10.1016/0013-7944(90)90328-E">
 

Influence of loading history on fatigue threshold behavior in a titanium alloy

Document Type

Article

Publication Date

1-1990

Abstract

A study was undertaken to investigate the effects of loading history on fatigue threshold behavior in Ti-6Al-2Sn-4Zr-6Mo. Two types of loading profiles were employed. The first type involved a gradual decreasing-ΔK history to reach the threshold condition. In this test type, two kinds of loading history were used; one was the standard ASTM decreasing ΔK test, while the other one maintained constant Kmax while Kmin was gradually increased. The second type of loading involved a sudden step decrease in ΔK while maintaining the same stress ratio to achieve a non-propagating condition. Crack opening displacement near the crack tip was measured using a laser interferometric displacement gage. This allowed crack closure levels to be accurately determined from which threshold stress intensity range, ΔKeff, th was determined. The ΔKeff, th was found to be constant for all tests in which the loading history involved a gradual change, i.e. ASTM decreasing ΔK and constant Kmax with increasing Kmin. However, the ΔKeff, th determined from the non-propagating condition in the tests involving a sudden change in loading did not coincide with the values from the tests involving a gradual change in loading. Thus, near-tip crack closure measurements and the use of an effective stress intensity range are unable to provide a unique value of threshold in tests when sudden changes in load history are compared with gradually decreasing load histories.

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Source Publication

Engineering Fracture Mechanics (ISSN 0013-7944)

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