Failure Mode and Fatigue Behavior of Flow Drill Screw Joints in Lap-Shear Specimens of Aluminum 6082-T6 Sheets Made with Different Processing Conditions 2018-01-1237

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 lap-shear 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.