In situ near-tip normal strain evolution of a growing fatigue crack

Ming-Liang Zhu, Y-W Lu, Colin John Lupton, Jie Tong

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Normal strains near a growing fatigue crack have been studied in situ using the Digital Image Correlation (DIC) technique in a compact tension specimen of stainless steel 316L under tension-tension cyclic loading. An error analysis of the measured displacements and strains has been carried out, and the results show that the precisions of displacements and strains in the direction perpendicular to the crack plane and ahead of the crack are better than those parallel to the crack plane and in the wake of the crack. The errors in the measured displacements are in the range of 0.06 to 0.1 m and between 0.2% and 0.4% for the measured strains, the latter are well below the critical strain at the onset of crack growth about 8%. Strain ratchetting was found ahead of the growing fatigue crack tip, albeit very close to the crack tip.
Original languageEnglish
Pages (from-to)950-955
JournalFatigue & Fracture of Engineering Materials & Structures
Issue number8
Early online date22 Jan 2016
Publication statusPublished - Aug 2016


  • DIC
  • crack tip
  • error analysis
  • fatigue crack growth
  • strain ratchetting


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