Abstract
In this work the boundaries of small-scale yielding (SSY) and
large-scale yielding (LSY) have been experimentally evaluated from the
analysis of crack tip opening displacement (CTOD) measured by Digital
Image Correlation (DIC). The approach published in a previous numerical
work [18] has been used to define the boundaries of SSY and LSY.
According to this approach, CTOD must be resolved into its elastic and
plastic components, analysing the ratio between the elastic CTOD range
and the total CTOD range ( Δδe/
Δδt) to define the boundary where SSY conditions
can be established. Three materials have been studied, commercially pure
titanium and 2024-T3 and 7050-T6 aluminium alloys, tested at different
stress ratio values (0.1 and 0.6 for titanium, and 0.1, 0.3 and 0.5 for
the aluminium alloys). SSY conditions are shown to dominate when
Δδe/ Δδt≥79% and ≥78%
for titanium and the two aluminium alloys, respectively. In addition,
LSY can be established when Δδe/
Δδt≤66.3% and ≤67.2% for titanium and for
2024-T3 and 7050-T6 aluminum alloys, respectively. Transition or LSY
conditions are more probable in fatigue tests conducted at low
R-ratio than in tests at high R-ratio. In addition, crack
lengths above 40% with respect to the width of the specimen promote
transition or LSY conditions. The results obtained in this work can
assist to a better understanding of the mechanisms driving fatigue crack
growth.