Abstract:
The interaction between residual stress and fatigue crack growth rate has been
investigated in middle tension and compact tension specimens machined from a
variable polarity plasma arc welded aluminium alloy 2024-T351 plate. The
specimens were tested at three levels of applied constant stress intensity
factor range. Crack closure was continuously monitored using an eddy current
transducer and the residual stresses were measured with neutron diffraction. The
effect of the residual stresses on the fatigue crack behaviour was modelled for
both specimen geometries using two approaches: a crack closure approach where
the effective stress intensity factor was computed; and a residual stress
approach where the effect of the residual stresses on the stress ratio was
considered. Good correlation between the experimental results and the
predictions were found for the effective stress intensity factor approach at a
high stress intensity factor range whereas the residual stress approach yielded
good predictions at low and moderate stress intensity factor ranges. In
particular, the residual stresses accelerated the fatigue crack growth rate in
the middle tension specimen whereas they decelerated the growth rate in the
compact tension sample, demonstrating the importance of accurately evaluating
the residual stresses in welded specimens which will be used to produce damage
tolerance design data.
