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The fatigue limit and its elimination
Author(s) -
; Miller,
O’donnell
Publication year - 1999
Publication title -
fatigue and fracture of engineering materials and structures
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.887
H-Index - 84
eISSN - 1460-2695
pISSN - 8756-758X
DOI - 10.1046/j.1460-2695.1999.00204.x
Subject(s) - fatigue limit , fracture mechanics , fracture (geology) , structural engineering , limit (mathematics) , materials science , fatigue testing , cyclic stress , mechanics , crack closure , stress (linguistics) , limit load , forensic engineering , engineering , composite material , mathematics , physics , mathematical analysis , finite element method , linguistics , philosophy
The classical fatigue limit of ferrous metals is a consequence of testing materials at a constant range of cyclic stress and determining the cyclic stress range below which fatigue failures do not occur. This classical fatigue limit of a material is equated to the condition for which fatigue cracks can not propagate beyond microstructural barriers. This paper discusses the causes leading to the elimination of this fatigue limit, including the introduction of transitory cyclic‐dependent mechanisms and time‐dependent processes that will permit a previously non‐propagating crack to grow across the different threshold states expressed in terms of linear‐elastic fracture mechanics (LEFM), elastic–plastic fracture mechanics (EPFM) and microstructural fracture mechanics (MFM). These transitory mechanisms and processes include different loading and environmental conditions, which in a long‐life engineering plant (e.g. 30 years lifetime) can lead to apparently premature failures. Of greater concern is the creation of a new crack‐initiation zone, i.e. a transfer from a surface‐generated crack to an internal‐generated crack that eventually dominates the fatigue failure event. The impact of these conditions on the elimination of the classical fatigue limit necessitates changes in Design Codes of Practice, and such changes are discussed in relation to the extremely long‐lifetime regime (10 7 < N f < 10 12 cycles‐to‐failure) which is increasingly applicable to the modern day engineering plant.