Pulsating Torsion Fatigue Test of a Large Size Hollow Shaft Fabricated of Steel Plate

概要

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As part of a programme for developing a contra-rotating propeller of ships, a static torsion test of a large size hollow shaft of welded steel plate structure and a pulsating torsion fatigue test of a 1/2.45 scale model hollow shaft were performed. The full size hollow shaft of welded steel plate structure subjected to the static torsion test in which it was loaded with a torsion about 3.6 times (116 TON-M) the maximum design torque remained intact with no crack developed on both outside and inside. In the repeated torsion fatigue test of the scale model hollow shaft, the pulsating torsion fatigue strength (τ_ω) turned out about 8.0 kg/mm^2 for over 2×10^7 cycles. In both tests the fatigue cracks occurred on the inside walls of the hollow shafts, and mainly in the crater site of short bead of the tack weld on the backing strip. Cracks propagated roughly at 45° to the axial direction, which is-a typical feature of fatigue failure due to torsion. Since the effect of mean stress is insignificant in torsion fatigue tests, the results of the present tests were compared with the results of completely-reversed torsion fatigue tests on a hollow shaft specimen of a hot-drawn low-carbon steel pipe. Comparison shows that the torsion fatigue strength of a welded hollow shoft, due to a notch, etc. caused by the geometrical defect of weld, is considerably inferior to that of a non-welded hollow shaft.
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