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Overload effects on fatigue crack‐tip fields under plane stress conditions: surface and bulk analysis
Author(s) -
LOPEZCRESPO P.,
WITHERS P. J.,
YUSOF F.,
DAI H.,
STEUWER A.,
KELLEHER J. F.,
BUSLAPS T.
Publication year - 2013
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 - 10.1111/j.1460-2695.2012.01670.x
Subject(s) - crack closure , materials science , plasticity , stress intensity factor , composite material , stress concentration , crack tip opening displacement , structural engineering , residual stress , plane stress , digital image correlation , stress (linguistics) , tension (geology) , crack growth resistance curve , yield (engineering) , paris' law , fracture mechanics , compression (physics) , finite element method , engineering , linguistics , philosophy
The surface crack opening displacements are characterised by digital image correlation for a (thin) plane stress 316 stainless steel compact tension sample subjected to an overload event. This supports a traditional plasticity‐induced closure interpretation showing a knee in the closure response prior to overload, an absence of closure in the accelerated growth regime followed by accentuated closure in the retardation regime. By contrast, measurement of the mid‐thickness elastic strain field behind and ahead of the crack made by synchrotron X‐ray diffraction shows no evidence of significant crack face contact stresses behind the crack tip on approaching minimum loading. Rather the changes during loading and overloading can mostly be explained by a simple elastic plastic analysis using a value of the yield stress intermediate between the initial yield stress and the UTS. This shows very significant compressive reverse plastic strains ahead of the crack that start to form early during unloading. At the moment it is not clear whether this difference is because of the increasing stress intensity applied as the crack grows, or for some other reason, such as prevention of the crack faces closing mid‐thickness due to the reverse plastic zone.