Effects of tensile overloads on crack closure and crack propagation rates in 7050 aluminum

✍ Scribed by R.D. Brown; J. Weertman

• Publisher: Elsevier Science
• Year: 1978
• Tongue: English
• Weight: 996 KB
• Volume: 10
• Category: Article
• ISSN: 0013-7944
• DOI: 10.1016/0013-7944(78)90040-1

✦ Synopsis

Ah&act-It has been suggested that the crack closure concept can account for the retardation in crack growth rate following removal of tensile overloads. To test this possibility measurements of effective stress were made on center notched cracked specimens during tests in which tensile overloads were applied. A comparison of the changes in crack growth rate and in effective stress following removal of the overload indicates that the crack growth rate reaches a minimum value before the effective stress does indicating that the closure concept cannot account for the decrease in crack growth rate. Additional evidence for the inability of crack closure to account for the retardation in crack growth rate is provided by specimens run at a high mean stress and then overloaded. No crack closure is observed when there is a high mean stress present, yet the crack growth rate does decrease by an amount about the same as that observed at low mean stresses where crack closure is present. Measurements of closure stress and effective stress were obtained from loaddisplacement curves recorded using an extensometer mounted across tbe crack on the specimen centerline. This procedure also enabled us to measure the distance over which the crack faces were in contact when the stress was at its minimum value in the stress cycle. The length of crack closed reached a minimum value later than did either the crack growth rate or the effective stress. It occurred when the crack tip had propagated nearly across the plastic zone created by the application of the overload.