THE ROLE OF FAILURE MODE, RESISTANCE SPOT WELD AND ADHESIVE ON THE FATIGUE BEHAVIOR OF WELD-BONDED ALUMINUM

Fatigue behavior of the weld-bonded (combination of welding and adhesive bonding) aluminum joint was investigated as part of a study attempting to replace steel with aluminum in the lightweight vehicle structure. Aluminum 5754-H40 alloy and bis-pheniol-A epoxy adhesive were used in specimen fabrication. Test results showed that weld-bonded aluminum had a slightly lower fatigue resistance than the adhesive-bonded aluminum (i.e., the presence of the resistance spot weld decreases the fatigue strength by 11% at 3 x 10(6) cycles) but a much higher fatigue resistance than the aluminum and steel spot welds. Microscopic examinations showed that failure of weld-bonded aluminum occurred by either ''nugget-through'' where failure originated from the weld nugget, or ''adherend-tearing'' where failure started from the edge of adherend overlap. Statistical analyses of the test results of weld-bonded aluminum indicated that fatigue strength is not significantly affected by the failure modes.