What is it about?
Each submersion of the sub from the sea level to the deep-sea leads to the variation of the pressure from 1 atm to 400 atm. For example, each diving cycle with the high mean pressure results nearly 50% damage pro cycle. This means, that the sensitivity is 50%.
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Why is it important?
The mean stress sensitivity varies significantly, if the environmental conditions differ. For example, the mean stress sensitivity under water could be much higher, than the mean stress sensitivity in dry atmosphere. The explanation is the following. Water reduces the crack resistance. Accordingly, the crack extends much quicklier in the wet medium and the fatigue life shrinks dramatically. Finally, when the fatigue life is exhausted, the final breakage occurs. The final breakage means the catastrophic end of life of the structural component or, for the critical structural components, the whole unit.
Perspectives
The careful evaluation of the fatigue life in the whole range of mean stress and stress amplitudes is essential for the proper design of most man-powered vehicles. The evaluation of fatigue life requires the testing under correct environment conditions, because wet environment can dramatically decrease the fatigue life of structure. Perhaps, the incorrect test procedure is responsible for the loose of "Titan" sub in the actual case.
Vladimir Kobelev
Uni Siegen
Read the Original
This page is a summary of: Effects of Mean Stress and Multiaxial Loading on the Fatigue Life of Springs, Eng—Advances in Engineering, June 2023, MDPI AG,
DOI: 10.3390/eng4020095.
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