Abstract
Plate-Bending-Vibration (PBV) type fatigue testing machines, which can carry out fast and low-cost fatigue tests of welded joints subject to wave loads with high frequency vibration, have been developed. These machines are designed for plate bending type fatigue tests, and wave load is applied by using motors with eccentric mass. Springing vibration is superimposed by attaching an additional vibrator to the test specimen, and whipping vibration is superimposed by hammering. PBV machines can drastically reduce the testing time and the electricity to be used for high frequency superimposed fatigue tests. It is found that the fatigue life under constantly high frequency superimposed loads can be predicted with acceptable accuracy by the modified Miner rule when rainflow stress counting is performed and S-N curve is modified so that it fits the equivalent stress range's Ps=50% curve. It has also been found that the fatigue lives are prolonged substantially than estimated when the high frequency components are superimposed intermittently. This means that the application of Miner rule to rainflow counting might lead to over conservative estimates under real stress sequences in which springing and whipping occur intermittently. The validity of rainflow counting method should be further examined by carrying out fatigue tests with realistic stress histories which emulate intermittent occurrence of springing and whipping in ship structure.
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