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Title: Explanation of an apparent abnormality in fatigue crack growth rate curves in titanium alloys

Abstract

A surprising phenomenon is investigated where titanium alloys exhibit no threshold fatigue crack growth value if K{sub max} in the K{sub max}-constant testing procedure exceeds a certain value. The crack growth rate increases with decreasing {Delta}K up to final fracture. The phenomenon was found repeatedly for Ti-6Al-2Sn-4Zr-6Mo above K{sub max} = 21 MPa{radical}m (equal to 72% of K{sub IC}), and its causes were investigated. The same crack growth rates as in the K{sub max}-constant test were reproduced by two independent experimental procedures, the so-called ``jump`` test and sustained K cracking experiments along with a calculation. It is demonstrated that the observed phenomenon is not a special crack growth feature or a new phenomenon, but simply caused by time-dependent crack growth, which is known to exist in titanium alloys or steels. Fractographic work revealed that intergranular crack growth along {alpha} and transformed {beta} grain boundaries increases with decreasing {Delta}K and increasing K{sub max} value, accompanied by creep deformation in the transformed {beta} grains. The conditions for time-dependent cracking are believed to be a sufficiently high stress and strain field in the crack tip region, along with hydrogen-assisted cracking.

Authors:
 [1]
  1. Air Force Research Lab., Wright-Patterson AFB, OH (United States). Materials and Manufacturing Directorate
Publication Date:
OSTI Identifier:
684382
Resource Type:
Journal Article
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 47; Journal Issue: 11; Other Information: PBD: 8 Sep 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; FATIGUE; TITANIUM BASE ALLOYS; CRACK PROPAGATION; FRACTURE MECHANICS; STRESS INTENSITY FACTORS; FRACTOGRAPHY

Citation Formats

Lang, M. Explanation of an apparent abnormality in fatigue crack growth rate curves in titanium alloys. United States: N. p., 1999. Web. doi:10.1016/S1359-6454(99)00181-0.
Lang, M. Explanation of an apparent abnormality in fatigue crack growth rate curves in titanium alloys. United States. doi:10.1016/S1359-6454(99)00181-0.
Lang, M. Wed . "Explanation of an apparent abnormality in fatigue crack growth rate curves in titanium alloys". United States. doi:10.1016/S1359-6454(99)00181-0.
@article{osti_684382,
title = {Explanation of an apparent abnormality in fatigue crack growth rate curves in titanium alloys},
author = {Lang, M.},
abstractNote = {A surprising phenomenon is investigated where titanium alloys exhibit no threshold fatigue crack growth value if K{sub max} in the K{sub max}-constant testing procedure exceeds a certain value. The crack growth rate increases with decreasing {Delta}K up to final fracture. The phenomenon was found repeatedly for Ti-6Al-2Sn-4Zr-6Mo above K{sub max} = 21 MPa{radical}m (equal to 72% of K{sub IC}), and its causes were investigated. The same crack growth rates as in the K{sub max}-constant test were reproduced by two independent experimental procedures, the so-called ``jump`` test and sustained K cracking experiments along with a calculation. It is demonstrated that the observed phenomenon is not a special crack growth feature or a new phenomenon, but simply caused by time-dependent crack growth, which is known to exist in titanium alloys or steels. Fractographic work revealed that intergranular crack growth along {alpha} and transformed {beta} grain boundaries increases with decreasing {Delta}K and increasing K{sub max} value, accompanied by creep deformation in the transformed {beta} grains. The conditions for time-dependent cracking are believed to be a sufficiently high stress and strain field in the crack tip region, along with hydrogen-assisted cracking.},
doi = {10.1016/S1359-6454(99)00181-0},
journal = {Acta Materialia},
number = 11,
volume = 47,
place = {United States},
year = {1999},
month = {9}
}