Effect of loading frequency on crack growth rate
TWI successfully determined the effect of loading frequency on FCGR in the sour environment for the armour wire specimens. The figure below shows the FCGR in the sour environment normalised with the FCGR given in BS 7910 for steels in air. It can be seen that the FCGR of armour wire in the sour environment increased sharply with decreasing loading frequency, with a normalised FCGR value being increased from ~3 at 1Hz to ~11 at 0.1Hz, and to ~21 at 0.03Hz [1].
Future developments
Following the success of the tests in the sour environment, we are planning to investigate the use of frequency scanning testing of armour wire specimens in other corrosive environments.
References
[1] Krishnan V K, Asher S, Doynov K and Zhang Y H, 2014: “Flexible armour wires: fatigue load frequency effects and an accelerated pitting methodology”, published in OMAE2014 Conference, 8-13 June, San Francisco, Paper No. OMAE2014-24048.
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