Abstract
Fatigue crack propagation rates were measured in a carbon-manganese structural steel in laboratory air, distilled water, and natural lake water over a wide range of testing frequencies with triangular waveforms at low values of stress ratio R. The aqueous environments were found to increase the crack propagation rates over the values measured in air by up to a factor of 7, but the degree of enhancement was found to be frequency dependent. Waveforms with a very fast rise-time such as negative sawtooth or square wave did not lead to environmental enhancement of fatigue crack propagation rates. In addition, extended hold periods of up to 600 s at the maximum stress of the fatigue cycle did not affect fatigue crack growth for the conditions studied. Growth rates increased with increasing water temperature over the range 25–85°C, with an apparent activation enthalpy of 19.2 kJ mol−1 (4.6 kcal g−1 mol−1).
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