Failure mode and fatigue behavior of flow drill screw (FDS) joints in lap-shear specimens of aluminum
6082-T6 sheets made with different processing conditions are investigated based on the experimental
results and a structural stress fatigue life estimation model. Lap-shear specimens with FDS joints
without clearance hole and lap-shear specimens with stripped FDS joints with clearance hole were
made and then tested under quasi-static and cyclic loading conditions. Optical micrographs show
the failure modes of the FDS joints without clearance hole (with gap) and the stripped FDS joints
with clearance hole under quasi-static and cyclic loading conditions. The fatigue failure mode of the
FDS joints without clearance hole (with gap) in lap-shear specimens is similar to those with clearance
hole. The fatigue lives of lap-shear specimens with FDS joints without clearance hole are lower than
those with clearance hole for given load ranges under cyclic loading conditions. The fatigue failure
mode of the stripped FDS joints in lap-shear specimens with clearance hole is different from that
of the FDS joints in lap-shear specimens with and without clearance hole. The fatigue lives of lapshear
specimens with stripped FDS joints with clearance hole are slightly lower than those with the
non-stripped FDS joints without clearance hole. A set of closed-form structural stress solutions with
consideration of the gap is developed to estimate the fatigue lives of the FDS joints without clearance
hole (with gap) in lap-shear specimens. The fatigue life predictions for lap-shear specimens
with FDS joints without clearance hole (with gap) in general agree with the experimental results.