsible for various susceptibilities to sensitisation) one obtains very clear conclusions from 20 specimens each of them showed stress corrosion cracking after only 24 hours, so long as the carbon content lied in the range 0.06-0045%. In the process cracks with... 

Any test (several such tests are used) in which time to failure of smooth specimens is determined is an overall measure of the incubation period to initiate a crack, the ability to resist the propagation of a stress corrosion crack and the ability to resist final mechanical fracture. Since this test does not indicate the relative merits of an alloy in each individual aspect of the... 

Controlled Strain-rate Tests Controlled strain-rate tests were first developed by Parkins (see Ugiansky and Payer ) for the study of stress-corrosion cracking. These took the form of constant strain-rate tests (also known, perhaps more accurately, as constant extension-rate tests). Since then alternative forms of test have been developed to modify the conditions under which the specimen is exposed. 

Pre-cracked specimens are sometimes useful for other reasons than the analysis that they afiford in relation to stress-intensity factors. Such applications may be associated with the simulation of service situations, the relative ease with which stress-corrosion cracks can be initiated at pre-cracks or the advantages that sometimes accrue from the propagation of a single crack. The claim that has sometimes been made of pre-cracked specimen tests-that they circumvent the initiation stage of cracking in plain specimens, erroneously assumed invariably to be related to the creation of a corrosion pit that provides a measure of stress concentration approaching that... 

Recommended practice for examination and evaluation of pitting corrosion Test method for determining susceptibility to stress corrosion cracking of high-strength aluminium alloy products Test method for pitting and crevice corrosion resistance of stainless steels and related alloys by the use of ferric chloride solution Recommended practice for preparation and use of direct tension stress corrosion test specimens... 

---