Failure Mode and Fatigue Behavior of Flow Drill Screw Joints in Lap-Shear Specimens of Aluminum 6082-T6 Sheets of Different Thicknesses

Failure mode and fatigue behavior of flow drill screw (FDS) joints in lap-shear specimens of aluminum 6082-T6 sheets of different thicknesses are investigated based on the experimental results and a structural stress fatigue life estimation model. Lap-shear specimens of different thicknesses with FDS joints with clearance hole were made and tested under quasi-static and cyclic loading conditions. Optical micrographs show the failure modes of the FDS joints with clearance hole in lap-shear specimens of different thicknesses under quasi-static loading conditions. Under quasi-static loading conditions, as the thickness increases, the FDS joint failed from the penetration of the screw head into the upper sheet to the failure of the screw between the two sheets. Optical micrographs also show the failure modes of the FDS joints with clearance hole in lap-shear specimens of different thicknesses under cyclic loading conditions. The failure modes under cyclic loading conditions are different from those under quasi-static loading conditions. Under cyclic loading conditions, the FDS joints mostly failed near the screws in the lower sheets of thinner specimens and also failed under the screw heads in the upper sheets of thicker specimens. A set of closed-form structural stress solutions based on a new central bending solution is adopted to estimate the fatigue lives of the FDS joints with clearance hole in lap-shear specimens. The fatigue life estimations in general agree with the experimental results.