Overload effect on the fatigue crack propagation in large-scale tubular joints

This paper examines the overloading effect on the fatigue crack propagations monitored in a large-scale tubular X-joint specimen under two separate cyclic tests. The first cyclic test applies a constant-amplitude brace in-plane bending to the joint, with a single cycle of 150% overload before the crack depth reaches the mid-thickness of the chord. The second fatigue test applies two batches of cyclic loads, with the amplitude of the second batch at 66% of the former. The X-joint specimen experiences a 150% overload cycle during the first batch of loading, followed by the second batch after it has recovered from the overload effect. The experimental results reveal that deep surface cracks experience more significant overload retardation than does a shallow fatigue crack. The Paris law estimation indicates that the single overload cycle applied in the first specimen leads to a 7% increase in the fatigue life of the X-joint.